Micro/nanostructural Characteristic Changes in the Mandibles of Rats after Injection of Botulinum Neurotoxin

: Our objective was to perform a quantitative evaluation of changes in the micro/nanostructural characteristics of entheses in rats with reduced masticatory muscle functional pressure, with the aim of elucidating the mechanism whereby masticatory muscle functional pressure contributes to growth and development of the mandible from a biomechanical per-spective. Male Wister rats aged 4, 11, 18 and 25 weeks were divided into a Botox group injected with a botulinum toxin serotype A formulation to reduce muscle function (BTX) and a control group (CTRL). They were euthanized 6 weeks later and bone quality at the masseter insertion at the mandibular was analyzed. In the BTX group, the number of fibrous chon drocytes at entheses was significantly lower than in the CTRL group at all ages. The diameter of collagen fiber bundles in rats in the BTX group injected with BoNT/A during their growth phase was significantly smaller than that of rats in the CTRL group. In the mandibles of rats in the CTRL group the preferential alignment was consistent with the orientations of the muscle and tendon, but in growing rats treated with BTX, it was less closely aligned with the orientations of the muscle and tendon.