Emax Abap Material ((INSTALL))
Despite these favorable properties, there is concern regarding the fracture resistance of all-ceramic restorations in situations where masticatory loads are higher, such as fixed partial dentures in the posterior region. These concerns are most relevant for all-ceramic restorations fabricated from dissimilar materials in the form of layered core-veneer structures. Systematic reviews of the clinical survival of contemporary all-ceramic core-veneer prostheses highlight that mechanical failures occur primarily in the form of chipping or delamination in the veneering layer.1,8 Based on a longitudinal 5-year evaluation, this treatment modality is similar (93.8%) to metal-ceramic crowns (95.7%).1 However, it is far from the ideal situation, and consequently, different approaches have been developed to prevent mechanical failures.
Emax Abap Material
Heat pressing techniques using highly controlled temperature and pressure conditions have been employed to apply the veneering ceramic to a prefabricated core to mitigate some of the limitations associated with manual veneering. This approach can reduce the incidence of internal defects in the veneer layer and allows ceramic materials with improved mechanical properties to be used for veneering, including leucite glass-ceramics14,15 or lithium disilicate glass-ceramics.13,16 However, heat pressing also results in residual stress states and requires additional manual steps, including wax pattern generation.
As an alternative, computer-aided design/computer-aided manufacture (CAD/CAM) workflow has been developed to fabricate both the veneer and framework structures from homogenous ceramic blocks that have been manufactured in optimized conditions.17 The two CAD/CAM parts are subsequently joined using a composite resin layer (Rapid Layer Technique, VITA Zahnfabrik, VITA Zahnfabrik, Bad Säckingen, Germany)18 or with a low fusing temperature glass-ceramic (IPS e.max CAD Veneering Solutions, CAD-on technique, Ivoclar Vivadent, Schaan, Liechtenstein).19 The fracture resistance of the resulting ceramic bilayer will depend on many geometric, material, and processing variables,18,19 and the interface between the two layers for core-veneer all-ceramic restorations has been identified to be important in determining the fracture behavior.18,20 It is proposed that effective stress transfer mediated by a stable joint between layers promotes greater fracture resistance under masticatory forces.21-28 However, these techniques have not been compared before regarding stress distribution and fatigue survival.
Clinical studies have shown an acceptable success rate for veneered Y-TZP restorations; however, the most common cause for early failures is veneer material chipping or delamination.8,30 This study demonstrated that the technique used to create the interface between veneering ceramic and Y-TZP core could affect FDP survival. FDP fabricated using the conventional stratification technique exhibited cracks and voids near the core-veneer interface and within the veneering ceramic, and all the test specimens failed before 2106 cycles. In contrast, all the specimens fabricated with a CAD/CAM veneer layer survived until 2106 cycles (Figure 4). Mechanical cycling, when performed on test specimens immersed in a wet environment, consists of a more representative condition that leads to slow crack growth, decreasing the ceramic fracture resistance over time.31,32 Many cyclic fatigue studies are short due to the time constraints associated with this method. In this study, approximately 8.5 years of clinical use was simulated, exceeding the five years (1.2 million cycles) that is commonly reported.33,34