Abstract
Exposure of denture base acrylic resins to the oral environment and storage media for extended periods of time results in colour change due to changes in the properties of the material. The purpose of this in vitro study was to assess the colour stability of high-impact heat-polymerized denture base acrylic resin (HI PMMA) impregnated with zirconia nanoparticles after storage in distilled water (DW) and denture cleaners such as Steradent (STD) and Milton (MIL) for 180 days. Ninety specimens of PMMA + Zirconia nanocomposite with varying nanoparticle concentrations (1.5 wt.%, 3.0 wt.%, 5.0 wt.%, 7.0 wt.% and 10 wt.%) were prepared with a diameter and thickness of 25 ± 1.0 mm × 2 ± 0.1 mm and divided into six groups, while each group was further divided into three subgroups: storage in DW (control), STD and MIL. Colour changes were measured with a Minolta Chroma Meter (Minolta, Osaka, Japan), and assessed using the CIE L*a*b* colorimetric system. Data were statistically analysed for colour change with Friedman’s Two-way and Kruskal-Wallis tests at a pre-set alpha value level of 0.05. The colour change (ΔΕ) exhibiting significant differences were found among all groups immersed in denture cleaners, and all values increased with time. According to the National Bureau of Standards, the control group displayed the lowest colour change value (ΔΕ = 1.22), and the highest value was for 10 wt.% ZrO2 while stored in MIL (ΔΕ = 6.07). The values of colour change for storage in water ranged from 0.49 (control) to 1.82 (10 wt.% ZrO2). The colour change value for the composite group containing 3 wt.% zirconia was clinically acceptable. However, high concentrations of denture cleaners should be avoided, and the shortest cleaning time is recommended to improve the clinical life of the nanocomposite denture base.
Highlights
Poly-methyl methacrylate (PMMA) acrylic resin has been accepted as the material of choice for constructing artificial denture bases since the beginning of the twentieth century [1]
The aim of this study was to evaluate the effect of adding zirconia nanoparticles at different concentrations to high-impact PMMA on colour change when stored in distilled water (DW) and two different media of denture cleaners Steradent (STD) and Milton (MIL) for up to 180 days
For all groups and after all immersion durations, there was a difference in colour change between the samples immersed in DW and the other solutions (Table 5)
Summary
Poly-methyl methacrylate (PMMA) acrylic resin has been accepted as the material of choice for constructing artificial denture bases since the beginning of the twentieth century [1]. PMMA resin has been reinforced with butadiene-styrene rubber to develop high-impact PMMA in an attempt to improve its physical and mechanical properties. These materials are provided in a powder-liquid form and processed in the same way as other conventional heat-polymerized methyl methacrylate resins [2]. The study concluded that antimicrobial action of the cleaner in the mouth could resist plaque formation [4]. Their daily use may impact the physical properties of the denture base resin, affecting its surface roughness, hardness, gloss or color [5]. A lack of information on using cleaning solutions correctly may affect the denture properties [6]
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