JP2004049577A - Laser irradiation apparatus for dental treatment / prevention - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for dental treatment/prevention/diagnosis which has a control means to optimize the interaction between lasers and living organisms and a means to avoid false laser irradiation/excessive laser irradiation. <P>SOLUTION: This apparatus for dental treatment/prevention with lasers has a laser emission part which enables high power density irradiation with lasers having the wavelength of 9.0 μm ± 0.3 μm, for example irradiation of an affected part with lasers having the peak power density equal to or more than 1-10 MW/cm<SP>2</SP>for dental caries treatment and enables low power density irradiation with lasers having the wavelength of 9.7 μm ± 0.3 μm, for example irradiation of the affected part with lasers having the peak power density of approximately 100-1000kW/cm<SP>2</SP>for dental caries prevention by modifying surfaces of the dentin. The apparatus includes a device which detects impact noises at a laser irradiated area to determine the laser irradiated area and/or the laser irradiation time by the changes in the impact noises caused by irradiating the affected part with lasers and monitors it. <P>COPYRIGHT: (C)2004,JPO

Description

【００１２】
照射時間は１００ｓである。スポットの形状は楕円形であり、スポットの大きさは２６０μｍ×３５０μｍで、このスポット面積は２．８６×１０^−３ｃｍ^２であった。
図２に実験装置の配置図を示す。照射システムは、縮少光学系、偏光子、Ｈｅ−Ｎｅレーザー、放物面ミラー、パワー・メータ、顕微鏡、および試料ステージからなる。ＭＩＲ−ＦＥＬのビーム・サイズは、縮少光学系を用いて、直径約５０ｍｍから約１０ｍｍに縮少した。ＺｎＳｅ偏光子により、平均パワーを２〜３５ｍＷ内で変化させた。平均パワーは照射直前にパワー・メータで測定した。試料は試料ステージに水平に置き、放物面ミラーで集光したビームを照射した。集光ビームの形状はほぼ楕円形であり、半値全幅で、２６０μｍ　×３５０μｍ（誤差〜２０μｍ）であった。
【００１３】
９．７μｍの自由電子レーザー（ＦＥＬ）照射をしたときの象牙質表面の構造変化を図３に図面に変わる写真で示す。写真は走査型電子顕微鏡（ＳＥＭ：Ｈｉｔａｃｈｉ，　Ｌｔｄ．，　Ｊａｐａｎ，　Ｓ−４２００）によって測定した。ＳＥＭ像の（ａ）、（ｂ）、（ｃ）、（ｄ）、（ｅ）は、それぞれ平均パワー３ｍＷ、６ｍＷ、１１ｍＷ，１６ｍＷ、３３ｍＷにおけるものである。像の拡大率は３００倍。白の矢印は同一方向を示す。ＳＥＭ像を見ると、平均パワーの増大に伴いクレーターの深さと直径が深く、大きくなることがわかる。クレーターの周辺部分及び／またはクレーター中心部に、多孔質のひび割れ状の構造や溶融したバブル状の構造が認められる。
図３の（ｆ）は切削の空間プロファイルを示している。図３の（ｆ）の横軸は位置（μｍ）を示し、縦軸は切削の深さ（μｍ）を示している。１６ｍＷ照射の空間プロファイルのデータが、中心部付近で消失しているのは、検出限界が原因である。表面形状は表面プロフィル装置（ＵＬＶＡＣ，　Ｊａｐａｎ，　ＤＥＫＴＡＫ３）で測定した。測定精度は１ｎｍであった。前述したように、平均パワーの増大と共に切削深さも増大する。切削深さは、（ａ）が１．８５μｍ、（ｂ）が１４．５μｍ、（ｃ）が３２．８μｍ、（ｄ）が４０μｍ未満、（ｅ）が４４μｍであった。ここでは、切削深さを象牙質表面から最深部までの距離として定義した。
【００１４】
次に本発明者らは、牛歯歯頸部象牙質を用いて象牙質の耐酸性向上に関する検討を中赤外自由電子レーザー（ＭＩＲ‐ＦＥＬ）を用いて行った。象牙質は　７０％のハイドロキシアパタイト（Ｃａ_１０（ＰＯ_４）_６（ＯＨ）_２：ＨＡｐ）、１２％の水、１８％の有機物から構成されており、象牙細管等の複雑な構造を有している。象牙質の耐酸性向上には、（１）硬組織であるＨＡｐの結晶性の向上、（２）不純物（水、有機物）の除去、（３）象牙細管の密閉等が同時に要求される。
低侵襲治療には象牙質の除去量を最小限に抑えることが重要となる。中赤外光照射による象牙質表面改質の最適パラメータ領域を定量化する為に、本発明者らは、ＨＡｐのＰＯ_４伸縮振動モード由来の吸収帯領域（８．８−１０．６μｍ）において、波長・平均パワーをパラメータとして牛歯象牙質照射実験を行った。このときの照射時間は１００秒であった。象牙質の表面改質は（１）切削深さ、（２）中赤外吸収スペクトル、（３）元素組成から評価した。照射後の切削深さを表面粗さ計で測定し、最大切削深さが３μｍ以下の場合を１Ａと分類し、３−１０μｍ以下を１Ｂと分類し、１０μｍ以上となる場合を１Ｃと分類し、３つの領域に分類した。次に、フーリエ変換型赤外吸収スペクトル測定装置（ＦＴ‐ＩＲ）で測定した照射後の象牙質の吸収スペクトルから、最大吸収波長の９．７μｍ付近から９．０μｍ付近へのシフトが観測された。合成ＨＡｐの吸収ピーク波長は９．０μｍ近傍であり、この波長のシフトは象牙質のＨＡｐ化、即ち結晶性の向上を示唆するものである。吸収ピークシフトの有無により、シフトが無い場合を２Ａと分類し、シフトが有る場合を２Ｂと分類した。さらに、象牙質はＨＡｐ、エナメル質に比べて多くのリンを含んでいる為、表面改質には元素組成の制御つまりリンの選択的な除去を行う必要がある。ここでは、元素組成をＣａに対するＰの元素比（Ｐ／Ｃａ比）として定義した。Ｐ／Ｃａ比は象牙質では０．６５８±０．０２、エナメル質では０．５８３±０．０２、合成ＨＡｐでは０．５４９±０．０２であった。Ｐ／Ｃａ比において０．５８３以下を３Ａと分類し、０．５８３以上を３Ｂと分類した。
【００１５】
レーザー照射後の切削の深さについての実験結果を図４に示す。図４の（ａ）は、照射波長λが象牙質における最大吸収波長λ_ｄｅｎ以上の場合を示し、図４の（ｂ）は照射波長λが象牙質における最大吸収波長λ_ｄｅｎ未満の場合を示している。図４の横軸は平均パワー（ｍＷ）および平均パワー密度（Ｗ／ｃｍ^２）を示し、縦軸は切削の深さ（μｍ）を示す。薄色の矢印は測定限界の上限および下限を示す。切削の程度を１Ａ（０−３μｍ）、１Ｂ（３−１０μｍ）、１Ｃ（１０μｍ以上）に分類した。図４（ａ）と図４（ｂ）には、それぞれ照射波長領域λ≧λ_ｄｅｎおよびλ＜λ_ｄｅｎにおける、切削深さと平均パワー（平均パワー密度）との相関が示されている。λ≧λ_ｄｅｎではλ_ｄｅｎの近辺で、平均パワーの低い領域（５ｍＷ以下）でも、かなりの切削量が認められたが、平均パワーの高い領域（２０ｍＷ以上）では、λ_ｄｅｎ近辺の切削深さはわずかに減少した。λ＜λ_ｄｅｎで平均パワーを増した場合には、実験した照射波長範囲ではいずれも切削深さが増大した。既述したように、切削の程度をおおむね三つのグループに分類した。つまり、（１）１Ａ（わずかな切削）、（２）１Ｂ（中程度の切削）および、（３）１Ｃ（顕著な切削）である。１Ａから１Ｃグループに対応するレーザーパラメータはそれぞれ次のようになる。（１）１０．６μｍおよび１０．３μｍでは、平均パワーが１０ｍＷ未満、１０．０μｍ以下では、平均パワーが５ｍＷ未満；（２）１０．６μｍでは平均パワーが１０ｍＷ〜１５ｍＷ、１０．３μｍでは、平均パワーが約１０ｍＷ、１０．０μｍでは平均パワーが５ｍＷ〜１０ｍＷ、９．８μｍおよび９．７μｍでは平均パワーが５ｍＷ〜７−８ｍＷ、９．５μｍ以下では平均パワーが５ｍＷ〜１０ｍＷ；（３）１０．６μｍでは平均パワーが１５ｍＷ以上、１０．３μｍおよび１０．０μｍでは平均パワーが１０ｍＷ以上、９．７μｍおよび９．８μｍで平均パワーが７−８ｍＷ以上、９．５μｍ以下では平均パワーが１０ｍＷ以上。このように、切削の程度は波長及び／または平均パワーに強く依存することがわかった。
【００１６】
次に中赤外（ＭＩＲ）の吸収スペクトルを検討した。レーザー照射前後のＭＩＲ吸収スペクトルをＦＴ−ＩＲ（Ｈｏｒｉｂａ．　Ｊａｐａｎ，ＦＴ−５２０）で測定した。ＦＴ−ＩＲの測定範囲は３〜１４μｍ、分解能は０．０１μｍ未満であった。
９．７μｍのＦＥＬ照射をしたときの象牙質の吸収スペクトルを平均パワーごとに示す（図５）。図５の横軸は波長（μｍ）を示し、縦軸は吸光度（ａ．ｕ．）を示す。各曲線はそれぞれ３ｍＷ、６ｍＷ、１１ｍＷ、１６ｍＷ、２２ｍＷ、３３ｍＷ、および未照射（斜線入り白線）の場合を示す。
平均パワーを増加するにつれて吸光度は長波長側から徐々に低下し、その結果、最大吸収波長は短波長側にシフトする。平均パワーが低い領域（１１ｍＷ以下）ではスペクトル幅が狭くなり、平均パワーが高い領域（１６ｍＷ以上）ではスペクトル幅は広くなる。低パワー領域での吸収スペクトルはＨＡｐのものとほとんど同じである。すなわち、最大吸収波長のシフトは、象牙質の表面が改質されてＨＡｐ状の物質になったことを示す。高パワー領域では、吸光度が全体的に減少しており、ＰＯ_４振動モード成分が象牙質表面から消失したことを示唆している。また、水および有機物による６．０−７．０μｍの弱い吸収帯は、最大吸収波長のシフトにともなって完全に消失した。
図６には、照射後象牙質の最大吸収波長に対する平均パワーおよび照射波長依存症を示す。図６の（ａ）は、照射波長λが象牙質における最大吸収波長λ_{ｄｅ ｎ}以上の場合を示し、図６の（ｂ）は照射波長λが象牙質における最大吸収波長λ_ｄｅｎ未満の場合を示している。図６の横軸は平均パワー（ｍＷ）および平均パワー密度（Ｗ／ｃｍ^２）を示し、縦軸は最大吸収波長（μｍ）を示す。９．８μｍ（図６（ａ）の黒ひし形を付した線）および１０．０μｍ（図６（ａ）の灰色三角を付した線）を除くいずれの場合にも、図５に示した結果と同様に、平均パワーの増大につれて最大吸収波長は、ヒドロキシアパタイトの最大吸収波長λ_ＨＡｐ＝９．０μｍへシフトした。特に、照射波長λ_ｄｅｎまたはλ_ＨＡｐ付近では、比較的低いパワー領域においても有意のシフトが観察された。これらの照射波長領域を、それぞれ（１）λ_ｄｅｎ付近を２Ａと分類し、および（２）λ_ＨＡｐ付近を２Ｂと分類した。２Ａ領域および２Ｂ領域のレーザーパラメータは、それぞれ、（１）１０．６μｍでは平均パワーが１０ｍＷ未満、１０．３μｍ以下では平均パワーが５ｍＷ未満；（２）１０．６μｍでは平均パワーが１０ｍＷ以上、１０．３μｍ以下では平均パワーが６−８ｍＷ以上である。
このように、象牙質の表面改質（スペクトル変化）は主に２Ｂパラメータ領域で起こることがわかった。ＰＯ_４振動モード由来の強い吸収帯は、図５で説明したように、高パワー領域（１５ｍＷ以上）では消失してしまう。
【００１７】
次に、歯の組織における元素組成を検討した。元素組成はエネルギー分散式Ｘ線スペクトロメーター（Ｈｏｒｉｂａ，Ｊａｐａｎ、ＥＭＡＸ−５７７０）で測定した。エネルギー分解能は１４４ｅＶ以下であり、ＰのＣａに対する組成比で表わされる。未照射の象牙質、エナメル質、ＨＡｐのＰ／Ｃａ比は、それぞれ０．６５８±０．０２，０．５８３±０．０２，０．５４９±０．０２である。象牙質は比較的多くのＰ核種を含む。これは象牙質の吸収スペクトル幅がエナメル質のＨＡｐと比較して広いことと一致している。
元素組成の実験結果を図７に示す。図７には、Ｐ／Ｃａ比に対する平均パワーおよび照射波長依存性を示す。図７の（ａ）は、照射波長λが象牙質における最大吸収波長λ_ｄｅｎ以上の場合を示し、図７の（ｂ）は照射波長λが象牙質における最大吸収波長λ_ｄｅｎ未満の場合を示している。図７の横軸は平均パワー（ｍＷ）および平均パワー密度（Ｗ／ｃｍ^２）を示し、縦軸はＰ／Ｃａ比を示す。薄色の矢印は測定限界の下限を示すものである。Ｐ／Ｃａ比を次の二つの領域に分類する。すなわち、（１）３Ａ（エナメル質からＨＡｐ）と、（２）３Ｂ（象牙質からエナメル質）である。３Ａおよび３Ｂ領域のレーザーパラメータは次のとおりである：（１）１０．６μｍでは平均パワーが１５ｍＷ以上、９．７−１０．３μｍでは平均パワーが７ｍＷ以上、９．５μｍ以下では平均パワーが１０ｍＷ以上；（２）１０．６μｍでは平均パワーが１５ｍＷ未満、９．７−１０．３μｍでは平均パワーが７ｍＷ未満、９．５μｍ以下では平均パワーが１０ｍＷ未満である。
これらの結果からＰ／Ｃａ比が平均パワーおよび照射波長に依仔することが示された。いずれの場合にも、低平均パワー領域（１０ｍＷ以下）においては平均パワーが増すとＰ／Ｃａ比は急激に減少するが、高平均パワー領域（２０ｍＷ以上）ではＰ／Ｃａ比は平均パワーによらず一定である。これは、低パワー領域ではＰ核種が優先的に除去され、高パワー領域ではすべての物質が象牙質から除去されることを示す。また、約２５ｍＷを超える高平均パワー領域ではＰ／Ｃａ比を計測することができなかったが、これはＰ核種が象牙質の表面層から顕著に除去されたことによると考えられる。
【００１８】
このようにして、照射の波長・平均パワーによる表面改質の程度をマクロ的に検討し、次のグループに分類した：（１）切削深さ（１Ａ−１Ｃ）、（２）ＭＩＲ吸収スペクトル（２Ａ，２Ｂ）、（３）元素組成（３Ａ、３Ｂ）。各グループに属する被照射象牙質は、それぞれ物理的・化学的性質が異なっている。
象牙質はエナメル質にくらべて、加熱や切削などのレーザーによる影響を受けやすい。これは象牙質に有機物や水が多く含まれているためである。さらに、ＭＩＲ領域のレーザー光は、生体組織に吸収されやすいために、熱源として作用する。そのため、対象物位に選択的に反応を起こさせるのに必要なレーザーのパラメータを定量的かつ定性的に探索することが非常に重要である。
【００１９】
図８に、平均パワー（２−３５ｍＷ）／波長（８．８−１０．６μｍ）のパラメータに対する実験結果のまとめを示す。図８の横軸は、平均パワー（ｍＷ）、平均パワー密度（Ｗ／ｃｍ^２）を示し、図８の縦軸は照射波長（μｍ）を示す。矢印は象牙質における最大吸収波長λ_ｄｅｎおよびヒドロキシアパタイトの最大吸収波長λ_ＨＡｐを示す。楕円は象牙質の切削を最小限に抑えた上で、、効果的に表面改質できるパラメーター領域を示す。
これらの結果から次のことがわかった。（１）象牙質表面は強吸収領域のレーザー波長、特にλ_ｄｅｎ、の付近で顕著に表面改質される。表面改質とは、照射部位の構造上、吸収スペクトル上、元素組成上の変化を指している。長波長側（１０．３μｍ以上）では、吸収係数が低いために、レーザーによる改質は十分に行われない。以前に行ったＣＯ_２レーザーによるエナメル質の耐酸性付与実験においても、λ_ｄｅｎ付近の照射波長によって、う蝕に対する物理的・化学的性質が効果的に改善された。象牙質切削量を抑えて、表面の物理・化学的性質を変化させるためには、まず第一には、レーザーの波長と平均パワー密度とを、図８の大きな楕円（９．４−１０．３μｍおよび１０−２０Ｗ／ｃｍ^２）の範囲に設定することが好ましい。この範囲では、図５および図７に示したように、Ｐ核種は象牙質表面から選択的に除去される。これは、以前に報告した照射象牙質からアブレーションされイオンの質量スペクトルが示した観測結果と、おおむね合致していた。さらに、同様のレーザー条件において、照射後の象牙質の再結晶化が明確に認められた。（２）第二にはレーザーの波長と平均パワー密度とを、図８の小さな楕円（８．８−９．４μｍおよび１０−１５Ｗ／ｃｍ^２）の範囲に設定するのが好ましい。この範囲では、Ｐ／Ｃａ比は３Ｂパラメータ領域（象牙質−エナメル質領域）に入っているが、最大吸収波長のシフトが観測された。（３）図４（ａ）で説明したように、λ_ｄｅｎ付近においては、高平均パワー照射において切削深さが減少する。λ_ｄｅｎ付近においては、レーザー照射中に吸収波長がλ_ｄｅｎからλ_ＨＡｐへと急速にシフトする。これは、レーザーのエネルギーが時間と共に象牙質中に吸収されなくなることを示唆している。前述したように、顕著な切削には必ず波長シフトが伴う。したがって、硬組織を効果的に切削するのに最適と思われる波長は、高結合エネルギーのＰＯ_４振動モード由来のλ_ＨＡｐ付近、９．０μｍ付近である。
【００２０】
これらの実験では、入力のパラメータとして平均パワーを用いた。表面改質はマイクロ秒オーダーの時間スケールで起こる。したがって、レーザーパワーとしては、通常用いられる１秒間当たりの平均パワーではなく、マクロパルス当たりのピークパワーとして考えなくてはならない。マクロパルスのパルス幅は約１５μｓであるから、マクロパルス当たりのピークパワー密度数百ｋＷ〜数ＭＷ／ｃｍ^２のオーダーとなる。
【００２１】
次に、本発明者らは、図１２の丸印で示したレーザーパラメータ下におけるレーザー誘起音と象牙質表面改質の相関性について調べた。具体的には、レーザー誘起音強度、吸収ピーク波長のシフト、切削の深さの時間的変化を測定・比較し、レーザー誘起音による象牙質表面改質のモニタリングの可能性について検討を行った。
【００２２】
牛歯歯頸部から切り出した面積約５ｍｍ×５ｍｍ、厚さ約１ｍｍの板状の象牙質をサンプルとして用いた。表面粗さによる光の散乱の影響を抑える為、サンプル表面の粗さを１μｍ以下にまで研磨した。ＭＩＲ−ＦＥＬ発振装置から供給されるＦＥＬ光を放物面鏡により集光し、集光スポットサイズは２６０μｍ×３５０μｍ（半値全幅）であった。照射波長（９．０、９．３、９．６、１０．３、１０．６μｍ）、照射時間（０．２、０．５、１、２、３、５、１０ｓｅｃ）、平均パワー密度（７、１４、２８、４２Ｗ／ｃｍ^２）を照射パラメータとして変化させた。可聴域コンデンサマイクロフォン（測定可能範囲：０．０１−２０ｋＨｚ、指向性無し）を照射位置から約３ｃｍ離れた場所に設置した。照射パラメータ間の感度を一定に保つ為に、実験中はマイクロフォンの位置、データ取得に関するセットアップを固定した。そして、音響信号解析ソフト（Ｓｏｕｎｄ　Ｆｏｒｇｅ）を用いて音響信号を時間波形として計算機に転送、保管した。
【００２３】
使用したＭＩＲ−ＦＥＬのパルス構造は、ミクロパルスとマクロパルスから成る二重パルス構造を有している。最小パルスはパルス幅約５ｐｓのミクロパルスであり、パルス間隔は４４．８ｎｓである。マクロパルスとは約３３０個のミクロパルス群を指し、パルス幅は約１５μｓ、パルス間隔は０．１ｓである。象牙質とレーザー光との相互作用の熱緩和過程を考慮すると、マクロパルス中のミクロパルス群は連続波として見なすことができ、照射効果はミクロパルス群の熱蓄積効果によって引き起こされる。即ち、パワー密度としては１秒間当たりのエネルギー密度（Ｊ　／　ｃｍ^２　／　ｓ）ではなく、マクロパルス当たりのエネルギー密度（Ｊ　／　ｃｍ^２　／　ｍａｃｒｏｐｕｌｓｅ）として考えるべきである。また、マクロパルス間での熱蓄積効果はなく、誘起される相互作用は１マクロパルス毎の積算となる。
【００２４】
照射波長９．０μｍ、９．６μｍ、１０．６μｍにおけるレーザー誘起音強度の時間的変化（０−　１０ｓ）を図９に示す。図９の横軸は照射時間（秒）を示し、縦軸は誘起音強度（ａ．ｕ．）を示す。図９の（ａ）は照射波長９．０μｍの場合を示し、図９（ｂ）は照射波長９．６μｍの場合を示し、図９の（ｃ）は照射波長１０．６μｍの場合を示す。丸印を付した線は、平均パワー密度が４２Ｗ／ｃｍ^２を示し、四角印を付した線は、平均パワー密度が２８Ｗ／ｃｍ^２を示し、三角印を付した線は、平均パワー密度が１４Ｗ／ｃｍ^２を示し、バツ印を付した線は、平均パワー密度が７Ｗ／ｃｍ^２を示す。マイクロフォンの絶対較正を行っていない為、観測される誘起音強度を絶対値として評価することはできないが、各照射パラメータ間の相対的な変化として定量的に比較できる。これら、観測結果を（１）時間変化、（２）波長依存性、（３）パワー依存性という観点から説明する。
【００２５】
時間変化としては、レーザー誘起音強度は照射時間と共に単調に減衰し、数秒後には一定となった（図９参照）。また、照射直後から一定値を取る場合も観測され、９．０μｍ・７Ｗ／ｃｍ^２、１０．６μｍ・７−１４Ｗ／ｃｍ^２では信号強度は０．０３−０．０４程度であったが、この信号レベルはノイズレベルとみなされる。
波長依存性では、照射波長が象牙質の吸収ピーク波長９．７μｍに近づくにつれて、誘起音強度は大きくなるという傾向が全ての照射時間領域において観測された。また、パワー依存性では、照射平均パワー密度の増加に伴い、誘起音強度もそれに応じて大きくなった。レーザー誘起音強度が照射時間と共に変化に伴って変化することは注目すべきことであった。
【００２６】
次に、照射波長９．０μｍ、照射時間ｔ＝０．５、３、５秒における照射後の象牙質表面の空間プロファイルを図１０に示す。図１０の横軸は位置（μｍ）を示し、縦軸は切削の深さ（μｍ）を示す。図１０の（ａ）は照射時間が０．５秒の場合を示し、図１０の（ｂ）は照射時間が３秒の場合を示し、図１０の（ｃ）は照射時間が５秒の場合を示す。黒い実線は平均パワー密度が４２Ｗ／ｃｍ^２を示し、黒い破線は、平均パワー密度が２８Ｗ／ｃｍ^２を示し、灰色の破線は、平均パワー密度が１４Ｗ／ｃｍ^２を示し、細い実線は、平均パワー密度が７Ｗ／ｃｍ^２を示す。空間プロファイルは表面粗さ計（ＵＬＶＡＣ、ＤＥＫＴＡＫ３）を用いて測定精度１ｎｍで測定した。切削の深さは、サンプル表面から照射痕の最深部までの距離として定義した。各照射パラメータに対する切削の深さの平均パワー密度依存性および時間変化について説明する。平均パワー密度の増加に伴い、切削の深さは増大するが、低平均パワー密度領域（７Ｗ／ｃｍ^２）では、象牙質表面に形態的変化は観測されなかった。これにより、照射波長９．０μｍでは象牙質の切削の閾値は７−１４Ｗ／ｃｍ^２間にあることが分かった。各照射パワー密度における時間ｔ＝０．５、３、５　秒の切削深さ（（μｍ）で表示）はそれぞれ次のようになった。７Ｗ／ｃｍ^２（０．０２、０．０２、０．０２）、１４Ｗ／ｃｍ^２（２．６７、６．４２、４．７）、２８　Ｗ／ｃｍ^２（１８．４、３１．４、３２．３）、４２Ｗ／ｃｍ^２（２６．３、４８．７、５７．１）。このように、切削の深さには顕著な照射時間依存性があり、特に誘起音の時間領域１（減衰フェーズ）では効果的に象牙質の切削が起こる一方、時間領域２（一定フェーズ）においては切削効果がほとんどないことが明らかとなった。
【００２７】
次に、照射波長９．０μｍ、照射時間ｔ＝０．５、３、５秒における照射後の象牙質の中赤外吸収スペクトルを図１１に示す。図１１の横軸は波長（μｍ）を示し、縦軸は吸光度（ａ．ｕ．）を示す。図１１の（ａ）は、照射時間が０．５秒の場合を示し、図１１の（ｂ）は、照射時間が３秒の場合を示し、図１１の（ｃ）は照射時間が５秒の場合を示す。太い黒い実線は平均パワー密度が４２Ｗ／ｃｍ^２を示し、太い黒灰色線は、平均パワー密度が２８Ｗ／ｃｍ^２を示し、灰色の線は、平均パワー密度が１４Ｗ／ｃｍ^２を示し、細い実線は、平均パワー密度が７Ｗ／ｃｍ^２を示す。灰色の細線は未照射の場合を示す。中赤外吸収スペクトルは、ＦＴ−ＩＲ装置（ＨＯＲＩＢＡ、ＦＴ　−　５２０）の顕微反射法を用いて測定し、測定波長範囲は３−１４μｍ、波長分解能は０．０１μｍであった。顕微反射法から得られる吸光度は、サンプル表面の反射率と象牙質の吸収特性の両者に依存する為、吸光度の絶対値に関する評価はできない。非照射象牙質の中赤外吸収スペクトルには、９．７μｍ、９．０μｍに２つの振動モード成分が存在し、ダブルピークを形成する（図１１参照）。同様に、照射後のスペクトルも９．０、９．３、９．７μｍのいずれかに吸収ピークを持つダブルピークのスペクトルとなる。その為、９．３μｍ或いは９．７μｍに対する９．０μｍの吸光度比Ｒ_Ａはスペクトル変化を示す指標として扱うことができる。照射前はＲ_Ａ＜１であり、Ｒ_Ａ≧１となる。即ち、Ｒ_Ａ≧１は吸収ピーク波長が９．０μｍ近傍にシフトしたことを意味する。ここで、Ｒ_Ａ＝１を中赤外吸収スペクトルから見た表面改質の閾値としてみなす。
【００２８】
次に（１）低パワー密度領域（７　Ｗ／ｃｍ^２）、（２）中パワー密度領域（１４、２８　Ｗ／ｃｍ^２）、（３）高パワー密度領域（４２Ｗ／ｃｍ^２）に分類し、吸収スペクトルの時間変化についてそれぞれ述べる。（１）ｔ＝０．５ｓでは、吸収スペクトルには変化が観測されず、非照射象牙質のスペクトルとほぼ同じであった。ｔ＝３ｓ及び５ｓでは、９．７μｍ付近の吸収ピークがわずかに短波長側にシフトしており、９．１μｍ付近に新たな吸収ピークが現れた。この時、Ｒ_Ａは０．４１８（ｔ＝０．５ｓ）、０．６５４（ｔ＝３ｓ）、０．７４３（ｔ＝５ｓ）と１以下であり、表面改質の閾値以下であった。（２）ｔ＝０．５ｓでは、９．７μｍ付近の吸収ピークが消失し、９．４μｍ付近に新たな吸収ピークが出現した。ｔ＝３ｓ及び５ｓでは、吸収ピーク波長の９．０μｍへの波長シフトが観測された。１４Ｗ／ｃｍ^２ではＲ_Ａ＝０．９１８（ｔ＝０．５ｓ）、１．１５（ｔ＝３ｓ）、１．２６（ｔ＝５ｓ）、２８Ｗ／ｃｍ^２ではＲ_Ａ＝０．８７７（ｔ＝０．５ｓ）、１．６０（ｔ＝３ｓ）、１．６１（ｔ＝５ｓ）となり、０．５−３ｓ間においてＲ_Ａの変化、波長シフトが観測される一方、３−５ｓ間では顕著なスペクトルの変化は観測されなかった。（３）照射時間に関わらず、照射後の吸収ピーク波長は９．０μｍ付近であった。Ｒ_Ａはそれぞれ１．５４（ｔ＝０．５ｓ）、１．４２（ｔ＝３ｓ）、１．２４（ｔ＝５ｓ）と表面改質の閾値を超えており、高平均パワー密度では吸収ピークシフトの照射時間依存性は観測されなかった。（１）−（３）により、照射パワー密度によって吸収ピーク波長のシフトには異なる照射時間依存性があることが分かった。
【００２９】
以上の考察では、象牙質の切削・表面改質（吸収ピーク波長のシフト）とレーザー誘起音強度との相関性を、象牙質表面改質の最適レーザーパラメータ領域に含まれる照射波長（９．０μｍ、９．６μｍ）、平均パワー密度１４Ｗ／ｃｍ^２における観測データを主に用いて検討した。
次に、本実験で使用した照射パラメータを、発生したレーザー誘起音の最大強度Ｉ_ｍａｘによって次の４つのグループに分類する（図１２参照））。図１２は図８に衝撃音の観測結果として４Ａ〜４Ｄの分類を新たに付加したものである。図１２で使用している（４Ａ）はＩ_ｍａｘ＜０．０５、（４Ｂ）は０．０５＜Ｉ_ｍａｘ＜０．１、（４Ｃ）は０．１＜Ｉ_ｍａｘ＜０．５、（４Ｄ）はＩ_ｍａｘ＞０．５である。前述してきたように、誘起音強度は象牙質の吸収特性、照射平均パワー密度に応じて変化する。つまり、レーザー誘起音強度は象牙質に吸収されたレーザーエネルギーに強く依存する。吸収エネルギーはレーザー生体相互作用を支配するパラメータの１つである為、レーザー誘起音強度からレーザー生体相互作用の種類・程度を推定することが可能となる。象牙質表面改質の最適波長領域内（図１２の楕円内及びその近傍）の９．６μｍを例として考えると、レーザー誘起音強度の領域４Ａ−４Ｂ、４Ｃ、４Ｄはそれぞれ１Ａ／２Ａ／３Ｂ（変化なし）、１Ｂ／２Ｂ／３Ａ（吸収ピーク波長シフト＝象牙質のＨＡｐ化）、１Ｃ／２Ｂ／３Ａ（切削）の相互作用領域に相当する。したがって、音響信号レベルにより治療中に相互作用の種類やその程度をリアルタイムモニタリングできる。
【００３０】
次に、照射平均パワー密度１４Ｗ／ｃｍ^２における照射波長９．０μｍ、９．６μｍのレーザー誘起音強度、切削深さ、吸収ピーク比の時間変化を図１３に示す。図１３の横軸は時間（秒）を示し、縦軸は誘起音強度（ａ．ｕ．）を示す。図１３の（ａ）は照射波長９．０μｍの場合を示し、図１３の（ｂ）は照射波長９．６μｍの場合を示す。丸印を付した線は、誘起音強度を示し、四角印を付した線は、切削の深度を示し、三角印を付した線は、吸収ピーク比を示す。すでに述べたように、誘起音強度は両照射波長共に数秒後で一定値を取る。切削深さ、吸収ピーク比共に、誘起音の時間領域１（減衰フェーズ）では明らかに変化しているにも関わらず、時間領域２（一定フェーズ）では顕著な変化が観測されなかった。これは、時間領域２では象牙質の吸収特性の変化（吸収ピーク波長シフト）に伴いレーザーが効率的に象牙質に吸収されず、所望の相互作用がそれ以上誘起されないことを意味している。したがって、誘起音強度の時間推移から、所望の相互作用の終了をモニタリングできる。
以上のように、レーザー誘起音強度から相互作用の種類・程度が、その時間推移から相互作用の終了をリアルタイムモニタリングできる可能性を示した。前者はレーザー治療における過照射・誤照射の回避、後者は治療行為のエンドポイントの決定に繋がる。
【００３１】
レーザー誘起音と象牙質の表面改質・切削との相関性を調べる為に、中赤外ＦＥＬを用いて、レーザー誘起音強度及び象牙質の切削深さ・吸収ピーク波長シフトを測定した。これらの観測結果より、次のことが明らかとなった。（１）レーザー誘起音はレーザー照射直後から発生し、単調的に減衰し、数秒後には一定値となった。誘起音が変化している時間領域では、象牙質のスペクトル変化（表面改質）や切削といった相互作用が頻繁に起こる一方、誘起音が一定な時間領域では顕著な相互作用は観測されなかった。（２）表面改質の最適照射波長である９．０μｍ、９．６μｍでは、誘起音強度の信号レベルが相互作用の種類・程度（変化なし、表面改質、切削等）に依存する傾向が見られた。（１）よりレーザー治療のエンドポイントの決定、（２）より過照射・誤照射の回避、に関する情報を照射中にリアルタイムで得ることができる。このように、低侵襲治療技術の一手法としてレーザー誘起音によるリアルタイムモニタリング手法の可能性・有効性を明らかにした。本発明で用いた照射波長は現在治療用レーザーとして用いられている炭酸ガスレーザーの発振帯域とほぼ一致しており、この技術を応用したレーザー歯科治療照射装置の開発が可能となる。
【００３２】
以上で説明してきたように、本発明ではレーザーによる歯科治療・予防におけるレーザーの波長、平均パワー密度、及び衝撃音についての相関を検討し、これらの間に極めて有用な相関があることを見出した。これらの結果をまとめると次のようになる。
１．虫歯の予防
本発明は、レーザーの照射により、象牙質の表面改質ができ、耐酸性・機械強度の向上が計られるが、このためにレーザーパラメーターを最適化し、かつ象牙質の切削量を最小限にした象牙質の表面改質を目的にしている。そして、本発明は、レーザーを対象に効率よく吸収させるために、つまり、熱効果を有効に利用するために、照射レーザーの波長には対象物質の吸収ピーク波長（象牙質の吸収ピーク波長：９．７μｍ近傍）を用いること、切削量を最小限に抑えるために、照射ピークパワー密度（Ｗ／ｃｍ^２）を高精度に制御し、数百ｋＷ／ｃｍ^２程度（これを低強度パワー照射と呼ぶ）にすることを特徴とするものである。
２．虫歯の治療。う蝕部の切除。
本発明は、う蝕部の高効率な切削、つまり、機械的（衝撃的）効果を有効に利用することを目的している。そして、本発明は虫歯の治療、う蝕部の効率的な切削のために、比較的高強度パワー密度照射（数ＭＷ／ｃｍ^２以上）を用いること、照射後の歯質硬組織の最大吸収波長は９．０μｍ近傍に必ず変化することから、照射レーザーの波長を９．０μｍ近傍に設定しておけば常にレーザー光は硬組織内に吸収され、熱、熱応力に変換し、対象部位を効率的かつ選択的に切削できることを特徴とするものである。
【００３３】
また、本発明は、レーザーによる歯科の治療・予防において、その場でのモニタリング手法としてレーザー誘起衝撃音の検出を提供するものである。
本発明は、レーザー誘起衝撃音はレーザーの吸収、温度上昇、熱膨張に伴って圧力波としてレーザー照射中に発生し、その強度は照射部位の吸収特性を反映するものであることを明らかにし、本発明はこれによるレーザーの過照射や誤照射を回避する手段を提供するものである。
１．過照射の回避（レーザー照射のエンドポイント決定）。
虫歯の予防及び虫歯の治療のいづれの場合も、前記してきた本発明の手法によりレーザー照射の波長などの条件を最適化することができ、効率良くレーザーと生体との相互作用を対象部位に起こすことができる。つまり、治療・予防中は衝撃音の強度は強いが、改質による最大吸収波長のシフト（虫歯予防の場合）や蒸散による硬組織の切削（虫歯治療の場合）によって、衝撃音信号の強度は次第に低下し、ついには一定値になることを本発明が初めて明らかにし、一定な音響信号は相互作用が非効率になったことを意味しており、それ以上は熱損傷につながる恐れがでてくることから、音響信号が一定値を取る時間を治療・予防のエンドポイントとすれば過照射を回避でき、本発明はこのための手法を提供するものである。
２．誤照射の回避。
誤照射の部位として最も考えられる部位は、口中の軟組織である。レーザーの照射による衝撃音の強度は照射部位の物質の吸収特性を反映し、本発明で使用する９．０−９．７μｍ近傍の吸収係数は、硬組織と軟組織では大きく異なり、硬組織が圧倒的に大きい。つまり、硬組織切除・改質用の本発明のレーザーのパラメータ下では、軟組織の場合、発生する音は極めて小さく、レーザー照射直後に衝撃音が検出されない場合、それは軟組織への照射、つまり、誤照射をしたことがわかる。したがって、この場合、速やかにレーザーを遮断することによって誤照射を回避できる。本発明はこのための手法を提供するものである。
【００３４】
以上のような本発明の手法をまとめたのが図１４である。図１４は本発明による歯科治療・予防をフロチャートにまとめたものである。
虫歯の予防（象牙質の表面改質）のためには９．７μｍ近傍の波長のレーザーを使用し、これを目的の部位に照射する。照射開始時に、レーザー誘起衝撃音の音響強度（Ｐａ）を検出し、これが小さい場合には、誤照射であることからレーザーの照射を中止する。また、Ｐａが大きい場合には照射を継続し、Ｐａが変化している間はレーザーの照射を継続する。Ｐａが変化せず一定値になったら、改質が完了したのであるから、レーザーの照射を中止する。これで、目的部位における虫歯の予防（象牙質の表面改質）が完了したことになる。
虫歯の治療（う蝕部の切削）のためには、９．０μｍ近傍の波長のレーザーを使用し、これを目的の部位に照射する。照射開始時に、レーザー誘起衝撃音の音響強度（Ｐａ）を検出し、これが小さい場合には、誤照射であることからレーザーの照射を中止する。また、Ｐａが大きい場合には照射を継続する。レーザーの照射によりう蝕部の吸収ピーク波長が９．７μｍ近傍から９．０μｍ近傍にシフトする。このシフトにより効率的な切削が可能となる。そして、Ｐａが変化している間はレーザーの照射を継続する。Ｐａが変化せず一定値になったら、切削が完了したのであるから、レーザーの照射を中止する。これで、目的部位における虫歯の治療（う蝕部の切削）が完了したことになる。
【００３５】
即ち、本発明はレーザーの波長及び照射強度をパラメータとした新規の歯の治療・予防方法を提供するものである。より詳細には、本発明は、歯のう蝕の治療のために波長が９．０μｍ±０．３μｍであって高パワー密度照射のレーザー光を患部に照射することからなるレーザーによる虫歯の治療方法、及び歯の象牙質の表面改質による虫歯予防のために波長が９．７μｍ±０．３μｍであって低パワー密度照射のレーザー光を患部に照射することからなるレーザーによる虫歯の予防方法を提供するものである。
また、本発明は、レーザー誘起衝撃音を検知することによるレーザーによる歯の治療・予防方法におけるレーザーの誤照射及び過照射を回避する方法を提供するものである。より詳細には、本発明は、レーザーによる歯の治療・予防方法において、患部へのレーザー光の照射による衝撃音の変化によりレーザー光の照射部位及び／又はレーザー光の照射時間を判定するためのレーザー光の照射部位における衝撃音を検出し、レーザー光の照射開始時の照射部位における衝撃音が小さい場合には、レーザー光の照射が中止されることからなるレーザーの誤照射を回避する方法、及びレーザー光の照射時の照射部位における衝撃音が一定になった場合には、レーザー光の照射が中止されることからなるレーザーの過照射を回避する方法を提供するものである。
【００３６】
さらに、本発明は、前記してきた歯科治療・予防のための治療・予防装置を提供するものである。本発明のレーザー光による歯の治療・予防用装置は、レーザー源及びレーザー照射部、並びにレーザー光の波長の選択部、及び／又はレーザー光の照射強度の調整部を有するものである。さらに、レーザー光の照射部位におけるレーザー誘起衝撃音を検出し、これをモニタリングできる装置としてレーザー誘起衝撃音の検知部、及び音響強度測定部を有するものが挙げられる。
本発明のレーザー光による歯の治療・予防用装置のレーザー源としては、９．０μｍ近傍及び９．７μｍ近傍の波長のレーザーを出力できるものであれば特に制限はない。レーザー源としては、各々の波長について１個又は２個以上のレーザー源を有していても良いし、ひとつのレーザー源で波長を変換できるようにしていてもよい。具体的なレーザー源としては、自由電子レーザー、炭酸ガスレーザー、Ｈｅ−Ｎｅレーザーなどが挙げられる。これらのレーザーはパルス状でレーザー光を供給できるものが好ましい。パルスは、ミクロパルスでもあってもよいし、マクロパルスであってもよいし、これらの組み合わせであってもよい。レーザー源で発生したレーザーは、適当な光路を経てレーザー照射部に供給される。
照射されるレーザーの波長は、９．０μｍ近傍又は９．７μｍ近傍であり、ヒドロキシアパタイトの最大吸収波長近傍、又は歯の象牙質の最大吸収波長近傍であればよい。具体的な波長としては、９．０μｍ近傍の波長としては、８．７〜９．３μｍ、即ち９．０μｍ±０．３μｍが好ましく、より詳細には９．０μｍ±０．２μｍ、９．０μｍ±０．１μｍが挙げられる。また、９．７μｍ近傍の波長としては９．４〜１０．０μｍ、即ち９．７μｍ±０．３μｍが好ましく、より詳細には９．７μｍ±０．２μｍ、９．７μｍ±０．１μｍが挙げられる。本発明のレーザー光による歯の治療・予防用装置のレーザー光の波長の選択部としては、レーザー源から供給されるレーザーを９．０μｍ近傍の波長のレーザーと、９．７μｍ近傍の波長のレーザーを選択できるものであればよい。レーザー源を選択して波長を選択できるものであってもよいし、レーザーの光路において波長を選択できるものであってもよい。
【００３７】
本発明のレーザー光による歯の治療・予防用装置のレーザー光の照射強度の調整部としては、高パワー密度照射と低パワー密度照射を調整できるものであればよく、調整手段としては特に制限はない。調整手段としては、レーザーの出力を調整してもよいし、照射部位におけるスポットの大きさ（焦点）を調整することによりパワー密度を調整してもよい。
本発明のレーザー光の照射強度としては、高パワー密度照射として平均パワー密度で１５Ｗ／ｃｍ^２以上、好ましくは２０Ｗ／ｃｍ^２以上、２５Ｗ／ｃｍ^２以上、又は３０Ｗ／ｃｍ^２以上であり、低パワー密度照射が平均パワー密度で１５Ｗ／ｃｍ^２未満、好ましくは１０Ｗ／ｃｍ^２以下、又は７Ｗ／ｃｍ^２以下である。本発明ではレーザーの入力のパラメータとして平均パワーを用いた。歯の治療・予防においては、マイクロ秒オーダーの時間内にも起り得ることから、平均パワーについては、通常用いられる１秒間当たりの平均パワーではなく、マクロパルス当たりのピークパワーとして考えるほうが、本発明を実施する上で重要となる。そうすると、マクロパルスのパルス幅はマイクロ秒オーダー、例えば約１５μｓであるから、それによって発生するピークパワー密度はメガワットのオーダーとなる。即ち、パワー密度としては１秒間当たりのエネルギー密度（Ｊ　／　ｃｍ^２　／　ｓ）ではなく、マクロパルス当たりのエネルギー密度（Ｊ　／　ｃｍ^２／マクロパルス）として考えるべきである。してみれば、本発明の高パワー密度照射としてマクロパルス当たりのパワー密度に換算して示すと、マクロパルスの長さにもよるが数ＭＷ／ｃｍ^２以上、数十ＭＷ／ｃｍ^２以上、例えば、１ＭＷ／ｃｍ^２以上、５ＭＷ／ｃｍ^２以上、７ＭＷ／ｃｍ^２以上、１０ＭＷ／ｃｍ^２以上、又は２０ＭＷ／ｃｍ^２以上ということもできる。
また、本発明の低パワー密度照射では、マクロパルス当たりのパワー密度に換算して示すと、数百ｋＷ／ｃｍ^２〜数ＭＷ／ｃｍ^２程度、例えば、１００ｋＷ／ｃｍ^２〜１０ＭＷ／ｃｍ^２程度、３００ｋＷ／ｃｍ^２〜５ＭＷ／ｃｍ^２程度、５００ｋＷ／ｃｍ^２〜５ＭＷ／ｃｍ^２程度ということもできる。
【００３８】
本発明のレーザー光による歯の治療・予防用装置のレーザー照射部としては、目的の部位に正確にレーザーを照射できるものであれば、特に制限はない。固定式のものであっても、可動式のものであってもよい。また、手に持てる小型のものであってもよいが、手によるブレを防止できるようにブレ防止の処置がこうじられているものが好ましい。レーザー照射部には可視光によりレーザー照射位置を表示できる照射位置表示装置が設けられているものであってもよい。
本発明のレーザー光による歯の治療・予防用装置のレーザー光の照射部位におけるレーザー誘起衝撃音を検出し、これをモニタリングできる装置としては、レーザー誘起衝撃音の検知部及び音響強度測定部からなるものが好ましい。
本発明のレーザー光による歯の治療・予防用装置のレーザー誘起衝撃音の検知部としては、レーザー誘起衝撃音を検知できるものであればよく、可聴域、超音波域であってもよい。例えば、可聴域マイクロフォン（測定可能範囲：０．０１−２０ｋＨｚ）や、３０ｋ〜１００ＭＨｚ程度の超音波を検知できるものであってもよい。本発明のレーザー誘起衝撃音の検知部は、照射位置からのレーザー誘起衝撃音を検知できる任意の位置に設置することができるが、例えばレーザー照射位置から１〜１５ｃｍ、１〜１０ｃｍ、１〜５ｃｍの範囲の任意の位置に設置することができる。本発明のレーザー誘起衝撃音の検知部は、例えば、レーザー照射部の中に組み込まれたものであってもよい。
本発明のレーザー光による歯の治療・予防用装置の音響強度測定部としては、レーザー誘起衝撃音を音響強度として、好ましくはデジタル化された音響強度として、測定し、データ化できるものであればよい。
【００３９】
本発明のレーザー光による歯の治療・予防用装置は、本発明の趣旨に沿っている範囲において、前記した部分のほかに任意に他の部分を付加することができる。例えば、レーザーの波長と照射強度とを組み合わせたパラメーターを記憶できる記憶部、前記記憶部のデータに基づいてレーザーの波長と照射強度をセットにして調整し得る調整部、音響強度測定部からのデータを処理する処理部、当該処理部の処理結果に応じてレーザー光の照射を調整できる調整部、レーザー照射位置における治療・予防の状況を映像化できる映像部などを必要に応じて設置することができる。
【００４０】
本発明のレーザー光による歯の治療・予防用装置の態様としては、レーザー源及びレーザー照射部、並びにレーザー光の波長の選択部を有する装置、レーザー源及びレーザー照射部、並びにレーザー光の照射強度の調整部を有する装置があげられるが、好ましい態様としてはレーザー源及びレーザー照射部、並びにレーザー光の波長の選択部及びレーザー光の照射強度の調整部を有する装置が挙げられる。また、レーザー源及びレーザー照射部、並びにレーザー誘起衝撃音の検知部、及び音響強度測定部を有するものが挙げられる。より好ましい態様としては、レーザー源、レーザー照射部、及びレーザー光の波長の選択部、並びにレーザー誘起衝撃音の検知部、及び音響強度測定部を有する装置や、レーザー源、レーザー照射部、及びレーザー光の照射強度の調整部、並びにレーザー誘起衝撃音の検知部、及び音響強度測定部を有する装置が挙げられる。さらに好ましい態様としては、レーザー源、レーザー照射部、レーザー光の波長の選択部、及びレーザー光の照射強度の調整部、並びにレーザー誘起衝撃音の検知部、及び音響強度測定部を有する装置が挙げられる。
【００４１】
より詳細には、本発明は、（１）レーザーによる歯の治療・予防用の装置であって、歯のう蝕の治療のために波長が９．０μｍ±０．３μｍであって高パワー密度照射のレーザー光を患部に照射し得るレーザー照射部を有することを特徴とするレーザー光による歯の治療・予防用装置、（２）レーザーによる歯の治療・予防用の装置であって、歯の象牙質の表面改質による虫歯予防のために波長が９．７μｍ±０．３μｍであって低パワー密度照射のレーザー光を患部に照射し得るレーザー照射部を有することを特徴とするレーザー光による歯の治療・予防用装置、（３）レーザーによる歯の治療・予防用の装置であって、歯のう蝕の治療のために波長が９．０μｍ±０．３μｍであって高パワー密度照射のレーザー光を患部に照射し得るレーザー照射部、及び歯の象牙質の表面改質による虫歯予防のために波長が９．７μｍ±０．３μｍであって低パワー密度照射のレーザー光を患部に照射し得るレーザー照射部を有することを特徴とするレーザー光による歯の治療・予防用装置、（４）レーザーによる歯の治療・予防用の装置であって、患部へのレーザー光の照射による衝撃音の変化によりレーザー光の照射部位及び／又はレーザー光の照射時間を判定するためのレーザー光の照射部位におけるレーザー誘起衝撃音を検出し、これをモニタリングできる装置を有していることを特徴とするレーザー光による歯の治療・予防用装置、並びに（５）レーザーによる歯の治療・予防用の装置であって、歯のう蝕の治療のために波長が９．０μｍ±０．３μｍであって高パワー密度照射のレーザー光を患部に照射し得るレーザー照射部、及び歯の象牙質の表面改質による虫歯予防のために波長が９．７μｍ±０．３μｍであって低パワー密度照射のレーザー光を患部に照射し得るレーザー照射部、並びにレーザー光の照射部位におけるレーザー誘起衝撃音を検出し、これをモニタリングできる装置を有することを特徴とするレーザー光による歯の治療・予防用装置を提供するものである。
【００４２】
本発明のレーザー光による歯の治療・予防用装置の例を図１５に示す。本発明のレーザー光による歯の治療・予防用装置１０は、レーザー光の波長の選択部を操作するための選択ボタン１及び２によりレーザーの波長が選択できるようになっており、レーザー光の照射強度の調整部を操作するためのツマミ１１が設けられている。歯の治療・予防用装置１０から出力されたレーザ光は、レーザ光伝送用ファイバー７によりレーザー照射部４に伝送され、歯９の患部８に照射される。レーザー照射部位から発せられるレーザ誘起衝撃音は、レーザー誘起衝撃音の検知部５により集音され、衝撃音伝送用ファイバー６により歯の治療・予防用装置１０に内蔵されている音響強度測定部に伝送される。この例の歯の治療・予防用装置１０は、出力波形表示部３及び出力パワーメーター１２を備えている。
この例の装置１０により歯９の治療・予防を行う方法を説明する。歯９のう蝕部８を治療する場合には、レーザーの波長選択ボタン２を操作してレーザの波長を９．０μｍとし、出力パワー調節ツマミ１１を操作して出力を高パワー密度照射ができるように調整する。レーザー照射部４から照射されるレーザー光を患部８に照射し、その際のレーザー誘起衝撃音をレーザー誘起衝撃音の検知部５により集音し、衝撃音が大きいことを確認した後、レーザーの患部８への照射を継続する。衝撃音が一定になったら、レーザー出力を中止して治療を完了する。歯９の象牙質の表面改質による予防を行う場合には、レーザーの波長選択ボタン１を操作してレーザの波長を９．７μｍとし、出力パワー調節ツマミ１１を操作して出力を低パワー密度照射ができるように調整する。レーザー照射部４から照射されるレーザー光を患部８に照射し、その際のレーザー誘起衝撃音をレーザー誘起衝撃音の検知部５により集音し、衝撃音が大きいことを確認した後、レーザーの患部８への照射を継続する。衝撃音が一定になったら、レーザー出力を中止して歯の予防を完了する。
【００４３】
本発明によれば、レーザーによる歯の治療・予防において、歯のう蝕部や歯石の切削、及び歯の象牙質の表面改質におけるレーザーの最適化が可能となり、また、レーザー誘起衝撃音を基準にしてレーザの誤照射や過照射を客観的な基準により判断でき、歯の治療・予防におけるレーザの誤照射や過照射を確実に回避することができる。
【００４４】
【実施例】
以下、実施例により本発明をより具体的に説明するが、本発明はこれら実施例により何ら限定されるものではない。
【００４５】
実施例１　（レーザーのパラメーターについての試験）
（１）レーザー装置
歯の表面処理に必要なパラメータ（波長や平均パワー密度等）をマクロ的にそして定性的に解析するため、中赤外自由電子レーザー（ＭＩＲ−ＦＥＬ）を使って象牙質に対する一連の実験を行なった。本試験で使用したＭＩＲ−ＦＥＬは、マクロパルスとミクロパルスという二重のパルス構造をもっている。マクロパルスとミクロパルスのパルス幅／パルス間隔はそれぞれ、１５μｓ／０．１ｓおよび５ｐｓ／４４．８ｎｓである。ひとつのマクロパルスは３３０個のミクロパルスからなる。ここで、着目すべきは平均パワー密度或いはマクロパルスのピークパワー密度であって、ミクロパルス当たりのピークパワー密度ではない。その理由は、組織への加熱効果は、ミクロパルスではなく、ほとんどがマクロパルスによって惹起されるからである。
照射波長は象牙質のＰＯ_４振動モード由来の吸収帯（８．８−１０．６μｍ）の範囲で変化させた。使用したレーザーパラメーターを表１に示す。照射時間は１００ｓである。図２に実験装置の配置図を示す。ＭＩＲ−ＦＥＬのビーム・サイズは、縮少光学系を用いて、直径約５０ｍｍから約１０ｍｍに縮少した。ＺｎＳｅ偏光子により、平均パワーを２〜３５ｍＷ内で変化させた。平均パワーは照射直前にパワー・メータで測定した。試料は試料ステージに水平に置き、放物面ミラーで集光したビームを照射した。集光ビームの形状はほぼ楕円形であり、半値全幅で、２６０μｍ　×３５０μｍ（誤差〜２０μｍ）であった。スポットの大きさは実験を通じて変えなかった。試料の位置を正確に定めるため、ｘ、ｙ、ｚ軸のマイクロメータつきの試料ステージと、顕微鏡およびＭＩＲ−ＦＥＬに同軸のＨｅ−Ｎｅビームを使用した。
（２）象牙質
使用した歯頸部象牙質は牛歯から得た平板状のもので、長さ５ｍｍ、幅５ｍｍ、厚さ１ｍｍであった。ＭＩＲ−ＦＥＬビームのスポットの大きさは、象牙質の最大吸収波長の付近においてその光侵入の深さに比べて十分大きいことから、この象牙質は、ほぼ無限大の固体試料とみなすことができた。表面粗さによる光の散乱を避けるため、象牙質試料は研磨により表面粗度を１μｍ以下とした。レーザー照射前に、すべての試料について表面粗度、ＭＩＲスペクトル、元素組成を測定した。
（３）測定系
象牙質の表面改質の程度は、次の実験データにより評価した。切削の深さは表面粗度の測定により行った。ＭＩＲ吸収スペクトルはフーリエ変換型赤外スペクトル測定装置（ＦＴ−ＩＲ）で行った。元素組成はエネルギー分散式Ｘ線スペクトロメーターにより行った。
これらの試験結果を図３〜図７に示す。
【００４６】
実施例２　（レーザー誘起音測定実験及び装置）
牛歯歯頸部から切り出した面積約５　ｍｍ×５　ｍｍ、厚さ約１　ｍｍの板状の象牙質をサンプルとして用いた。表面粗さによる光の散乱の影響を抑える為、サンプル表面の粗さを１μｍ以下にまで研磨した。
ＭＩＲ−ＦＥＬ発振装置から供給される自由電子レーザー（ＦＥＬ）光を放物面鏡により集光した。実施例１の照射実験と同一の照射系を用い、集光スポットサイズは２６０μｍ×３５０μｍ（半値全幅）であった。照射波長はそれぞれ９．０μｍ、９．３μｍ、９．６μｍ、１０．３μｍ、１０．６μｍであった。照射時間はそれぞれ０．２秒、０．５秒、１秒、２秒、３秒、５秒、１０秒であった。平均パワー密度はそれぞれ７Ｗ／ｃｍ^２、１４Ｗ／ｃｍ^２、２８Ｗ／ｃｍ^２、４２Ｗ／ｃｍ^２であった。これらを照射パラメータとして変化させた。
可聴域マイクロフォン（測定可能範囲：０．０１−２０ｋＨｚ）を照射位置から約３ｃｍ離れた場所に設置した。照射パラメータ間の感度を一定に保つ為に、実験中はマイクロフォンの位置、データ取得に関するセットアップを固定した。そして、音響信号解析ソフト（Ｓｏｕｎｄ　Ｆｏｒｇｅ）を用いて音響信号を時間波形として計算機に転送・保管した。
本実験で使用したＭＩＲ−ＦＥＬのパルス構造は、ミクロパルスとマクロパルスから成る二重パルス構造を有している。最小パルスはパルス幅約５ｐｓのミクロパルスであり、パルス間隔は４４．８ｎｓである。マクロパルスとは約３３０個のミクロパルス群を指し、パルス幅は約１５μｓ、パルス間隔は０．１ｓである。象牙質とレーザー光との相互作用の熱緩和過程を考慮すると、マクロパルス中のミクロパルス群は連続波と見なすことができ、照射効果はミクロパルス群の熱蓄積効果によって引き起こされる。即ち、パワー密度としては１秒間当たりのエネルギー密度（Ｊ　／　ｃｍ^２　／　ｓ）ではなく、マクロパルス当たりのエネルギー密度（Ｊ　／　ｃｍ^２　／　ｍａｃｒｏｐｕｌｓｅ）として考えるべきである。また、マクロパルス間での熱蓄積効果はなく、誘起される相互作用は１マクロパルス毎の積算となる。
これらの実験結果を図９〜１１及び図１３に示す。
【００４７】
【発明の効果】
歯硬組織におけるレーザー歯科治療には、エナメル質や象牙質表面の耐酸性を向上させる虫歯予防、及びう蝕部や歯石を除去する虫歯治療等がある。両者ともにレーザー光による熱的・機械的相互作用による物理的・化学的・形態的変化を利用したものであり、現在まで、レーザー歯科治療に関する研究が数多くなされているが、臨床のレーザー治療では、患者の個体差、照射パワー密度の安定性、照射中の環境の変動等によって、所望の相互作用のみを効率良く起こすことが困難であった。また、正常な組織への熱的・機械的損傷といった副作用・逆作用に関する報告例も少なくない。
本発明はレーザー歯科治療・予防におけるこれら諸問題を克服するものであり、レーザー歯科治療・予防の臨床的な実現に大きく寄与するものである。即ち、本発明はレーザー歯科治療・予防におけるレーザー照射の最適化条件を提供し、レーザーによる歯科治療及び予防を低侵襲的かつ確実に行うことができる方法及びそのための装置を提供するものである。また、対象部位の変性状態及び相互作用の種類・程度をレーザー照射中にリアルタイムモニタリングすることが必要となるが、本発明はそのためのモニタリング技術としてレーザー誘起音に着目できることを明らかにしたものである。これによりレーザー歯科治療・予防における誤照射の問題や過照射の問題を確実に回避することができ、レーザー歯科治療・予防における副作用や逆作用を解消した。
中赤外レーザーを用いた歯象牙質表面改質による耐酸性の付与は、高齢者の歯根面における虫歯予防の一手法として注目されているが、本発明により高齢者であっても安全で確実な治療・予防を行うことができるようになった。
【図面の簡単な説明】
【図１】図１は、歯質硬組織であるエナメル質、象牙質、及びヒドロキシアパタイト（ＨＡｐ）の吸収曲線を示す。図１の横軸は波長（μｍ）を示し、縦軸は吸光度を示す。黒線は象牙質（Ｄｅｎｔｉｎ）の吸収を示し、白灰色線はエナメル質（Ｅｎａｍｅｌ）の吸収を示し、黒灰色線はヒドロキシアパタイト（ＨＡｐ）の吸収をそれぞれ示す。
【図２】図２は、本発明の照射配置図を示すものであり、照射システムは、縮少光学系、偏光子、Ｈｅ−Ｎｅレーザー、放物面ミラー、パワー・メータ、顕微鏡、および試料ステージからなる。
【図３】図３は、９．７μｍの自由電子レーザー（ＦＥＬ）照射をしたときの象牙質表面の構造変化を示した図面に変わる走査型電子顕微写真である。図３の（ａ）、（ｂ）、（ｃ）、（ｄ）、（ｅ）は、それぞれ平均パワー３ｍＷ、６ｍＷ、１１ｍＷ，１６ｍＷ、３３ｍＷにおけるものである。像の拡大率は３００倍。白の矢印は同一方向を示す。図３の（ｆ）はクレーターの空間プロファイルを示している。図３の（ｆ）の横軸は位置（μｍ）を示し、縦軸は切削の深さ（μｍ）を示している。
【図４】図４は、レーザー照射後の切削の深さについての実験結果を示す。図４の（ａ）は、照射波長λが象牙質における最大吸収波長λ_ｄｅｎ以上の場合を示し、図４の（ｂ）は照射波長λが象牙質における最大吸収波長λ_ｄｅｎ未満の場合を示している。図４の横軸は平均パワー（ｍＷ）および平均パワー密度（Ｗ／ｃｍ^２）を示し、縦軸は切削の深さ（μｍ）を示す。薄色の矢印は測定限界の上限および下限を示す。
【図５】図５は、９．７μｍのＦＥＬ照射をしたときの象牙質のスペクトルの平均パワー依存性を示したものである。図５の横軸は波長（μｍ）を示し、縦軸は吸光度（ａ．ｕ．）を示す。各曲線はそれぞれ３ｍＷ、６ｍＷ、１１ｍＷ、１６ｍＷ、２２ｍＷ、３３ｍＷ、および未照射（斜線入り白線）の場合を示す。
【図６】図６は、最大吸収波長に対する平均パワーおよび照射波長の依存性を示す。図６の（ａ）は、照射波長λが象牙質における最大吸収波長λ_ｄｅｎ以上の場合を示し、図６の（ｂ）は照射波長λが象牙質における最大吸収波長λ_ｄｅｎ未満の場合を示している。図６の横軸は平均パワー（ｍＷ）および平均パワー密度（Ｗ／ｃｍ^２）を示し、縦軸は最大吸収波長（μｍ）を示す。
【図７】図７は、Ｐ／Ｃａ比に対する平均パワーおよび照射波長の依存性を示す。図７の（ａ）は、照射波長λが象牙質における最大吸収波長λ_ｄｅｎ以上の場合を示し、図７の（ｂ）は照射波長λが象牙質における最大吸収波長λ_ｄｅｎ未満の場合を示している。図７の横軸は平均パワー（ｍＷ）および平均パワー密度（Ｗ／ｃｍ^２）を示し、縦軸はＰ／Ｃａ比を示す。薄色の矢印は測定限界の下限を示すものである。
【図８】図８は、平均パワー（２−３５ｍＷ）／照射波長（８．８−１０．６μｍ）のパラメータに対応する実験結果のまとめを示す。図８の横軸は、平均パワー（ｍＷ）、平均パワー密度（Ｗ／ｃｍ^２）を示し、図８の縦軸は照射波長（μｍ）を示す。矢印は象牙質における最大吸収波長λ_ｄｅｎおよびヒドロキシアパタイトの最大吸収波長λ_ＨＡｐを示す。楕円は顕著に切削することなく、効果的に改質することができるパラメーター領域を示す。
【図９】図９は、波長９．０μｍ、９．６μｍ、１０．６μｍにおけるレーザー誘起音強度の時間的変化（０−１０秒）を示す。図９の横軸は時間（秒）を示し、縦軸は誘起音強度（ａ．ｕ．）を示す。図９の（ａ）は照射波長９．０μｍの場合を示し、図９（ｂ）は照射波長９．６μｍの場合を示し、図９の（ｃ）は照射波長１０．６μｍの場合を示す。丸印を付した線は、平均パワー密度が４２Ｗ／ｃｍ^２を示し、四角印を付した線は、平均パワー密度が２８Ｗ／ｃｍ^２を示し、三角印を付した線は、平均パワー密度が１４Ｗ／ｃｍ^２を示し、バツ印を付した線は、平均パワー密度が７Ｗ／ｃｍ^２を示す。
【図１０】図１０は、照射波長９．０μｍ、照射時間ｔ＝０．５、３、５秒における照射後の象牙質表面の空間プロファイルを示す。図１０の横軸は位置（μｍ）を示し、縦軸は切削の深さ（μｍ）を示す。図１０の（ａ）は照射時間が０．５秒の場合を示し、図１０の（ｂ）は照射時間が３秒の場合を示し、図１０の（ｃ）は照射時間が５秒の場合を示す。黒い実線は平均パワー密度が４２Ｗ／ｃｍ^２を示し、黒い破線は平均パワー密度が２８Ｗ／ｃｍ^２を示し、灰色の破線は平均パワー密度が１４Ｗ／ｃｍ^２を示し、細い実線は平均パワー密度が７Ｗ／ｃｍ^２を示す。
【図１１】図１１は、照射波長９．０μｍ、照射時間ｔ＝０．５、３、５秒における照射後の象牙質の中赤外吸収スペクトルを示す。図１１の横軸は波長（μｍ）を示し、縦軸は吸光度（ａ．ｕ．）を示す。図１１の（ａ）は、照射時間が０．５秒の場合を示し、図１１の（ｂ）は、照射時間が３秒の場合を示し、図１１の（ｃ）は照射時間が５秒の場合を示す。太い黒い実線は平均パワー密度が４２Ｗ／ｃｍ^２を示し、太い黒灰色線は、平均パワー密度が２８Ｗ／ｃｍ^２を示し、灰色の線は、平均パワー密度が１４Ｗ／ｃｍ^２を示し、細い実線は、平均パワー密度が７Ｗ／ｃｍ^２を示す。灰色の細線は未照射の場合を示す。
【図１２】図１２は、本実験で使用した照射パラメータを、発生したレーザー誘起音の最大強度Ｉ_ｍａｘによって４つのグループに分類した結果を示す。図１２は図８に衝撃音の観測結果として４Ａ〜４Ｄの分類を新たに付加したものである。
【図１３】図１３は、照射平均パワー密度１４Ｗ／ｃｍ^２における照射波長９．０μｍ、９．６μｍのレーザー誘起音強度、切削の深さ、吸収ピーク比の時間変化を示す。図１３の横軸は時間（秒）を示し、縦軸は誘起音強度（ａ．ｕ．）を示す。図９の（ａ）は照射波長９．０μｍの場合を示し、図１３の（ｂ）は照射波長９．６μｍの場合を示す。丸印を付した線は、誘起音強度を示し、四角印を付した線は、切削の深度を示し、三角印を付した線は、吸収ピーク比を示す。
【図１４】図１４は、発明による歯科治療・予防をフロチャートにまとめたものである。
【図１５】図１５は、本発明のレーザー光による歯の治療・予防用装置の例を示す。
【符号の説明】
１　　レーザー光の波長の選択部を操作するための波長選択ボタン
２　　レーザー光の波長の選択部を操作するための波長選択ボタン
３　　表示部
４　　レーザー照射部
５　　レーザー誘起衝撃音の検知部
６　　衝撃音伝送用ファイバー
７　　レーザ光伝送用ファイバー
８　　歯９の患部
９　　歯
１０　　本発明のレーザー光による歯の治療・予防用装置
１１　　レーザー光の照射強度の調整部を操作するためのツマミ
１２　　出力パワーメーター
１３　　エナメル質
１４　　象牙質[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus capable of performing caries prevention and treatment by laser irradiation, determining an irradiation site at the same time, and controlling irradiation conditions. More specifically, laser light capable of selectively preventing caries (improving dentin surface), treating caries (removing caries), and / or determining laser irradiation conditions (detecting laser-induced impact sounds) The present invention relates to a device for treating and preventing teeth by using the method.
More specifically, the present invention relates to an apparatus for treating and preventing teeth with a laser, which has a wavelength of 9.0 μm ± 0.3 μm and has a high power density for treating dental caries. An apparatus for treating and preventing teeth by laser light, comprising a laser irradiation part capable of irradiating light to an affected part, and an apparatus for treating and preventing teeth by laser, wherein a surface modification of dentin of teeth is performed. The treatment and prevention of tooth by laser light, having a laser irradiation part having a wavelength of 9.7 μm ± 0.3 μm and capable of irradiating the affected part with a laser light of low power density irradiation to prevent dental caries. Device for treating and preventing teeth with a laser, which is used to determine a laser beam irradiation site and / or a laser beam irradiation time based on a change in an impact sound caused by laser beam irradiation on an affected part. Detecting the impact sound at the irradiation site of Heather light relates to the treatment and prevention device of the teeth by a laser beam, characterized in that it has a which can be monitored devices.
[0002]
[Prior art]
A method using a laser has been developed as an alternative to a mechanical drill for cutting cavities. Laser caries treatment has attracted attention as a treatment method with less discomfort like a mechanical drill and less burden on the patient. 2. Description of the Related Art Conventionally, laser light of various wavelengths in the ultraviolet, near-infrared, and mid-infrared light regions has been used for cutting and modifying dental hard tissue with a laser. For example, in the method described in Japanese Patent Publication No. 9-506525, laser light having a wavelength of 300 to 600 nm, preferably 320 to 410 nm is used, and in Japanese Patent Application Laid-Open No. 5-506593, laser light having a wavelength of 320 to 520 nm is used. The use is described. Japanese Patent Application Laid-Open No. 2000-302622 describes a method for modifying a tooth by giving a tooth modifying agent comprising an apatite precursor a vibration having a wavelength of less than 8.8 to 10 μm.
[0003]
As described above, tooth hard tissue dental treatment by laser irradiation includes not only tooth decay treatment for cutting the haptic part of the hard tissue, but also tooth decay prevention for improving the acid resistance of enamel and dentin surfaces. Both use physical, chemical, and morphological changes in tooth tissue due to photo-thermal and mechanical interaction, and always have the side effect of heat damage to hard and soft tissues.
It is well known that dental dentin is more soluble than enamel due to the action of acid in the oral cavity. Both tooth dentin and enamel are mainly composed of hydroxyapatite (HAp: Ca₁₀(PO₄)₆(OH)₂), But their crystallinity and elemental composition are different from each other. Dentin has low crystallinity, contains excess P nuclides, other substances such as water and organic substances, is brittle, and is easily soluble in acids. Enamel is highly crystalline, hard, and hardly soluble in acids. For this reason, even if the enamel is carious, if the dentin can be recrystallized to form an enamel-like or HAp-like layer on its surface, ie, the surface of the dentin Modification to make it similar to enamel will lead to prevention of dental caries. In addition, it is also effective in preventing dental caries in the root surface of the elderly. Such surface modification refers to physical, chemical, and structural changes in the structure, including recrystallization, and surface modification such as recrystallization occurs on the order of 1000 ° C. Alternatively, because the temperature range is higher and the time range is on the order of microseconds, a pulse laser that can heat the surface layer of the object in a short time and locally can be applied to make it non-invasive and efficient. It is important to recrystallize dentin.
Ogino et al. Showed that dentin surface modification was performed by irradiating a free electron laser (FEL) with a wavelength of 9.4 μm to form a HAp-like layer (S. Ogino, et al., SPIE). Proceedings, {2922, {184-192} (1996)). It is explained that the surface modification in this method may be due to both the annealing effect of the laser and the change in elemental composition. The former is the result of heating and the latter is the result of the selective removal of P nuclides from the irradiated dentin (S. Ogino, et al., Nucl. Instr. And Meth. B, 144, 236-239). (1998)). On the other hand, studies performed on HAp coated on metal substrates show that the P nuclide is selectively depleted due to its high volatility, ie, due to heating and not to ablation. It has also been reported that there is no such substance (V. \ N. \ Bragratshvili, \ et \ al., \ Appl. \ Phys. \ Let., \ 66, \ 2451-2453} (1995). In addition, only a limited number of studies have been conducted on the effect of mid-infrared (MIR) pulse laser irradiation on dentin (eg, D. N. Dederich, et al., Ａｓ Lasers in Life). Sciences, {2, {39-51} (1988), etc.). Therefore, the mechanism of dentin surface modification has not yet been fully elucidated.
[0004]
Thus, a technique using a laser for preventive treatment of teeth has been developed. However, these technologies apply the photothermal interaction, light shock interaction, and photochemical interaction between the laser and the living body, and the parameter ranges (wavelength, power density, etc.) of the laser that cause each action, for example, The photothermal interaction is in the low power density region (0.1-several MW / cm).²), The light shock interaction is in the high power density region (several MW / cm)²The above-mentioned details have not been studied in detail, and the conditions of the incident laser for realizing only the desired therapeutic effect are controlled with high accuracy, and only the interaction suitable for that is excited and examined. No device for treatment or diagnosis has been developed.
For this reason, in the conventional laser device for dental treatment, the wavelength, power density, pulse width, etc. of the laser used for the treatment are not optimized, so that not only the desired therapeutic effect cannot be obtained, but also the The risk of side effects due to irradiation / erroneous irradiation was also great.
In severe cases, adverse effects such as thermal damage or destruction of normal parts due to over-irradiation or erroneous irradiation have been reported. In order to overcome these problems, there is a need for a precise control means for performing a treatment by causing only a desired laser biological interaction in a limited interaction region.
In addition, there was no laser irradiation apparatus mainly for dentin surface modification by laser.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide an apparatus for treating, preventing, and diagnosing teeth, which realizes optimization of interaction between a laser and a living body and has control means for optimization.
More specifically, prevention of tooth decay (modification of dentin surface) and treatment of tooth decay (removal of carious parts) are efficiently and minimally realized only at the target site, ie, prevention of tooth decay (surface of dentin). Modification) uses mainly photothermal interaction to minimize the amount of dentin cut and increase the acid resistance and mechanical strength of the dentin. In caries treatment (removal of carious parts), the area around the absorption area is used. It is an object of the present invention to provide a dental treatment / prevention / diagnosis device capable of controlling optimal conditions for mainly using light impact interaction to realize high-efficiency cutting in order to suppress thermal damage of teeth.
Another object of the present invention is to provide an apparatus for treating, preventing, and diagnosing teeth provided with means for avoiding erroneous irradiation and over-irradiation of laser light in treating, preventing, and diagnosing teeth. With conventional laser devices, it was not possible to objectively grasp the end point of treatment by laser irradiation, and the end point had to be determined based on the physician's subjective judgment and empirical rules. Irradiation side effects have been a problem. When the laser used is infrared light or ultraviolet light, the optical path is invisible, so it is not only impossible to check the irradiation spot visually, but also objectively to irradiate the correct part. It was not possible to determine whether the laser light was correctly irradiated on the target site, and there was a problem of erroneous irradiation of the laser light. In order to avoid such erroneous irradiation / overirradiation, it is essential to monitor the target site during laser treatment / prevention in situ, but the present invention provides a simple, accurate and objective monitoring means, and the provision of such means. The present invention provides an apparatus for treating, preventing, and diagnosing a tooth.
[0006]
[Means for Solving the Problems]
The present inventors studied the light absorption characteristics of tooth enamel and dentin in detail, and studied the change of the impact sound due to laser irradiation in detail to control the laser irradiation conditions, By monitoring the sound, it was possible to selectively prevent and treat caries by laser light, and found that erroneous or over-irradiation of laser light could be avoided.
[0007]
That is, the present invention relates to an apparatus for treating and preventing teeth with a laser, which has a wavelength of 9.0 μm ± 0.3 μm and is irradiated with a high power density, for example, a peak power density, for treating dental caries. 1 to 10 MW / cm²The present invention relates to an apparatus for treating / preventing teeth with laser light, which has a laser irradiation part capable of irradiating the above-mentioned laser light to an affected part.
The present invention also relates to an apparatus for treating and preventing teeth with a laser, which has a wavelength of 9.7 μm ± 0.3 μm and has a low power density for preventing tooth decay due to surface modification of dentin. For example, 100 to 1000 kW / cm in peak power density²The present invention relates to an apparatus for treating / preventing teeth with laser light, which has a laser irradiation part capable of irradiating the affected part with the following laser light.
Further, the present invention relates to an apparatus for treating and preventing teeth with a laser, which has a wavelength of 9.0 μm ± 0.3 μm and has a high power density irradiation, for example, a peak power density, for treating dental caries. 1 to 10 MW / cm²A laser irradiation part capable of irradiating the above laser beam to the affected part, and a low power density irradiation having a wavelength of 9.7 μm ± 0.3 μm for prevention of tooth decay due to surface modification of the dentin of teeth, for example, peak power density 100 to 1000 kW / cm²The present invention relates to an apparatus for treating / preventing teeth with laser light, which has a laser irradiation part capable of irradiating the affected part with the following laser light.
Further, the present invention is an apparatus for treating and preventing teeth with a laser, which is used for determining a portion to be irradiated with laser light and / or an irradiation time of laser light based on a change in an impact sound caused by the irradiation of the laser light to an affected part. The present invention relates to a device for treating / preventing teeth with laser light, comprising a device capable of detecting and monitoring an impact sound at a laser light irradiation site.
[0008]
The present inventors have studied the light absorption characteristics of enamel and dentin, which are hard dental tissues.
FIG. 1 shows the absorption curves of enamel, dentin, and hydroxyapatite (HAp), which are hard dental tissues. The horizontal axis in FIG. 1 shows the wavelength (μm), and the vertical axis shows the absorption intensity. The black line indicates the absorption of dentin, the white gray line indicates the absorption of enamel, and the black gray line indicates the absorption of hydroxyapatite (HAp). These are the phosphate ions (PO₄Due to the stretching vibration of ()), strong absorption is exhibited in the mid-infrared region of 9.0 to 10.0 μm. As shown in FIG. 1, the maximum absorption wavelength λ of dentin and enamel_denIs about 9.7 μm, and the maximum absorption wavelength λ of HAp_HApIs about 9.0 μm. The dentin absorption spectrum clearly shows two components, one of which is the maximum absorption wavelength λ._denIs at about 9.7 μm, and the other is in the shoulder on the shorter wavelength side (see also the enlarged spectrum of unirradiated dentin shown in FIG. 5). The component on the long wavelength side is PO having a low binding energy.₄The component on the short wavelength side is composed of PO having high binding energy.₄The interaction between the laser and the tissue is expected to strongly depend on the irradiation wavelength. Further, in dentin, there is a weak absorption band attributable to organic substances and water in a region of 6.0 to 7.0 μm.
[0009]
The present inventors conducted a series of experiments on dentin using MIR-FEL in order to macroscopically and qualitatively know the parameters (wavelength, average power density, etc.) necessary for surface modification. The MIR-FEL at the FEL research facility (iFEL) of Osaka University has a double pulse structure of a macro pulse and a micro pulse. The pulse width / pulse interval of the macro pulse and the micro pulse is １５15 μs /0.1 s and ５5 ps / 44.8 ns, respectively. One macro pulse consists of ~ 330 micro pulses. Here, what should be noted is the average power density or the peak power density of the macro pulse, not the peak power density per micro pulse. The reason for this is that the heating effect on the tissue is mostly caused by macropulses, not micropulses. Average power density 1W / cm²Is 1 (W / cm) when converted to the peak power density per macro pulse.²) / 10 (Hz) / 15 (μs) = 6.6 kW / cm²It becomes. Hereinafter, the description will be made using the average power (W) as the input power. Originally, it should be expressed as the peak density per macro pulse.
[0010]
An experiment was conducted by irradiating a MIR-FEL to a bovine dentin plate sample. Wavelength is dentin PO₄The absorption band derived from the molecular vibration mode was changed in the range of 8.8-10.6 μm. Table 1 shows the laser parameters used.
[0011]
[Table 1]

[0012]
The irradiation time is 100 s. The spot shape is elliptical, the spot size is 260 μm × 350 μm, and the spot area is 2.86 × 10^-3cm²Met.
FIG. 2 shows the layout of the experimental apparatus. The illumination system consists of a reduction optics, polarizer, He-Ne laser, parabolic mirror, power meter, microscope, and sample stage. The beam size of the MIR-FEL was reduced from about 50 mm in diameter to about 10 mm using a reduction optical system. The average power was varied within a range of 2-35 mW with a ZnSe polarizer. Average power was measured with a power meter immediately before irradiation. The sample was placed horizontally on a sample stage and irradiated with a beam focused by a parabolic mirror. The shape of the condensed beam was almost elliptical, and the full width at half maximum was 260 μm × 350 μm (error: ２０20 μm).
[0013]
FIG. 3 shows a photograph, which is replaced with a drawing, showing a structural change of the dentin surface when irradiated with a 9.7 μm free electron laser (FEL). The photograph was measured by a scanning electron microscope (SEM: Hitachi, Ltd., Japan, S-4200). (A), (b), (c), (d), and (e) of the SEM images are at average powers of 3 mW, 6 mW, 11 mW, 16 mW, and 33 mW, respectively. The magnification of the image is 300 times. White arrows indicate the same direction. The SEM image shows that the depth and diameter of the crater become deeper and larger as the average power increases. A porous crack-like structure or a molten bubble-like structure is observed in the peripheral part of the crater and / or in the center of the crater.
FIG. 3F shows a spatial profile of cutting. The horizontal axis in (f) of FIG. 3 indicates the position (μm), and the vertical axis indicates the cutting depth (μm). The fact that the spatial profile data of the 16 mW irradiation disappears near the center is due to the detection limit. The surface shape was measured with a surface profile device (ULVAC, @Japan, @ DEKTAK3). The measurement accuracy was 1 nm. As described above, the cutting depth increases as the average power increases. The cutting depth was 1.85 μm for (a), 14.5 μm for (b), 32.8 μm for (c), less than 40 μm for (d), and 44 μm for (e). Here, the cutting depth was defined as the distance from the dentin surface to the deepest part.
[0014]
Next, the present inventors have studied the improvement of acid resistance of dentin using bovine cervical dentin using a mid-infrared free electron laser (MIR-FEL). Dentin is 70% hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: HAp), 12% water, 18% organic matter, and has a complicated structure such as dentinal tubules. Improving the acid resistance of dentin requires simultaneously (1) improving the crystallinity of HAp, which is a hard tissue, (2) removing impurities (water and organic substances), and (3) sealing the dentin tubule.
It is important for minimally invasive treatment to minimize dentine removal. In order to quantify the optimal parameter region for dentin surface modification by irradiation with mid-infrared light, we used HAp PO₄In the absorption band region (8.8-10.6 μm) derived from the stretching vibration mode, a bovine dentin irradiation experiment was performed using the wavelength and average power as parameters. The irradiation time at this time was 100 seconds. The surface modification of dentin was evaluated from (1) cutting depth, (2) mid-infrared absorption spectrum, and (3) elemental composition. The cutting depth after irradiation is measured with a surface roughness meter, and the maximum cutting depth of 3 μm or less is classified as 1A, 3-10 μm or less as 1B, and 10 μm or more as 1C. , Classified into three regions. Next, from the absorption spectrum of the dentin after irradiation measured by a Fourier transform infrared absorption spectrum measuring device (FT-IR), a shift of the maximum absorption wavelength from around 9.7 μm to around 9.0 μm was observed. . The absorption peak wavelength of the synthetic HAp is around 9.0 μm, and this wavelength shift suggests dentin denaturation, that is, an improvement in crystallinity. Depending on the presence or absence of an absorption peak shift, the case without a shift was classified as 2A, and the case with a shift was classified as 2B. Furthermore, since dentin contains more phosphorus than HAp and enamel, it is necessary to control the element composition, that is, selectively remove phosphorus, for surface modification. Here, the element composition is defined as the element ratio of P to Ca (P / Ca ratio). The P / Ca ratio was 0.658 ± 0.02 for dentin, 0.583 ± 0.02 for enamel, and 0.549 ± 0.02 for synthetic HAp. In the P / Ca ratio, 0.583 or less was classified as 3A, and 0.583 or more was classified as 3B.
[0015]
FIG. 4 shows the experimental results of the cutting depth after laser irradiation. FIG. 4A shows that the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denFIG. 4B shows the case where the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denThe case of less than is shown. The horizontal axis in FIG. 4 is the average power (mW) and the average power density (W / cm).²), And the vertical axis indicates the cutting depth (μm). Light colored arrows indicate the upper and lower limits of the measurement limit. The degree of cutting was classified into 1A (0-3 μm), 1B (3-10 μm), and 1C (10 μm or more). FIGS. 4 (a) and 4 (b) show the irradiation wavelength range λ ≧ λ, respectively._denAnd λ <λ_den2 shows the correlation between the cutting depth and the average power (average power density). λ ≧ λ_denThen λ_denIn the vicinity of, a considerable amount of cutting was observed even in a region with a low average power (5 mW or less), but in a region with a high average power (20 mW or more), λ_denThe cutting depth in the vicinity has decreased slightly. λ <λ_denWhen the average power was increased, the cutting depth increased in all the irradiation wavelength ranges tested. As described above, the degree of cutting was roughly classified into three groups. That is, (1) 1A (slight cutting), (2) 1B (medium cutting), and (3) 1C (significant cutting). The laser parameters corresponding to groups 1A to 1C are as follows. (1) At 10.6 μm and 10.3 μm, the average power is less than 10 mW; below 10.0 μm, the average power is less than 5 mW; (2) At 10.6 μm, the average power is 10 mW to 15 mW; (3) 10. Power is approximately 10 mW, average power is 5 mW to 10 mW at 10.0 μm, average power is 5 mW to 7-8 mW at 9.8 μm and 9.7 μm, and average power is 5 mW to 10 mW at 9.5 μm or less; The average power is 15 mW or more at 6 μm, the average power is 10 mW or more at 10.3 μm and 10.0 μm, the average power is 7-8 mW or more at 9.7 μm and 9.8 μm, and the average power is 10 mW or more at 9.5 μm or less. Thus, the degree of cutting was found to be strongly dependent on wavelength and / or average power.
[0016]
Next, the mid-infrared (MIR) absorption spectrum was examined. MIR absorption spectra before and after laser irradiation were measured by FT-IR (Horiba. Japan, FT-520). The measurement range of FT-IR was 3 to 14 μm, and the resolution was less than 0.01 μm.
The absorption spectrum of the dentin when irradiated with 9.7 μm FEL is shown for each average power (FIG. 5). The horizontal axis in FIG. 5 indicates the wavelength (μm), and the vertical axis indicates the absorbance (au). Each curve shows the case of 3 mW, 6 mW, 11 mW, 16 mW, 22 mW, 33 mW, and the case of non-irradiation (hatched white line).
As the average power increases, the absorbance gradually decreases from the long wavelength side, with the result that the maximum absorption wavelength shifts to the short wavelength side. The spectrum width is narrow in a region where the average power is low (11 mW or less), and the spectrum width is wide in a region where the average power is high (16 mW or more). The absorption spectrum in the low power region is almost the same as that of HAp. That is, the shift in the maximum absorption wavelength indicates that the surface of the dentin has been modified into a HAp-like substance. In the high power region, the absorbance decreases overall, and PO₄This suggests that the vibration mode component disappeared from the dentin surface. Further, the weak absorption band of 6.0 to 7.0 μm due to water and organic matter completely disappeared with the shift of the maximum absorption wavelength.
FIG. 6 shows the average power and the irradiation wavelength dependence with respect to the maximum absorption wavelength of the dentin after irradiation. FIG. 6A shows that the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._{de n}FIG. 6B shows the case where the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denThe case of less than is shown. The horizontal axis in FIG. 6 is the average power (mW) and the average power density (W / cm).²) And the vertical axis indicates the maximum absorption wavelength (μm). In each case except for 9.8 μm (line with black diamonds in FIG. 6A) and 10.0 μm (line with gray triangles in FIG. 6A), the results shown in FIG. Similarly, as the average power increases, the maximum absorption wavelength becomes the maximum absorption wavelength λ of hydroxyapatite._HAp= 9.0 μm. In particular, the irradiation wavelength λ_denOr λ_HApIn the vicinity, a significant shift was observed even in a relatively low power region. These irradiation wavelength regions are respectively represented by (1) λ_denClassify the neighborhood as 2A, and (2) λ_HApThe vicinity was classified as 2B. The laser parameters in the 2A region and the 2B region are (1) an average power of less than 10 mW at 10.6 μm, an average power of less than 5 mW at 10.3 μm or less, and (2) an average power of 10 mW or more at 10.6 μm. At 0.3 μm or less, the average power is 6-8 mW or more.
Thus, it was found that dentin surface modification (spectral change) mainly occurred in the 2B parameter region. PO₄The strong absorption band derived from the vibration mode disappears in the high power region (15 mW or more) as described in FIG.
[0017]
Next, the elemental composition in the tooth tissue was examined. The element composition was measured with an energy dispersive X-ray spectrometer (Horiba, Japan, EMAX-5770). The energy resolution is 144 eV or less, and is represented by the composition ratio of P to Ca. The unirradiated dentin, enamel, and HAp have a P / Ca ratio of 0.658 ± 0.02, 0.583 ± 0.02, 0.549 ± 0.02, respectively. Dentin contains relatively many P nuclides. This is consistent with the fact that the absorption spectrum width of dentin is wider than that of enamel HAp.
FIG. 7 shows the experimental results of the element composition. FIG. 7 shows the average power and the irradiation wavelength dependency with respect to the P / Ca ratio. FIG. 7A shows that the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denFIG. 7B shows the case where the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denThe case of less than is shown. The horizontal axis in FIG. 7 is the average power (mW) and the average power density (W / cm).²), And the vertical axis indicates the P / Ca ratio. Light colored arrows indicate the lower limit of the measurement limit. The P / Ca ratio is classified into the following two regions. That is, (1) 3A (enamel to HAp) and (2) 3B (dentin to enamel). The laser parameters in the 3A and 3B regions are as follows: (1) Average power is 15 mW or more at 10.6 μm, average power is 7 mW or more at 9.7-10.3 μm, and average power is 10 mW at 9.5 μm or less. (2) The average power is less than 15 mW at 10.6 μm, the average power is less than 7 mW at 9.7-10.3 μm, and the average power is less than 10 mW at 9.5 μm or less.
These results indicate that the P / Ca ratio depends on the average power and the irradiation wavelength. In any case, the P / Ca ratio sharply decreases as the average power increases in the low average power region (10 mW or less), but the P / Ca ratio depends on the average power in the high average power region (20 mW or more). Constant. This indicates that P nuclides are preferentially removed in the low power region and all substances are removed from dentin in the high power region. Further, the P / Ca ratio could not be measured in the high average power region exceeding about 25 mW, which is considered to be due to the significant removal of the P nuclide from the surface layer of dentin.
[0018]
In this way, the degree of surface modification by the wavelength and average power of irradiation was examined macroscopically and classified into the following groups: (1) cutting depth (1A-1C), (2) MIR absorption spectrum ( 2A, 2B), (3) Elemental composition (3A, 3B). Irradiated dentin belonging to each group has different physical and chemical properties.
Dentin is more susceptible to lasers such as heating and cutting than enamel. This is because dentin contains a lot of organic matter and water. Furthermore, the laser light in the MIR region easily functions as a heat source because it is easily absorbed by living tissue. Therefore, it is very important to search quantitatively and qualitatively for the parameters of the laser necessary for causing the target position to react selectively.
[0019]
FIG. 8 shows a summary of the experimental results for the parameters of average power (2-35 mW) / wavelength (8.8-10.6 μm). The horizontal axis in FIG. 8 is the average power (mW) and the average power density (W / cm).²), And the vertical axis in FIG. 8 indicates the irradiation wavelength (μm). Arrow indicates maximum absorption wavelength λ in dentin_denAbsorption wavelength λ of hydroxyapatite and hydroxyapatite_HApIs shown. The ellipse indicates a parameter region where surface modification can be performed effectively while minimizing dentin cutting.
The following was found from these results. (1) The dentin surface has a laser wavelength in the strong absorption region, particularly λ_den, Are significantly modified in the vicinity of. Surface modification refers to changes in the structure, absorption spectrum, and elemental composition of the irradiated site. On the long wavelength side (10.3 μm or more), the modification by laser is not sufficiently performed because the absorption coefficient is low. Previous CO₂In the enamel acid resistance test using laser,_denThe near irradiation wavelength effectively improved the physical and chemical properties against caries. To change the physical and chemical properties of the surface while suppressing the amount of dentin cut, first of all, the wavelength of the laser and the average power density are changed by using a large ellipse (9.4-10. 3 μm and 10-20 W / cm²) Is preferably set. In this range, as shown in FIGS. 5 and 7, the P nuclide is selectively removed from the dentin surface. This was largely consistent with previously reported observations of the mass spectra of ions ablated from irradiated dentin. Furthermore, under the same laser conditions, recrystallization of the dentin after irradiation was clearly observed. (2) Second, the wavelength of the laser and the average power density were calculated using the small ellipse (8.8-9.4 μm and 10-15 W / cm) in FIG.²) Is preferably set. In this range, the P / Ca ratio falls within the 3B parameter region (dentin-enamel region), but a shift in the maximum absorption wavelength was observed. (3) As described with reference to FIG._denIn the vicinity, the cutting depth decreases at high average power irradiation. λ_denIn the vicinity, the absorption wavelength is λ during laser irradiation._denTo λ_HApShifts rapidly to This suggests that the laser energy will not be absorbed into the dentin over time. As described above, remarkable cutting always involves a wavelength shift. Therefore, the wavelength that appears to be optimal for effectively cutting hard tissue is the PO of high binding energy.₄Λ from vibration mode_HApAround 9.0 μm.
[0020]
In these experiments, the average power was used as the input parameter. Surface modification occurs on a time scale on the order of microseconds. Therefore, it is necessary to consider the laser power as a peak power per macro pulse, not an average power per second which is generally used. Since the pulse width of the macro pulse is about 15 μs, the peak power density per macro pulse is several hundred kW to several MW / cm.²Of the order.
[0021]
Next, the present inventors investigated the correlation between the laser-induced sound and the dentin surface modification under the laser parameters indicated by the circles in FIG. Specifically, we measured and compared the laser induced sound intensity, the shift of the absorption peak wavelength, and the temporal change of the cutting depth, and examined the possibility of monitoring the dentin surface modification by the laser induced sound.
[0022]
A plate-shaped dentin having an area of about 5 mm × 5 mm and a thickness of about 1 mm cut out from the cervix of the bovine teeth was used as a sample. In order to suppress the influence of light scattering due to the surface roughness, the sample surface was polished to a roughness of 1 μm or less. FEL light supplied from the MIR-FEL oscillation device was condensed by a parabolic mirror, and the condensed spot size was 260 μm × 350 μm (full width at half maximum). Irradiation wavelength (9.0, 9.3, 9.6, 10.3, 10.6 μm), irradiation time (0.2, 0.5, 1, 2, 3, 5, 10 sec), average power density ( 7, 14, 28, 42 W / cm²) Was changed as the irradiation parameter. An audible condenser microphone (measurable range: 0.01-20 kHz, no directivity) was installed at a location about 3 cm away from the irradiation position. In order to keep the sensitivity between irradiation parameters constant, the microphone position and data acquisition setup were fixed during the experiment. Then, the sound signal was transferred to a computer as a time waveform and stored using sound signal analysis software (Sound @ Forge).
[0023]
The pulse structure of the used MIR-FEL has a double pulse structure including a micro pulse and a macro pulse. The minimum pulse is a micro pulse having a pulse width of about 5 ps, and the pulse interval is 44.8 ns. A macro pulse refers to a group of about 330 micro pulses, and has a pulse width of about 15 μs and a pulse interval of 0.1 s. Considering the thermal relaxation process of the interaction between dentin and laser light, the micropulses in the macropulse can be considered as continuous waves, and the irradiation effect is caused by the heat accumulation effect of the micropulses. That is, the energy density per second (J 密度 / cm)²エ ネ ル ギ ー / s), not the energy density per macro pulse (J / cm)²/ Macropulse). In addition, there is no heat accumulation effect between macro pulses, and the induced interaction is integrated for each macro pulse.
[0024]
FIG. 9 shows the temporal change (0- 10 s) of the laser-induced sound intensity at the irradiation wavelengths of 9.0 μm, 9.6 μm, and 10.6 μm. The horizontal axis in FIG. 9 indicates the irradiation time (second), and the vertical axis indicates the induced sound intensity (au). FIG. 9A shows a case where the irradiation wavelength is 9.0 μm, FIG. 9B shows a case where the irradiation wavelength is 9.6 μm, and FIG. 9C shows a case where the irradiation wavelength is 10.6 μm. The circled line indicates that the average power density is 42 W / cm.²And the line with a square mark indicates that the average power density is 28 W / cm.²And the line with a triangle indicates that the average power density is 14 W / cm.², The line with the cross mark has an average power density of 7 W / cm²Is shown. Since the absolute calibration of the microphone has not been performed, the observed induced sound intensity cannot be evaluated as an absolute value, but can be quantitatively compared as a relative change between irradiation parameters. These observation results will be described in terms of (1) time change, (2) wavelength dependence, and (3) power dependence.
[0025]
As for the time change, the laser-induced sound intensity monotonously attenuated with the irradiation time, and became constant a few seconds later (see FIG. 9). In addition, a case where a constant value is taken immediately after irradiation is observed, and 9.0 μm · 7 W / cm², 10.6μm ・ 7-14W / cm²Although the signal strength was about 0.03-0.04, this signal level is regarded as a noise level.
In the wavelength dependence, the tendency that the induced sound intensity increased as the irradiation wavelength approached the absorption peak wavelength of the dentin of 9.7 μm was observed in all irradiation time regions. In the power dependence, as the irradiation average power density increased, the induced sound intensity also increased accordingly. It was noteworthy that the laser-induced sound intensity changed with the irradiation time.
[0026]
Next, FIG. 10 shows a spatial profile of the dentin surface after irradiation at an irradiation wavelength of 9.0 μm and irradiation times t = 0.5, 3, and 5 seconds. The horizontal axis in FIG. 10 indicates the position (μm), and the vertical axis indicates the cutting depth (μm). 10A shows a case where the irradiation time is 0.5 seconds, FIG. 10B shows a case where the irradiation time is 3 seconds, and FIG. 10C shows a case where the irradiation time is 5 seconds. Is shown. The black solid line indicates that the average power density is 42 W / cm.²The black dashed line indicates that the average power density is 28 W / cm²The gray dashed line indicates that the average power density is 14 W / cm.²And the thin solid line indicates that the average power density is 7 W / cm.²Is shown. The spatial profile was measured with a measurement accuracy of 1 nm using a surface roughness meter (ULVAC, DEKTAK3). The cutting depth was defined as the distance from the sample surface to the deepest part of the irradiation mark. The dependence of the cutting depth on the average power density and the change over time for each irradiation parameter will be described. As the average power density increases, the cutting depth increases, but the low average power density region (7 W / cm²In (), no morphological change was observed on the dentin surface. Thereby, at the irradiation wavelength of 9.0 μm, the threshold value for cutting dentin is 7-14 W / cm.²I knew it was in between. The cutting depths (expressed in (μm)) at times t = 0.5, 3, and 5 seconds at each irradiation power density were as follows. 7W / cm²(0.02, 0.02, 0.02), 14 W / cm²(2.67, 6.42, 4.7), 28 ° W / cm²(18.4, 31.4, 32.3), 42 W / cm²(26.3, 48.7, 57.1). As described above, the cutting depth has a remarkable irradiation time dependency. In particular, in the time domain 1 (attenuation phase) of the induced sound, the cutting of the dentin occurs effectively, while in the time domain 2 (the constant phase). It was found that there was almost no cutting effect.
[0027]
Next, the mid-infrared absorption spectrum of dentin after irradiation at an irradiation wavelength of 9.0 μm and irradiation times t = 0.5, 3, and 5 seconds is shown in FIG. The horizontal axis in FIG. 11 indicates the wavelength (μm), and the vertical axis indicates the absorbance (au). 11A shows a case where the irradiation time is 0.5 seconds, FIG. 11B shows a case where the irradiation time is 3 seconds, and FIG. 11C shows a case where the irradiation time is 5 seconds. Is shown. The thick black solid line indicates that the average power density is 42 W / cm.²The thick black-gray line indicates that the average power density is 28 W / cm²And the gray line indicates that the average power density was 14 W / cm.²And the thin solid line indicates that the average power density is 7 W / cm.²Is shown. The gray thin line shows the case without irradiation. The mid-infrared absorption spectrum was measured using a micro-reflection method of an FT-IR apparatus (HORIBA, FT-520), and the measurement wavelength range was 3 to 14 μm and the wavelength resolution was 0.01 μm. Since the absorbance obtained by the microreflection method depends on both the reflectance of the sample surface and the absorption characteristics of dentin, it is not possible to evaluate the absolute value of the absorbance. In the mid-infrared absorption spectrum of the non-irradiated dentin, there are two vibration mode components at 9.7 μm and 9.0 μm, forming a double peak (see FIG. 11). Similarly, the spectrum after irradiation is a double peak spectrum having an absorption peak at any of 9.0, 9.3, and 9.7 μm. Therefore, the absorbance ratio R of 9.0 μm to 9.3 μm or 9.7 μm_ACan be treated as an index indicating a spectrum change. R before irradiation_A<1 and R_A≧ 1. That is, R_A≧ 1 means that the absorption peak wavelength shifted to around 9.0 μm. Where R_A= 1 is regarded as a threshold value for surface modification as viewed from the mid-infrared absorption spectrum.
[0028]
Next, (1) a low power density region (7 ° W / cm²), (2) Medium power density region (14, 28 ° W / cm)²), (3) High power density region (42 W / cm²), And the change over time of the absorption spectrum will be described. (1) At t = 0.5 s, no change was observed in the absorption spectrum, which was almost the same as the spectrum of the non-irradiated dentin. At t = 3 s and 5 s, the absorption peak around 9.7 μm was slightly shifted to the shorter wavelength side, and a new absorption peak appeared around 9.1 μm. At this time, R_AWas 0.418 (t = 0.5 s), 0.654 (t = 3 s), and 0.743 (t = 5 s), which were 1 or less, which were below the surface modification threshold value. (2) At t = 0.5 s, the absorption peak around 9.7 μm disappeared, and a new absorption peak appeared around 9.4 μm. At t = 3 s and 5 s, a wavelength shift of the absorption peak wavelength to 9.0 μm was observed. 14W / cm²Then R_A= 0.918 (t = 0.5 s), 1.15 (t = 3 s), 1.26 (t = 5 s), 28 W / cm²Then R_A= 0.877 (t = 0.5 s), 1.60 (t = 3 s), 1.61 (t = 5 s), and R_A, And a remarkable change in spectrum was not observed between 3 and 5 seconds. (3) Regardless of the irradiation time, the absorption peak wavelength after irradiation was around 9.0 μm. R_AAre 1.54 (t = 0.5 s), 1.42 (t = 3 s), and 1.24 (t = 5 s), respectively, which exceed the surface modification thresholds. Irradiation time dependence was not observed. From (1) to (3), it was found that the shift of the absorption peak wavelength has different irradiation time dependence depending on the irradiation power density.
[0029]
In the above discussion, the correlation between the cutting and surface modification of the dentin (shift of the absorption peak wavelength) and the laser-induced sound intensity was determined by comparing the irradiation wavelength (9.0 μm) included in the optimal laser parameter region for dentin surface modification. , 9.6 μm), average power density 14 W / cm²We mainly used the observation data at.
Next, the irradiation parameters used in this experiment were changed to the maximum intensity I of the laser-induced sound generated._maxInto the following four groups (see FIG. 12). FIG. 12 is a diagram in which classifications of 4A to 4D are newly added to FIG. 8 as observation results of the impact sound. (4A) used in FIG._max<0.05, (4B) is 0.05 <I_max<0.1, (4C) is 0.1 <I_max<0.5, (4D) is I_max> 0.5. As described above, the induced sound intensity changes depending on the absorption characteristics of the dentin and the irradiation average power density. That is, the laser-induced sound intensity strongly depends on the laser energy absorbed in the dentin. Since the absorbed energy is one of the parameters governing the laser bio-interaction, it is possible to estimate the type and degree of the laser bio-interaction from the laser-induced sound intensity. Considering, as an example, 9.6 μm in the optimal wavelength region of dentin surface modification (in and near the ellipse in FIG. 12), the laser-induced sound intensity regions 4A-4B, 4C, and 4D are 1A / 2A / 3B, respectively. (No change) 1B / 2B / 3A (absorption peak wavelength shift = HAp conversion of dentin), which corresponds to the interaction region of 1C / 2B / 3A (cut). Therefore, the type and degree of the interaction can be monitored in real time during the treatment based on the acoustic signal level.
[0030]
Next, an irradiation average power density of 14 W / cm²FIG. 13 shows the time-dependent changes in the laser-induced sound intensity, the cutting depth, and the absorption peak ratio at the irradiation wavelengths of 9.0 μm and 9.6 μm in the measurement. The horizontal axis in FIG. 13 represents time (seconds), and the vertical axis represents induced sound intensity (au). FIG. 13A shows a case where the irradiation wavelength is 9.0 μm, and FIG. 13B shows a case where the irradiation wavelength is 9.6 μm. The line with a circle indicates the induced sound intensity, the line with a square indicates the depth of cutting, and the line with a triangle indicates the absorption peak ratio. As described above, the induced sound intensity takes a constant value after several seconds at both irradiation wavelengths. Although both the cutting depth and the absorption peak ratio clearly changed in the time domain 1 (attenuation phase) of the induced sound, no remarkable change was observed in the time domain 2 (constant phase). This means that in the time region 2, the laser is not efficiently absorbed into the dentin due to the change in the absorption characteristics of the dentin (absorption peak wavelength shift), and the desired interaction is not induced any more. Therefore, the end of the desired interaction can be monitored from the time transition of the induced sound intensity.
As described above, the possibility of real-time monitoring of the type and degree of the interaction based on the laser-induced sound intensity and the end of the interaction based on the time transition is shown. The former leads to avoiding over-irradiation and erroneous irradiation in laser treatment, and the latter leads to the determination of the end point of the treatment.
[0031]
In order to examine the correlation between laser-induced sound and surface modification / cutting of dentin, laser-induced sound intensity, cutting depth of dentin, and absorption peak wavelength shift were measured using mid-infrared FEL. From these observations, the following became clear. (1) The laser-induced sound was generated immediately after laser irradiation, attenuated monotonously, and became constant after a few seconds. Interactions such as dentin spectrum change (surface modification) and cutting frequently occur in the time domain in which the induced sound changes, but no remarkable interaction was observed in the time domain in which the induced sound was constant. (2) At the optimum irradiation wavelengths of 9.0 μm and 9.6 μm for surface modification, the signal level of the induced sound intensity tends to depend on the type and degree of interaction (no change, surface modification, cutting, etc.). Was seen. Information regarding (1) determining the end point of laser treatment and (2) avoiding over-irradiation / erroneous irradiation can be obtained in real time during irradiation. Thus, the possibility and effectiveness of the real-time monitoring method using laser-induced sound as one of the minimally invasive treatment techniques was clarified. The irradiation wavelength used in the present invention substantially matches the oscillation band of a carbon dioxide laser currently used as a treatment laser, and it is possible to develop a laser dental treatment irradiation apparatus to which this technology is applied.
[0032]
As described above, in the present invention, the correlation between the laser wavelength, the average power density, and the impact sound in dental treatment / prevention using a laser was examined, and it was found that there was an extremely useful correlation between them. . These results are summarized as follows.
1. Prevention of tooth decay
In the present invention, the surface of dentin can be modified by laser irradiation, and acid resistance and mechanical strength can be improved.For this purpose, the laser parameters have been optimized and the amount of dentin cut has been minimized. It is intended for dentin surface modification. Then, in order to make the target efficiently absorb the laser, that is, to effectively use the thermal effect, the present invention sets the wavelength of the irradiation laser to the absorption peak wavelength of the target substance (the absorption peak wavelength of the dentin: 9). .7 μm), and the irradiation peak power density (W / cm²) Is controlled with high accuracy and several hundred kW / cm²(This is called low-intensity power irradiation).
2. Treatment of caries. Removal of caries.
An object of the present invention is to effectively use a highly efficient cutting of a carious part, that is, a mechanical (impact) effect. In addition, the present invention provides relatively high intensity power density irradiation (several MW / cm) for the treatment of tooth decay and the efficient cutting of carious parts.²Above), since the maximum absorption wavelength of dental hard tissue after irradiation always changes to around 9.0 μm, if the irradiation laser wavelength is set to around 9.0 μm, the laser light will always be hard tissue. And is converted into heat and thermal stress, so that the target portion can be efficiently and selectively cut.
[0033]
The present invention also provides detection of laser-induced impact sound as an on-site monitoring technique in laser treatment and prevention of dentistry.
The present invention clarifies that laser-induced impact sound is generated during laser irradiation as a pressure wave with laser absorption, temperature rise, and thermal expansion, and that the intensity reflects the absorption characteristics of the irradiated part. The present invention provides means for avoiding over-irradiation or erroneous irradiation of the laser.
1. Avoid over-irradiation (determination of laser irradiation end point).
In both cases of prevention of caries and treatment of caries, conditions such as the wavelength of laser irradiation can be optimized by the method of the present invention described above, and the interaction between the laser and the living body is efficiently caused at the target site. be able to. In other words, the intensity of the impact sound is strong during treatment / prevention, but the intensity of the impact sound signal is increased due to the shift of the maximum absorption wavelength due to the modification (for caries prevention) and the cutting of hard tissue due to evaporation (for caries treatment). The present invention reveals for the first time that it gradually decreases and eventually reaches a constant value, and a constant acoustic signal means that the interaction has become inefficient, beyond which it can lead to thermal damage. Therefore, over-irradiation can be avoided if the time when the acoustic signal takes a constant value is set as the treatment / prevention end point, and the present invention provides a method for this purpose.
2. Avoid false irradiation.
The most conceivable site for erroneous irradiation is the soft tissue in the mouth. The intensity of the impulsive sound due to laser irradiation reflects the absorption characteristics of the substance at the irradiated site, and the absorption coefficient near 9.0-9.7 μm used in the present invention differs greatly between hard tissue and soft tissue. Large. In other words, under the parameters of the laser of the present invention for cutting and modifying hard tissue, the generated sound is extremely small in the case of soft tissue, and if no impact sound is detected immediately after laser irradiation, it means that the soft tissue is irradiated, that is, it is erroneous. It can be seen that irradiation was performed. Therefore, in this case, erroneous irradiation can be avoided by immediately shutting off the laser. The present invention provides a technique for this.
[0034]
FIG. 14 summarizes the above-described method of the present invention. FIG. 14 is a flowchart summarizing dental treatment and prevention according to the present invention.
For prevention of tooth decay (surface modification of dentin), a laser having a wavelength of about 9.7 μm is used, and this is irradiated to a target site. At the start of the irradiation, the acoustic intensity (Pa) of the laser-induced impact sound is detected. If the sound intensity is small, the irradiation of the laser is stopped due to erroneous irradiation. When Pa is large, irradiation is continued, and while Pa is changing, laser irradiation is continued. When Pa does not change and reaches a constant value, the laser irradiation is stopped because the reforming has been completed. This completes the prevention of tooth decay at the target site (surface modification of dentin).
For treatment of tooth decay (cutting of carious parts), a laser having a wavelength of about 9.0 μm is used, and this is irradiated to a target site. At the start of the irradiation, the acoustic intensity (Pa) of the laser-induced impact sound is detected. If the sound intensity is small, the irradiation of the laser is stopped due to erroneous irradiation. When Pa is large, irradiation is continued. Laser irradiation shifts the absorption peak wavelength of the carious part from around 9.7 μm to around 9.0 μm. This shift enables efficient cutting. Then, while Pa is changing, laser irradiation is continued. When Pa does not change and reaches a constant value, the cutting is completed, and the laser irradiation is stopped. This completes the treatment of caries (cutting of carious parts) at the target site.
[0035]
That is, the present invention provides a novel tooth treatment / prevention method using laser wavelength and irradiation intensity as parameters. More specifically, the present invention relates to a method for treating dental caries by irradiating a diseased part with a laser beam having a wavelength of 9.0 μm ± 0.3 μm and high power density irradiation for treating dental caries. Method of preventing dental caries by irradiating the affected part with a laser beam having a wavelength of 9.7 μm ± 0.3 μm and low power density irradiation for preventing dental caries by modifying the surface of the dentin of the tooth Is provided.
Another object of the present invention is to provide a method for avoiding erroneous irradiation and over-irradiation of a laser in a method for treating and preventing teeth with a laser by detecting a laser-induced impact sound. More specifically, the present invention relates to a method for treating / preventing teeth with a laser, in which a laser light irradiation site and / or a laser light irradiation time is determined based on a change in an impact sound caused by laser light irradiation on an affected part. A method of detecting an impact sound at a laser light irradiation site and avoiding erroneous laser irradiation, in which the laser light irradiation is stopped if the impact sound at the irradiation site at the start of laser light irradiation is small, Another object of the present invention is to provide a method for avoiding over-irradiation of a laser beam, in which the irradiation of the laser beam is stopped when the impact sound at the irradiation site at the time of the laser beam irradiation becomes constant.
[0036]
Further, the present invention provides a treatment / prevention device for the above-mentioned dental treatment / prevention. The apparatus for treating / preventing teeth with laser light according to the present invention includes a laser source and a laser irradiation unit, a laser light wavelength selection unit, and / or a laser light irradiation intensity adjustment unit. Further, as a device capable of detecting and monitoring a laser-induced impact sound at a laser beam irradiation site, a device having a laser-induced impact sound detection unit and an acoustic intensity measurement unit is exemplified.
The laser source of the dental treatment / prevention device using laser light of the present invention is not particularly limited as long as it can output a laser having a wavelength of about 9.0 μm and a wavelength of about 9.7 μm. As the laser source, one or two or more laser sources may be provided for each wavelength, or the wavelength may be converted by one laser source. Specific examples of the laser source include a free electron laser, a carbon dioxide laser, and a He—Ne laser. It is preferable that these lasers can supply laser light in a pulse form. The pulse may be a micro pulse, a macro pulse, or a combination thereof. The laser generated by the laser source is supplied to a laser irradiation unit via an appropriate optical path.
The wavelength of the laser to be irradiated is around 9.0 μm or around 9.7 μm, and may be near the maximum absorption wavelength of hydroxyapatite or near the maximum absorption wavelength of dentin of teeth. As a specific wavelength, a wavelength near 9.0 μm is preferably 8.7 to 9.3 μm, that is, 9.0 μm ± 0.3 μm, and more specifically, 9.0 μm ± 0.2 μm and 9.0 μm. ± 0.1 μm. The wavelength near 9.7 μm is preferably 9.4 to 10.0 μm, that is, 9.7 μm ± 0.3 μm, and more specifically, 9.7 μm ± 0.2 μm and 9.7 μm ± 0.1 μm. Can be As the laser beam wavelength selection unit of the dental treatment / prevention device using a laser beam of the present invention, a laser supplied from a laser source may be a laser having a wavelength of approximately 9.0 μm or a laser having a wavelength of approximately 9.7 μm. Anything can be selected as long as it can be selected. The wavelength may be selected by selecting a laser source, or the wavelength may be selected in the optical path of the laser.
[0037]
The adjustment unit of the laser light irradiation intensity of the apparatus for treating and preventing teeth with laser light of the present invention may be any unit that can adjust high power density irradiation and low power density irradiation, and the adjusting unit is not particularly limited. Absent. As the adjusting means, the output of the laser may be adjusted, or the power density may be adjusted by adjusting the size (focus) of the spot at the irradiation site.
The irradiation intensity of the laser beam of the present invention is 15 W / cm in average power density as high power density irradiation.²Or more, preferably 20 W / cm²Above, 25W / cm²Or more, or 30 W / cm²Above, low power density irradiation is 15 W / cm in average power density²Less than 10 W / cm²Below, or 7W / cm²It is as follows. In the present invention, the average power is used as a parameter of the laser input. In the treatment and prevention of teeth, since it can occur within a time of the order of microseconds, it is better to consider the average power as the peak power per macro pulse, rather than the average power per second normally used. It is important in implementing. Then, since the pulse width of the macro pulse is on the order of microseconds, for example, about 15 μs, the peak power density generated thereby is on the order of megawatts. That is, the energy density per second (J 密度 / cm)²エ ネ ル ギ ー / s), not the energy density per macro pulse (J / cm)²/ Macropulse). Thus, when the high power density irradiation of the present invention is expressed in terms of the power density per macro pulse, it depends on the length of the macro pulse, but is several MW / cm.²Above, several tens MW / cm²As described above, for example, 1 MW / cm²Above, 5MW / cm²Above, 7 MW / cm²More than 10 MW / cm²Or more, or 20 MW / cm²The above can also be said.
In the low power density irradiation of the present invention, when converted to the power density per macro pulse, it is several hundred kW / cm.²~ Several MW / cm²Degree, for example, 100 kW / cm²-10 MW / cm²Degree, 300 kW / cm²~ 5MW / cm²About 500kW / cm²~ 5MW / cm²It can also be called a degree.
[0038]
The laser irradiating unit of the apparatus for treating and preventing teeth with laser light according to the present invention is not particularly limited as long as it can accurately irradiate a target part with a laser. It may be a fixed type or a movable type. In addition, a small hand-held device may be used, but a hand-shake-preventing measure is preferably used to prevent hand-shake. The laser irradiation unit may be provided with an irradiation position display device capable of displaying the laser irradiation position with visible light.
The device capable of detecting and monitoring a laser-induced impact sound at a laser-irradiated portion of the apparatus for treating and preventing teeth with laser light according to the present invention includes a laser-induced impact sound detection unit and a sound intensity measurement unit. Are preferred.
The detection unit of the laser-induced impact sound of the apparatus for treating and preventing teeth with laser light according to the present invention may be any unit that can detect the laser-induced impact sound, and may be in the audible range or the ultrasonic range. For example, an audible microphone (measurable range: 0.01 to 20 kHz) or an ultrasonic wave of about 30 to 100 MHz may be detected. The laser-induced impact sound detection unit of the present invention can be installed at any position where the laser-induced impact sound from the irradiation position can be detected, for example, 1 to 15 cm, 1 to 10 cm, 1 to 5 cm from the laser irradiation position. Can be installed at any position within the range. The laser-induced impact sound detection unit of the present invention may be, for example, one incorporated in a laser irradiation unit.
As the sound intensity measuring unit of the apparatus for treating and preventing teeth with laser light of the present invention, a laser-induced impact sound can be measured as sound intensity, preferably as digitized sound intensity, as long as it can be measured and converted into data. Good.
[0039]
The tooth treatment / prevention device using a laser beam according to the present invention can arbitrarily add other parts in addition to the above-described parts within a range in accordance with the gist of the present invention. For example, a storage unit that can store a parameter that combines the wavelength of the laser and the irradiation intensity, an adjustment unit that can adjust the wavelength and the irradiation intensity of the laser as a set based on the data of the storage unit, data from the sound intensity measurement unit Processing unit, an adjustment unit that can adjust the irradiation of laser light according to the processing result of the processing unit, an image unit that can visualize the status of treatment and prevention at the laser irradiation position, and the like can be installed as necessary. it can.
[0040]
Embodiments of the apparatus for treating / preventing teeth with laser light of the present invention include a laser source and a laser irradiation unit, and an apparatus having a laser light wavelength selection unit, a laser source and a laser irradiation unit, and a laser light irradiation intensity. Examples of preferred embodiments include a laser source and a laser irradiation unit, and a device having a laser light wavelength selection unit and a laser light irradiation intensity adjustment unit. In addition, a laser source and a laser irradiation unit, a laser-induced impact sound detection unit, and a sound intensity measurement unit may be used. As a more preferred embodiment, a laser source, a laser irradiation unit, and a laser light wavelength selection unit, and a device having a laser-induced impact sound detection unit, and a sound intensity measurement unit, a laser source, a laser irradiation unit, and a laser An apparatus having a light irradiation intensity adjustment unit, a laser-induced impact sound detection unit, and a sound intensity measurement unit may be used. More preferred embodiments include an apparatus having a laser source, a laser irradiation unit, a laser light wavelength selection unit, and a laser light irradiation intensity adjustment unit, and a laser-induced impact sound detection unit, and a sound intensity measurement unit. Can be
[0041]
More specifically, the present invention relates to (1) an apparatus for treating and preventing teeth with a laser, which has a wavelength of 9.0 μm ± 0.3 μm and a high power density for treating dental caries. An apparatus for treating / preventing teeth by laser light, comprising: a laser irradiation part capable of irradiating an affected part with laser light for irradiation; (2) an apparatus for treating / preventing teeth by laser, comprising: A laser beam having a wavelength of 9.7 μm ± 0.3 μm and having a laser irradiation part capable of irradiating a low power density irradiation laser beam to an affected part for preventing dental caries by dentin surface modification. A device for treating and preventing teeth, (3) a device for treating and preventing teeth with a laser, which has a wavelength of 9.0 μm ± 0.3 μm and has a high power density for treating dental caries. That can irradiate the affected part with laser light A laser irradiation part having a wavelength of 9.7 μm ± 0.3 μm and capable of irradiating the affected part with a laser beam of low power density irradiation in order to prevent caries by modifying the surface of the dentin of the tooth; (4) A device for treating and preventing teeth with laser light, and (4) a device for treating and preventing teeth with laser, wherein a laser beam irradiates a laser beam to a diseased part, and a laser beam irradiating part changes. And / or a device capable of detecting and monitoring a laser-induced impact sound at a laser light irradiation site for determining a laser light irradiation time, for treating / preventing teeth with laser light. A device for treating and preventing teeth with a laser, the laser having a wavelength of 9.0 μm ± 0.3 μm and a high power density irradiation for treatment of dental caries. A laser irradiation part capable of irradiating the affected part with a laser beam, and a laser light of a low power density irradiation having a wavelength of 9.7 μm ± 0.3 μm for preventing tooth decay by surface modification of dentin of the tooth. An object of the present invention is to provide a laser treatment / prevention device using laser light, which has a laser irradiation part and a device capable of detecting and monitoring a laser-induced impact sound at a laser light irradiation site.
[0042]
FIG. 15 shows an example of a dental treatment / prevention apparatus using laser light according to the present invention. The laser treatment / prevention apparatus 10 of the present invention for a tooth treatment / prevention is capable of selecting a laser wavelength by using the selection buttons 1 and 2 for operating a selection section of the laser light. A knob 11 for operating the strength adjustment unit is provided. The laser light output from the dental treatment / prevention device 10 is transmitted to the laser irradiation unit 4 by the laser light transmission fiber 7 and is irradiated on the affected part 8 of the tooth 9. The laser-induced impact sound emitted from the laser-irradiated part is collected by the laser-induced impact sound detection unit 5 and is transmitted to the acoustic intensity measurement unit built into the tooth treatment / prevention device 10 by the impact sound transmission fiber 6. Transmitted. The dental treatment / prevention device 10 of this example includes an output waveform display unit 3 and an output power meter 12.
A method for treating / preventing the teeth 9 using the device 10 of this example will be described. When treating the carious part 8 of the tooth 9, the laser wavelength selection button 2 is operated to set the laser wavelength to 9.0 μm, and the output power adjustment knob 11 is operated to irradiate the output with high power density. Adjust as follows. The affected part 8 is irradiated with laser light emitted from the laser irradiation part 4, and the laser-induced impact sound at that time is collected by the laser-induced impact sound detection part 5, and after confirming that the impact sound is loud, the laser Irradiation to the affected part 8 is continued. When the impact sound becomes constant, the laser output is stopped and the treatment is completed. When prevention is performed by modifying the dentin surface of the teeth 9, the laser wavelength selection button 1 is operated to set the laser wavelength to 9.7 μm, and the output power adjustment knob 11 is operated to reduce the output to a low power density. Adjust so that irradiation is possible. The affected part 8 is irradiated with laser light emitted from the laser irradiation part 4, and the laser-induced impact sound at that time is collected by the laser-induced impact sound detection part 5, and after confirming that the impact sound is loud, the laser Irradiation to the affected part 8 is continued. When the impact sound becomes constant, stop laser output and complete tooth prevention.
[0043]
According to the present invention, in the treatment and prevention of teeth by laser, it is possible to optimize the laser in the cutting of carious parts and tartar of teeth, and in the surface modification of dentin of the teeth, and to reduce the laser-induced impact sound Erroneous irradiation or over-irradiation of the laser can be determined based on an objective criterion based on the standard, and erroneous irradiation or over-irradiation of the laser in the treatment and prevention of teeth can be reliably avoided.
[0044]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
[0045]
Example 1 (test for laser parameters)
(1) Laser device
In order to analyze macroscopically and qualitatively the parameters (wavelength, average power density, etc.) required for tooth surface treatment, a series of experiments on dentin were performed using a mid-infrared free electron laser (MIR-FEL). Was. The MIR-FEL used in this test has a double pulse structure of a macro pulse and a micro pulse. The pulse width / pulse interval of the macro pulse and the micro pulse is 15 μs / 0.1 s and 5 ps / 44.8 ns, respectively. One macro pulse consists of 330 micro pulses. Here, what should be noted is the average power density or the peak power density of the macro pulse, not the peak power density per micro pulse. The reason for this is that the heating effect on the tissue is mostly caused by macropulses, not micropulses.
Irradiation wavelength is dentin PO₄It was changed in the range of the absorption band (8.8-10.6 μm) derived from the vibration mode. Table 1 shows the laser parameters used. The irradiation time is 100 s. FIG. 2 shows the layout of the experimental apparatus. The beam size of the MIR-FEL was reduced from about 50 mm in diameter to about 10 mm using a reduction optical system. The average power was varied within a range of 2-35 mW with a ZnSe polarizer. Average power was measured with a power meter immediately before irradiation. The sample was placed horizontally on a sample stage and irradiated with a beam focused by a parabolic mirror. The shape of the condensed beam was almost elliptical, and the full width at half maximum was 260 μm × 350 μm (error: ２０20 μm). The spot size was not changed throughout the experiment. To accurately position the sample, a sample stage with micrometer in x, y, z axes and a He-Ne beam coaxial with the microscope and MIR-FEL were used.
(2) Dentin
The cervical dentin used was a flat plate obtained from bovine teeth, having a length of 5 mm, a width of 5 mm, and a thickness of 1 mm. Since the size of the spot of the MIR-FEL beam is sufficiently large in the vicinity of the maximum absorption wavelength of the dentin compared to the depth of light penetration, this dentin can be regarded as an almost infinite solid sample. Was. To avoid scattering of light due to surface roughness, the dentin sample was polished to a surface roughness of 1 μm or less. Before laser irradiation, the surface roughness, MIR spectrum, and element composition of all samples were measured.
(3) Measurement system
The degree of dentin surface modification was evaluated by the following experimental data. The cutting depth was determined by measuring the surface roughness. The MIR absorption spectrum was measured with a Fourier transform infrared spectrum measuring device (FT-IR). The element composition was measured by an energy dispersive X-ray spectrometer.
The test results are shown in FIGS.
[0046]
Example 2 (Laser-induced sound measurement experiment and device)
A plate-shaped dentin having an area of about 5 mm × 5 mm and a thickness of about 1 mm cut out from the cervix of the bovine teeth was used as a sample. In order to suppress the influence of light scattering due to the surface roughness, the sample surface was polished to a roughness of 1 μm or less.
Free electron laser (FEL) light supplied from the MIR-FEL oscillation device was collected by a parabolic mirror. Using the same irradiation system as in the irradiation experiment of Example 1, the size of the focused spot was 260 μm × 350 μm (full width at half maximum). The irradiation wavelengths were 9.0 μm, 9.3 μm, 9.6 μm, 10.3 μm, and 10.6 μm, respectively. The irradiation times were 0.2 seconds, 0.5 seconds, 1 second, 2 seconds, 3 seconds, 5 seconds, and 10 seconds, respectively. Average power density is 7W / cm each², 14W / cm², 28W / cm², 42W / cm²Met. These were changed as irradiation parameters.
An audible microphone (measurable range: 0.01-20 kHz) was installed at a location about 3 cm away from the irradiation position. In order to keep the sensitivity between irradiation parameters constant, the microphone position and data acquisition setup were fixed during the experiment. Then, the sound signal was transferred and stored as a time waveform to the computer using sound signal analysis software (Sound @ Forge).
The pulse structure of the MIR-FEL used in this experiment has a double pulse structure including a micro pulse and a macro pulse. The minimum pulse is a micro pulse having a pulse width of about 5 ps, and the pulse interval is 44.8 ns. A macro pulse refers to a group of about 330 micro pulses, and has a pulse width of about 15 μs and a pulse interval of 0.1 s. Considering the thermal relaxation process of the interaction between dentin and laser light, the micropulses in the macropulse can be regarded as continuous waves, and the irradiation effect is caused by the heat accumulation effect of the micropulses. That is, the energy density per second (J 密度 / cm)²エ ネ ル ギ ー / s), not the energy density per macro pulse (J / cm)²/ Macropulse). In addition, there is no heat accumulation effect between macro pulses, and the induced interaction is integrated for each macro pulse.
The results of these experiments are shown in FIGS.
[0047]
【The invention's effect】
Laser dental treatments for hard tissues include dental caries prevention for improving the acid resistance of enamel and dentin surfaces, and caries treatment for removing carious parts and tartar. Both use physical, chemical and morphological changes due to thermal and mechanical interaction by laser light.To date, many studies on laser dental treatment have been made, but in clinical laser treatment, Due to individual differences among patients, stability of irradiation power density, fluctuation of environment during irradiation, etc., it has been difficult to efficiently generate only desired interaction. In addition, there are many reports on side effects and adverse effects such as thermal and mechanical damage to normal tissues.
The present invention overcomes these problems in laser dental treatment and prevention, and greatly contributes to the clinical realization of laser dental treatment and prevention. That is, the present invention provides an optimized condition of laser irradiation in laser dental treatment / prevention, and provides a method and apparatus for performing dental treatment and prevention by laser with low invasiveness and reliability. In addition, it is necessary to monitor the degenerative state of the target site and the type and degree of interaction during laser irradiation in real time, and the present invention has clarified that laser-induced sound can be focused on as a monitoring technique therefor. . As a result, the problem of erroneous irradiation and the problem of over-irradiation in laser dental treatment / prevention can be reliably avoided, and side effects and adverse effects in laser dental treatment / prevention have been eliminated.
The addition of acid resistance by modifying the tooth dentin surface using a mid-infrared laser has attracted attention as a method of preventing tooth decay on the tooth root surface of the elderly, but the present invention is safe and reliable even for the elderly. Treatment and prevention can be performed.
[Brief description of the drawings]
FIG. 1 shows the absorption curves of enamel, dentin and hydroxyapatite (HAp), which are hard tissues of teeth. The horizontal axis in FIG. 1 shows the wavelength (μm), and the vertical axis shows the absorbance. The black line indicates the absorption of dentin, the white gray line indicates the absorption of enamel, and the black gray line indicates the absorption of hydroxyapatite (HAp).
FIG. 2 shows the illumination arrangement of the present invention, wherein the illumination system includes a reduction optics, a polarizer, a He-Ne laser, a parabolic mirror, a power meter, a microscope, and a sample. Consists of stages.
FIG. 3 is a scanning electron micrograph showing a structural change on the dentin surface when irradiated with a 9.7 μm free electron laser (FEL), which is replaced by a drawing. (A), (b), (c), (d), and (e) of FIG. 3 are at average powers of 3 mW, 6 mW, 11 mW, 16 mW, and 33 mW, respectively. The magnification of the image is 300 times. White arrows indicate the same direction. FIG. 3F shows the spatial profile of the crater. The horizontal axis in (f) of FIG. 3 indicates the position (μm), and the vertical axis indicates the cutting depth (μm).
FIG. 4 shows an experimental result of a cutting depth after laser irradiation. FIG. 4A shows that the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denFIG. 4B shows the case where the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denThe case of less than is shown. The horizontal axis in FIG. 4 is the average power (mW) and the average power density (W / cm).²), And the vertical axis indicates the cutting depth (μm). Light colored arrows indicate the upper and lower limits of the measurement limit.
FIG. 5 shows the average power dependence of the dentin spectrum when irradiated with 9.7 μm FEL. The horizontal axis in FIG. 5 indicates the wavelength (μm), and the vertical axis indicates the absorbance (au). Each curve shows the case of 3 mW, 6 mW, 11 mW, 16 mW, 22 mW, 33 mW, and the case of non-irradiation (hatched white line).
FIG. 6 shows the dependence of average power and illumination wavelength on the maximum absorption wavelength. FIG. 6A shows that the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denFIG. 6B shows the case where the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denThe case of less than is shown. The horizontal axis in FIG. 6 is the average power (mW) and the average power density (W / cm).²) And the vertical axis indicates the maximum absorption wavelength (μm).
FIG. 7 shows the dependence of average power and irradiation wavelength on P / Ca ratio. FIG. 7A shows that the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denFIG. 7B shows the case where the irradiation wavelength λ is the maximum absorption wavelength λ in the dentin._denThe case of less than is shown. The horizontal axis in FIG. 7 is the average power (mW) and the average power density (W / cm).²), And the vertical axis indicates the P / Ca ratio. Light colored arrows indicate the lower limit of the measurement limit.
FIG. 8 shows a summary of experimental results corresponding to parameters of average power (2-35 mW) / irradiation wavelength (8.8-10.6 μm). The horizontal axis in FIG. 8 is the average power (mW) and the average power density (W / cm).²), And the vertical axis in FIG. 8 indicates the irradiation wavelength (μm). Arrow indicates maximum absorption wavelength λ in dentin_denAbsorption wavelength λ of hydroxyapatite and hydroxyapatite_HApIs shown. The ellipse indicates a parameter region that can be effectively modified without significant cutting.
FIG. 9 shows a temporal change (0-10 seconds) of laser-induced sound intensity at wavelengths of 9.0 μm, 9.6 μm, and 10.6 μm. The horizontal axis in FIG. 9 indicates time (seconds), and the vertical axis indicates induced sound intensity (au). FIG. 9A shows a case where the irradiation wavelength is 9.0 μm, FIG. 9B shows a case where the irradiation wavelength is 9.6 μm, and FIG. 9C shows a case where the irradiation wavelength is 10.6 μm. The circled line indicates that the average power density is 42 W / cm.²And the line with a square mark indicates that the average power density is 28 W / cm.²And the line with a triangle indicates that the average power density is 14 W / cm.², The line with the cross mark has an average power density of 7 W / cm²Is shown.
FIG. 10 shows a spatial profile of a dentin surface after irradiation at an irradiation wavelength of 9.0 μm and irradiation times t = 0.5, 3, and 5 seconds. The horizontal axis in FIG. 10 indicates the position (μm), and the vertical axis indicates the cutting depth (μm). 10A shows a case where the irradiation time is 0.5 seconds, FIG. 10B shows a case where the irradiation time is 3 seconds, and FIG. 10C shows a case where the irradiation time is 5 seconds. Is shown. The black solid line indicates that the average power density is 42 W / cm.²The black dashed line indicates that the average power density is 28 W / cm²The gray dashed line indicates that the average power density is 14 W / cm.²And the thin solid line indicates that the average power density is 7 W / cm.²Is shown.
FIG. 11 shows mid-infrared absorption spectra of dentin after irradiation at an irradiation wavelength of 9.0 μm and irradiation times t = 0.5, 3, and 5 seconds. The horizontal axis in FIG. 11 indicates the wavelength (μm), and the vertical axis indicates the absorbance (au). 11A shows a case where the irradiation time is 0.5 seconds, FIG. 11B shows a case where the irradiation time is 3 seconds, and FIG. 11C shows a case where the irradiation time is 5 seconds. Is shown. The thick black solid line indicates that the average power density is 42 W / cm.²The thick black-gray line indicates that the average power density is 28 W / cm²And the gray line indicates that the average power density was 14 W / cm.²And the thin solid line indicates that the average power density is 7 W / cm.²Is shown. The gray thin line shows the case without irradiation.
FIG. 12 is a graph showing the irradiation parameters used in this experiment and the maximum intensity I of the generated laser-induced sound._maxThe results of classification into four groups are shown below. FIG. 12 is a diagram in which classifications of 4A to 4D are newly added to FIG. 8 as observation results of the impact sound.
FIG. 13 shows an irradiation average power density of 14 W / cm.²5 shows the time-dependent changes in the laser-induced sound intensity, the cutting depth, and the absorption peak ratio at the irradiation wavelengths of 9.0 μm and 9.6 μm. The horizontal axis in FIG. 13 represents time (seconds), and the vertical axis represents induced sound intensity (au). FIG. 9A shows a case where the irradiation wavelength is 9.0 μm, and FIG. 13B shows a case where the irradiation wavelength is 9.6 μm. The line with a circle indicates the induced sound intensity, the line with a square indicates the depth of cutting, and the line with a triangle indicates the absorption peak ratio.
FIG. 14 is a flowchart summarizing dental treatment and prevention according to the present invention.
FIG. 15 shows an example of an apparatus for treating / preventing teeth with laser light according to the present invention.
[Explanation of symbols]
1 Wavelength selection button for operating laser wavelength selection section
2. Wavelength selection button for operating the laser wavelength selection section
3 Display
4 laser irradiation part
5 Detection part of laser-induced impact sound
6 Fiber for transmission of impact sound
7 Fiber for laser light transmission
8 Tooth 9 affected area
9 teeth
10} Device for treatment and prevention of teeth by laser beam of the present invention
11 Knob for operating the adjustment part of laser beam irradiation intensity
12 output power meter
13 enamel
14 dentin

Claims (16)

An apparatus for treating and preventing teeth with a laser, which has a wavelength of 9.0 μm ± 0.3 μm and is capable of irradiating a high power density laser beam to an affected part for treating dental caries. A device for treating and preventing teeth by laser light, comprising a part. A device for treatment and prevention of teeth with a laser, which has a wavelength of 9.7 μm ± 0.3 μm and is irradiated with a laser beam of low power density irradiation to an affected area to prevent dental caries by modifying the surface of the dentin of the teeth. An apparatus for treating / preventing teeth with laser light, comprising a laser irradiation part capable of irradiation. An apparatus for treating and preventing teeth with a laser, which has a wavelength of 9.0 μm ± 0.3 μm and is capable of irradiating a high power density laser beam to an affected part for treating dental caries. It has a laser irradiation part whose wavelength is 9.7μm ± 0.3μm and which can irradiate the affected part with a laser beam of low power density irradiation for prevention of dental caries by surface modification of the dentin of the tooth. Equipment for treatment and prevention of teeth with laser light. The dental treatment / prevention device according to any one of claims 1 to 3, further comprising a laser light wavelength selection unit and / or a laser light irradiation intensity adjustment unit. The dental treatment / prevention device according to any one of claims 1 to 4, further comprising a device capable of detecting and monitoring an impact sound at a portion irradiated with the laser beam. The dental treatment / prevention / diagnosis device according to claim 5, wherein the device capable of detecting and monitoring an impact sound at a laser beam irradiation site is a device capable of detecting and monitoring an ultrasonic or audible sound. The dental treatment / prevention device according to any one of claims 1 to 6, wherein the laser light wavelength selector can select a wavelength of 9.0 µm ± 0.3 µm and a wavelength of 9.7 µm ± 0.3 µm. High power density radiation is not less peak power density at 1~10MW / cm ² or more, according to claim 1, low power density radiation is 100~1000kW / cm ² about the peak power density of teeth Equipment for treatment and prevention. The dental treatment / prevention / diagnosis device according to any one of claims 1 to 8, wherein the laser light source is a free electron laser. The dental treatment / prevention / diagnosis device according to any one of claims 1 to 8, wherein the laser light source is a carbon dioxide laser. An apparatus for treating / preventing teeth with a laser, wherein a laser light irradiation part and / or a laser light irradiation part is used to determine a laser light irradiation part and / or a laser light irradiation time based on a change in an impact sound caused by the laser light irradiation on an affected part. An apparatus for treating / preventing teeth with a laser beam, comprising an apparatus capable of detecting and monitoring an impact sound in a dental apparatus. The dental treatment / prevention device according to claim 11, wherein the device capable of detecting and monitoring an impact sound at a laser beam irradiation site is a device capable of detecting and monitoring an ultrasonic or audible sound. The dental treatment / prevention device according to claim 11 or 12, wherein when the impact sound at the irradiation part at the start of the laser light irradiation is small, the irradiation of the laser light is stopped to avoid erroneous irradiation. 13. The dental treatment / prevention device according to claim 11, wherein the laser light irradiation is stopped to avoid over-irradiation when the impact sound at the irradiation part at the time of laser light irradiation becomes constant. . The dental treatment / prevention device according to any one of claims 11 to 14, further comprising a laser light wavelength selection unit and a laser light irradiation intensity adjustment unit. The dental treatment / prevention device according to any one of claims 1 to 15, wherein the laser irradiation device is further provided with an irradiation position display device.

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