WO2012059908A1

WO2012059908A1 - Multi-threaded dental implant

Info

Publication number: WO2012059908A1
Application number: PCT/IL2010/000902
Authority: WO
Inventors: Ilya Mushayev
Original assignee: Ilya Mushayev
Priority date: 2010-11-01
Filing date: 2010-11-01
Publication date: 2012-05-10

Abstract

The present invention relates to a tapered implant for insertion into a bore hole arranged in bone tissue, said implant having a cancellous portion, and a cortical portion having an axial length such that, when installed in the bore hole, the engagement of said cortical portion with the bone tissue will generally be confined to the cortical bone tissue layer. Said cortical portion presents an outer surface which is threaded for accomplishing said engagement, and has an outer design such that, when being screwed into said bore hole under action of a screwing torque, said cortical portion acts so as to increase the compression of the cortical bone tissue.

Description

MULTI-THREADED DENTAL IMPLANT

FIELD OF THE INVENTION

The present invention relates generally to the field of endosseous screw type dental implants and more specifically to the field of tapered endosseous screw type dental implants .

BACKGROUND OF THE INVENTION

Screw type implants are implants having outer surfaces being threaded and which are used as anchoring members for different prostheses, such as dental and orthopedic prostheses. This type of implant is screwed into a bore hole arranged in the bone tissue of a bone tissue structure at a site where a prosthesis is required. The bore hole may be formed to a shape generally corresponding to the shape of the implant, although slightly smaller in size. These implants may be provided with self-cutting edges, so as to cut one or more internal threads in the inner wall of the bore hole during the screwing in of the implant. If there are no self-cutting edges, the bore must be internally threaded before insertion of the implant.

Bone tissue has two components, cancellous bone tissue and cortical bone tissue. The major part of a bone is normally built up of the cancellous bone tissue, which is a relatively soft tissue in the interior of the bone. The cortical bone tissue is harder and normally forms a relatively thin layer surrounding the cancellous bone. Thus, in their final position, screw implants of the type described would typically be in contact with cancellous bone tissue along a larger part of its length, and with cortical bone tissue only at a shorter portion at one end of the implant.

When a screw type implant is in anchored position in the bone tissue, a superstructure for carrying a prosthetic part may be secured to the implant. In the case when a screw implant will be used to secure a dental prosthesis, the superstructure will typically comprise an abutment or transmucosal component, which engages the implant to bridge the gingiva overlaying the maxilla or mandible at the implant site. The prosthetic part, e.g. a crown, a bridge or a denture is then secured to the abutment. The implant could also be formed integrally with a superstructure, such as a transgingival component, on which for example a crown is directly secured. A problem occurring when using many prior art screw type implants is referred to as the bone resorption problem. Bone resorption is a term used for a process in which, once an implant is installed in the bone tissue, the bone surrounding the implant tends to degenerate. This is highly undesired, since a diminished amount of bone surrounding the implant will lead to diminished stability and sometimes result in failure of the prosthesis. This is particularly the case because bone resorption primarily occurs in the cortical bone, which, as mentioned above, is the hardest part of the bone. Once bone resorption is a fact, secondary problems may also appear. Such secondary problems, particularly related to dental implants, are for example deposition of plaque, resulting in inflammation in the gingival tissue surrounding the implant, or down- growth of gingival tissue along the exposed end of the implant. Also, the aesthetic appeal of the implant is undermined by bone tissue resorption, which is an important drawback in particular when the implant is intended for dental applications since dental prosthesis form part of the field of cosmetic surgery.

According to the inventors' belief, it is important to ensure a proper loading of the implant, since both a mechanical over-stimulation and an understimulation of the bone tissue have been seen to cause bone resorption.

SUMMARY OF THE INVENTION

The object of the invention is to provide a well functioning implant in number of important aspects, such as providing stable primary fixation, initial stability and proper loading of the bone tissue while not being prone to marginal bone resorption. The above mentioned object is achieved by a screw implant for insertion into a bore hole arranged in bone tissue, said implant having a cancellous portion, and a cortical portion having an axial length such that, when installed in the bore hole, the engagement of said cortical portion with the bone tissue will generally be confined to the cortical bone tissue layer. Said cortical portion presents an outer surface which is threaded for accomplishing said engagement, and has an outer design such that, when being screwed into said bore hole under action of a screwing torque, said cortical portion acts so as to increase the compression of the cortical bone tissue only.

The term "cortical bone engagement portion" is used to define a portion of the implant that, in an implanted state, would mainly be engaged with the cortical bone tissue layer. For simplicity, the term will hereinafter in the description and in the claims be referred to as "cortical portion". Similarly, the term "cancellous bone engagement portion" will be referred to as "cancellous portion" and refers to a portion of the implant that would mainly be engaged with cancellous bone tissue. A general idea of the invention is thus to provide an implant having a cortical portion that, when being screwed into a bore hole under action of a screwing torque, acts so as to increase the compression of the cortical tissue in generally radial directions.

For accomplishing the engagement of the cortical portion with cortical bone, the cortical portion is provided with a threaded outer surface. With "threaded" is meant a surface allowing the portion to function as a screw. Thus, any surface having a helical arrangement fulfilling this purpose would be confined in the term "threaded", for example a surface having a series of discontinuous protrusions, subsequently following ribs or a conventional thread. At present, a surface presenting a conventional thread seems to be the most advantageous alternative.

The threaded surface is useful in that its engagement with the cortical bone tissue will increase the friction between the cortical bone and the implant, thus contributing to the distinct rise in screwing torque needed when the cortical portion is screwed into the bore hole. Owing to this effect, the compression of cortical bone tissue can be held smaller that what would be necessary if a smooth surface was used, which is advantageous as discussed above. Further, during screwing in of the implant, the threaded surface urges the cortical portion down into the bore hole, compressing the cortical tissue in essentially radial directions. Without the threaded surface, mere might be an increased risk that forces from the bone tissue which counteract the screwing in of the cortical portion overcome the forces urging the cortical portion downwardly. In that case, the screwing torque applied to the implant would act only to

rotate the implant, but not to advance it in a longitudinal direction, whereby internal threads cut in the bore hole may be damaged. Another advantage with threaded surfaces is mat they have been shown beneficial to bone tissue ingrowth and are useful to enable proper load distribution to the surrounding bone tissue. Due to the load distribution function, they are useful to stimulate bone growth and inhibit marginal bone resorption. Also, the threaded outer surface of the cortical portion will contribute to the primary fixation and initial stability of the implant.

Now returning to the definition of the cortical and cancellous portions of the implant. Normally, an implanted screw implant is in contact with both cancellous bone tissue and cortical bone tissue. However, since the cortical bone tissue constitutes a relatively thin layer around the bone, the major part of the length of a screw implant will be in contact with the cancellous bone. Thus, the length of the cortical portion of an implant will be relatively short in relation to the implant length, as it should largely correspond to the thickness of the cortical bone tissue layer. Said thickness varies with the type of bone, the implantation site, and individually from patient to patient. A normal thickness would be around 0.5-1 mm to 3 mm.

When discussing cortical and cancellous tissue in this application, reference is made to normal cases of bone tissue structures, as described above. There are however unusual cases, where the bone comprises almost only cortical tissue. The unusual cases are the result of a process of transformation of the bone tissue, which might occur in particular regarding the lower jaw of patients mat have used loose overdentures for a long time. The implant of the invention is primarily designed to be useful for the normal cases, although it may also function when used for the unusual cases.

Throughout the description and the claims, any reference to directional terms as "up" and "down" and related terms such as top, bottom, below etc referring to the implant should be interpreted as "up" meaning towards the head end or trailing end, i. e. the coronal end of the implant, and "down" meaning towards the insertion end, i. e. the apical end of the implant. Thus the "lower part" of the implant would refer to the part that would first be introduced into a bore hole. Obviously, mis does not constitute any restriction regarding in what actual directions the implant may be implanted and used.

The cortical portion of an implant according to the invention would be positioned at the uppermost end of the implant, so as to be in engagement with the cortical bone tissue when the implant is in its final position.

According to a further aspect of the invention, there is provided a screw implant for insertion into a bore hole arranged in bone tissue, comprising a lower cylindrical cancellous portion and an upper conical cancellous portion presenting a conical outer surface, wherein said implant is provided with a cortical portion, having an axial length such that, when installed in the bore hole, the engagement of said cortical portion with the bone tissue will generally be confined to the cortical bone tissue layer.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example, embodiments of the present invention will now be described with reference to the accompanying figures of drawings in which:

FIG. 1 is a side view illustrating an embodiment of the dental implant of the present invention.

FIG. 2 is a side view illustrating a cortical portion of die dental implant of d e present invention.

FIG. 3 is a side view illustrating another embodiment of the dental implant of the present invention.

FIG. 4 is a side view illustrating yet another embodiment of the dental implant of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The implants 1,12,13 having a generally tapered or conic like shape are dental implants for insertion into a bore hole drilled in the bone tissue of a maxilla or mandible, for anchorage of a prosthesis. The implants 1,12,13 are made from commercially pure titanium, a titanium alloy, another biocompatible metal or metal alloy or a ceramic to promote osseointegration of the implants with the bone tissue of the boundary walls of the bore hole.

The length of the implants 1,12,13 is preferably between 6-16 mm and the width is preferably between 3-6 mm. The implants have a cancellous portion 2 presenting a tapered outer surface, and a cortical portions 3,3a,3b having an axial length up to 3.2 mm so as to, when installed in a bore hole in bone tissue, generally engage the cortical bone tissue layer. An uppermost section 7 of the implant 1 is smooth and cone shaped with its smaller diameter directed towards the top of the implant. The axial extent of the uppermost section 7 is preferably small, up to 0.5 mm compared to the total length of the implant 1 when in place in a bone, the uppermost section is the only part of the implant that is accessible from outside of the bone.

The outer surface of the implants 1,12, 13 is provided with a first and a second threads 6 and 5, respectively. The thread 6 is provided on the cortical portions 3,3a,3b of the implants 1,12,13 and the thread 6 could be a single thread or preferably a multiple thread 10a, 10b, for example a double or a quadruple thread. The threads 6 are sometimes called "micro-threads" and have been shown to be particularly advantageous when provided on the upper part of dental implants, where their presence inhibit marginal bone resorption.

The second thread 5 is provided on the cancellous portion 2 of implants 1,12,13. This second thread is a single thread , having a thread with a height being larger than 0.2 mm.

The external threads 5 and 6 include a progressively changing profile. At the apical end 8, die thread 5 is sharp and narrow in order to facilitate cutting and self- tapping into bone. As the thread 5 progresses toward the implant cortical portion 3, it becomes increasingly broader or wider in cross-sectional profile. Similar, at the start of the cortical portion 3, the thread 6 is sharp and narrow in order to facilitate cutting and self- tapping into cortical bone. As the thread 6 progresses towards the implant coronal end 9, it becomes increasingly broader or wider in cross-sectional profile. The increasing breadth of the threads 5 and 6 facilitates compression of the cortical and cancellous bone previously tapped by the sharp coronal thread profiles. Bone compression increases the stability of the implant. As seen in the drawings the implants 1,12,13 have plurality of cutting recesses or grooves 4 circumferentially distributed about the circumference of the apical end 8 of the implants 1,12,13 for self-tapping of the implants 1,12,13 when being screwed into the bore hole. If the implants 1,12,13 are not provided with cutting recesses 4, the bore hole may be internally threaded before the implant is inserted.

The start of the cortical portions 3a,3b of the implants 12,13 has a width larger than a width of the coronal end 9 of the implants 12,13, thus creating cortical portions 3a,3b of inverse tapered shape. These inverse tapered cortical portions 3a, 3b facilitates bone growth on the im plants 12, 13.

The implants 12,13 have a thread 5 with increased width 11, which facilitates implant insertion into the bone. Although illustrative embodiments have been shown and described, a wide range of modification change and substitution is contemplated in the foregoing disclosure and in some instances, some features of the embodiments may be employed without, a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the embodiments disclosed herein.

Claims

1. A tapered dental implant having a cortical portion and a cancellous portion, and characterized by a micro-thread with a progressively changing profile, provided on the cortical portion of said dental implant.

2. A tapered dental implant of claim 1 , wherein said micro-thread is a multiple thread.

3. A tapered dental implant of claim 1 , wherein said micro-thread is a double thread.

4. A tapered dental implant of claim 1 , wherein said micro-thread is a triple thread.

5. A tapered dental implant of claim 1 , wherein said micro-thread is a quadruple thread.

6. A tapered dental implant of any one of the claims 1-5, additionally comprising a thread with a progressively changing profile, provided on the cancellous portion of said dental implant.

7. A tapered dental implant of claim 6, additionally comprising one or more cutting recesses provided on the apical end of said implant.

8. A tapered dental implant of claim 6 or 7, wherein said thread on the cancellous portion has a height larger than 0.2 mm.

9. A tapered dental implant of any one of the previous claims, wherein said cortical portion has an inverse tapered shape.

10. A tapered dental implant of any one of the previous claims, wherein said implant is made of titanium.

11. A tapered dental implant of any one of the claims 1-9, wherein said implant is made of titanium alloy.

12. A tapered dental implant of any one of the claims 1-9, wherein said implant is made of biocompatible metal.

13. A tapered dental implant of any one of the claims 1-9, wherein said implant is made of metal alloy.

14. A tapered dental implant of any one of the claims 1-9, wherein said implant is made of ceramic material.

15. A tapered dental implant of any one of the previous claims, wherein said implant has a length between 6-16 mm and the width between 3-6 mm.

16. A tapered dental implant of any one of the previous claims, wherein said cortical portion of said implant has a length up to 3.2 mm.