Effect of various solvents on the repairability of aged CAD/CAM provisional restorative materials with flowable resin composite: an in vitro study.

Background: Increased bond strength between aged CAD/CAM (Computer-Aided Design and Computer-Aided Manufacturing) provisional restorative materials is essential for reparability. This study investigated the impact of three different solvents and airborne-particle abrasion on the shear bond strength (SBS) of aged CAD/CAM provisional restorative materials, which are milled PMMA and 3D-printed resin with flowable resin composite.

Methods: 3D-printed resin and milled PMMA (N = 160 per type) were fabricated into cylindrical shapes (5 mm in diameter, 5 mm in height), aged by 5,000 thermocycling cycles, and randomize divided at random into five groups (N = 32) based on surface modification protocols: control; non-surface modification, MEK; application with methyl ethyl ketone, THF; application with tetrahydrofuran, Alc; application with isopropyl alcohol, and APA; airborne-particle abrasion with 50-µm alumina oxide particle. The shear bond strength was tested by a universal testing machine with a notch-edged blade placed parallel to the bonded interphase and a crosshead speed of 1 mm/min until failure occurs. Failure modes analyzed under a ×40 stereomicroscopy. Scanning electron microscopy (SEM) at ×1000 magnification was used to evaluate the qualitative surface morphology (N = 2). The surface roughness was measured using a noncontact surface roughness analyzer at ×50 magnification (N = 10). A high-performance adsorption analyzer was used to determine the specific surface area (N = 10), and the data were analyzed two-way ANOVA with Bonferroni post-hoc test.

Results: SBS results (mean (95% confidence interval) in MPa) revealed that for both the 3D-printed resin and milled PMMA, the samples in the MEK (3D-printed, 23.2 (21.1-25.2); milled, 16.9 (15.3-18.5)), THF (3D-printed, 27.2 (26.0-28.5); milled,18.4 (16.8-20.0)), and APA groups (3D-printed, 27.9 (26.1-29.8); milled, 19.0 (17.2-20.7)) had significantly greater SBSs than did the samples in the Alc (3D-printed, 16.1 (14.4-17.7); milled, 12.2 (10.5-13.9)) and control groups (3D-printed, 11.7 (10.3-12.9); milled, 11.6 (10.8-12.4)). Compared with milled PMMA, 3D-printed resin presented a greater SBS across all surface modifications, except in the control group, where milled PMMA performed better. Failure mode analysis revealed total adhesive failure in the control and Alc groups, whereas APA resulted in 50% cohesive failure, mixed failure was shown more in 3D-printed resin THF and MEK groups (30%) compared to milled PMMA, THF and MEK group groups (10%). SEM analysis indicated that surface modifications produced rougher surfaces, The surface roughness (µm) was highest in the APA groups for both materials (3D-printed, 1834.2 (1803.8-1864); milled, 1052.8 (1027.0-1078.5)). The specific surface area (m/g) was highest in the THF (5.22 (5.18-5.26)), MEK (5.18 (5.11-5.25)) and APA groups (5.17 (5.07-5.26)) of milled PMMA, but in the 3D-printed resin, the THF (4.95 (4.84-5.07)) and MEK groups (4.83 (4.77-4.89)) exhibited highest specific surface area.

Conclusion: The application of APA techniques and surface modification using THF and MEK solvents can enhance the shear bond strength of aged milled PMMA and 3D-printed resin provisional restorative materials to flowable resin composites, as compared to the Alc and control groups. Additionally, the effectiveness of the surface modification of APA, THF, and MEK is indicated by dominant cohesive and mixed failure. SEM, surface roughness, and specific surface area indicated that surface morphology change in both CAD/CAM provisional restorative materials.