Using Coben Analysis To Evaluate The Therapeutic Effect Of Maxillary Protraction On Maxillary Maldevelopment

ObjectiveCephalometrics is an important technique in orthodontics,which can be used to diagnose,make treatment plans and carry on researches.Nowadays tens of cephalometric techniques have been developed,including Coben analysis. Coben analysis works mainly by measuring distance between points and lines to disclose the relationships among teeth and bones,which could supply valuable information for the diagnosis,treatment planning and research on malocclusion.This kind of cephalometic analysis is more visual and understandable comparing with angle analysis.Treatment plans are made according to pathogenic mechanisms of Angle ClassⅢand malocclusions with different mechanisms calls for different treatments. As well acknowledged, it is feasible to treat the skeletal classⅢmalocclusion with maxillary maldevelopment by protraction face mask in the pubertal period.Articles show that different angle analysis has been used to illustrate the pathogenic mechanisms of skeletal Angle ClassⅢmalocclusion and evaluate the effect of protraction on maxillary maldevelopment,but no such information is found by Coben analysis.In this article,advantages of Coben analysis are discussed by comparing results of Coben analysis and angle analysis which show the effects of protraction on skeletal Angle ClassⅢmalocclusion.The conclusions will provide evidence for further clinical application of Coben analysis.Methods33 patients from the Orthodontic department of Jilin University Stomatology Hospital,who were diagnosed as skeletal ClassⅢmalocclusion with maxillary maldevelopment,were selected as the subjects in this research.All the subjects had characters as follow:anterior teeth crossbite,absence of width deficiency,in the second or third stage according to the cervical vertebral maturation(CVM)method which means all the subjects in the peak of the skeletal maturity.Clinical documents such as cephalometric radiographs, orthopantomographies,photos, record casts and records were well kept.Each subject received maxillary protraction by face mask with 450-500g force and a direction of downward and forward pull of 20-30°to the occlusal plane. The face mask was used for 12-14 hours and the course of treatment lasted for 6-12 months. Cephalometric radiographs were taken before treating and just after correction of the anterior crossbite,and then Coben analysis and angle analysis were done.Data from the analysis was obtained by SPSS 17.0 software and paired-samples T test was carried out to check the differences between Coben analysis and angle analysis on evaluating the therapeutic effect of maxillary protraction on maxillary maldevelopment.Results1.the changes in the depth of facies cranii after maxillary protraction Paired-samples T test was used to analyze the changes in the depth of facies cranii after maxillary protraction.It was found that Ba-N and Ba-A increased significantly (P <0.001).Among the measurements in the mid-face Ptm-A increased significantly (P <0.001) while Ba-S and S-Ptm hardly changed.The depth of the lower face(Ba-Pog) decreased(P <0.01),in which Ar-Go decreased significantly(P <0.001) while Ba-Ar and Go-Pog hardly changed.The mandible length of Ar-Go(AL) and Go-Pog(MP) both increased.2. the changes in the height of facies cranii after maxillary protraction Analyze the changes in the depth of facies cranii after maxillary protraction by the paired-samples T test. It was found that N-Me significantly increased(P <0.001) while N-Go decreased (P <0.05). Among the measurements in the back facial height,S-Ar and S-Go decreased in some extent while N-S and Ar-Go nearly kept stable. Among the measurements in the front facial height ANS-Me and LI-Me increased while the others decreased.The ratio of the height and depth of facies cranii significantly increased(P <0.001).3.Results of the angle analysis after maxillary protraction The angle analysis in Hua Zheng cephalometric software of Beijing University includes several distance measurements such as U1-NA,L1-NB,Pg-NB which would be analyzed in this article.Among the results in Hua Zheng cephalometric software of Beijing University,all of the angle measurements changed statistically except L1/NB.SNA,ANB,U1/NA, U1/SN, MP/SN, MP/FH and Y axial angle significantly increased while SNB,U1/L1, FH-NP and L1/MP decreased in different extents.In the distance measurements U1-NA significantly increased(P <0.001) while no change were found at L1-NB and Pg-NB.Conclusion1.Comparing with angle analysis,Coben analysis is more accurate and more visual in identifying the pathogenic mechanisms of Angle ClassⅢmalocclusion.It provides evaluation on the effects of maxillary protraction in detail by analyzing the inner craniofacial structure.2.Satisfying effects can be obtained by treating skeletal Angle ClassⅢmalocclusion with maxillary maldevelopment by protraction face mask in the pubertal period.3. Maxillary protraction significantly improves maxillary maldevelopment with a main pathogenic mechanism of small Ptm-A in Coben analysis.4.It is suggested that Coben analysis should be widely applied in domestic clinic.