Lateral expansion of the rat lower dental arch by applying an active plate model to the mandibular first molar region: observation of histological changes in the lower alveolar bone over a 2-week period.

Lateral expansion of the lower dental arch has rarely been conducted clinically because the structure of the lower jaw is considered to be unsuitable for this type of treatment. However, successful lateral expansion of the lower dental arch using SCHWALZ, an orthopedic appliance has been reported in recent years. Therefore, an experimental study was performed to examine the histological changes in the lower alveolar bone when lateral expansion is applied to the lower dental arch for periods of up to 2 weeks. An active plate model based on the Schwarz appliance was attached to the first molar region in rats. The distance between the right and left first molars was measured, and the mandible and first molar tooth were processed for light microscopy at different times after the fitting. The lateral expansion caused by lateral movement of the right and left first molars following the application of the active plate amounted to an average of 1.06 mm over a period of 14 days. Alkaline phosphatase/tartrate-resistant acid phosphatase staining revealed bone deposition on the periosteal surface of the buccal alveolar bone and the periodontal surface of the lingual alveolar bone, whereas bone absorption was observed on the periodontal surface of the buccal alveolar bone and the periosteal surface of the lingual alveolar bone. These findings demonstrate that lateral expansion of the lower dental arch through the application of an active plate model was achieved by bony deposition and absorption of alveolar bone, similar to the process that occurs in association with lateral expansion of the upper dental arch.