Effect of accelerated aging on the microhardness and color stability of flexible resins for dentures

Abstract

Acrylic resins have been widely used due to their acceptable esthetics and desirable characteristics such as easy handling, good thermal conductivity, low permeability to oral fluids and color stability. Flexible resins were introduced on the market as an alternative to the use of conventional acrylic resins in the construction of complete and partial removable dentures. Although these resins present advantages in terms of esthetics and comfort, studies assessing chromatic and microhardness alterations of these materials are still scarce in the related literature. The aim of this study was to evaluate the chromatic and microhardness alterations of two commercial brands of flexible resins in comparison to the conventional resin Triplex when submitted to accelerated aging. The resins were manipulated according to manufacturers' instructions and inserted into a silicone matrix to obtain 21 specimens divided into 3 groups: Triplex, Ppflex and Valplast. Triplex presented the highest microhardness value (p < 0.05) for all the aging periods, which was significantly different from that of the other resins, followed by the values of Valplast and Ppflex. Comparison between the flexible resins (Ppflex and Valplast) revealed a statistically significant difference (p < 0.05) as regards color. The flexible resin Ppflex and the conventional resin Triplex presented no statistically significant difference (p < 0.05) as regards aging. The accelerated aging significantly increased the microhardness values of the resins, with the highest values being observed for Triplex. Valplast presented the greatest chromatic alteration after accelerated aging.

Effects of different surface treatments and accelerated artificial aging on the bond strength of composite resin repairs

“…Under the action of repeated cycles of UV-B light exposure and distilled water condensation, artificial aging simulates the chemical and physical oral environments, producing, in a relatively short period, degradation similar to that which a composite resin would undergo in its clinical life. 9,10,15,17 The resins that were repaired in 24 h (except Groups 1B, 2A, and 4A) achieved high bond strength values, with no statistically significant differences in comparison with the control group. This likely occurred because the final curing of the composite resin occurred approximately 72 h following the restoration, and, during this period, non-reacted monomers are still found in the resin.…”

“…14,15 Thermal cycling, 2,3,5,6,14 storage of the dry material at 37 o C in acids, and immersion in water, artificial saliva, or hot water [1][2][3][4]7,16 are some of the Graph 1 -Failure mode distribution according to surface treatment and repair and mechanical assay methodology.…”

Effect of different solutions on color stability of acrylic resin-based dentures

“…1,6,9 The acrylic resin material was packed into the molds, and the polymerization cycles were performed (Table 1).…”

“…1,6,9 Color changes were evaluated by visible ultraviolet refraction spectrophotometry with a UV-2450 reflectance spectrophotometer (Shimadzu, Nakagyo-ku, Japan). 1,6,9,24,25 Color changes were calculated according to the International Commission on Illumination.…”

“…5,6 Color stability is one of the most important clinical properties for dental materials, and color change may be an indicator of aging or damaging of materials. 1,2,[7][8][9] Furthermore, the aesthetic appearance of a prosthesis is certainly an important feature required by patients and must satisfy their expectations. 10 Braz Oral Res., (São Paulo) 2014;(28)1:1-7…”