GB2425727A

GB2425727A - Dental implant screw that produces less compressive stresses in surrounding bone

Info

Publication number: GB2425727A
Application number: GB0507354A
Authority: GB
Inventors: Osama Abdalla Abu Hammad; Malik Ismail Zar E Hudieb
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-04-12
Filing date: 2005-04-12
Publication date: 2006-11-08
Anticipated expiration: 2025-04-12
Also published as: GB0507354D0; GB2425727B

Abstract

A dental implant formed from a number of components 1, 3, 4, 5, 17, 22 has reliefs or tolerances 6, 12, 13 between the respective components. The screw threads 14, 15 of the implant are also formed with a relief or tolerance so that there is only minimal contact between the screw thread 14, 15 and the receiving thread. Under a horizontal load the components on the side to which the load is applied impart a pulling force or tension onto the implant and the reliefs or tolerances allow the side away from the horizontal load to produce a reduced compressive load as the components move out of contact.

Description

Osama Abdalla Abu-Hammad Malik Ismail Zar'e Hudieb

DENTAL IMPLANT PRODUCING LESS BONE STRESSES

TECHNICAL FIELD OF THE INVENTION

This new invention relates to a dental implant that reduces the bone compressive stresses at the bending side at the neck of the implant upon horizontally loading the abutment. The dental implant can be used in extra-oral dental applications and can be used in any non-dental applications whenever its action is favourable for that situation.

BACKGROUND

A dental implant in its most popular form has the following components: + prosthetic screw; + abutment screw; + abutment and *:* implant body.

In some types the implant might have fewer components e.g. some implants consist of an implant body and a press fit abutment designed to receive a cemented prosthesis on top with no abutment screw or prosthetic screw.

P 1209 The implant body resides in bone and attaches stiffly to this tissue after proper healing period, a phenomenon called osseointegration. Usually the abutment connects to the top (coronal aspect) of the implant body by means of the abutment screw that fits and gains retention from the implant body. The dental prosthesis fits over the abutment and attaches to the assembly by means of the prosthetic screw. Prosthetic screw fits into and gains retention from the abutment screw.

All loads applied onto an implant can eventually be analysed into a vertical and a horizontal component. Horizontal loads or horizontal components of loads are forces acting at right angles to the long axis of the implant and their action will bend the implant towards one side. This side will be referred to as: the bending side. The other side will be referred to as: the non-bending side.

Loading a dental implant horizontally will result in high compressive stress values in the bone around the neck of the implant at the bending side.

The appearance of these stresses is due to the transferral of the load to the prosthetic screw and the abutment. These components will move towards the bending side and will push and press against the body of the implant at the bending side. The implant body as a result will press against adjacent bone at the bending side resulting in the appearance of these high stress values. Vertical forces and loads result in considerably lower stress values relative to horizontal loads.

This stress is condemned for the bone resorption phenomenon that takes place around the neck of the implant. If resorption continues, it might lead to the mobility and loss of the dental implant. P1209

SUMMARY OF THE INVENTION

The new invention employs structural modifications to all components so they will have a different mechanical interaction. Under horizontal loads these new components will pull the body of the implant at the non-bending side towards the bending side, and will not push the body of the implant at the bending side towards adjacent bone that surrounds the neck of the implant. This will result in tension at the non-bending side and less compression at the bending side. This makes the action of these new components similar to the action of the periodontal ligament around natural teeth.

This behaviour of the different components of the implant can be achieved by establishing a certain mechanical relationship between the different components. These mechanical relationships can be one or more of the following: ** The construction of the abutment with projections extending from the apical aspect engaging a trough or ditch within the coronal aspect of the body of the implant. Only the internal aspects (surfaces) of the abutment projections should exhibit contact with the external facing walls of the internal surfaces of the ditches within the body of the implant. All other surfaces should be relieved i.e. should not be in contact. The inner surfaces of abutment projections can be constructed straight or divergent downwards. When abutment projections are constructed divergent, corresponding ditches should not obstruct the fitting of these projections into them.

*:* Modifying thread shape and design for the abutment screw and / or the prosthetic screw. With an ideal thread the angle P1209 between the top of the thread and the body of the screw should be acute, while the angle between the bottom surface of the thread and the body of the screw should be obtuse. The internal threading within the body of the implant or the body of the abutment screw that will receive the prosthetic screw and the abutment screw should correspond to the shape of these threads but should be also modified so that the contact between the threads and the receiving internal threads is minimal.

The thread and its corresponding receiving internal thread should have minimal contact at the top surface of the thread. A gap should exist between the thread and the receiving internal thread at other surfaces.

This relief (i.e. degree of misfit) between the threads and the corresponding receiving internal threads should be adequate enough to avoid any contact between threads and receiving internal threads at all other locations.

The thread is directed upwards and will make a contact with the corresponding receiving internal thread at the top surface of the thread as a direct effect of screwing the screw downwards and the accumulating p reload.

When the mechanical relationship incorporated in the implant includes the above described abutment projections, such a relief should also be present between the remainder of abutment screw and the body of the :... __,..

II J IIdl IL.

To enhance the above described action of these mechanically related components, the sides of the body of the implant may be vertically sectioned for a variable distance downwards allowing these sections to P1209 move independently.

These sections if carried out within the body of the implant can be filled with a low modulus of elasticity material such as hydroxyapatite reinforced polyethylene or a similar material that can osseointegrate with adjacent bone. This material will seal the inside of the implant from surrounding body fluids while allowing for differential movements of the different surfaces of the sectioned body of the implant.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. Below is a description of the accompanying drawings: Figure 1: Longitudinal section of abutment implant assembly with the embodiment of the invention showing the abutment I body of implant relationship, and the abutment screw I body of implant relationship.

Figure 2: The profile of the thread and the receiving internal thread of the threaded components in the assembly.

Figure 3: Close up showing the relationship between surfaces of the abutment, abutment screw and the implant under horizontal load.

Figure 4: The apical end of the abutment showing metal P1209 projections and the non-threaded coronal aspect of the abutment screw. The remainder of the abutment screw has been removed from this image.

Figure 5: The coronal end of the body of implant showing ditches, vertical cuts in the body of the implant and the low modulus of elasticity material filling the spaces between the separate walls.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1: This example embodiment of the invention shows only a contact between the inner surfaces of the abutment extensions that are designed to engage the top surface of the body of the implant and the ditches that are prepared at the top surface of the implant to receive them. Surfaces of the abutment shoulder 7 that get in contact with the base of the head 5 of the abutment screw are inclined with the contact areas facing outwards 18. Other surfaces of the abutment are not making any contact with neither the body of the implant 12 nor abutment screw.

I is the prosthesis or false tooth. 2 is the head of abutment screw, 3 is its shank. 4 is the abutment. 5 is the head of the abutment screw and 6 is the opening in the abutment screw to receive prosthetic screw. 7 is the shoulder of abutment providing support for abutment screw 18. These structures meet only along an inclined surface as illustrated. 8 is an elastic rubber band (0 ring) to seal the interface between the abutment and the body of the implant from the oral cavity. 9 is the level of bone. 10 represent the inclined interface along which the apical projections of the abutment and the surfaces of the ditches in the body of the implant meet. P1209

12 is relief between the outer surface of the abutment projections and the adjacent surface of the receiving ditch. 13 is the shank of the abutment screw. 14 are the threads of the prosthetic screw making minimal contact with the receiving internal threads within the body of the abutment screw at their top surfaces. 15 are the threads of the abutment screw making minimal contact with the receiving internal threads 16 within the body of the implant at their top surfaces. 17 is the body of the abutment screw.

19 is cortical bone around the neck of the implant. This region of bone displays the highest stress recordings in bone secondary to vertical or horizontal loading. 20 is the coronal aspect of the body of the implant. 21 and 22 are the apical ends of abutment screw and the body of the implant respectively.

Figure 2: The profile of the threads 2 and the receiving internal threads 3 of the threaded components in the assembly. Angle between top surface of the thread and the body I of the threaded component 81 is less than 900, while the angle between the bottom surface of the thread and the body of the threaded component 82 is more than 900. The receiving internal threads 3 within the bodies of tapped structures should not necessarily correspond to the inclinations of the thread but should establish a line contact 5 with the top surface of the threads. 4 is another example of what the receiving internal thread shape might look like.

Figure 3: This illustration is a close up of the assembly under horizontal load 22 acting towards one side of the implant (the bending side): The threads of the prosthetic screw at the non-bending side 23 will move upwards against the corresponding receiving internal threads within the abutment screw resulting in horizontal forces 25 dragging the far surface of the abutment screw towards the bending side. The abutment projections will contact the surfaces of the ditches coronally at 26 resulting P1209 also in a force of similar direction 27. Abutment projections will separate from the surfaces of the ditches at 28. As a result of forces 25, threads of abutment screw 30 will pull the receiving internal threads of the body of the implant towards the bending side at 29.

On the other side of the assembly however, the threads of the prosthetic screw will move away from receiving internal threads of the abutment screw 31, also the head of the abutment screw will move away 32 from the top surface of the shoulder of the abutment 33. Moreover, the abutment projections will make an apical contact with the surfaces of the ditches at 34 resulting in a force acting on the abutment towards the non- bending side. Also, threads of the abutment screw will release the receiving internal threads of the body of the implant 35.

Figure 4: Shows the abutment 4 with the apical abutment projections. 10 is the external facing surface of the internal wall of the projections and 11 is the internal facing surface of the external wall of the projections.

Contact with the body of the implant will take place along the external facing surface of the internal walls 10. 3 is the shank of the abutment screw, the remainder of the screw is not shown.

Figure 5: 12 are ditches within coronal surface of the body of the implant 19. Engagement of abutment projections with external facing surfaces of the internal walls of these ditches 36 is advantageous as has been described in Figure 3. Also engagement of projections in these ditches will provide anti-rotation action to prosthesis.

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Claims

1. An implant having a root as the basic component designed for being implanted in living bones or inserted in supporting media with an uppermost end to which the other component(s) attach and a lowermost end and a varying number of other extra components designed for connecting the implant to an upper structure such as a restoration that might be exposed to various external vertical and horizontal forces in relation to the longitudinal axis of the implant, with every accessory implant component fitting into and having relation to one or more other implant components through a special attachment mechanism, which is designed so as to transfer the external horizontal forces that are directed in a perpendicular direction to the longitudinal axis of the implant from the uppermost component downwards through the other implant components finally to the underlying bone or supporting media, in a way so that the special design of these attachment mechanism(s) will generate the majority of the component forces onto the side of the root (that is located at the side corresponding to the origin of the external horizontal force) to move it towards the longitudinal axis of the implant, while at the other side of the implant, and due to the presence of a relief (tolerance) within the attachment mechanism(s) joining the inter- relating components, these components will tend to release each other reducing the values of bending forces that will bend this side of the root towards the adjacent bone or supporting media present at the outside of the body of the implant.

2. An implant as claimed in claim 1 where the said attachment mechanism between the different components constitutes of a thread with modified design in one implant component where the - 10- P1209 upper angles formed between the threads of this component and the longitudinal axis of the component are acute while the lower angles between the threads and the longitudinal axis of the component are obtuse, with the receiving internal threads in the adjacent component being designed so that the only contact with the corresponding threads is minimal and located at the upper surface of the thread.

3. An implant as claimed in claim I where the said attachment mechanisms between the different components can be projections from the upper component engaging a modified troughs or ditches in the lower component so that the intimate contact will be present only along the wall of the trough that is closer to the longitudinal axis of the implant while all other surfaces of the trough are relatively free from any contact with the other component.

4. An implant as claimed in claim I where the said attachment mechanisms between the different components can be metal projections from a lower component engaging modified troughs or ditches in an upper component so that the intimate contact will be present only along the wall of the trough that is located far from the longitudinal axis of the implant while all other surfaces of the trough are relatively free from any contact with the metal projection coming from the lower component.

5. An implant as claimed in claim 1 where the attachment mechanism between the different components is: threads in one component to internal threads in the other component as claimed in claim 2 or projections in one component engaging ditches or troughs in the other component as claimed in claims 3 and 4 or a combination of the two mechanisms.

6. An implant as claimed in any preceding claim where the attachment mechanisms between the different components are -11 - P1209 present at the top or the middle or the lower level of the implant body or any combination of these.

7. An implant as claimed in any preceding claim where the trough or ditch in any component is present along the upper, middle or lower part of the body of the component or any combination of these.

8. An implant as claimed in any preceding claim where the port of entry to the trough opens towards the uppermost end, lowermost end or the longitudinal axis of the component 9. An implant as claimed in any preceding claim where the said attachment mechanism between the different components is present between the root component of the implant and the supporting media either alone or in conjunction with this mechanism existing between the different implant components as well, wherein the root component of the implant will be considered as the upper component while the supporting media will constitute the lower component as stated in claim 2,3 and 4.

lOAn implant as claimed in claim 9 where the outside body of the implant is treated or modified by appropriate coating materials to allow the intimate contact between the body of the implant and the bone or the supporting media only at the appropriate locations of the implant's threads or extensions as dictated by claim 2, 3 and 4.

11. An implant as claimed in any preceding claim where the body of the implant is sectioned vertically at its uppermost end downwards to a varying distance downwards with the section lines filled with a low modulus of elasticity material that will allow the different implant sections to move irrespective of the other sections providing that this low modulus of elasticity material is compatible with the media that receives and supports the implant.

12.An implant as claimed in any preceding claim where the implant is constructed from a material compatible with and suitable to the - 12 P1209 supporting media or the place in which it is implanted such as a biocompatible material or metal or plastic or wood or any combination of these.

13. An implant as claimed in any preceding claim where the load bearing structure attached on top of the implant is retained by screw or screws or retained by cement or retained by a combination of the two methods.

14.An implant which is substantially as described with reference to the drawings.

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