ABSTRACT
Objective To study the influence of different root exposure in long-term effect of crown lengthening .Methods To-tally 142 teeths(66 of the front teeths ,46 of premolars teeths ,30 of molars teeths ) of 110 patients collected from August 2010 to October 2012 in stomatological hospital to affiliated zunyi medical college were chosen as research subjects ,then they were randomly divided into the experimental group and the control group .There were 33 anterior teeths ,23 premolar teeths and 15 molar teeths in each group .The experimental group accepted 3 mm root exposure while the control group accepted 4 mm root exposure .The post-operative effect of the two groups was compared .Results The tooth mobility of the anterior cases of control group after 3 months was statistically higher than that of the experimental group (P0 .05) .The bleeding index after 3 months ,the anterior teeths ,premo-lar teeths and molar teeths of the experimental group was statistically higher than that of the control group (P0 .05) .The postoperative probing difference of depth and attachment loss between the two groups showed no statistically significant (P>0 .05) .Conclusion The root exposure of 3 mm and 4 mm both have a significant effect in crown lengthening .But for the aesthetic point of view ,3 mm should be taken as the root exposure of the anterior cases .