Efeitos da fratura de corpo da mandíbula no crescimento da maxila e da mandíbula: estudo experimental em ratos jovens

Abstract

Purpose: To analyze the effects of detachment and repositioning of the medial pterygoid muscle on the growth of the maxilla and mandible of young rats through cephalometry. Methods: Thirty one-month-old Wistar rats were used, distributed into three groups: experimental, sham-operated and control. In the experimental group, unilateral detachment and repositioning of the medial pterygoid muscle was performed. The sham-operated group only underwent surgical access, and the control group did not undergo any procedure. The animals were sacrificed at the age of three months. Their soft tissues were removed and the mandible was disarticulated. Radiographs of the skull in axial projection and the hemimandibles in lateral projection were obtained, and cephalometry was performed. The values obtained were subjected to statistical analyses among the groups and between the sides in each group. Results: There were significant differences in the length of the mandible relative to the angular process in the experimental group and in the height of the mandibular body in the sham-operated group. Conclusion: The experimental detachment and repositioning of the medial pterygoid muscle during the growth period in rats affected the growth of the angle region, resulting in asymmetry of the mandible. Key words: Pterygoid muscle. Maxillofacial development. Growth and development. Rats. RESUMO Objetivo: Avaliar os efeitos do descolamento e reposicionamento do músculo pterigoideo medial no crescimento da maxila e mandíbula em ratos jovens por meio de cefalometria. Métodos: Foram utilizados 30 ratos Wistar com um mês de idade, distribuídos em três grupos: experimental, controle-operado e controle. No grupo experimental, o descolamento unilateral e reposicionamento do músculo pterigoideo medial foi realizado. O grupo controle-operado foi submetido somente ao acesso cirúrgico e para o grupo controle nenhum procedimento foi realizado. Os animais foram sacrificados aos três meses de idade. Os tecidos moles foram removidos e a mandíbula foi desarticulada. Radiografias axiais do crânio e laterais das hemimandíbulas foram obtidas e a cefalometria foi realizada. Os valores obtidos foram submetidos a análises estatísticas entre os grupos e entre os lados em cada grupo. Resultados: Houve diferenças significantes no comprimento da mandíbula relativo ao processo angular no grupo experimental e na altura do corpo mandibular no grupo controle operado. Conclusão: O descolamento e reposicionamento experimental do músculo pterigoideo medial durante o período de crescimento em ratos comprometeu o crescimento na região de ângulo, resultando em assimetria da mandíbula. Descritores: Músculo pterigoideo. Desenvolvimento maxilo facial. Crescimento e desenvolvimento. Ratos.

Effects of the unilateral removal and dissection of the masseter muscle on the facial growth of young rats

“…17 Occlusal disturbances were considered the main cause of asymmetry of the midface after experimental mandibular fractures. 5,18 Gross modifi cations in the form of the mandible occurred after resections of the masseter and temporal muscles in the young rat, supporting the functional matrix theory of the mandibular growth. 9,19 Similar fi ndings are reported after the denervation of the masseter muscle.…”

“…2,3 Resection of the cartilaginous nasal septum promoted severe facial deformity. 4 Also, osteotomies that simulated a mandibular fracture in the growing period had as consequences asymmetries of the maxilla and the mandible, 5 or lessening of the mandible. 6 It has been demonstrated that the masticatory muscle function is a determinant of the quality of bone of the growing mandible.…”

Effects of detachment and repositioning of the medial pterygoid muscle on the growth of the maxilla and mandible of young rats

“…The smaller volume of these muscles indicates that this was a consequence of the surgical procedure. Surgical access at young ages may have negative effects on the growth of the maxilla and mandible 4,5 .…”

“…This finding is probably due to compensation for muscle activity and the intense adaptive capability consequent to extrinsic mechanical factors, which results in growth compensation 21 . Other studies inducing condylectomy or fracture of the mandibular body may have promoted abnormalities in the maxilla that could be explained by the influence of occlusal intercuspation 1,4,5 .…”

“…Thus, an injury to these structures may have negative results in relation to mandibular growth 2,3 . Furthermore, the growth of the maxilla can be affected by the influence of occlusal intercuspation 1,4 .…”