الفهرس 
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Abstract
This study was designed to study the effect of degree of axial wall taper and the technique of internal surface treatment of the crown on the marginal fit and fracture resistance of two all-ceramic crown system ( IPS e.max and Zirconia).
Specially designed stainless steel dies were constructed and
a total number of 60 all-ceramic crowns (30 crowns Lithium disilicate and 30 crowns zirconia).Non-anatomical crowns ( 8 mm diameter, 9 mm height, 2 mm occlusal thickness and margin thickness 1 mm) of both materials were fabricated according to the manufacturer’s instructions for each material. According to the technique of internal surface treatment each group were subdivided into three subgroups for each degree-taper.
Subgroup A (5 samples) in which the crowns were acid etched with VITA ceramics Etch acid gel, 9% concentration. According to the manufacturer instructions VITA Ceramics Etch was applied to the internal surfaces of the crowns with a small brush for 60 seconds.
Subgroup B (5 samples) in which the fitting surfaces of the crowns were sand blasted with 150 mm AL2O3 at a maximum pressure of 4 bar for 30 seconds at an approximate distance of 2 cm.
Subgroup C ( 5 samples) in which the fitting surface of the crowns were
Sixty epoxy resin (Chemapoxy 150 Transparent) dies were fabricated by introducing the polymerizing resin into Additional polymerization silicon mold (KERR Extrude Medium) of the master dies. The adhesive resin 3M RelyXtm ARC was used for cementation of the crowns. 3M RelyXtm ceramic primer was applied to the pretreated bonding surface of the restoration while Scotch bond etchant was applied to the epoxy resin dies according to the manufacturer instruction. Single Bond Adhesive was applied to the die and the inner surface of the restoration and an appropriate amount of cement was dispensed and mixed for 10 seconds. A thin layer of cement was applied evenly distributed over the bonding surface of the restorations.
The restorations were seated slowly with gentle finger pressure for 1 minute. Excess luting material was removed with sponge pellets immediately. As soon as they were completely seated, the crowns were placed under a constant static load (3KG) for 10 minutes to ensure an effective flow of the cement and maximal adaptation to the abutment and each cement surface/margin was light cured for 40 seconds.
The samples were tested to determine vertical cervical marginal accuracy using a stereomicroscope using a fixed magnification of 40X, Then each sample was mounted such that testing force will be directed down the long axis of the tooth. Using a Universal-testing machine (LIoyd instrument LR 5K), the force was applied to the flat occlusal surface of the crown until fracture. The cross-head speed was 1 mm/ min. The very first discontinuity resulting from an early crack or catastrophic failure of crown and/or die was detected.
The recorded data were collected and tabulated for evaluation. Data analysis was performed in several steps. Initially, descriptive statistics for each subgroup result. One way analysis of variance ANOVA followed by Newman Keuls post hoc-tests were used to detect significance between surface treatment. Student t-test was performed to detect significance between tapers. Three-factor analysis of variance ANOVA test of significance comparing variables (Ceramic, taper and surface treatment) affecting mean values. Statistical analysis was performed using Aasistat 7.6 statistics software for Windows. P values ≤ 0.05 are considered to be statistically significant in all tests.
Conclusions
Within the limitation of this study the following conclusions could be obtained;
1. The fracture resistance of the zirconia crowns was significantly higher than that of e.max crowns.
2. Increase in the degree of taper that lead to increase in fracture resistance regardless the type of ceramic.
3. Increase in the degree of taper that lead to increase marginal fit regardless the type of ceramic.
4. The marginal gap of Zirconia crowns has non-significant higher mean value than e.max in both before and after cementation.
5. The crowns were treated with acid etching surface treatment shown better marginal adaptation than crowns treated with tribochemical coating and sandblasting surface treatment regardless the type of ceramic and degree of taper.
6. The crowns were treated with tribochemical coating shown better fracture resistance than crowns treated with sandblasting and acid etching surface treatment regardless the type of ceramic and degree of taper.