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Biomedical subjects

J P van Loon

Publications and source records attributed to J P van Loon.

11 recordsLinked to original sources
PubMed2002

Groningen temporomandibular joint prosthesis. Development and first clinical application.

Patients with a severely degenerated temporomandibular joint (TMJ) may benefit from an alloplastic TMJ replacement. The aim of the study was to develop a safe and properly functioning TMJ prosthesis. The design was based on imitation of anterior condylar translation by an inferiorly located centre of rotation, unrestricted mandibular movements by a double articulation, correct fit to the skull by a self-adjusting skull part consisting of two connected parts, and stable fixation by bone screws that are rigidly connected to the prosthesis parts. The prosthesis consists of a titanium skull part with ceramic inlay, a titanium mandibular part with a ceramic spherical head, and an intervening polyethylene disc. Titanium-alloy bone screws are used for fixation. All parts are available in a number of different shapes. In vitro laboratory and in vivo animal tests showed a low wear rate, the possibility of a close fit to the skull, a stable fixation, sufficient mechanical strength, appropriate choice of materials and proper functioning. Thereafter the step to first patient application was made. First patient application was carried out without adverse events. In conclusion, the presented TMJ prosthesis passed the pre-clinical tests and has progressed to clinical application. The fit to the skull, the expected lifetime of the device and the reliability of the implantation procedure require further evaluation in well-designed clinical trials.

Adult↗
PubMed2000

A short-term study in sheep with the Groningen temporomandibular joint prosthesis.

As part of the pre-clinical testing process of a newly developed temporomandibular joint (TMJ) prosthesis, animal experiments were performed. In 14 sheep, the right TMJ was replaced by the developed TMJ prosthesis. The prosthesis consisted of a skull part, a mandibular part and an intervening polyethylene disc. In the first series (6 sheep), three designs were tested, differing in the applied metal (stainless steel or titanium) and in the fitting method of the skull part (a fitting member or bone cement). The sheep were sacrificed after 8-16 weeks. In the second series (8 sheep), the preferred titanium fitting member design was applied, and the sheep were sacrificed after 2-10 weeks. One sheep was excluded because no correct position of the prosthesis parts could be achieved. At sacrifice, the removal torque of the screws was measured, and the surrounding tissues were harvested for histologic examination. The sheep recovered well and functioned until the end of the scheduled sacrifice date. Encountered problems were two disc dislocations, one fistula formation, and one screw failure. All mandibular parts were clinically stable, as were most skull parts with a fitting member, and one of both skull parts fitted with bone cement. The clinically observed stability was confirmed by the removal torque values, which indicated well-integrated screws. It is concluded that the TMJ prosthesis could remain stable and functional over the initial healing period. The main restriction of the sheep model is the much larger translatory capacity compared with patients, which adversely influences tissue healing.

Animals↗
PubMed2000

Fitting a temporomandibular joint prosthesis to the skull.

Fitting a temporomandibular joint (TMJ) prosthesis to the skull by using stock prostheses seems to be an appropriate method. However, fitting the skull with one stock part requires many differently shaped parts. Therefore, we fitted the skull with two connected stock parts. The aim of the study was to test whether it is possible to achieve a close fit to the skull with this design, with a maximum of 10 different parts. The articular eminence was fitted with a gully-shaped fitting member, which was rotationally connected to a basic part that fitted to the lateral side of the TMJ. The relevant dimensions of 20 dry skulls were measured and the results were used to derive the optimal dimensions of the prosthesis parts. Prototypes were subsequently fabricated. The fit of the prototypes was tested by measuring the maximum gap between fitting member and skull. All skulls could be fit with a set of four different basic parts and three different fitting members. The average maximum gap between fitting member and skull was 0.20 mm (range 0.11-0.43 mm). It was concluded that a close fit to the skull can be achieved with two connected stock parts and with a total number of seven parts.

Feasibility Studies↗
PubMed2000

Design and wear testing of a temporomandibular joint prosthesis articulation.

As part of the development of a total temporomandibular joint prosthesis, a prosthesis articulation was designed. The articulation consists of a spherical head (ball) of the mandibular part, rotating against an enveloping ultra-high-molecular-weight polyethylene (UHMWPE) disc with a flat cranial side, which slides along the opposing skull part. The aim of this study was to determine the in vitro wear rate of the articulation, and to predict the in vivo wear rate from the results. Based on a disc thickness of 5 mm and a ball diameter of 8 mm, the stresses within the disc were calculated by means of a finite element computer model. The wear rate of the ball-disc articulation was determined by in vitro wear tests, with a stainless-steel ball rotating against a UHMWPE disc in a serum-based lubricant. Eight discs were tested for seven million cycles each. The in vitro wear rate of the disc-skull part articulation was calculated from the test results of the ball-disc articulation. The maximum Von Mises' stress was less than the yield strength of UHMWPE and, therefore, was sufficiently low. The in vitro wear rate of the ball-disc articulation was 0.47 mm3 per million cycles. The in vivo expected total wear rate is 0.65 mm3 per year, corresponding with a yearly decrease of disc thickness of 0.0094 mm. Although it is difficult to judge whether this wear rate is sufficiently low, because the influence of UHMWPE wear particles in the TMJ region is unknown, both the expected wear rate and the decrease of thickness appear to be acceptable.

Alloys↗
PubMed1999

A computer study of fracture mobility and strain on biodegradable plates used for fixation of mandibular fractures.

PURPOSE: This computer-based study was done to determine whether a small biodegradable plate system was suitable for internal fixation of mandibular fractures. MATERIALS AND METHODS: In a three-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. Simulated solitary angle, body, and symphysis fractures were fixed with one titanium miniplate, one polylactide (PLA) midiplate, one PLA maxiplate, or two PLA midiplates. Fractures with and without interfragmentary bone contact were studied. In the case of fractures with bone contact, the loads were transmitted through the fracture surfaces and the plate; when there was no contact, the loads were transmitted only through the plate. Maximum fracture mobility was set at 150 microm. Maximum plate strain was set at the yield strain of PLA and titanium. RESULTS: For fractures without interfragmentary bone contact, all plate fixations resulted in a fracture mobility and plate strain higher than the limits set, except for the symphysis fracture fixed with two PLA midiplates. Interfragmentary bone contact significantly reduced fracture mobility and plate strain. For the angle fracture with bone contact, all PLA plate fixations resulted in a fracture mobility above the limit, whereas the titanium miniplate fixation had a fracture mobility below the limit. For the body and symphysis fracture with bone contact, only double PLA midiplate fixation resulted in a fracture mobility below the limit. CONCLUSIONS: From a mechanical point of view, based on the computer model, small PLA plates are only suitable for symphysis fractures with and without interfragmentary bone contact and for body fractures with interfragmentary contact. However, fixation with two PLA plates is always necessary to provide sufficient reduction of fracture mobility and plate strain.

Absorbable Implants↗
PubMed1999

The theoretical optimal center of rotation for a temporomandibular joint prosthesis: a three-dimensional kinematic study.

A unilateral temporomandibular joint (TMJ) prosthesis may cause dysfunction of the contralateral, natural TMJ because of lack of translatorial movements of the prosthetic side. The natural translatorial capacity of the mandible can be restored in part by a TMJ prosthesis with a fixed center of rotation (CR), positioned inferiorly to the center of the natural mandibular condyle. The aim of this study was to determine the optimal position for the fixed CR of a unilateral TMJ prosthesis. A mathematical model was used to analyze different positions of the CR. These positions were evaluated based on the calculated rotation of the mandible in the frontal (theta f) and horizontal (theta h) plane, and the mediolateral movement (MLM) of the contralateral natural condyle. For current TMJ prostheses, with the CR positioned in the center of the natural condyle, theta h exceeded the natural limits. When the CR was shifted inferiorly, all parameters improved, particularly theta h. The addition of an anterior shift to an inferior shift slightly worsened theta f, while the addition of a posterior shift to an inferior shift slightly improved theta f and worsened MLM. We concluded that the functioning of the contralateral TMJ improves by shifting the CR inferiorly. An anterior shift may be added to remain within the contour of the mandibular ramus. The proposed position of the CR is 15 mm inferior to the center of the natural condyle, combined, if necessary, with an additional anterior shift of 5 mm.

Humans↗
PubMed1998

Loading of a unilateral temporomandibular joint prosthesis: a three-dimensional mathematical study.

The load on the prosthetic side and the influence of the design on the remaining natural contralateral TMJ must be known before a unilateral temporomandibular joint (TMJ) prosthesis can be developed. The aim of the present study was to determine the maximum loading of the TMJ prosthetic side and the natural contralateral TMJ and to investigate the influence of the location of the center of rotation of the prosthesis on the maximum loading. For this purpose, a mathematical model of the mandible with a unilateral TMJ prosthesis with a fixed center of rotation (CR) was developed. The location of the CR of the TMJ prosthesis was varied from the middle of the natural mandibular condyle to 15 mm inferior to this location. Although the maximum joint reaction forces changed as a result of a unilateral TMJ prosthesis, the trend of the loading curves was similar to that of an intact mandible. A unilateral TMJ prosthesis resulted in a 50% higher loading of the prosthetic side, while the load on the natural contralateral TMJ remained within normal limits. The maximum load on the prosthetic side occurred during molar bites and could reach 100 N in the cranial direction, 30 N in the ventral direction, and 25 N in the medio-lateral direction. The location of the CR did not have a significant influence on the loading of the TMJ prosthesis and the natural contralateral TMJ.

Adult↗
PubMed1997

A three-dimensional study of bending and torsion moments for different fracture sites in the mandible: an in vitro study.

The aim of the study was to determine and compare bending and torsion moments across mandibular fractures, for different positions of the bite point and different sites of the fracture. Three identical resin mandibles, each with a single fracture, were used. The fracture sites were in the angle, body and symphyseal regions. A polyethylene bone plate was used for fixation. Simulated bite forces were applied at 13 bite points. For each bite point, the displacements of the fragments were registered and converted into bending and torsion moments across the fracture. Positive bending moments were defined as those moments that caused compression at the lower border and tension at the alveolar side of the mandible; negative bending moments did the opposite. Angle fractures had relatively high positive bending moments. Body fractures had positive as well as negative bending moments and the highest torsion moments. Symphyseal fractures had negative bending moments only and relatively high torsion moments. It was found that angle, body and symphyseal fractures each have a characteristic load pattern. These load patterns should play a decisive role in the treatment of mandibular fractures with regard to number and positioning of plates.

Adult↗
PubMed1996

A three-dimensional study of loads across the fracture for different fracture sites of the mandible.

The loads across the fracture depend on variables such as position of the fracture and the bite point. Up to now, no study has described systematically the influence of these two variables on these loads. The aim of this study was to describe and compare value and direction of the loads across the fracture for different positions of fractures in the mandible. In a three-dimensional model, bending and torsion moments and shear forces were compared for five mandibular fractures. The fractures were located in, respectively, the angle, posterior body, anterior body, canine and symphysis region. Positive bending moments were defined to give compression at the border, negative bending moments to give compression at the alveolar side of the mandible. The angle and posterior body fracture have high positive bending moments, small torsion moments and high shear forces. The anterior body, canine and symphysis fracture have high negative bending moments and high torsion moments with similar maximum values. The number of bite points with negative bending moments were different for all fractures. These bite points were always located on the fractured side. It is concluded that mandibular fractures can be divided roughly into two groups with similar load patterns across the fracture. One group consists of angle and posterior body fractures, the other group consists of anterior body, canine and symphysis fractures.

Adult↗
PubMed1995

Evaluation of temporomandibular joint prostheses: review of the literature from 1946 to 1994 and implications for future prosthesis designs.

PURPOSE: This article describes the useful elements of applied temporomandibular joint (TMJ) prostheses and discusses the factors necessary to be addressed in an appropriate TMJ prostheses design. MATERIALS AND METHODS: Information about TMJ prostheses was gathered by a literature search. Only designs with the primary intention of true joint replacement were selected. The designs were divided in fossa-eminence, condylar, and total joint replacements, which are reviewed separately. RESULTS: A fossa-eminence prosthesis can be fixed by a metal plate screwed to the root of the zygomatic arch. A condylar prosthesis can be fixed by a metal plate screwed to the mandibular ramus and fitted by bending the plate or using different sizes. All reviewed designs resulted in a loss of translational movements of the mandible, especially in an anterior direction. Although the recent designs use the same materials as are used in hip and knee joint prostheses, the wear properties of the existing TMJ prostheses are still unknown. CONCLUSIONS: A future prosthesis must imitate the anterior movement of the mandible when the mouth is opened and also allow some mediolateral movement. The fitting to the skull is still a major problem, as is the combination of the required motions and low wear rates. To confirm good clinical performance of a new TMJ prosthesis, long-term follow-up studies are necessary.

Evaluation Studies as Topic↗