The Clinical Study Of Distalizating Maxillary Molar After Maxillary Second Molar Extraction

ClassⅡmalocclusion is one of the most common malocclusion in china. The incidence of ClassⅡmalocclusion in Chinese juvenile is reported to be 23%. The specific characteristics of classⅡmalocclusion can include a protrusion of the maxillary or upper dental arch, a retrusion of the mandible, deep overjet and overbite, incongruous profile, and distal malocclusion of the first molars and canines. According to etiopathology, it can be classified into 2 types: dental and skeletal malocclusion. Since last century, the method of distalizating maxillary molar has become an important and effective technique to correct Class2 dental malocclusion and moderate space deficiency. Recently there are lots of researches about the different methods of molar distalization and the efficacy of each different method. The study of distalizing molar after the maxillary second molar extraction is rare to report. But in clinical analysis we discovered that maxillary second molar extraction not only can make molar distalization more efficient but also facilitate the eruption of the third molar and decrease the relapse. ObjectiveThe study was conducted to examine the clinical effect and the peculiarity of distalizing maxillary first molar after maxillary second molar extraction. comparing the effect of three different positions of the maxillary second molar. And provide theoretical foundations for clinical indication and treatment principle. Methods and resultsPart 135 patients with ClassⅡmalocclusions were divided into 3 groups, all patients treated by distalization of maxillary molar were collected. LSD t-test was used to compare the 13 different indexes including cephalometric indexes, incisor and molar changes of pretreatment and posttreatment.The results show that there are statistically significant differences in the velocities of molar distalization are 0.96±0.29mm/Mo,0.79±0.39mm/Mo,0.61±0.40mm/Mo, and the distal tipping of maxillary first molar are 0.12±3.09°,0.58±4.57°,1.80±5.00°, there are no statistically significant differences in distalization of maxillary second premolar, intrusion of upper incisors, and extrusion of molars.Part 215 sub-ClassⅡpatients (8 boys and 7 girls)with permanent dentition were chosen, and were treated by distalization of maxillary molar after maxillary second molar extraction ClassⅡside with headgear using the force of 200g . Matched t-test was conducted to compare 12 indexes of cranio-facial hard and soft tissue changes of pretreatment and posttreatment.The statistical result shows that the therapy time of ditalizing maxillary first molar is 3.05Mo, the velocity is 0.96mm/Mo,and the 1-NA, Ls-E, Li-E, Cm-Sn-Ls, A'Ls-FH, A'Ls-B'Li all reduced compared to pretreatment. It is statistical significant differences.ConclusionDistalization of maxillary first molar after maxillary second molar extraction can spend shorter therapy time but achieve more space. Obviously this method is more efficient than distalize molar before maxillary second molar eruption. Headgear guarantee the anchorage, so can provide the space to intrude the incisors. Distalizing maxillary first molar after maxillary second molar extraction is an efficient method for correcting ClassⅡmalocclusion.