WO2008155637A1

WO2008155637A1 - Dental implant with an optimized external thread profile

Info

Publication number: WO2008155637A1
Application number: PCT/IB2008/001603
Authority: WO
Inventors: Anitua Eduardo Aldecoa
Original assignee: BTI Biotechnology Insttitute
Current assignee: BTI Biotechnology Insttitute
Priority date: 2007-06-18
Filing date: 2008-06-16
Publication date: 2008-12-24
Anticipated expiration: 2009-12-18
Also published as: ES2332841B1; ES2332841A1; AR068320A1; CL2008002204A1

Abstract

Dental implant (1) provided with a threaded part (2) whose thread profile has a trapezoidal section, comprising a short side (4), a thread crest (5), a long side (6) and a thread trough (7), with the particularity that the part of the thread profile aimed in the direction of the longitudinal axis (8) forms an acute angle (10) with said longitudinal axis (8), the angle (10) being similar to the profile of a natural tooth. With these characteristics, the performance of the threaded profile of the dental implant (1) reproduces the performance of the unthreaded profile of a natural tooth. In other words, a dental implant (1) is obtained that, in addition to being self-tapping, presents mechanical properties and bone stress distribution similar to those of a natural tooth.

Description

DENTAL IMPLANT WITHAN OPTIMIZED EXTERNALTHREAD

PROFILE

DESCRIPTION

Field of the Invention

The invention relates to a dental implant for the insertion of dentures or false teeth in a patient's mouth.

Prior Art

As known, dental implants are extremely small threaded parts which are inserted into a patient's mouth's bone, and to which a false tooth or denture is attached. The implant and denture insertion process is usually the following: using the appropriate tools, a cavity is made in the patient's bone; then, the implant is introduced by threading it into the bone cavity; a period of weeks or months goes by until the implant is osteointegrated in the patient's bone; finally, one or several artificial teeth are attached to the implant by means of a screw or other accessories.

The dental implant consists essentially of two parts: a head, which provides the implant with the required connection means for connecting the screw, the false tooth and other pieces used temporarily in the insertion of the implant or permanently in the insertion of the false tooth; a point, or external threaded part, which enables the dental implant to be attached to the patient's bone.

The connection of the dental implant to the patient's bone must be sufficiently robust to withstand the stress received by the dental implant during the useful life of the false tooth without the connection between the dental implant and the bone deteriorating. Stress may be lateral, although it is essentially longitudinal (in the direction of the implant's axis), originating when chewing with the false tooth. The invention aims to offer a new external thread design for the dental implant that, among other advantages, improves the connection between the dental implant and the bone, allowing this connection to optimally withstand the stress arising from normal use of the false tooth during its useful life. In other words, the new external thread design aims to minimize the stress transferred to the bone by the implant's external thread and therefore increase the implant's success rate (whereby "success" is understood to be the fact that the implant fully oseointegrates).

Brief Description of the Invention

The object of the invention is a dental implant equipped with a threaded part whose thread profile essentially seeks to fulfil two requirements. Firstly, the implant according to the invention seeks mechanical properties and stress distribution in the bone that are similar to those of a natural tooth (considering the connection of the natural tooth to the bone as optimal, as a result of thousands of years of evolution). It must be taken into account that excessive stress transferred from the dental implant to the bone as a. result of the use of the dental implant during its useful life may cause damage and even the death of the bone tissue. Secondly, the threaded part must be self-tapping, in other words, it must allow the dental implant to create a threaded connection with the bone as it is being inserted. For this, the dental implant according to the invention presents a thread profile with a trapezoidal section (in other words, with a short side, a thread crest, a long side and a thread trough), with the peculiarity that substantially the entire part of the thread profile aimed in the direction of the longitudinal axis forms an acute angle with this longitudinal axis, whereby this angle is similar to the profile of a natural tooth. In other words, the thread crest and the thread trough have a significantly reduced length with respect to the length of the long side, whilst the long side forms an acute angle with the longitudinal axis in the direction of the load force (following detailed observation of the profile of a natural tooth, it has been found that this profile presents an acute angle in the direction of the load force which ensures that the stress distribution in the bone is as low as possible). With these characteristics, the dental implant threaded profile succeeds in reproducing performance similar to that of the unthreaded profile of a natural tooth.

Additionally, the angle between the short side and the longitudinal axis is at least twice that of the angle between the long side and the longitudinal axis, so as to ensure that the long side transfers the stress to the bone in the same way as a natural tooth and that the short side allows easy insertion of the dental implant in the bone.

In order to determine the improvements obtained by the invention, a computer simulation of the mechanical behaviour of a dental implant according to the invention has been carried out, compared with a dental implant fitted with a conventional thread profile, i.e., a triangular thread profile (with a section in the shape of an equilateral triangle). More specifically, the stress transferred by the implant to the bone has been simulated, bearing in mind that the stress on the bone must be as low as possible as it is responsible for a phenomenon known as bone withdrawal. Also, excessive stress may produce ischemia, which is one of the most determining factors for implant failure. In this simulation it has been confirmed that the maximum stress peak occurs in the contact between the bone and the first spire of the threaded part (in other words, the spire closest to the head of the implant). Stress then decreases in the following spires, being practically inexistent as of the sixth/seventh spire both in conventional implants and in the implant according to the invention. Additionally, it has been concluded in this simulation that the dental implant according to the invention manages to reduce the stress in the bone described by about 20%, increasing the implant's chance of success.

Brief Description of the Figures

The details of the invention can be appreciated in the accompanying figures, which do not intend to limit the scope of the invention:

- Figure 1 shows a frontal view of a first embodiment of the dental implant according to the invention, inserted in a bone.

- Figure 2 shows an enlarged view of the thread profile of the dental implant of the previous figure. - Figure 3 is a graph that represents the stress (in MPa) transferred by the implant to the bone in accordance with the angle (in degrees) between the long side and the longitudinal axis of the dental implant. - Figure 4 is a graph that represents the stress (in MPa) transmitted by the implant to the bone in accordance with the thread step (in millimetres) of the threaded part of the dental implant.

- Figure 5 is a graph that represents the stress (in MPa) transferred by the implant to the bone in accordance with the thread depth (in millimetres) of the threaded part of the dental implant.

Detailed Description of the Invention

Figure 1 shows a frontal view of the dental implant according to the invention. The dental implant (1), which is shown inserted in a patient's bone (3), is elongated in shape, along a longitudinal axis (8). The dental implant (1) comprises a threaded part (2) which connects it to the patient's bone (3).

Figure 2 shows an enlarged view of the thread profile of the threaded part (2) of Figure 1. The threaded part (2) has a trapezoidal section, formed of a short side (4), a thread crest (5), a long side (6) and a thread trough (7).

The long side (6) forms an acute angle (10) with the longitudinal axis (8), whereby this angle (10) is similar to that of the profile of a natural tooth. This angle (10) is preferably between 5 and 40°, due to the fact that this range of angles has been observed in natural teeth that have been studied during the development of this invention. In a particularly advantageous form, this angle (10) will take a value of between 10 and 20°, for which the computer simulation has indicated that the distribution of stress between the dental implant (1) and the bone (3) is optimal. Figure 3 shows a graph of the stress (in

MPa) transmitted by the dental implant (1) to the bone (3) in accordance with the angle (10) (in degrees) between the long side (6) and the longitudinal axis (8). As can be seen in the figure, if an angle (10) of between 10 and 20° is used, the stress transferred to the bone (3) is minimal. Angle (10) values of less than 10° are considered to be difficult to manufacture.

It must be pointed out that, once the range of values of the angle (10) that makes the performance of the dental implant (1) optimal (between 10 and 20°) was determined, analysis on natural teeth was performed once more, observing that the majority of the natural teeth analysed have an angle of between 10 and 20°. In other words, the optimal angle (10) to obtain a self- tapping dental implant (1) with performance as similar as possible to a natural tooth matches, with a high correlation, the angles measured in natural teeth. In a computer simulation of a natural tooth carried out later in the same way as the computer simulation for the thread profile of the dental implant, it has then been verified that the configuration observed in natural teeth (which is supposed to be optimum following millions of years of evolution of the human being) is effectively the configuration that produces the lowest stress peak on the tooth.

On another hand, the angle (9) is at least twice the angle (10), which allows that the threaded part (2) is self-tapping and, at the same time, that the amount of the threaded part (2) set out in a longitudinal direction at a different angle to that of the long side (6) is minimized. With the same objective of minimizing the areas set out at a different angle to that of the long side (6), the thread crest (5) and the thread trough (7) are of a significantly reduced length with respect to the length of the long side (6).

The angle (9) between the short side (4) and the longitudinal axis (8) is preferably between 70 and 40°. Angles (9) within this range are the optimal values in order to simplify the insertion of the dental implant (1) into the bone (3), requiring a lower insertion torque applied on the implant than with angles outside this range, as indicated in the computer simulation. The computer simulation has also provided the result that the value of the angle (9) does not have an influence in the transfer of stress to the bone (3).

The thread step (11) visible in Figure 2 is between 5 and 2 times less than the diameter (12) of the dental implant (1). These values enable the dental implant according to the invention to be inserted using the conventional implant insertion method, which simplifies the insertion of the dental implant. Outside this range, the required number of times the implant must be turned or threaded (and therefore the torque applied) during the insertion of the implant into the bone would be so different that current procedures would not be valid. In a particularly advantageous manner, the thread step (11) is between 3.5 and 2.7 times less than the diameter (12) of the dental implant (1), as the greatest reduction of stress transferred is obtained in this sub-range. For example, for a dental implant (1) with a diameter (12) of 4 mm, the thread step (11) is preferably between 1.15 and 1.50 mm as between these values it is guaranteed that the stress transferred to the bone (3) by the dental implant (1) is minimal, as can be seen in Figure 4.

The thread depth (13) is between 20 and 12 times less than the diameter (12) of the dental implant (1). Like in the previous case, these values allow inserting the dental implant (1) using the same procedures according as with conventional dental implants. In a particularly advantageous manner, the thread depth (13) is between 18 and 15 times less than the diameter (12) of the dental implant (1), as this is the sub-range in which a greater reduction in the stress transferred is achieved. For example, for a dental implant (1) with a diameter (12) of 4 mm, the thread depth (13) is preferably between 0.20 and 0.27 mm as between these values it is guaranteed that the stress transferred by the dental implant (1) to the bone (3) is minimal, as can be seen in Figure 5.

For example, for a dental implant (1) with a diameter of 5 mm, the invention establishes an optimum thread profile with the following characteristics: a thread depth (13) of 0.3 mm (16.7 times less than the diameter), a thread step (11) of 1.5 mm (3.33 times less than the diameter), an angle (9) between the short side (4) and the longitudinal axis (8) of 55°, an angle (10) between the long side (6) and the longitudinal axis of 15°, a 0.05 mm long thread crest (5) and a 0.05 mm long thread trough (7) (both of which are significantly reduced with respect to the length of the long side (6), which is around 1.88 mm). A dental implant (1) characterized by these values can be inserted according to conventional dental implant insertion methods, eases the threading of the implant in the bone, is easily manufactured and also transfers stress in such a way that the maximum stress peak is around 20% less than that of a conventional dental implant.

Claims

1. Dental implant (1), formed along a longitudinal axis (8) and which comprises a threaded part (2) to connect the dental implant (1) to a patient's bone (3), where the thread profile of the threaded part (2) has a trapezoidal section consisting of a short side (4), a thread crest (5), a long side (6) and a thread trough (7), characterized in that:

- the short side (4) is substantially shorter than the long side (6), - the long side (6) forms an acute angle (10) with the longitudinal axis (8), whereby this angle (10) is similar to the profile of a natural tooth,

- the thread crest (5) and the thread trough (7) have a substantially cero length with respect to the length of the long side (6), - the angle (9) is at least twice the angle (10).

2. Dental implant (1), according to claim 1, characterized in that the angle (10) formed by the long side (6) and the longitudinal axis (8) is between 5 and 40°.

3. Dental implant (I)₅ according to claim 2, characterized in that the angle (10) formed by the long side (6) and the longitudinal axis (8) is between 10 and 20°.

4. Dental implant (1), according to claim 1, characterized in that the angle (9) formed by the short side (4) and the longitudinal axis (8) is between 70 and 40°.

5. Dental implant (1), according to claim 1, characterized in that the thread step (11) is between 5 and 2 times less than the diameter (12) of the dental implant (1).

6. Dental implant (1), according to claim 5, characterized in that the thread step (11) is between 3.5 and 2.7 times less than the diameter (12) of the dental implant ( 1 ) .

7. Dental implant (1), according to claim 1, characterized in that the thread depth (13) is between 20 and 12 times less than the diameter (12) of the dental implant (1).

8. Dental implant (1), according to claim 1, characterized in that the thread depth (13) is between 18 and 15 times less than the diameter (12) of the dental implant (1).