Aim: Marginal fit evaluation of diverse all ceramic systems before and after thermal aging Objectives: To assess the impact of thermocycling on marginal adaptations of CAD/CAM ceramic crowns manufactured from distinctive prefabricated blocks. Background: Good marginal adaptation guarantees gingival health and comes about in less cement disintegration and few occasions of caries and discoloration improper marginal fit lead to plaque maintenance, microleakage and cement breakdown. Marginal accuracy can be measured via inspection, exploratory probing and radiographic examination. Glass ceramics are used to replace missing or damaged tooth structure because of their high translucency, superior biocompatibility and low thermal conductivity. However, they are brittle materials which display a high compressive and low tensile strength. Zirconia is a strong substitute veneering for glass ceramics, but it has more opacity. That opacity decreased recently by addition of more translucent feldspathic porcelain to achieve the desired esthetics. Methods: Four groups of 20 crowns each (Celtra DUO, e-max CAD, bilayered zirconia and monolithic zirconia) were cemented on identical all ceramic artificial teeth. Marginal gaps measured before and after thermal aging as half of specimens were thermocycled 500 times between the maximum and minimum temperatures that the mouth is subjected to (5±1°C and 55±1°C) respectively. Statistical analysis was performed using Graph-Pad In-Stat statistics software for Windows. Results: Marginal gaps of all tested materials within clinical range (<120 μm). The highest marginal gap mean value and standard deviation (SD) before and after thermal aging recorded with bilayered zirconia (39.73 ± 9.43) and (50.23 ± 14.6) respectively. E-max CAD showed the lowest values before thermal aging (19.65 ± 10.2) while Celtra DUO showed the lowest values after thermal aging (32.21 ± 7.88) with significance between all groups except Celtra DUO before and after thermal aging. Irrespective of material type, totally it was found that thermally aged groups recorded higher marginal gap mean value (41.56 μm) than non-aged ones mean value (28.94 μm) with statistical significance. Conclusion: Bilayered zirconia recorded the highest marginal gap in aged and non-aged subgroups among all tested all ceramic systems with statistical significance. E-max CAD and Celtra DUO recorded the lowest marginal gaps. Thermal aging increased marginal gap mean values as a total result of all ceramic systems.

Purpose. The main purpose of this study was to assess the radiopacity of contemporary restorative computer-aided design (CAD)/computer-aided manufacturing (CAM) materials and the impact of material composition as measured by energy-dispersive X-ray spectrophotometry (EDX) on radiopacity. Materials and Methods. Ten specimens of six CAD/CAM materials with 1 mm thickness were produced and then digitally radiographed with an aluminum (Al) step-wedge (SW) and 1 mm thick tooth slice. The specimen mean gray values (MGVs) were recorded in pixels and compared to an Al-SW, dentin, and enamel of equal thickness. For the elementary analysis of the composition of the materials, EDX was performed. Results. The recorded MGVs ranged between 21.20 ± 4.94 and 238.5 ± 13.61 pixels. Materials were sorted according to the MGVs descendingly, Prettau, Vita Suprinity, Vita Enamic, Shofu, Pekkton, and BioHPP. Prettau and Vita Suprinity had significantly higher MGV than dentin and 1 mm thick Al. In comparison, Vita Enamic had a slightly higher value than dentin and 1 mm thick Al. Although Pekkton and BioHPP had MGV significantly lower than dentin and 1 mm thick Al, Shofu had a significantly lower value than dentin and nonsignificantly lower than 1 mm thick Al (p < 0.05). According to EDX analysis, the examined materials contained several components in varying quantities of radiopacity. Conclusions. The radiopacity of only three studied materials exceeded the International Organization for Standardization’s minimum standards (ISO).

Objective: Comparison of fracture resistance of different ceramic restorations.Methodology: 64 ceramic crowns were fabricated. They were divided into 4 equal groups according to the type of ceramic used (16 each). Group I: lithium disilicate, Group II: Zirconia reinforced lithium silicate, Group III: monolithic zirconia and Group IV: bilayered zirconia. Models of prepared teeth #14 were used as abutments. Eight specimens from each group were subjected to thermocycling between 55° C and 5° C. Fracture resistance was tested for the specimens. The load to fracture was recorded. Mean value for each group was calculated and differences between groups were tested for statistical significance. One fractured specimen from each group was scanned by scanning electron microscope to determine the failure mode.Results: it was found that the highest fracture resistance mean value was recorded with monolithic zirconia group followed by lithium disilicate group then bilayered zirconia group while the lowest fracture resistance mean value was recorded for zirconia reinforced lithium silicate group and this was statistically significant. The four tested groups showed lower fracture resistance mean values after thermocycling. The fractography showed that surface defects were the origin of fracture in glass ceramic groups. While monolithic zirconia showed internal surface cracks. Conclusions:Within the limitations of this study, the following conclusions can be drawn: monolithic zirconia has the highest fracture resistance among the tested groups, while zirconia reinforced lithium silicate group has the lowest fracture resistance. Thermal aging significantly reduces the fracture resistance in the four tested groups.

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