Abstract:

Objective To measure the vertical height of mesio- distal marginal ridge to cusp in posterior teeth, which may be helpful to brackets positioning. Methods The study groups comprised of 60 patients（30 men, 30 women, mostly aged 12 - 14 years） who underwent orthodontic treatment without tooth extraction and matched the Andrews normal occlusion standard after treatment. Study model of each patient was made. Three- dimensional laser measurer was used to evaluate the vertical height of mesio- distal marginal ridge to mesial cusp in posterior teeth. The data were stored in a personal computer and submitted to statistical analysis of paired t test. Results No statistical significant difference was found in the same teeth between men and women. Not only in maxilla but also in mandible, there was no significant difference between the left and the right（P>0.05）. The average vertical height of maxillary first premolars was （1.70±0.50）mm, the maxillary second premolars was （1.24±0.45）mm, and for maxillary first molars, the result was （0.83±0.40）mm. The difference between each result was statistically significant（P< 0.01）. The average vertical height of mandibular first premolars was（2.25±0.45）mm, the mandibular second premolars was （1.55±0.45）mm, and for mandibular first molars, the result was （1.18±0.40）mm. The difference between each result was statistically significant（P<0.01）. Conclusion The vertical height of brackets position in posterior teeth should be considered to guarantee that mesio- distal marginal ridges of deferent posterior teeth located in the same plane, so that satisfying goal could be achieved. If the vertical height in the first molar was X mm, the vertical height in the second premolar should be（X+0.5）mm, and（X+1.0）mm might be suit for the first premolar.

Key words: marginal ridge, bracket positioning, preadjusted appliance