The study of the relapse of hard and soft tissue after maxillary protraction

Yang, Jun Ho; Park, Soo Byung; Son, Woo Sung

Abstract

The purpose of this stdudy was to evaluate the effect of maxillary protraction and the relapse of hard and soft tissue after maxillary protraction. For this study 29 patients who were treated with maxillary protractor and labiolingual archwire were selected. Their mean age was 9 years 4 months and mean treatment period was 8.5 months. Lateral cephalograms were taken at pretreatment, immediately after treatment and one to three months after removal of the maxillary protractor. They were traced on skeletodental and soft tissue structures based on Burstone's analysis and analyzed by QuickCeph Image Digitizing System(ORTHODONTIC PROCESSING). The mean and standard deviation between pretreatment and posttreatment and between posttreatment and retention period for each cephalometric variable were calculated. Student t-test was used to determine the statistical significance of the changes in each variable. Correlation coefficients between hard tissue and soft tissue I were used to determine interrelationship. The results were as follows: 1. After maxillary protraction, the maxilla and maxillary dentition moved antero-inferiorly, the mandibld and mandibular dentition moved postero-inferiorly and palatal plane rotated antem-superiorly by 0.59degrees. 2. After maxillary protraction, the soft tissue of upper lip moved antero-inferiorly with the movement of hard tissue but the antero-posterior position of lower lip was stable in spite of the change of hard tissue. The thickness of upper lip was decreased and that of lower lip was increased after maxillary protraction. 3. During the retention period, the position of jaws was relatively stable but upper and lower anterior teeth and antero-superiorly rotated palatal plane relapsed to original position. 4. During the retention period, the soft tissue of lips was stable antero-posteriorly and moved more inferiorly than posttreatment 5. The correlation coefficients between the postion of upper and lower incisal edge and that position of lips were high, especially in horizontal change.