Comparative study of flexural strength test methods on CAD/CAM Y-TZP dental ceramics

Clinically,fractures are the main cause of computer-aided design and computer-aided manufacturing(CAD/CAM)3 mol%-yttria-stabilized tetragonal zirconia polycrystal(Y-TZP)all-ceramic dental restorations failure because of repetitive occlusal loading.The goal of this work is to study the effect of test methods and specimen’s size on the flexural strength of five ceramic products.Both biaxial flexure test(BI)and uni-axial flexure tests(UNI),including three-point flexure test(3PF)and four-point flexure test(4PF),are used in this study.For all five products,the flexural strength is as follows:BI>3PF>4PF.Furthermore,specimens with smaller size(3PF-s)have higher values than the bigger ones(3PF).The difference between BI and UNI resulted from the edge flaws in ceramic specimens.The relationship between different UNI(including 3PF-s,3PF and 4PF)can be explained according to Weibull statistical fracture theory.BI is recommended to evaluate the flexural strength of CAD/CAM Y-TZP dental ceramics.

A New Technology of Microcrystallizing Leucite to Reinforce Dental Glass Ceramics

The key technology and the main mechanism of microcrystallizing leucite to reinforce dental glass ceramics were investigated.The feedstock powders were selected,mixed according to the ratios of the theoretical composition of leucite,ball-milled,melted at 1600℃ and then cooled to room temperature quickly.The cooled clinkers were ball-milled again to 4 μm.After cold-isostatic pressure molded and air sintered at 1500℃ for 1 h,the dental glass ceramics were fabricated.They have following characteristics:excellent mechanical properties (mean compressive strength is 206.6 MPa),low sintering temperature and good reoccurrence to keep steady quality.

Effect of Sintering Temperature on Aging Resistance and Mechanical Properties of 3Y-TZP Dental Ceramic

In order to investigate the effect of sintering temperature on aging properties and mechanical properties of 3Y-TZP dental ceramic in simulated oral environment, 3Y-TZP nanopowder compacts were pressurelessly sintered at 1 350℃, 1 400 ℃, 1 450 ℃,1 500 ℃, respectively, then were treated by soaking in artificial saliva （65 ℃, pH=7） for two months. The treated specimens sintered at 1 350 ℃ showed there was no phase transformation but whose strength and toughnesswere significantly improved （P〈0.05）, while those sintered at 1 400 ℃- 1 500 ℃ revealed a small amount of phase transformation and insignificant mechanical reinforcement （P〉0.05）. No microcracks were detected but increment in lattice volume was found in all specimens. Lowering sintering temperature favors aging resistance and mechanical reinforcement of 3Y-TZP in a simulated oral environment.

Influence of cyclic loading on the fracture toughness and load bearing capacities of all-ceramic crowns

The purpose of this study was to investigate how cyclic loading influenced the fracture toughness of hot-press lithium disilicate and zirconia core materials and whether there was an increase in the propensity for crown failure. Two types of all-ceramic crowns including the IPS e.max Press system （n=24） and the Lava zirconia system （n=24）, were selected. Sectioned specimens were subjected to cyclic loading with the maximum magnitude of 200 N （R=0.1） until two million cycles. The material properties including Young＇s modulus （E） and hardness （H） and the fracture toughness （K,c） of the core materials were evaluated using indentation methods （n= 12 each）. The load-bearing capacities of the specimens were examined by means of monotonic load to fracture （n=12 each）. It was found that the material properties, including E, Hand Knc, of the two types of dental ceramics, were reduced. Statistical analysis indicated that there were no significant influences of fatigue loading on material properties E and H for both types of dental ceramics or Kgc for zirconia, while for the IPS e.max Press core, K,c, which was parallel to the direction of the lithium disilicate crystals, was significantly reduced （P-0.001）. A conclusion was drawn that zirconia possesses high mechanical reliability and sustainable capacity to resist fatigue loading, while fatigue loading remarkably degraded the anisotropic mechanical behaviour of hot-press lithium disilicate ceramics.

Role of MgF2 addition on high energy ball milled kalsilite:Implementation as dental porcelain with low temperature frit

Porcelain fused to metal(PFM)has received great attention over the last few years due to its importance in the dentistry.Kalsilite(K_(2)O·Al_(2)O_(3)·SiO_(2))is a high thermal expansion porcelain,suitable for bonding to metals.However,kalsilite is a metastable phase which gets converted into crystalline leucite upon heating.In the current work feasibility of developing stable kalsilite phase,dispersion of MgF2 in it as an additive and using mechanochemical synthesis are studied.Micro fine dental material has been formulated by mixing prepared kalsilite with low temperature frit(LTF)in different ratio.The crystalline phases evolved in fired powders are characterized by powder X-ray diffraction(XRD)technique.Kalsilite with different ratio of LTF has been cold pressed and heat treated to examine its coefficient of thermal expansion(CTE),flexural strength,apparent porosity(AP),bulk density(BD)and microstructure.Results indicate that MgF_(2) addition and high milling duration help in kalsilite stabilization.Temperature also plays an important role in this stabilization,and at 1100℃single phase kalsilite formation is observed.Present outcomes demonstrate that it is easily possible to synthesize a stable single phase kalsilite with desirable properties.