The Stability Of Mandible In Patients With Skeletal Class Ⅲ Treated By Surgery-First Approach

Objective:To explore the mandible stability of patients with skeletal class Ⅲ treated with Surgery-First Approach(SFA)verus Ortho-First Approach(OFA).Methods:This was a retrospective study.Fifteen patients with skeletal class Ⅲ underwent SFA were selected from 2014 to 2017 in the department of orthodontics,the affiliated hospital of Qingdao university.Meanwhile fifteen underwent OFA were selected as control.The lateral cephalometric radiographs were taken before surgery(T0)、two week after surgery(T1)and at finish of treatment(T2).The changement of point B and point Pog in the horizontal dimension was measured between T0 to T1:ΔTa= Ι T1-T0 Ι,ΔTa was the amount of mandibular setback during surgery.The changement of point B and point Pog in the horizontal and vertical dimension and the changement of angle SNB was measured between T1 to T2 after removing of the mandibular rotation :ΔTb=ΙT2-T1’Ι,ΔTb was the amount of mandibular relapse.Testing whether there was a correlation between the relapse of mandible and the setback of mandible during surgery in group SFA.The results were compared statistically between the two groups.Results:During the period from T0 to T1,the point B setback 7.11±1.02 mm and the point Pog setback 7.50±0.60 mm in group SFA;the point B setback 7.34±0.68 mm and the point Pog setback 7.19 ± 0.68 mm in group OFA.There was no statistical difference between the two groups(P > 0.05).There was weak correlation between the amount of mandibular setback and the amount of mandibular relapse.During the period from T1 to T2 in group SFA,the point B moved forward1.43±0.48 mm,downward 2.25±0.95 mm;Meanwhile the point Pog moved forward2.07±0.70 mm,downward 2.18±0.79 mm;and the angle of SNB increased 0.97±0.62°. While,the point B moved forward 1.41±0.62 mm,downward 1.51±0.73 mm;the point Pog moved forward 1.92±0.60 mm,downward 1.60±0.75 mm;and the angle SNB increased 0.96±0.59°.The results showed no statistically significant differences in the horizontal dimension(P > 0.05),but the difference was statistically significant in the vertical dimension(P < 0.05)between the two groups.Also,there were no statistical difference in the changement of SNB angle(P > 0.05)between the two groups.Conclusion:There is no correlation between the amount of mandibular setback and the stability of mandibular in horizontal dimension.The similar mandibular stability can be obtained in patients with skeletal Class III treated by SFA versus patients treated by OFA in the horizontal dimension.but the mandibular stability is lower in the vertical dimension.It is suggested that the vertical allowance should be given to the Surgery-First Approach.