A Novel Method to Detect 3D Mandibular Changes Related to Soft-Diet Feeding

Abstract

Craniofacial morphology varies among individuals, which is regulated by the interaction between genes and the environment. Soft-diet feeding is a widely-used experimental model for studying the association between the skeletal morphology and muscle-related loading on the bone. Traditionally, these studies have been based on linear and angular measurements provided on two-dimensional (2D) radiographs in the lateral view. However, 2D observation is based on simplification of the anatomical structures and cannot detect three-dimensional (3D) changes in detail. In this study, we newly developed a modified surface-based analysis with micro-3D computed tomography (CT) to examine and detect the 3D changes in the mandible associated with soft-diet feeding. Mice at 3 weeks of age were fed a powdered soft-diet (SD) or hard-diet (HD) of regular rodent pellets until 9 weeks of age. Micro-CT images were taken at age 9 weeks to reconstruct the anatomical architecture images. A computer-generated averaged mandible was superimposed to directly visualize the morphological phenotypes. Gross observation revealed the apparent changes at the posterior body of the mandible, the angular process and the condyle between HD and SD mice. Significant differences in the mapping indicated the regions of significant displacement in the SD mice over the averaged 3D image of the HD mice. This map revealed that vertical displacement was most evident in 3D changes. We also noted a combination of vertical, transverse and anteroposterior directions of displacement in the condylar growth, resulting in complicated shape changes in the whole condylar process in SD mice. In contrast, transverse displacement was more significant in the coronoid process. The map analysis further showed the significant outward displacement of the inner surface of the alveolar process, which consequently resulted in thinning of the alveolar process.

Masseter muscle atrophy impairs bone quality of the mandibular condyle but not the alveolar process early after induction

“…During development, the mouse mandible changes its shape and size as a result of the eruption of the teeth and the increase of the biomechanical input from masticatory muscles after weaning . These changes affect differently the alveolar process and the mandibular condyle during the transition from juvenile to adult . The maturation of bone in the alveolar process is reached before the ramus, including the mandibular condyle .…”

“…37 These changes affect differently the alveolar process and the mandibular condyle during the transition from juvenile to adult. 6,7,25,38 The maturation of bone in the alveolar process is reached before the ramus, including the mandibular condyle. 39 The mandibular condyle in rodents is influenced by higher mechanical stress than the alveolar process during mastication.…”

“…5 Also, a change in the dietary regimen from hard to soft food in young adult mice results in a decrease in masseter mass 6 and alters the shape and size of the mandibular condyle [6][7][8] and the alveolar process. 6,7 Moreover, decreased loading using soft diet showed a detrimental effect on subchondral bone in the mandibular condyle of adult mice of both sexes, but the impairment on cell maturation in the condylar cartilage was exclusively found on female individuals. 9 An alternative approach to reduce masticatory load is the intramuscular injection of botulinum toxin type A (BoNTA).…”

“…In turn, altered masticatory loading after masseter muscle resection in young rats leads to asymmetrical growth and reduced bone quality of the mandibular condyle . Also, a change in the dietary regimen from hard to soft food in young adult mice results in a decrease in masseter mass and alters the shape and size of the mandibular condyle and the alveolar process . Moreover, decreased loading using soft diet showed a detrimental effect on subchondral bone in the mandibular condyle of adult mice of both sexes, but the impairment on cell maturation in the condylar cartilage was exclusively found on female individuals …”

Altering calcium and phosphorus levels in utero affects adult mouse mandibular morphology

“…Post-pubertal hypercalcemia may reduce muscle strength and function, 33 and a reduction of masticatory muscles function decreases mandibular size. 34,35 The offspring in our study were exposed to experimental diet throughout pregnancy and continued from birth until weaning (newborn to 3-week old). Our future study will not expose offspring after birth to delineate specific in utero effects.…”