Effects Of Orthodontic Treatment By Tooth Extraction And Non-extraction On Soft Tissue Of Profile And Front With Skeletal Class ? Malocclusion

Objective: Comparing the changes of soft and hard tissue profiles and the frontal lips morphology after orthodontic treatment for skeletal Class ? malocclusion by tooth extraction and non-extraction,the effects of the two methods on the changes of soft tissues were studied and the correlation between soft tissue and hard tissue was explored?Methods: According to the inclusion criteria,32 cases of skeletal class ? patients without potential development were selected,according to whether the four first premolars were extracted,cases were divided into two groups:tooth extraction group(14 persons)and tooth non-extraction group(18persons).Cephalometric radiographs and frontal photographs were taken for each patient before and after treatment,a total of 43 landmarks and 60 linear and angular measurements were selected.The statistical analysis was performed with SPSS 21.0.Results:1 Frontal photographsIn the tooth extraction group,the total heights of lower lip vermilion and the area of lower lip was significantly decreased after treatment than those before treatment(P<0.05).The total heights of lip vermilion and the area of upper lip was increased,whereas the ratio of length-width of lip vermilion was decreased during treatment in the tooth non-extraction group(P<0.05).The changes in values of the total heights of lips,the area of the lips,the ratio of the upper lip vermilion to the upper lip and the length-width ratio of lip vermilion were different between two groups after treatment(P<0.05).2 Cephalometric radiographsThe height of lower anterior face was increased,the lower incisor and the point of infradentale was retracted,the upper and lower first molars distance was increased and the convexity of lower lip was decreased due to the orthodontic treatment in the tooth extraction group(P < 0.05).In the tooth non-extraction group after treatment,the mandible was rotated backwards,the relative position of the upper and lower jaws was improved,the upper incisor moved forward,the angle between upper and lower incisors was decreased,the point of superior prosthion moved forward,the concave soft tissue profile was improved,the upper lip moved forward,the depth of mentolabial sulcus deepened(P<0.05).The changes in values of upper and lower incisors,lower lip protrusion,infradentale points,upper lip angle,lower lip angle,angle between upper and lower lip showed difference between two groups during treatment(P<0.05).3 CorrelationPearson's analysis showed positively correlation between the change of lips convexity and upper and lower jaw displacement in both groups(P <0.05).The change of upper lip convexity was related to the movement of the upper incisors in the tooth extraction group and the movement of the upper and lower incisors in the tooth non-extraction group.The change of lower lip convexity was related to the movement of the lower incisors in both groups(P<0.05).In the tooth extraction group,the change of lower lip thickness was negatively correlated with rotation of the mandibular plane;in the tooth non-extraction group,changes in thickness of subnasale and soft chin were positively correlated with the rotation of the mandibular plane,while the change of soft chin thickness showed positively correlated with the increase of facial angle,the indentation thickness of lower lip were negatively correlated with the movement of the lower incisors(P<0.05).The reduce of total heights of the upper lip area were positively related to the upper and lower jaw displacement in the tooth extraction group;the change in total height of the lower lip vermilion were positively correlated with rotation of the mandibular plane,the change between lower lip vermilion height and facial angle wasnegatively correlation in the tooth non-extraction group(P<0.05).Conclusion:For skeletal Class ? malocclusion patients with compensatory treatment,sagittal changes in incisors related to the convexity in lips.In the tooth non-extraction group,the soft tissue profile was improved mainly by the upper lip advancement while the exposed amount of lip vermilion was increased after treatment.In the tooth extraction group,the soft tissue profile was improved mainly by the lower lip retraction while the exposed amount of lip vermilion was decreased after treatment,but the excessive lower lip retraction would worsen the concave profile,excessive decrease in the amount of lip vermilion would affect frontal esthetics.Therefore,tooth extraction of skeletal class ? patients should be careful.