A Cephalometric Study Of Different Saggital Skeletal Pattern By Beta Angle Analysis

Estimation of relationship between maxilla and mandible in saggital direction plays an pivotal role in the process of clinical diagnosis and treatment plan designing, and that is especially precise for patients with cranio-facial deformity who require for orthodontic or orthognathic surgery treatment. Pathogenesis of dentofacial deformity is complex and its exact mechanism has not been understood. Anteroposterior relationship between upper and lower jaw may have significant effect on facial esthetics and jaw function. In a word, appropriate distinguishing of dentofacial deformity pattern will contribute to treatment objectives establishing and good treatment result achieving.After the introduction of X-ray technology, application of this emerging technology has promised to afford us more information on dental, jaw and cranio-facial discrepancy. Since cephalometric measurements were introduced by Broadbent in 1931, more than 100 kinds of cephalometric measurements have been developed by orthodontists as an aid in diagnosis. Cephalometric measurements aiming at providing an evaluation of the anteroposterior relationship between maxilla and mandible include ANB, AB plane angle, Wits appraisal etc.Beta angle analysis was introduced by Baik in 2004, and it was designed to avoid the shortcoming of previous analysis of cephalometric measurements in evaluating anteroposterior jaw discrepancy. Beta angle analysis is simply an adjunctive diagnostic aid that may be useful in assessing the severity of skeletal dysplasia in the saggital direction. As we all known, dentofacial deformity present intra-racial variation, cephalometric norms with regard to gender and age in Chinese population should been evaluated so as to establishing cephalometric standards for clinical application of Beta angle.This study was aimed to apply"Beta Angle"into evaluation anteroposterior relationship between maxilla and mandible and to establish cephalometric norms with regard to gender and age in Chinese population as an adjunctive diagnostic aid in dentofacial deformity.Material and methods:1,This study comprised 341subjects in XI'AN , and they were divided into 12 groups according to age, gender and skeletal pattern. They underwent cephalometrics analysis.The Beta angle and Alpha angle were measured and collected.The mean angle value in each group was compared mutually by statistical analysis (student-t test).ROC curve was used to establish reference range of the Beta angle.2,To measure Beta angle variation in mandibular rotation and effective length ratio(K)of maxilla to mandible and to caculate the arithmetic mean and standard deviation respectively .The relationship of the three parameters was analysed with the software"mat lab".3,To evaluate how landmark location variation of condylar center affect value of Beta angle by geometric analysis.Results:1,Both gender and age had no significant effect on value of Beta angle. The cephalometric standards for Beta angle in skeletal ClassⅠwas 31°—39°. Beta angle value more than 39°can be regarded as a predictor of skeletal ClassⅡmalocclusion, and Beta angle value less than 31°as skeletal ClassⅢmalocclusion.2,With the increasing of the mandibular rotation angle(C) , Beta angle show the tendency to decrease. And more large value of K ,more prominent the tendency will be .In skeletalⅡrelationship ,variation of Beta angle caused by mandibular rotation was limited in 2.62°.3,landmark location variation of condylar center in certain range may not lead to significant variation of Beta angle value.Conclusions:1,Beta angle value ranging from 31°to 39°can be used as the cephalometric standards for skeletal ClassⅠ.2,In skeletalⅡpatients , the effect of the mandibular rotation on the Beta angle was not notable and Beta angle show adequate validity. 3,landmark location variation of condylar center in certain range may not affect distinguishing of dentofacial deformity pattern.