الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
The present study is an invitro study which was conducted to asses the fracture resistance of the zirconia reinforced lithium silicate crowns “Celtre Press” compared to the lithium disilicate crowns “IPS e-max press”
Fourteen samples were calculated and divided into two equal groups; seven samples of each group, according to the material of construction:
group A: Seven crowns (n=7) fabricated with IPS e-max Press material
group B: Seven crowns (n=7) fabricated with Celtra Press material
After that a stainless steel die was fabricated to simulate the prepared upper first premolar to receive the all ceramic crown with 12 degree taper, 4mm height and 1mm wide deep chamfer finish line. The stainless steel die was then duplicated into fourteen epoxy resin dies using silicone impression material.
The stainless steel die was scanned with extraoral scanner then fourteen CAD-CAM wax patterns were milled and seven wax crowns were pressed with IPS e-max press material and the other seven wax crowns were pressed with Celtra press one. After that power firing of Celtra press crowns was made to obtain their maximum strength and finishing, polishing and glazing were made for crowns of the tested groups according to manufacture recommendation.
The crowns were then seated onto their corresponding dies and cemented using Calibra universal self adhesive resin cement after being treated with hydrofluoric acid and silane coupling agent to ensure high bond strength.
The samples were maintained under constant pressure during cementation by using a specially designed cementation device for standardization of the cementation procedure. After that all samples were subjected to thermocycling and cyclic loading (37500 cycles representing clinically 3 months at the “5-55 C water baths” with load 50 N) to simulate the clinical conditions.
Crowns were then subjected to fracture resistance testing under a compressive mode of load applied occlusally using a metallic rod with round tip (3.8 mm diameter) attached to the upper movable compartment of testing machine traveling at cross-head speed of 1mm/min with tin foil sheet in-between with a loadcell of 5 kN and the load required to fracture was recorded in Newton by using computer software.
The following results were obtained:
The mean ± SD values of fracture resistance were recorded for lithium disilicate “ e.max group” was (1706.01 ±154.32 N) meanwhile the mean ± SD value recorded with zirconia reinforced lithium silicate group “celtra group” was (1550.67±196.71 N). It was found that lithium disilicate “IPS e.max press” group recorded statistically non-significant higher fracture resistance mean value than zirconia reinforced lithium silicate “Celtra Press” group as indicated by t-test (t=1.5, P=0.1590 > 0.05)