Comparative Study on Color Stability of Denture Reline Polymers When Using Microwave and Chemical Disinfection

This study investigated the color stability of reline resin after two methods of disinfection i.e
microwave disinfection and chemical disinfection. A stainless steel mold with a breakaway
compartment (10 mm in diameter by 0.7 mm thickness) was made to fabricate specimens of various
resins. Each material was mixed according to manufacturer’s instructions and applied into the mold.
Prior to color stability testing, specimens were cleaned in distilled water for 20 minutes to kill any
microorganisms that may had contaminated the discs during fabrication. And then specimens were
immersed in Sodium Perborate Monohydrate 200 ml of solution for 15 days and micro waved for 15
days so that it is comparable to chemical disinfection soaking. The color stability of each specimen
was measured again using spectrophotometer and values were obtained. The data of ΔE, ΔL, Δb, Δa
were analysed by 2 way repeated measures ANOVAs test. Significant statistic changes in color
parameters ΔL, Δa, Δb of the reline resin DPI, Ufi Gel Hard and Kooliner were observed when
dentures were disinfected by Sodium Perborate Monohydrate 2% solutions. The color stability of the
reline resin was influenced by time, regardless of disinfection or non disinfection. This can be
attributed to bleaching (whitening) effect of reline material. Discoloration of resin based materials may
be caused by intrinsic or extrinsic factors. Intrinsic factors are related to internal alterations in
material resulting from physicochemical reactions or residual monomer oxidation with time. Thus the
initiator, quantity and type of monomer and the polymerisation efficiency can affect the color
stability of resin based materials. The color stability deviation value ΔE significantly increased to
maximum for chemical disinfectant, least for Control group and intermediate for microwaved group.
Ufi Gel showed the highest deviation ΔE and Control Group showed the lowest deviation according to
results.