Evaluation of the cumulative effect of surface polishability of a microhybrid nanocluster light-curing composite by rotary tool systems

Abstract. The aesthetics of composite restoration are determined not only by color and shape, but also by the optical properties of the surface — gloss, transparency and refraction. High-quality polishing forms a uniform microstructure with minimal roughness, restores gloss comparable to natural enamel, and increases biocompatibility and durability of treatment. The most stable aesthetic result is provided by multi-stage polishing systems based on aluminum oxide, capable of evenly removing both the matrix and the filler of the composite.; their effectiveness depends on the processing steps, the type of composite, the particle size of the filler, the hardness of the abrasive and the compliance of the system with the manufacturer's recommendations. However, data on the cumulative effect of polishing and the comparative effectiveness of specific rotor systems remain limited. The aim of the study was to evaluate the cumulative effect of the surface polishability of a microhybrid nanocluster light-curing composite in a comparative aspect of rotary tool systems. Materials and methods. The surface of the enamel of natural teeth was used as a reference. 80 samples of a microhybrid nanocluster light-curing composite with five levels of transparency were produced: opaque dentin, dentine, enamel, cutting edge and transparent liquid-flowing material. The rotary multi-stage polishing system was tested at each transparency level. Polishing was carried out as standard, according to the instructions, without cooling, with the measurement of heat release from the surface. Statistical processing was performed in Microsoft Office Excel 2024 and Statistica 13.3 with the calculation of M, m, SD; The differences were considered significant at p0.05. The study was approved by the Local Ethics Committee of Sechenov University. Results. The surface of the Dentlight composite after polishing by all systems significantly differed from the standard of natural enamel (p0.01), regardless of the transparency level. RoundFlex and RoundFlex T formed a more hydrophilic surface (θw 73.53°-84.25°), but caused heating to 70°C. StarFlex/Septum provided the most hydrophobic values (104.39°-112.64°, except for the cutting edge — 79.11°) when heated to 35-45°C. Enforce Pin showed the smallest wetting angle on the enamel (67.48°) and minimal heat generation (27-30°C on the transparent layer). Ensmart Pin stably formed hydrophobic surfaces (all values 101°) at 30-45°C. Diamond Sun was characterized by moderate hydrophobicity (78.68°-94.15°) and the most gentle temperature regime (no higher than 40°C; 28-32°C on opaque dentin), Diamond Moon — higher θw (up to 108.66°) and heating up to 45°C. Conclusions. None of the polishing systems reproduced the reference parameters of the enamel surface (p0.01). More hydrophobic surfaces were formed by StarFlex/Septum and Ensmart Pin, while hydrophilic surfaces were formed by RoundFlex and RoundFlex T (heating to 70°C). The Enforce Pin provided the smallest wetting angle on the enamel (67.48°), but did not reproduce the standard on other layers. Diamond Sun was characterized by the most gentle temperature regime (no higher than 40 °C). The data obtained substantiate the need for a differentiated selection of the polishing protocol, taking into account the restoration layer and a comprehensive assessment of systems not only in terms of smoothness and wettability, but also in terms of thermal safety.