Effect of polishing and denture cleansers on the surface roughness of new-generation denture base materials and their color change after cleansing

Abstract

Purpose: To evaluate the effect of polishing and denture cleansers on the surface roughness (R_a) of new-generation denture base materials that are additively, subtractively, and conventionally fabricated, while also assessing their color change after cleansing.

Material and methods: One hundred and fifty disk-shaped specimens (Ø10 × 2 mm) were prepared from five denture base materials (one subtractively manufactured nanographene-reinforced prepolymerized polymethylmethacrylate (PMMA) (SM-GC), one subtractively manufactured prepolymerized PMMA (SM-PM), two additively manufactured denture base resins (AM-DT and AM-ND), and one heat-polymerized PMMA (CV) (n = 30). The R_a of the specimens was measured before and after conventional laboratory polishing, while color coordinates were measured after polishing. Specimens were then divided into three subgroups based on the denture cleanser: distilled water, 1% sodium hypochlorite (NaOCl), and effervescent tablet (n = 10). The R_a and color coordinates were remeasured after nine cleansing cycles over a period of 20 days. The CIEDE2000 formula was used to calculate the color differences (ΔE₀₀). Two-way analysis of variance (ANOVA) was used to analyze the R_a values before (n = 30) and after (n = 10) cleansing, while repeated measures ANOVA was used to analyze the R_a of material-time point pairs within each denture cleanser (n = 10). ΔE₀₀ data after denture cleansing was also analyzed by using two-way ANOVA (n = 10) (α = 0.05).

Results: Before polishing, R_a varied significantly among the materials. SM-GC and SM-PM had the lowest and AM-ND the highest R_a values (P < 0.001). Polishing significantly reduced R_a of all materials (P < 0.001), and after polishing, R_a differences among materials were nonsignificant (P ≥ 0.072). Regardless of the denture cleanser, the R_a of AM-DT, AM-ND, and CV was the highest before polishing when different time points were considered (P < 0.001). After cleansing, AM-ND had the highest R_a of all the materials, regardless of the cleanser (P ≤ 0.017). AM-DT had higher R_a than SM-PM when distilled water (P = 0.040) and higher R_a than SM-GC, SM-PM, and CV when NaOCl was used (P < 0.001). The type of cleanser significantly influenced the R_a of AM-DT, AM-ND, and CV. For AM-DT, NaOCl led to the highest R_a and the tablet led to the lowest R_a (P ≤ 0.042), while for AM-ND, distilled water led to the lowest R_a (P ≤ 0.024). For CV, the tablet led to lower R_a than distilled water (P = 0.009). Color change varied among the materials. When distilled water was used, SM-GC had higher ΔE₀₀ than SM-PM and AM-DT (P ≤ 0.034). When NaOCl was used, AM-ND had higher ΔE₀₀ than SM-GC, SM-PM, and AM-DT, while CV and SM-GC had higher ΔE₀₀ than SM-PM and AM-DT (P ≤ 0.039). Finally, when the tablet was used, AM-ND and CV had the highest ΔE₀₀, while AM-DT had lower ΔE₀₀ than SM-GC (P ≤ 0.015).

Conclusions: The tested materials had unacceptable surface roughness (>0.2 μm) before polishing. Roughness decreased significantly after polishing (<0.2 μm). Denture cleansers did not significantly affect the surface roughness of the materials, and roughness remained clinically acceptable after cleansing (<0.2 μm). Considering previously reported color thresholds, AM-ND and CV had unacceptable color change regardless of the denture cleanser, and the effervescent tablet led to perceptible, but acceptable color change for SM-GC, SM-PM, and AM-DT.

Keywords: additive manufacturing; chemical disinfection; color change; denture base; surface roughness.