Mandibular Vectorial Cephalometric Analysis In North China People

Objectives:Cephalometrics measurement plays an important role in orthognathic surgery on treatment planning, prediction and evaluation of the correction of dentomaxillofacial deformities. Traditionally, clinical application of cephalometry concerned single index rather than multiple indices correlation analysis. Therefore, the influence of functional status on morphological remodeling could not be demonstrated directly. This study focused on exploring the more effective index in order to probe the interrelation between development or remodeling of the mandible and the functional status in mandibles and to investigate such interrelationship in North Chinese people. The authors introduced a new cephalometric landmark--vectorial point of gonial angle (Gov) which has combined the extent variable of ramus/body of mandible and gonial angle variable at the same time, and then observation and statistically comparison of the difference of Gov distribution between normal people and bony Angle Class III dentomaxillofacial deformity cases were performed.Materials and methods:lateral cephalometric radiographs of 29 normal Tianjin local people (18-25years) and 15 Angle Class III patients (18-25years, ANB<-4°) were collected and analysed in aspect of the distribution of Gov in calibrated coordinate system by M point as the coordinate origin. The dispersal of Gov point, and other relevant measures concerning mandibular morphological characteristics in different group were analyzed and then statistically processed. All the cephalograms were analyzed by the same interne under supervision of experienced senior orthognathic surgeon, each cephalogram being examined two times on different days.Results:Repeated cephalometric analysis excluded identifiable intra-observer error. The barycenter of all Gov points distribution area located at X=-5.02 cm and Y =-7.65cm. The highest level of 95% confidence range among all measured distance between Gov variables and the barycenter is 1.15cm. The statistical difference of Gov location between diagnosed Angle Class III deformity patients and normal people was observed significant, as well as those within Angle Class III patients pre-and postoperatively. Nevertheless, there was no significant difference of the dispersal of Gov between normal person and postoperative Angle Class III patients. On the other hand, no identifiable difference between bony Angle Class III patients and normal people in terms of distance of vectorial point of gonial angle to mandibular foramina were recorded.Discussions and conclusions:Focused on the interconnection between morphology and function, author introduced a new pre-surgery cephalometric index—Gov. Combined morphological properties with vectorial variations, the new cephalometric landmark point Gov showed sensitive difference between dentomaxillofacial deformity patients and normal people. Furthermore, this new cephalometric index showed satisfactory stability and reproducibility. At the same time, the results implied that to a certain extent the measurement of the location of Gov could be used as a new criterion for preoperatively predictable planning and/or postoperative evaluation in orthognathic surgery.