A comparative study of second molar impaction rates in patients treated with and without lip bumper therapy.

摘要

Background and significance. Lip bumpers have been proposed as a way to increase arch length. Studies in the literature describe well, their effect on mandibular incisors and first molars. Molars tend to tip back from 2.2° to 8.0° and incisors tend to tip forward 2.4° to 5.2°. In addition, significant increases are made to the mandibular transverse dental dimensions when a lip bumper is used.;Methods. 165 patient chart records were used in this study. An experimental group of 97 lip bumper treated patients were evaluated for mandibular second molar impaction during the course of their treatment. The thirteen patients in the experimental group whose mandibular second molars were impacted and thirteen randomly selected experimental group patients without second molar impactions had three measurements made on their pretreatment panoramic radiographs. Measurements were made between mandibular first and second molars for intermolar angulation, intermolar distance, and second molar distance to the occlusal plane. A control group of 56 patients treated orthodonfically without a lip bumper were also evaluated for mandibular second molar impaction during the course of their treatment.;Results. Class I experimental patients and class I control patients had no statistically significant difference in second molar impaction rate. Class II experimental patients and class II control patients also had no statistically significant difference in second molar impaction rate. Intermolar angulation, intermolar distance, and distance to occlusion measurements showed no statistically significant difference for the subcategories of each measurement between impacted and non-impacted teeth.;Conclusions. In this study, lip bumper therapy did not lead to a statistically significant increased number of mandibular second molar impactions when compared to a similar group of orthodontic patients treated without lip bumper therapy. Panoramic radiograph measurements of the distance and angulation between the mandibular first and second molars, and the distance to occlusion were not statistically different between subcategories of these measurements for impacted and non-impacted teeth.;Purpose. This study aimed to examine if there was an increase in mandibular second molar impaction rate with early use of a lip bumper. As a secondary purpose, this study attempted to evaluate some parameters that might assist the clinician when using a lip bumper if there might be an increase risk of mandibular second molar impaction.