Abstract
Background:Several factors might affect the fracture resistance of all-ceramic crowns, including cement thickness.Aim:To evaluate the influence of cement thickness on the fracture resistance.Objective:To determine the effect of varying the adhesive gap thickness on the fracture loads of all-ceramic CEREC 3D molar crowns.Methods:Standardized prepared epoxy resin molar dies (Viade Inc.) were fabricated. A standard molar crown was designed using a CEREC 3D machine (Sirona Dental Systems). Twenty-four crowns were milled from Vita Mark II blocks (Vita Zahnfabrik), using adhesive gap settings of 30, 60 and 90 µm (n=8). A dual-cure resin cement (PanaviaF 2.0, Kuraray) was used to cement the crowns to their respective dies, following manufacturer's recommendation. After 1 week of storage in distilled water at 37°C, each crown was loaded in compression until complete failure in a universal testing machine (Instron 8501) and fracture loads (N) were recorded. Fractured specimens were sectioned to determine cement thickness. Sections were examined using a traveling light microscope to measure cement thickness. Data were statistically analyzed using one-way ANOVA test and Pearson's correlation at (α=0.05).Results:The mean fracture loads and standard deviation values in N were 1,267.57 (122.82), 1,225.20 (179.46) and 1,180.76 (161.77) for the crowns with 30, 60 and 90µm, respectively. ANOVA indicated no significant differences among mean fracture strength values (p= 0.55). All crowns failed in a catastrophic mode and were not repairable.Conclusions:Adhesive cement gap as achieved with three CEREC 3D settings from 30 to 90µm had no significant effect on fracture strength of crowns made from Vita Mark II blocks.
Highlights
The growing demand for esthetics in combination with health and environmental concerns about some metallic restorations stimulated the profession to explore and consider metal-free tooth-colored alternatives
analysis of variance (ANOVA) indicated no significant differences among mean fracture strength values (p = 0.55)
Adhesive cement gap as achieved with three CEREC 3D settings from 30 to 90μm had no significant effect on fracture strength of crowns made from Vita Mark II blocks
Summary
The growing demand for esthetics in combination with health and environmental concerns about some metallic restorations stimulated the profession to explore and consider metal-free tooth-colored alternatives. Till the introduction of Computer-aided Designing/ Computer-aided Manufacturing (CAD/CAM) technology, the only options available for controlling the cement thickness were controlling the thickness of the die spacer paint, either by controlling the number of application or using materials with low film thickness [18], or controlling the thickness of the foil layer/s which are used for the production of porcelain jacket crowns [12]. Both methods are neither accurate nor precise. Several factors might affect the fracture resistance of all-ceramic crowns, including cement thickness
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