Unilateral Loss of Maxillary Molars in Young Mice Leads to Bilateral Condylar Adaptation and Degenerative Disease

Abstract

The adaptive response of the mandible and temporomandibular joint (TMJ) to altered occlusion in juvenile patients is presently unclear. To address this question, we established a mouse model in which all molars were extracted from the maxillary right quadrant in prepubertal, 3-week-old mice and analyzed morphological, tissue, cellular, and molecular changes in the mandible and condyle 3 weeks later. Unilateral loss of maxillary molars led to significant, robust, bilateral changes, primarily in condylar morphology, including anteroposterior narrowing of the condylar head and neck and increased convexity at the condylar surface, as determined by geometric morphometric analysis. Furthermore, both condyles in experimental mice exhibited a degenerative phenotype, which included decreased bone volume and increased mineral density near the condylar head surface compared to control mice. Changes in condylar morphology and mineralized tissue composition were associated with alterations in the cellular architecture of the mandibular condylar cartilage, including increased expression of markers for mature (Col2a1) and hypertrophic (Col10a1) chondrocytes, suggesting a shift toward differentiating chondrocytes. Our results show significant bilateral condylar morphological changes, alterations in tissue composition, cellular organization, and molecular expression, as well as degenerative disease, in response to the unilateral loss of teeth. Our study provides a relatively simple, tractable mouse tooth extraction system that will be of utility in uncovering the cellular and molecular mechanisms of condylar and mandibular adaptation in response to altered occlusion.

The effect of tooth loss on the temporomandibular joint space: A CBCT study

“…According to Rosado et al ( 2021 ), there is a notable decrease in bone volume in the glenoid fossa among those who are edentulous. Furthermore, a further investigation conducted by Chen et al ( 2022 ) revealed that the loss of teeth, even unilaterally, can lead to a reduction in condyle bone volume in an in vivo experimental model. Hence, the duration of edentulism may influence the morphological alterations of the condylar process and, consequently, its positioning within the TMJ.…”

The effect of orthodontic treatment with premolar extraction against the temporomandibular joint and masticatory muscles: A review

“…The TMJ is classified as a compound joint. The TMJ consists of hard tissue, soft tissue, ligaments, muscles of mastication and neck, nerves, and blood vessels [1,10,11]. There are two main movements at the TMJ joint (Figure 2 and 3), namely rotation and glide or translational movement.…”

“…Glide or translational movement (Figure 4) is a movement in which each object point moves concurrently with the same speed and direction. Translation happens when the (lower) jaw moves forward, protruding more so that the ramus, condyles, and teeth all move in the same degree and direction of inclination in the masticatory system [1,9,10,12].…”