الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 147 |  |  |
| | | from | 147 | | |
Abstract
In this study, two materials [IPS e-max CAD (EX), VITA ENAMIC (EN)], and four different preparation designs were investigated for their effect on marginal adaptation and fracture resistance. A total of fifty-six (n=56) caries free human mandibular molars were used. According to the materials, teeth were divided into two main groups (Ex and En) (n=28) which were further subdivided into eight subgroups according to the four preparation design (EX& EN, D1, D2, D3, D4 ) (n=7).
Control groups (D1) received MOD cavity preparation, with isthmus depth of 2 mm, width 3 mm, while proximal box were reduced 1.5 mm below the pulpal floor. Cavity walls were diverged occlusally about 6°, all the walls were rounded and smoothened to avoid any sharp preparations. The remaining groups received the same MOD preparation of the control groups (D1) in addition: in group (D2) the buccal cusps were reduced by 1.5 mm, in group (D3) the lingual cusps were reduced by 1 mm, while in group (D4) the buccal and lingual cusps were reduced by 1.5 and 1 mm respectively. All of the occlusal preparations were done with 90° cavosurface margins.
All the prepared samples were scanned using CEREC Omnicam scanner and the preparations were checked by the software for any sharpness and undercuts before restoration fabrications. All restorations were milled using Cerec MCXL 4.4 milling machine. The restorations were checked for seating on their corresponding preparations before final finishing and glazing.
Surface treatment was done on the fitting surface of all restorations before cementation. IPS e-max CAD and VITA ENAMIC were etched using 5% hydrofluoric acid 20 second and 60 seconds respectively then silanized for 60 seconds before cementation.
On the other hand all prepared teeth were selectively etched with 35% phosphoric acid for 20 seconds on the enamel margins. The etched surfaces were then rinsed with water spray and dried with compressed air. A micro-brush was used to distribute a thin layer of bonding agent on the enamel and dentine.
All samples were luted to the teeth using Duo-Link resin cement (automixed)
and inserted directly into the cavity of the prepared teeth.
The marginal gap between the restorations and each tooth were measured using a sterio- microscope at 26 pre-selected locations: five at the occluso-buccal wall, five in the occluso- lingual wall, eight at the mesial proximal box and eight at the distal proximal box (X 10) before, after cementation and after 10,000 thermal cycles.
After thermocycling all samples were loaded in the Universal testing machine in order to evaluate fracture resistance of all samples.
All the tested groups showed statistically significant differences in marginal adaptation between EX and EN samples in which EN samples showed the least marginal gap (60 µm) in comparison to EX samples (90 µm).
Regarding the preparation designs: there was a significance difference in marginal adaptation between the four designs in which D1 and D5 showed the least marginal gap among all designs. Moreover there was a significant difference on marginal gap at each time of measurements.
The test data of fracture resistance revealed that E-max CAD (2359 N) showed statistically significantly higher mean fracture resistance values than Vita Enamic (1813 N). On the other hand there was no statistically significant difference between mean fracture resistances between the four tested designs.