The effect of toothpaste and thermal aging on extrinsically stained additively manufactured zirconia: A comparative...

The purpose of this in vitro study was to compare the average surface roughness (R_a) and stain durability of extrinsically stained additively manufactured zirconia, after brushing with different toothpastes and thermal cycling, with those of subtractively manufactured zirconia and lithium disilicate.

Forty-eight disk-shaped specimens (Ø13 × 2 mm) were fabricated from an additively manufactured zirconia (INNI Cera BCM W1000, AM-ZR), a subtractively manufactured zirconia (VITA YZ ST, SM-ZR), and a subtractively manufactured lithium disilicate (UP.CAD HT, SM-LD) (N = 16 per material). One surface of each specimen was externally stained (B4, VITA AKZENT Plus) and glazed (VITA AKZENT Plus Glaze LT), after which baseline R_a and color measurements were recorded with a laser microscope and a spectrophotometer, respectively. Specimens were then subjected to 5000 cycles of brushing with either regular (RT) or whitening (WT) toothpaste (n = 8 per subgroup), 5000 cycles of thermal cycling, and a further 10,000 brushing cycles, with R_a and color measurements repeated after each step with the same equipment. Stain durability was assessed by calculating color differences (ΔE₀₀) between consecutive time points and between baseline and final measurements (total) using the CIEDE2000 formula. One-way analysis of variance and Tukey tests were used to compare the baseline R_a values of tested materials, while generalized linear model analysis was used to evaluate the effect of material type, toothpaste type, and time interval on R_a and ΔE₀₀ (α = 0.05).

SM-ZR had the lowest baseline R_a among the tested materials (p < 0.001). The three-way interaction among main factors affected the R_a and ΔE₀₀ values (p ≤ 0.041). SM-ZR had lower R_a than SM-LD at baseline and after thermal cycling with both toothpastes, as well as after the first brushing cycle with RT and the second brushing cycle with WT (p ≤ 0.025). It also had a lower R_a than AM-ZR after thermal cycling and the second brushing with WT (p ≤ 0.016). After thermal cycling, RT-brushed SM-ZR had lower ΔE₀₀ than RT-brushed AM-ZR and WT-brushed SM-ZR (p = 0.004). These specimens also had their lowest ΔE₀₀ after thermal cycling (p < 0.001). RT-brushed AM-ZR and SM-LD had lower ΔE₀₀ after thermal cycling and after the second brushing than their total ΔE₀₀ (p ≤ 0.027). After thermal cycling, ΔE₀₀ of AM-ZR and after the second brushing, ΔE₀₀ of SM-LD were lower than their total ΔE₀₀ when brushed with WT (p ≤ 0.001).

The R_a of AM-ZR was comparable to that of SM-ZR and SM-LD at all time points, in terms of the previously reported clinical acceptability threshold. The color change for all materials after aging, including two cycles of brushing with toothpaste and thermal cycling, was moderately unacceptable considering previously published thresholds.