Unilateral Disc Displacement Research Articles

Evaluation of the Effects of Temporomandibular Joint Disk Displacement and Its Progression on Dentocraniofacial Morphology in Symptomatic Patients Using Lateral Cephalometric Analysis

The aim of this study was to evaluate the effects of disk displacement (DD) and its progression on dentocraniofacial morphology in symptomatic patients and compare the results with asymptomatic volunteers. Skeletal and dental Class I female patients with DD, diagnosed using magnetic resonance imaging (MRI) and lateral cephalometric analysis were included in the study. Subjects were grouped as follows: control group with bilateral normal disk position (group 1, n=12), unilateral DD with reduction (group 2, n=16), bilateral DD with reduction (group 3, n=26), unilateral DD without reduction (group 4, n=12), and bilateral DD without reduction (group 5, n=8). Thirty-two (32) cephalometric variables were measured, and statistically significant differences were found in 11. Dental and soft tissue measurements did not reveal any differences, but variables related to the mandible showed statistically significant differences. Progression of DD was associated with an increase in all angular measurements related to vertical skeletal relationships and articular angle and a decrease in the ratio of posterior face height to anterior face height indicating clockwise rotation of the mandible. Similarly, the height of ramus was decreased with the progression of DD. The results of this study demonstrated that the presence of DD in skeletal Class I female patients effects facial morphology, and its progression makes the differences more significant and remarkable. These results emphasize the importance of early diagnosis and treatment in the management of DD.

Relationship between sounds and disc displacement of the temporomandibular joint using magnetic resonance imaging

Purpose: Magnetic resonance imaging (MRI) is useful for interpreting temporomandibular joint (TMJ) disorders including disc displacement. This study aimed to evaluate the relationship between TMJ sounds and disc displacement with and without reduction by clinical examination and MRI. Methods: A sample of 58 patients was clinically examined when after being referred to MRI due to signs and symptoms of unilateral or bilateral TMJ disc displacement. The diagnosis obtained using MRI was compared with the clinical findings for the presence or absence of articular sounds. Results: Most patients (n=39; 67%) had joint sounds manifested as clicking; the other 19 patients (33%) did not present sounds. Among the 39 patients with sounds, bilateral clicking was observed in 29 (74%), and unilateral clicking in 10 (26%) patients. Unilateral clicking was equally observed on the right and left sides, each occurring in 5 five patients (13%). Conclusion: The results suggest that articular sounds do not occur exclusively in TMJ with disc displacement with reduction. The presence or absence of joint sounds will not suffice as the only aspect criterion to be considered in the differential diagnosis of disc displacement with and without reduction.

The relationship between temporomandibular joint pathosis and muscle tenderness in the orofacial and neck/shoulder region

The objective of this study was to investigate the association between TMJ pain/disk pathosis and the muscle tenderness pattern in the orofacial and neck/shoulder region. One hundred seventy-one TMD patients were divided into 4 groups, including group 1: patients with painful unilateral TMJ disk displacement (DD); group 2: patients with painless unilateral TMJ DD; group 3: patients with painless bilateral TMJ DD; and group 4: patients with a bilateral normal TMJ disk position (n = 41). Each subject underwent muscle palpation and the side-by-side number of muscle tenderness points was combined as the number of muscle tenderness points on each side. Within each group, DD with and without reduction subjects were separated into subgroups and then were analyzed. In group 1, the median muscle tenderness points on the side with painful TMJ DD without reduction was significantly higher than on the normal side (P = .019), whereas the palpation scores for painless DD patients showed no significant difference between the DD and normal sides. These results indicated painful disk displacement to possibly be correlated with ipsilateral muscle tenderness.

Arthroscopic lysis and lavage are effective when arthrocentesis is not successful in TMJ ID and OA

Aims: This study aimed to analyse the effects of TMJ arthroscopic lysis and lavage for patients with internal derangement or osteoarthritis after conservative treatment and arthrocentesis had not been successful. Method: TMJ arthroscopic lysis and lavage were performed in 31 patients with unilateral disk displacement and/or osteoarthritis. Postoperative mouth-opening exercises were conducted together with intraoral administration of NSAIDs. Pre- and postoperative findings on maximal mouth opening and visual analogue scales (0–100) regarding pain at rest, pain with mandibular motion, pain on chewing and interference with daily life were compared before and after arthroscopic surgery.

Influence of unilateral disc displacement on the stress response of the temporomandibular joint discs during opening and mastication.

The temporomandibular joint plays a crucial role in human mastication acting as a guide of jaw movements. During these movements, the joint is subjected to loads which cause stresses and deformations in its cartilaginous structures. A perfect balance between the two sides of the joint is essential to maintain the physiological stress level within the tissues. Therefore, it has been suggested that a derangement of the joint is a contributing factor in the development of mandibular asymmetry, especially if problems of the temporomandibular joint start in childhood or adolescence. To analyze the movement of the mandible and the stresses undergone by the discs, two finite element models of the human temporomandibular joint including the masticatory system were developed, one corresponding to a healthy joint and the other with a unilateral anterior disc displacement with their movement controlled by muscle activation. A fibre-reinforced porohyperelastic model was used to simulate the behaviour of the articular discs. The stress distribution was analyzed in both models during free opening and closing, and during the introduction of a resistant force between incisors or molars. It was found that a slight unilateral anterior disc displacement does not lead to mandibular asymmetry but to a slight decrease of the maximum gape. With the introduction of a restriction between incisors, the maximum stresses moved to the anterior band in contrast to what happened if the restriction was imposed between molars where maximum stresses were located more posteriorly. Finally, the presence of a unilateral displacement of the disc involved a strong change in the overall behaviour of the joint including also the healthy side, where the maximum stresses moved to the posterior part.

Unilateral Posterior Crossbite is Not Associated with TMJ Clicking in Young Adolescents

Unilateral posterior crossbite has been considered as a risk factor for temporomandibular joint clicking, with conflicting findings. The aim of this study was to investigate a possible association between unilateral posterior crossbite and temporomandibular disk displacement with reduction, by means of a survey carried out in young adolescents recruited from three schools. The sample included 1291 participants (708 males and 583 females) with a mean age of 12.3 yrs (range, 10.1-16.1 yrs), who underwent an orthodontic and functional examination performed by two independent examiners. Unilateral posterior crossbite was found in 157 participants (12.2%). Fifty-three participants (4.1%) were diagnosed as having disk displacement with reduction. Logistic regression analysis failed to reveal a significant association between unilateral posterior crossbite and disk displacement with reduction (odds ratio = 1.3; confidence limits = 0.6-2.9). Posterior unilateral crossbite does not appear to be a risk factor for temporomandibular joint clicking, at least in young adolescents.

Discrimination of internal derangement of temporomandibular joint by lateral cephalometric analysis

The purposes of this study were to analyze the progress of internal derangement (ID) of the temporomandibular joint (TMJ) and to find critical yardsticks that can be used during lateral cephalometric analysis to identify subjects with potential ID. The sample consisted of 134 women whose primary complaints were malocclusions. They were divided into 5 groups based on the results of magnetic resonance imaging of bilateral TMJs: bilateral normal disc position, unilateral disc displacement with reduction (DDR) and contralateral normal disc position, bilateral DDR, unilateral DDR and contralateral disc displacement without reduction (DDNR), and bilateral DDNR. Thirty-six cephalometric variables from their lateral cephalograms were analyzed with 1-way ANOVA and discriminant analysis to determine the key factors in identifying subjects with TMJ ID. Backward positioning of the mandible, clockwise rotation of the mandible, proclination of the mandibular incisors, and increase in overjet intensified gradually with the progression of TMJ ID, and the subjects with bilateral DDNR showed the greatest changes in dentofacial morphology. Stepwise variable selection in discriminant analysis identified the following 2 variables: mandibular incisor to Frankfort horizontal plane angle and overjet. Discriminant analysis resulted in the correct classification of 79.1% of the subjects and showed that those with smaller mandibular incisor to Frankfort horizontal plane angles and larger overjets had high possibilities of TMJ ID. This study suggests that some cephalometric variables can be used as an auxiliary diagnostic tool to help identify patients with potential TMJ ID.

Comparison of skeletal and dental morphology in asymptomatic volunteers and symptomatic patients with unilateral disk displacement with reduction.

The purpose of this study was to evaluate the effect of unilateral disk displacement with reduction (UDDR) on the skeletal and dental pattern of affected individuals. There were 18 symptomatic female patients and 46 asymptomatic normal female volunteers. All study participants had bilateral high-resolution magnetic resonance scans in the sagittal (closed and open) and coronal (closed) planes to evaluate the temporomandibular joints. Linear and angular cephalometric measurements were taken to evaluate the skeletal, denture base, and dental characteristics of the two groups. Analysis of variance was used to compare the symptomatic with the control subjects. A few skeletal differences were found. There was an overall reduction in length of the anterior (S-Na) and posterior (S-Ba) cranial base measurements in the UDDR group. The cranial base angle was also increased. Both upper and lower dentures bases were retropositioned. The posterior ramal height (Ar-Go) was shorter in the symptomatic group. This study showed that alterations in skeletal morphology may be associated with UDDR. The mechanisms that produce DD or the mechanisms that cause this skeletal alteration are yet to be clarified. This study suggests that subjects with UDDR may manifest altered craniofacial morphology. The clinician should be aware of this possibility, especially for growing patients.

Analysis of kinesiograph recordings and masticatory efficiency after treatment of non-reducing disk displacement of the temporomandibular joint.

The purpose of this study was to clarify the kinesiographs of chewing movement and masticatory efficiency before and after treatment in patients with non-reducing disk displacement of the temporomandibular joint (TMJ). Twenty patients who were diagnosed with unilateral non-reducing disk displacement of the TMJ were treated with pumping of the joint with injection of sodium hyaluronate. Chewing movement patterns in these patients were evaluated, using mandibular kinesiography (MKG) at their initial visit and at mean 19-month follow-up and the results were compared. Masticatory efficiency was also measured. As controls, 23 volunteers without TMJ dysfunction were employed. Far from the results of normal volunteers, chewing movement patterns of the patients on MKG did not show deviation to the chewing side in the TMJ-unaffected-side chewing in the horizontal plane. However, such patterns of the patients became similar to those of normal volunteers after treatment. Masticatory efficiency of the patients improved after treatment, though it was impaired at initial visit. The MKG and masticatory efficiency test appeared to be a useful method of comparing masticatory function before and after treatment in patients with non-reducing disk displacement of the TMJ.

Long-term study of temporomandibular joint surgery with alloplastic implants compared with nonimplant surgery and nonsurgical rehabilitation for painful temporomandibular joint disc displacement

Purpose: The purpose of this study was to determine the long-term objective and subjective outcomes of temporomandibular joint (TMJ) implant surgery for the treatment of painful TMJ disc displacement using temporary Silastic (Dow Corning Corporation, Midland, MI), permanent Silastic, or Proplast (Vitek, Houston, TX) implants to replace the disc. These cases were compared with other cases of the same diagnosis treated with either nonsurgical rehabilitation or nonimplant surgery involving discectomy or disc repair procedures. Materials and Methods: A cross-sectional study was conducted among 466 patients who received treatment for unilateral or bilateral TMJ disc displacement before January 1, 1990. The 5 treatment groups noted above were compared for long-term outcomes. Objective outcome measurements for jaw function were performed using a calibrated examiner and the Craniomandibular Index (CMI). Subjective (self-reported) outcomes were obtained relative to jaw function (Mandibular Function Impairment Questionnaire [MFIQ]), symptom severity (Symptom Severity Index [SSI]), and the impact of pain (Global Pain Impact [GPI] scale). Results: The results, adjusted for gender, baseline tomogram score, and baseline symptom scores, showed that the nonsurgical rehabilitation group (n = 159) and the group having TMJ surgery without implants (n = 149) had statistically better results than the group who underwent surgery with a Proplast implant (n = 94). These between-group differences included both objective signs (CMI), and subjective reports of jaw function (MFIQ), symptom severity (SSI), and global pain impact (GPI). The MFIQ score associated with the nonsurgical rehabilitation group was also statistically better than for the Silastic implant groups, including both the temporary (n = 31) and permanent (n = 33) implants. Clinical differences between groups were slight. Conclusion: This study suggests that the use of interpositional disc implants in TMJ surgery is not associated with improved outcomes when compared with nonimplant surgery or nonsurgical rehabilitation. © 2002 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 60:1400-1411, 2002

Analysis of post-treatment electromyographs in patients with non-reducing disc displacement of the temporomandibular joint.

The purpose of this study was to clarify the electromyographic property of chewing movement before and after treatment in patients with non-reducing disc displacement of the temporomandibular joint (TMJ). Twenty patients who were diagnosed with unilateral non-reducing disc displacement of the TMJ were treated by pumping and injection of sodium hyaluronate into the joint. Chewing movement in these patients was evaluated by electromyography (EMG) at the initial visit and at mean 19-month follow-up and the results were compared. Chewing movement in 23 normal controls were also examined. Duration of contraction, cycle time and integrated value at the initial visit which were different from those in the controls without TMJ dysfunction tended to be at the control level mean 19 months after treatment of pumping and injection of sodium hyaluronate into the joint in patients with non-reducing disc displacement of the TMJ. Electromyography appeared to be a method of documenting the chewing movement which was impaired at initial visit improved after treatment in patients with non-reducing disc displacement of the TMJ.

Multifactorial comparison of disk displacement with and without reduction to normals according to temporomandibular joint hard tissue anatomic relationships

Statement of Problem. There is disagreement about the predictive value of temporomandibular joint tomographic anatomy in the diagnosis of internal derangements. Purpose. This study aimed to identify multifactorial temporomandibular hard tissue relationships that differentiate disk displacement with reduction and disk displacement without reduction from normals. Material and Methods. Temporomandibular joint tomograms from females diagnosed with unilateral disk displacement with (n=84) or without (n=78) reduction were compared to 42 asymptomatic normal joints with the use of 14 linear and angular measurements and 8 ratios. A validated classification tree model was tested for accuracy with sensitivity, specificity, goodness of fit, and the amount of log likelihood accounted for. The tree model was compared with a multiple logistic regression model and univariate testing. Results. The disk displacement with reduction tree model consisted of 3 disease and 2 normal pathways with interactions between fossa width to depth ratio, condyle position, and linear posterior joint space. This class was characterized by either a much wider- and shallower-than-average fossa shape and/or by a moderately posterior condyle position when the fossa shape was average to deeper and/or narrower. The logistic regression and univariate models also suggested wider and/or shallower fossae, as well as longer eminence length. The disk displacement without reduction tree model consisted of 2 disease pathways and 1 normal pathway. Interactions characterized this class by either a posterior to very posterior condyle position or by a much deeper than average fossa depth when the condyle position was concentric to anterior. The logistic regression model emphasized greater fossa depth and width versus normals. The tree models conservatively predicted the disease classes: Rescaled Cox and Snell R2 37.0%, sensitivity 70.2%, and specificity 90.5% for disk displacement with reduction; R2 28.8%, sensitivity 66.7%, and specificity 85.7% for disk displacement without reduction. Conclusion. Within the limitations of this study, hard tissue relationships revealed by central tomogram sections were able to model notable differences between disk displacement with reduction and disk displacement without reduction versus asymptomatic normals when temporomandibular joints were examined as a multifactorial system typified by interactions of fossa width to depth proportions and condyle position. While substantial, the hard tissue predicted only part of the biology. The model could be broadened by additional factors and interactions. (J Prosthet Dent 2002;87:298-310.)

Multifactorial modeling of temporomandibular anatomic and orthopedic relationships in normal versus undifferentiated disk displacement joints

Statement of Problem. There is persistent dispute about the diagnostic value of hard tissue anatomic relationships in predicting temporomandibular joint disorders and normals. Purpose. The goal of this study was identification of multifactorial temporomandibular hard tissue relationships that differentiate asymptomatic normal joints. Material and Methods. Central section lateral tomograms of 162 female temporomandibular joints with pooled diagnoses of unilateral disk displacement with and without reduction were compared to 42 female asymptomatic normal joints using 14 linear and angular measurements and 8 ratios. A validated classification tree model was tested for accuracy with sensitivity, specificity, goodness of fit, and the amount of the log likelihood accounted for. The tree model was compared with a multiple logistic regression model and univariate testing. Results. The classification tree model consisted of 3 asymptomatic and 4 disk displacement terminal nodes consisting of interactions of condyle position with measures of fossa size and shape, of which mainly average nonextreme measurements and more frequent concentric ranges typified the asymptomatic joints. The logistic regression and univariate models also incorporated condyle position and size, but the logistic regression accounted for less of the log likelihood than the tree (23.3% vs. 32.6% Rescaled Cox and Snell R2). The tree and the logistic regression models were moderately good predictors for distinguishing normals from disk displacement joints (sensitivity 67.9% and 72.2%, specificity 85.7% and 76.2%, respectively). Although the univariate analysis showed that the asymptomatic joints had smaller mean fossa width to fossa depth ratios (P<.0005), shorter mean eminence length (P<.007), and more concentric to anterior mean condyle position (P<.049), overlap in most of the ranges limited the predictive value. Conclusion. Within the limitations of this study, multifactorial analysis revealed that several subsets of asymptomatic temporomandibular joints could be distinguished from joints with disk displacement according to hard tissue measurements taken from central section tomograms. In general, asymptomatic normal joints were typified by interactions of less extreme ranges of fossa size, shape, and condyle position. (J Prosthet Dent 2002;87:289-97.)

Multifactorial analysis of differences in temporomandibular joint hard tissue anatomic relationships between disk displacement with and without reduction in women

Statement of problem. Without multifactorial models, it is difficult to resolve whether hard tissue tomographic relationships can distinguish differences between temporomandibular joint (TMJ) internal derangement diagnoses. Purpose. The purpose of this study was to use multifactorial models to examine whether there are hard tissue anatomic and orthopedic characteristics that distinguish temporomandibular joints with disk displacement with reduction from disk displacement without reduction. Material and methods. TMJ tomograms from female patients who had unilateral disk displacement diagnosed with (n = 84) or without (n = 78) reduction were compared with the use of 14 linear and angular measurements and 8 ratios. A representative classification tree model was tested for fit with sensitivity, specificity, accuracy, and likelihood accountability, and the results were compared with a multiple stepwise logistic regression model and univariate analysis. Results. Disk displacement without reduction joints had longer mean postglenoid fossa heights (P<.0005), greater mean fossa depth (P<.017), and narrower mean absolute superior joint spaces (P<.041) than disk displacement with reduction joints (univariate t test). The classification tree had 4 terminal nodes; to differentiate the joints, it used the eminence radius and the absolute superior joint space to anterior joint space ratio subordinate to the postglenoid process height. The tree model accounted for 31.4% of the likelihood (Rescaled Cox and Snell R2) with 73.5% accuracy (sensitivity 82.6% and specificity 65.4%). Disk displacement without reduction joints had either deeper posterior fossa walls or posterior walls of average length combined with a superior-to-anterior joint space ratio of less than 0.83; this suggests a more open-wedge-shaped anterior joint space combined with a less-rounded articular eminence. In contrast, most disk displacement with reduction joints had shorter posterior fossa wall height combined with more equal or larger superior-to-anterior joint spaces. The logistic regression model was less accurate than the classification tree model (sensitivity 60.9%, specificity 66.7%) and accounted for only 9.9% of the likelihood (Rescaled Cox and Snell R2) and 63.6% accuracy. The postglenoid process height was the strongest differentiating factor in all models. Conclusion. Hard tissue relationships revealed by central tomogram sections were able to model notable differences between disk displacement with and without reduction joints when examined as contingency-based multifactorial systems. (J Prosthet Dent 2001;86:407-19.)

The effect of surgically induced anterior disc displacement of the temporomandibular joint on the midface and cranial base.

The purpose of this study is to investigate the effect of unilateral TMJ disc displacement on the midface and cranial base. Thirteen 10-week-old rabbits, eight controls and five experimental were included in this study. The five experimental rabbits had surgically created unilateral disc displacement. Animals were sacrificed at 22 weeks and frontal, occlusal, and lateral oblique radiographs were made of the skulls. The occlusal radiograph demonstrated that the glenoid fossa on the experimental side was located more anterior. The oblique radiograph demonstrated the root of the zygomatic arch the experimental side was inferior. The anterior aspect of the fossa was more inferior on the frontal radiograph. A previous study suggested a shortening in the ramal height. This study suggests an alteration of the cranial articular fossa. Thus, it is suggested that disc displacement is capable of producing asymmetry in the developing mandible and cranial base.

Mandibular height asymmetry following experimentally induced temporomandibular joint disk displacement in rabbits

Objective. The purpose of this study was to test the hypothesis that nonreducing disk displacement of the temporomandibular joint causes mandibular asymmetry. Study design. Unilateral anterior temporomandibular joint disk displacement with intact posterior disk attachment was surgically created in the right joints of seven growing rabbits. In each of seven sham animals, the right temporomandibular joint was surgically opened without any disk manipulation. Seven animals served as references. For identification of ramal growth and inferior growth at the mandibular base, tantalum implants were inserted into the mandibular body. Lateral cephalograms were exposed repeatedly throughout the 3-month investigation period. Kruskal-Wallis one-way analysis of variance was used to compare the groups. Results. Compared with the sham and reference groups, the experimental group exhibited a deviant growth pattern, with inferiorly directed growth along the mandibular base and in the gonial area. The ramal height was significantly shorter on the side with disk displacement. No significant side difference was present in the sham and reference groups. Conclusions. Disk displacement can cause mandibular asymmetry in growing rabbits, including shortening of the mandibular ramus and excessive inferiorly directed bone growth along the lower border of the mandible.

Presence of denatured hemoglobin deposits in diseased temporomandibular joints

Purpose: The purpose of this study was to test the hypotheses that hemoglobin recovered by arthrocentesis of the superior joint space of symptomatic human temporomandibular joints (TMJs) is “old” hemoglobin that was not iatrogenically introduced by the arthrocentesis procedure and that it exists primarily in a non-native or denatured conformation state that may be sufficient to catalyze a reaction leading to the formation of damaging free radicals. Patients and Methods: Twelve patients diagnosed with a unilateral articular disk displacement with TMJ arthralgia were included in this study. A superior joint space arthrocentesis was performed in the affected TMJ, and outflow lavage volumes were collected in serial 2-mL fractions. α-Hemoglobin/albumin ratios were determined for each collected fraction by densitometric analysis of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). In addition, 3,3′,5,5′-tetramethylbenzidine (TMB) assays were used to determine the conformation state of the recovered hemoglobin. Results: High α-hemoglobin/albumin ratios relative to that of serum (at least 10 times greater) were observed in several collected fractions of TMJ lavage fluid in all subjects studied. Because the tissue half-life of hemoglobin is significantly longer than that of albumin, these findings indicate that much of the hemoglobin recovered by arthrocentesis of symptomatic TMJs represents “old” hemoglobin that was present in the joint before the procedure. Furthermore, based on reactivity in the TMB assay, we estimate that up to 89% of the α-hemoglobin present in TMJ lavage fluid samples exists in a denatured state. Conclusions: These results indicate that a significant amount of hemoglobin recovered by arthrocentesis of symptomatic TMJs exists in a denatured state and was present in the joint before arthrocentesis. Recent studies suggest that denatured hemoglobin may contribute redox active iron that can catalyze a reaction, leading to the formation of damaging free radicals. Such a process may represent one of the earliest molecular events involved in the pathogenesis of degenerative TMJ disease.

CPSC launches publication on product-related injuries

This retrospective study was designed to analyze the relationships between temporomandibular joint (TMJ) disk displacement and skeletal deformities in orthodontic patients. Subjects consisted of 460 adult patients. Before treatment, lateral cephalograms and TMJ magnetic resonance imaging (MRI) were recorded. Subjects were divided into six groups based on TMJ MRI according to increasing severity of TMJ disk displacement, in the following order: bilateral normal TMJs, unilateral disk displacement with reduction (DDR) and contralateral normal, bilateral DDR, unilateral disk displacement without reduction (DDNR) and contralateral normal, unilateral DDR and contralateral DDNR, and bilateral DDNR. Subjects were subdivided sagittally into skeletal Class I, II, and III deformities based on the ANB (point A, nasion, point B) angle and subdivided vertically into hypodivergent, normodivergent, and hyperdivergent deformities based on the facial height ratio. Linear trends between severity of TMJ disk displacement and sagittal or vertical deformities were analyzed by Cochran–Mantel–Haenszel test. The severity of TMJ disk displacement increased as the sagittal skeletal classification changed from skeletal Class III to skeletal Class II and the vertical skeletal classification changed from hypodivergent to hyperdivergent. There were no significant differences in the linear trend of TMJ disk displacement severity between the sexes according to the skeletal deformities. This study suggests that subjects with skeletal Class II and/or hyperdivergent deformities have a high possibility of severe TMJ disk displacement, regardless of sex.

Effect of a surgically created disk displacement on mandibular symmetry in the growing rabbit

The purpose of this study was to evaluate the contribution of unilateral disk displacement to growth changes in the young New Zealand White rabbit. Ten female rabbits aged 10 weeks were included in this study. The five experimental rabbits had unilateral anterior disk displacement surgery. The five controls had no surgery. The rabbits were killed at 22 weeks of age, and the mandibles hemisected and radiographed. Cephalograms were digitized and analyzed by conventional methods. The gross appearance showed shortening and flattening of the articulating surface in the experimental group (P < 0.05). No significant shortening and flattening was found in the control group. These observations suggest that surgically created internal derangement can produce altered growth in the mandible.

顎関節症のＭＲ画像による検討 臨床症状と円板動態異常との関連性について

MR imaging is useful in the diagnosis of bilateral internal derangement of the temporomandibular joint. This study was performed to investigate the correlation between clinical symptoms and displacement of the bilateral articular disk in patients with temporomandibular joint disorders (TMJD). A series of 170 patients who had signs and symptoms of TMJDs (TMJ pain, TMJ sound, trismus) were examined bilaterally by MR imaging. One hundred twenty-six patients had only unilateral symptoms, but 55 (44%) of them showed bilateral disk displacement. Among 93 patients with unilateral TMJ pain, 89% showed disk displacement (22 TMJs with reduction, 61 TMJs without reduction) on the symptomatic side, and 44% showed disk displacement on the asymptomatic side. Among 53 patients with unilateral TMJ sound, 96% showed disk displacement (28 TMJs with reduction, 23 TMJs without reduction) on the symptomatic side, and 53% showed disk displacement on the asymptomatic side. In patients with severe trismus (interincisal opening distance <39mm), unilateral or bilateral disk displacement without reduction was frequently found. The results indicate that examinations by MR imaging are important for the diagnosis of internal derangement of the temporomandibular joint.