Clinical analysis on eruption of third molars after extraction of second molars

Objective This retrospective study was conducted to assess the eruption of third molars after extracrtion of second permanent molars by using panoramic radiographs. Methods The subjects were 19 patients who had 34 permanent second molars extracted during or before orthodontic treatment. The position of the third molars was assessed from panoramic radiographs taken before second-molar extraction and 1year after extraction. Vertical and horizontal drift and angulation of the third molars were measured. Another 38 third molars in the unextract side were choosen as control group. Changes in third molar position from pretreatment to posttreatment between two groups were compared. Results 34 third molars of experimental group all erupted in different degree. Horizontal and vertical distances the maxillary third molars moved was in an average of 8. 41 mm and 7. 41 mm,the uprighted angulation in maxillary was average 16. 45°,The data in mandibular third molars were 6. 77 mm,4. 021 mm,and 7. 14°mm。It showed more vertical movement and more upright of the third molars in maxillary. Conclusion ①Our results suggest that second molar extraction may increase the rate of eruption of the third molars,and at the meanwhile decrease there impaction. ②The movement of maxillary third molars was faster than mandibular,it was seems that its positions were also better than that in mandibular third molars.