JP3645047B2 - Dental gypsum composition - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、歯科模型用材料，義歯埋没用材料などに使用される粉末状の歯科用石こう組成物に関するものであり、より詳細には、混合された四フッ化エチレン樹脂の撥水性によって硬化体の耐水性を改善できる歯科用石こう組成物に関するものである。
【０００２】
【従来の技術】
従来より歯科分野においては口腔内に装着されるインレー，クラウン，ブリッジ，部分床義歯，全部床義歯などの各種歯科修復物を作製する際に、その型材として歯科用石こう組成物が重要な材料として多岐に亘って使用されている。
例えば、ワックスパターンや蝋義歯などの作製の際に使用される作業用模型や顎模型などを作製するための石こう模型用材料，レジン義歯床を作製する際に蝋義歯を歯科用フラスコに埋没するための義歯埋没用材料などに使用されている。
【０００３】
これらの歯科用石こう組成物は、通常、半水石こうであるα−半水石こう（硬質石こう）及び／又はβ−半水石こう（焼石こう）を主成分とし、これに硬化遅延剤などの調整剤が加えられたものであり、粉末の形態で提供されている。
歯科医や技工士などは使用時に所定量の歯科用石こう組成物の粉末と練和用の水とをゴム製の小型ボール（ラバーボール）に採取し、石こうベラを用いて練和し、石こうスラリーとした後に、模型用として使用する場合には口腔内の印象採得した陰型内に注入して硬化させ口腔内状態を再現した作業用模型や顎模型を作製し、義歯埋没用として使用する場合には歯科用フラスコ内に注入して蝋義歯を埋没する目的で使用されている。
作業用模型や顎模型は歯科修復物を作製する際の基本となるものであり、高い寸法精度や滑沢な表面を有することは勿論のこと、特に金属修復物作製の際には修復物の原型となるワックスパターンが彫刻刀などを使用して作業模型上や顎模型上で直接作製されるという過酷な条件下での使用に耐え得る強さや硬さも要求されている。
【０００４】
歯科用石こう組成物の硬化機構は、以下に示すように、半水石こうが水と反応することにより二水石こうに変化し結晶化することによる硬化である。
CaSO4・1/2H2O ＋ 3/2H2O → CaSO4・2H2O
この硬化機構は水で硬化するものであることから、結果として、硬化体は水分に弱く、耐水性が不足する傾向にあり、この点が重要な問題点となっている。
実際の技工操作においては、作業用模型や顎模型上での歯科修復物設計のための色鉛筆での印記部分の消去，ワックスパターンパターン作製時に付着したワックス屑の除去，模型表面の汚れの除去，流蝋後の埋没面の洗浄などの際に、流水や温湯による洗浄や蒸気洗浄器からの高圧水蒸気の噴射による洗浄が頻繁に行われているが、硬化体が水分に弱く、耐水性が不足していることに起因して、表面が浸食されて作業模型や顎模型の細部形状が変化したり，エッジ部分が丸まったり，硬化体表面に荒れを生じたりして、最も重要で基本となる作業用模型や顎模型に寸法変化を引き起こし、その結果、精度の悪い歯科修復物が作製されてしまうという現象を引き起こしている。
【０００５】
【発明が解決しようとする課題】
本発明は前記従来技術の問題点を解決し、歯科用石こう組成物の硬化体の耐水性を向上させることによって、技工操作時の流水や温湯での洗浄や蒸気洗浄器での高圧水蒸気での洗浄に対しても耐水性の不足に起因する模型表面の浸食，細部形状の変化，表面荒れ等の発生を防止して、作業用模型や顎模型に寸法変化を引き起こすことがなく、優れた精度を有する歯科修復物を得ることを可能とする歯科用石こう組成物を開発することを課題とする。
【０００６】
【課題を解決するための手段】
本発明者らは、上記課題を解決するために鋭意研究した結果、予め歯科用石こう組成物粉末中に所定量の四フッ化エチレン樹脂を混合しておくことにより、四フッ化エチレン樹脂の撥水性の性質が半水石こうと水との反応により硬化した歯科用石こう組成物の硬化体の耐水性の向上に極めて有効に作用することを究明して本発明を完成したのである。更に、この歯科用石こう組成物にアルキルベンゼンスルフォン酸塩，アルキル硫酸塩から成る群より選ばれる１種又は２種以上の陰イオン系界面活性剤を混合すると、練和操作性が改善されることも究明したのである。
【０００７】
【発明の実施の形態】
即ち、本発明に係る歯科用石こう組成物は、
半水石こうと硬化遅延剤とから成る混合物100重量部に対し、四フッ化エチレン樹脂0.01〜0.5重量部が混合された第１の発明と、
半水石こうと硬化遅延剤とから成る混合物100重量部に対し、四フッ化エチレン樹脂0.01〜0.5重量部と、アルキルベンゼンスルフォン酸塩，アルキル硫酸塩から成る群より選ばれた１種又は２種以上の陰イオン系界面活性剤0.001〜0.05重量部とが混合された第２の発明と、
半水石こうと硬化遅延剤と硬化促進剤及び／又は硬化膨張抑制剤とから成る混合物100重量部に対し、四フッ化エチレン樹脂0.01〜0.5重量部が混合された第３の発明と、
半水石こうと硬化遅延剤と硬化促進剤及び／又は硬化膨張抑制剤とから成る混合物100重量部に対し、四フッ化エチレン樹脂0.01〜0.5重量部と、アルキルベンゼンスルフォン酸塩，アルキル硫酸塩から成る群より選ばれた１種又は２種以上の陰イオン系界面活性剤0.001〜0.05重量部とが混合された第４の発明と
から成るものである。
【０００８】
水溶液中で四フッ化エチレンを重合すると、平均粒径が0.05〜５μm程度の微細な粒子状の四フッ化エチレンの樹脂が得られる。この微細な樹脂の分子鎖は分子間凝集力が低く、僅かな圧縮・剪断応力を受けることにより微細な蜘蛛の巣状の繊維になる。このような蜘蛛の巣状の繊維の四フッ化エチレン樹脂を歯科用石こう組成物に分散させて存在させておいて水で練和すると、蜘蛛の巣状の繊維となった四フッ化エチレン樹脂が、歯科用石こう組成物の硬化体中の二水石こうの針状結晶の中に入り込むような形態で存在し、針状結晶の間隙に水分が浸入することを防止し、その結果として硬化体の耐水性を向上させることが可能となるのである。
【０００９】
具体的には、歯科用石こう組成物の製造中に半水石こうの粉砕過程でミルの中に粉末状の四フッ化エチレン樹脂を添加し、ミルによる剪断・圧縮応力を四フッ化エチレン樹脂にも負荷するのである。四フッ化エチレン樹脂は、分子鎖の主鎖のＣ−Ｃ結合は強固であるが、それに対して他の分子鎖に対する分子間引力は極端に小さいため、剪断・圧縮応力を負荷された四フッ化エチレン分子は微細に繊維化して蜘蛛の巣状の繊維となる。この繊維が石こう組成物中の微細な粒子に絡み付くような状態で存在して均一に分布し微細粒子を捕捉する。この現象は走査型電子顕微鏡の観察結果でも確認され、このことにより外観上では石こう組成物の粒子が凝集しているような現象を示すが、これは通常の粒子を造粒する操作により起こる微粒子の緻密な凝集とは異なり、微細な繊維の網目に微細粒子が捕捉された状態での軽度の粉体の凝集であるため、歯科用石こう組成物としての特性に影響を与える現象は生じない。そして、歯科用石こう組成物の粉末中に分散している繊維状の四フッ化エチレン樹脂は、歯科用石こう組成物が水で練和されると、硬化物中で針状に結晶化した二水石こうの間隙を埋めるように存在し、結晶粒子間に水分が浸入することを防止し、その結果として石こう硬化体の耐水性を向上させるのである。
しかし、四フッ化エチレン樹脂の混合量が0.01重量部未満では耐水性の向上が不十分であったので、四フッ化エチレン樹脂の混合量の下限を0.01重量部と設定した。
【００１０】
一方、四フッ化エチレン樹脂の混合量の上限を0.5重量部とした理由は、以下の通りである。
四フッ化エチレン樹脂は前述したように、剪断・圧縮応力を負荷されると微細に繊維化して蜘蛛の巣状の繊維となり、微細な粒子に絡みついた状態で歯科用石こう組成物の中に均一に分散して存在することが可能となる。しかしながら四フッ化エチレン樹脂の混合量が過剰になると、微細な粒子を捕捉するだけでなくより大きな粒子に対しても作用し、粉末が顆粒状に凝集する現象が生じる。ミルから歯科用石こう組成物の粉末を排出する工程は、ミルの蓋を開けてミルを回転させながら排出口から落下する粉末をホッパーで受けることにより行われるが、粉末粒子が過剰な四フッ化エチレン樹脂により顆粒状に凝集しているとミルの排出口から排出される粉末量が減少し、その結果として排出時間が可及的に増大する。ミルから排出する時の回転によっても、ミル内に残留した粉末は粉砕を受け続けるが、ミル粉砕の効率は粉末の量とミル玉との相対的な割合で決定され、ミル玉の割合が大きくなるほど粉砕効率は指数級数的に増大するためミルからの排出時間が長くなることによりミルから最終的に排出される粉末は最初に排出された粉末と比較して粉砕が過剰となって性質も全く異なってしまい、特性のバラツキが大きくなり安定した製品を供給することが不可能となってしまう。このような理由からミルからの排出時間の限度を鑑みて四フッ化エチレン樹脂の混合量の上限を0.5重量部と限定した。
【００１１】
四フッ化エチレン樹脂は撥水性が非常に強く、これを含有する歯科用石こう組成物を水で練和した場合に「水とのなじみ」と称する練和性に関する使用上の操作感に悪影響を与える。具体的には粉末と水との濡れ性が悪化し、短時間で粉末と水との混合ができず、水の上に粉末が浮いている状態になり、練和操作が行い難くなる。この性質は、歯科用石こう組成物自体の性能・性質には直接には影響を与えないが、練和性を始めとする使用時の操作性に問題を生ずる。この問題点を解決するためには、陰イオン系界面活性剤を混合し、粉末と水との濡れ性を改善して練和性の向上を図ることができる。
【００１２】
陰イオン系界面活性剤であるアルキルベンゼンスルフォン酸塩としてはドデシルベンゼンスルフォン酸ナトリウムなどが使用され、アルキル硫酸塩としてはラウリル硫酸ナトリウム，ラウリル硫酸カリウム，ミリスチル硫酸ナトリウム，セチル硫酸ナトリウム，ステアリル硫酸ナトリウムなどが使用される。
【００１３】
陰イオン系界面活性剤の混合量は、0.001重量部以上であれば「水とのなじみ」の改善が確認されたので、混合量の下限を0.001重量部と規定した。一方、混合量が多くなると、練和時の「水とのなじみ」は向上するが、「保存安定性」，「硬化時間」，「圧縮強さ」に悪影響を与えることが確認されたので、陰イオン系界面活性剤の混合量の上限を0.05重量部と規定した。
【００１４】
本発明に係る歯科用石こう組成物に用いられる半水石こうは、α−半水石こう，β−半水石こう，α−半水石こうとβ−半水石こうとの組み合わせがある。硬化体の圧縮強度は混水比によって著しい影響を受け、混水比が低いほど高い圧縮強度が得られる。従って、模型用材料として使用する場合などの高い強度が要求される際には、α−半水石こう単独又はα−半水石こうとβ−半水石こうとの組み合わせでもα−半水石こうの割合が多い低混水比のものが用いられ、義歯床作製の場合の義歯埋没用材料として使用する場合などの適度な強度と破砕し易さが必要とされる際には、β−半水石こう単独又はα−半水石こうとβ−半水石こうとの組み合わせでもβ−半水石こうの割合の多い高混水比のものが用いられる。
【００１５】
歯科用石こう組成物は、模型材料，義歯埋没用材料などの使用目的に応じて操作性や物理的性質が設定されるのであるが、半水石こう自体は硬化が速いため、通常、硬化遅延剤が加えられている。
硬化遅延剤としては、クエン酸塩，ホウ酸塩，カルボン酸塩，酢酸塩などの塩類や、デン粉，アラビアゴム，カルボキシメチルセルロース，ゼラチンなどの水溶性高分子から成る公知の硬化遅延剤が使用可能であり、通常、歯科用石こう組成物100重量部中に0.00001〜0.2重量部含有される。
【００１６】
また、微妙な硬化時間の調整などが必要とされる場合には、硬化促進剤が用いられることがある。硬化促進剤としては、NaCl，K2SO4などの無機酸や二水石こうの微粉末などの公知の硬化促進剤が使用され、通常、歯科用石こう組成物中に0.001〜２重量％含有される。硬化膨張値の調整が必要とされる場合には、硬化膨張抑制剤としての硫酸カリウム，塩化カリウム，酒石酸カリウムなどの可溶性カリウム塩から成る公知の硬化膨張抑制剤が使用され、通常、歯科用石こう組成物100重量部中に0.01〜１重量部含有される。その他、必要に応じて公知の着色剤や軽量化材が含有されてもよい。
【００１７】
【実施例】
以下、本発明に係る歯科用石こう組成物の実施例を挙げ本発明を更に詳細に説明する。
【００１８】
実施例１〜９，比較例１〜５
各実施例の配合及び特性は表１及び表２に纏めて示した。また各比較例の配合及び特性は表３及び４に纏めて示した。
【００１９】
《試料の作製》
各実施例，比較例は表に示した配合割合で、内容量100リットルの試験配合用ボールミルを用いて歯科用石こう組成物の総重量を50Kgとしたスケールによる粉砕・混合を行い試料作製を行った。初めに表１及び表３に示すα−半水石こう単独，β−半水石こう単独，又はα−半水石こうとβ−半水石こうとの組み合わせから成る半水石こうと四フッ化エチレン樹脂の粉末をミルに投入し、半水石こうが所定の粒度分布を示すまで粉砕した。粉砕後に硬化時間及び石こう泥の流動性を示す稠度などの特性を測定し、その結果に従って硬化遅延剤と、場合によっては硬化促進剤，硬化膨張抑制剤を投入し、更に場合によっては陰イオン系界面活性剤を混合した。混合後、ミルから排出し、ホッパーに貯蔵した。四フッ化エチレン樹脂の粉末は、粉砕・混合の工程で剪断・圧縮応力を負荷されて微細な繊維状となって歯科用石こう組成物の粉末中に均一に分散していた。ホッパーに貯蔵した歯科用石こう組成物から特性試験用として１Kgずつランダムに５回サンプリングし合計で５Kgの試料を採取し、試料として用いた。
【００２０】
《特性の試験方法》
それぞれの試料は、JIS T6605「歯科用硬石こう」及びJIS T6604「歯科用焼石こう」に定められた方法により物理的性質を測定した。
【００２１】
歯科用石こう組成物の硬化体の耐水性を評価する方法は、ＪＩＳ規格などでは制定されておらず、特に定義化されていない。しかし、硬化体を流水中に浸漬した場合には、流水面下の部分に浸食が認められ、流水面付近が最も浸食される。従って、その浸食の程度で耐水性の評価が可能である。そこで今回は以下に示す方法により評価した。
▲１▼ゴム型を使用し、各実施例，各比較例の歯科用石こう組成物を所定の混水量で練和して15×15×100mmの正四角柱の硬化体を作製する。
▲２▼37℃恒温槽内に24時間保存後、硬化体を室温まで放冷し、試験体中央部の４辺の長さを投影機によって測定する。
▲３▼容積約5.2リットルのトレー（25×35×６cm）に、硬化体を直立させランダムな位置に配置する。各実施例，各比較例について各５本の硬化体を配置する。
▲４▼このトレーを約３°傾斜させ、トレーに水（流量１リットル／分）を流し、直立させた硬化体の下半分程度が流水に浸される状態に保持し、１時間経過後に硬化体を取り出し、37℃恒温槽内でに24時間保存し乾燥させる。
▲５▼室温まで放冷後、硬化体の各辺の長さを再度投影機で測定し、試験前の各辺の長さとの差異を算出して、流水による浸食の度合いで耐水性を評価する。
【００２２】
保存安定性を評価する強制劣化試験の方法は、厚さ0.1mmのポリエチレンの袋に各実施例，各比較例の歯科用石こう組成物を１Kg採取し、密閉後、37℃，湿度100％の恒温恒湿槽に60日間保存した後、硬化時間を測定して強制劣化試験前の硬化時間との差異により保存安定性を評価する。
【００２３】
【表１】
【表２】
【表３】
【表４】
四フッ化エチレン樹脂混合による耐水性の向上の効果は、表１〜表４の配合と特性値の比較から確認することができる。表から明らかなように、各実施例においては四フッ化エチレン樹脂が0.01〜0.5重量部混合されており、四フッ化エチレン樹脂が歯科用石こう組成物の硬化体の針状結晶の間隙に存在して水分の浸入を防止して耐水性の向上が発揮されている。また四フッ化エチレン樹脂の混合量が多く、且つ陰イオン系界面活性剤が混合されていない実施例３については練和性の指標である「水とのなじみ」が「難」の評価であったが臨床上の使用は可能な範囲であった。
【００２８】
一方、四フッ化エチレン樹脂が混合されていない比較例１，４，５及び混合量が本発明の下限未満である比較例２においては、耐水性が低く流水による硬化体の浸食が大きく、この結果、臨床上では歯科修復物を作製するための基本となる作業模型，顎模型，蝋義歯埋没面が洗浄時に変形を生じ易くなり、寸法精度の劣る歯科修復物をもたらす原因となる。実施例１，２と比較例１，２を比較すると主成分は同一であり、相違点は四フッ化エチレン樹脂の混合量のみである。この比較から四フッ化エチレン樹脂の歯科用石こう組成物への混合は、硬化体の耐水性を著しく向上させることが確認され、その混合量の下限は0.01重量部が適当であることが確認できた。
【００２９】
四フッ化エチレン樹脂の混合量が本発明の上限を超え且つ陰イオン系界面活性剤を多量に混合してある比較例３では、四フッ化エチレン樹脂が0.8重量部混合されていても練和性の指標である「水とのなじみ」は「普通」の評価であり、現行の石こう組成物の製品と同等な練和操作性を有しているが、四フッ化エチレン樹脂が過剰に混合されたことにより歯科用石こう組成物をミルから排出する工程で粉末同士が凝集する現象が起きてミルの排出口から排出される量が減少し、排出のためのミルの回転がミル内に残留している粉末を粉砕して過剰粉砕になり、更に凝集が進行してミルからの排出が遅れるという悪循環が発生し、排出の初期と排出の最後では粉末の特性、特に硬化膨張値や硬化時間などの差異が大きくなってしまい、また排出の時間が長くなるために実際の操業が不可能となってしまった。ミルの排出において、排出の初期と排出の最後とで硬化膨張及び硬化時間の差異が臨床応用で問題の無い範囲を検討した結果、四フッ化エチレン樹脂の混合量の上限は0.5重量部が適当であることが判った。
【００３０】
また、表１の実施例１〜３において、撥水性の強い物質である四フッ化エチレン樹脂の混合量が0.01重量部（実施例１）と少ないと陰イオン系界面活性剤が配合されていなくとも練和性の指標である「水とのなじみ」の性質は「普通」で現行製品の歯科用石こう組成物とほぼ同様な練和性を有しているが、四フッ化エチレン樹脂の混合量が0.1重量部（実施例２）になると練和性の指標である「水とのなじみ」の性質は「やや難」の評価になる。更に、四フッ化エチレン樹脂の混合量が増加し、本発明の上限の0.5重量部（実施例３）になると練和性の指標である「水とのなじみ」の評価は「難」となる。この練和性の指標である「水とのなじみ」の評価において、「普通」，「やや難」及び「難」の評価は、現行製品の歯科用石こう組成物と比較したものであり、「普通」は現行製品と同等、「やや難」は現行製品よりもやや練和性が劣っている、「難」は現行製品より練和性がかなり劣っていることをそれぞれ示しているが、臨床上の使用は可能な範囲であった。
【００３１】
歯科用石こう組成物に、四フッ化エチレン樹脂を混合することにより練和性が低下することは上述の通りであるが、実施例４，５，７，９はこの特性を改良するために陰イオン系界面活性剤を混合したものであり、それによる練和性の向上が確認された。
具体的には、実施例２と実施例４との比較において配合上の差異は、四フッ化エチレン樹脂の混合量と陰イオン系界面活性剤の混合の有無である。実施例２は四フッ化エチレン樹脂の混合量が0.1重量部で陰イオン系界面活性剤の混合が無く、「水とのなじみ」は「やや難」となっている。一方、実施例４では四フッ化エチレン樹脂が実施例２よりも多い0.2重量部混合されているにも拘らず「水とのなじみ」は「普通」となっている。これは明らかに陰イオン系界面活性剤の混合効果である。
同様に実施例３と実施例５の比較においても陰イオン系界面活性剤の混合効果は明らかになる。実施例３と実施例５の差異は陰イオン系界面活性剤の混合の有無のみであり、混合されていない実施例３の「水とのなじみ」は「難」であったが、混合されている実施例５は「普通」になっており練和性の向上が確認されている。
【００３２】
実施例４は陰イオン系界面活性剤の混合量が非常に少なく0.001重量部であるが実施例２との比較から練和操作性の向上効果が確認されたため、陰イオン系界面活性剤の混合量の下限は0.001重量部が適当であることが確認できた。
陰イオン系界面活性剤の多量の混合は、強制保存後の硬化時間の遅延（保存安定性の低下）に最も顕著に現れる。従来製品の試験結果より強制保存後の硬化時間の遅延は６分00秒までならば臨床上の使用では問題がないことが検証されている。実施例５の陰イオン系界面活性剤の混合量は0.05重量部と本発明の上限であるが、強制保存後の硬化時間の遅延は３分00秒であり実用上は問題無い。他の陰イオン系界面活性剤の混合量が多い例（実施例７）でも硬化時間の遅延は３分00秒以内であった。しかしながら、比較例３は陰イオン系界面活性剤が0.1重量部と本発明の上限より多いため強制保存後の硬化時間の遅延時間が18分00秒と非常に大きくなり、保存安定性が悪く寸法精度の優れた歯科修復物の作製は困難となる。このように過剰な陰イオン系界面活性剤の混合は、歯科用石こう組成物の強制保存後の硬化時間の遅延が大きくなり実用に耐えられないものとなる。以上の結果より、陰イオン系界面活性剤の混合量の上限は0.05重量部が適当であることが確認できた。
【００３３】
【発明の効果】
以上に詳述した如く、本発明に係る歯科用石こう組成物は、四フッ化エチレン樹脂が微細な蜘蛛の巣状の繊維状になって歯科用石こう組成物粉末中に均一に分散していることにより、水と練和された際には歯科用石こう組成物の硬化過程において針状の二水石こうの結晶の間隙を埋めるように繊維化した四フッ化エチレン樹脂が存在して、結晶の間隙に水分が進入することを防止し、歯科用石こう硬化体の耐水性が向上する効果が得られるのである。
そして付随効果として、四フッ化エチレン樹脂を混合し、粉砕工程で繊維化することによる微細粒子捕捉効果により微細粉末の飛散が防止され、水との練和操作時に歯科用石こう組成物粉末の飛散が防止される効果も得られるのである。
また、撥水性の高い四フッ化エチレン樹脂を添加することによる練和操作性の悪化に対しては、アルキルベンゼンスルフォン酸塩，アルキル硫酸塩から成る群より選ばれた１種又は２種以上の陰イオン系界面活性剤を添加することにより解決することが可能となるのである。
このような種々の効果を有する本発明に係る歯科用石こう組成物の歯科分野に貢献する価値は非常に大きなものである。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a powdery dental gypsum composition used as a dental model material, a denture embedding material, and the like, and more specifically, a cured product by water repellency of a mixed tetrafluoroethylene resin. The present invention relates to a dental gypsum composition that can improve the water resistance of water.
[0002]
[Prior art]
In the field of dentistry, dental gypsum composition has been an important material for the preparation of various dental restorations such as inlays, crowns, bridges, partial dentures, and full dentures that are installed in the oral cavity. Widely used.
For example, materials for gypsum models to make working models and jaw models used in the production of wax patterns and dentures, and wax dentures are buried in dental flasks when making resin denture bases. It is used as a material for implanting dentures.
[0003]
These dental gypsum compositions are usually composed of α-half-hydrated gypsum (hard gypsum) and / or β-half-hydrated gypsum (calcined gypsum), which are half-hydrated gypsum, and adjustment of a curing retarder or the like. The agent is added and is provided in the form of a powder.
A dentist or technician collects a predetermined amount of dental gypsum composition powder and water for kneading into a small rubber ball (rubber ball), and kneads it with a gypsum spatula. When used as a model after slurrying, create a working model or jaw model that reproduces the oral state by injecting it into the negative mold obtained from the oral impression and using it for denture implantation In this case, it is used for the purpose of burying the wax denture by pouring it into the dental flask.
The working model and jaw model are the basis for the production of dental restorations. Of course, they have high dimensional accuracy and smooth surface, especially when making restorations of metal. There is also a demand for strength and hardness that can withstand use under harsh conditions in which a prototype wax pattern is directly produced on a work model or jaw model using a sculpture knife or the like.
[0004]
As shown below, the curing mechanism of the dental gypsum composition is curing by changing the hydrated gypsum to dihydrate gypsum by reacting with water and crystallizing.
CaSO 4・ 1 / 2H 2 O + 3 / 2H 2 O → CaSO 4・ 2H 2 O
Since this curing mechanism is cured with water, as a result, the cured body tends to be weak against moisture and lacks water resistance, which is an important problem.
In actual technical operations, erasing of marking parts with colored pencils for designing dental restorations on working models and jaw models, removal of wax debris adhered during wax pattern pattern preparation, removal of dirt on the model surface, When washing the buried surface after flowing wax, cleaning with running water or hot water or high pressure steam from a steam cleaner is frequently performed, but the cured product is weak against moisture and lacks water resistance. As a result, the surface is eroded and the detailed shape of the work model and jaw model changes, the edges become rounded, and the surface of the hardened body becomes rough. This causes a dimensional change in the working model and jaw model, and as a result, a phenomenon in which an inaccurate dental restoration is produced.
[0005]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the prior art and improves the water resistance of the cured body of the dental gypsum composition, so that it is washed with running water or hot water during technical operation or with high-pressure steam in a steam washer. Prevents erosion of the model surface due to lack of water resistance, changes in detail shape, surface roughness, etc. even when cleaning, and does not cause dimensional changes in the work model or jaw model, and has excellent accuracy It is an object of the present invention to develop a dental gypsum composition that makes it possible to obtain a dental restoration having the above.
[0006]
[Means for Solving the Problems]
As a result of diligent research to solve the above problems, the present inventors have mixed a predetermined amount of a tetrafluoroethylene resin in a dental gypsum composition powder in advance, thereby repelling the tetrafluoroethylene resin. The present invention has been completed by investigating that the aqueous property works extremely effectively on improving the water resistance of a cured product of a dental gypsum composition cured by the reaction between hemihydrate gypsum and water. Furthermore, when this dental gypsum composition is mixed with one or more anionic surfactants selected from the group consisting of alkylbenzene sulfonates and alkyl sulfates, kneading operability may be improved. It was investigated.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
That is, the dental gypsum composition according to the present invention is
A first invention in which 0.01 to 0.5 parts by weight of a tetrafluoroethylene resin is mixed with 100 parts by weight of a mixture composed of hemihydrate gypsum and a curing retarder;
One or more selected from the group consisting of 0.01 to 0.5 parts by weight of tetrafluoroethylene resin, alkylbenzene sulfonate, and alkyl sulfate with respect to 100 parts by weight of a mixture of hemihydrate gypsum and a retarder A second invention in which 0.001 to 0.05 parts by weight of an anionic surfactant is mixed;
A third invention in which 0.01 to 0.5 parts by weight of a tetrafluoroethylene resin is mixed with 100 parts by weight of a mixture comprising a hemihydrate gypsum, a curing retarder, a curing accelerator and / or a curing expansion inhibitor;
It consists of 0.01 to 0.5 parts by weight of tetrafluoroethylene resin, alkylbenzene sulfonate, and alkyl sulfate with respect to 100 parts by weight of a mixture of hemihydrate gypsum, cure retarder, cure accelerator and / or cure expansion inhibitor. It consists of 4th invention with which 0.001-0.05 weight part of 1 type, or 2 or more types of anionic surfactant chosen from the group was mixed.
[0008]
When ethylene tetrafluoride is polymerized in an aqueous solution, a fine particulate ethylene tetrafluoride resin having an average particle size of about 0.05 to 5 μm is obtained. This fine resin molecular chain has a low intermolecular cohesive force, and when subjected to a slight compression / shear stress, it becomes a fine cobweb-like fiber. Such a spider web-like fiber tetrafluoroethylene resin is dispersed in a dental gypsum composition and kneaded with water to form a spider web-like fiber. Is present in a form that penetrates into the needle-like crystal of dihydrate gypsum in the hardened body of the dental gypsum composition, and prevents moisture from entering the gaps of the needle-like crystal, resulting in the hardened body. This makes it possible to improve the water resistance.
[0009]
Specifically, during production of dental gypsum composition, powdered tetrafluoroethylene resin is added to the mill during the grinding process of hemihydrate gypsum, and shear / compressive stress by the mill is added to the tetrafluoroethylene resin. Load. In the tetrafluoroethylene resin, the C—C bond of the main chain of the molecular chain is strong, but the intermolecular attractive force to other molecular chains is extremely small. The ethylene fluoride molecules are finely fibrillated into spider web-like fibers. These fibers are present in a state of being entangled with fine particles in the gypsum composition, and are uniformly distributed to trap the fine particles. This phenomenon is also confirmed by the observation result of the scanning electron microscope, and this shows a phenomenon that the particles of the gypsum composition are aggregated on the appearance, but this is a fine particle generated by the operation of granulating ordinary particles. Unlike the fine agglomeration, a fine powder agglomeration in a state where fine particles are trapped in a fine fiber network does not cause a phenomenon that affects the properties as a dental gypsum composition. The fibrous tetrafluoroethylene resin dispersed in the powder of the dental gypsum composition was crystallized in a needle shape in the cured product when the dental gypsum composition was kneaded with water. It exists so as to fill the gap between the water and the gypsum, and prevents moisture from entering between the crystal particles, and as a result, improves the water resistance of the gypsum hardened body.
However, when the mixing amount of the tetrafluoroethylene resin was less than 0.01 parts by weight, the improvement in water resistance was insufficient, so the lower limit of the mixing amount of the tetrafluoroethylene resin was set to 0.01 parts by weight.
[0010]
On the other hand, the reason why the upper limit of the mixing amount of the tetrafluoroethylene resin is 0.5 parts by weight is as follows.
As described above, tetrafluoroethylene resin is finely fibrillated when subjected to shearing and compressive stress, forming spider web-like fibers, and uniformly in the dental gypsum composition entangled with fine particles. It is possible to exist in a distributed manner. However, when the mixing amount of the tetrafluoroethylene resin is excessive, not only fine particles are trapped but also acts on larger particles, and a phenomenon occurs in which the powder aggregates into granules. The process of discharging the dental gypsum composition powder from the mill is performed by opening the lid of the mill and receiving the powder falling from the outlet while rotating the mill with a hopper. If it is agglomerated by the ethylene resin, the amount of powder discharged from the outlet of the mill decreases, and as a result, the discharge time increases as much as possible. Although the powder remaining in the mill continues to be pulverized by the rotation when discharged from the mill, the efficiency of the mill pulverization is determined by the amount of the powder and the relative ratio between the mill balls and the ratio of the mill balls is large. As the grinding efficiency increases exponentially, the discharge time from the mill becomes longer, so that the powder finally discharged from the mill is excessively pulverized compared to the powder discharged first, and the properties are completely It becomes different and the characteristic variation becomes large, and it becomes impossible to supply a stable product. For these reasons, the upper limit of the mixing amount of the tetrafluoroethylene resin is limited to 0.5 parts by weight in consideration of the limit of the discharge time from the mill.
[0011]
Tetrafluoroethylene resin has a very strong water repellency, and when a dental gypsum composition containing it is kneaded with water, it adversely affects the operational feeling related to kneading, which is called “familiarity with water”. give. Specifically, the wettability between the powder and water deteriorates, the powder and water cannot be mixed in a short time, the powder floats on the water, and the kneading operation becomes difficult. This property does not directly affect the performance and properties of the dental gypsum composition itself, but causes a problem in operability during use including kneading properties. In order to solve this problem, an anionic surfactant can be mixed to improve the wettability between the powder and water, thereby improving the kneading property.
[0012]
Anionic surfactants such as alkylbenzene sulfonate include sodium dodecylbenzene sulfonate, and alkyl sulfates include sodium lauryl sulfate, potassium lauryl sulfate, sodium myristyl sulfate, sodium cetyl sulfate, and sodium stearyl sulfate. used.
[0013]
If the amount of the anionic surfactant mixed was 0.001 part by weight or more, improvement of “familiarity with water” was confirmed, so the lower limit of the amount of mixing was defined as 0.001 part by weight. On the other hand, as the mixing amount increases, the “familiarity with water” at the time of kneading is improved, but it has been confirmed that the “storage stability”, “curing time”, and “compressive strength” are adversely affected. The upper limit of the mixing amount of the anionic surfactant was defined as 0.05 parts by weight.
[0014]
Examples of the hemihydrate gypsum used in the dental gypsum composition according to the present invention include α-semihydrogypsum, β-semihydrogypsum, α-semihydrogypsum and β-semihydrogypsum combinations. The compressive strength of the cured body is significantly affected by the water mixture ratio, and the lower the water mixture ratio, the higher the compressive strength. Therefore, when high strength is required, such as when used as a model material, the proportion of α-hemihydrate gypsum even with α-hemihydrate gypsum alone or with a combination of α-hemihydrate gypsum and β-hemihydrate gypsum. When a moderately strong strength and ease of crushing are required, such as when using a denture base as a denture base material when a denture base is produced, a β-semihydrogypsum is often used. Even if it is individual or a combination of α-hemihydrate gypsum and β-half water gypsum, one having a high mixed water ratio with a large proportion of β-hemihydrate gypsum is used.
[0015]
Dental gypsum compositions have operability and physical properties that are set according to the purpose of use, such as model materials and denture-embedding materials. Has been added.
As curing retarders, known curing retarders composed of salts such as citrate, borate, carboxylate and acetate, and water-soluble polymers such as den powder, gum arabic, carboxymethylcellulose and gelatin are used. This is possible and is usually contained in an amount of 0.00001 to 0.2 parts by weight in 100 parts by weight of the dental gypsum composition.
[0016]
Moreover, a curing accelerator may be used when fine adjustment of the curing time is required. As the hardening accelerator, known hardening accelerators such as inorganic acids such as NaCl and K 2 SO 4 and fine powder of dihydrate gypsum are used, and usually 0.001 to 2% by weight is contained in the dental gypsum composition. The When it is necessary to adjust the curing expansion value, a known curing expansion inhibitor composed of a soluble potassium salt such as potassium sulfate, potassium chloride, or potassium tartrate is used as a curing expansion inhibitor. 0.01 to 1 part by weight is contained in 100 parts by weight of the composition. In addition, a known colorant or lightening material may be contained as necessary.
[0017]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples of the dental gypsum composition according to the present invention.
[0018]
Examples 1-9, Comparative Examples 1-5
The composition and characteristics of each example are summarized in Tables 1 and 2. The composition and characteristics of each comparative example are summarized in Tables 3 and 4.
[0019]
<< Sample preparation >>
In each example and comparative example, the mixing ratio shown in the table was used, and a sample was prepared by grinding and mixing on a scale with a total weight of dental gypsum composition of 50 kg using a test mixing ball mill with an internal volume of 100 liters. It was. First, the α-hemihydrate gypsum alone, β-hemihydrate gypsum alone, or the combination of α-hemihydrate gypsum and β-hemihydrate gypsum and tetrafluoroethylene resin shown in Tables 1 and 3 are used. The powder was put into a mill and pulverized until the hemihydrate gypsum showed a predetermined particle size distribution. After crushing, measure characteristics such as curing time and consistency indicating the fluidity of gypsum mud, and in accordance with the results, a curing retarder and, in some cases, a curing accelerator and a curing expansion inhibitor are added, and in some cases an anionic system Surfactant was mixed. After mixing, the product was discharged from the mill and stored in a hopper. The tetrafluoroethylene resin powder was subjected to shearing and compressive stress in the pulverization / mixing process to form fine fibers and was uniformly dispersed in the dental gypsum composition powder. From the dental gypsum composition stored in the hopper, a sample of 5 kg was collected by random sampling 5 times for 1 kg each for property test, and used as a sample.
[0020]
《Characteristic test method》
Each sample was measured for physical properties by a method defined in JIS T6605 “dental plaster” and JIS T6604 “dental plaster”.
[0021]
A method for evaluating the water resistance of a cured product of a dental gypsum composition has not been established in JIS standards or the like and is not particularly defined. However, when the cured body is immersed in running water, erosion is observed in the portion below the flowing water surface, and the vicinity of the flowing water surface is most eroded. Therefore, the water resistance can be evaluated by the degree of erosion. Therefore, this time, the following method was used for evaluation.
{Circle around (1)} Using a rubber mold, the dental gypsum composition of each example and each comparative example is kneaded with a predetermined amount of mixed water to prepare a 15 × 15 × 100 mm square prism hardened body.
{Circle around (2)} After storing in a 37 ° C. constant temperature bath for 24 hours, the cured body is allowed to cool to room temperature, and the lengths of the four sides at the center of the specimen are measured with a projector.
(3) Place the cured body upright on a tray (25 × 35 × 6 cm) with a volume of about 5.2 liters and place it in a random position. Five cured bodies are arranged for each example and each comparative example.
(4) Tilt this tray about 3 °, let water (flow rate 1 liter / min) flow through the tray, and keep the lower half of the upright cured body soaked in running water and harden after 1 hour Remove the body, store in a 37 ° C constant temperature bath for 24 hours and dry.
(5) After allowing to cool to room temperature, measure the length of each side of the cured body again with a projector, calculate the difference from the length of each side before the test, and evaluate the water resistance by the degree of erosion by running water To do.
[0022]
The forced deterioration test method for evaluating the storage stability is to collect 1 kg of dental plaster composition of each example and each comparative example in a 0.1 mm thick polyethylene bag, and after sealing, 37 ° C and 100% humidity. After storing for 60 days in a constant temperature and humidity chamber, the curing time is measured, and the storage stability is evaluated by the difference from the curing time before the forced deterioration test.
[0023]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
The effect of improving the water resistance by mixing the tetrafluoroethylene resin can be confirmed from the comparison of the formulations and characteristic values in Tables 1 to 4. As is apparent from the table, 0.01 to 0.5 parts by weight of tetrafluoroethylene resin is mixed in each example, and the tetrafluoroethylene resin is present in the interstices of the needle crystals of the cured body of the dental gypsum composition. Thus, water penetration is prevented and water resistance is improved. In Example 3 in which the amount of the tetrafluoroethylene resin mixed was large and no anionic surfactant was mixed, the “familiarity with water” index of kneadability was evaluated as “difficult”. However, clinical use was in the possible range.
[0028]
On the other hand, in Comparative Examples 1, 4 and 5 in which the tetrafluoroethylene resin is not mixed, and Comparative Example 2 in which the mixing amount is less than the lower limit of the present invention, the water resistance is low and the erosion of the cured body by running water is large. As a result, the working model, jaw model, and wax denture embedded surface, which are the basis for producing a dental restoration in clinical practice, are likely to be deformed during cleaning, resulting in a dental restoration with inferior dimensional accuracy. When Examples 1 and 2 are compared with Comparative Examples 1 and 2, the main components are the same, and the only difference is the amount of mixed tetrafluoroethylene resin. From this comparison, it was confirmed that the mixing of tetrafluoroethylene resin into the dental gypsum composition significantly improved the water resistance of the cured product, and the lower limit of the mixing amount was confirmed to be 0.01 parts by weight. It was.
[0029]
In Comparative Example 3 in which the mixing amount of the tetrafluoroethylene resin exceeded the upper limit of the present invention and a large amount of the anionic surfactant was mixed, even if 0.8 parts by weight of the tetrafluoroethylene resin was mixed, “Familiarity with water”, which is an index of sexuality, is rated as “ordinary” and has a kneading operability equivalent to that of current gypsum composition products, but it contains excessive mixing of tetrafluoroethylene resin. As a result, in the process of discharging the dental gypsum composition from the mill, the phenomenon of powder aggregation occurs, the amount discharged from the outlet of the mill decreases, and the rotation of the mill for discharging remains in the mill. A vicious cycle occurs in which the powder is pulverized and becomes excessively pulverized, and further, agglomeration progresses and the discharge from the mill is delayed. At the beginning and end of discharge, the characteristics of the powder, especially the expansion value and setting time Such as the difference between Between it has become impossible to actual operation for longer. As a result of examining the range where the difference in curing expansion and curing time between the initial stage of discharge and the end of discharge has no problem in clinical application, the upper limit of the mixing amount of tetrafluoroethylene resin should be 0.5 parts by weight. It turned out that.
[0030]
Further, in Examples 1 to 3 in Table 1, when the mixing amount of tetrafluoroethylene resin, which is a highly water-repellent substance, is as small as 0.01 part by weight (Example 1), an anionic surfactant is not blended. Both of them are “ordinary with water”, which is an index of kneadability, and are “ordinary” and have almost the same kneading properties as the dental gypsum composition of the current product. When the amount is 0.1 parts by weight (Example 2), the property of “familiarity with water”, which is an index of kneadability, is evaluated as “slightly difficult”. Furthermore, when the mixing amount of the tetrafluoroethylene resin is increased to 0.5 parts by weight (Example 3) which is the upper limit of the present invention, the evaluation of “familiarity with water” which is an index of kneadability becomes “difficult”. . In the evaluation of “familiarity with water”, which is an index of kneadability, the evaluations of “ordinary”, “slightly difficult” and “difficult” are compared with the dental gypsum composition of the current product. “Normal” is equivalent to the current product, “Slightly difficult” is slightly inferior to the current product, and “Difficult” is considerably inferior to the current product. The above use was to the extent possible.
[0031]
As described above, the kneadability is lowered by mixing the dental gypsum composition with the tetrafluoroethylene resin. However, Examples 4, 5, 7, and 9 are used in order to improve this property. It was a mixture of ionic surfactants, and it was confirmed that the kneading property was improved.
Specifically, the difference in formulation in the comparison between Example 2 and Example 4 is the presence or absence of the mixing amount of the tetrafluoroethylene resin and the mixing of the anionic surfactant. In Example 2, the mixing amount of the tetrafluoroethylene resin was 0.1 parts by weight, there was no mixing of the anionic surfactant, and “familiarity with water” was “slightly difficult”. On the other hand, in Example 4, although “0.2 parts by weight of the tetrafluoroethylene resin is mixed more than in Example 2,“ Familiarity with water ”is“ ordinary ”. This is clearly a mixing effect of an anionic surfactant.
Similarly, in the comparison between Example 3 and Example 5, the mixing effect of the anionic surfactant becomes clear. The difference between Example 3 and Example 5 was only the presence or absence of mixing of an anionic surfactant, and “Familiarity with water” of Example 3 that was not mixed was “difficult”, but was mixed. Example 5 is “ordinary” and the improvement of kneading property is confirmed.
[0032]
In Example 4, the mixing amount of the anionic surfactant was very small and 0.001 part by weight. However, since the effect of improving the kneading operability was confirmed by comparison with Example 2, the mixing of the anionic surfactant was performed. It was confirmed that 0.001 part by weight was appropriate for the lower limit of the amount.
The mixing of a large amount of an anionic surfactant is most prominent in the delay of the curing time after forced storage (decrease in storage stability). From the test results of conventional products, it has been verified that there is no problem in clinical use if the delay of the curing time after forced storage is up to 6:00 seconds. The mixing amount of the anionic surfactant of Example 5 is 0.05 part by weight, which is the upper limit of the present invention, but the delay of the curing time after forced storage is 3 minutes 00 seconds, and there is no practical problem. Even in the case where the amount of other anionic surfactants was large (Example 7), the delay of the curing time was within 3 minutes and 00 seconds. However, in Comparative Example 3, the amount of anionic surfactant is 0.1 parts by weight, which is larger than the upper limit of the present invention, so that the delay time of the curing time after forced storage becomes very large at 18 minutes 00 seconds, and the storage stability is poor. It is difficult to produce a highly accurate dental restoration. Thus, mixing of an excess of an anionic surfactant increases the delay of the curing time after forced storage of the dental gypsum composition and cannot be put into practical use. From the above results, it was confirmed that 0.05 part by weight was appropriate as the upper limit of the amount of the anionic surfactant mixed.
[0033]
【The invention's effect】
As described above in detail, in the dental gypsum composition according to the present invention, the tetrafluoroethylene resin is dispersed in the dental gypsum composition powder in the form of fine spider webs. Thus, when kneaded with water, there is a tetrafluoroethylene resin that is fiberized so as to fill the gaps in the crystal of acicular dihydrate gypsum during the curing process of the dental gypsum composition. This prevents moisture from entering the gap and improves the water resistance of the dental gypsum hardened body.
And as an accompanying effect, the dispersion of fine powder is prevented by mixing fine tetrafluoroethylene resin and fiberized in the pulverization process, so that the dispersion of fine powder is prevented during the kneading operation with water. The effect which prevents is also acquired.
Further, for the deterioration of kneading operability due to the addition of a highly water-repellent tetrafluoroethylene resin, one or more shades selected from the group consisting of alkylbenzene sulfonates and alkyl sulfates are used. This can be solved by adding an ionic surfactant.
The value of contributing to the dental field of the dental gypsum composition according to the present invention having such various effects is very great.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP26660996A JP3645047B2 (en) | 1996-09-18 | 1996-09-18 | Dental gypsum composition |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP26660996A JP3645047B2 (en) | 1996-09-18 | 1996-09-18 | Dental gypsum composition |
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| Publication Number | Publication Date |
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| JPH1087419A JPH1087419A (en) | 1998-04-07 |
| JP3645047B2 true JP3645047B2 (en) | 2005-05-11 |
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| JP26660996A Expired - Lifetime JP3645047B2 (en) | 1996-09-18 | 1996-09-18 | Dental gypsum composition |
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| JP2011213608A (en) | 2010-03-31 | 2011-10-27 | Gc Corp | Dental hydraulic temporary sealing material composition |
| CN117412733A (en) * | 2021-06-02 | 2024-01-16 | 吉野石膏株式会社 | Cast molding gypsum composition |
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