GB2416996A

GB2416996A - Dental implants

Info

Publication number: GB2416996A
Application number: GB0512339A
Authority: GB
Inventors: Colin Eric Chandler
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-08-10
Filing date: 2005-06-17
Publication date: 2006-02-15
Also published as: GB0417790D0; GB0512339D0

Abstract

A dental implant system comprises a thread insert (12) of biocompatible metal and a screw-threaded abutment (10) arranged to have an artificial tooth or denture plate fixed to it. The abutment has a parallel male thread (14) having a generally triangular tread profile. The tread insert comprises a helically-wound wire (18). The inwardly-facing surface of the wire provides a female thread having a generally triangular thread profile that is complementary to the thread profile of the abutment. The outwardly-facing surface of the wire provides a male thread having a generally triangular thread profile. The thread insert is suitable for being fitted into a parallel female-threaded hole (32) in a person's upper or lower jaw bone (28) and the abutment is suitable for being fitted into the thread insert so fitted into the jaw bone. The thread insert can immediately provide a strong well-defined screw thread which is not reliant on osseointegration for firmness and stability.

Description

TITLE

Dental implants

DESCRIPTION

This invention lies in the field of restorative dentistry and relates to a dental implant system, a dental implant and a dental implant method.

A number of different implant designs and techniques are known. The main ones that are most often used involve inserting a cylindrical titanium plug into a hole in the upper or lower jaw bone. The plug usually has external fins or a coarse external thread. The plug generally has either a central screw hole or a tapered central hole into which, after the plug has been inserted into the jaw bone, an individual abutment can be attached by a screw or, in some cases, press fitted. In the case of dentures, a plurality of plugs are used to secure one level of replacement teeth (denture plate). In order to provide a reasonably secure fit of a press-fit abutment in a tapered hole, expensive, very high precision machining is required. That is not so if a screw is used; however, the screw is necessarily small and needs to be done up very tightly, and screw breakage is a problem. The plug relies on osseointegration (or fusion) between the plug and the host bone, and it is usually necessary to allow at least four months to elapse while osseointegration occurs before final fitting of the prosthesis by way of a replacement tooth or teeth. Once the plug has been fitted, it cannot be adjusted and so dictates the height of a particular abutment. If a different height is required, a different size of abutment needs to be selected, or the plug needs to be ground down.

Aims of the present invention, or at least specific embodiments of it, are to avoid the need for such high precision machining, to avoid the use of such small screws that need to be done up so tightly and may break, to avoid the reliance on osseointegration and the time delay caused thereby, and to enable adjustment of the abutment.

In accordance with one aspect of the present invention, there is provided a dental implant system, comprising a thread insert (preferably of biocompatible metal such as titanium) and a screw-threaded abutment. The abutment has a parallel male thread having a generally triangular thread profile. The thread insert comprises a helically-wound wire. The inwardlyfacing surface of the wire provides a female thread having a generally triangular thread profile that is complementary to the thread profile of the abutment. The outwardly-facing surface of the wire provides a male thread having a generally triangular thread profile. The thread insert is - 2 suitable for being fitted into a parallel female-threaded hole in a person's upper or lower jaw bone. The abutment is suitable for being fitted into the thread insert so fitted into the jaw bone.

The abutment is arranged to have an artificial tooth or denture plate fixed to it.

In territories where the law permits patent protection for methods of dental surgery, a second aspect of the present invention provides a dental implant method, using the system of the first aspect of the invention. The method comprises the steps of: forming a parallel female- threaded hole in a patient's upper or lower jaw bone; fitting the thread insert into the hole; and then fitting the abutment into the thread insert. An artificial tooth or denture plate can then be fixed to the abutment.

With the invention, the thread insert can immediately provide a strong well-defined screw thread, into which the abutment can be fitted, which is not reliant on osseointegration for firmness and stability. It is therefore unnecessary to wait several months before the artificial tooth or denture plate is fitted. It will be appreciated, however, that in time the jaw bone will fuse to the thread insert. Because the threads are parallel, rather than, say, tapered: (a) the depth to which the abutment is inserted into the thread insert in the jaw bone is not predetermined and can therefore be selected and adjusted by the dental surgeon; and (b) the abutment does not cause the thread insert to expand Mdially to any significant extent the further the abutment is driven in, an action that might otherwise cause the jaw bone to fracture. The cross-section of the wire of the thread insert may be such that the major diameter of the thread on the abutment is only very slightly smaller than the minor diameter of the thread in the hole in the bone, so that for a given size hole in the bone the abutment may have a relatively large diameter and therefore relatively high strength.

Provided that osseointegration does not occur between the jaw bone and the abutment, the depth to which the abutment is inserted into the thread insert can be adjusted after initial fitting, and the abutment can be removed completely if need be, all without damage to the jaw bone. In order to prevent osseointegration between the jaw bone and the abutment, the thread insert is preferably coil bound (i.e. there is no substantial gap between one turn and the next) when the pitch of the helix is equal to the pitch of the thread on the abutment (i.e. once the implant has been fitted).

In order that the thread insert takes up relatively little space, the wire of the thread insert preferably has a substantially diamond-shaped cross-section (although the innermost and outermost vertices of the diamond shape may be slightly rounded or bevelled). The innermost - 3 and outermost included angles of the diamond-shape are preferably each about 60 degrees, the other two included angles each being about 120 degrees.

In order that the abutment has sufficient cross-section to have sufficient strength, the nominal diameter of the thread of the abutment is preferably at least 2.5 mm, and more preferably at least 3mm. However, in order not to weaken the jaw bone unduly, the nominal diameter of the thread of the abutment is preferably no more than 5 mm.

In order to resist any tendency for the abutment to work loose in service, the thread insert may have a locking or grip coil for binding on the thread of the abutment. For example, one turn of the thread insert may have a polygonal, rather than circular, shape.

The dental implant system preferably further includes an artificial tooth or denture plate arranged to be affixed to the abutment.

The dental implant system preferably also further includes at least one tap for tapping, in a hole in bone, a female thread having a generally triangular thread profile that is complementary to the thread profile of the male thread of the thread insert, and in this case the system may further include a drill for forming the hole in the bone of a tapping size suitable for the tap.

According to a third aspect of the invention, there is provided a dental implant formed from a dental implant system according to the first aspect of the invention, the abutment being screwed into the thread insert, and the artificial tooth or denture plate preferably being fixed to the abutment.

The invention also extends to the dental implant in service, i.e. with the thread insert screwed into a parallel female-threaded hole in a person's upper or lower jaw bone.

A specific embodiment of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a pillar abutment of a dental implant; Figure 2 is an oblique view of a thread insert of the dental implant; Figures 3 to 10 are views on a smaller scale of a jaw bone, partly sectioned, showing various stages in the fitting of a dental implant, namely: Figure 3 after drilling of a pilot hole; Figure 4 while drilling a tapping hole; - 4 Figure 5 after drilling the tapping hole Figure 6 while tapping the hole; Figure 7 after tapping the hole; Figure 8 while fitting the thread insert; Figure 9 after fitting the thread insert; and Figure 10 after fitting the pillar abutment; and Figure 11 is a view of the jaw bone after fitting an artificial tooth to the pillar insert.

Referring to the drawings, the dental implant comprises a pillar abutment 10 (see Figure 1), a thread insert 12 (see Figure 2) and an artificial tooth 13 (see Figure 11). The dental implant system also comprises various tools used for fitting the implant.

The pillar abutment 10 is an elongate member having a parallel male screw thread 14 extending part-way along its length from one end. The thread may be a standard ISO metric thread, such as M2.5 (2.5 mm diameter x 0.45 mm pitch), M3 (3 mm diameter x 0.5 mm pitch, M4 (4 mm diameter x 0.? mm pitch) or M5 (5 mm diameter x 0.8 mm pitch) with a thread angle of 60 degrees. The other end 16 of the pillar abutment 10 is shaped so as to enable the artificial tooth to be fixed thereto. The pillar abutment 10 is made from titanium or other material such as surgical stainless steel and may be plated for example with gold.

The thread insert 12 is formed by a parallel helical coil 18 of wire of titanium or other biocompatible metal. The wire has a cross-section generally in the shape of a diamond with outermost and innermost included angles equal to the thread angle of the thread 14 on the pillar abutment 10, i.e. 60 degrees, and so the other two included angles of the diamond shape are degrees. The outermost and innermost vertices of the diamond shape may be slightly rounded or bevelled. The pitch of the coil 18, when coil bound, is equal to the pitch of the thread 14 on the pillar abutment to. The inner diameter of the coil 18, when relaxed, is slightly greater than the minor diameter of the thread 14 on the pillar abutment. At one end of the coil 18, the end portion of the wire is bent inwardly at right angles to form a tang 20 that extends diametrically part-way across the end of the coil 18. Part-way along the coil 18, one of the turns of the coil 18 is formed with a series of kinks 22 rather than being smoothly curved so as to provide a grip coil 24. The length of the thread insert 12 is preferably about equal to the length of the thread 14 on the pillar abutment and is preferably not less than the nominal diameter of the thread 14 on the pillar abutment to and may be as large as five times the nominal diameter of the thread 14. - s -

In order to fit the implant, a pilot hole 26 (Figure 3) is drilled in the jaw bone 28 to a depth slightly greater than the length of the thread 14 on the pillar abutment 10.

The diameter of the pilot hole 26 is then opened out in one or more stages so as to minimise heat generation in the bone 28 using increasing diameter drills until a tapping hole 30 is formed with a tapping drill 31 (Figures 4 and 5). The diameter of the tapping hole 30 is equal to or slightly greater than the nominal diameter of the thread 14 on the pillar abutment 10, e.g. 2.6mmforM2.5,3.1mmforM3,4.2mmforM4and5.2mmforM5.

The tapping hole 30 is then tapped with a tap 33 (Figure 6) having a pitch and thread angle that are equal to the pitch and thread angle of the thread 14 on the pillar abutment 10 and having a major diameter that is equal to the outer diameter of the thread insert 12 when it is snugly wrapped around the thread 14 on the pillar abutment 10, i.e. about 2.9 mm for M2.5, 3.5 mm for Ma, 4.6 mm for M4 and 5.7 mm for M5. A screw-threaded hole 32 (Figure 7) is therefore formed in the jaw bone 28 having a female thread 34 that is complementary to the male thread formed by the thread insert 12 when it is snugly wrapped around the thread 14 on the pillar abutment 10. A single tap 33 may be used, but preferably the hole 32 is tapped in two or three stages, for example using a first (or roughing or taper) tap and a second (or intermediate or finishing) tap, or using a first tap, second tap and plug (or bottoming) tap, so as to achieve a better quality thread 34.

The thread insert 12 is then fitted into the threaded hole 32 using an insertion tool 35 (Figure 8). The insertion tool 35 has a shaft formed at one end with a male thread 37 equal in pitch and profile to the thread 14 on the pillar abutment 10, but of slightly smaller diameter.

The insert 12 is threaded onto the insertion tool (and is therefore a sloppy fit while the insert 12 is relaxed) until the tang 16 engages with a protrusion 39 formed on the end face of the tool 35.

The insert 12 is then offered up to the hole 32, tang-16-end first, and threaded into the hole 32 by turning the tool. As it enters the hole 32, the coil of the insert 12 is compressed radially slightly by the bone 28 and frictionally engages the bone. However, by driving the insert 12 using the tang 16 at the leading end of the insert 12, the insert 12 does not jam during insertion.

In order to assist insertion, the insertion tool 35 may have a collar that pre-compresses the insert around the threaded shaft prior to insertion. Also, the shaft of the insertion tool 35 need not be threaded. The thread insert 12 is inserted to a depth in the bone 28 such that the trailing end of the insert 12 is about one turn below the surface of the bone 28. The tool 35 is then unscrewed, leaving the insert 12 jammed in the hole 32 due to its frictional engagement with the bone 28 (Figure 9) and leaving a hole 34 in the bone 28 with a metal female thread, provided by the - 6 insert 12, (Figure 5) that complements the male thread 14 on the pillar abutment 10 in diameter, pitch and thread profile.

The pillar abutment 10 is then screwed into the hole 34 to the required depth (Figure 10). For the first few turns, the abutment 10 should be a good running fit. However, the thread 14 on the pillar abutment 10 will then encounter the grip coil 24, and it may then be necessary to use a tool in order to turn the abutment 10. The grip coil 24 is arranged to prevent the abutment 10 turning during service after the implant procedure has been completed.

Once the abutment has been fitted, an impression may be made of the patient's teeth 36, gum 38 and the projecting portion 16 of the pillar abutment 10, and an artificial tooth 13 may then be manufactured from the impression and cemented to the projecting portion 16 of the pillar abutment 10 (Figure 11). Alternatively, a plurality of abutments 10 may be fitted to a patient's jaw bone 28, and a denture plate may be fixed to the projecting portions 16 of the abutments 10.

It will be appreciated that many modifications and developments may be made to the embodiment of the invention described above. For example, instead of using an ISO metric thread, a British Association thread may be used, in which case the thread 14 on the pillar abutment may be 6BA (2. 8 mm diameter x 0.53 mm pitch), 4BA (3.6 mm diameter x 0.66 mm pitch) or 2BA (4.7 mm diameter x 0.81 mm pitch) with a thread angle of 47/' degrees, or an American unified thread with a thread angle of 60 degrees may be employed. Alternatively, non-standard threads may be used. Also, instead of employing the grip coil 24, a biocompatible thread-locking compound may be used.

It should be noted that the embodiment of the invention has been described above purely by way of example and that many other modifications and developments may be made thereto within the scope of the present invention. - 7

Claims

1. A dental implant system, comprising a thread insert and a screwthreaded abutment, the abutment having a parallel male thread having a generally triangular thread profile, the thread insert comprising a helically-wound wire, the inwardly-facing surface of the wire providing a female thread having a generally triangular thread profile that is complementary to the thread s profile of the abutment, the outwardlyfacing surface of the wire providing a male thread having a generally triangular thread profile, the thread insert being suitable for being fitted into a parallel female-threaded hole in a person's upper or lower jaw bone, the abutment being suitable for being fitted into the thread insert so fitted into the jaw bone, and the abutment being arranged to have an artificial tooth or denture plate fixed thereto.

2. A dental implant system as claimed in claim 1, wherein the thread insert is coil bound when the pitch of the helix is equal to the pitch of the thread on the abutment.

3. A dental implant system as claimed in claim 1 or 2, wherein the wire of the thread insert has a substantially diamond-shaped cross-section.

4. A dental implant system as claimed in claim 3, wherein the innermost and outermost included angles of the diamond shape are each about 60 degrees, the other two included angles each being about 120 degrees.

5. A dental implant system as claimed in any preceding claim, wherein the nominal diameter of the thread of the abutment is at least 2.5 mm.

6. A dental implant system as claimed in any preceding claim, wherein the nominal diameter of the thread of the abutment is at least 3 mm.

7. A dental implant system as claimed in any preceding claim, wherein the nominal diameter of the thread of the abutment is no more than 5 mm.

8. A dental implant system as claimed in any preceding claim, wherein the thread insert has a locking or grip coil for binding on the thread of the abutment.

2s

9. A dental implant system as claimed in any preceding claim, further including an artificial tooth or denture plate arranged to be affixed to the abutment. - 8

10. A dental implant system as claimed in any preceding claim, further including at least tap for tapping a female thread in a hole in bone having a generally triangular thread profile that is complementary to the thread profile of the male thread of the thread insert.

11. A dental implant system as claimed in claim 9, further including a drill for forming the hole in the bone of a tapping size suitable for the tap.

12. A dental implant system substantially as described with reference to the drawings.

13. A dental implant formed from a dental implant system as claimed in any of claims 1 to 9, the abutment being screwed into the thread insert.

14. A dental implant as claimed in claim 13 when dependent on claim 9, wherein the artificial tooth or denture plate is fixed to the abutment.

1S. A dental implant as claimed in claim 13 or 14, wherein the thread insert is screwed into a parallel female-threaded hole in a person's upper or lower jaw bone.

16. A dental implant substantially as described with reference to the drawings.