Dental restoration structure

Abstract: A self-cutting implant (12) anchorable in a jawbone is provided. Also provided is a crown structure (10) formed from a collar (106) including aligned bores (100,124). In addition, a process for making the crown structure is provided.

Description: Field of the Invention This invention relates to dental implants, in particular to self-cutting implants, and to associated dental restoration structures. Background of the Invention Dental restoration structures are known as illustrated by U.S. Patent Nos. 5,199,873 to Schulte et al (WO-A-93/06786), and 4,932,868 to Linkow et al, and by Ledermann et al, Schweiz Monatsschr. Zahnmed. , vol. 101 (5), pp. 611-617 (1991). In this respect, prior workers have made a considerable effort to provide an improved implant. Implant failure can lead to significant destruction of alveolar bone. It has been found through prior effort that self-tapping implants are advantageous. Also found to be beneficial are single body implants. Commercial implants include the self-tapping, single body implant described in the Ledermann et al publication. This implant has a tapered profile and longitudinal grooves that form cutting teeth. An interior cavity includes a hexagonally-shaped, upper portion for receiving an abutment member having a longitudinal bore, and a lower portion for engaging threads of a screw for securing the abutment member to the implant. The abutment member is used to connect the implant to a crown structure. However, pressure-induced bone resorption or necrosis may occur with the implant. Additionally, when the abutment member is secured to the implant by rotation of the abutment screw, undesirable additional cutting of bone or detachment may occur due to engagement of the implant cutting teeth. A crown structure often used with the implant of the Ledermann et al publication, includes a transverse inclined bore for coaxial alignment with a corresponding transverse inclined bore of the abutment member. In this case, the crown structure is attached to a crown end of the abutment by means of a transverse screw threaded into the aligned bores. The bore in the crown structure may advantageously be slightly higher than the bore in the abutment to produce a press fit of the crown to the implant when the bores are aligned by use of the screw. Commercial crown structures for use with implants are typically prepared from a block of gold of about 2 to 3 mm thickness. These crown structures are formed to have an appropriate interior shape by removal of gold from the gold block. The process is labor-intensive and costly. Accordingly, there continues to be a need for improved dental implants and for less expensive dental crowns for use with implants. Likewise, there is a need for a process for making less expensive dental crowns for use with implants. Summary of the Invention In accordance with the present invention, a dental restoration structure as defined in claim 1 is provided. In the detailed description of the invention that follows, there are essentially described only preferred embodiments of this invention, simply by way of illustration of the best mode contemplated of carrying out this invention. As will be realized, this invention is capable of other and different embodiments, and its several details are capable of modification in various respects, all without departing from the invention. Accordingly, the drawing and the detailed description are to be regarded as illustrative in nature, and not as restrictive. Brief Description of the Drawing Reference is now made to the accompanying drawing, which forms a part of the specification of the present invention. Fig. 1 is a partial cross-sectional view of a preferred dental restoration structure in accordance with the present invention; Fig. 2 is an enlarged, cross-sectional view of a portion of the implant of the dental restoration structure of Figure 1, implanted in a bone mass; Fig. 3 is a cross-sectional view of the implant taken substantially along line 3--3 of Figure 1; Fig. 4 is a cross-sectional view similar to Figure 3, showing alternative cutting teeth; Fig. 5 is an exploded, partial cross-sectional view of the crown/tooth structure, transverse screw, abutment screw, and abutment of the dental restoration structure of Figure 1; Figure 6 is a perspective view of an alternative abutment; Figure 7 is a perspective view of a collar useful in making the crown structure of Figure 1; Figures 8 and 9 depict steps in a process for making the crown structure of Figure 1; and Figure 10 is an enlarged, cross-sectional view of the crown structure of Figure 1. Detailed Description of the Invention As indicated above, the present invention relates to an advantageous dental restoration structure including a novel thread cutting implant. The invention further relates to a novel crown structure. This dental restoration structure is useful in the maxilla and mandible for individual crowns, tissue bars, constructions, overdentures and complete implant-borne bridges. Referring to Figure 1, a preferred dental restoration structure 10 in accordance with the present invention, includes a self-cutting implant 12 anchorable in a jawbone, a connecting member or abutment 14 fastenable to the implant by an abutment screw 16, a crown structure 20 securable to the abutment by a transverse screw 22, and a tooth structure 24 overlaying and bonded to the crown structure. Advantageously, preferred implant 12 includes a generally cylindrical neck 26 and a tapered, thread cutting portion 28. Neck 26 has a peripheral wall 30 that is generally parallel to a longitudinal axis 32 of the implant and dental restoration structure, whereas thread cutting portion 28 tapers in the direction of a tip 34, which is preferably blunt. Preferably, the peripheral wall of the implant neck is smooth, and very preferably the wall is polished. The lack of threads on the peripheral wall facilitates cleaning. Moreover, inflammation-free mucosa integration and the formation of a junctional epithelium may result. A typical length of the peripheral wall ranges from about 1 mm to 3 mm. The thread cutting portion of the implant includes a plurality of self-tapping threads or cutting teeth 40. This feature beneficially avoids the need to tap threads into an implant bed before insertion of the implant. Referring also to Figure 3, which indicates the direction of rotation of the implant and cutting teeth, the cutting teeth include a leading edge 42 for cutting into the jawbone of a patient, and a peripheral edge 44 for providing an anchoring action. Preferably, the thread cutting portion of the implant is slightly roughened to promote osseointegration. A suitable roughening will typically be about 50 to 100 nm. Roughening may be provided by, for instance, anodizing to provide a ceramic-like surface. This slightly roughened surface combined with the use of self-tapping, cutting teeth to cut the final bed, promotes exceptional osseointegration. The implant is advantageously made of pure titanium having a surface layer of titanium dioxide (rutile). Accordingly, peri-implant soft tissue and bone do not directly contact titanium metal. With reference to Figures 1 and 2, the implant advantageously has a stepped profile. In particular, a bottom wall 46 of the implant neck is generally perpendicular with respect to the peripheral wall of the generally cylindrical neck to provide a stepped joining of the neck and thread cutting portion 28. This advantageous structure may be contrasted to the bottom wall of the cylindrical neck of the Linkow et al implant, which provides a tapered joining of the neck and threaded portion thereof. In addition, in the present invention, a root end 48 of the implant neck is of a diameter greater than any diameter of the tapered cutting portion. More particularly, the peripheral edge of each of the cutting teeth adjacent the implant neck, is stepped in from the plane of the peripheral wall of root end 48. These cutting teeth include the cutting teeth designated 40A,40B in Figures 1 and 2. This beneficial structure is in contrast to the corresponding threads of the Schulte et al implant, which extend beyond the plane of the peripheral wall of the root end of the cylindrical neck thereof. As a result of these features, a depth-limiting step or ledge is formed for limiting depth of an implant, so as to reduce pressure-induced bone resorption or necrosis. A typical depth is illustrated in Figure 2, in which bone structure is designated 50 and the crest of bone is designated 52. An especially suitable angle of taper of the thread cutting portion of the implant is about 5°. Other angles of taper may, of course, be used. As indicated in Figure 1, the thread cutting portion is continuously tapered to tip 34. As a result, a cutting action is provided along its entire length. This advantageous implant structure may be contrasted with the stepped, tapering implant structure of Schulte et al, in which the diameters of successive steps decrease toward the implant tip. Referring to Figures 1 and 3, grooves 54 in the thread cutting portion of the implant provide cutting teeth 40 each having cutting leading edge 42, and in addition increase the implant surface area, which assists force distribution. Beneficially, grooves 54 extend from near blunt tip 34 into root end 48 of the implant neck. Disposed lateral to grooves 54 are short grooves (not shown), also longitudinally aligned, that extend from tip 34 approximately to root ends of grooves 54. In combination with grooves 54, these grooves provide cutting teeth the length of the tapered portion of the implant, and provide for channeling of bone fragments from the borehole. However, grooves 54 may not extend so far into the implant neck as to allow incursion of food and bacteria. Longitudinal alignment of a groove with longitudinal axis 32 results in cutting leading edges 42 of the groove generally forming a common plane. With continued reference to Figure 3, cutting teeth 40 each include a point 56 joining leading edge 42 to peripheral edge 44. In addition, each cutting tooth includes an edge 58 opposite to leading edge 42, and joined to peripheral edge 44 by a pointed junction 60. Opposite edge 58 may be, like the leading edge, sharp for a cutting action. Alternatively, referring to Figure 4, an implant 12' may beneficially include cutting teeth 40', which have a non-cutting edge 58' opposite to a leading edge 42', and a peripheral edge 44'. Consistent therewith, opposite edge 58' may be blunt or dull, and the peripheral edge may be joined to opposite edge 58' by a rounded junction 60'. With reference again to Figures 1 and 2, a crown end 62 of the implant neck includes an annular raised step 64 of smaller diameter than the diameter of the root end of the neck. Surface 66 of the raised step and surface 68 of the crown end function as bearing surfaces. More particularly, generally horizontal surface 68 serves as a bearing surface for crown/tooth structure 20,24; and generally horizontal surface 66 of the raised step functions as a bearing surface in addition for abutment 14. Joining surfaces 66,68 is a peripheral wall 72, indicated in Figure 2, of the annular raised step 64. Referring particularly to Figure 2, a recess or cavity 74 in the interior of the implant includes a portion 76 for receiving an implant end 78 of abutment 14. Preferably, portion 76 is provided with a shape or configuration for preventing rotation of the abutment with respect to the implant. Any suitable anti-rotation shape may be used. Portion 76 may also serve to receive an inserted tool to enable a torque to be exerted about longitudinal axis 32 of the implant during implantation. Toward the root end of the implant, cavity 74 includes a lower portion 80 of smaller diameter than portion 76, for engaging threads of abutment screw 16, as shown in Figure 1. With reference particularly to Figure 5, abutment 14, which serves to couple the crown/tooth structure to the implant, has a stepped exterior profile. More particularly, implant end 78 of the abutment is of smaller cross-section than an adjoining crown end 82 thereof, and a seating surface 84 joins implant end 78 and crown end 82. As shown in Figure 1, seating surface 84 bears upon surface 66 of raised step 64 of the implant. Implant end 78 of the abutment preferably has a locking peripheral surface 86 for engaging a mating surface in portion 76 of implant cavity 74, so as to secure the abutment against rotation with respect to the implant. As may be understood, cooperation of the lateral surfaces of the implant end of the abutment with mating surfaces of the implant cavity results in an anti-rotational lock. Crown end 82 of the abutment has a generally cylindrical, peripheral wall 87. Crown end 82 tapers to a boss 88, preferably having a hexagonal external shape for preventing rotation of the crown/tooth structure with respect to the abutment. The interior of the abutment includes a longitudinal bore 90 for receiving abutment screw 16. The longitudinal bore has an annular shoulder 92 for engagement by a slotted head 94 of connecting screw 16. The abutment is fixedly joined to the implant by means of the abutment screw, which has a threaded root end 96 for engaging lower portion 80 of the implant cavity. As shown in Figures 1, 3 and 5, the direction of the threads of root end 96 of screw 16 is opposite to the direction of the cutting teeth of the implant. This highly beneficial feature prevents engagement of cutting edges 42 of the cutting teeth during tightening of connecting screw 16. Additionally, in cooperation with cutting teeth having non-cutting edges opposite to cutting edges, as exemplified in Figure 4, this feature prevents a cutting action of the cutting teeth opposite to the original direction of implanting, during tightening of screw 16. As may be understood, instead of a clockwise threading of the implant and a counterclockwise threading of the abutment screw, as shown in the drawing, the threading of the implant and abutment screw may be reversed. The longitudinal bore of the abutment suitably may include a threaded portion 98 at the crown end of the abutment. When the abutment is secured in place, the longitudinal bore thereof is coaxial with longitudinal axis 32 of the implant and dental restoration structure. Referring particularly to Figure 5 again, the abutment further advantageously includes a transverse bore 100 aligned at an obtuse angle α to longitudinal axis 32. Beneficially, this angle may be about 120°. Transverse bore 100 is preferably threaded for engagement of transverse screw 22. As will become understood, the transverse bore, transverse screw and a corresponding bore 102 of crown structure 20 advantageously cooperate to bias the crown/tooth structure against bearing surfaces 66,68 of the crown end of the implant neck. In this way, tight, gap-free contact is provided. With reference to Figure 6, an alternative abutment 14' is shown for use with a dental bridge. As may be seen, a crown end 82' of abutment 14' has a conical shape rather than the cylindrical shape of crown end 82 of abutment 14, and lacks a boss. Otherwise, generally speaking, abutment 14' includes the structural features described for abutment 14, including a transverse bore 100'. Accordingly, corresponding numbers are used to designate corresponding features. As may be understood, other connecting members suitable for connecting an implant in accordance with the present invention, with conventional attachable dental structures may be used. The novel crown structure of the present invention is now described. Referring again to Figure 5, and in addition to Figures 7 and 10, a preferred crown structure 20 in accordance with the present invention, includes a layer 104 to which tooth structure 24 is bonded, and an integral collar 106 to which layer 104 is bonded. With particular reference to Figures 5 and 10, layer 104 may, as shown therein, overlay or partially surround collar 106. When layer 104 overlays the collar, it is not necessary for the collar to be made of a material bondable to porcelain or other tooth-colored restoration material. However, in any event, layer 104 should be of such a material or should be overlayed by such a material. It is well known to use gold for bonding porcelain. Accordingly, if desired, layer 104 and the collar may be gold or a suitable alloy. A particularly useful material for layer 104 is a composite metal alloy comprised of about 88% gold and about 9% platinum group metals, commercially available under the trademark CAPTEK. When fired, a layer of this alloy is beneficially provided with a three-dimensional network of capillaries, and is highly dense with exceptional strength. When this type of material is used, layer 104 may advantageously have a thickness of about 0.3 to 0.5 mm. It will be understood that the thickness of layer 104 may vary depending upon the material selected to form the layer, with material providing a relatively stronger layer typically requiring relatively less thickness. In this respect, impact, load and fatigue strength are important considerations. Because, generally speaking, a relatively thinner layer is relatively more cost-effective, layer 104 will usually be as thin as practicable. Collar 106 of crown structure 20 includes bore 102 for receiving transverse screw 22. Bore 102 is inclined at an obtuse angle to longitudinal axis 32 corresponding to the angle of the transverse bore of the abutment to the longitudinal axis. Moreover, bore 102 is disposed for coaxial alignment with the transverse bore of the abutment when the crown structure is secured to the abutment by the transverse screw. However, to provide gap free, biased contact, the path of bore 102 is preferably slightly further from a wall 108 of the crown structure than the path of the transverse bore is from seating surface 84 of the abutment. Alignment of the paths is achieved by use of the transverse screw. This feature also beneficially exerts pressure against the inserted transverse screw to prevent its loosening. Suitably, to this end, there may be an about 0.05 mm difference between the locations of these paths. Referring particularly to Figures 5 and 10, the crown structure advantageously has a mating interior shape and dimensions 110 for fitting over crown end 82 of the abutment, as well as over surfaces 66,68 and peripheral wall 72 of the crown end of the implant neck. A suitable process for manufacture of crown structure 20 is now described with reference to Figures 7 to 10. Collar 106 is slipped over a model 114 of abutment 14 so as to surround a generally cylindrical, peripheral wall 187 of the model. As may be understood from the preceding description, the model advantageously has an inclined transverse bore 200 located slightly higher than inclined transverse bore 100 of abutment 14. Otherwise, the model corresponds to the exterior of the crown end 82 of abutment 14. Accordingly, corresponding numbers are used to designate corresponding features. However, in addition, the model includes annular steps 116,118, of which step 116 corresponds to annular raised step 64 of the implant. The model, typically made of gypsum or plaster, is prepared by a conventional molding technique. Collar 106 includes bosses 120,122, which respectively include bores 124,126, which are aligned to form bore 102 for receiving transverse screw 22. Bore 126 is preferably a blind bore. The collar further includes an interior wall 128 having a shape and dimensions that mate with peripheral wall 187 of the model at an angle appropriate for coaxially aligning bore 102 of the collar with transverse bore 200 of the model. Transverse screw 22 is used to secure the collar to an appropriate location on the model for alignment of the bores, thereby forming the structure of Figure 8. Thereafter, the structure of Figure 8 is placed in a press former 130 having an interior shape defined by an inner wall 132, and generally corresponding to the exterior shape of the structure of Figure 8. Inner wall 132 is spaced from the exterior of the structure of Figure 8 by a distance appropriate to form a gap 134 that provides layer 104 of corresponding thickness. Then, the material for forming layer 104 is added to the press former. After the material has hardened, the press former is removed and layer 104 is processed appropriately. In the case of a CAPTEK material, a press former is not necessary. Rather, a layer of the CAPTEK material may be applied over the exterior of the structure of Figure 8 and formed to the exterior shape thereof. Thereafter, heat is applied in accordance with the CAPTEK technique. Removal of the transverse screw precedes removal of the model so as to provide the crown structure of Figure 10. The crown structure is now ready for conventional porcelain to crown bonding technique. As may be understood, crown structure 20 is useful with other dental implants. To this end, the abutment may be modified as appropriate. The implant bed is typically prepared using drill bits of increasing diameter for making a pilot hole. The pilot hole is provided with a cylindrical upper end for receiving the implant neck, and a tapered root end for receiving the tapered, threaded portion of the implant. After the implant bed has been prepared, implant 12 is inserted into the pilot hole and slowly rotated into the osseous bed in a clockwise direction. At a suitable time interval after implantation, the implant end of the abutment is firmly fixed in the implant cavity using abutment screw 16, which is advantageously rotated in a counterclockwise direction. Thereafter, the crown structure with its porcelain bake is seated over the crown end of the abutment, so that bore 102 of the crown structure and transverse bore 100 of the abutment are in approximate coaxial alignment. Then, transverse screw 22 is inserted into bore 102 and through transverse bore 100 to force bores 102,100 into alignment and thereby seat the crown/porcelain structure firmly against bearing surfaces 66,68 of the implant. The present invention may be carried out with various modifications without departing from the essential attributes thereof, and accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

Claims: A dental restoration structure comprising a crown structure (20) and means (14) for connecting the crown structure (20) to an implant (12), the connecting means (14) comprising a crown end (82) comprising an inclined transverse bore (100), the crown structure comprising a correspondingly inclined bore (102) for coaxial alignment with the inclined transverse bore (100), and the crown structure (20) having a cavity of a mating shape and dimensions (110) for fitting over the crown end (82) of the connecting means (14), characterized in that the crown structure (20) comprises a layer (104) to which a tooth structure (24) is bonded, and an integral collar (106) comprising aligned bores (124,126) and to which the layer (104) is bonded, and in that the aligned bores (124,126) form the inclined bore (102). The dental restoration structure of claim 1, characterized in that the integral collar (106) is overlayed by the layer (104). The dental restoration structure of claim 1 or 2, characterized in further comprising securing means (16) comprising a threaded root end (96) for securing the connecting means (14) to the implant (12) which comprises a cavity (74) for engagement by the threaded root end (96), and in that the implant (12) further comprises a thread cutting portion (28) having generally longitudinally disposed grooves (54') providing cutting teeth (40') comprising a cutting leading edge (42') defining a first thread direction, and the threaded root end (96) has a thread direction opposite to the first thread direction, and the grooves (54') provide opposite to the cutting leading edge (42'), a non-cutting edge (58') upon the securing means (16) being rotated opposite to the first thread direction to secure the connecting means (14). The dental restoration structure of claim 3, characterized in that the implant (12) further comprises a generally cylindrical neck (26), wherein a bottom wall (46) of the neck (26) is disposed generally perpendicular to a peripheral wall (30) of the neck (26) to provide a stepped joining of the neck (26) and the thread cutting portion (28), wherein the thread cutting portion (28) further comprises a tip (34) and has a peripheral edge defined by peripheral edges (44) of cutting teeth (40) and tapered toward the tip (34), and wherein the cutting portion peripheral edge adjacent the neck (26) is stepped in from the peripheral wall (30) of the neck (26). The dental restoration structure according to claim 1, characterized in that it comprises an implant (12) anchorable in a jawbone, securing means (16) comprising a threaded root end (96) for securing the connecting means (14) to the implant (12), wherein the implant (12) comprises a cavity (74) for receiving an implant end (78) of the connecting means (14) and for engagement by the threaded root end (96), and also comprises a thread cutting portion (28) having generally longitudinally disposed grooves (54') and cutting teeth (40'), that the grooves (54') provide cutting teeth (40') comprising a cutting leading edge (42') defining a first thread direction, that the threaded root end (96) of the securing means (16) has a thread direction opposite to the first thread direction, and that the grooves (54') provide, opposite to the cutting leading edge (42'), a non-cutting edge (58') upon the securing means (16) being rotated opposite to the first thread direction to secure the connecting means (14).

Inventors: BRESSMAN ROBERT A, MEGERT DANIEL, BRESSMAN, ROBERT A., MEGERT, DANIEL
Applicants: BRESSMAN ROBERT A, MEGERT DANIEL, BRESSMAN, ROBERT A., MEGERT, DANIEL
Application year: 1995
Main classification: A61C8
IPC codes: A61C8