Three-Dimensional Analysis of Posterior Mandibular Displacement in Rats

Abstract

Mandibular protrusion and its treatment is challenging for the orthodontist. The aim of the present research was to identify macroscopic changes in the mandible, based on three-dimensional Cone Beam Computed Tomography analysis. Seventy-two male Wistar rats were divided into two equal groups, experimental (group A) and control (group B). Each consisted of three equal subgroups of 12 rats (A1, A2, A3, B1, B2, B3). Full-cast orthodontic intraoral devices were attached to the maxillary incisors of the experimental animals, and effected functional posterior mandibular displacement. Throughout the experimental period, all animals were fed with mashed food. Animals were sacrificed at 30 days (A1, B1), 60 days (A2, B2) and 90 days (A3, B3). At the 60th day of the experiment, the orthodontic devices were removed from the remaining experimental subgroup A3. Measurements revealed significant differences in the anteroposterior dimensions between experimental and control subgroups. However, the observed changes in the vertical dimensions, Condylion/Go'-Menton and the Intercondylar distance proved insignificant. Posterior mandibular displacement of the mandible in growing rats affects the morphology of the mandible and culminates in the development of a smaller mandible at a grown age.

Keywords: class III malocclusion; condylar growth; mandibular growth; mandibular length; mandibular posterior displacement; orthodontic treatment; rat.

Figure 1

The modified orthodontic intraoral device cemented to the maxillary incisors.

Figure 2

Anatomic landmarks detected in Cone Beam CT reconstructed images.

Figure 3

(a) Linear measurements: Go’–Menton (mandibular body length a); Go–Menton (mandibular body length b); Coronoid–Menton; Condylion/Go’–Menton (Condylion height); Condylion–Go’ (Ramus height); Condylion–Menton; Condylion–Id; Condylion–I’ (mandibular length); Incisal–Id; Incisal–I’. (b) Linear measurement: Condylion right–Condylion left (Intercondylar distance).

Figure 3

(a) Linear measurements: Go’–Menton (mandibular body length a); Go–Menton (mandibular body length b); Coronoid–Menton; Condylion/Go’–Menton (Condylion height); Condylion–Go’ (Ramus height); Condylion–Menton; Condylion–Id; Condylion–I’ (mandibular length); Incisal–Id; Incisal–I’. (b) Linear measurement: Condylion right–Condylion left (Intercondylar distance).

Figure 4

Estimated mean difference (Final–Initial) and 95% Confidence Interval per group and timing in Go’–Menton (mandibular body length a).

Figure 5

Estimated mean difference (Final–Initial) and 95% Confidence Interval per group and timing in Go–Menton (mandibular body length b).

Figure 6

Estimated mean difference (Final–Initial) and 95% Confidence Interval per group and timing in Condylion–I’ (mandibular length).

Figure 7

Estimated mean difference (Final–Initial) and 95% Confidence Interval per group and timing in Condylion/Go’–Menton (Condylion height).