T. L. Hansson

Malocclusion associated with temporomandibular joint changes in young adults at autopsy

The purpose of this study was to identify variables of malocclusion that might be associated with previously reported temporomandibular joint morphologic findings. Before removing the left TMJ from each of 96 cadavers (age means equals 26.4 +/- 6.8 years), an intraoral examination was performed. Angle classification, crossbite, overbite, and overjet were evaluated. These parameters were analyzed with respect to their association with the following TMJ features: overall shape of the condyle and temporal bone, gross and histologic evidence of remodeling, and position of the articular disk. When combined with age, Angle Class II and III dentitions were associated with temporal and condylar deviation in form (DIF) (P less than 0.05) and more Class II dentitions were accompanied by histologic evidence of remodeling changes in the TMJs. Crossbite was associated with increasing presence of DIF in all components (P less than 0.01). Anterior crossbite was associated with DIF on the articular eminence (P less than 0.01). Deep overbite was more common in persons with flat condyles, open mandibular fossae, and anterior extension of the temporal articular surfaces (P less than 0.05). Abnormal overjet was more evident in those with DIF in the disk (P less than 0.05); greater overjet was associated with disk displacement (P less than 0.05). Considered together, abnormal overbite and overjet were associated with more extensive DIF on the condyle (P less than 0.05). In conclusion, malocclusion was associated with morphologic changes in the TMJ, particularly when combined with age. This evidence supports the belief that longer exposure to malocclusion may be associated with more extensive TMJ changes.

Histomorphometric analysis of cartilage and subchondral bone in mandibular condyles of young human adults at autopsy

After demineralization, sagittal sections were made from the lateral, the central and the medial parts of 33 mandibular condyles from people aged 20 to 36 years, and studied for undifferentiated mesenchymal (UM) cells, cartilage and subchondral bone, the thickness of which were measured. Two condyles showed a continuous layer of UM cells extending all over. In 13 condyles, UM cells were absent; 18 condyles showed variability in UM cell occurrence in one or more out of the nine standardized areas. In 14 condyles, non-hypertrophic cartilage was present, 10 condyles showed hypertrophic cartilage and in nine condyles hyperplastic cartilage. Hyperplastic cartilage was associated with minimal numbers of UM cells. In combination with hypertrophic cartilage the UM cell layer appeared less irregular. Of nine condyles with incongruence of the cartilage-bone interface and the articular surface, seven showed hyperplastic cartilage. Six out of these seven were free of bony changes. A negative correlation was found between the presence of UM cells and the condylar-cartilage thickness (p less than 0.05). These results suggest that condylar changes are initiated by alterations in the cartilage and that changes in the bone are secondary.

Histomorphometry of age and sex changes in mandibular condyles of young human adults

Changes in cartilage, subchondral bone and their interface were studied using sagittal (6-8 micron thick) sections from the lateral, central, and medial parts of 21 condyles (11 males and 10 females; aged 18-36 years). The presence of undifferentiated mesenchymal (UM) cells in the proliferative zone of the cartilage was noted. Five condyles were judged to be immature because they had hypertrophic cartilage, cartilage resorption and bone formation at the cartilage-bone interface, no compact bone in their anterior and the superior regions, and the many cartilage rests in subchondral bone. Four of these immature specimens were from males. Immature specimens had quantitatively thicker cartilage (p less than 0.01), thinner subchondral bone (p less than 0.005), and less bone, more vascular spaces and more cartilage rests, both at the cartilage-bone interface and in the subchondral bone (p less than 0.001). Of the 16 mature condyles, the older had fewer UM cells in the proliferative layer, thicker compact bone (p less than 0.05), less vascular spaces at the cartilage-bone interface (p less than 0.05) and more bone and less vascular spaces in the compact bone (p less than 0.05 and p less than 0.01 respectively). No significant differences were found between mature condyles of males and females, but females had more UM cells, less hyperplastic cartilage and fewer irregularities at the cartilage-bone interface.

Histomorphometric analysis of human mandibular condyles

DIF. Condylar changes were more extensive. Disc displacement was found in 11.6% (1 l/95) of TMJs (7/95 partial, 4/9.5 complete) and was more common in women (P < 0.05). Folding and deformation was associated with disc displacement and its direction was mainly anteromedial. Condyles without changes were elliptical and rounded whereas condyles with changes were cylindrical and flat or gable-shaped (P < 0.01). Silhouettes of each condyle type were predictable across reference planes (P < 0.01). DZF is common in this sample and its associution with TMJ form has application in radiologic diagnosis. The frequency of disc displacement and its increased presence in females corroborates findings in living subjects.