Directional characteristics of incipient temporomandibular joint disc displacements: A magnetic resonance imaging study.

INTRODUCTION: Disc displacement (DD) is common in adolescents, but not much is understood about its cause. Assessment of the directionality of incipient DDs may provide clues about the etiology. METHODS: The sample consisted of magnetic resonance images of 143 temporomandibular joints with incipient DD from 89 preorthodontic patients (mean age, 10.8 years). The severity of DD was evaluated by grading the degree of displacement depicted in the images in the sagittal and coronal planes, and each incipient DD was categorized based on the directionality. RESULTS: Of the 143 incipient DDs, rotational anterolateral DD (43.36%) and partial anterior DD in the lateral portion (27.27%) were the most common; rotational anteromedial DD (9.09%) and partial anterior DD in the medial portion (1.40%) accounted for only 10.49%. Anterior DD was seen in 12.59%. Pure sideways shift was rare; lateral DD was seen in 2.80%, and medial DD in 3.50%. Thus, the lateral part of the joint was involved in a majority of the incipient DDs and the medial part far less. No sex difference was noted in this trend, but the difference between the right and left sides was statistically significant. CONCLUSIONS: These results indicate a predilection for the lateral part of the joint in incipient DDs and may have etiologic implications.

Novel 3-dimensional analysis to evaluate temporomandibular joint space and shape.

INTRODUCTION: The purpose of this study was to present and validate a novel semiautomated method for 3-dimensional evaluation of the temporomandibular joint (TMJ) space and condylar and articular shapes using cone-beam computed tomographic data. METHODS: The protocol for 3-dimensional analysis with the Checkpoint software (Stratovan, Davis, Calif) was established by analyzing cone-beam computed tomographic images of 14 TMJs representing a range of TMJ shape variations. Upon establishment of the novel method, analysis of 5 TMJs was further repeated by several investigators to assess the reliability of the analysis. RESULTS: Principal components analysis identified 3 key components that characterized how the condylar head shape varied among the 14 TMJs. Principal component analysis allowed determination of the minimum number of landmarks or patch density to define the shape variability in this sample. Average errors of landmark placement ranged from 1.15% to 3.65%, and none of the 121 landmarks showed significant average errors equal to or greater than 5%. Thus, the mean intraobserver difference was small and within the clinically accepted margin of error. Interobserver error was not significantly greater than intraobserver error, indicating that this is a reliable methodology. CONCLUSIONS: This novel semiautomatic method is a reliable tool for the 3-dimensional analysis of the TMJ including both the form and the space between the articular eminence and the condylar head.

Prevalence of disc displacement of various severities among young preorthodontic population: a magnetic resonance imaging study.

PURPOSE: There has been no study on the prevalence of disc displacement (DD) of different levels in children and adolescents with adequate sample size using magnetic resonance images (MRIs). This retrospective cross-sectional study was designed to investigate the relationship between increasing age and the prevalence of DD of various severities in a young preorthodontic population. MATERIALS AND METHODS: Of 199 preorthodontic patients aged 6 to 15 years visiting a private orthodontic office for initial examination, 153 patients with signs and symptoms of temporomandibular joint (TMJ) disorders had MRIs of their TMJs taken for further evaluation. Of those, 302 TMJs from 151 patients' MRIs of diagnostic quality were divided into three age groups (I: 6 to 9, II: 10 to 12, and III: 13 to 15 years). DD of each patient was categorized based on its severity from stage 0 (normal) to stage 4 (total DD without reduction). The distribution of DD stages in each age group was plotted on a line graph and statistically analyzed for intergroup comparison. RESULTS: A graphical representation of the results clearly demonstrated a trend for higher occurrence of more advanced DD with an increase in age. No gender difference was observed. Statistical analysis showed that DD was significantly more advanced in group II than group I (p < 0.01) and group III than group I (p < 0.01). CONCLUSIONS: The study revealed a high prevalence of DD in the young preorthodontic population and significant increase in the proportion of patients with more advanced stages of DD in older patients.

Assessment of optimal condylar position in the coronal and axial planes with limited cone-beam computed tomography.

PURPOSE: No quantitative standards for the optimal position of the mandibular condyle in the glenoid fossa are yet available in the coronal and axial planes. We previously reported measurements of this position in the sagittal plane, using recently developed limited cone-beam computed tomography (LCBCT) capable of imaging the craniofacial structures with high accuracy. In this study, we assessed the optimal condylar position in the coronal and axial planes. MATERIALS AND METHODS: The study included 24 joints in 22 asymptomatic patients (10 male, 12 female; age range 12-25 years, mean age 18 years) who had no disc displacement as confirmed by magnetic resonance imaging. Their joints had optimum function with the starting and end points of all functional jaw movements coincident with maximum intercuspation. Joint-space distances between the condyle and glenoid fossa were measured at the medial, central, and lateral positions in the coronal plane, and medial and lateral positions in the axial plane. RESULTS: The mean coronal lateral space (CLS), coronal central space (CCS), and coronal medial space (CMS) were 1.8 ± 0.4 mm, 2.7 ± 0.5 mm, and 2.4 ± 0.5 mm, respectively. The ratio of CLS to CCS to CMS was 1.0 to 1.5 to 1.3. The mean axial medial space (AMS) and axial lateral space (ALS) were 2.1 ± 0.6 mm and 2.3 ± 0.6 mm, respectively. There were no significant sex differences in these measurements. CONCLUSIONS: These coronal and axial data, along with previously reported sagittal data, might provide norms for 3D assessment of optimal condylar position with LCBCT.