الفهرس 
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Abstract
This study to assess effect of different polishing pressures (either Light, medium and heavy) and surface condition (either dry or wet) using one step polishing system on the surface roughness of the nano-filled and nano hybrid composites.
A total of 100 specimens were prepared from nanofilled (Filtek Z350 XT) and nanohybrid (Filtek Z250 XT) were used in this study. The specimens were divided into two main groups according to the type of resin composite used (A). The first group (A1) nano-filled composite and the second group (A2) nanohybrid composite. Each group was then subdivided into five subgroups (B), the first subgroup (B0) was the control group as the specimens were only cured upon a celluloid matrix without being subjected to any polishing protocol, the second subgroup (B1) was subjected to intermediate (F=100 gm) then light pressure (F=30gm) during the polishing procedure, the third subgroup (B2) was subjected to heavy (F=300gm) then intermediate pressure (F=100gm) while polishing, the fourth subgroup (B3) was subjected to heavy force (F=300 gm) then light force (F=30gm) while polishing and the fifth subgroup (B4) was subjected to heavy then intermediate force. Each subgroup except the control subgroup was divided into two classes according to the surface condition (C) during polishing (either dry (C1) or wet (C2)).
Cylindrical discs of light-cured resin composite (nanofilled and nanohybrid composites), 10 mm in diameter and 5 mm in thickness, were prepared in a Teflon mold.
The polishing procedure was performed as follows:
Class 1 and 2: nanofilled and nanohybrid composite discs were only cured upon a celluloid matrix without being subjected to any polishing protocol.
Class 3: nanofilled composite discs were subjected to intermediate (F=100 gm) for 20 s then light pressure (F=30gm) for 20 s in dry condition without coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 4: nanofilled composite discs were subjected to heavy (F=300gm) for 20 s then intermediate pressure (F=100gm) for 20 s then light force (F=30gm) for 20 s in dry condition without coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 5: nanofilled composite discs were subjected to heavy force (F=300 gm) for 20 s then light force (F=30gm) for 20 s in dry condition without coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 6: nanofilled composite discs were subjected to heavy (F=300gm) for 20 s then intermediate force (F=100 gm) for 20 s in dry condition without coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 7: nanofilled composite discs were subjected to intermediate (F=100 gm) for 20 s then light pressure (F=30gm) for 20 s in wet condition with coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 8: nanofilled composite discs were subjected to heavy (F=300gm) for 20 s then intermediate pressure (F=100gm) for 20 s then light force (F=30gm) for 20 s in wet condition with coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 9: nanofilled composite discs were subjected to heavy force (F=300 gm) for 20 s then light force (F=30gm) for 20 s in wet condition with coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 10: nanofilled composite discs were subjected to heavy (F=300gm) for 20 s then intermediate force (F=100 gm) for 20 s in wet condition with coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 11: nanohybrid composite discs were subjected to intermediate (F=100 gm) for 20 s then light pressure (F=30gm) for 20 s in dry condition without coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 12: nanohybrid composite discs were subjected to heavy (F=300gm) for 20 s then intermediate pressure (F=100gm) for 20 s then light force (F=30gm) for 20 s in dry condition without coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 13: nanohybrid composite discs were subjected to heavy force (F=300 gm) for 20 s then light force (F=30gm) for 20 s in dry condition without coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 14: nanohybrid composite discs were subjected to heavy (F=300gm) for 20 s then intermediate force (F=100 gm) for 20 s in dry condition without coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 15: nanohybrid composite discs were subjected to intermediate (F=100 gm) for 20 s then light pressure (F=30gm) for 20 s in wet condition with coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 16: nanohybrid composite discs were subjected to heavy (F=300gm) for 20 s then intermediate pressure (F=100gm) for 20 s then light force (F=30gm) for 20 s in wet condition with coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 17: nanohybrid composite discs were subjected to heavy force (F=300 gm) for 20 s then light force (F=30gm) for 20 s in wet condition with coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
Class 18: nanohybrid composite discs were subjected to heavy (F=300gm) for 20 s then intermediate force (F=100 gm) for 20 s in wet condition with coolant. Then specimens were rinsed and dried with air/water syringe for a total of 10 s.
All specimens were stored in 100% humidity container at 37o C for 24 hours before being scanned with Environmental scanning electron microscopy (SEM) to evaluate average surface roughness (Ra).
the specimens were scanned using scanning electron microscope at 1000x magnifications using backscattered electron detector (BSED). After which the 1000x scan of each specimen was analyzed using Gwyddion 2.56, (An SPM data visualization and analysis tool) supported by the Czech Metrology Institute, 2020) in order to gain the average surface roughness (Ra) of each specimen. For image analysis, the scanned picture was imported using the Gwydion Software then ”calculate roughness parameters” option was selected to start retrieving the surface roughness average (Ra) data. Measuring average surface roughness was done at four consistent levels, 2 horizontal planes and 2 vertical planes perpendicular on others and dividing the scan into thirds, to ensure that the whole scan surface is equally represented in the resulting value. Then, the Surface Roughness Average (Ra) values collected from each sample were inserted into an Excel sheet for mean value calculations. The quantitative data were collected and used to perform the statistical analysis and results for each group. The data were statically analyzed. Numerical data were presented as mean and standard deviation (SD) values. They were explored for normality by checking the data distribution, and using Shapiro-Wilk test. Data showed parametric distribution and were analyzed using three-way ANOVA followed by Tukey’s post hoc test. Comparison of main and simple effects were done utilizing one-way ANOVA followed by Tukey’s post hoc test and the pooled error term of the three-way model. P-values were adjusted for multiple comparisons utilizing Bonferroni correction. The significance level was set at p < 0.05. Statistical analysis was performed with R statistical analysis software version 4.3.0 for Windows.
Conclusions:
Under the limitations of the current study the following conclusions were derived:
1. The surface roughness of resin composite after polishing is highly affected by the type of composite used.
2. One step polishing system is considered as an effective polishing tool for nano-filled and nano-hybrid composites.
3. Press-on force during polishing procedure as well as surface condition (either dry or wet) have a profound effect on the surface roughness of nano-filled and nano-hybrid resin composites.
4. Heavy pressure in combination with dry surface is considered the most efficient polishing protocol to minimize the surface roughness of nano-filled and nano-hybrid resin composite with one step polishing system.