Effect of Long-Term Aging of Light-Polymerized Denture Reline Materials.

Objectives: Denture reline can improve adaptation to the basal seat mucosa. However, long-term use of these dentures may lead to the deterioration of reline materials. Although aging studies on soft-reline materials exist, reports on hard reline materials, especially light-polymerized types, are limited. This study evaluated the aging of surface characteristics under simulated oral conditions.
Methods: Two reline materials - a light-polymerized material (Hikari Liner, Tokuyama) and an auto-polymerizing material (Rebase III, Tokuyama) - along with a denture base polymethyl methacrylate (PMMA; Acron, GC), were tested. Ten discs (10 mm x 10 mm x 2 mm) of each material were fabricated and polished (1500 grid abrasive paper). Specimens were immersed in artificial saliva at 37 degrees Celsius for 180 days. Surface roughness, color difference, and contact angle were measured at specific time points. Surface observations were performed using scanning electron microscopy (SEM). Statistical analysis was conducted using the Friedman test and pairwise comparisons (compared to 0 and each day) with Bonferroni correction (α = 0.05).
Results: Surface roughness of the light-polymerized material significantly increased after 150 days and 180 days (p=0.035 for both). For the auto-polymerizing material, significant changes were observed after 120 days, 150 days, and 180 days (p=0.035 for all). Color difference clearly changed after 120 days for auto-polymerizing material. Contact angles did not exhibit significant changes. SEM images revealed polymer detachment and deformation on the specimen surfaces.
Conclusions: The surface characteristics of reline materials changed over time in a simulated oral environment. Significant surface changes were observed after 120 days for the auto-polymerizing material and after 150 days for the light-polymerized material, suggesting progressive surface degradation over time.