Prolonged post-washing in ethanol decreases bond strength of additively manufactured crown materials

This study aimed to investigate the effect of post-washing duration and crown thickness on the bond strength between additively manufactured crown materials and dental cement in vitro.

Rectangular-shaped specimens of two thicknesses (1.5 and 2.0 mm) were additively manufactured from permanent VarseoSmile Crown (VC) and long-term temporary NextDent (ND) materials. The specimens were post-washed (n = 160) in ethanol for 5 min, 10 min, 1 h, and 8 h then cemented with dual-cure resin cement. Twenty PMMA (TC) were milled as a control. A chevron-notch test was performed to measure the maximum load until failure (N). Interfacial bond strength (J/m²) was calculated and statistically analysed. The mode of failure was analysed by scanning electron microscopy (SEM).

There was a significant difference in the bond strength between all groups (p < 0.01). VC at 1.5mm thickness post-washed for 10 min showed the highest mean bond strength (1.77 ±0.96 J/m²) while VC at 2.0mm thickness post-washed for 8 h showed the lowest (0.22 ±0.10 J/m²). Exposure to ethanol for 8 h resulted in lower bond strength. Within the type of material, there were no differences in bond strength between the thicknesses when post-washed for the same duration.

Prolonged post-washing of AM crown materials can significantly decrease the bond strength to resin cement. There were no differences between the permanent and long-term temporary AM materials. When post-washed for 5 min, AM materials observed comparable or higher bond strength values compared to PMMA.

The output of this research serves as a guide for dental practitioners, emphasising the importance of adhering to correct post-washing procedures for optimal bond strength of additively manufactured crown materials.