Cephalometric Study Of Different Appliance In Maxillary Protraction In The Treatment Of Skeletal Class Ⅲ Malocclusion In Mixed Dentition

Objective: This study was conducted to evaluate the skeletal effect and dental anchorage of modified maxillary protraction appliance combined with bilateral maxillary first molar bands-transpalatal arch(TPA)-Nance arch,compared with traditional appliance,with or without rapid maxillary expansion(RME)for the patients with skeletal Class Ⅲ malocclusion in mixed dentition.This study will provide a reliable experiment basis for clinical treatment for patients with different ages.Methods: A total of 40 subjects with skeletal Class Ⅲ malocclusion in mixed dentition were divided into two groups,Group A and Group B.Group A is under the condition of bilateral maxillary first molar bands-TPA-Nance arch appliance;Group B is set to bilateral maxillary first molar and premolar(or second deciduous molar)bands-TPA appliance.Each group was divided into two groups respectively.The patients in Group a received maxillary protraction alone,as a comparison,the other Group b received maxillary protraction with RME.The name of the group was 1(two bands group),2(two bands with RME group),3(four bands group),4(four bands with RME group).There were ten subjects in each group.All lateral cephalograms,before and after the treatment,were measured.The data before and after the treatment of each group was analyzed by paired sample t-test to investigate the treatment effect.The difference between groups was analyzed by independent sample t-test to investigate the treatment difference.Results: The sagittal relationship of maxilla and mandible of all groups showed the different degree in improvements;the maxilla moved forward and downward,the mandible rotated backward and downward.All groups showed labial inclination of upper incisors,the lingual inclination of lower incisors,and maxillary first molar medialization in different degree.Anterior overjet and molar sagittal relationship had significant improvement.1 After the treatment of maxillary protraction,for the skeletal part,ANB,Wits,SNA,NA-PA,and Ptm-ANS in each group were significantly increased(P<0.01),SNB decreased.SN-PP at group 1 and 2 were significantly decreased(P<0.05),the Y axis at group 1 and 2 were significantly increased(P<0.05),MP-SN and Co-Po at group 1,2 and 3 were significantly increased(P<0.05).Maxillary vertical distance ANS-X at group 1,2 and 4 were significantly increased(P<0.05),A-X had no statistically significance before and after treatment.Maxillary sagittal distance ANS-Y and A-Y in each group were significantly increased(P<0.05).Mandibular vertical distance B-X at group 1,2 and 3 were significantly increased(P<0.05),Po-X in each group were significantly increased(P<0.05),mandibular sagittal distance B-Y at group 2and 4 were significantly decreased(P<0.05),Po-Y at group 2 were significantly decreased(P<0.05).Co-X,Co-Y,Ar-X and Ar-Y had no statistically significance before and after treatment.Cephalometric items mentioned above showed no statistic differences between groups,except that Ptm-ANS had statistically significance between group 2,4 and group 3,4(P<0.05),NA-PA had statistically significance between group 1and 2(P<0.05).2 After the treatment of maxillary protraction,for the dental effects,the U1-SN in each group were significantly increased(P<0.05),L1-MP and L1-NB decreased(P<0.05),SN-OP at group 1 and 3 were significantly decreased(P<0.05).Maxillary tooth vertical distance Is-X,Ms-X and sagittal distance Is-Y,Ms-Y in each group were significantly increased(P<0.05).Mandibular tooth vertical distance Ii-X at group 2 and Mi-X in each group were significantly increased(P<0.05),sagittal distance Ii-Y at group 1,2 and 4 were significantly decreased,Mi-Y at group 1 and 2 were significantly increased(P<0.05).Cephalometric items mentioned above showed no statistic differencesbetween groups,except that Is-Y had statistically significance between group1,2 and group 2,4(P<0.05),Ms-Y had statistically significance between group 1,2 and group 1,3(P<0.05),Ii-Y and Mi-Y at group 1and 2 had statistically significance(P<0.05).Conclusion:1 Using modified maxillary protraction appliance could promote maxillary growth and improve the sagittal relationship of maxillary and mandibular significantly to treat the patients with skeletal Class Ⅲ malocclusion in mixed dentition.2 Using modified maxillary protraction appliance with RME could reduce the labial inclination of upper incisors and maxillary first molar medialization,showed better control of anchorage on upper incisors and maxillary first molar than traditional appliance.