AU3754699A

AU3754699A - Apparatus for and method of laser surgery of hard tissues

Info

Publication number: AU3754699A
Application number: AU37546/99A
Authority: AU
Inventors: Baruch Ben-Dor; Shimon Eckhouse; Ziv Karni; Michael Kreindel; Boris Vayneberg
Original assignee: Opusdent Ltd
Current assignee: Opusdent Ltd
Priority date: 1998-04-30
Filing date: 1999-04-21
Publication date: 1999-11-16
Anticipated expiration: 2019-04-21
Also published as: EP1079744A1; IL139350A0; CA2331113A1; AU742054B2; EP1079744A4; WO1999055243A1

Description

WO 99/55243 PCT/US99/08751 1 APPARATUS FOR AND METHOD OF LASER SURGERY OF HARD TISSUES 5 FIELD AND BACKGROUND OF THE INVENTION The present invention relates to an apparatus for and further to a method of performing laser surgeries in hard biological tissues and, more particularly, to an apparatus for and method of ablating hard biological o10 tissues characterized by low water content. Directing coherent radiation from a laser at a target is a well known method for precisely cutting that target by ablating or vaporizing a portion thereof. When the target is a soft living tissue, the dynamic nature of the 15 target poses special problems. For example, fluids such as blood may flow into the area of the cut, obscuring that area and absorbing part of the energy that otherwise would go into ablating the target. U.S. Pat. application No. 08/904,249 teaches a method of laser surgery suited for soft tissues (e.g., soft dental tissue, gums), wherein two 20 coherent radiation sources are used concurrently and coaxially for shallow ablating combined with deeper coagulation of the soft tissue, thereby preventing bleeding which otherwise interferes with ablation. However, as further detailed hereinunder, different problems are presented and different solutions are to be sought for laser surgeries of hard 25 tissues, such as hard dental tissues (enamel and dentine of the teeth) or bones, which are tissues characterized by low water content. It is well known that a major constituent of biological tissues is water. Soft tissues contain about 70 % - 80 % water by weight, however, hard tissues, e.g., enamel and dentine in the tooth contain lower amount of 30 water, in the range of about 2 % - 20 %.

WO 99/55243 PCT/US99/08751 2 Ablation of biological tissues can be strongly effected using coherent radiation in the near infrared spectral range in which water has strong absorption peaks. However, the relative amount of water in the tissue dictates the 5 ablation efficiency and the penetration depth of near infrared radiation, wherein ablation is higher as the content of water is higher, and vice versa, whereas, penetration is higher as the content of water is lower, and vice versa. Therefore, different considerations must be taken when attempting ablation of soft vs. hard biological tissues in this spectral range. 10 Early surgical laser systems were based on Nd:YAG (neodymium: ytterium-alluminum-garnet) gain media which outputs at 1.06 microns. Due to the relatively small absorption of this wavelength in water, and therefore low ablation efficiency and high penetration depth into the tissue, such laser systems were not commonly used in dentistry for hard tissue due 15 to their low efficiency and associated thermal damage to the tooth pulp tissue and nerve. Combining special optics with Nd:YAG gain media, coherent radiation output at 1.44 microns can be obtained. Despite the fact that the absorption of this wavelength in water is many times higher than at 1.06 20 microns, still penetration depth remains high enough to render this optically modified laser unusable for hard tooth tissue ablation. Next, the applicability of Holmium YAG (Ho:YAG) lasers which radiate at 2.06 microns was explored. The absorption coefficient of water at this wavelength is more then two hundred times greater than at 1.06 25 microns, and therefore, much more energy is absorbed in surfacial layers of a treated tissue, which decreases the energy fraction that penetrates deeper into the tissue and therefore decreases thermal associated damages. More recently the Erbium YAG (Er:YAG) laser was probed for use in biological tissue ablation. Its radiation wavelength (2.94 microns) 30 matches the strongest water absorption peak in the infrared spectral range, WO 99/55243 PCT/US99/08751 3 which renders the absorption of this wavelength by water hundreds of times higher than, for example, the wavelength generated by Ho:YAG lasers. Er:YAG laser systems are therefore of choice for hard tissue ablation which are low in water content, since due to the high absorption of Er:YAG 5 radiation by water effective ablation associated with reduced penetration depth and minimal thermal damage are obtained. The water content in dentine is typically about 20 % and in enamel it is typically about 2-10 %. The high absorption of Er:YAG laser radiation by water in the hard tissue of a tooth allows effective ablation of enamel and 10 dentine. The penetration depth of the Er:YAG laser radiation into enamel and dentine is in the range of 3 to 7 microns. Roughly, this means that about 70 % of the incident energy is absorbed in these layers. However, at least 10 % of the Er:YAG laser energy penetrates twice as deeper. The deep 15 penetrating tail of the incident radiation produces residual heat that causes strong local heating of the treated tooth. The local temperature at the treated area can reach hundreds of degrees Centigrade. This high temperature may cause damage to the soft tissue within the tooth which is vital for its survival. Furthermore, it vaporizes water from the tooth tissue. 20 A decrease in the water content in the tissue reduces its absorption properties and consequently increases the penetration and residual heat effects and decreases the effectivity of ablation. Increasing the hydration of hard tissue at the treated area is currently effected by applying water spray onto the treated tooth. This method is 25 limited by the water penetration rate into the hard tissue of the tooth. It is, however, not effective at high repetition rate of laser operation. Thus, there are several problems that should be solved before the Er:YAG lasers can be efficiently used in dentistry. The most important problem to be solved is the heating of the tooth. It was shown that WO 99/55243 PCT/US99/08751 4 increasing the temperature at 5 oC for 1 min is sufficient to lead to necrosis of the pulp tissue and nerve. To solve this problem one can use relatively slow pulse repetition rate and/or cool the tooth surface with water, however, this results in slow, 5 inefficient ablation. Yet another problem of Er:YAG lasers is the cracking of the treated tooth tissue due to the shock waves that propagate into the tooth. Such cracks have been noted mainly while using higher radiant energies. As a result, the use of relatively low-energy pulses for safely treatment of dental o10 hard tissues is required. This in-turn reduces ablation efficiency. Thus, when used in dentistry, Er:YAG laser parameters are typically set to compromise and satisfy all of the factors herein described, resulting in low and slow ablation capabilities. The use of Er:YAG and other lasers in the 1.5-3.5 spectral range for 15 ablating dental hard tissues is described in, for example, U.S. Pat. Nos. 5,257,935 and 5,342,198 to Vassiliadis et al. CO2 lasers have also been attempted in hard tissue dentistry. CO2 lasers emit at 9.0 to 10.6 microns and are therefore efficiently absorbed by hydroxyapatite which is a natural constituent of hard biological tissues such 20 at teeth and bones. However, using CO 2 lasers, researchers have found that at energies sufficient for effective teeth ablation, a detrimental phenomenon of plasma generation near or at the tooth surface is experienced. There is thus a widely recognized need for, and it would be highly advantageous to have, a laser apparatus and method for laser surgery of 25 hard tissue devoid of the above limitations. SUMMARY OF THE INVENTION According to the present invention there is provided an apparatus for and a method of ablating a target site of a hard biological tissue, such as 30 enamel, dentine and bone tissue WO 99/55243 PCT/US99/08 7 51 5 According to further features in preferred embodiments of the invention described below, the apparatus comprising (a) a first radiation source activatable of producing a first output having a wavelength of between 1.5 and 6.5 microns; (b) a second radiation source activatable of 5 producing a second output having a wavelength of between 9.0 and 10.6 microns; (c) a delivering arrangement for effecting coaxiallity of the first and second outputs and for concurrently delivering the outputs to the target site; wherein the first and second outputs are selected such that concurrent delivery of the first and second outputs to the target site ablates the hard o10 tissue at the target site. According to further features in preferred embodiments of the invention described below, the method comprising the steps of (a) selecting a first radiation source activatable of producing a first output having a wavelength of between 1.5 and 6.5 microns; (b) selecting a second radiation 15 source activatable of producing a second output having a wavelength of between 9.0 and 10.6 microns; (c) using a delivering arrangement, coaxially and concurrently delivering the first and second outputs to the target site; wherein the first and second outputs are selected such that the coaxial and concurrent delivery of the first and second outputs to the target site ablates 20 the hard tissue at the target site. According to still further features in the described preferred embodiments the first and second radiation sources are each independently a laser. According to still further features in the described preferred 25 embodiments the first radiation source is a laser selected from the group consisting of Holmium doped laser, Erbium doped laser and carbon mono oxide laser. Preferably, Er:YAG, Er:YSGG or Ho:YAG. According to still further features in the described preferred embodiments the first wavelength is selected from the group consisting of 30 2.06, 2.78 and 2.94 microns.

WO 99/55243 PCT/US99/08751 6 According to still further features in the described preferred embodiments the first output further has a beam cross sectional geometry at the target area selected from the group consisting of a full spot and a hulled spot. 5 According to still further features in the described preferred embodiments the spot has a size of between 0.1 millimeters and 5 millimeters, preferably, 0.2 millimeters and 1.5 millimeters. According to still further features in the described preferred embodiments the full spot is selected substantially round, square or o10 triangular. According to still further features in the described preferred embodiments the full spot is top hat. According to still further features in the described preferred embodiments the hulled spot is selected substantially circular, square, 15 triangular or cross-shaped. According to still further features in the described preferred embodiments the first output is pulsating. According to still further features in the described preferred embodiments the pulsation is selected having pulses with very short 20 rising/falling time in a range of less than several microseconds. According to still further features in the described preferred embodiments the pulsation has a repetition rate of 1 Herz to 100 Herz. According to still further features in the described preferred embodiments the pulsation is selected having a pulse duration of between 25 several picoseconds to several milliseconds. Preferably between 50 microseconds and 800 microseconds. According to still further features in the described preferred embodiments the pulsation is selected having a pulse energy of between 0.1 millijouls to 5 jouls. Preferably between 50 millijouls to 1.0 jouls.

WO 99/55243 PCT/US99/08751 7 According to still further features in the described preferred embodiments the pulsation is selected having a pulse energy fluence of between 5 jouls per square centimeter to 200 jouls per square centimeter. According to still further features in the described preferred 5 embodiments the delivering arrangement includes a focusing arrangement for focusing the first and second outputs on one end of an optical fiber. According to still further features in the described preferred embodiments the delivering arrangement includes a telescope for focusing the first and second outputs. o10 According to still further features in the described preferred embodiments the delivering arrangement includes a delivering vehicle selected from the group consisting of a hollow waveguide, an optic fiber, an optic fiber bundle, and an articulated arm. According to still further features in the described preferred 15 embodiments the delivering arrangement includes a contact tip at a distal end thereof. According to still further features in the described preferred embodiments the second radiation source is a carbon dioxide laser. According to still further features in the described preferred 20 embodiments the second wavelength is selected from the group consisting of 9.3 and 9.6 microns. According to still further features in the described preferred embodiments the second output further has a beam cross sectional geometry at the target area selected from the group consisting of a full spot and a 25 hulled spot. According to still further features in the described preferred embodiments the spot has a size of between 0.1 millimeters and 5 millimeters. Preferably, between 0.2 millimeters and 1.5 millimeters.

WO 99/55243 PCT/US99/08751 8 According to still further features in the described preferred embodiments the full spot is selected substantially round, square or triangular. According to still further features in the described preferred 5 embodiments the hulled spot is selected substantially circular, square, triangular or cross-shaped. According to still further features in the described preferred embodiments the second output is pulsating. According to still further features in the described preferred 10 embodiments the pulsation has a repetition rate of 1 Herz to 100 Herz. According to still further features in the described preferred embodiments the pulsation is selected having a pulse duration of between several picoseconds to several milliseconds. Preferably between 50 microseconds to 1 millisecond. 15 According to still further features in the described preferred embodiments the pulsation is selected having a pulse energy of between 0.1 millijouls to 5 jouls. According to still further features in the described preferred embodiments the pulsation is selected having a pulse energy fluence of 20 between 1 jouls per square centimeter to 200 jouls per square centimeter. According to still further features in the described preferred embodiments the first and second outputs are both pulsating and the first and second outputs are at least partially overlapping in time. According to still further features in the described preferred 25 embodiments the first and second outputs are both pulsating and the first and second outputs are non-overlapping in time. According to still further features in the described preferred embodiments the first and second outputs are both pulsating synchronously. According to still further features in the described preferred 30 embodiments the first and second outputs are both pulsating simultaneously.

WO 99/55243 PCT/US99/08751 9 According to still further features in the described preferred embodiments the first and second outputs are both pulsating alternately. According to still further features in the described preferred embodiments the first output is absorable mostly by water in the hard tissue, 5 whereas the second output is absorbable mostly by hydroxyapatite in the hard tissue. The present invention successfully addresses the shortcomings of the presently known configurations by providing apparatus and method for ablating hard tissues such as tooth tissue with reduced heating effects. 10 BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 is a schematic depiction of a laser apparatus according to the 15 present invention; FIG. 2 shows a comparison of the absorption coefficients of water and hydroxyapatite; FIG. 3 shows a detailed transmission curve of hydroxyapatite; FIG. 4 is a plot of an Er:YAG laser pulse before and after tails 20 reshaping according to the present invention; FIGs. 5a-d show alternative radiation delivering vehicles according to the present invention; FIG. 6 shows a contact tip preferably employed with the delivering vehicles according to the present invention; 25 FIG. 7 demonstrates several possible pulse relations according to the present invention; and FIG. 8 shows a plurality of spot shapes generated by the apparatus according to the present invention.

WO 99/55243 PCT/US99/08751 10 DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is of an apparatus and method which can be used for ablating hard tissues characterized by low water content. Specifically, the present invention can be used for dental treatment, for 5 effectively and efficiently ablating enamel and dentine, while maintaining heat production in a treated tooth as low as possible, under damaging levels. Although these specific procedures most commonly are performed on human patients, it will be appreciated by those ordinarily skilled in the art that the method and apparatus described herein are equally applicable to 10 surgical procedures carried out on lower mammals. The principles and operation of the apparatus and method according to the present invention may be better understood with reference to the drawings and accompanying descriptions. Before explaining at least one embodiment of the invention in detail, 15 it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology 20 employed herein is for the purpose of description and should not be regarded as limiting. Referring now to the drawings, Figure 1 illustrates an apparatus according to the present invention, which is referred to hereinbelow as apparatus 20. 25 Thus, apparatus 20 serves for ablating a target site 22 of a hard 24, such as enamel or dentine in a tooth, or bone tissue. Apparatus 20 includes a first radiation source 26. Source 26 is activatable of producing a first output 28 having a wavelength of between 1.5 and 6.5 microns.

WO 99/55243 PCT/US99/08751 11 Apparatus 20 further includes a second radiation source 27. Source 27 is activatable of producing a second output 30 having a wavelength of between 9.0 and 10.6 microns. Apparatus 20 further includes a delivering arrangement 32 for 5 effecting coaxiallity of first 28 and second 30 outputs and for concurrently delivering these outputs to target site 22. To this end, arrangement 32 is preferably equipped with a beam combiner 23, which includes two prisms 23a and 23b, as well known in the art. 10 First 28 and second 30 outputs are selected such that concurrent and coaxial delivery thereof to target site 22 ablates hard tissue 24 at target site 22. According to a preferred embodiment of the present invention, first 26 and second 27 radiation sources are each independently a coherent 15 radiation source such as a laser. However, as will be appreciated by one ordinarily skilled in the art, other coherent radiation sources, e.g., those equipped with suitable filters may alternatively be employed. Lasers are presently preferred due to the high energy radiation they are capable of efficiently producing. 20 Thus, first radiation source 26 is preferably a solid state laser, such as, but not limited to Holmium doped laser, e.g., Ho:YAG laser emitting at 2.06 microns, Erbium doped laser, e.g., Er:YAG laser emitting at 2.94 microns, Er:YSGG laser emitting at 2.78 microns or carbon mono-oxide (CO) laser emitting between 5 and 6.5 microns. 25 Wavelength selection as describe herein is carefully designed for efficient ablating of low water content hard tissues. The lower spectral range (1.5-6.5 microns) is designed to be absorbed by water in the hard tissue, whereas the upper spectral range (9.0-10.6 microns) is designed to be absorbed by hydroxyapatite in the hard tissue.

WO 99/55243 PCT/US99/08751 12 As a result, although the overall energy invested in the hard tissue is increased and ablating is more efficient, heating is decreased as compared with the use of, for example Er:YAG laser alone. The Erbium doped laser, which is presently the laser of choice for 5 the low spectral range, is set in its optimal parameters as, for example, known from the prior art, whereas the carbon dioxide laser adds ablating energy to render ablation more efficient. Figure 2 shows a comparison of the absorption coefficients of water and hydroxyapatite. Please note that at 2.94 (the wavelength of Er:YAG 10 laser) the major absorption is in water, while at wavelengths of carbon dioxide lasers, hydroxyapatite is the dominant absorbent. In Figure 3 a detailed transmission curve of the hydroxyapatite is given. From this curve one learns that the most optimal upper spectral range is 9.3-10 microns, preferably about 10 microns. 15 According to a preferred embodiment of the present invention first output 28 is selected pulsating, preferably at 1 Herz to 100 Herz, more preferably 1-30 Herz. The rising/falling of the pulse shape, especially of first output 28, should be as sharp as possible to avoid unnecessary heating. A usual pulse 20 shape of free running laser is demonstrated in Figure 4. Significant parts of the pulse (the left and right tails which are shown in black) are below ablation threshold and thus contribute solely to heating of the treated tooth and to water vaporization. The pulsation of output 28 is preferably selected having a pulse 25 duration of between several picoseconds to several milliseconds, more preferably, between 50 microseconds and 800 microseconds. Selecting pulse duration as described may, for example, be effected by a Q-switch, as well known in the art.

WO 99/55243 PCT/US99/08751 13 The pulse duration should be compatible with the thermal relaxation time of a layer having a thickness which equals the penetration depth of the radiation. The penetration depths of Er:YAG radiation into enamel and dentine 5 are in the range of 3 to 7 micrometers. The relaxation time is evaluated using the following equation: t = d 2 /a, where t is a thermal relaxation time, d is the penetration depth and a is the diffusivity. Taking c - 4.6 x 10- 3 cm 2 /sec, one obtains a minimal pulse duration of about 50 microseconds. The pulsation is further selected having a pulse energy of preferably 10 between 0.1 millijouls to 5 jouls, more preferably between 50 millijouls to 1.0 jouls. It is preferably further selected of having a pulse energy fluence of between 5 jouls per square centimeter to 200 jouls per square centimeter. According to yet another preferred embodiment of the present invention delivering arrangement 32 includes a focusing arrangement 34 for 15 focusing first 28 and second 30 outputs on one end 36 of an optical fiber 38. Preferably, delivering arrangement 32 includes a telescope, as indicated in Figure 1 by a pair of lenses 40, for focusing first 28 and second 30 outputs. As specifically shown in Figures 5a-d, delivering arrangement 32 includes a delivering vehicle 42, such as, but not limited to, a hollow 20 waveguide 44, an optic fiber 46, an optic fiber bundle 48 or an articulated arm 50. A Ho:YAG laser has the advantage of producing radiation that propagates through glass or quartz, so that optical fibers made of glass or quartz may be used to conduct the radiation to the treated site. 25 The radiation produced by an Er:YAG laser or by a carbon dioxide laser must be conducted to the treatment site by a hollow waveguide, or by optical fibers made of exotic materials such as, but not limited to, crystalline silver halides. As shown in Figure 6, according to a preferred embodiment of the 30 present invention delivering arrangement 32 includes a contact tip 52 at a WO 99/55243 PCT/US99/08751 14 distal end 54 thereof, shown in Figure 1. Tip 52 is preferably selected conical and serves for carefully delivering outputs 28 and 30 to treated area 22 of tissue 24. According to a preferred embodiment of the present invention 5 second radiation source 27 (Figure 1) is a carbon dioxide laser, emitting at 9.3 or 9.6 microns. Like first output 28, according to a preferred embodiment of the present invention second output 30 is pulsating, e.g. in a repetition rate of 1 Herz to 100 Herz, preferably 1 Herz to 30 Herz. 10 The pulsation of second output 30 is preferably selected having a pulse duration of between several picoseconds to several milliseconds, more preferably 50 microseconds to 1 millisecond. The pulsation is preferably further selected having a pulse energy of between 0.1 millijouls to 5 jouls. 15 At round spot size of 1 millimeter in diameter the pulse energy of 30 should be in the range of 7.5 millijouls and to 1.5 jouls. At round spot size of 0.75 millimeters diameter the pulse energy of second output 30 should be in the range of 4.5 millijouls and 900 millijouls. The pulsation of second output 30 is preferably further selected 20 having a pulse energy fluence of between 1 jouls per square centimeter to 200 jouls per square centimeter. As shown in Figure 7, according to a preferred embodiment of the present invention first 28 and second 30 outputs are both pulsating. According to one embodiment the pulses of first 28 and second 30 25 outputs are at least partially overlapping in time (compare plots a and b) or alternatively non-overlapping in time or pulsating alternately (compare plots a and d). Preferably, first 28 and second 30 outputs are both pulsating synchronously (compare plot a to either plot b, c, or d).

WO 99/55243 PCT/US99/08751 15 Also preferably, first 28 and second 30 outputs are both pulsating simultaneously (compare plots a and c). It should be understood that all of these options and other (e.g., non synchronized or random pulsations) fall within the scope of the phrase 5 "concurrently delivering the first and second outputs to the target site", which relates to the outputs as wholes rather than to pulse fractions thereof. As shown in Figure 8, according to a preferred embodiment of the present invention either first 28 and/or second 30 outputs have a beam cross sectional geometry at target area 22 of either full spot 60 or a hulled spot 62. 10 Regardless of its geometry, the general size of the spot is preferably selected between 0.1 millimeters and 5 millimeters. For root canals treatment it is preferably selected about 0.2 millimetres in general size, whereas for caries removal it is preferably selected about 1.5 millimetres in general size. 15 A full spot according to the present invention is preferably selected either substantially round 64, square 66 or triangular 68. Similarly, a hulled spot according to the present invention is preferably selected substantially circular 70, square 72, triangular 74, cross shaped 76 or including several sub spots 78. 20 As used herein the term "hulled spot" refers to a spot that no more than 50 % of the area dictated by its periphery, as indicated, for example, by broken line 80 in Figure 8, includes radiation. According to a preferred embodiment of the present invention the spots of first 28 and second outputs are co-localized and/or co-shaped. 25 One ordinarily skilled in the art would know how to devise optics for obtaining the preferred beam cross sectional (spot) geometry at target area 22 as herein described. Ringed spots (such as, for example, hulled circular spots) are of special interest because they increase the effectivity of drilling into the hard 30 tissue.

WO 99/55243 PCT/US99/08751 16 As already mentioned, one of the problems associated with Er:YAG lasers when ablating hard tissues is access heating, which limits ablating efficiency. Ablating a tissue in a ring fashion as compared to full ablation, results in a similar result, since the tissue within the ring, although not 5 irradiated is disconnected from the main tissue bulk, becomes fragile, and therefore can be easily removed. Doing so, the amount of radiation per area unit is increased, while the total amount of energy invested may be maintained unchanged. As a result, ablation is improved, while heating and water vaporization effects are minimized. 10 Further according to the present invention there is provided a method of ablating a target site of a hard biological tissue, such as enamel, dentine and bone tissue. The method includes the following steps. First, a first radiation source is selected activatable of producing a first output having a wavelength of between 1.5 and 3.6 microns. 15 Second, a second radiation source is selected activatable of producing a second output having a wavelength of between 9.0 and 10.6 microns. Third, a delivering arrangement is used for coaxially and concurrently delivering the first and second outputs to the target site, 20 wherein the first and second outputs are selected such that the coaxial and concurrent delivery of the first and second outputs to the target site ablates the hard tissue at the target site. Although the invention has been described in conjunction with 25 specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims

1. An apparatus for ablating a target site of a hard biological tissue, such as enamel, dentine and bone tissue, the apparatus comprising: (a) a first radiation source activatable of producing a first output having a wavelength of between 1.5 and 6.5 microns; (b) a second radiation source activatable of producing a second output having a wavelength of between 9.0 and 10.6 microns; (c) a delivering arrangement for effecting coaxiallity of said first and second outputs and for concurrently delivering said outputs to the target site; wherein said first and second outputs are selected such that concurrent delivery of said first and second outputs to the target site ablates the hard tissue at the target site.

2. The apparatus of claim 1 wherein said first and second radiation sources are each independently a laser.

3. The apparatus of claim 1, wherein said first radiation source is a laser selected from the group consisting of Holmium doped laser, Erbium doped laser and carbon mono-oxide laser.

4. The apparatus of claim 1, wherein said first wavelength is selected from the group consisting of 2.06, 2.78 and 2.94 microns.

5. The apparatus of claim 1, wherein said first output further has a beam cross sectional geometry at the target area selected from the group consisting of a full spot and a hulled spot. WO 99/55243 PCT/US99/08751 18

6. The apparatus of claim 5, wherein said spot has a size of between 0.1 millimeters and 5 millimeters.

7. The apparatus of claim 5, wherein said full spot is selected substantially round, square or triangular.

8. The apparatus of claim 7, wherein said full spot is top hat.

9. The apparatus of claim 5, wherein said hulled spot is selected substantially circular, square, triangular or cross-shaped.

10. The apparatus of claim 1, wherein said first output is pulsating.

11. The apparatus of claim 10, wherein said pulsation is selected having pulses with very short rising/falling time in a range of less than several microseconds.

12. The apparatus of claim 10, wherein said pulsation has a repetition rate of 1 Herz to 100 Herz.

13. The apparatus of claim 10, wherein said pulsation is selected having a pulse duration of between several picoseconds to several milliseconds.

14. The apparatus of claim 10, wherein said pulsation is selected having a pulse energy of between 0.1 millijouls to 5 jouls. WO 99/55243 PCT/US99/08751 19

15. The apparatus of claim 10, wherein said pulsation is selected having a pulse energy fluence of between 5 jouls per square centimeter to 200 jouls per square centimeter.

16. The apparatus of claim 1, wherein said delivering arrangement includes a focusing arrangement for focusing said first and second outputs on one end of an optical fiber.

17. The apparatus of claim 1, wherein said delivering arrangement includes a telescope for focusing said first and second outputs.

18. The apparatus of claim 1, wherein said delivering arrangement includes a delivering vehicle selected from the group consisting of a hollow waveguide, an optic fiber, an optic fiber bundle, and an articulated arm.

19. The apparatus of claim 1, wherein said delivering arrangement includes a contact tip at a distal end thereof.

20. The apparatus of claim 1, wherein said second radiation source is a carbon dioxide laser.

21. The apparatus of claim 1, wherein said second wavelength is selected from the group consisting of 9.3 and 9.6 microns.

22. The apparatus of claim 1, wherein said second output further has a beam cross sectional geometry at the target area selected from the group consisting of a full spot and a hulled spot. WO 99/55243 PCT/US99/08751 20

23. The apparatus of claim 22, wherein said spot has a size of between 0.1 millimeters and 5 millimeters.

24. The apparatus of claim 22, wherein said full spot is selected substantially round, square or triangular.

25. The apparatus of claim 22, wherein said hulled spot is selected substantially circular, square, triangular or cross-shaped.

26. The apparatus of claim 1, wherein said second output is pulsating.

27. The apparatus of claim 26, wherein said pulsation has a repetition rate of 1 Herz to 100 Herz.

28. The apparatus of claim 26, wherein said pulsation is selected having a pulse duration of between several picoseconds to several milliseconds.

29. The apparatus of claim 26, wherein said pulsation is selected having a pulse energy of between 0.1 millijouls to 5 jouls.

30. The apparatus of claim 26, wherein said pulsation is selected having a pulse energy fluence of between 1 jouls per square centimeter to 200 jouls per square centimeter.

31. The apparatus of claim 1, wherein said first and second outputs are both pulsating and said first and second outputs are at least partially overlapping in time. WO 99/55243 PCT/US99/08751 21

32. The apparatus of claim 1, wherein said first and second outputs are both pulsating and said first and second outputs are non overlapping in time.

33. The apparatus of claim 1, wherein said first and second outputs are both pulsating synchronously.

34. The apparatus of claim 1, wherein said first and second outputs are both pulsating simultaneously.

35. The apparatus of claim 1, wherein said first and second outputs are both pulsating alternately.

36. The apparatus of claim 1, wherein said first output is absorable mostly by water in said hard tissue, whereas said second output is absorbable mostly by hydroxyapatite in said hard tissue.

37. A method of ablating a target site of a hard biological tissue, such as enamel, dentine and bone tissue, the method comprising the steps of: (a) selecting a first radiation source activatable of producing a first output having a wavelength of between 1.5 and 6.5 microns; (b) selecting a second radiation source activatable of producing a second output having a wavelength of between 9.0 and 10.6 microns; (c) using a delivering arrangement, coaxially and concurrently delivering said first and second outputs to the target site; WO 99/55243 PCT/US99/08751 22 wherein said first and second outputs are selected such that said coaxial and concurrent delivery of said first and second outputs to the target site ablates the hard tissue at the target site.

38. The method of claim 37 wherein said first and second radiation sources are each independently a laser.

39. The method of claim 37, wherein said first radiation source is a laser selected from the group consisting of Holmium doped laser, Erbium doped laser and carbon mono-oxide laser.

40. The method of claim 37, wherein said first wavelength is selected from the group consisting of 2.06, 2.78 and 2.94 microns.

41. The method of claim 37, wherein said first output further has a beam cross sectional geometry at the target area selected from the group consisting of a full spot and a hulled spot.

42. The method of claim 41, wherein said spot has a size of between 0.1 millimeters and 5 millimeters.

43. The method of claim 41, wherein said full spot is selected substantially round, square or triangular.

44. The method of claim 43, wherein said full spot is top hat.

45. The method of claim 41, wherein said hulled spot is selected substantially circular, square, triangular or cross-shaped.

46. The method of claim 37, wherein said first output is pulsating. WO 99/55243 PCT/US99/08751 23

47. The method of claim 46, wherein said pulsation is selected having pulses with very short rising/falling time in a range of less than several microseconds.

48. The method of claim 46, wherein said pulsation has a repetition rate of 1 Herz to 100 Herz.

49. The method of claim 46, wherein said pulsation is selected having a pulse duration of between several picoseconds to several milliseconds.

50. The method of claim 46, wherein said pulsation is selected having a pulse energy of between 0.1 millijouls to 5 jouls.

51. The method of claim 46, wherein said pulsation is selected having a pulse energy fluence of between 5 jouls per square centimeter to 200 jouls per square centimeter.

52. The method of claim 37, wherein said delivering arrangement includes a focusing arrangement for focusing said first and second outputs on one end of an optical fiber.

53. The method of claim 37, wherein said delivering arrangement includes a telescope for focusing said first and second outputs.

54. The method of claim 37, wherein said delivering arrangement includes a delivering vehicle selected from the group consisting of a hollow waveguide, an optic fiber, an optic fiber bundle, and an articulated arm. WO 99/55243 PCT/US99/08751 24

55. The method of claim 37, wherein said delivering arrangement includes a contact tip at a distal end thereof.

56. The method of claim 37, wherein said second radiation source is a carbon dioxide laser.

57. The method of claim 37, wherein said second wavelength is selected from the group consisting of 9.3 and 9.6 microns.

58. The method of claim 37, wherein said second output further has a beam cross sectional geometry at the target area selected from the group consisting of a full spot and a hulled spot.

59. The method of claim 58, wherein said spot has a size of between 0.1 millimeters and 5 millimeters.

60. The method of claim 58, wherein said full spot is selected substantially round, square or triangular.

61. The method of claim 58, wherein said hulled spot is selected substantially circular, square, triangular or cross-shaped.

62. The method of claim 37, wherein said second output is pulsating.

63. The method of claim 62, wherein said pulsation has a repetition rate of 1 Herz to 100 Herz. WO 99/55243 PCT/US99/08751 25

64. The method of claim 62, wherein said pulsation is selected having a pulse duration of between several picoseconds to several milliseconds.

65. The method of claim 62, wherein said pulsation is selected having a pulse energy of between 0.1 millijouls to 5 jouls.

66. The method of claim 62, wherein said pulsation is selected having a pulse energy fluence of between 1 jouls per square centimeter to 200 jouls per square centimeter.

67. The method of claim 37, wherein said first and second outputs are both pulsating and said first and second outputs are at least partially overlapping in time.

68. The method of claim 37, wherein said first and second outputs are both pulsating and said first and second outputs are non-overlapping in time.

69. The method of claim 37, wherein said first and second outputs are both pulsating synchronously.

70. The method of claim 37, wherein said first and second outputs are both pulsating simultaneously.

71. The method of claim 37, wherein said first and second outputs are both pulsating alternately.

72. The method of claim 37, wherein said first output is absorable mostly by water in said hard tissue, whereas said second output is absorbable mostly by hydroxyapatite in said hard tissue.