الفهرس 
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Abstract
This present investigation was carried on 90 sound mandibular first molars, collected from patients aging from 40-50 years old. The teeth were stored in distilled water at room temperature to prevent their dehydration. The proximal surfaces of the teeth were disked flat, parallel to each other and perpendicular to the occiusal surface. The teeth surfaces were equally divided into two main different groups, of 90 surface each, re1ativ’ to the type of composite used, i.e., microfilled or hybrid. Each group was equally divided into three subgroups, of 30 surfaces each, relative to the bonding agents used, i.e. Scotch bond Multi-purpose, Vitra bond, and Tenure. Each subgroup was equally divided into three subdivisions of 10 surfaces each, i.e., enamel, dentin and enamel & dentin. Each subdivision was equally divided into two classes of 5 surfaces each relative to aging time, i.e., 48 hours and 6 months. After the application of the bonding agelit, the composite was applied using a stainless steel de of 6 mm. x 6 mm. x 3 mm. dimensions. The composite was applied, by layering technique and photo-cured for 40 seconds. After polymerization the samples were sheared off. Two specimens of fractured samples for each class for each division for each subgroup for each group was prepared for SFM examination at 7500X magnification.