Color stability of 3D-printed denture resins: effect of aging, mechanical brushing and immersion in staining medium

Abstract

PURPOSE This in-vitro study evaluated and compared the color stability of 3D-printed and conventional heat-polymerized acrylic resins following aging, mechanical brushing, and immersion in staining medium. MATERIALS AND METHODS Forty disc-shaped specimens (10 mm in diameter and 3 mm thick) were prepared from two 3D-printed [DentaBASE (DB) and Denture 3D+ (D3D)] and one conventional polymethylmethacrylate (PMMA) denture materials. The specimens were thermo-cycled, subjected to mechanical brushing, and were immersed in either coffee, lemon juice, coke, or artificial saliva (AS) to simulate one and two years of oral use. Color measurements of the specimens were recorded by a spectrophotometer at baseline (T0), and after one (T1) and two years (T2) of simulation. The color changes (∆E) were determined and also quantified according to the National Bureau of Standards (NBS) units. Descriptive statistics, followed by factorial ANOVA and Bonferroni post-hoc test (α=.05), were applied for data analysis. RESULTS The independent factors, namely material, staining medium, and immersion time, and interaction among these factors significantly influenced ∆E ( P <.009). Irrespective of the materials, treatments, and time, the highest and the lowest mean ∆Es were observed for PMMA in lemon juice (4.58 ± 1.30) and DB in AS (0.41 ± 0.18), respectively. Regarding the material type, PMMA demonstrated the highest mean ∆E (2.31 ± 1.37), followed by D3D (1.67 ± 0.66), and DB (0.85 ± 0.52), and the difference in ∆E between the materials were statistically significant ( P <.001). All the specimens demonstrated a decreased color changes at T2 compared to T1, and this difference in mean ∆E was statistically significant ( P <.001). CONCLUSION The color changes of 3D-printed denture resins were low compared to conventional heat polymerized PMMA. All the tested materials, irrespective of the staining medium used, demonstrated a significant decrease in ∆E values over time.

Thermal-cycling, simulated brushing, and beverages induced color changes and roughness of CAD/CAM poly (methyl methacrylate) denture resins

“…Next, the specimens were polished (Derotor, London, England) for 90 s using a slurry of pumice and water. All the specimens underwent ultrasonic cleaning in distilled water for 5 min and dried with absorbent paper for baseline colour and surface roughness measurements [17].…”

“…The brushing parameters applied were 356 rpm, 200 g vertical load, 3.8 cm stroke path and 17,800 brushing cycles (50 min). The slurry was refilled during the brushing, and toothbrushes were replaced every 4,500 cycles as per the recommendations of the American Dental Association (ADA), which states that toothbrushes be replaced 3-4 months [17].…”

“…This ensured even exposure of both specimen surfaces to the beverages. The total immersion period was 168 h that equalled one year of oral exposure [17], and the beverages were changed every 24 h. The specimens were taken out from the vials, cleaned under running water, and stored in distilled water for 24 h before final colour and surface roughness measurements [17].…”

“…The ΔE values over the AT limit (ΔE=2.7) is not clinically acceptable [23]. In correlating the colour values to the clinical environment, the ΔE was converted to National Bureau of Standards (NBS) using equation (2): [17].…”

“…Nevertheless, the continuous action of toothbrush bristle and toothpaste particles contributes to an increased roughness on the denture surface that could facilitate microbial accumulation, plaque retention and colour instability [13,15,16]. This could be further aggravated by the low pH of the commonly consumed beverages which has a detrimental effect on the denture surface in the form of resin matrix softening, eroding of denture surface and disintegration of the resin material particles [17].…”