Objective To compare the tooth mass quantity discrepancy needed to be compensated by different treatment plans of extraction of cases with congenital missing single mandibular incisor for the sake of reaching appropriate treatment plan.

Methods: Tooth mass and basal bone mass were measured with electronic vernier and a computer aided dental cast measurem ent and analysis system developed by faculty of stomatology of Kunming Medical C ollege in 91 individuals with normal occlusion and 101 with dental crowding aged from 16 to 26 years old(on the average age of 21).

Objective To investigate Bolton index of Angle's ClassII2 malocclusion patients and to study the influences of an upper and lower tooth size relations on the symptoms and curative effect in them.

The degree of external curvature of the roots of the mandibular third molars and the measurements of maxillary third molars\' coronal length,coronal thickness and cervical thickness had significant difference between men and women(P<0.