الفهرس 
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Abstract
The purpose of this study was to determine the effect of different bonded restorations on the fracture load of human maxillary first premolars at different aging periods.
A total of 75 intact human maxillary first premolar teeth of similar size and shape were chosen and standardized slot MOD cavities were prepared following standardized dimensions of ½ bucco-lingual intercuspal distance for the width and 4 mm from the cusp tip for the depth.
The teeth were equally divided into five groups of 15 each according to the type of restorative treatment received. In the first group (group m1), teeth were restored with bonded amalgam while in the second group (group m2), teeth were restored with hybrid composite and in the third group (group m3), teeth were restored with packable composite. Sound (unprepared) teeth and prepared (unrestored) teeth were the negative (group m-ve) and the positive (group m+ve) control groups respectively.
Each group of teeth was subdivided into three sub-groups according to the aging periods of one month, three months and six months in distilled water at 37ºC using thermostatically controlled incubator.
Assessment of fracture load of the teeth was carried out using a universal testing machine with a specially constructed steel attachment, in order to be in contact only with the inclined planes of the tooth and away from the restoration. The fracture load test was performed with a full-scale cell load of 250 kgs., running at a crosshead speed of 0.5mm/min.
The results revealed that there was no significant difference for the effect of different aging periods on the fracture load of the teeth. Teeth restored with hybrid composite showed the highest mean fracture load value among the bonded restorative materials followed by packable composite restorations and finally the bonded amalgam restorations.
Furthermore, sound teeth showed the highest mean fracture load value between all the tested groups, while the lowest mean fracture load value was recorded by prepared (unrestored) teeth.
Under the circumstances of this study, the following conclusions were drawn:
1-Aging periods up to six months in distilled water at 37°C do not affect the fracture load of human maxillary first premolar teeth.
2-Resin composition, filler distribution, and viscosity of a composite resin material may affect significantly the fracture load value of teeth restored with a composite resin.
3-Packable composite does not improve the fracture load value of teeth more than bonded amalgam.
4- MOD cavity preparation decreases the fracture load value of the teeth by approximately 70% from that of sound teeth.
Recommendations:
On the basis of these findings, preservation of the maximum amount of tooth structure remains the principle procedure in operative dentistry, as none of the bonded restorative materials used in this study could compensate the lost amount of tooth structure, in spite of the great development in material technology.