Effect of Staining and Bleaching on Surface Roughness of Different Nano Hybrid Resin Composite Materials

Aims: The purpose of this study was to evaluate the effects of staining by coffee and In-office bleaching by 30% hydrogen peroxide on surface roughness of two different Nano Hybrid composite and Omnichroma resin-based composite. Materials and Methods: In this in vitro experimental study, 32disc samples were fabricated from each type of the Nano-Hybrid resin composite materials, each sample measured 5 mm in diameter and 2 mm in height. The samples for each composite group were then sub-divided randomly into four sub-groups (n=8). In control sub-groups, samples were stored in artificial saliva at 37°C for 1 week. Samples of Staining sub-groups were stored in a coffee solution for 48h at 37°C. Samples of Staining Bleaching sub-groups were stained in a coffee solution for 48 h at 37°C then bleached with 30% H2O2. Samples of Bleaching sub-groups were bleached with 30% H2O2. The surface roughness measurements were taken for all samples of each sub-group; the measurements for control sub-groups considered as baseline data. Non-parametric tests were used for statistical analysis at P≤0.05. Results: The surface roughness measurements of all sub-groups for both tested materials didn’t exceed the critical value (Ra< 0.2 μm) with no significant difference among all sub-groups (P >0.05). Conclusion: Surface roughness of the two tested Nano-Hybrid resin composite materials were neither influenced by coffee staining nor by inoffice bleaching with 30% H2O2.


INTRODUCTION
Resin composites are popular esthetic restorative materials used in dentistry for their excellent optical appearance, adequate strength, and their ability to be bonded to tooth structure [1] . When applying a composite restoration, one of the major objectives is to obtain restoration with smooth surfaces and without porosities; surface roughness is an important characteristic that determines the clinical success of the composite restorative materials as restorations with rough surfaces enhance plaque accumulation, discoloration, gingival irritation and secondary caries [2] . Oral environment and routine food habits can affect surface properties of resin composites and ultimately affect the durability of composite restoration in the long term.
Also, some dental treatments like tooth bleaching can have a negative influence on resin composite restorations; tooth bleaching is a simplified and non-invasive approach for tooth whitening which is based mainly on oxidation by hydrogen peroxide or one of its precursors [3] . Resin composites are more susceptible to adverse changes by tooth bleaching compared to other tooth-colored restorative materials due to the presence of organic matrix in their composition; peroxides in the bleaching agents might induce degradation of the polymer network of resin composites which may enhance surface roughness [4] .
The response of resin composite restorations to whitening materials depends on several factors such as the type and percentage of both organic matrix and fillers of resin composites, concentration and application time of the bleaching agent [3] .   Table (1).  [4] . The Polyurethane mold was positioned on a transparent celluloid strip over a glass slab and filled with the tested material, then the surface of the mold was covered with another transparent celluloid strip and a glass slab [5] . The transparent celluloid strip will improve the surface quality of the composite sample by limiting the oxygen inhibiting layer [6] . The mold was then compressed with A 500gm load for 30 seconds to allow the excess material to leak out and to obtain parallel surfaces [5] . The load was then discontinued and the for 24 hours [7] . The samples of each composite material were randomly divided into two major groups :

Statistical analysis
Statistical analyses were performed

RESULTS
The

DISCUSSION
This study examined the influence of staining by coffee and bleaching by 30% H2O2 on surface roughness of two different Nano Hybrid resin composite materials.
Coffee was selected in the present study because it is a very frequently consumed beverage. Also, tooth bleaching has become a routine treatment in common dental practice, so the effect of bleaching agents on morphological and surface texture of composite restorative materials should also be considered [8] .
The increase in fluid uptake (water sorption) was attributed to the incorporation of hydrophilic monomers in the resin matrix. Bis-GMA and TEGDMA are hydrophilic monomers due to the presence of hydroxyl group in their chemical structure; in contrast, (UDMA) is less hydrophilic with low water sorption than Bis-GMA and TEGDMA, so it's more resistant to staining and solubility and changes in surface texture [1] . The surface roughness of restorative materials has been a major concern for researchers and  [2,8] who also concluded that staining by coffee didn't increase the surface roughness of composite samples. These results may be attributed to low water sorption rate or low resin content for these two materials. With respect to filler system, resin composites with high filler loading and small filler size are expected to have good characteristics and more resistant to degradation and changes in surface topography with less response to staining solutions and bleaching agents [10] . content is expected to be more pronounced to degradation by bleaching materials [8] .
Also, the effect of high energy free radicals liberated from peroxides at the resin-filler interface might cause complete or partial filler-matrix detachment and water uptake that accelerates the hydrolytic degradation of resin composites leading to more separation and debonding of filler particles and ultimately increased surface roughness of restorative material [11] . Gül et al [8] reported that bleaching procedures caused a significant increase in surface roughness in tested samples and referred this result to degradation of the composite resin matrix.