Abstract:
A system for delivering a CO 2  laser beam to the roots of a tooth is provided. The system includes a laser beam source, a first fiber having a first diameter connected to the laser beam source at its proximal end and to a hand piece at its distal end, the hand piece including an optical assembly operative to transfer the beam from the distal end of the first fiber to the proximal end of a second fiber having a second diameter smaller than the first diameter with substantial power loss.

Description:
FIELD OF THE INVENTION 
     The present invention relates to apparatus and method for delivering a CO 2  laser beam generally and more particularly to apparatus and method for delivering a CO 2  laser beam which is particularly useful for the class of dental procedures known as root canal procedures. 
     BACKGROUND OF THE INVENTION 
     In certain dental applications, it is advisable to perform root canal procedures after drilling the tooth to the root. At present, any infection occurring after the root cavity treatment is usually dealt with by a course of antibiotics. Treatment with antibiotics is not local and also delays the continuation of the treatment after the root cavities have been made since the effect of the antibiotics is not immediate. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a system and method for local sterilization of the drilled-out interior of the root of a tooth by the application of a laser beam. 
     According to one aspect of the present invention a low power CO 2  laser beam applied to the root itself through the drilled cavity prevents infection caused by contamination during the drilling process. 
     There is thus provided, in accordance with a further aspect of the present invention, a fiber based delivery system terminating in a short tapered fiber cone whose dimensions are small enough to be inserted into the drilled cavity such that the distal end of the fiber lies close to or within the root of the tooth. 
     Still further, there is provided according to yet another aspect of the present invention, an optical relay system between the master delivery fiber and the tapered cone. In this way, the delivery of at least 2 watts and up to 4 watts of power can be achieved without the fiber tip heating up by more than about 5° C. In this way laser delivery to the root of the tooth can be achieved without effectively raising the temperature of the body of the tooth itself. 
     There is provided, in accordance with an aspect of the present invention, a system for delivering a laser beam to the roots of the tooth. The laser beam is a CO 2  beam. The system includes a laser beam source, a first fiber having a first diameter connected to the laser beam source in its proximal end and to a hand piece in its distal end, the hand piece including an optical assembly operative to transfer the beam from the distal end of the first fiber to the proximal end of a second fiber having a second diameter smaller than the first diameter with substantial power loss. 
     Furthermore, in accordance with an embodiment of the present invention, the hand piece includes a relay lens facing the distal end of the first fiber, and an aperture stop for transferring a portion of the laser beam to the proximal end of the second fiber. 
     Still further, there is provided according to yet another embodiment of the present invention, a system for delivering a CO 2  laser beam which includes a laser beam source, a first fiber having a first diameter connected to the laser beam source in its proximal end and to a hand piece in its distal end, the hand piece including an optical assembly operative to transfer the beam from the distal end of the first fiber to a the proximal end of a second fiber having a second diameter smaller than the first diameter with substantial power loss. 
     In addition, in accordance with an embodiment of the present invention, the hand piece includes a relay lens facing the distal end of the first fiber, an aperture stop for transferring a portion of the laser beam to the proximal end of the second fiber, whereby the quality of the beam entering the second fiber is improved, minimizing thermal damage to the tooth. 
     Furthermore, in accordance with an embodiment of the present invention, the system further includes a reflecting element disposed intermediate the aperture and the proximal end of the second fiber for deflecting the laser beam to the second fiber. The second diameter of the second fiber is small enough to allow insertion of the second fiber into the roots of a tooth. 
     Furthermore, the second fiber is disposable and the first and second fiber does not substantially heat up during operation. The angle between the hand piece and the second fiber is 110 degrees. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the following description and accompanying drawings, while the scope of the invention is set forth in the appended claims. 
     FIG. 1 is a pictorial illustration of a system for delivering a CO 2  laser beam, constructed and operative in accordance with a preferred embodiment of the present invention; and 
     FIG. 2 is an illustration of the hand piece of the system of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is now made to FIGS. 1 and 2 which illustrate the laser delivery system, generally referenced 10, of the present invention. Laser delivery system 10 comprises a CO 2  laser source 12 coupled to a master fiber delivery system 14. Master fiber 14 is coupled to a short conical tapered fiber 16 via a chuck 17 of the hand piece 18. The hand piece 18 includes an optical assembly 20 including a relay lens 22, held in the optical assembly 20 by an aperture stop 23 with an aperture 24 extending therethrough and deflecting mirror 26. In the preferred embodiment fiber 16 is operative to deliver a CO 2  laser beam to the roots of a tooth 100 in order to prepare the tooth after root cavities have been made. 
     In its preferred, but non limiting operation, laser delivery system 10 is used for pre-root canal procedures, such as sterilizing the root cavities or drying the root cavities prior to root canal procedures. 
     In the illustrated embodiment, CO 2  laser 12 is coupled to the hollow silver master fiber 14 having a length of about 1 meter to enable the dentist to operate conveniently. In the preferred embodiment, the fibers and a hollow silver waveguide with dielectric coating disclosed in U.S. Pat. No. 5,325,458 to Morrow et al. incorporated herein by reference. Alternatively, any other type of fiber conducting CO 2  laser radiation may be used, for example hollow teflon silver coated fiber or solid silver halide fiber, all well known in the art. 
     Handpiece 18 comprises a system of holding and centering the master fiber 14 a certain distance from the relay lens 22. The image of the end of the master fiber 14 is focused onto the entry port of the short tapered fiber 16. Between the lens and the tapered fiber (taper) 16 there is a deflecting mirror 26 which creates a convenient 110 degrees between the axis of the master fiber 14 and the axis of the tapered fiber 16 to facilitate work on teeth. 
     A particular feature of the present invention is that it provides a low power transfer of the laser beam from fiber 14 to fiber 16. 
     Since most fiber delivery systems for CO 2  lasers have large numerical aperture outputs due to imperfections in the surface quality of the fiber, the exit angle of the fiber is always greater than the input angle. For the present system, a non-limiting example of a 1 meter length hollow silver fiber 14 of 1 mm internal diameter has an exit numerical aperture of 0.06 whereas the input numerical aperture from the laser is only 0.03. 
     The end of the fiber 14 has to be imaged onto the entrance surface of a tapered fiber 16. The dimensions of the tapered fiber can be internal diameter from 0.7 to 0.3 mm over a length of about 20 mm with an outside diameter at the distal end of about 0.45 mm since fiber 16 is preferably disposable and is entered into the roots of a tooth. 
     The optical assembly 20 of handpiece 18 is designed to bridge the above differences. In the preferred embodiment, the relay lens 22 used in the handpiece images the 1 mm exit face of the master fiber 14 to an image size of 0.4 mm. Then, in this way all the rays forming a focus after the deflecting mirror 26 will be perfectly coupled into the 0.7 mm inside diameter of the tapered fiber 16. 
     Since the numerical aperture of the master fiber 14 is 0.06 (3.5° half angle) then after the relay lens the numerical aperture entering the taper 16 will be 0.15. (To increase power transfer of the taper 16 itself it is desirable that the numerical aperture of the cone of rays entering the taper be as small as possible.) With larger numerical apertures, the power transfer of the taper 16 itself is lower and this power loss manifests itself in a very large rise in temperature. In such a case, the taper 16 becomes very hot and would cause thermal damage to the inside of the tooth. 
     It is therefore desirable to aperture the beam before it strikes the input surface of the tapered fiber. Such aperturing will not affect the size of the focused beam at the entrance surface of the taper but will reduce the numerical aperture of entrance beam. In this way, the power transfer of The taper itself will increase. The overall power transfer of the handpiece will, however, be reduced by this technique. However, with this procedure for root canals only about up to 4 watts of power need to be delivered by the taper. In the present laser system, the maximum output power of the master fiber 14 is 15 watts. 
     Table 1 below shows results of power transfer of the taper itself as a function of size of aperture with corresponding numerical aperture entrance to the taper. The power transferred from the end of the master fiber through the pinhole is also indicated. 
     
                       TABLE______________________________________                 CA         B           Power       DPinhole Diameter     Input Numerical                 Transferred Power TransferAperture (mm.)     Aperture to Taper                 by Pinhole  of Taper Itself______________________________________8         0.15        100%        68.8%6         0.11        96.9%       69.4%5         0.09        87.5%       73.2%4         0.076       71.9%       78.3%3         0.057       51.6%       81.0%2         0.038       26.6%       88%______________________________________ 
    
     As can be seen from the table, the overall power transfer of the handpiece [pinhole transfer×power transfer of taper 16 itself] is greater for a pinhole diameter of 8 mm. than for one of 2 mm. However, the power transfer of the taper 16 itself is greatest with the 2 mm. aperture, resulting in the minimum amount of heat buildup in the taper itself. This effect, as already explained, is very desirable and in our system we chose an aperture diameter of 3.5 mm. In the actual handpiece design as shown in FIG. 2 the inside diameter effectively blocks all rays emitted from the master fiber 14 such that after the relay lens 22 the numerical aperture entering the taper does not exceed 0.066. 
     That is, all rays that would have entered the taper at a numerical aperture greater than 0.066 have been blocked. 
     While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various changes and modifications may be made without departing from the spirit and scope of the present invention. For example, fiber 14 may be replaced by a multiple-section light-guide or be at other desirable length. Another example is that for each tooth the length of fiber 16 may be adjusted. Further, fiber 16 may be marked so that the dentist can know the depth of penetration. 
     It will be further appreciated that the present invention is not limited by what has been described hereinabove and that numerous modifications, all of which fall within the scope of the present invention, exist. Rather the scope of the invention is defined by the claims which follow: