Characteristics Of Reference Points In Bracket Positioning On Normal Occlusion In Teenagers

Precision bracket placement is the foundation of successful orthodontic treatment. However, how to place brackets is still controversial. There are three methods we usually use in clinical operation. Using the center of the clinical crown as a reference point for bracket placement; McLaughlin and Bennett calculated bracket heights statistically to produce their bracket placement chart; placing bracket to level the marginal ridges. Researchers present these methods by the reference of the center of the clinical crown and the marginal ridges. Orthodontics has the largest number of teenage patients. Therefore, it is worthwhile doing a research on the reference points such as the clinical crown or the marginal ridges. The result can be used to guide bracket placement.In this study, model analysis was carried out in a 2D model measuring instrument and electronic digital indicator.The characteristics of the clinical crown and the marginal ridges are supposed to show up.The study was divided into two parts as follows:Part one Development of a 2D model measuring instrument could be used in dental field.ObjectiveTo introduce the development of a simplified 2D model measuring instrument , and to compare the measurement with manual measurement.MethodsA 2D model measuring instrument can be development by modified electronic digital indicator and lucite. Repeated measurements on Spee depth on right side,width between lower and upper canines of 30 plaster models were acquired to value the reliability of the new measurement and the validity was investigated through the correlation analysis between the new and manual measurements.ResultsThe correlation coefficients obtained in reliability validation were 0.978,0.957,0.987,while those obtained in validity validation were 0.954,0.951,0.986.ConclusionA 2D model measuring instrument can be developed by the application of simple device. Measuring method using a 2D model measuring instrument was accurate,and reliable for both clinic and research purposes.Part two Research of reference point in bracket positioning on normal occlusion in Guangzhou teenagersObjectiveInvestigate the regularity of marginal ridge on normal occlusion in teenagers. Evaluate the practicality of using the center of the clinical crown , MBT bracket place chart or marginal ridges in positioning brackets and then to provide the reference for bracket placement in orthodontics.MethodsSelect 59 Guangzhou teenagers with normal occlusion. All of them are treated with ultrasonic scaling. Get the plaster models with silicone rubber and anhydrite. Measure the features of the center of the clinical crown and marginal ridges by a 2D model measuring instrument and electronic digital indicator.Results(1)Get the difference height of marginal ridge, the height of the center of the clinical crown, the line of the center of the clinical crown and sagittal curve of occlusion. The lines were undergoing Pearson correlation analysis.(2)The data of height difference of marginal ridges followed a normal distribution and there was no significant difference in that between the left and the right, nor the man and the woman. The marginal ridges of different posterior teeth were not located in the same plane.(3)There was no significant difference in the center of the clinical crown between the man and the woman. There was a set of a reference value of the center of the clinical crown in Guangzhou.(4)The line of the center of the clinical crown and sagittal curve of occlusion were both a regular turning curve. They were significantly correlated with each other.ConclusionThere are restrictions on the methods of using the center of the clinical crown, MBT bracket place chart or marginal ridges in positioning brackets.