Biomedical subjects

L G de Bont

Publications and source records attributed to L G de Bont.

At least 19 recordsLinked to original sources

PubMed2003

[Treatment of the obstructive sleep-apnea syndrome in adults].

When treating the obstructive sleep-apnoea syndrome (OSAS), conservative management and the correction of treatable stenoses in the upper airway should be considered first. If these measures are neither effective nor applicable, then continuous positive airway pressure (CPAP) is the preferred treatment. Surgical interventions should only be considered after failure of non-surgical treatment modalities. Pharmacological management of OSAS is usually only indicated as a form of supplementary treatment in specific patients. Oral-appliance therapy appears to be of value in the management of OSAS and, in specific groups of patients, seems likely to offer a good alternative to CPAP in the future.

Female↗

PubMed2001

[Manpower shortage in oral and maxillofacial surgery--a serious problem in the Netherlands].

In the Netherlands there is currently a shortage of oral and maxillofacial surgeons. This shortage will increase between 2001 and 2010. It is analyzed that early retirement and reduction of working hours are the major factors which contribute to the shortage which will cause serious problems till 2010. Solutions will focus on increasing training capacity, reduction of training time and on various forms of substitution.

Dentistry↗

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

Comparison of two systems for rigidly connecting 2.0-mm bone screws to an implantable device: in vitro stability testing.

The stability of a screw-fixed implantable device can be improved by eliminating the freedom of movement between the screws and the device. Two systems have been developed for rigidly connecting 2. 0-mm bone screws to an implantable device, and the aim of this study was to test and compare the stability of the two systems. In system A, a fixing disc locked the screw-head. In system B, the thread of the screw locked directly into the device. The stability of the connection was tested by measuring the resistance against a torque on the screw, against shear loading, against push-out loading, and against dynamic shear loading (70 N) for 5 million cycles. Both systems met the required minimum values for the resistance against a torque, shear loading and push-out loading, and dynamic shear loading did not cause movements between the screw and the device. We conclude that both systems are stable, but prefer system B because it is easier to make and implant than system A.

Bone Plates↗

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

Wear-testing of a temporomandibular joint prosthesis: UHMWPE and PTFE against a metal ball, in water and in serum.

For a temporomandibular joint prosthesis, an estimation of the wear rate was needed, prior to patient application. Therefore, we determined the in vitro wear rate of the ball-socket articulation of this prosthesis, consisting of a metal head and an ultra-high molecular weight polyethylene (UHMWPE) cup. The basic testing configuration consisted of one 8-mm diameter stainless-steel ball, rotating between two conforming cups with a minimum thickness of 5 mm. For validation of the testing apparatus, two cup materials, in two lubricants, were tested. Both cup materials, UHMWPE and polytetrafluoroethylene (PTFE) were tested in deionized water, as well as in a serum-based solution. For UHMWPE in serum, eight samples were tested, for the other combinations four samples. For UHMWPE, the tests ran for 7 million cycles, for PTFE between 0.8 and 1.7 million cycles. For UHMWPE, the wear rate was 0.006 and 0.47 (mm3/10(6) cycles), in water and in serum, respectively. For PTFE, the wear rate was 2.8 and 47 (mm3/10(6) cycles), in water and in serum, respectively. For reason that testing in serum simulates the in vivo situation best, it was concluded that the wear rate of the TMJ prosthesis articulation is 0.47 (mm3/10(6) cycles), which is considered acceptable.

Biocompatible Materials↗

PubMed1999

Arthroscopic findings in osteoarthritic temporomandibular joints.

PURPOSE: This article reports on the results of a study of the arthroscopic findings in the joint surfaces of osteoarthritic temporomandibular joints (TMJs). PATIENTS AND METHODS: Arthroscopy was performed in the upper joint compartment of 40 TMJs in 40 patients. Thirty-one TMJs that were diagnosed with osteoarthritis (OA) constituted the OA group. On the basis of the presence of symptoms related to disc displacement and perforation, OA subgroups were defined. Nine TMJs that were not involved with OA constituted the control group. During the examination, various arthroscopic variables were recorded. Differences between groups and between subgroups were tested statistically. RESULTS: In the OA group, several arthroscopic variables were found significantly more frequently than in the control group. These included retrodiscal tissue redundancy, adhesions, and heightened attachment to the posterior wall of the glenoid fossa; articular disc displacement and limited mobility; and cartilage degeneration in the articular eminence. Moreover, in the OA group, disc displacement was found significantly more frequently in the period after 6 months than during the first 6 months of clinical signs and symptoms. Anterodiscal hypervascularity was found significantly more frequently during the first year than after the first year, as well as more during the first 2 years than after the first 2 years of clinical signs and symptoms, whereas a lowered attachment on the anterior slope of the articular eminence was found significantly more often after 2 years than during the first 2 years of clinical signs and symptoms. CONCLUSIONS: The findings in this study suggest that OA of the TMJ may initially result in synovial tissue hypervascularity, creeping synovitis, and redundancy, and subsequently in adhesion formation and a reduction of the posterior and anterior recess. Because of cartilage fibrillation on the articular eminence, and the subsequently reduced surface smoothness, the articular disc may become displaced. Eventually, disc mobility is limited, and adhesions and a reduced posterior and anterior recess prevail.

Adult↗

PubMed1999

Influence of mandibular length on mouth opening.

Theoretically, mouth opening not only reflects the mobility of the temporomandibular joints (TMJs) but also the mandibular length. Clinically, the exact relationship between mouth opening, mandibular length, and mobility of TMJs is unclear. To study this relationship 91 healthy subjects, 59 women and 32 men (mean age 27.2 years, s.d. 7.5 years, range 13-56 years) were recruited from the patients of the Department of Oral and Maxillofacial Surgery of University Hospital, Groningen. Mouth opening, mobility of TMJs and mandibular length were measured. The mobility of TMJs was measured as the angular displacement of the mandible relative to the cranium, the angle of mouth opening (AMO). Mouth opening (MO) correlated significantly with mandibular length (ML) (r = 0.36) and AMO (r = 0.66). The regression equation MO = C1 x ML x AMO + C2, in which C = 0.53 and C2 = 25.2 mm, correlated well (r = 0.79) with mouth opening. It is concluded that mouth opening reflects both mobility of the TMJs and mandibular length.

Adolescent↗

PubMed1999

Therapeutic outcome assessment in permanent temporomandibular joint disc displacement.

In permanent temporomandibular disc displacement (TMJ-DD) outcome studies many authors claim positive effects of arthroscopic surgery, arthrocentesis and physical therapy. This literature review was undertaken to analyse whether the claimed effects are based on acceptable methodology. The recorded papers were analysed by two independent observers according to (1) method of investigation, (2) therapeutic intervention studied, (3) therapeutic outcome variables used, and (4) claimed effectiveness of the intervention. Agreement between observers was calculated. Twenty-four papers were found in which therapeutic outcome of interventions on temporomandibular disorders were studied. Six studies applied a true experimental design. Each of these six studies compared a different set of interventions. Twenty-two papers used maximal mouth opening (MMO) as an outcome variable, nine studied pain intensity on a visual analogue scale, one paper assessed the mandibular function impairment questionnaire. Kappa for overall agreement concerning the reviewing criteria was 0.82 (P < or = 0.001). No distinguishing effects on MMO, pain or function impairment were reported between arthroscopic surgery, arthrocentesis and physical therapy. Results of methodological sound outcome studies evaluating the effects of arthroscopic surgery, arthrocentesis and physical therapy are needed.

Arthroscopy↗

PubMed1999

Mandibular condyle fractures: a consensus.

A consensus was obtained following a two-day international conference to review the management of mandibular condyle fractures. Whilst areas of disagreement still exist, there are many areas of agreement. It is hoped this editorial will stimulate debate leading to internationally accepted guidelines.

Humans↗

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↗

PubMed1999

Smallest detectable difference in outcome variables related to painful restriction of the temporomandibular joint.

The smallest detectable difference is the smallest statistically significant change in measurement results. In the field of temporomandibular disorders, the smallest detectable difference is not a commonly used concept. Most outcome studies are based on comparisons of group means, although this does not provide information about individual changes or about the clinical relevance thereof. The smallest detectable difference for maximal mouth opening was calculated from previously published reliability coefficients and the standard deviations of different samples of healthy subjects and patients with complaints of the temporomandibular joint. The smallest detectable difference of pain intensity measured with different visual analogue scales was calculated from the reliability coefficients and standard deviations of a heterogeneous group of pain patients. The smallest detectable difference of function impairment was calculated for a group of patients with complaints of the temporomandibular joint. For maximal mouth opening in healthy subjects, the smallest detectable difference was 5 mm. Repeated measurements improved it to 3 mm. The smallest detectable difference on a visual analogue scale was 28 mm for actual pain intensity and 22 mm for minimal pain as well as for maximal pain intensity. For total function impairment of patients with complaints of the temporomandibular joint, the smallest detectable difference was 8 units on a 0 to 68 scale.

Adult↗

PubMed1999

The smallest detectable difference of mandibular function impairment in patients with a painfully restricted temporomandibular joint.

Mandibular functions such as speech, laughing, yawning, mastication, and taking a large bite may be impaired if temporomandibular disorders exist. The Mandibular Function Impairement Questionnaire is a validated instrument that scores perceived difficulty of representative mandibular functions in relation to jaw complaints. However, the reliability of the Mandibular Function Impairment Questionnaire has never been adequately tested. Generalizability and decision studies are currently proposed to assess the reliability of a measurement device. The smallest detectable difference is the smallest statistically significant amount of change to be detected with a measurement device. The purpose of this study was to assess the reliability of the Mandibular Function Impairement Questionnaire in terms of the smallest detectable difference. Twenty-five consecutive patients with painfully restricted temporomandibular joints completed the Mandibular Function Impairement Questionnaire on two separate measurement days, one week apart, using two consecutive sessions per day. Spearman's r was calculated for test-retest reliability. Variance components such as patients, measurement days, repetitions, and all their interactions were analyzed in the generalizability study. In the decision study, the smallest detectable difference was calculated for different days and repetitions. Spearman's r varied from 0.69 to 0.96. The between-patient variance and the error variance contributed 81% and 19% to total variance, respectively. The Mandibular Function Impairment Questionnaire is a reliable instrument for the assessment of mandibular function impairment. The minimal amount of change to be detected is 14 units on a scale of 0 to 68. Reliability in terms of the smallest detectable difference increases if the measurement is repeated twice on two separate days: The smallest detectable difference improves to 10 units.

Adult↗

PubMed1999

Correlation between arthroscopically observed changes and synovial light microscopic findings in osteoarthritic temporomandibular joints.

The aim of this study was to determine the correlation between arthroscopically observed (ASC) changes in the synovial membrane and other joint components and synovial light microscopic (LM) findings in the temporomandibular joint (TMJ). Synovial membrane biopsies were obtained during unilateral arthroscopy in forty patients. Thirty-one patients were diagnosed with TMJ osteoarthritis (OA) and nine patients with non-osteoarthritic conditions of their TMJs. Correlations between ASC and synovial LM findings were analyzed with Cohen's Kappa and Spearman's rank correlation tests. Values for Kappa of 0.6 and higher and values for a correlation coefficient of 0.7 and higher were considered satisfactory. No correlations were found in the retrodiscal tissue biopsies. In the anterodiscal tissue biopsies, ASC hypervascularity correlated with LM intima cell shape and cell density. ASC lowered attachment to the anterior slope of the articular eminence correlated with the LM presence of a fibrous intima matrix. In several TMJs, a high concurrence was observed between ASC and LM pathologic changes. The severity of pathologic changes as observed by LM was, however, often less than was suggested arthroscopically.

Adult↗

PubMed1998

Synovial inflammation in arthroscopically obtained biopsy specimens from the temporomandibular joint: a review of the literature and a proposed histologic grading system.

Data indicate that the synovial lining of the temporomandibular joint (TMJ) in some respects differs from other joints. The normal variation in morphology of the synovial lining of the TMJ is quite great, whereas the variation in pattern of pathologic changes appears to be relatively small (ie, synovial inflammation is not of the severity as that in other joints). In the current review, a system for histologic grading of synovial inflammation is proposed. The system is based on semiquantitative evaluation of the following set of parameters: 1) synovial lining cell layers; 2) vascularity (number or size of vascular profiles); and 3) Inflammatory cell infiltrate (commonly lymphocytes).

Arthroscopy↗

PubMed1998

Temporomandibular joint osteoarthritis and crystal deposition diseases: a study of crystals in synovial fluid lavages in osteoarthritic temporomandibular joints.

To study the presence of crystals in synovial fluid lavages of osteoarthritic temporomandibular joints (TMJs), in order to evaluate the possible role of these crystals in the osteoarthritic (OA) process, synovial fluid lavage samples of the upper joint compartment from 44 TMJs were obtained prior to arthroscopy. The OA group consisted of 32 TMJs. The control group consisted of 12 TMJs that had been diagnosed with other nonosteoarthritic conditions. The lavage samples were analysed as wet preparations, unstained and stained, with ordinary light, polarized light and compensated polarized light for the presence of crystals and white blood cells. One sample was prepared for subsequent electron microscopic (EM) examination. Synovial fluid lavage analysis of osteoarthritic TMJs did not show any monosodium urate monohydrate or calcium pyrophosphate dihydrate crystals. However, in three lavages, particles which possibly contained calcium were identified with alizarin red S staining. White blood cells were occasionally seen. Synovial fluid analysis of the lavages of the control TMJs did not reveal any crystals. EM examination of synovial fluid lavage from an osteoarthritic TMJ failed to clearly show crystal formation. Concurrence of TMJ crystal deposition and OA appears less prominent than in other synovial joints. We conclude that crystals probably do not play an important role in TMJ OA.

Adult↗

PubMed1998

Ratio between vertical and horizontal mandibular range of motion.

Mandibular range of motion (ROM), vertical and horizontal, is often measured as a part of a diagnostic assessment of temporomandibular joint disorders. In the literature, a fixed ratio between the vertical and the horizontal ROM has been suggested, i.e. 4:1. The ratio is frequently used to predict the vertical ROM on the basis of the horizontal ROM and vice versa. However, no scientific data are available to substantiate the ratio suggested. The aim of this study was to determine whether the fixed ratio of 4:1 exists and, if so, whether this ratio has a predictive value. Vertical and horizontal mandibular ROM was measured in 91 healthy subjects, 59 women, and 32 men (mean age 27.2 years, s.d. 7.4 years) using vernier callipers. We found a mean ratio between vertical and horizontal ROM ranging from 6.0:1-6.6:1. On an individual basis the ratio ranged from 3.6-15.5. Correlations between vertical and horizontal ROM were weak. On the basis of the results on this study it is concluded that the ratio between vertical and horizontal ROM is approximately 6:1 rather than 4:1, and that the ratio has poor predictive value.

Adolescent↗