Effects of buccal shields on the maxillary dentoalveolar structures and the midpalatal suture--histologic and biometric studies in rabbits.

The mechanism of the buccal shields with regard to regulating the transversal relationship of the maxillary dental arch is uncertain. The periosteal pull theory, growth at the midpalatal suture and changes in equilibrium have all been proposed as explanatory factors. The aim of the study was to investigate the transversal development of the dental arch and the osseous remodeling at the lateral surfaces of the maxillary alveolar process and in the midpalatal suture after stretching the bucca (cheek) with buccal shields in the vestibulum. Ten New Zealand white male rabbits 12 weeks old were used. The animals were divided into two groups (control and experimental). Initial and final impression had been taken from the two groups and plaster models were made using biometric analysis in all animals of each group. Transversal measurements were taken of the distances between the maxillary right and left teeth. Tetracycline hydrochloride and Alizarin complexone were used to label the mineralizing tissues. After the animals had been killed, the biopsies from the midpalatal suture, the alveolar wall, and the periosteum were studied under a microscope. The results from the biometric analysis showed maxillary dental arch expansion in the two groups that was significantly larger in the experimental group. Microscopically, the growth at the midpalatal suture was also significantly larger in the experimental group, while no significant differences were found at the maxillary alveolar bone in the two groups. The conclusions drawn from this study are that the vestibular buccal shields bring about an increased expansion of the maxillary dental arch and increased growth at the midpalatal suture. No increased bone deposition was found at the buccal dentoalveolar wall, inducing doubts as to the accuracy of the periosteal pull theory for widening of the dental arch.