CA2019334C - Laser apparatus for treating bone and tooth tissue - Google Patents

Abstract

A method and apparatus for cutting tooth tissue by generating laser radiation at a wavelength which is absorbed more strongly by hydroxyapatite than by water; producing a succession of pulses of the generated radiation with an energy level, pulse duration, and repetition rate selected to cut the tooth tissue without causing harmful side effects; and concentrating the radiation pulses on the tissue to a spot sufficiently small to cause cutting of the tissue.
Laser radiation having a selected wavelength and in the form of pulses having a selected pulse duration, repetition rate and energy content per pulse, is employed for performing a variety of dental and medical procedures, including treatment of cysts and granulomas in the gum, and cutting of dentin, cementum, dental root material, bone and metal. Cavities and openings in teeth and bones can be filled with a mixture containing hydroxyapatite and phosphoric acid, mixed together to form a paste, and the resulting mixture, after being introduced into the opening or cavity, can be cured and hardened by application of pulses of defocussed laser radiation.

Description

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SURGICAL TREATMENT METHOD AND INSTRUMENT
BACKGROUND OF THE INVENTION
The present invention relates to surgical and dental procedures utilizing laser radiation. The invention relates more particularly to surgical and dental treatment procedures and instruments utilizing laser radiation for the removal of tooth and gum tissue.
In dental procedures, it is freguently desirable to remove portions of tooth enamel and dentin, and in certain cases, portions of gum tissue, in an accurately controlled manner and there has been a growing interest in the use of laser radiation for performing such procedures. The use of laser radiation is attractive because, particularly with the aid of optical fibers, such radiation can be focused to a very small area and is thus compatible with the dimensional scale of dental procedures. Moreover, laser radiation procedures can be performed without recourse to an anesthetic.
While a number of devices of this type have been proposed, they have not proven to be of practical use notably because even the most effective of those devices already proposed are useful only under limited and very precisely defined conditions.
The enamel and dentin of a tooth include, as one component, hydroxyapatite, which is in amorphous form in the dentin and crystalline form in the enamel.
These portions of a tooth additionally include organic tissues and water, but have no vascular system. Healthy dentin is in mineralized form, while dentin which has experienced decay is in demineralized form. Dentin has a relatively high percentage of organic tissue, around percent, and also a high percentage of water. These percentages increase considerably in decayed dentin.
Tooth pulp and the gum surrounding the teeth consist of vascularized organic tissue containing both hemoglobin and water. Each of these components has a different response to laser radiation.
Thus, it has been found, that hydroxyapatite absorbs laser radiation in the wavelength ranges of 9 -li , such as produced by COz lasers, and also in the wavelength range 0.5 - 1.06 ~ , which includes the wavelength that can be produced by a YAG laser.
The laser radiation absorption by the various parts of a tooth at various wavelengths is influenced by the absorption of the radiation energy by the water component thereof. The greater the absorption by water, the less energy is available for absorption by the other components. Since the wavelengths of the radiation emitted by COz lasers is absorbed to a large extent by water, this radiation has minimal cutting effect on enamel or dentin, and less of a cutting effect on mineralized dentin than on demineralized dentin.
On the other hand, it has been found that radiation at a wavelength of 1.06 is absorbed to a lesser degree by water, and therefore has a greater effect on mineralized tissues. Laser radiation at a wavelength of 0.532 a is not absorbed at all by water and can be effective on mineralized tissues if a sufficiently high, and thus dangerous, power level is employed.
As regards vascularized tissues, radiation at the wavelengths emitted by CO~ lasers has an effective cutting action because of its absorption by water, radiation at a wavelength of 1.06 ~ does not have any effect, and radiation at a wavelength of 0.532 ~ has a cutting effect on soft tissues because, although not absorbed by water, it is well absorbed by hemoglobin.
While a particular wavelength may inherently have a cutting effect on enamel or dentin, it has been found that the practical utilization of radiation at such a wavelength for dental procedures is highly dependent on the form in which the radiation is applied, L

with respect to energy level, pulse duration and repetition rate. Specifically, efforts to apply such radiation in the form of high energy pulses of short duration have been found to produce a highly localized temperature increase, resulting in differential thermal expansion which can cause mechanical damage to the tooth as well as vascular damage to pulp tissue. Conversely, low energy pulses of long duration cause a more widespread heating of the tooth which results in patient discomfort as well as pulp damage due to heating.
In the treatment of various dental. and other medical conditions, it is frequently necessary to remove bone, dentin, cementum or dental root material, and it is desirable to do so without subjecting the patient to adverse side effects.
Frequently, when performing medical procedures within the oral cavity, the practitioner encounters metal bodies introduced by previous dental procedures, such bodies being constituted by metal filling material, metal pins, and chrome posts used to secure dental prostheses in place, and it is necessary to cut these bodies, again without producing harmful side effects.
Also, dental practitioners frequently encounter cysts and granulomas, which occur in the gum adjacent the apex of a tooth, and it is necessary to destroy, or at least substantially reduce, these growths.
Furthermore, while a number of dental filling materials are presently available, there is a continuing need for material which can fill not only dental cavities, but also cavities existing in, or created in, bone material, and which will have a hardness comparable to that of the natural material which it replaces and form a strong bond with the wall of the cavity or opening.

SUM~SARY OF TAE INVERTTI0~1 It is an object of the present invention to effectively employ laser radiation in a variety of surgical operations involving cutting, by vaporization, of both tooth and gum tissue, as well as other vascularized body tissue.
Another object of the invention is to eliminate significant drawbacks of laser treatment systems which have previously been proposed.
A further object of the invention is to provide a single laser treatment device which can perform a variety of operations.
Yet another object of the invention is to perform dental treatments employing laser radiation in a manner to minimize or completely eliminate undesirable side effects of the treatment.
A specific object of the invention is to employ laser radiation to cut mineralized dental tissue without requiring high energy levels.
A further specific object of the invention is to employ laser radiation to cut soft tissue without requiring high energy levels.
A more specific object of the invention is to employ laser radiation for selectively cutting bane, dentin, cementum and dental root material, as well as metal bodies found in the mouth, without exposing the patient to adverse side effects, and particularly burning of tissue adjacent the area being treated.
Another object of the invention is to provide a novel filling material for filling cavities or openings in both teeth and bones, and to employ laser radiation for promoting hardening of such filling material.
Yet another abject of the invention is to provide an improved treatment for cysts and granulamas in bones and in the gum.

According to one aspect of the invention, the above objects are achieved by a method for filling an opening in tooth or bone material comprising:
forming a paste composed of a liquid and a powder containing hydroxyapatite:
filling the opening with the paste; and irradiating the paste which fills the opening with laser radiation in order to bond the hydrnxyapatite to material surrounding the opening.
l0 According to another aspect of the invention, the objects are achieved by a method of treating a cyst or granuloma in the gum at the apex of a tooth canal, or in bone, comprising:
opening the canal to the vicinity of the apex;
inserting an optical fiber having an output end into the canal so that the output end is located at the apex and conducting a succession of pulses of radiation through the fiber so that the radiation exits from the output end, impinges on and opens the foramen, and then impinges on and at least reduces the cyst or granuloma.
According to yet another aspect of the invention, the objects are achieved by a method for cutting bone, dentin, cementum and dental root material in the body, comprising: generating laser radiation having a wavelength suitable for cutting such material;
producing successive pulses of the radiation with an energy level, pulse duration and repetition rate selected to cut the material without causing harmful side effects: concentrating the radiation pulses on the material to a spot sufficiently small to cause cutting of the material; and, simultaneously with the step of concentrating, directing a cooling fluid onto the spot.
According to still another aspect of the invention, the objects are achieved by a method for cutting metal bodies in the mouth of a patient, comprising: generating laser radiation having a ~~~~~~3~

wavelength suitable for cutting the metal; producing successive pulses of the radiation with an energy level, pulse duration and repetition rate selected to cut the metal without causing harmful side effects;
concentrating the radiation pulses on the metal to a spot sufficiently small to cause cutting of the metal;
and, simultaneously with the step of concentrating, directing a cooling fluid onto the spot.

BRIEF DESCR7(FTION OF T~' DRAWING
The sole Figure is a cross-sectional view of a preferred embodiment of an instrument for performing laser radiation treatments according to the invention.

~fl~~~~4 DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is based essentially on the discovery that laser radiation can be used to cut, by vaporization, both tooth and gum material, as well as other vascularized tissue, with essentially no adverse side effects, if specific parameters are established for the laser radiation.
According to the present invention, the drawbacks described earlier herein can be eliminated, or at least substantially minimized, and an effective cutting action can be achieved, by the use of laser radiation preferably at a wavelength of 1.06 ~ in the form of pulses having an energy content of between 10 and 100 mJ, with a pulse duration of the order of 100 -300 microseconds, and a repetition rate of the order of 50 Hz, and with the radiation beam concentrated at a spot, at the treatment location, of the order of 200 -A pulse duration of 100 - 300 ~C sec. has been found to be sufficiently long to avoid subjecting the tissue being treated to thermal shocks but sufficiently short to enable effective control of the heating action to be maintained.
According to the invention, laser radiation at a wavelength of 1.06 , which can be produced by an Nd YAG laser, can be used for cutting, or vaporizing demineralized, i.e., decayed, enamel and dentin, without endangering gum tissue. Laser radiation at a wavelength of .532 ~ , which can also be produced by an Nd YAG
laser, can also be used, but this requires great care because it has been found that radiation at this wavelength will also cut gum tissue. Therefore, radiation at this wavelength can be used when it is desired to cut gum tissue.
Further, applicant has discovered that laser radiation at the wavelength of 1.06 ~S can be made to cut'healthy, or mineralized, dentin, and healthy enamel, ~~~~~~4 which was not heretofore considered possible, if a dark colored region is first provided at the spot where cutting is to begin. Specifically, it has been found that the absorption of energy at the wavelength of 1.06 PLC by dark materials is sufficient to enable laser radiation having a suitable energy level to create a plasma which causes vaporization of dentin tissue.
Applicant has further discovered that once a plasma cloud capable of vaporizing dentin has been established at a dark colored region, the laser beam can be displaced at a controlled speed from the dark colored region so that the plasma cloud will remain intact and vaporization of healthy dentin will continue.
For cutting dentin and enamel, laser radiation at a wavelength of 1.06 should be used. Radiation at a wavelength of 0.532 ~ has been found to be effective only if applied at dangerously high energy levels.
Since radiation at 0.532 ~ can efficiently cut vascularized tissue, it can be used for general surgical procedures. In this case, the radiation pulses should have an energy level of not greater than io mJ, with a pulse duration of 100 - 300 p sec., and the radiation may be focussed to a spot 200 - 600 ~ in diameter. A pulse repetition rate of the order of 50 Hz may be employed.
The Figure illustrates a handpiece for supplying laser radiation in a form suitable for performing the operations described above. A housing 2 is provided in the form normally utilized for handpieces, which housing would be configured in a manner known in the art for ease of manipulation. The interior of housing 2 is provided with an optical fiber 4 having an input end coupled to a source 6 of monochromatic light, such as an Nd YAG laser producing radiation at a wavelength of 1.06 . Light source 6 is connected to an operating power source 8 which supplies pulses sufficient to cause light source 6 to produce light pulses having the desired parameters.
The free end of fiber 4, in the vicinity of the free end of housing 2, is supported by a suitable support plate 1o to direct light radiation onto a curved mirror 12 which deflects the radiation onto the receiving end of a further optical fiber 14. Mirror 12 additionally performs a focusing action which can focus the radiation emerging from fiber 4 to a point within fiber 14, preferably in the vicinity of the outlet end thereof. This will help to assure that the light emerging from fiber 14 can be concentrated at a sufficiently small spot on the tooth to be treated.
Fiber 14 preferably has a very small diameter, possibly of the order of 250 ~.
Housing 2 additionally contains a hollow tube 16 which is connected to a source 18 of water and/or air and which has an outlet end positioned to direct a stream of the fluid supplied by source 18 into the immediate vicinity of the tooth region to which laser radiation is being applied.
In accordance with a particular novel feature of the invention, a plate 20 which is capable of influencing the laser radiation so as to double its frequency is slidably mounted on source 6 and is connected to a control handle 22 so as to be slidable, by manipulation of handle 22, between the illustrated position, where plate 20 is interposed in the light path between source 6 and fiber 4, and a retracted position, where plate 20 does not intersect the light path. With this simple arrangement, the handpiece is given the capability of applying either 1.06 ~ or 0.532 radiation to the area to be treated, so that only a single laser device need be provided for the selective performance of procedures with radiation of either wavelength.

~01~~'~4 For performing endodontic treatments within a tooth canal, fiber 14 can be given a suitable length and diameter to be introduced into a canal in order to apply the radiation to the canal walls for widening the canal preparatory to filling.
According to a particular aspect of the invention, the requisite dark spot can be formed simply by applying a small amount of graphite, such as used in pencils, with the aid of a small amount of glue. In fact, it has been found possible to achieve the desired result by applying a small quantity of glue to the point of a sharpened pencil and then rubbing the pencil point at the desired location.
For removal of decay, the radiation can have a wavelength of 1.06 and be in the pulsed form described above.
To dissipate the heat generated by the radiation, water and/or air should be sprayed onto the tooth in the vicinity of the spot which is being irradiated. The rate of flow of fluid depends on the extent to which the fluid absorbs the radiation. For example, water absorbs radiation at 1.06 at a very low level, but higher than radiation at 0.532 Therefore, water would be delivered at a higher rate when the latter radiation wavelength is being employed.
When the radiation is applied to demineralized enamel or pathological dentin, a dark spot is not necessary and a plasma forms at the irradiation spot and the affected material is volatilized at and around the spot. The extent of the plasma tends to increase in a short time and this allows for the possibility of reducing the pulse energy to between 10 and 20 mJ.
When cutting normal tissue, the radiation wavelength can be 1.06 ~ , which requires application of a dark spot, and will not affect soft tissues, or 0.532 PL~u , which can cut either hard tissues, i.e., dentin and enamel, or soft, vascularized tissues. Each wavelength will be preferable for certain purposes.
Thus, the invention provides four operating modes responsive to different needs:
1) Far cutting demineralized enamel and pathological dentin, use is made ~f radiation at a wavelength of 1.06 ~C , an energy level of 20 - 50 mJ, and with the pulse parameters described earlier herein.
Labelling with a dark spot is not required.
2) For cutting n~rmal enamel and dentin, the radiation would have the same parameters as for mode 1), but the starting point would be labelled with a dark spot.
3) For cutting any tissue, the same parameters as for mode 1) would be employed, with labelling with a dark spot where possible.
4) For cutting vascularized tissue, including gum and other soft body tissue, laser radiation at a wavelength of 0.532 ~ would be used, composed of pulses having an energy level of no greater than 10 mJ, without requiring labelling with a dark spot.
Far dental treatments, a cooling spray will be used whenever the operation generates a sufficient level of heat.
The application of laser radiation in all of the procedures to be described herebelow can be carried out with the apparatus described above and illustrated in the Figure.
According to the invention, a filling material for teeth is constituted by a mixture formed from a liquid component composed of phosphoric acid and water and a powder component composed of a ceramic and hydroxyapatite, with the ingredients mixed in a proportion to form a paste having a consistency such that the paste is workable and sufficiently self-supporting to be applied to the opening with a spatula and remain in place, and laser radiation having the characteristics to be described below is applied to cure and harden the mixture and bond it to the tooth. The proportions of the mixture are not critical, however, the following are preferred:
Liquid: Phosphoric acid 40%
water 60%
Powder: Ceramic 80%
Hydroxyapatite 20%
If the proportion of hydroxyapatite is increased, more energy is required to harden the mixture: if it is decreased, the strength of the resulting bond is reduced.
The ceramic component may be composed of corderite, silica or silicium oxide, or aluminum oxide, for example. The powder components will have the grain sizes normally used for dental filling materials.
The liquid and powder components should be mixed together just prior to introduction into the opening to be filled.
The radiation applied during this treatment has a wavelength of 1.06 ~ and is composed of pulses preferably having a duration of the order of 0.4 ms, a repetition rate of the order of 50 Hz and an energy per pulse in the range of 20-100 mJ. However, in contrast to the various cutting operations to be described in detail below, the beam should here be defocussed to be at least approximately coextensive with the exposed surface of the filling material. This can easily be achieved by varying the spacing between the radiation output surface of the handpiece and the tooth surface, the area of illumination being readily visible.
The application of radiation to the filling material will promote the growth of a crystal structure in that material and create a strong bond between the hydroxyapatite and the surrounding tooth material.

The radiation will be applied until a crystal structure appears, this generally requiring application of the radiation for a period of 10-30 seconds.
The above described filling material and radiation can be used for filling breaks or gaps in bone material.
According to another aspect of the invention, radiation having the above-described characteristics can be employed for treating a cyst or granuloma adjacent a l0 tooth apex, or in bone. For this purpose, after the canal had been opened to the foramen, a narrow optical fiber, having a diameter of around 200~e, for example, is threaded into the canal up to the foramen, and radiation having the characteristics described above for cutting soft tissue is delivered through the fiber to cut the foramen and then eliminate the cyst or granuloma.
For this operation, use is preferably made of radiation having a wavelength of 1.06 ~ , a pulse duration of the order of 0.4 ms, a pulse repetition rate of the order of 50 Hz and an energy content per pulse of 50-400 mJ:
In further accordance with the invention, it is possible to cut, without burning, bone, root, dentin and cementum in periods of the order of seconds by applying radiation of the type described above together with irrigation with a water/air mixture to control the thermal laser beam cutting action. In this case, the radiation wavelength is 1.06 ~ , the pulse duration is of the order of 0.8-1.2 ms, the pulse repetition rate is in the range of 30-50 Hz and the energy content per pulse is 200-400 mJ. This can be done without first forming a dark spot where the radiation is first applied. However, application of a dark spot will increase energy absorption and thus speed the cutting operation. In addition, a dark spot can be applied when it is desired to preliminarily mark or outline with a low energy beam the place to be cut.

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In addition, radiation having form described above for cutting bone can further serve to cut metal parts in the mouth, such as metal fillings, pine, or chrome tooth prosthesis posts. For this purpose laser 5 radiation will be created and directed to the material to be cut in the manner described above.
In the performance of all of the cutting operations described above, the light output surface of the handpiece is positioned to focus the radiation to a 10 small spot, preferably having a diameter of the order of 200-600 Vie.
When dentin is cut with the aid of an optical fiber in contact with the dentin, the end of the fiber in contact with the dentin is subject to destruction.
15 Therefore, it is desirable to use a relatively long fiber which will be replaced after a period of use. While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.
The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (7)

1. Apparatus for cutting a material selected from bone, enamel, dentin, cementum and dental root material compris-ings:
a) means for generating laser radiation at a wave-length which is suitable for cutting the material;
b) means connected to said generating means for causing said generating means to produce a succession of pulses of the generated radiation with an energy level, pulse duration, and repetition rate selected to cut the material;
c) means disposed for concentrating the radiation on the material to a spat sufficiently small to cause cutting of the material; and d) means disposed for supplying a cooling fluid to the region of the spot simultaneously with application of the radiation, said fluid containing water;
wherein the material is cut without harmful side effects when the radiation is concentrated on the material simultaneously with the supplying of cooling fluid.

2. Apparatus as defined in claim 1 wherein the wavelength of the radiation is between 0.5 µ and 1.1 µ.

3. Apparatus as defined in claim 2 wherein the wavelength of the radiation is about 0.532 µ or 1.06 µ.

4. Apparatus as defined in claim 1 wherein said means for concentrating the radiation comprise an optical fiber.

5. Apparatus as defined in claim 4 wherein said optical fiber hoe a diameter sufficiently small to permit insertion of said fiber into a tooth canal.

6. Apparatus as defined in claim 1 wherein said cooling fluid comprises a mixture of air and water.

7. Apparatus as defined in claim 1 wherein said cooling fluid comprises an air-water spray.