Effects of eruption space and molar agulations on third molar eruption

Objective To find evidences for clinical treatment program by investigating the variables in the third molar between the subjects with impacted third molars and those with erupted ones. Methods 86 subjects (37 males,49 females) with an average age of 25.4 years old were chosen and divided into impacted and erupted groups. Standardized panoramic radiographs were taken and the indexes of the third molar angulation, mesiodistal crown width , eruption space, and the ratio between them were analyzed.Results In the maxilla, the eruption space of erupted group was 1.95 mm larger than that of the impacted group ([WTBX]P0.01).The average difference of the angle between the long axis of the third molar and the second molar was 12.53 degrees(P0.01). Mesiodistal crown width of the erupted group was smaller than that of the impacted group and the difference was 0.7 mm(P0.05). In mandible, the eruption space of erupted group was larger than that of the impacted group and the difference was 3.33 mm (P0.01). The average difference of the angle between the long axis of the third molar and the occlusal plane was 32.48 degrees(P[WTBZ]0.01). The average ratios between the eruption space and mesiodistal crown width in the impacted and erupted groups were 0.85 and 1.15, respectively (P0.01). The impacted and erupted groups had no significant differences in respect to mesiodistal crown width of the third molar. Conclusion The eruption space and third molar angulation could affect the eruption of third molar. Molar angulation is more important to the maxillary third molar. To mandibular third molar inadequate eruption space or more mesioangulation of the third molar results in molar impaction.