الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Tooth colored restorative materials have been increasingly used m restorative dentistry to achieve one of the main objectives of restorative dentistry, which is restoration of esthetics. Composites are currently the best materials that fulfill the requirement of excellent
esthetics and durability. (21
It is clear that composite resin still suffers from polymerization shrinkage, (IS) that causes gap formation and weak mechanical properties in comparison to metallic restorative materials. These drawbacks negatively affects the clinical performance of composite resin restorations especially when used in the posterior region, while there is an increase demand for tooth-colored restorations.
Recently, new light curing techniques were developed aiming to improve the mechanical properties and the clinical performance oflight cured tooth colored restorative materials and to control one of the main problems in composite resin, which is polymerization shrinkage. Contraction creates polymerization stresses up to 130 kg/cm2 between the composite and the cavity walls leading to gap formation that can allow marginal leakage, (I) and results in sensitivity and recurrent caries. (431
One of these techniques is the ”Soft start technique” which depends on electronic modulation of the light intensity in a two-step mode. It is reported that this technique results in stress-free hardening of light-cured restorative materials, and renders them with lower probability of brittle fracture in addition the improvment of the adhesion to cavity margins which reduces marginal gap formation.
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Most of the problems associated with composite resm restorations can be related directly or indirectly to polymerization shrinkage. Various techniques have been suggested to decrease the adverse effects of polymerization shrinkage. This research was designed to investigate the effect of three polymerization techniques, namely:
1- Soft start technique
2- An alternative technique for reducing the initial light intensity via filtration with rubber dam sheets.
3- An alternative technique for reducing the initial light intensity via filtration with cellophane papers.
In comparison to the conventional curing technique as a control, on the marginal gap formation, fracture strength and surface microhardness oflight cured composite resin.
A total of 120 disc specimens were constructed from hybrid composite resin restorative material of standard shade A3. The specimens were constructed in teflon molds with an internal diameter of five millimeters and a height of two millimeters. The specimens were divided into four major groups, 30 specimens each, according to the curing technique used, where the first group was cured via conventional curing to serve as control, the second group was cured via soft start curing, the third group was cured through rubber dam sheets, and lastly the fourth group was cured through cellophane papers. Each group was further subdivided into three equal subgroups, ten specimens each, according to the property to be tested. The first subgroup was tested for gap distance, the second for fracture strength, and lastly the third for surface micro hardness.