State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
Discipline of Orthodontics, Department of Oral Sciences, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.
Am J Orthod Dentofacial Orthop. 2024 Feb;165(2):232-244. doi: 10.1016/j.ajodo.2023.09.009. Epub 2023 Oct 28.
Mandibular asymmetry has negative impacts on maxillofacial aesthetics and psychological well-being. This study investigated the effects of unilateral injection of botulinum toxin type A (BTX-A) into the masseter muscle on mandibular symmetry.
Forty Wistar rats (4-week-old) were divided into 4 groups (n = 10): control, group 1 (1U BTX-A), group 2 (3U BTX-A), and group 3 (1U BTX-A for 3 times). BTX-A was injected into the right masseter of treatment groups. Cone-beam computerized tomography scans were taken before the injection and then at 2 weeks, 4 weeks, and 6 weeks after injection. Histologic and immunohistochemical staining were done for the condylar cartilage. RNA sequencing and quantitative reverse transcription polymerase chain reaction were used to detect gene expression in the angular process.
In Groups 2 and 3, the right angular process length and the ramus height were reduced 4 weeks after injection, resulting in the mandibular midline deviating to the right side; the right condylar cartilage had reduced thickness and decreased expression of RUNX2, SOX9, and COL II (P <0.05). Two hundred sixty-one genes were differentially expressed (256 downregulated) in the angular process at 3 days post-BTX-A injection, and the calcium signaling pathway was unveiled through the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. Furthermore, TRPC1, Wnt5a, CaMKII, Ctnnb1, and RUNX2 expression were significantly downregulated at 1 and 3 days postinjection.
Unilateral injection of BTX-A into the masseter muscle in adolescent rats induces mandibular asymmetry by suppressing the angular process growth on the injected side.
下颌骨不对称会对面部美学和心理健康产生负面影响。本研究旨在探讨单侧注射肉毒毒素 A（BTX-A）于咬肌对面部下颌骨对称性的影响。
将 40 只 4 周龄 Wistar 大鼠随机分为 4 组（n=10）：对照组、1U BTX-A 组、3U BTX-A 组和 1U BTX-A 注射 3 次组。于治疗组大鼠右侧咬肌注射 BTX-A。于注射前、注射后 2 周、4 周和 6 周分别进行锥形束计算机断层扫描。对髁突软骨进行组织学和免疫组织化学染色。采用 RNA 测序和实时定量聚合酶链反应检测角状突的基因表达。
在注射后 4 周，2 组和 3 组大鼠右侧角状突长度和升支高度减小，导致下颌中线偏向右侧；右侧髁突软骨厚度变薄，RUNX2、SOX9 和 COL II 表达减少（P<0.05）。BTX-A 注射后 3 天，角状突中有 261 个基因表达差异（256 个下调），京都基因与基因组百科全书通路富集分析揭示了钙信号通路。进一步研究发现，TRPC1、Wnt5a、CaMKII、Ctnnb1 和 RUNX2 的表达在注射后 1 天和 3 天显著下调。
在青春期大鼠的咬肌内单侧注射 BTX-A 可通过抑制注射侧角状突的生长，导致下颌骨不对称。
