Hard Tissue Changes Of Skeletal Class ⅢMalocclusion After Maxillary Protraction

Objective:Skeletal class Ⅲ malocclusion has a trend of getting worse with age, which affect not only the patient’s chewing and pronunciation, but also affect the facial appearance and even the patients’ mental health. Because the growth of mandibula can not be easily predicted, there is no better way to inhibit its growth.Maxillary protraction in the treatment of skeletal class Ⅲ malocclusion has been widely recognized. Orthopedic force can pull the maxilla forward before the growth peak of puberty, thereby improving the dismatching of maxilla and mandibula in the sagittal direction. This study compared the early and late stages of puberty by application of maxillary protraction in the changes of the hard tissue before and after treatment on lateral cephalometrie radiographs. We are going to discuss the effects of maxillary protraction on the teeth, bones at different ages.Methods:According to the cervical maturity classification,28subjects with maxillary retrusion were divided into the early treatment group (Cvsl-3) and the late treatment group (Cvs4-6),both of the two groups has14subjects. Using Winceph6.0software to measure the changes of the angles and displacements of those markers on lateral cephalometrie radiographs. Paired T-test are used to compare the changes before and after maxillary protraction inside the two groups.The differences after and before protraction between the two groups use independent samples T-test.Results:Both the early and late treatment groups show significant orthopedic effect, point A has significantly forward after treatment.SNA increases by3.26±1.59°in the early group and2.59±3.09°in the late group after protraction on average; ANB increases by4.49±1.20°in the early group and3.64±1.85°in the late group after protraction on average, there are highly significant differences before and after treatment.There also show significant increase of the maxillary incisors proclination and Wits value,downward and backward rotation of mandible. The early group showed decrease of SNB after treatment while the late group has more lingual inclination of lower incisors.But there is no statistical difference between the two groups.Conclusions:The results of this study indicated that maxillary protraction is a reasonable method for the children with maxillary retrusion at the early and late stages of puberty.