How Glass-Ceramic Blocks Are Manufactured for CAD/CAM Applications
Using glass-ceramic blocks for CAD/CAM applications like cad cam zirconia involves several steps. Some of the main steps include the processing of the glass-ceramic, modifying the block, and machining the block. There are also many different types of glass-ceramics that are used. These include lithium disilicate, alumina, and VS zirconia.
Lithium disilicate glass ceramics
CAD/CAM technology is an ideal technique for manufacturing lithium disilicate glass ceramics. This material has good mechanical and optical properties and can be bonded to dental substrates with adhesives. However, the final performance of this material as a dental material is dependent on the type of adhesive used.
A recent study investigated the fracture resistance of lithium disilicate molar crowns. The fracture toughness of lithium disilicate is similar to that of dentin and is higher than that of feldspathic ceramic. However, lithium disilicate suffers from microcracks that can result in fractures. The aim of this study was to assess the fracture resistance of lithium disilicate copings after occlusal adjustments.
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Alumina based polycrystalline ceramics
CAD/CAM procedures such as cad cam block have played an important role in the development of high strength polycrystalline ceramics. These ceramics are suitable for fabricating three-element crowns, bridge copings, and metal free superstructures on implant abutments.
In-ceram zirconia is a modification of In-ceram alumina. It is composed of 67% aluminm oxide particles and 33% partially stabilized zirconium oxide. This material has a flexural strength of 600-800 MPa. However, it has lower fracture toughness than In-ceram alumina. It has been recommended for posterior crowns.
The IPS e-max press is a lithium disilicate pressed glass ceramic. It has better translucency and physical properties than IPS Empress. It has been introduced by Ivoclar Vivadent in 2005.
VS zirconia reinforced lithium silicate glass-ceramic
VS zirconia reinforced lithium silicate glass-ceramic blocks for CAD/CAM applications are manufactured for anterior single-unit crowns, inlay/onlay, veneers, and occlusal abutments. They offer a higher fracture toughness, more flexural strength, and increased resistance to fissure propagation. They are indicated for anterior and posterior single-unit crowns, inlay/onlay, and veneers. In addition, zirconia reinforced lithium silicate glass-ceramics are more biocompatible than lithium disilicate glass-ceramics.
In vitro mechanical properties of zirconia reinforced lithium silicate glass-ceramic were assessed ub cad cam block. The material’s bond strength, brittleness index, elastic modulus, and hardness were measured using a Berkovich diamond tip. These parameters were correlated to changes in the material’s plasticity.
Thermocycling was also evaluated. The flexural strength and bond strength of mTBS ceramics were decreased after thermocycling. Thermocycling also decreased the bond strength of zirconia.
Elastic/Young modulus
Various types of glass-ceramic materials are suitable for CAD/CAM applications. These include lithium disilicate glass ceramics (LDGC), leucite glass ceramics (LGCC) and polymer infiltrated ceramic network filler (PICNF).
These materials differ from each other in their stiffness and elasticity. Their internal structure is relatively homogeneous and reduced voids, cracks and isolated defects were observed. These characteristics set the mechanical properties of the materials.
In this study, the influence of thickness on fracture resistance was investigated. Six resin composite blocks were evaluated for their microhardness and flexural modulus. The Weibull modulus (m) was also determined. Specimens with higher m values were observed to be more fracture resistant. The m value was calculated from the unloading segment of the load-displacement curve.
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Flexural strength
CAD/CAM blocks for a variety of applications are emerging on the market, however, there is little independent information available on their mechanical properties. It is therefore important to base material selection on evidence. To better understand the mechanical properties of CAD/CAM blocks and dental cad cam, an experimental study was performed.
The aim of the study was to assess the flexural strength of lithium silicate glass-ceramics, which have been recently introduced. In addition, the flexural strength of resin composite blocks used in CAD/CAM applications was also evaluated.
The test specimens were fabricated using stainless steel bars. They were then polished with 600, 800 and 1000 grit SiC papers. The final dimensions were checked with a digital caliper. The measurements were made according to ISO 6872:2015. Then, flexural strength, fracture toughness, and fracture resistance were measured.
Fracture toughness
Various studies have been conducted on fracture toughness of glass-ceramic blocks for CAD/CAM applications. In this study, various monolithic, high translucent glass-ceramic block materials were investigated. The chemical content and microstructure of these materials was also investigated. In addition, the effects of processing on the fracture resistance were also studied.
Five test groups were formed based on the indicated dental cad cam blocks materials. The blocks were tested for fracture resistance using a computer-controlled material testing machine. The coping thickness was also evaluated. The mean fracture resistance was calculated. Data was presented as minimum, maximum, mean, and standard deviation. The coping thickness was found to have a significant effect on the mean fracture resistance.
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