The effects of gradually induced backward movement of the mandible by a Twin Inclined Plane Device in rats

Abstract Objective: To develop a model of gradually induced backward movement of the mandible under normal masticatory action and to examine morphological changes in the mandible and condylar cartilage in rats. Materials and Methods: The newly developed Twin Inclined Plane Device (TIPD) was composed of upper and lower posterior metal crowns with a long inclined plane on both sides separately and was applied in experimental groups of 6-week-old male Wister rats. After 3, 14, 30, and 60?days, the rats were euthanatized and samples were collected. Various measurements and hematoxylin-and-eosin stains were performed. Results: From day 30 on, the length of the condylar process was shorter in the TIPD groups than in the control groups (P < .05). The angulation of the condylar process axis to the mandibular plane was greater in the TIPD groups (P < .01). The thickness of the condylar cartilage in the posterior part of the posterior region was thinner in the TIPD groups (P < .05) on day 30 and even thinner (P < .01) on day 60; from day 30 on, the thickness in the anterior part of the posterior region was thicker in the TIPD groups (P < .01). Conclusion: TIPD can successfully induce backward movement of the mandible under normal masticatory action. TIPD can cause region-specific changes in condylar cartilage and leads to a continuous remodeling.