Effect of pH and concentrations of ethanol on surface change and color stability of heat-activated denture base resin

Abstract

Complete dentures are mostly fabricated by using acrylic resin. Consumption of certain beverages may affect the esthetic and physical properties of acrylic resin. Due to its low pH, ethanol can produce erosion and alter some properties of acrylic resin, as well. This study evaluated the change in surface and color of conventional heat-activated denture base resin by subjecting it to different pH and concentrations of ethanol at different time intervals.

A heat-activated denture base resin (SR Triplex Hot, Ivoclar Vivadent, Liechtenstein, Europe) was used as a material of this study. Fifty specimens (20 mm x 20 mm x 2 mm) were prepared by manufacturer’s instruction and divided into 5 groups which were a control group (PBS, pH 7.4), group 1 (PBS + HCl, pH 4.0), group 2 (PBS + NaOH, pH 10.0), group 3 (PBS + Ethanol, ethanol concentration 20 %) and group 4 (PBS + Ethanol, ethanol concentration 40 %) for each test solution. All groups were mixed with green pigment and prepared as the test solutions. The specimens were immersed into the groups at 37 ℃ and stored for 10 days. After 5 and 10 days of immersion, the surface roughness (Ra) and color difference (ΔE) of the specimens were measured. The color change was checked by a Spectrophotometer (CM-3500d, MINOLTA, Japan) using a CIE Lab system. The surface roughness tester (Mitutoyo Corp, Kawasaki, Japan) was used to measure the surface roughness of the specimens and the surface morphologies were observed by SEM.

According to the results of color change, no significant difference was observed among groups at T1 (p>0.05). However, group 4 at T2 showed significant difference that compared with the other groups (p<0.05). There was significant different between T1 and T2 in group 4 (p<0.05). When surface roughness of groups analyzed, the highest surface roughness was observed in group 4 followed by group 3 at T2. However, group 4 was only found significant difference at T1 (p<0.05). There was no significant different between the pH variations groups (group 1 and 2) and the control group (p>0.05). The surface became rougher with time in group 3, 4 (p<0.05). SEM evaluation at 200 x magnification showed a slightly more irregular surface in group 3 and a distinct irregular feature in group 4.

From the obtained results, it was concluded that denture base resin is not recommended to immerse in ethanol for cleaning and disinfection.