Study On Mesiodistal Tooth Size And The Relationship Between Upper And Lower Teeth Dimension Of Normal Occlusion From Han People In Xi'an

To measure the study model is one of the important means of clinical diagnosis, treatment design and scientific research work. And the normal dentition structure could be seen as reference for evaluate the malocclusion. Correcting the dentition deformity demands the bite to be good relations, Upper and lower teeth should match each other. In 1958 and 1962, Bolton proposed the concept of Bolton analysis respectively. Bolton analysis is on the basis of evaluating tooth and bone mass relations, to further analysis whether the upper and lower teeth are coordinated, which can help us predict the over bite, over jet and molar relationships nearly the end of treatment. Number of studies about Bolton analysis of the normal occlusion, the results exist differences, especially the anterior ratio. The large number of domestic and international study has confirmed that the size of human tooth exist differences between the different races, the different regions and the different times. Clinical Orthodontics concerning the teeth size must be based on the analysis of the national characteristics of the region, in order to get good treatment effect. There are fewer reports in this regard about Xi'an.This study, using epidemiological investigation, selected normal dentitions as a study in Xi'an, the average age of which is 18 years old. All individuals are Han people. Application of orthodontic vernier caliper extracts the required date information, using proper statistical analysis to process experimental data. On the basis of this date of the Mesiodistal tooth width, the mean and standard deviation were calculated for the size of the teeth. Then the normal range was obtained for the anterior and overall tooth size ratio. The relationship between upper and lower teeth dimension of normal occlusion was analyzed from Han people in Xi'an. To evaluate the effect of incisor crown thickness and lip inclination on final occlusion and the accuracy of Bolton analysis in predicting final occlusion.Main experiments are as follows:1. Obtain the normal distribution of each dental crown widthThe study models conforming to inclusion criteria of 52 male and 55 female with normal occlusion were selected. Survey results indicate that: There are certain gender differences, and these differences are not in a level. There is a significant statistical difference between male group and female group in the upper incisors, lateral incisor teeth, canine, the first permanent molars and the mandibular canine, premolars crown width. Men's average tooth size is greater than women's.2. Analyzing the normal range of upper and lower tooth mass ratio and the correlation between upper and lower teeth dimension of normal occlusionThe results of this study are: anterior teeth ratio is 78.32%±3.01; the total tooth rate is 91.10%±2.27. There was significant correlation between the upper and lower tooth (ranterior = 0.754, rtotal=0.851). According to the significant correlation, the regression equation that was used to quantify the tooth size discrepancies was expressed.3. Analysis the change of ideal anterior ratio as the increasing of thickness of upper incisors or the marginal ridgeAs crown thickness increased, to achieve the ideal intermaxillary occlusion, its corresponding anterior tooth ratio gradually become smaller. This prompted us: Bolton analysis was not always accurate in predicting final occlusion. The change of thickness of upper incisors or the marginal ridge affects the ideal anterior ratio.4. To establish a normal bite, whether there was a compensatory effect between the lip inclination of anterior tooth and the ideal anterior ratioFor normal occlusion, there was no significant correlation between anterior teeth ratio and the lip inclination of anterior tooth. (After measuring the lip inclination on 107 normal cephalometric films, and calculating the anterior tooth ratio on the study model, then the correlation relationships between them could be analyzed. It was found there was no significant correlation between the two, which suggested the compensatory effect between the lip inclination of anterior tooth and the ideal anterior ratio doesn't exist in normal occlusion).To sum up, this research obtained the normal distribution of crown width and analyzed the relationship between upper and lower teeth dimension of normal oc- clusion from Han people in Xi'an. The normal range was obtained for the anterior and overall tooth size ratio. In this study, to achieve the ideal occlusion, it is foun- d its corresponding anterior tooth ratio gradually become smaller as crown thick- ness increased. To establish normal occlusion, there was no significant correlation between anterior teeth ratio and the lip inclination of anterior tooth.