Comparative evaluation of the shear bond strength between surface-treated fused deposition modeling-printed...

The difference in bonding behavior between fused deposition modeling (FDM) polyetheretherketone (PEEK) and autopolymerized denture base acrylic resin (Cold-PMMA) has not yet been clarified, particularly with respect to the bonding reliability of additively manufactured PEEK when used with commonly applied clinical PMMA materials.

The purpose of this in vitro study was to evaluate the shear bond strength of FDM PEEK and Cold-PMMA with different adhesives and surface treatments.

Disk-shaped PEEK specimens (N=144) were fabricated with PEEK filaments using the FDM method and dental milling machine with PEEK disks. Three types of surface treatments were performed on the bonding surfaces of the FDM and milled PEEK: no surface treatment (NT); airborne-particle abraded (AA); and abrasive paper (AB). This was followed by 2 adhesive conditions: with adhesive and without adhesive (CAD/CAM resin adhesive; Shofu). Then, autopolymerized-PMMA (Fit Resin; Shofu) was poured and polymerized to complete preparation of the specimens. Half of the specimens (n=72) were immersed in 37 °C ultrapure water for 24 hours. The other half (n=72) underwent 5000 thermal cycles (between 5 °C and 55 °C) before testing. Specimens were distributed into 24 experimental groups according to manufacturing method, surface treatment, adhesive condition, and storage condition (n=6 per group). A shear bond strength test was performed using a universal tester. Normality was assessed using the Shapiro-Wilk test and rejected (P<.05). Therefore, a Scheirer-Ray-Hare test was used for the 2 groups based on the manufacturing method. When significant interactions were detected, the simple main effects of adhesive and surface treatment were analyzed using the Kruskal-Wallis test and Dunn test with Bonferroni correction. The Mann-Whitney U test was used to assess the thermal cycling effects (α=.05).

Interactions were found in both groups (FDM PEEK P<.001; Milled PEEK P<.001). In both manufacturing methods, shear bond strengths followed the order of AA > AB > NT, with the AA groups exhibiting the strongest results for the water-immersed and thermal-cycled groups. In FDM PEEK, AA groups exhibited significantly higher shear bond strength than NT groups under all conditions. Within the AB groups, shear bond strength was significantly higher with adhesive than without adhesive under all conditions (P<.05).

Airborne-particle abrasion was the most effective surface treatment of bonding FDM PEEK and Cold-PMMA, providing clinically relevant guidance for material selection and surface preparation. Adhesive application demonstrated partial efficacy, whereas thermal cycling caused a significant decrease under most bonding conditions.