Altered mandibular growth under functional posterior displacement in rats

Abstract

Objective: To test the null hypothesis that there is no difference in mandibular growth between growing rats with posterior functional mandibular displacement and growing rats without functional mandibular displacement.

Materials and methods: Twenty female Wistar rats (5 weeks old) were randomized into two groups: (1) control and (2) mandible posterior displacement in the occluded condition induced by an occlusal guiding appliance. After 8 weeks all animals were sacrificed, cone beam computed tomography scan images of the heads were taken using the classic I-CAT, and acrylic rapid-prototyped templates of the mandibles were constructed. Mandibular length, ramus height, and intercondylar distance were measured. Mandibular length and ramus height were submitted to the two-way analysis of variance, while intercondylar distance was analyzed by nonpaired Student's t-test.

Results: Mandibular length was bigger (P < .0001) in the control than in the experimental group, but no significant difference was found between the left and right sides (P = .9380). No significant differences were observed for ramus height and intercondylar distance.

Conclusions: The results of this study demonstrated that functional posterior displacement of the mandible in growing rats resulted in shorter mandibular length.

Figure 1

Occlusal guiding appliance attached to the maxillary incisors to induce posterior displacement of the condyles in the occluded condition.

Figure 2

Measurements of mandible templates. (a) Lateral view: A, mandibular length, from the most distal point on the condyle articular surface to the most anterior point on the lingual aspect of the incisor alveolus and B, ramus height, from the most superior point on the condyle to the most inferior point on the angular process. (b) Upper view: C, intercondylar distance, as the greatest distance between the lateral surfaces of the condyles.