ABSTRACT
INTRODUCTION: In this preliminary study, we investigated early histologic changes of paradental tissues in response to a clear plastic appliance in rats. METHODS: Fifteen rats were divided into 3 groups. Group I was the untreated controls; group II received a clear plastic appliance made from a model, with the maxillary left first molar repositioned mesially 0.5 mm from the origin; and group III had a closed-coil spring to move the molar mesially. Specimens were prepared in parasagittal sections, and changes in paradental tissues were evaluated on days 1, 4, and 7 by light microscopy. RESULTS: In group II, the periodontal ligament (PDL) was compressed in the bifurcation and apical areas of the roots of the molar. On day 7, the PDL of the apical and distal aspects of the roots and the bifurcation area showed further compression, with the PDL of the roots stretched along the mesial side. In group III, a disorganized and compressed PDL in the mesial cervical half and interradicular septum was observed, and the stretched fibers were at the distal aspects of the roots after days 4 to 7. CONCLUSIONS: Early histologic changes in response to the clear plastic appliance were intrusion and distal tipping despite the intended mesial movement. In this rat model, the observed histologic changes were subject to the direction and magnitude of forces generated by the clear aligner.
