الفهرس 
Resin Composite Restoration:
Resin composite polymerization shrinkageOnly 14 pages are availabe for public view
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Abstract
The goal of adhesive and restorative dentistry is to improve and achieve an adequately adaptation and strong bonding at tooth/ resin restoration interface to get optimum retention, minimal or absent of microleakage, color stability and clinical restorative stability. Bulk-fill composite materials are being developed for preparation depths of up to 4 mm in an effort to simplify and improve the placement of direct composite posterior restoration. With considering the pre-heating of dental resin composites, also dramatically decreases the curing time required for light polymerization with the added benefit of reduction of polymerization shrinkage and stresses, greater depth of cure of the restorative composite and increased chemical degree of conversion. The polymerization shrinkage stress is associated with two main clinical problems; cuspal deflection and microleakage. Cuspal deflection can act as a preloading that facilitate fracture of the tooth under tension and may represent the main cause of failure through composite curing. It may cause enamel cracks, and sense clinically by the patient as postoperative sensitivity and pain. Two main groups of biomechanical factors affect the amount and type of cuspal deflection, the geometrical factors including cavity dimension and thickness of cavity walls and the material properties factors as polymerization shrinkage, elastic modulus, flow and hygroscopic expansion of composite material and described as clinical factors which include placement technique, direct or indirect restoration, light curing unit type and protocol and environmental thermo/mechanical fluctuation stresses. The recent emergence of different types of adhesive bonding agents in the market have resulted in dentists facing difficulty in choosing the most suitable material for their patients. One of the factors to be considered is the clinical performance of an adhesive bonding agent. The clinical performance of current adhesives has significantly improved with resin restorations contributing to a highly predictable level of clinical success. Several studies reported that in-vitro testing is the most effective method to screen adhesives and characterize the physical durability of new restorative materials. Aging restorations and subjecting them to cyclic thermal and/or mechanical loading are treatment methods commonly in vitro microleakage and adaptability testing to simulate that may take place during the service life of a restoration. Different regimens have been used for thermocycling of dental restorations with recommended temperatures ranging between 4° and 60°C. Composite restorations were shown to exhibit significantly increased leakage after thermocycling even when subjected to relatively few cycles. Determined the gap/ gap-free using Autodesk AutoCAD program which considered as a commercial computer-aided design (CAD) and drafting software application and provides for extremely accurate to scale drawings. it can be used for measuring of length of the total outline of the cavities, also it can be used to measure the length of the gaps formed between restoration and tooth structure after scanning the specimen by scanning electron microscope. This in vitro studied the adaptability of conventional vs viscalor bulkfill composite resin in restoring simple class I box-shaped cavities and effect of thermal loading using Scanning electron microscope (SEM). Forty extracted human sound molars were selected. The teeth were fixed with sticky wax to the base of plastic cylinder. The cylinder was filled with self-curing acrylic resin so that only root was embedded within the self curing acrylic resin. Standardized class I, box-shaped preparations were manually made with a butt joint cavo-surface enamel margins. The cavities were prepared using fissure carbide bur with water spray and finished with fine grained flame burs. All specimens were stored in artificial saliva in an incubator at 37°C and 100% humidity throughout all the steps of the study to more closely resemble a clinical situation. The teeth were randomly divided into two main groups (n=20 teeth each).