| Titanium has been widely used in oral medicine as a biological material with its excellent physical, chemical and biological properties. It has now developed to the 3rd generation. The research direction is to develop a new titanium alloy which has better biocompatibility, lower modulus and more excellent performance. It also does not contain potential toxic elements such as aluminum and vanadium. Because of its low modulus and excellent alloy properties,β-type titanium alloy has become the focus of attention at home and abroad in recent years. But most of these titanium alloy products are foreign research and development and our R & D in medical titanium alloys are relatively backward, which limits its application in China. Ti-24Nb-4Zr-7.9Sn (wt%, referred to as TNZS) alloy is a new low modulusβtype titanium alloy. It was developed by Shenyang Metal Research Institute. It maintains excellent mechanical properties of new titanium alloys and also has a lower elastic modulus, as low as 33GPa, closer to the elastic modulus of bone (10-30GPa) and dentin (12-18.6GPa). It is a very promising titanium alloy in Prosthodontics and dental implants. Early results show that: The alloy has good mechanical properties and biological properties, which meet the requirements for dental materials. Now It is a ideal material for implants, hook and post and core. But in the clinical routine conditions for titanium casting, the castability of Ti-24Nb-4Zr-7.9Sn alloy is low, so the clinical applications of the alloy has been limited.This study is to discussion the regular pattern of effect of different investment materials and diameter of sprue and length of sprue on the castability of Ti-24Nb-4Zr-7.9Sn alloy, and find out the most suitable investments and diameter of sprue and length of sprue for it, improve its castability. We also examine surface reaction layer of the alloy and the fitness of casting crown, preliminary evaluate alloy casting accuracy, support experimental basis for further clinical application.Objective:To analyze the the influence of different investment materials and different diameter of sprue and different length of sprue on the castability of Ti-24Nb-4Zr-7.9Sn alloy, find out the most suitable investment materials and diameter of sprue and length of sprue for the alloy, improve it castability and examine surface reaction layer of the alloy and the fitness of casting crown, preliminary evaluate alloy casting accuracy, support experimental basis for further clinical application.Methods:1. Net patterns were applied in this study. Ti-24Nb-4Zr-7.9Sn alloy were casted respectively in 3 kinds of investment materials and three diameter of sprue and three length of sprue. The castability value was obtained by counting the complete segment of the cast alloy grid. do statistical factorial design analysis for the data . 2. The castings of Ti-24Nb-4Zr-7.9Sn alloy were invested in investment material based by MgO. The roughness and the status of sticky powder were macroscopically observed. The structure of reaction layer was observed with scanning electron microscopy (SEM) and metallurgical microscope. The element composition was analyzed with energy dispersive spectrum (EDS). The hardness and thickness of reaction layer were observed with microhardness apparatus3. Standard cast specimens and round capsules simulating post tooth crowns were made. The marginal opening of the metal full-crown was measured with SEM, observe the marginal adaptation between the edge of casting crowns and the edge of standard specimenResults:1. The castability of Ti-24Nb-4Zr-7.9Sn alloy at room temperature can be improved by improving the investment materials and casting sprue diameter and length. The investment materials and diameter of sprue and length of sprue have different levels of effects on castibility of Ti-24Nb-4Zr-7.9Sn alloy. Magnesia Series is most suitable for Ti-24Nb-4Zr-7.9Sn alloy. In this group the net patterns can get the best castability ,and the castability of the specimens in each group reduce or increase flow the change of the diameter of sprue and the length of sprue, but still can not believe that interaction exist among the three elements. The results showed that Magnesia Series is most suitable for Ti-24Nb-4Zr-7.9Sn alloy, the diameter of sprue should be 5mm, the length of the sprue also should also be 5mm, selected group of MgO bonded2. The interfacial reaction between MgO bonded and Ti-24Nb-4Zr-7.9Sn alloy is light, surface reaction layer is thin, only about 20μm,It meet the clinical requirements.3. The full-crowns of Ti-24Nb-4Zr-7.9Sn alloy casted in Magnesia series investment material is complete. Marginal adaptation is good. The fitness can achieve to the requirments in clinical practice.
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