Effect of Excessive Washing and Frosty Appearance on Mechanical and Optical Properties of 3D Printed Restorative...

To evaluate the effect of the washing process on the mechanical and optical properties of a 3D printed resin indicated for indirect restorations and to determine possible solutions to reverse the negative effects of excessive washing.

A 3D printed resin (Sprintray Ceramic Crown) was used to test three-point flexural strength, Vickers hardness, degree of conversion on the surface (DC_s) and 0.1 mm depth of the material (DC_d), translucency parameter (TP), and color changes (ΔE). Samples were divided into five groups based on their washing process, including manufacturer's recommendation as a negative control (NC), excessive washing in a pre-programmed washing unit as a positive control (PC), PC cleaning followed by brushing with 99% isopropyl alcohol (EC), PC cleaning followed by coating with a thin layer of uncured resin (RC), and PC cleaning followed by infiltrating resin into the surface with a brush (RI). Data were analyzed with a one-way ANOVA test and Tukey post hoc analysis (α = 0.05).

Excessive washing (PC) resulted in a significant reduction in flexural strength, DC_s, DC_d, and TP in comparison to NC (p < 0.001) and exceeding the acceptable threshold (ΔE > 2.8). Among the three approaches to reverse the negative effect of excessive washing (EC, RC, and RI groups), only RI resulted in flexural strength, hardness, DC_d, and TP with no significant difference from the NC group (p < 0.05) and color changes below the perceptible threshold (ΔE < 1.1).

Excessive washing resulted in lower flexural strength, surface hardness, degree of conversion, and translucency. Among different methods to reverse these negative effects, infiltration of fresh resin was the most effective method.

Excessive washing of 3D printed resin intended for long term indirect restoration in a pre-programmed washing unit resulted in a significantly weaker and more opaque material, resulting in compromised clinical performance of the material and potentially lower light penetration for curing of the resin cement. Infiltration of fresh resin was an effective method to regain mechanical and optical properties.