The Design And Development Of The Lithium Disilicate Glass-Ceramic With High Translucency

The lithium disilicate glass-ceramics as one of the most promising dental restorative materials have been clinically used in dental restoration due to their high mechanical property,suitable translucency and good biocompatibility.However,the lithium disilicate glass-ceramic products in our country are completely imported from abroad,so they are very expensive,limiting their wide application in our country.Besides,the relatively low translucency of the commercial lithium disilicate glass-ceramics greatly limits its application in dental restorations,such as the ceramic veneer and anterior teeth.It is therefore of great importance to develop the lithium disilicate glass-ceramics with high translucency to expand their current application in dental restoration on one hand,and to develop the lithium disilicate glass-ceramics with new intellectual property right on the other hand.A calculation procedure to determine the crystallization kinetic parameters by using a non-isothermal method was proposed in the present investigation.Firstly the crystallization mechanism was determined and then the activation energy E was calculated based on the crystallization mechanism.The calculation procedure takes the intrinsic relationship between the activation energy E and the crystallization mechanism into account,which can solve the problem that the traditional method can not acquire the actual activation energy and predict the controllability of a glass system.Therefore,the content of the component?Al₂O₃?which largely affects the controllability of the glass system was optimized based on the proposed calculation procedure.It is found that when the content of the Al₂O₃ is about 3mol%,the glass system has the lowest activation energy,indicating that the crystallization process of the glass system can be easily controlled;and at the same time,the bulk crystallization can be realized.Then a further investigation on optimizing the composition was made.Ultimately,a parent glass was designed and optimized.The glass system can fulfill all the following requirements:good glass forming ability,controllable crystallization process,volume crystallization,and precipitation of the Li2SiO3 and Li₂Si₂O₅ step by step.The effects of single-stage heat treatment and two-stage heat treatment on the crystal growth in the lithium disilicate glass-ceramics were systematically investigated to provide an effective guidance on controlling the size of Li₂Si₂O₅ crystals.Experimental study demonstrates that the two kinds of heat treatment procedures have no obvious effect on the crystalline phase,in contrast,they have great influence on the microstructures of the glass-ceramics.The nucleation of the two-stage treatment is more effective than that of the single-stage treatment,resulting in the smaller lithium disilicate crystals.Besides,the size of the crystals in the glass-ceramics prepared by two-stage treatment is affected by both the heat treatment temperature and the heat treatment time.The size of Li₂Si₂O₅ crystals increases with increasing the heat treatment temperature.With prolonging the heat treatment time,the crystals will coarsen and lead to the non-uniform of the crystalline size.While,the size of the crystals in the glass-ceramics developed by single-stage treatment is mainly influenced by the treatment temperature.With the heat treatment temperature increases,the size of Li₂Si₂O₅ crystals also increases.However,the size of Li₂Si₂O₅ crystals is hardly affected by the treatment time.It was found that the lower Li₂Si₂O₅ crystallization temperature is favorable to refine the size of Li₂Si₂O₅ crystals,improving the translucency of the glass-ceramics,while,appropriate high Li₂Si₂O₅ crystallization temperature is beneficial to the growth of Li₂Si₂O₅ crystals,leading to the enhancement of mechanical property.Therefore,based on the above variation,the directional regulation of the Li₂Si₂O₅ crystalline size form 100nm to 1.5?m and the qualitative control of the translucent and mechanical properties were realized.Ultimately,the lithium disilicate glass-ceramics with the translucency in the range of 13.96?52.29,the flexural strength 335-455MPa and the fracture toughness 2.06?2.98MPa m1/2 are prepared.In addition,the most translucent glass-ceramics developed in the present study has the similar mechanical property with the commercial lithium disilicate glass-ceramics,but its translucency is much higher than that of the most translucent commercial lithium disilicate glass-ceramic?Tp value improved by 33 when the thickness is 1 mm?,which will expand the current applications of the lithium disilicate glass-ceramics,such as the ceramic veneer and anterior crown.