Abstract:
The invention concerns a drill assembly for preparing a prosthetic crown-receiving tooth, wherein said drills ( 1 ) are of the type comprising an active part and at least an inactive part. Each of the drills ( 1 ) comprises a distal end ( 12 ) shaped like a sphere portion having an inactive part ( 13 ) and an active part ( 11 ), one of which consists of a spherical cap in apical position with a small circle ( 14 ) having a radius much smaller than its bending radius.

Description:
RELATED U.S. APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO MICROFICHE APPENDIX 
     Not applicable. 
     FIELD OF THE INVENTION 
     The object of the present invention is a set of burs for preparing a tooth with a view to placing a prosthetic crown. 
     BACKGROUND OF THE INVENTION 
     Before placing a prosthetic crown on a tooth, it is necessary to machine said tooth, so as to remove the material that will be replaced by said prosthetic crown. 
     Since the size characteristics of the prosthetic crown should preferably be identical to those of the initial tooth, the four faces and the crown portion of said tooth are machined. 
     The operation is particularly delicate, since it is absolutely necessary to spare the papilla and the gum and to avoid damaging the adjacent teeth that are often very close to the tooth to be treated, whereby one should know that the practitioner has not always a bearing point at his disposal. 
     Furthermore, in order to achieve a perfect adjustment of the prosthetic crown, it is necessary for the faces to be homothetically machined according to the drawings, whereby one should know that, in the case of an incisor, the vestibular face is convex and the lingual face is concave, that, in the case of the pre-molar and the molar teeth, the faces are convex and that, in addition, the convex faces are so both in the cervical-occiusal direction and in the mesio-distal direction. 
     Currently, to achieve this aim, the preparation of a tooth starts by making a mesio-distal groove, then the occlusal portion and then the cervical portion are machined using the bottom of said groove as a depth control; while the last operation consists of creating a shoulder at the level of the collar, the fillet of which is preferably at a right angle in front of the gum papilla. 
     The drills that allow carrying out these operations are e.g. of the kind of those disclosed in FR 2,481,105 and in DE 2,012,268. These drills include, in a known way, one or several active portions and one or several inactive portions that provide the practitioner with a bearing point, without damaging the bearing area. 
     However, the burs of this kind do not allow the practitioner to prepare a tooth in a fully calm way, because of the requirements to be fulfilled. 
     Though the active portions of these burs indeed provide for a bearing point for carrying out the machining, they do not allow controlling the machining depth, namely when making the cervical fillet. 
     From GB 379,200 are known so-called “BATT” drills for intra-coronary use that allow, in particular, the ablation of the pulp ceiling, im order to treat the pulp eviction in the best possible way. These burs can have an ovoid or elongated shape and include, each, two portions, an active proximal portion and an inactive distal end. The bur is cylindrical, cylindrical-conical or ovoid and its distal end is semi-spherical in the case of the cylindrical and cylindrical-conical burs and parabolic in the case of the ovoid burs, the inactive portion covering at least the semi-spherical area in the case of the cylindrical and cylindrical-conical burs and a parabolic area of a height substantially equal to or larger than the radius of curvature of the end portion im the case of the ovoid burs. 
     Because of these features, namely the inactivity of the distal portion, these burs only allow boring out a cavity through a pivotal motion and a sliding about a point of the inactive portion. Because of its relatively large surface, namely with respect to its radius of curvature, the inactive portion is suitable only for machining a pulp ceiling and can in no way allow machining the coronary portion of a tooth. 
     From FR 2,716,795, there are also known dental burs including at least an inactive portion and an active portion, which are aimed at preparing a tooth with a view to placing a prosthetic crown. These drills, which must allow machining the tooth simultaneously over its full height, do not allow an accurate work and, in particular, do not to control the machining depth, namely when these drills have a flat active distal end. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is aimed at providing a set of burs for preparing a tooth, with a view to placing a prosthetic crown, that allows coping with the various above-mentioned drawbacks. 
     The set of burs for preparing a tooth with a view to placing a prosthetic crown, in which said burs are of the kind including an active portion and at least one inactive portion, is characterized mainly in that each of them includes a distal end having the shape of a portion of a sphere that has an inactive portion and an active portion, one of which consists of a spherical cap in an apical position having a small circle with a radius much smaller than its radius of curvature. 
     According to the invention, the apical spherical cap is inactive. 
     According to a particular embodiment of the set of burs according to the invention, one bur includes a head having the shape of a sphere or the like. 
     According to another particular embodiment of the set of burs according to the invention, one bur has the shape of a cylinder, the cylindrical surface of which is inactive and the distal end of which has the shape of a spherical cap with a radius of curvature larger than that of said cylinder. 
     According to a particular embodiment of the set of burs according to the invention, one bur has the shape of a cylinder, its cylindrical surface being inactive, while its distal end, which has the shape of a spherical cap with a radius of curvature larger than that of said cylinder, has, besides an inactive apical cap, an inactive peripheral area, so that the active portion of said distal end extends over a spherical ring. 
     According to another particular embodiment of the set of burs according to the invention, one bur has a cylindrical or cylindrical-conical shape the cylindrical or cylindrical-conical surface of which is active, while the distal end is semi-spherical. 
     According to the invention, the apical spherical cap is active. 
     According to a particular embodiment of the set of burs according to the invention, one said bur has the shape of a cylinder, its cylindrical surface being inactive, while its distal end, which has the shape of a spherical cap with a radius of curvature larger than that of said cylinder, has an active apical spherical cap bordered by an inactive spherical ring. 
     According to another particular embodiment of the set of burs according to the invention, one said bur has the shape of a cylinder, its cylindrical surface being inactive, while its distal end, which has the shape of a spherical cap with a radius of curvature larger than that of said cylinder, has an active apical spherical cap bordered by an inactive beveled rim. 
    
    
     The advantages and the features of the set of burs according to the invention will become apparent when reading the following description, which refers to the attached drawing that shows one non-restrictive embodiment of it. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the attached drawings, the following views are shown. 
     FIG. 1 a  is a partial elevation view of one bur of the set of burs according to the invention. 
     FIG. 1 b  shows a plan view of the end of the same bur. 
     FIGS. 2 a  and  2   b  show partial elevation views of burs of a known kind that can be used together with the set of burs according to the invention. 
     FIG. 3 a  shows a partial elevation view of another bur of the set of burs according to the invention. 
     FIG. 3 b  shows a plan view of the end of the same bur. 
     FIG. 4 a  shows a partial elevation view of another bur of the set of burs according to the invention. 
     FIG. 4 b  shows a plan view of the end of the same bur. 
     FIG. 5 a  shows a partial elevation view of another bur of the set of burs according to the invention. 
     FIG. 5 b  shows a plan view of the end of the same bur. 
     FIG. 6 a  shows a partial elevation view of another bur of the set of burs according to the invention. 
     FIG. 6 b  shows a plan view of the end of the same bur. 
     FIG. 7 a  shows a partial elevation view of another bur of the set of burs according to the invention. 
     FIG. 7 b  shows a plan view of the end of the same bur. 
     FIGS. 8 a  and  8   b  show schematic cross-sectional vestibular-lingual views of an incisor during the machining of the latter by means of a bur of the set of burs according to the invention. 
     FIGS. 9 a ,  9   b ,  9   c ,  9   d ,  9   e ,  9   f ,  9   g ,  9   h  and  91  show cross-sectional vestibular-lingual views of an incisor during successive steps of its preparation by means of the set of burs according to the invention. 
     FIGS. 10 a ,  10   b ,  10   c ,  10   d ,  10   e ,  10   f  and  10   g  show front schematic views of the same incisor during some of the same successive steps of the same preparation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     When referring to FIG. 1 a , one can see a bur  1  that is part of the set of burs according to the invention for preparing a tooth, with a view to placing a prosthetic crown. 
     The bur has a smooth shaft  10  that bears, at its end, a sphere  11 , the surface of which is active, except for the apical end of the distal portion  12  that consists of a non-active spherical cap  13 , as shown in FIG. 1 b.    
     The spherical cap  13  is delimited by a small circle  14  with a radius by far smaller than the radius of curvature of said spherical cap, in this case that of sphere  11 . By way of an example, in the case of bur  1 , the radius of the small circle  14  represents one third of the radius of curvature of sphere  11 . 
     The distal end  12  thus includes not only an inactive apical portion, but also an active portion that is in the form of a spherical ring. 
     Referring to FIGS. 2 a  and  2   b , one can see burs  2  and  2 ′ of a known kind frequently used for preparing a tooth; bur  2  is namely a so-called “BATT” bur. Bur  2  shown in FIG. 2 a  has an active conical surface  20  and an inactive rounded semi-spherical end  21 , while bur  2 ′, shown in FIG. 2 b , has an active conical surface  20 ′ and an inactive sharp end  21 ′; burs  2  and  2 ′ can be used in association with the set of burs according to the invention, as will be seen further in the description. 
     Referring to FIG. 3 a , one can see a bur  3 , which includes a smooth shaft  30  bearing, at its end, an out of round ball  31 , the surface of which is active, as well as its semi-spherical distal end  32 , except for its apical end that consists of a non-active small spherical cap  33 , as shown in FIG. 3 b.    
     When referring to FIG. 4 a , one can see a bur  4  that consists of a cylinder  40 , the cylindrical surface  41  of which is inactive and the distal end  42  of which has the shape of a portion of a sphere with a radius of curvature by far larger than that of cylinder  40 , so that it consists of a spherical cap. There is an apical end  43  in the form of an inactive spherical cap and an inactive peripheral area  44 , which border an active semi-spherical area  45 , as can be seen in FIG. 4 b.    
     When referring to FIG. 5 a , one can see a bur  5  that consists of a cylinder  50 , the cylindrical surface  51  of which is inactive and the distal end  52  of which, having the shape of a portion of a sphere with a radius of curvature larger than that of the cylinder  50 , so that it consists of a spherical cap, is active, except for the apical end  53  that consists of an inactive spherical cap, as can be seen in FIG. 5 b.    
     When referring now to FIGS. 6 a  and  6   b , one can see a bur  6  that consists of a cylinder  60 , the cylindrical surface  61  of which is inactive and the distal end  62  of which, having the shape of a portion of a sphere with a radius of curvature by far larger than that of the cylinder  60 , so that it consists of a spherical cap, has an active apical portion  63  having the shape of a spherical cap peripherally bordered by an inactive area  64  having the shape of a spherical ring. 
     One should note that, according to a variant, not shown, the inactive area  64  can be formed by a beveled rim. 
     When referring now to FIG. 7, one can see a bur  8  that consists of a cylinder  80  having an active cylindrical surface  81 , as well as a distal end  82  having an active semi-spherical shape, except for the apical portion  83  that is inactive and that has the shape of a cap the small circle  84  of which is by far smaller than that of the semi-spherical distal portion  82 . 
     According to a variant, not shown, of the bur  8 , the cylinder  80  can be replaced by a cylindrical-conical body. 
     When referring now to FIGS. 8 a  and  8   b , one can see the way of use of a bur from the set of burs according to the invention, in this case a spherically shaped bur  1 , on an incisor  7 , the striped area of the latter corresponding to the material thickness to be removed. 
     In FIG. 8 a , it can be seen that bur  1  is laterally brought close to the incisor  7  and parallel to the axis of the latter. The penetration of sphere  11  into the material is not possible axially, because of the inactive cap  13 ; it is limited in depth by the smooth shaft  10  that abuts against the upper edge of the created cavity. 
     When referring now to FIG. 8 b , one can see that, by inclining the bur  1  with respect to the incisor  7 , the depth of the created cavity can be increased, which depth is then limited by the cap  13 . From the position shown, the sphere  11  can be moved only according to a mesio-distal motion, while maintaining a constant depth, without any risk of perforation. The choice of the diameter of the sphere  11  determines the depth of the cavity or of the groove to be made. 
     Hereafter will be described the way of use of the burs  1 ,  2 ,  2 ′,  3 ,  4 ,  5 ,  6  and  8 , with reference to FIGS. 9 a ,  9   b ,  9   c ,  9   d ,  9   e ,  9   f ,  9   g ,  9   h  and  9   i  and to FIGS. 10 a ,  10   b ,  10   c ,  10   d ,  10   e ,  10   f  and  10   g , which represent different steps of the preparation of an incisor  7 . 
     When referring to FIGS. 9 a  and  10   a , one can see that the first step of the preparation consists in creating in the first place, at half height of the vestibular convex face  71 , by means of a bur  1 , a mesio-distal groove  70 , as shown only in FIG. 1 a , of a desired thickness, while sparing the adjacent teeth, i.e. choosing a bur  1  of an adequate diameter. As we have seen above, the groove  70  is created while resting on the shaft  10  and inclining it in order to achieve a sufficient penetration, which is possible on the vestibular face  71 . 
     Bur  1  can work only according to a swinging motion in locked positions on the shaft and on the inactive end  13 , which limits the penetration of the bur  1 . 
     The next step consists in creating in the vestibular face  71  a mesio-distal groove  72  at the occlusal level in the vicinity of the incisive edge, about 2 millimeters away from it, also by means of bur  1  used in the same way as for creating the groove  70 . 
     The next step, not shown, consists in marking the bottom of the groove  72  by applying on it a dyestuff, the bottom of the groove  72  serving as a depth reference. 
     When referring now to FIGS. 9 b  and  10   b , one can see that the next step consists in removing as homothetically as possible the vestibular-occlusal face  73  by means of a bur  2 , while resting, with the inactive end  21  of the latter, in the groove  70  and taking care not to remove the marking on the bottom of the groove  72 . 
     After machining the vestibular-occlusal face  73 , it should preferably be marked completely, in order to preserve it during the next steps. 
     When referring now to FIGS. 9 c  and  10   c , one can see that the next step consists in re-tapering the tooth  7  through machining all the faces of the tooth, in the direction of the axis of insertion, by means of a bur  2 ′, or  2 , while resting at the cervical level  74  with the inactive end  21 ′ or  21 , while sparing the papilla and the adjacent teeth. 
     The choice of the bur depends on the space between teeth when the teeth do not enter into contact with each other, a bur  2  is preferably used. 
     The next steps consist in making the cervical fillet, which is the most delicate operation during the preparation of the tooth  7 . 
     When referring to FIGS. 9 d  and  10   d , one can see that in a first moment is created, within the desired limit, a peripheral pre-cervical groove  75 , by means of a bur  1  the active spherical end  11  of which has a sufficiently small diameter to be able to pass through the space between teeth without damaging the adjacent teeth. 
     As can be seen in FIGS. 9 a  and  10   a , the groove  75  of the bed of portion  21  of bur  2  that tapers everything. 
     One should note that this operation can also be carried out by means of bur  8  or any of its variants. 
     Afterwards, as shown in FIGS. 9 f  and  10   f , one has to use again a bur  1  of an appropriate diameter, which can be blocked by its shaft  10  and its inactive cap  13 , and swung according to an axis close to the axis of insertion, in order to maintain over the full periphery a groove of a constant thickness. 
     Then, with reference to FIGS. 9 g  and  10   g , a bur  2  is used to taper the tooth  7 . The burs  1  and  2  or  8  will be used alternately, until achieving a fillet  76  of about 10/10. 
     One should note that for carrying out the fillet, one preferably uses a bur  8 , which can allow avoiding the alternate use of a bur  2  and a bur  1 , since, contrarily to bur  2 , the semi-spherical distal portion  82  of bur  8  is an active portion, which authorizes a machining substantially equivalent to that of bur  1 . 
     The finishing of the fillet  76  is shown in FIG. 9 h ; it is achieved by using successively burs  4 ,  5  and  6 . 
     Bur  4  is used to regularize the surface of fillet  76  and bring it into its final situation. The inactive peripheral area  44  allows the bur  4  to be placed at the final level of the sulcus, by softly pushing back the papilla without attacking it. 
     On the other hand, bur  4  can round the cervical-axial angle, hence, bur  5  can cope with this drawback, however, taking care to keep it constantly in contact with the axial wall, in order to avoid creating an undercut at that level and destroying the papilla. 
     Regularizing the surface of the fillet can also be done by means of bur  6 , the inactive peripheral area  64  of which allows, on the one hand, limiting an eventual sinking, on the other hand, avoiding creating an undercut and, furthermore, avoiding attacking the gum papilla. 
     The next step consists in treating the lingual face  77 , which is concave, by reducing it, as well as the incisive edge, by means of a bur  3 , as shown in FIG. 10 i , after having created in it, in the same way as for the vestibular-occlusal face  73 , two mesio-distal grooves  78  and  79  by means of a bur  1 . 
     Finally, when the fillet has been carried out, the tooth  7  can be polished so as to eliminate the various markings used, while taking care not to touch the fillet that must remain very clearly at about 90°, in front of the gum papilla. 
     The burs  1 ,  3 ,  4 ,  5  and  8  according to the invention, used as described above, allow preparing a tooth without any risk of damaging it. 
     They cannot dig axially, since their apical end is inactive and arranged in the same convex plane as the active surface. 
     As regards bur  6 , it allows, complementarily to burs  4  and  5 , finishing the cervical fillet, the rounded shape of its distal end  62  facilitating controlling its displacement. 
     The burs object of the present invention allow machining the surface of a tooth with their distal end, while impeding or limiting its axial penetration, which authorizes a highly controlled and, thus, entirely safe work.