Color evaluation of a dielectric mirror coating using porcine tissue and prosthetic gingival material: a comparison of two models.

Abstract

The aim of this study was to firstly evaluate the esthetics of a dielectric multilayer coating on titanium below porcine tissue (in vitro porcine model). Secondly, a polymer model was used to investigate the same samples to compare the models to each other and discuss their validity for optical assessment of esthetic coatings for implant applications. A dielectric mirror coating was deposited on titanium substrates (Ti- Bragg) and tested below porcine tissue and polymer platelets of three test thicknesses (1mm, 2mm and 3mm). Titanium without coating (Ti) was used as a negative control. Furthermore, the substrates were subjected to three different surface treatments (polished, machined and sand-blasted). The color difference values ΔL, Δa, Δb and ΔE were calculated for each sample. In total, six samples were tested in both models. Statistical analysis of the data (one sample Wilcoxon test, Kruskal-Wallis with Bonferroni-Holm corrected Mann-Whitney post hoc tests for multiple testing) was conducted for each sample in both evaluation methods. In the in vitro porcine model, sand-blasted Ti-Bragg and Ti samples showed ΔE values significantly above the threshold value of 3.70, indicating a dark appearance of the 1 mm thick covering tissue. As the test thickness increased, polished and machined Ti-Bragg samples were significantly invisible (ΔE<3.70 with P<0.05). Excessive brightening effects from Ti-Bragg samples were not observed from the in vitro porcine model, but below polymer platelets the samples exhibited significantly high ΔL values, which also resulted in a significant and visible color change (ΔE>>3.70 with P<0.05). Ti-Bragg was suggested to be an appropriate coating system for dental implants to improve the soft tissue esthetics. The design of this coating system can be adjusted by varying different parameters to satisfy the requirements of an esthetic coating. The polymer model is valid for test thicknesses of 2 and 3mm, however, one might have to increase the thickness to 1.5mm or alter the composition of the resin for 1mm thick platelets to increase the opacity and therefore adapt to the soft tissue situation.