Tribological and Topographical Characteristics of Nano-Processed Coating for Aesthetic Restorative Materials

Background: Tooth-colored restorative materials have been widely used for aesthetic purposes in restorative dentistry. The gradual loss due to degradation or wear of the damaged surfaces leads to the roughening of the restoration and accordingly influences its esthetic and clinical longevity. Objectives: To assess the feasibility of nano-filled resin coating of aesthetic restorations materials which is as an essential step for GI and an optional protocol for resin composites. Thus, the tribological feature (wear resistance) and consequent topographical characteristics (microstructure, surface roughness and hardness) of the resin composite and GI either coated or uncoated are investigated. Materials and methods: A total of forty samples were fabricated using nanohybrid composite (Tetric N-Flow Bulk Fill) and conventional GI (Fuji IX GP fast); 20 samples each. Half of the samples were covered with resin nano-filled resin coating (EQUIA Coat). Each sample was stored individually in 3 mL distilled water at 37°C for 24 hrs., dried and weighed. Then, specimens were subjected to tooth brushing abrasion wear (~100000 cycles) using especially designed tooth brushing holder device followed by reweighing to determine the amount of weight loss. Surface morphology was examined by SEM, surface roughness was mapped out using AFM as well as VHN were determined. The data was statistically analyzed using SPSS. Results: The nanofilled resin coated samples for each tested material recorded insignificant wear resistance with its corresponding uncoated samples (0.0020±0.0000 & 0.0018±0.00045 for coated and uncoated resin composite respectively) and (0.0034±0.00055 & 0.0026±0.00055 for coated and uncoated GI respectively). The existence of coating evidently reduced the surface roughness of both aesthetic materials as examined by SEM and measured by AFM. Regarding surface hardness, the lowest significant mean values (55.94 ± 0.99 & 56.24± 2.34 were recorded by coated resin composite and coated GI, respectively) compared with uncoated ones (82.22± 3.94 & 71.82± 4.90 for uncoated resin composite and uncoated GI respectively). Conclusions: The wear resistance of the nano-filled resin coating per se is analogous to those of the uncoated aesthetic restorative materials after exposure to prolonged brushing. The coating evidently reduced the surface roughness of both investigated aesthetic materials; however, it has significantly lower hardness values. Thus, on the clinical point of view, the capability of the nano-filled resin coating to reduced surface roughness of both aesthetic restorative materials and its persistence against abrasion wear would allow more glossy appearance and maintain healthy oral condition.