Dental restoration structure

A self-cutting implant anchorable in a jawbone is provided. In a preferred embodiment, cutting teeth of the implant include a non-cutting edge opposite to a cutting leading edge. Also provided is a crown structure formed from a collar including aligned bores. In addition, a process for making the crown structure is provided.

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. Pat. Nos. 
5,199,873 to Schulte et al, 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 
including a novel self-cutting implant anchorable in a jawbone, is 
provided. Beneficially, the implant includes a generally cylindrical neck, 
and a tapered, thread cutting portion that includes cutting teeth. 
Individual cutting teeth include a cutting leading edge, and a peripheral 
edge for anchoring the implant. Advantageously, a bottom wall of the 
implant neck is generally perpendicular to a peripheral wall of the neck 
to provide a stepped joining of the neck and the thread cutting portion. 
In addition, the peripheral edges of the cutting teeth adjacent the 
implant neck, are beneficially stepped in from a plane formed by the 
peripheral wall. As a result, depth of the implant is limited and 
pressure-induced bone resorption or necrosis is reduced. 
Also provided is a dental restoration structure including a self-cutting 
implant anchorable in a jawbone, a crown/tooth structure, means for 
connecting the crown/tooth structure to the implant, and means for 
securing the connecting means to the implant. In this embodiment of the 
invention, the implant includes a thread cutting portion including cutting 
teeth each including a cutting leading edge, and the implant has a thread 
direction defined by the cutting teeth. In addition, the implant is 
provided with a cavity for receiving an implant end of the connecting 
means and for engagement by a threaded root end of the securing means; and 
the threaded root end has a thread direction advantageously opposite to 
the implant thread direction. As a result, engagement of the cutting edges 
of the cutting teeth is prevented when the securing means is rotated to 
secure the abutment within the implant. 
Beneficially, individual cutting teeth may also include a non-cutting edge 
opposite to the cutting leading edge. As a result, cutting action of the 
cutting teeth opposite to the original direction of implanting, is 
prevented when the abutment is secured using the reverse-threaded screw. 
Also provided is a dental restoration structure including a novel crown 
structure. Advantageously, the crown structure includes a layer to which a 
tooth structure is bonded, and an integral collar including aligned bores 
and in bonding contact with the layer. Suitably, the layer overlays the 
collar. 
The crown structure has a mating interior shape and dimensions for fitting 
over a crown end of means for connecting the crown structure to an 
implant. Beneficially, the aligned bores of the collar of the crown 
structure form an inclined bore for coaxial alignment with a 
correspondingly inclined, transverse bore of the crown end of the 
connecting means. 
Also provided is a process for making a novel crown structure in accordance 
with the invention. In accordance with the process, a collar including 
aligned bores, is disposed around a model of the crown end of the 
connecting means. The model has an inclined transverse bore 
correspondingly inclined as that of the crown end of the connecting means. 
The bores of the collar and model are aligned, and a member is inserted 
into the aligned bores to secure the collar onto a proper location of the 
model, which typically has a generally cylindrical, crown end. 
Then, the exterior of the resulting structure is overlayed with a material 
suitable for forming the crown layer, such that a layer generally 
corresponding to the exterior shape is formed. After further processing 
appropriate to the material selected, the crown structure 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.

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 and process for 
making the 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 FIG. 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 FIG. 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 FIGS. 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 FIGS. 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 FIG. 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.degree.. Other angles of taper may, of course, be used. 
As indicated in FIG. 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 FIGS. 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 FIG. 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 FIG. 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 FIGS. 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 FIG. 2, of 
the annular raised step 64. 
Referring particularly to FIG. 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 FIG. 1. 
With reference particularly to FIG. 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 FIG. 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 FIGS. 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 FIG. 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 
2 of the implant and dental restoration structure. 
Referring particularly to FIG. 5 again, the abutment further advantageously 
includes a transverse bore 100 aligned at an obtuse angle e to 
longitudinal axis 32. Beneficially, this angle may be about 120.degree.. 
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 FIG. 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 FIG. 5, and in addition to FIGS. 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 FIGS. 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 FIGS. 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 FIGS. 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 FIG. 8. 
Thereafter, the structure of FIG. 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 FIG. 8. Inner wall 
132 is spaced from the exterior of the structure of FIG. 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 FIG. 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 FIG. 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 spirit or 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.