Short-Term Changes in Occlusal Forces Do Not Affect Mandibular Condylar Form in Mature Mice

The premature loss of primary teeth in children may lead to numerous issues, such as decreased arch length/width/perimeter and increased malocclusion, increasing the need for orthodontic treatment. Moreover, a decrease in occlusal forces due to premature, unilateral tooth loss in the upper right quadrant in immature mice (i.e., pre-puberty), may lead to significant bilateral changes in the skull form (i.e., shape and size), especially the mandibular condyles after 3 weeks. In the present study, we aimed to determine the extent of the mandibular and condylar changes after unilateral tooth loss in mature mice (i.e., post-puberty) within the same 3-week time frame.

We extracted the three maxillary right molars in 8-week-old mice and analysed the skulls after 3 weeks. Eight-week-old mice are sexually and dentally mature, as mice reproduce at 6 weeks of age. We examined the skulls of control (non-extracted) and experimental (extracted) mice using micro-computed tomography (microCT), geometric morphometrics, linear measurements, and histology, focusing on the mandibular condyle and neck.

We performed three pairwise comparisons: non-extracted (left) vs. extracted (right) sides in the same experimental mouse; left side (non-extracted) of experimental mice vs. left side of wildtype mice; and right side (extracted) of experimental mice vs. right side of wildtype mice. We observed no or little change in mandibular and condylar forms in all three pairwise comparisons within the 3-week time frame.

Unlike in immature mice where significant bilateral changes in the shape and size of the mandibular condyles were observed within 3 weeks after tooth loss, we did not observe any significant changes to the mandible and condyles when teeth were extracted in mature mice within the same 3-week time frame. Thus, our current study suggests that whereas normal occlusal forces are essential for the proper growth and development of the mandible and condyles in immature mice, unilateral occlusal changes do not alter the form of the mandible or condyles in mature mice within the same time frame.