RESUMO
Objective To compare changes in dental arch and soft and hard tissue produced by the Damon Q self-ligating bracket and 3M metal bracket with non-extraction treatment in maxillary mild-to-moderate crowding cases. Meth-ods Eighty seven patients were selected in our study, who were assigned to 4 groups by the crowding degree of maxillary and appliance type:ⅠandⅡcrowding degree using Damon Q self-ligating bracket groups (41 cases);ⅠandⅡcrowding de-gree 3M metal bracket groups (46 cases). We measured lateral cephalometric radiographs and dental casts at both beginning and end of treatment. Paired t-tests and group t-tests were used in statistical analysis to compare the alteration in dental arch and soft and hard tissue. Results There was significant increase in width and length of maxillary dental arch by non-extraction treatment withⅠandⅡcrowding degree maxillary, but the results of both groups were not of statistical difference. To compare hard and soft tissue in two groups withⅡcrowding degree maxillary, the reduction of nasolabial angle, angle of inclination of upper lip, angle of upper lip and lower lip had obvious statistical significance and it is more prominent in self-ligating bracket group than in conventional bracket group. Conclusion Using non-extraction treatment, when maxillary crowding is moderate, ,Damon Q self-ligation bracket group result in more prominent changes of upper lip protrusion than 3M bracket with more marked crowding . Therefore, clinical doctors should pay more attention to choose bracket and treat-ment system for patients with marked crowding of maxillary dentition.