Research On Direct Manufacturing Process Of Customized Lingual Brackets By Selective Laser Melting

Lingual orthodontics is a novel technology of clinical dentistry and emerges an expanding adoption for its advantages of invisibility, good utility and extensive disease adaptability. However, the commonly used lingual bracket at present is mass and standardizing production, which has the drawback of mismatch for individual cases. Customized lingual orthodontic system has been developed abroad, but less researches or documents concerning the customized lingual technique could be found at home. Foreign researchers invited rapid prototyping technology to obtain wax pattern, and then manufactured the customized lingual orthodontic brackets by using the investment casting method, which obviously bears the problem of complicated process. Selective Laser Melting is a new rapid prototyping technology for directly producing complicated metallic parts. Researches on the design and direct manufacturing of customized lingual bracket by Selective Laser Melting is of great significance for developing domestic customized lingual orthodontic system.This paper first studied the action principle of customized lingual arch wire and the brackets. According to its functional requirements, the placing plane and shape of the arch wire were determined. Then the customized lingual brackets were designed referring to the structure of the lingual bracket in market.Secondly, stainless steel 316L was chosen as experimental material. Single track scanning, layer scanning and multi-layer scanning experiments were carried out on the SLM rapid prototyping equipment DiMetal-280. On basis of analyzing the forming process and the effects of the parameters on final parts quality, the processing technique was determined and the processing parameters were optimized. This paper also put forward an interlayer-stagger scanning strategy, which helped improve the density of the molding entity. Based on the fundamental researches of SLM shaping metal parts, the experiments of forming brackets with SLM were implemented in order to find out the clues of obtaining brackets of good qualities including normal producing process and key technique parameters.Thirdly, the melt gathering and balling phenomenon occurring in multi-layer forming were analyzed to deepen the understanding to such phenomena and to explore their causes. On this basis, the eliminating effects of interlayer-stagger scanning strategy to the melt gathering and balling were confirmed and the forming mechanism in overlapping was analyzed.Results showed that interlayer-stagger scanning strategy could effectively eliminate the melt gathering and balling phenomenon during multi-layer forming, and significantly improve the surface quality, density and precision of the brackets. There were three patterns available in interlayer-stagger scanning strategy: intra-lay overlapping, inter-lay overlapping and mixed overlapping. Among these the inter-lay overlapping which promises high size precision in three dimensions is preferred for forming brackets.At the final, a comprehensive processes including case diagnose, bracket design, bracket forming and orthodontic were finished and evaluated. The brackets were produced by using SLM under interlayer-stagger scanning strategy and with such optimized parameters: P=150W,V=300 mm?s-1,d=0.08mm,h=0.02mm. The orthotherapy experiment was undertaken by simulating on Typodont model, which demonstrated that the integrated methods of designing and manufacturing lingual orthodontic brackets were preliminarily usable and reliable.