The initial observation on the third molar eruption after the first molar extraction followed by orthodontic treatment

Objective:To observe the effects of first molar extraction on the eruption of third molar(M3).Methods:30 cases of mandible and 20 cases of maxillas were divided into non-extraction,first premolar(4-extraction)and first molar extraction(6-extraction)groups respectively.The pretreatment and posttreatment panoramic radiographs were analysed.Changes in the third molar eruptive angle and space were compared among these groups.Results:1.There were significant differences in the change in the third molar eruptive space and space/width ratio among three groups(P0.05).Space change in 6-extraction group was larger than that in 4-extraction group,and that in 4-extraction group was larger than non-extraction group.2.The eruptive angles of the mandible third molar were not significantly different among 6-extractiongroup,4-extraction group and non-extraction group;as for the maxilla third molar,the eruptive angles in 6-extraction group were increased more than that in 4-extraction group and non-extraction group.Conclusion:The maxilla first molar extraction can significantly advance the eruption space and angles of the third molar.The mandible first molar extraction can increase the third molar eruptive space,but has no effect on the eruption angles.