In-vitro evaluation of surface roughness of three different pediatric crowns following brushing with toothpastes of varying abrasiveness

Objective: The aim of this study was to evaluate, in vitro, the surface roughness of three different pediatric crowns after simulated long-term clinical toothbrushing using a brushing simulator with children's toothpastes of varying abrasivity and distilled water, by means of high-resolution surface analysis techniques. Materials and Methods: In this study, three different types of pediatric crowns were used: stainless steel crowns (NuSmile®, USA), pediatric zirconia crowns (NuSmile®, USA), and 3D-printed pediatric resin crowns (Senertek P CrownV4, Turkey). A total of 60 crowns of identical size were divided into three main groups (n=20), each subdivided into four subgroups (n=5). Subgroups were brushed with children's toothpastes of high (RDA=103), medium (RDA=80), and low (RDA=35) abrasivity, while the control group was brushed with distilled water. Toothbrushing simulation was performed using a brushing simulator under a constant force of 200 gF with soft-bristled brushes at 10,000, 30,000, and 50,000 cycles. Surface roughness values (Ra) and topographical surface maps of all specimens were measured at baseline and after each brushing interval using atomic force microscopy (AFM, Park XE-100E, Park Systems, Korea). Morphological surface evaluations before and after brushing were conducted using scanning electron microscopy (SEM, LEO 1430 VP, Germany). Data were analyzed using a three-way robust ANOVA, with a significance level set at p<0.05. Findings: According to the robust ANOVA results, crown type (Q=5022.32; p<0.001), toothpaste type (Q=253.24; p<0.001), and brushing cycle count (Q=1586.01; p=0.001) had statistically significant effects on surface roughness. In addition, all two-way and three-way interactions between these variables were also found to be significant (p<0.001). The mean Ra values were measured as 152.5 µm for the PRK group, 51.7 µm for the SSC group, and 36.6 µm for the PZC group. Among the toothpaste groups, the highest mean Ra value was observed in the AF group (87 µm), while the lowest was in the control group brushed with distilled water (69.7 µm). The highest surface roughness value (222.1 µm) was recorded in the PRK group brushed with AF toothpaste after 50,000 cycles. These findings indicate that surface roughness varies significantly depending on both the material type and brushing conditions. Conclusion: As a result of the study, an increase in surface roughness was observed in all crown groups with increasing brushing cycles and toothpaste abrasivity, with the least change noted in the PZC group. Given their superior esthetic and mechanical properties, PZC crowns may be recommended for long-term clinical use. However, for crowns used beyond three years, polishing or replacement may be advisable. Keywords: Atomic force microscopy, Brushing simulator, Pediatric resin crowns, Relative Dentin Abrasivity Surface roughness