Effect of Nano Ceramic Coating on Color Stability of Polymethylmethacrylate: In Vitro and Clinical Study

Dental implant therapy is widely used to rehabilitate edentulous patients to overcome the limitations of conventional dentures. Treatment includes implant-retained overdentures and fixed complete dentures fabricated with polymethylmethacrylate (PMMA). Previous studies have shown that titanium dioxide (TiO2) coating on PMMA via Atomic Layer Deposition (ALD) has improved surface properties. However, the effect of this TiO2 coating on color is unknown. The goals of this study are to: (1) determine the color difference between PMMA before and after TiO2 coating; and (2) evaluate the color perceptibility and acceptability of PMMA with TiO2 coating. 45 PMMA 10x10x2 mm specimens were fabricated using light, original and dark pink Lucitone 199 according to manufacturer’s protocol. 10 specimens from each group underwent deposition of TiO2 coating using ALD. All specimens were measured with a spectroradiometer (PR 650; PhotoResearch Inc) before and after coating. Color difference (ΔE) before and after coating was calculated with Commission Internationale d’Eclairage formula 2000. Data were analyzed using ANOVA to compare the differences among the 3 groups (α<0.05). In each group, the recorded ΔE was compared to the perceptibility (ΔE = 1.71) and acceptability threshold (ΔE = 4.00) of PMMA by using independent t-tests (α<0.05). A clinical survey used to examine perception and acceptability of PMMA samples with and without TiO2 coating was conducted on 24 patients and 10 prosthodontists. Color change was observed after the deposition of TiO2 coating on all groups, light (ΔE =3.2 ± 0.8), original (ΔE =3.1 ± 0.7) and dark pink (ΔE =3.3 ± 1.2). The original samples had the least color change. There was no statistical significant difference among 3 groups (p=0.845). The ΔE of light (p<0.001), original (p<0.001), and dark pink (p=0.002) acrylic was significantly higher when compared to the established perceptibility threshold. However, this ΔE was significantly lower compared to the established acceptability threshold for light (p=0.01) and original (p=0.004) specimens. The clinical survey is consistent with the in vitro study as it demonstrated that generally a color difference was perceived but was clinically acceptable. This novel TiO2 coating via ALD on PMMA resulted in perceptible color changes, but color changes were generally still clinically acceptable.