Effects of different orthodontic treatment methods on mandibular third molar eruption

Objective:To compare the effects of different orthodontic treatment methods on the eruption of mandibular third molar(M3).Methods:80 posttreatment adult patients were selected for the study.154 mandibular M3 were divided into three groups according to the extraction conditions of unilateral mandibular teeth.40 were treated without extraction(non-extraction group),66 were treated with the extraction of first premolar(4-extraction group),and 48 were treated with the extraction of second premolar(5-extraction group).The pretreatment and posttreatment panoramic radiographs were analysed.The angulation and the eruption space of mandibular M3 were measured.The eruption levels of 116 third molars were evaluated according to the posttreatment panoramic radiographs.Results:There were no significant differences in the change in mandibular M3 angulation from pretreatment to posttreatment groups(P0.05).But there were significant differences in the change in mandibular M3 space among three groups(P0.01).Space change in 5-extraction group was larger than that in 4-extraction group,and 4-extraction group was larger than non-extraction group.The eruption level of the M3 after orthodontic treatment was significantly higher in 5-extraction group than in non-extraction group and 4-extraction group(P0.05).Conclusion:For adult orthodontic patients,mandibular M3 angulation changes regardless of the method of orthodontic treatment.But the space changes are significantly different,the weaker of the anchorage,the more spaces increased,the more improvement in eruption.