Abrasive Resistance Of Lithium Disilicate Glass-ceramic And Leucite Reinforced Glass-ceramic

Due to the excellent esthetics characteristics, moderate mechanical behavior and good processing technic, hot pressing casting glass ceramics commonly used in clinical practices are popular among oral physicians and patients. However, there is long-term and avoidless abrasion on antagonist natural teeth when dental ceramic restoration functions in the mouth. Excessive wear of restoration may cause problems such as destruction of teeth occlusal surface, exfoliation and jackknifing of the restoration. Through learning about wear behavior, wear mechanism and influence factors of dental ceramic material, the oral physicians can choose appropriate repairing material according to specific conditions of the patients. Meanwhile, it is helpful for people to research and develop dental restorative materials more suitable for oral environment.Study on the abrasion performance of hot pressing casting glass ceramic at home and abroad mainly focuses on the abrasion of ceramic at some point in time. However, according to the classical theory of tribology, ceramic wear behavior has time dependence,and wear behaviors have great differences in different periods of wear process. Therefore, wear characteristics between ceramics and teeth or other antagonist materials are hard to be grasped dynamically and deeply if one only depends on wear changes in short period. For this reason, this experiment chooses two kinds of hot pressing casting glass ceramics commonly used in clinical practices--lithium disilicate glass ceramic and leucite groundmass glass ceramic as the research objects. Through analysis of wear mechanism from perspectives of own factors and external environment of the ceramic, this experiment aims to learn about the evolution of the wear behavior of castable ceramic dynamically when time changes, and to provide some references for clinical reasonable evaluation on dental ceramic materials.AIM: Through research on mechanical behavior and microstructure of lithium disilicate glass ceramic and leucite reinforced glass ceramic, two kinds of hot pressing casting glass ceramics and steatite ceramics constitute biological friction pairs. The author tries to observe the changes of wear behaviors of two pairs of biological friction pairs as time passes in wet and dry environment. This simulation aims to provides experimental data for deep knowledge of the influence which the external environment and the own factors of dental ceramic materials have on wear mechanism, and for comprehensive improvement of all-ceramic restorative materials.METHOD: 1. Microstructures and mechanical behaviors of lithium disilicate glass ceramic and leucite groundmass glass ceramic: measure the bending strength of the two kinds of castable ceramics with three-point-bend method, and prepare ten samples; then measure the hardness and elastic modulus of the ceramics with nanoindenter and carry on X-ray diffraction phase analysis; finally give acid etching to the two kinds of ceramics with a certain concentration of hydrofluoric acid and carry on metal spraying, scanning electron microscopy observation and EDAX analysis on the ceramic specimens before and after acid etching respectively.2. The influence from wet environment on the wear mechanisms of lithium disilicate glass ceramic and leucite groundmass glass ceramic: use lithium disilicate glass ceramic, leucite groundmass glass ceramic and steatite ceramics to constitute biological friction pairs respectively, prepare six samples for each group; perform wear test in environment of distilled water and no water through use of friction wear testing machine and keep cycles of 1,000,000 times. When the cycles reach for 100,000 times, scan with 3D surface topography and calculate the wear volume of two kinds of castable ceramics in two kinds of lubricating conditions, measure the volume loss of the jaw steatite porcelain, and finally draw material wear curve; observe and test the wear appearance with scanning electron microscope respectively in the early, middle and late period of wear. 3. The influence from dry environment on the wear mechanisms of lithium disilicate glass ceramic and leucite groundmass glass ceramic: use lithium disilicate glass ceramic, leucite groundmass glass ceramic and steatite ceramics to constitute biological friction pairs respectively, prepare six samples for each group; perform wear test in environment of distilled water and no water through use of friction wear testing machine and keep cycles of 1,000,000 times. When the cycles reach for 100,000 times, scan with 3D surface topography and calculate the wear volume of two kinds of castable ceramics in two kinds of lubricating conditions, measure the volume loss of the jaw steatite porcelain, and finally draw material wear curve; observe and test the wear appearance with scanning electron microscope respectively in the early, middle and late period of wear. 4. The influence from environment on the wear mechanisms of lithium disilicate glass ceramic and leucite groundmass glass ceramic: use lithium disilicate glass ceramic, leucite groundmass glass ceramic and steatite ceramics to constitute biological friction pairs respectively, prepare six samples for each group; perform wear test in environment of distilled water and no water through use of friction wear testing machine and keep cycles of 1,000,000 times. When the cycles reach for 100,000 times, scan with 3D surface topography and calculate the wear volume of two kinds of castable ceramics in two kinds of lubricating conditions, measure the volume loss of the jaw steatite porcelain, and finally draw material wear curve; observe and test the wear appearance with scanning electronmicroscope respectively in the early, middle and late period of wear. After the two kinds of castable ceramic specimens are steeped in deionized water for seventy two hours, carry on X-ray diffraction phase analysis to analyze if ceramic surfaces have hydration that influences wear behavior.RESULT: 1. Hardness of lithium silicate glass ceramic and leucite reinforced glass ceramic were(743.72±28.74) HV,(677.57±9.19) HV, elastic modulus were(90.96±2.78) GPa,(58.86±0.75) GPa and bending strength were(340.40±62.79) MPa,(145.60±17.82) MPa. Hardness, elastic modulus, bending strength of leucite reinforced glass ceramics were less than lithium disilicate glass ceramics and the difference has statistical significance. According to the analysis result of X-ray diffraction, both of lithium disilicate glass ceramic and leucite groundmass glass ceramic are bipolar polycrystalline materials which comprise the amorphous glass substrate and crystalline grain. The principal crystalline phase of the former is Li2Si2O5, and the principal crystalline phase of the latter is KAl Si2O6. According to scanning electron microscopy results, the surfaces of the two kinds of materials are quite smooth after polishing; glass matrix dissolves and grain is exposed after acid etching; leucite crystals are distributed in irregular polygon. Besides, lithium disilicate crystals have high percentage and the crystals are needle-like and distributed in interlaced and dense form. Energy spectrum analysis shows that the basic composition of leucite groundmass glass ceramic is Si O2-Al2O3-K2 O, and the basic composition of lithium disilicate glass ceramic is Si O2-Li2O-K2 O. 2. In the system environment of simulation of oral chewing movement, the wear volumes of the two kinds of castable ceramics show a trend of linear increase as time passes. There is no significant difference between them. The wear appearance of leucite groundmass glass ceramic shows furrow caused by abrasive wear, and cracks and debris caused by fatigue wear. However, the wear appearance of lithium disilicate glass ceramic is mainly the furrow caused by abrasive wear and the furrow becomes more superficial and more intensive as time goes. Compared to leucite groundmass castable ceramic, thecommonly used lithium disilicate castable ceramic in clinical practices causes little wear volume of the jaw material and plays a protective role for the jaw material. 3. In dry environment, the wear volume of friction pair composed by leucite groundmass castable ceramic and steatite ceramics is significantly higher than that of friction pare composed by lithium disilicate castable ceramic and steatite ceramic. According to the electron microscope result, surface grinding crack of leucite groundmass castable ceramic and steatite ceramics is mainly composed of furrow and rough surface without debris; surface of lithium disilicate castable ceramic and steatite ceramic is mainly furrow, and the surface becomes smooth as time goes. 4. Under different environment, the wear results of the two kinds of castable ceramics are quite different. The wear volume of lithium disilicate glass ceramic in water is much higher than the wear volume in dry environment. The electron microscope result indicates lithium disilicate crystalline grains take off in large amounts when they are in water environment, and this causes vast improvement of wear volume. The wear results between leucite groundmass glass ceramic and the two kinds of steatite ceramics are very consistent. The volume wear volume in water environment is less than that in dry environment, because the movement of water lets the abrasive dust move away from the wear contact region in time and reduces the happening of the abrasive wear.CONCLUSION: In oral humid environment, the mechanical properties and abrasive resistance of lithium disilicate glass ceramic and leucite groundmass glass ceramic have no significant differences, although the former has more excellent microscopic structure and the latter has weaker performance; in dry environment, the abrasive resistance of lithium disilicate glass ceramic is obviously better than that of leucite groundmass glass ceramic; compared to leucite groundmass castable ceramic, lithium disilicate castable ceramic plays a protective role for the jaw material. This research result is helpful for people to deeply understand the wear characteristics of the dental ceramic and the jaw material, to compare the properties of different ceramic restorative materials comprehensively, and to furtherimprove the properties of all-ceramic materials.