الفهرس 
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Abstract
Polymerization shrinkage is a critical factor affecting the longevity and acceptability of dental composite resins. This shrinkage of resin composites can be expressed in two phases: pregel & postgel phases. During the pregel polymerization, composite is able to flow & the stress within the structure is relieved (37-59-87-88-89). After gelation, flow ceases and cannot compensate for shrinkage stresses. Postgel polymerization consequently results in significant stresses in the surrounding tooth structure and composite tooth bond. (87