Shear bond strength of resin to additively manufactured zirconia with different surface treatments

Background Additive manufacturing is increasingly being utilized for dental restorations, but debonding remains a common issue with zirconia restorations. In particular, there is limited research on the bonding properties between additively manufactured (AM) zirconia and resin cement. Aim This study aimed to evaluate and compare the shear bond strength (SBS) of resin to milled and AM zirconia, and to investigate the effect of different surface treatments. Material and methods Milled and AM zirconia specimens were subjected to various surface treatment methods: wet-polished group (M-W&A(W)), where milled or AM zirconia was wet-polished with no additional treatment; primer group (M-P&A(P)), where wet-polished zirconia was treated with primer; glass spray group (M-G&A(G)), where wet-polished zirconia was coated with glass; and the bare group (A(B)), consisting of unpolished AM zirconia with preserved surface texture. Shear bond strength, surface roughness, morphology, and elemental distribution were analyzed using a universal mechanical testing machine, laser scanning microscope, scanning electron microscope, and micro X-ray fluorescence spectrometer, respectively. Results The untreated groups showed the lowest SBS values (M-W=6.82 +/- 2.35 MPa, A(W)=10.86 +/- 3.79 MPa), while the highest SBS values were observed in the glass coating groups (M-G=23.06 +/- 3.86 MPa, A(G)=25.96 +/- 5.60 MPa). There was no significant difference in SBS between milled and AM zirconia with the same surface treatment. Additionally, the bare AM zirconia group exhibited slightly higher SBS than that of the wet-polished AM zirconia group. Conclusions Surface treatments significantly enhance the shear bond strength between AM zirconia and resin, achieving bond strength levels comparable to those of milled zirconia. In addition, the unique surface textures of AM zirconia, enabled by its design and manufacturing flexibility, hold potential to further enhance bond properties.