الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Composite resins are widely used dental materials since they restore both function and esthetics of dental tissues. They are expected to have physical properties comparable to those of tooth enamel and dentin and provide a long life of service. Despite its increasing use in the posterior teeth, these materials still present problems related to marginal integrity and leakage, mostly due to their inherent polymerization shrinkage.
To minimize polymerization shrinkage, dental material manufacturers previously advised placing composite resins in increments not larger than 2-3 mm before it is polymerized. Even though, there are also some disadvantages to this technique. Increments may increase the potential of voids to form between composite layers. Moreover, the risk of contamination leading to a compromised restoration is adversely impacted by the time it takes to place, adapt and cure each increment.
A new generation of so-called ’bulk-fill’ composites has been introduced. These materials are suitable for insertion in a 4 mm bulk placement due to their reduced polymerization stress and their high reactivity to light curing. Consequently, problems arise from polymerization shrinkage and restoration time could be reduced without compromising the quality of cure.
The present study was conducted to evaluate marginal microleakage of nano-hybrid bulk-fill composite, and compare it to incrementally placed conventional nano-hybrid composite when used to restore proximal cavities in primary molars.
The study sample included 44 non carious second primary molars extracted for orthodontic purpose or near their shedding time. Standardized proximal cavities were prepared. Teeth were then divided randomly into 2 equal groups. group I were restored with Tetric EvoCeram bulk-fill composite, group II were restored with GrandioSO incrementally placed conventional composite. All prepared cavities were etched with phosphoric acid for 20 seconds, rinsed for 20 seconds, and excess moisture was removed with an air syringe. Total-etch adhesive was applied according to manufacturer’s instructions. Etchants and adhesives were from the corresponding manufacturers of the composites to avoid possible incompatibilities. All teeth were stored in distilled water for 24 hours at 37°C.
Restored teeth were subjected to 1000 cycle between 5 °C and 55 °C in controlled water bath with a dwell time of 30 seconds in each bath. The entire surface of each tooth (with exception of the restorations and 1 mm around) were covered with double layer of nail polish to ensure a proof isolation of the teeth surfaces against dye penetration. All specimens were immersed in 2% methylene blue solution for 24 hours at 37°C. After dye exposure, the teeth were bisected longitudinally in a mesisodistal direction parallel to the long axis through the center of the restoration with discs that were replaced every five specimens. The sectioning resulted in two approximately equal parts which were both analyzed for microleakage under a stereomicroscope at a magnification of x20.Microleakage was assessed according to the scoring system described by Radhika et al in 2010.
The results showed that there were no statistically significant difference has been found in microleakage scores of group I at occlusal and cervical margin at (p=1.000), also in group II, no statistically significant difference has been found between occlusal and cervical margins at (p=0.366). Comparing the combined occlusal and cervical microleakage scores of group I and group II, bulk- fill composite showed lower microleakage scores than incrementally placed conventional composite with no statistically significant difference at (p=0.24).
Based on the results of the present study, bulk-fill composite restoration marginal integrity was comparable to incrementally placed conventional composite in proximal cavities of primary molars.