Morphology of the temporomandibular joint in subjects with Class II Division 2 malocclusions.

INTRODUCTION: Temporomandibular joint (TMJ) morphology has not been studied adequately in subjects with various types of malocclusion, and it is not known if TMJ morphology and facial morphology are related. Such knowledge might assist in the establishment of biological treatment strategies, especially when the TMJ is the target of the treatment plan. The aim of this study was to explore the morphological characteristics of the TMJ in subjects with skeletal Class II Division 2 malocclusions. METHODS: The material consisted of corrected lateral tomograms of 94 joints in 47 subjects with Class II Division 2 malocclusions (age range, 8.3-42.8 years). The subjects were divided into 5 groups according to age. RESULTS: Intragroup comparisons showed statistically significant differences for condylar angle, condylar position, eminence height, eminence inclination, ramus height, and condylar-neck height. These differences were found mainly between the youngest and oldest groups. The Pearson correlation coefficient was greater than 0.60 for eminence height and eminence inclination, eminence height and ramus inclination, eminence inclination and ramus inclination, fossa posterior-eminence midpoint and fossa posterior-eminence top, and fossa posterior-eminence midpoint and fossa posterior-fossa roof. Condylar shape was most often round, followed by oval, flattened, and triangular; fossa shape was most often oval, followed by triangular, trapezoidal, and round. CONCLUSIONS: The results suggest that (1) fossa morphology and condylar length attain their final sizes early; (2) articular eminence and ramus morphology (height, inclination) have great variability; (3) some joint components such as eminence height with eminence inclination, eminence height with ramus inclination, eminence inclination with ramus inclination, and fossa anteroposterior dimensions are highly correlated with each other; and (4) the most prevalent condylar and fossa anteroposterior shape is oval.

Condyle and fossa shape in Class II and Class III skeletal patterns: a morphometric tomographic study.

INTRODUCTION: The purpose of this investigation was to study the shapes of the condyle and the glenoid fossa in patients with Class II Division 1, Class II Division 2, and Class III malocclusions. METHODS: Axially corrected tomograms of 189 patients were used (109 Class II Division 1, 47 Class II Division 2, and 33 Class III). Five points on the condyle and 7 on the outline of the fossa were digitized. Size was assessed by the centroid size of each structure, and measurements of shape were made by principal component analysis of the Procrustes residuals. RESULTS AND CONCLUSIONS: Inspection of the principal components of shape showed that shape variability of the condyle was mainly related to inclination of the condylar head; shape variability of the fossa was related to inclination of the eminence and fossa height. Centroid size was correlated to age in the Class III group only. Condylar and fossa shapes were found to be different between the groups; the Class III group had a more elongated and anteriorly inclined condylar head and a wider and shallower fossa. In the Class III group, the condyle was closer to the roof of the fossa. The 2 Class II divisions differed only in the position of the condyle in the fossa, which was situated more anteriorly in the Class II Division 1 group.

Effect of loading rate on bond strength.

The purpose of this study was to examine the effect of loading rate on the bond strength of brackets bonded to enamel. Forty premolars were used and brackets were bonded with a chemically cured or a light-cured adhesive, mounted on a testing machine, and debonded under shear stress at two loading velocities: a standard 1 mm/min, and a fast 200 mm/min which better approximates the actual jaw velocity during chewing. Bond strength results (N) were analyzed with two-way analysis of variance (loading rate, adhesive) (alpha = 0.05). An increased loading rate resulted in decreased bond strength, probably due to the induction of a stiff body response and elimination of the viscoelastic properties of the resin. The results indicated a similar effect on both chemically cured and light-cured adhesives, thus emphasizing the need for standardized test conditions in bond strength protocols. The implication of loads generated during chewing must be considered when estimating the long-term survival of the bond.

The treatment effect of mandibular protrusive appliances on the glenoid fossa for Class II correction.

A study was undertaken to determine the contribution of glenoid fossa modification in the correction of skeletal Class II malocclusions. Individually corrected lateral tomograms of 35 patients (18 boys and 17 girls) between the ages of 7.96 and 15.06 years were used. The subjects were selected on the basis of the criteria that they were suitable for treatment with a mandibular protrusive appliance (activator). The mean duration of activator treatment was 1.33 years. Tomograms were taken on a pre- and posttreatment basis. The tomograms were scanned and digitized on screen using a common software program. Points were located on each tomogram and specific linear measurements were used to evaluate any changes in glenoid fossa morphology. Paired t-tests were applied for the left and right sides separately and between the before and after treatment measurements. Paired t-tests were also applied between the left and right sides to test for any difference between the sides. The results of this study demonstrated that there are no positive radiographically depictable contributions from glenoid fossa modification for the correction of skeletal Class II malocclusions treated with mandibular protrusive appliances (activators). In addition, no statistically significant differences were found between right and left sides denoting relative symmetry. It is concluded that, contrary to animal research and magnetic resonance findings, it seems possible that glenoid fossa modeling is not induced by mandibular protrusive appliances during treatment of skeletal Class II problems.

Salivary metal levels of orthodontic patients: a novel methodological and analytical approach.

The purpose of this study was to qualitatively and quantitatively assess the nickel, chromium, and ferrous levels in a population of 17 orthodontic patients undergoing treatment, compared with seven untreated individuals, employing a novel methodological approach and a new analytical technique. Salivary samples obtained from patients before and after rinsing with double distilled water were processed for Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) for simultaneous estimation of the concentration of the metallic elements. No statistically significant difference was detected between control and patient groups with respect to salivary metal content, regardless of element. The range of salivary metal levels found did not exceed those of daily intake through food and air. The lack of a continuous monitoring scheme for salivary metal concentrations in real time may impose substantial obstacles to defining the release rate of metals in vivo. The results of this study emphasize the necessity of incorporating the dimension of time in assessing the release potential of orthodontic alloys.

The effect of mandibular protrusive (activator) appliances on articular eminence morphology.

In studying the response of the glenoid fossa to mandibular protrusive appliances, apart from the condyle, much attention has been focused on what happens to the posterior wall of the fossa (post-glenoid process). Remarkably, the articular eminence has been overlooked, although it is the most adaptive area of the temporomandibular joint. The purpose of this study was to explore the type of response of the articular eminence morphology to the use of mandibular propulsive appliances (activators). The study material consisted of individually corrected pre- and posttreatment lateral tomograms of 35 patients (18 boys and 17 girls) who had been diagnosed as suitable for treatment with a mandibular protrusive appliance (activator). The tomograms were scanned and digitized on screen, and points located on each tomogram and linear measurements were used to evaluate any change in glenoid fossa morphology. Paired t-tests were applied separately for the left and right sides to compare pre- and posttreatment measurements. Paired t-tests were also applied to test any difference between the left and right sides. The results of this study show that there is no statistically significant change in articular eminence morphology (height and inclination) as a result of using mandibular protrusive appliances.

Role of suprahyoid musculature on mandibular morphology and growth orientation in rats.

This study was undertaken in rats to study the influence of the suprahyoid muscles on mandibular growth, morphology, and orientation. The aim was to investigate the effect of bilateral suprahyoid muscle myectomy on the skeletal growth and orientation of the mandible and on its orientation in rats. Forty-eight 4-week-old rats were divided into 2 experimental and 2 control groups as follows: A, 12 animals in which bilateral excision of the anterior digastric muscle was performed; B, 12 animals in which bilateral excision of the anterior digastric, transverse mandibular, and mylohyoid muscles was performed; C, 12 animals that were sham-operated bilaterally without any muscular excision; D, 12 control animals not subjected to any operation. The experimental period was 30 days. Lateral and dorsoventral radiographs were taken on days 1 and 30, after muscular excision. Cephalometric analysis was performed for each animal according to a method and procedure established in our laboratory and described earlier. The findings support the occurrence of decreased mandibular growth in the group in which bilateral digastric, transverse mandibular, and mylohyoid excision was performed as compared with controls. In addition, the mandible in the bilateral digastric excision group exhibited a more upward orientation. It was thus proven that the absence of the suprahyoid musculature does affect both skeletal growth and orientation of the mandible.

Changes in articular eminence inclination during the craniofacial growth period.

The articular eminence of the temporomandibular joint dictates the path and type of condylar-disk complex movement. It has been suggested that a steep articular eminence inclination may predispose to temporomandibular joint dysfunction. When using functional appliances in orthodontic therapy, the bite registration is greatly affected by the articular eminence inclination. Furthermore, the articular eminence morphology has been related to specific facial types. Knowledge of how the articular eminence inclination behaves during the craniofacial growth period could help establish more biological treatment modalities. We took silicone impressions of both left and right articular fossae from 90 dried skulls. This sample consisted of three equal subgroups of skulls, each group presenting a deciduous, mixed, or permanent dentition. After the impression had set, they were removed and cut into sagittal sections 2.5 mm thick. The three middle sections were photocopied and enlarged by 200%. The inclination of each section was calculated trigonometrically, and the mean value was assigned to the inclination of the respective eminence. The data indicated that the inclination of the articular eminence changes rapidly until the completion of deciduous dentition, attaining more or less 45% of its adult value. By the age of 10 years, it was 70%-72% completed, and by the age of 20 years, it was 90%-94% completed. In conclusion, normally, the articular eminence inclination shows a symmetrical growth pattern, and it grows at a very rapid rate, attaining almost half of its adult value by the age of two years.

The postglenoid tubercle: prevalence and growth.

AIM: To quantify the prevalence and growth of the postglenoid tubercle in a skull sample and in children. MATERIAL: a) ninety skulls ranging in age from between 2 years and adulthood, b) sixtyfour corrected lateral tomograms of left and right temporomandibular joints of 32 boys and girls. Their age range was between 9 and 11 years. METHOD: Impressions of the temporal fossae of the skull material were taken with a silicone type impression material, using a face-bow for leveling the base of the impression parallel to the FH plane. Each impression was divided into two halves along a paramedian plane from the tip of the postglenoid tubercle through the middle of the articular eminence and the surface was photocopied to a 200% scale. Height was measured with an electronic caliper. The presence or absence of a postglenoid tubercle was established on the corrected tomograms. FINDINGS: Seventy-nine percent of the skulls had a postglenoid tubercle. It steadily enlarged and reached almost its final dimension by the age of 13 years. On corrected tomograms, 66% of the children showed a postglenoid tubercle. CONCLUSIONS: a) the postglenoid tubercle exists in a high percentage of human temporomandibular joints b) growth is almost completed by the age of 13, and c) there exists a right-left symmetry.