Effects of Botulinum Toxin A on Condylar Subchondral Bone Mass.

BACKGROUND

The management of temporomandibular disorders (TMD) remains challenging, with its underlying pathological mechanisms requiring further investigation. This study aimed to explore the effects of Botulinum Toxin A (Botox A) on the lateral pterygoid (LP) muscle and its impact on condylar subchondral bone mass.

METHODS

Rats were randomly assigned to either an experimental group (injected with Botox A) or a control group (injected with an equal volume of 0.9% normal saline). All rats were sacrificed at 2-, 4-, 8-, or 12-weeks post-injection. The right condyles were harvested and analyzed using Micro-computed tomography (CT) scanning and hematoxylin-eosin staining to evaluate changes in the condylar subchondral bone. Osteoclast activity in the subchondral bone was assessed via tartrate-resistant acid phosphatase (TRAP) staining. The activities of osteoclasts and osteoblasts in subchondral bone were detected by western blotting.

RESULTS

At 2-weeks post-Botox A injection, the trabecular number (Tb.N) was significantly lower (p < 0.01). At 2- and 4-weeks, bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) were significantly lower (p < 0.05), while trabecular space (Tb.SP) and the ratio of bone surface area to bone volume (BS/BV) were significantly increased in the experimental group compared to control group (p < 0.05). At 8-weeks, BS/BV remained significantly elevated (p < 0.05), but no significant differences were observed in Tb.N, Tb.Th, BV/TV, or Tb.Sp at 8- and 12- weeks. Osteoclast numbers in the condylar subchondral bone were significantly higher in the Botox A group at 2-, 4-, and 8-weeks compared to the control group (p < 0.05). Additionally, protein expression levels of osteocalcin (OCN) and type I collagen (COL1A1) were markedly increased in the experimental group at 8- and 12-weeks (p < 0.05).

CONCLUSIONS

Botox A induces a significant reduction in condylar subchondral bone mass in rats during the early post-injection period, with subsequent time-dependent recovery.