Bone tissue is continuously restructured in response to changes in applied force, such as those associated with exercise and locomotion. Examining how the structure of the jawbone varies with masticatory force may illuminate the mechanisms that lead to the reconstruction of bone tissue. In other words, foods that require more chewing force may lead to increased bone formation and impact the shape of the jawbone.
Researchers at Tokyo Medical and Dental University, the Japan Agency for Medical Research and Development, and Kyoto University have uncovered how and under what circumstances jawbone reconstruction takes place. While previous studies have correlated the hardness of food with jaw structure, whether masticatory force could directly impact bone structure was unclear.
In the new study, the researchers found new information about the cellular and molecular changes that enable bone to adapt to changes in mechanical stress. The researchers created a novel mouse model of increased mastication in which mice were fed harder foods to increase chewing force and predicted if increased chewing directly led to changes in jawbone structure using a computer simulation.
Histological and gene expression analyses revealed that the mechanical loading onto the jawbone changes cytokine expression of the osteocytes in the bone, resulting in enhanced bone formation.
“Although there was existing evidence for the correlation between variations in facial profile and differences in mastication force, evidence for causation was lacking,” said Masamu Inoue of the Tokyo Medical and Dental University and co-first author of the study. “Additionally, the absence of an animal model of increased mastication made it difficult to study this topic in prior research.”
The researchers found that the width of the masseter muscle, which is critical for mastication, increased in the mice fed a hard diet. The hard diet led to more activation in the primary cortex of the brain, which controls the masticatory muscles. Thus, the hard diet increased chewing and the amount of force applied to the jawbone.
In vivo microcomputed tomography analysis showed that mechanical load onto the jawbone by the hard diet affected its shape in the way predicted by the computer simulation. The simulation also indicated that these morphological changes redistributed the mechanical stress generated in the bone by the hard diet, indicating that the jawbone is able to adapt its shape to changes in mechanical force.
Additionally, the researchers found that increasing the force applied to the jawbone stimulated osteocytes to produce more IGF-1, one of the main growth factors that promote bone formation. This alteration led to bone formation, resulting in morphological changes in the jawbone.
“Our data indicate that masticatory force can prompt changes in facial structure by modulating the function of cells that regulate bone reconstruction,” said coauthor Tomoki Nakashima of the Tokyo Medical and Dental University. “This discovery, that increased chewing itself can directly change the shape of the jawbone, could facilitate the development of treatments for skeletal abnormalities, such as jaw deformities.”
The study, “Forceful Mastication Activates Osteocytes and Builds a Stout Jawbone,” was published by Scientific Reports.