Development of new high-strength dental cutting ceramic materials Fu Qiang, Zhao Yunfeng, Li Yan, Fan Danni, Qi Feng (Department of Prosthodontics, School of Stomatology, Sun Yat-sen University, Guangzhou 510060, Guangdong, China) Glass ceramics were obtained, and the crystal phase composition of glass ceramics was analyzed by X-ray diffraction. , and measure the strength of the material with a three-point bending method. The results obtained a new type of cutting ceramics containing calcium mica, the highest three-point bending strength (210 2 ± 147) MPa Conclusion By changing the crystal structure of the interior of the phlogopite glass ceramic can be a new type of dental cutting ceramics with higher strength.
1 Materials and methods 1.1 Equipment and materials High-temperature box resistance furnace (Jiangsu) SEM temperature controlled electric furnace (Chongqing), X-ray diffractometer (XRD) (D/MAX-2000B, Japan Science) Differential Thermal Analyzer (DTA) (PTC-10A type, Japan Science), Instron-4302 electronic tensile testing machine (UK), chemical reagents, platinum crucibles.
2 Selection of Raw Material Formulation and Preparation of Base Glass Aluminosilicate base glass was designed based on the DicorMGC formulation of fluorophlogopite and the CaO-K2O-Al23-Si2-F multicomponent system phase diagram. The chemical reagents were respectively ball milled and dried according to the composition of A and B (Table 1). They were melted at 1 400-1600° for 2-4 h, poured into the mold, and annealed at a glass transition temperature (500-600°C). Basic glass.
1.3 Preparation of Ceramic Materials and Identification of Crystalline Phase Compositions Using the results of differential thermal analysis, the glass was insulated at a certain temperature range (800-1200°) for 4-6. The basic glass was subjected to crystallization heat treatment, and a large amount of crystals were precipitated inside. Glass ceramic material.
Dental ceramic repair materials can be divided into traditional slurry sintered ceramics, foundry ceramics, cutting ceramics, hot pressed ceramics, and infiltrated ceramics, depending on the manufacturing technology. Among them, cutting ceramics combines advanced computer-aided design/assisted manufacturing technology with the advantages of rapidity, simplicity, and accuracy; and by providing large-scale industrial production of pre-formed porcelain blocks, it can better control the mechanical properties and optical properties of ceramic materials. (Color, Transparency, etc.) Therefore, currently cutting ceramics have been widely used in dental restorations (inlays), veneers, and crown bridges both in foreign countries and in China. However, only two or three kinds of cutting ceramic materials are used in clinical practice, and the performance is not yet ideal. Taking Dicoi.MGC as an example, this ceramic is a fluorophlogopite glass ceramic with good machinability, but due to its low strength (bending strength 80-150 MPa), the breakage rate is high in clinical applications. The range of application has been greatly reduced and is limited to inlays, veneers or anterior crowns. The methods of strengthening ceramics such as polishing, tempering, and ion exchange, which have been studied in the past, have not fundamentally changed the disadvantages of low material strength. To this end, the authors intend to develop a new type of high-strength, calcium mica-based cutting glass-ceramic materials based on the analysis of the internal crystal structure of fluorophlogopite glass-ceramics.
Fund Project: National Natural Science Foundation of China (39970799) Natural Science Foundation of Guangdong Province (010755); Guangdong Provincial Medical Research Fund (A2001046)> Fu Qiang (1972―), Male, Liuan, Anhui, Oral Clinical Lecturer Zhao Yunfeng, MD, West China School of Stomatology, Sichuan University
The chemical composition of the samples of Table 1 was analyzed by X-ray diffraction (XRD) for the crystalline phase composition of the ceramics.
4 Determination of strength of ceramic materials The two ceramic samples A and B obtained were cut into 20 mm X 3 mm X 2 mm test bars with diamond internal circular saws, 6 for each sample. The three-point bending strength was measured on an Instron-4302 mechanical testing machine with a span of /=16 mm and a loading speed of 0.5 2 . Results of the X-ray diffraction analysis of the two material samples are shown in Fig. 2. XRD is a modern identification of the phase composition of the material. Analytical test methods, the interplanar spacing d and the relative intensity I of the diffraction peak determined by the angular position (20) of the diffraction pattern on the diffraction pattern are the intrinsic properties of the material, the diffraction pattern of the object to be measured and the powder diffraction card ( CPDF) known d, I octoconumeric control, look for the same or similar images, you can determine the type of crystal phase. The three characteristic peaks of the calcium-mica powder diffraction card correspond well to the diffraction patterns of 9.1°, 27.6°, and 29.2°, respectively. It can be seen from the experiment that the glass ceramic material containing calcium mica has obtained B. Strength test results show that the three-point bending strength of material B reaches the highest (210.2±147) MPa. Materials Reinforcement Methods There are two major methods for strengthening ceramic materials, surface strengthening and self-reinforcement. Surface hardening refers to tempering, ion exchange, and other methods to increase the strength of the material. Some scholars have used surface polishing, tempering, ion exchange, and other surface-enhanced methods to enhance the strong rf57 of dental ceramics and achieved certain results. However, these methods generally only increase the strength of the surface layer of the material, and cannot fundamentally change the disadvantage of low material strength. For example, the use of ion-exchange method to enhance ceramics is to treat the surface layer of ceramics. The larger Na+ ions in the treatment agent replace the smaller Na+ ions in the ceramic, resulting in a compressive strength in the surface layer of the ceramic. improve. However, under the effect of chewing and abrasion, once the thin layer with a surface thickness of 16-18 Mm is worn away, the ion exchange can completely disappear. At this time, the material will suddenly burst (catastrophic failure). 8. Ceramic materials The self-enhancement means to change the chemical structure inside the material to increase the strength of the material.
For example, a dispersed second phase such as a crystal can be added to a ceramic glass matrix, since the glass matrix forms an ionic bond around the crystal when the ceramic is sintered. In this way, when the microcracks are expanded, they are hindered by the crystal phase and are branched, deflected, or passivated, thereby increasing the surface energy of the fracture, making the ceramic more resistant to external forces and increasing the strength. In addition, when the thermal expansion coefficient of the crystal phase is slightly higher than that of the glass phase, the glass phase will be under compressive stress when cooled, which will also help to improve the tensile strength. 3. The self-reinforcement is to improve the material composition of the material from the inside of the material as a whole. Studies with heat treatment programs have yielded a strength of iblishnfl that is more pronounced than that of surface-strengthened fleas and is not reduced or eliminated by external factors.
At present, in the field of enhancement research of dental ceramics, surface hardening methods have been rarely reported. The main research focus has been on various methods for self-enhancement of ceramics, such as adding crystalline phases with large crystal strength.
3.2 The theoretical basis for the development of new high-strength ceramic materials The strength of glass-ceramics is generally affected by the inherent strength of the crystal and the crystal size, content, shape distribution and other factors, in which the inherent strength of the crystal has a more important role and two tetrahedron and Mg2+ ions A layered structure is formed, and the layered structures are connected by K+ (or Na+) ions. Since K+ is connected to 12 zeros, its bond strength is only one-twelfth that of the KO key, which is much weaker than the Mg-0 key. Obviously, the mechanical strength of the mica crystals is mainly determined by the bonding strength of the K+ (or Na+) ions between the layers. Based on this, considering the use of Ca2+ instead of K+, that is, replacing phlogopite with calcium mica, the field strength of the interlaminar ions is increased (Ca2+ is 1.78 and K+ is 0.57), and the mechanical strength of the calcium mica crystals will be better than that of the phlogopite. A greater degree of improvement to increase the strength of mica glass ceramics. The three-point bending strength of ordinary fluorophlogopite glass-ceramic materials (such as DicorMGC) containing K+ (or Na+) ions is 150 MPa. The strength of the calcium-containing mica glass ceramics developed in this experiment can reach 210 MPa, which is significantly higher than that of the former. . The experimental results confirm the previous theoretical design.
3.3 Difficulties in the development of new ceramic materials and the development of key glass ceramics rely on the preparation of the base glass and the control of the crystallization heat treatment process. AmDent pays strong. A preliminary study on a new type of machinable ceramic material for dental CAD/CAM. Chengdu: West China University of Medical Sciences, 2000. Zhejiang University. Silicate chemistry. Beijing: Building Industry Press, 1980.3335. Macmillan, PW. Glass-ceramics. Translated by Wang Yiqian. Beijing: Building Industry Press, 1988.109159. (Editor Liu Qinghai) On the 12th, more than 70 teachers and students from the medical statistics, statistics, and applied mathematics majors from universities across the country gathered at the School of Public Health, Sun Yat-sen University, and participated in the seminar. Dr. Fang Jiqian, the director of the Department of Medical Statistics and Epidemiology, chaired the "Modern Medical Statistics Workshop." Participants unanimously reported that participating in this workshop was fruitful. They not only learned about the frontier areas of modern medical statistics, but also appreciated the grace of excellent Chinese statisticians.
(Hao Yuantao)
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