Validity of computed tomography in imaging thin walls of the temporal bone.

OBJECTIVES: To evaluate the validity of computed tomography (CT) for reproduction of the bone margins of the temporomandibular joint (TMJ). METHODS: Seven TMJ specimens were examined with a CT and then cryosectioned. The bone separating the TMJ from the middle cranial fossa, middle ear and external auditory canal was measured as the full width at half maximum (FWHM). Measurements were compared with the true thickness of the bone wall. RESULTS: There was good agreement when the bone walls were thicker than 1 mm: accuracy was influenced only by the angle of the bone wall to the scanning plane. Conversely, bone walls thinner than 1 mm were reproduced with a magnification that increased with decreasing bone thickness. The difference increased further as the inclination of the bone wall became greater. CONCLUSION: Measurements performed at FWHM are reliable within +/- 10% for bone walls more than approximately 1 mm thick which form an angle of less than 35 degrees to the perpendicular of the scanning plane. For bone walls thinner than 1 mm and for those thicker than 1 mm with an inclination exceeding approximately 35 degrees, partial volume effects result in a progressively increasing magnification of bone thickness.

Bone demarcation of the temporomandibular joint. Validity of clinical assessment of bone thickness by means of CT.

PURPOSE: To study the CT depiction of bone demarcations in the temporomandibular joint, using conventional window level and window width; and to evaluate observer performance in estimating bone thickness in these images. MATERIAL AND METHODS: Seven joint specimens were imaged by CT and then cryosectioned. The measurements of bone wall thickness in the images were compared to the true bone thickness at each cutting level. In addition, 4 experienced radiologists estimated the thickness of the bone walls in the images. RESULTS: The relative difference between the CT reproduction and the true bone thickness was small for bone walls thicker than 2 mm. This difference increased with the decrease in bone thickness and the increase in the inclination of the bone wall from the perpendicular to the image plane. Bone walls thinner than 1 mm were reproduced as considerably thicker than their true thickness. This resulted in a clinical overestimation of bone thickness. CONCLUSION: Both the CT representation and the interpretation of bone demarcation in the temporomandibular joint may constitute a problem. Partial volume averaging effects can result in an overestimation of bone dimensions amounting to 200% for thin bones. The central white zone in images of thin bone walls obtained with the parameters described here could serve as an indicator that could help to reduce the risk of overestimating bone thickness.

Classification and prevalence of temporomandibular joint disk displacement in patients and symptom-free volunteers.

The purposes of this study were to develop a classification system for disk displacement in the temporomandibular joint (TMJ) and to study the prevalence of the various types of TMJ disk displacement in patients and symptom-free volunteers. The study was based on bilateral MRIs of 243 patients and 57 symptom-free volunteers. Eight different types of disk displacements were identified in addition to the superior disk position and a tenth indeterminate category. Superior disk position was observed bilaterally in 18% of the patients and bilaterally in 70% of the symptom-free volunteers.

Effect of maxillomandibular fixation on condylar growth in juvenile Macaca mulatta: a cephalometric and histologic study.

The effect of maxillomandibular fixation on the growth of the mandibular condyle was studied in eight control and eight experimental male juvenile monkeys. All animals had metallic implants placed throughout the craniofacial complex in order to facilitate cephalometric analysis of growth-related changes in the maxillomandibular complex during jaw immobilization. Every 3, 6, 12, and 24 wk after insertion of the appliance two experimental animals were killed for histologic analysis. Cephalometric analysis indicated no major deviation from normal maxillary or mandibular growth in the experimental animals. The condylar growth in the experimental animals was comparable with that of the controls. Histologic analysis indicated that the articular connective tissue in experimental joints remained the same thickness as in the controls. On the postero-superior aspect of the condyle, the thickness of the prechondroblastic-chondroblastic cell layer was reduced by 70-80% in the experimental animals. On the posterior aspect this cell layer was not visible after 12 wk of fixation, but was replaced by a periosteum-like, cell-rich tissue which appeared to be active in appositional formation of cancellous bone. These results indicate that long-term maxillomandibular fixation does not cause major alterations in the growth of condyle or the entire mandible despite a profound decrease of the prechondroblastic-chondroblastic cell layer in the postero-superior and posterior regions of the condyle. The growth is probably due to a compensatory appositional bone formation along the surface of the condyle. It is also concluded that jaw mobility is not a prerequisite for normal maxillary or mandibular growth.

Coronoid process elongation in rhesus monkeys (Macaca mulatta) after experimentally induced mandibular hypomobility. A cephalometric and histologic study.

The present study provided an experimental model that allowed a cephalometric and histologic analysis of craniofacial growth in monkeys with induced translatory impairment of the mandibular condyle. Cauterization was performed anterior to the joint in nine experimental rhesus monkeys, while eight animals served as control subjects. The experimental procedure produced mandibular hypomobility in six animals, in three by means of temporomandibular joint ankylosis and in three by means of dense scar tissue formation anterior to the joint. In the remaining three experimental animals no restriction of mandibular mobility was created. Mandibular hypomobility was found to induce elongation of the coronoid process and was also associated with bone deposition in the gonial region. In contrast, normal remodeling of the gonial region was found in the experimental animals with normal range of movements and in the control animals.

Intraindividual change in the occurrence of Passavant's ridge due to change in velopharyngeal sphincter function: a videofluoroscopic study.

Passavant's ridge was studied by means of videofluoroscopy and nasopharyngoscopy in 80 patients with hypernasal speech. In patients with Passavant's ridge an improvement of the sphincter function was found to be associated with an enlargement of the ridge. It was also observed that the ridge could disappear if complete velopharyngeal closure was achieved without surgical intervention of the ridge area. The results indicate that Passavant's ridge is of compensatory origin.

Lingual numbness and speech articulation deviation associated with temporomandibular joint disk displacement.

A prospective investigation of 208 patients with painful, arthrographically verified temporomandibular joint disk displacement revealed that seven patients (3%) demonstrated lingual numbness associated with speech articulation impairment. The speech disorder was characterized primarily by a distortion in the production of /s,r,d, and t/. The lingual numbness and the speech disorder had in all cases started in association with a painful onset of permanent displacement of the temporomandibular joint disk. Local anesthetic blocking of the auriculotemporal nerve eliminated both joint pain and muscle pain and normalized tongue sensitivity and speech articulation. Placebo injections of saline solution resulted in no change. The explanation of the phenomenon is that the course of the lingual nerve for these seven patients was through the lateral pterygoid muscle rather than mesial to the muscle bundles and that an arthrokinetic myospasm resulted in compression of the lingual nerve. In order to test the hypothesis that the condition of lingual nerve entrapment in the lateral pterygoid muscle does exist, the course of the nerve was studied at dissection in 52 specimens from 26 cadaver heads. In 49 of the specimens, the lingual nerve descended deep to the lateral pterygoid muscle as has been traditionally defined. However, in three specimens, the nerve passed through the inferior belly of the muscle, revealing the condition of lingual nerve entrapment.

Velopharyngeal movement patterns in patients alternating between oral and glottal articulation: a clinical and cineradiographical study.

Eight patients who presented velopharyngeal incompetence and who spontaneously alternated between oral and glottal stop articulation were cineradiographically examined in lateral and frontal projections to compare their oral stops and glottal stop substitutions. A cineradiographic frame-by-frame analysis of the movements of the velum and the lateral and posterior pharyngeal walls was performed. During glottal stop substitutions and coarticulation involving glottal stops and oral lingual or bilabial stop gestures, all patients demonstrated either no velopharyngeal movement or impaired movement, mostly affecting the lateral pharyngeal walls. In contrast, during oral stops, moderate-to-good velopharyngeal movements were produced. Poor quality or absence of velopharyngeal movement associated with glottal stop substitutions may be misinterpreted as weakness or inability to perform motor activity. Presurgical cineradiographic or fluoroscopic analysis of a patient's speech with regard to velopharyngeal movements should therefore be based on speech sequences free from glottal stop substitutions. A careful speech analysis should also precede presurgical cineradiography.