Research and Education
Optical properties and surface roughness of prepolymerized poly(methyl methacrylate) denture base materials

https://doi.org/10.1016/j.prosdent.2018.03.001Get rights and content

Abstract

Statement of problem

Studies of the color stability, relative translucency, and surface roughness of newly introduced computer-assisted design and computer-assisted manufacturing (CAD-CAM) prepolymerized poly(methyl methacrylate) (PMMA) denture base materials are lacking.

Purpose

The purpose of this in vitro study was to evaluate the color stability, relative translucency, and surface roughness of conventional and different prepolymerized CAD-CAM PMMA denture base materials after coffee thermocycling (CTC).

Material and methods

Six disk-shaped specimens (10×2 mm) were prepared from 3 different brands of prepolymerized CAD-CAM PMMA and a conventional heat-polymerized PMMA denture base material (N=24). Specimens were polished conventionally in 2 stages. The specimens were subjected to 5000 coffee thermocycles. The surface roughness (Ra) of each specimen was measured 3 times before and after CTC, using a contact profilometer, and the mean roughness (Ra) values were calculated. The color coordinates of the specimens were determined by using a noncontact spectroradiometer, and color differences and relative translucency parameter (RTP) values were calculated by using CIEDE2000 color difference and RTPCIEDE2000 formulas. ANOVA was used to analyze surface roughness values, CIEDE2000 color differences, and RTP values (α=.05).

Results

CTC did not change the color of the tested materials. However, with regard to relative translucency, 2-way ANOVA revealed a significant interaction between the material and CTC (P=.011). Also, although CTC increased the surface roughness of all tested materials (P=.031), Ra values were lower than the plaque accumulation threshold of Ra=0.2 μm.

Conclusions

Mean color changes in all materials were clinically imperceptible after 5000 coffee thermocycles. One tested material had significantly lower relative translucency than other materials before and after CTC. The surface roughness values of all tested denture base materials were below the plaque accumulation threshold.

Section snippets

Material and Methods

Three different brands of prepolymerized PMMA and a conventional heat-polymerized PMMA denture base material, as described in Table 1, were tested for color stability, relative translucency, and surface roughness before and after CTC. Six disk-shaped (10×2 mm) specimens were prepared for each resin material as follows: prepolymerized PMMA denture base materials were designed as standard tessellation language (STL) files, 10 mm in diameter, and milled by using a CAD-CAM milling system (M1 Wet

Results

Means and 95% confidence limits for color differences due to CTC for different acrylic materials are presented in Figure 1. The material tested was not found to affect these color difference values (dfnum=3, dfden=20, F-ratio=1.03, P=.401).

Means and 95% confidence limits for RTP values are presented in Figure 2 for all subgroups. ANOVA for these data are provided in Table 2 and revealed significant interactions between the material and CTC. For each material, no significant differences were

Discussion

The first null hypothesis, that the material would not affect the color change due to CTC, was accepted as the material was not found to have an effect on this color change and the mean color difference for each material after CTC was below the perceptibility threshold.23 The second null hypothesis that neither material nor CTC would affect the relative translucency was rejected because of the significant interaction between the material and CTC on the relative translucency of the materials

Conclusions

Within the limitations of this in vitro study, the following conclusions were drawn:

  • 1.

    Material was not found to affect the color change due to coffee thermocycling (CTC) after 5000 cycles. All materials studied had imperceptible color changes after this CTC.

  • 2.

    The Merz Dental GmbH prepolymerized PMMA material had the lowest relative translucency values before and after CTC.

  • 3.

    The surface roughness of the specimens was higher after CTC regardless of the material.

  • 4.

    All tested denture base materials had a

Acknowledgments

The authors thank Merz Dental GmbH for supplying the materials used in this study.

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