Study On The Association Of Dental Maturation And Skeletal Age In Adolescents With Mandibular Retrusion And Andibualr Protrusion

The sagittal skeletal deformities with mandibular retrusion and mandibularprotrusion are common in Chinese population. The aim of this study was toinvestigate the association between dental development and skeletal maturation inChinese adolescents with retrusive or protrusive mandible. This study willprovide a guideline for orthodontists to choose proper treatment timing forchildren with either mandibular protrusion or mandibular retrusion. The sampleconsists of records of adolescent patients who have registered in the departmentof orthodontic, School of Stomatology, Fourth Military Medical University from2005 to 2007 according to the standard criteria. These subjects were divided intomandibular retrusive group (deep overjet, short lower 1/3 facial height, retrusivemandibule, ClassⅡ/ClassⅠmolar relationship, normal SNA angle, SNB angle <77.6°, ANB angle> 5°) and mandibular protrusive group (anterior teeth crossbite,ClassⅢmolar relationship, ANB angle <0°, no functional shift of mandible, or第四军医大学硕士学位论文 mandible could retrude, but ANB angle < 0°with apparent anterior teethcompensation). The dental age and DMS variation were evaluated according toDemirjian's method using panoramic radiograph and the CVM changes weredetermined according to Hassel and Farman's method using cephalometricradiograph.Results:1. Dental age difference between patients with mandibular retrusion andmandibular protrusion: (1) The angle of ANB in two groups showed significantdifference, which indicated significant sagittal skeletal deformity. The ages ofpatients were distributed equally. The difference between dental age and thebiological age were minor with 0.3 years in mandibular retrusion group and 0.1years in mandibular protrusion group, which demonstrated a slight tendencytoward more advanced dental age in mandibular retrusion group, however, theresults didn't show any significant difference(P＞0.05). (2) For the severeskeletal deformity cases with normal SNA angle, SNB angle < 77.6°, ANB angle> 5°in mandibular retrusion group or normal SNA angle, ANB angle＜-2°inmandibular protrusion group, the difference between dental age and biologicalage was still minor with 0.4 years in mandibular retrusive group and 0.2 years inmandibular protrusive group. The difference was insignificant(P＞0.05).2. Variation of skeletal age in mandibular retrusion and mandibular protrusiongroup: (1) Skeletal age of mandibular protrusive patients was average 6 monthsahead of biological age, which was clinically significant but no statisticallysignificant, P＞0.05. (2) For the severe skeletal deformity cases with normal SNAangle, SNB angle < 77.6°, ANB angle > 5°in mandibular retrusion group ornormal SNA angle, ANB angle＜-2°in mandibular protrusion group, theskeletal age of mandibular protrusive patients was 8 months ahead of those with mandibular retrusion which was statistically insignificant different(P＞0.05).Conclusions:1. No statistically significant differences in the dental development wereidentified between Chinese adolescent with mandibular retrusion and mandibularprotrusion, which prompted that no clear correlation between dental maturationand sagittal mandibular discrepancy. Chinese adolescent with mandibularretrusion has a milder early dental development tendency than those withmandibular protrusion showing clinical insignificance.2. No statistically significant differences in the skeletal Maturation weredetected between Chinese adolescent with mandibular retrusion and mandibularprotrusion,which revealed that no obvious association between skeletaldevelopment and sagittal mandibular discrepancy. The skeletal development ofmandibular protrusive patients was 6 months earlier than that of cases withmandibular retrusion showing certain clinical significance.