الفهرس 
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Abstract
Laboratory processed composite or indirect composite overcomes several problems that faced the dental practitioners to restore large posterior cavities. According to their method of fabrication and their composition, they provide excellent marginal gap, decrease polymerization shrinkage and improve wear resistance however their bonding process is challenge. Lack of the unreacted methacrylates due to secondary curing makes surface treatments before cementation mandatory. The successful bond strength ensures good marginal fit and the longevity of the restoration.
For marginal fit evaluation: A total 60 upper premolar teeth were embedded in a copper ring filled with auto polymerized acrylic resin (14 mm in diameter) up to 2 mm below the cemento-enamel junction and received mesio-occlusal-distal (MOD) inlay cavity preparation, impressions were taken using a polyvinyl siloxane material (3M ESPE, USA) and master dies were fabricated. The master dies were divided into two groups according to the types of composites were used for build up the inlays group A (SR Nexco) (Ivoclar Vivadent AGS chaan, Liechtenstein) and group B (GRADIA PLUS) (GC, Tokyo, Japan). Composite build up was done using incremental technique and curing was done by light‐emitting diode curing unit(Woodpecker, LED.D, China) for 20 seconds then secondary cured for 11minuts for SR NEXCO and 3 min for GRADIA INDIRECT using Photopol pro vacuum (A5407V Dentalfarm, Italy) .Each main group were subdivided into three subgroups according to surface treatments which were received to the fitting surface: group 1A(sandblasting by aluminum oxide particles+silane) group 2A(sandblasting by aluminum oxide particles + Hydrofluric acid etching+silane) group 3A(sandblasting by aluminum oxide particles + MONO BOND etch and prime) same surface treatments were used for subgroups 1B, 2B&3B respectively The cementation was done using GCEM link Ace (dual cure resin cement GC, Tokyo, Japan) All the specimens were thermocycled for 500 cycles from 5 to 55 c. Marginal gap evaluated under stereomicroscope at 12 selected locations, four at the proximal surface and two at the gingival margin 6 on the occlusal surface (3occlusobuccal and 3 occlusolingual).
For microshear bond strength test: sixty cylindrical specimens were prepared from two types of indirect composite and divided into 2 groups (n=30). group A: SR NEXCO and group B: Gradia Plus. Specimens with dimensions (2 mm length and 1 mm width) was prepared using a polyethylene tube (BioFlon IV cannula, India). Composite specimens were precured for 20 seconds by Light Emitting Diode curing unit. The secondary curing was done inside a Photopol pro vacuum light cure box GRADIA PLUS for 3 minutes and 11 minutes for SR NEXCO. After secondary curing each main group was subdivided into three subgroups according to their surface treatment: subgroup 1A (sandblasting by aluminum oxide particles followed by silane), subgroup 2A (sandblasting by aluminum oxide particles + Hydrofluric acid etching+silane) and subgroup 3A (sandblasting by aluminum oxide particles + MONOBOND Etch and prime) same surface treatments were used at subgroups 1B, 2B&3B respectively. The treated composite specimens were cemented to a flat dentin surface of 10 molar teeth (6 specimens 3 from each group) using G-CEM LINKACETM. All the specimens were thermocycled for 500 cycles from 5 to 55C, and then microshear bond strength test was done in a Universal Testing Machine 0.5 mm/min (Instron model3345, England). Failure modes were evaluated under stereomicroscope and classified as cohesive, adhesive or mixed failures.
The results regarding marginal fit: there was a significant difference proximally (p<0.001) and occlusally (p<0.001) between the six subgroups while there was no significant difference between the subgroups gingivally. Pair wise comparisons revealed that there was a significance difference at the occlusal surface of group A (SR NEXCO) between subgroups 1A and 2A (p <0.001) and between subgroups 1A and 3A (p=0.042). Additionally There was a significance difference at the proximal surface between subgroups 1B and 3B (p<0.001) additionally, between subgroups 2B and 3B (p<0.001).
For microshear results: Statistical significant difference was noticed between subgroups 1A and 2A (p=0.043) and between subgroups 1A and 3A (p=0.013) .Moreover, there was a statistically significant difference between subgroups 1B and 2B (p=0.002) and between subgroups 1B and 3B (p2=0.044). According to the mode of failure mixed were more common in subgroups 1A, 1B and 3B while adhesive failures were predominates in other subgroups except for subgroup 2B half of the specimens were adhesive failures and the other were mixed failures Furthermore, cohesive failures represented 10% in subgroup 1A.