الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
The aim of this study was to evaluate the effect of the crystallization process on the fracture resistance and failure mode of two forms of zirconia reinforced lithium silicate CAD/CAM fabricated crowns, by comparing the fracture resistance and failure mode of the partially crystallized form (VITA SUPRINITY®) to the fully crystallized form (Celtra® Duo).
According to sample size calculation, a total of sixteen restorations were constructed. The samples were divided into two equal groups, eight samples for each group according to the material type used:
- group (S): Eight crowns samples (n=8) fabricated of VITA SUPRINITY® CAD/CAM blocks
- group (C): Eight crowns samples (n=8) fabricated of Celtra® Duo CAD/CAM blocks.
An acrylic right first mandibular molar was prepared according to regular dimensions of all ceramic restorations preparation guidelines with an occlusal reduction of 1.5 mm, axial reduction of 1mm, circular shoulder finish line of 1mm thickness with rounded internal angle and 6 degree occlusal convergence angle. Preparation was performed manually by an experienced practitioner and the bucco-lingual and mesio-distal convergence angles of the tooth preparations were checked and confirmed by using dental surveyor. The prepared acrylic tooth was then duplicated into sixteen epoxy resin dies using silicon impression material.
The prepared acrylic tooth was scanned by 3 shape D500 extra oral scanner and then milled by Sirona MCX5 milling machine using VITA SUPRINITY® blocks and Celtra® Duo CAD blocks to produce eight VITA SUPRINITY® crowns and eight Celtra® Duo crowns respectively. After milling, VITA SUPRINITY® restorations were crystallized in a ceramic furnace (programat P300) to reach the fully crystallized form. VITA AKZENT plus glaze was then used for glazing of the VITA SUPRINITY® restorations while glazing of Celtra® Duo crowns was performed with Densply Sirona universal overglaze. After glazing cycles were accomplished, cleaning of the restorations and surface treatment to the fitting surfaces of all restorations was performed. Crowns were then seated on their corresponding dies and cemented with self-adhesive resin cement under a constant load of 50 N using a specially designed loading device for standardization purpose.
All samples were subjected to fracture resistance testing under a compressive load at the center of their long axes using computer controlled universal testing machine with a load cell of 5 kilo newton. Load was applied by a metallic rod with spherical tip (5.8 mm diameter) that contacts the occlusal surface of the restoration at cuspal inclinations and attached to the upper movable compartment of testing machine and of a cross-head speed of 1mm/min. Data was collected, tabulated and statistically analyzed
The fracture pattern and mode of failure of all samples were then examined.
The following results were obtained:
No statistically significant difference was found between (VITA SUPRINITY®) and (Celtra® Duo) where (p=0.471). The highest mean value was recorded with (Celtra® Duo), while the lowest mean value was recorded with (VITA SUPRINITY®).
For VITA SUPRINITY® group all samples showed favorable mode of failure, while for the Celtra® Duo group both favorable and acceptable modes of failure were found among samples.