The Basic Research Of A Novel Mica-glass-ceramic Based On Fluorophlogopite (KMg₃AlSi₃O₁₀F₂) For Dental Application

For the excellent aesthetics performance, chemical stability and biocompatibility, the all-ceramic materials have been widely applied in dental clinic. Moreover, the innovative introduction of CAD/CAM technique initiated the technical revolution of fixed-denture manufacturing.The major feature of machinable ceramics is good cutability with the CAD/CAM technique. Using this material, restoration can be made at the chairside in one visit without the need for impression or laboratory assistance. However, the brittleness and low tensile strength of conventional ceramics is still a big obstacle for long-term clinical application of all-ceramic material. The cut-behavior-modality of ceramics is fragile micro-crack expandision and production of particle trimmings. Growth of microscopic flaws formed during processing and surface damage generated during service might lead to the final catastrophic fracture or margin failure of restoration. Besides, the heat treatment procedures and technics are complicated. Therefor, the exploitation of ductile machinable dental ceramic would bring a promising outlook to the dental restoration.For the purpose of exploiting new ductile machinable dental ceramic, a novel mica-glass-ceramic based on SiO2-B2O3-K2O-Na2O- Li2O-Al2O3-ZnO-MgO-F was studied in this research .This material is characterized by excellent ductile cutability just like metal cutting. When the propotion of mica reached about 30%, continuous girdle-shaped chips, instead of particle trimmings, came up in the condition of high speed cutting. In order to select the optimal crystallization heat-treatment condition, the effects of heat treatment and the possible mechanism of the ductile-cut behavior of the material were investigated.According to different crystallization techniques, standardized specimens were divided into 7 groups. Control(Vita MarkⅡ)group was used to measure the mechanical properties by drilling and turning test. Flexible strength and Vickers hardness test were also performed. Microstructure was analyzed by scanning electron microscopy(SEM) and X-ray diffraction(XRD).The conclusions were as follows:1.The machinability of this new material was superior to Vita MarkⅡ. 2.In this study, the machinability of this material was closely related to the crystallization temperature and duration. When crystallized at 680℃(60min),continuous band chips were formed in machining at a high velocity. As the temperature and duration of crystallization increasing, there was a decreasing trend for the machinability.3 . The flexible strength of this material was significantly influenced by the temperature and duration of crystallization. With the rise of crystallization temperature and duration, there was a peak(>170MPa) of flexible strength at 680℃for 120min.4.The Viker's hardness of tested groups was increasing with the rise of crystallization's temperature and duration, but lower than the control group.5.The optimal machinability was achieved when the proportion of mica reached about 30%. The mechanism of this surprising property was the combination of mica crystal guidance for crack propagation and the ability of glass phase to produce intense shearing strain.6.The optimal heat treatment for crystallization is 680℃for 60min.