Cephalometric Variables To Predict Prognosis Of Early Class ? Malocclusion Treated By Maxillary Protraction

ObjectivePrognosis is the main limitation of interceptive treatment of Class ? malocclusions.The interceptive procedures of rapid maxillary expansion(RME)and face mask therapy performed in mixed dentition are capable of achieving immediate overcorrection.But whether to maintain the facial and occlusal morphology for a few years is still an unresolved question.The purpose of this study was to evaluate the long term stability of RME and face mask therapy in the treatment of Class ? malocclusions in the mixed dentition when facial growth was close to completion.Furthermore,this study aimed at identifying the possible predictive variables and established a predictive model for the long-term stability of maxillary protraction therapy of Class ? patients.This predictive model was expected to be used clinically.MethodsThe clinical data was selected from the patients who received orthodontic treatment in 2008-2012.Cephalometric analysis of 40 Class ? female patients(mean age of 7.3 years)was performed at treatment onset and after a mean period of 6 years and 10 months at pubertal growth completion,patients were divided into two groups according to the relationship of occlusal: success group(20 individuals)and failure group(20 individuals).The data analyzed in this study conclude:(1)Independent t-test was used to compare the difference between the success group and failure group.(2)Discriminant analysis was applied to the cephalometric variables at treatment onset.Finally,the efficiency of the discriminant analysis model was tested Results(1)The factors which would increase the risk of unstable long-term stability include: a decreasing function of S-Ar(P=0.039),AB-MP(P=0.030)and N-A-Pog(P=0.037)and an increasing function of U lip-E line(P=0.019)and Pt-SBL(P=0.028).(2)Three predictor variables(S-Ar,AB-MP and Pt-SBL)were found by stepwise procedure.Individual score==0.289 ×(S-Ar)—0.203 ×(Ptm-FH)+ 0.178 ×(AB-MP)-16.664.When individual score >1.125,the long term result would be successful.When individual value score <1.125,the long term result would be unsuccessful.The results of treatment with RME and face mask therapy at growth completion in Class ? patients could be predicted with a probability of 92.5%.For the success group,85% patients can be correctly predicted.For the failure group,100% patients can be correctly predicted.ConclusionThis investigation analyzed the cephalometric variables from Class ? female patients who received RME and face mask therapy and selected three cephalometric variables that might predict the outcomes of orthopedic treatment with RME and face mask therapy which include S-Ar,Ptm-FH and AB-MP.These results suggest that Class ? growing patients with small posterior basal length,the lower position of the pterygoid,and obtuse chin angle are highly associated with unsatisfactory treatment outcomes after pubertal growth.The prediction model was tested to be clinically useful,and needs improvement to increase the hit rate.