Effects of functional mandibular lateral shift on craniofacial growth and development in growing rats

Abstract

Background Unilateral posterior crossbite, one of the most frequent malocclusions, is often associated with functional lateral shift of the mandible. Although the effects of functional lateral shift on the mandible and temporomandibular joint have been examined in various animal experiments, cranial and maxillary changes have received less attention. Objective The aim of this study was to investigate the effects of functional lateral shift on the craniofacial complex in growing rats. Methods Eighty 5‐week‐old male Sprague–Dawley rats were randomly divided into an experimental group (n = 40), which received an oblique guide appliance that shifted the mandible to the left during closure, and a control group (n = 40). The rats were scanned by cone‐beam computed tomography at 3 days and 1, 2, 4 and 8 weeks. The dimensions of the mandibular bone, condyle, maxilla and cranium were measured. Results The mandibles of rats in the experimental group were smaller than those of the rats in the control group and were asymmetrical. The condyles of the rats in the experimental group were thinner than those of the control rats. The condylar length on the ipsilateral side was shorter and wider than that on the contralateral side from 4 to 8 weeks. No significant differences in cranial length or height were observed between the experimental and control groups. The height of the upper first molar and alveolar bone on the contralateral side was significantly smaller than that on the ipsilateral side and in the controls from 4 to 8 weeks. Conclusion Functional shift in the mandible produces morphological asymmetries in the mandible and maxillary region and may cause bilateral condylar degenerative changes.

Reversible Effects of Functional Mandibular Lateral Shift on Masticatory Muscles in Growing Rats

“…The contralateral side was loaded with more compressive forces via FMLS when the rats closed their mouths, which was similar to those forces experienced during incising. Moreover, considering the asymmetric mandibular ramus height observed in previous FMLS animal models [ 40 ], together with the fact that different distances between muscle attachment sites lead to the stimulation or inhibition of muscle growth [ 41 ], we postulate that a longer ramus on the non-deviation side has a positive impact on muscle hypertrophy. Thus, the masticatory muscles alter and adapt to asymmetric changes in the mandible and condylar cartilage during FMLS.…”