Background: In man, botulinum toxin type A (BTX) is injected in masticatory muscles for several indications such as trismus, bruxism, or masseter hypertrophy. Bone changes in the mandible following BTX injections in adult animal have therefore became a subject of interest. The aim of this study was to analyse condylar and alveolar bone changes following unilateral injections of BTX.
Methods: Unilateral injections of BTX were done in Mus masseter and Mus temporalis in adult rats. Mature male rats (n=15) were randomised into 2 groups: control (CTRL; n=6) and BTX group (n=9). Rats of the BTX group received a single injection of BTX into right Mus masseter and temporal muscles. Rats of the CTRL group were similarly injected with saline solution. Rats were sacrificed 4 weeks after injections. Masticatory muscles examination and microcomputed tomography (microCT) were performed.
Results: BTX rats presented a significant loss of weight (p<0.05) from weeks 2 to 4. Atrophy of the right Mus masseter and Mus temporalis was observed in all BTX rats. MicroCT analysis showed significant bone loss in the right alveolar and condylar areas in BTX rats. Decrease in bone volume reached -20% for right alveolar bone and -35% for right condylar bone. A hypertrophic bone metaplasia at the Mus Digastricus enthesis was found on every right hemimandible in the BTX group and none in the CTRL group.
Conclusions: BTX injection in masticatory muscles leads to a significant and major mandible bone loss. These alterations can represent a risk factor for fractures in human. The occurrence of a hypertrophic bone metaplasia at the Mus Digastricus enthesis may constitute an aetiological factor for tori.
Disclosure: The authors declared no competing interests. JDKD received a scholarship from the ARS (Agence régionale de santé) « Pays de la Loire ».