The effect of mechanical and chemical surface pretreatment on the repair bond strength of resins used in additive or subtractive manufacturing of definitive prostheses.

Statement Of Problem Although minimally invasive repair of existing resin-based restorations is clinically advantageous, the effects of different surface pretreatments on additively and subtractively manufactured resins remain insufficiently studied. This lack of evidence hinders the development of a standardized and reliable protocol for the repair of such materials.Purpose This in vitro study aimed to evaluate the impact of different mechanical and chemical surface pretreatments (airborne-particle abrasion, grinding, universal adhesive application, or no treatment) on the shear bond strength (SBS) of composite resin repairs on hydrothermally aged resin-based materials, used either additively or subtractively for definitive fixed dental prostheses.Material And Methods A total of 240 resin disks (Ø10×2 mm) were fabricated using 3 additive manufacturing resins (C&B Permanent; Tera Harz TC-80DP; and Crowntec); and 1 subtractive manufacturing resin (Brillant Crios) (n=60 each). All specimens underwent hydrothermal aging through 5000 thermal cycles between 5 °C and 55 °C. Disks were randomly assigned into 3 mechanical pretreatment groups: airborne-particle abrasion with 50 µm Al₂O₃ particles, grinding with a diamond rotary instrument, or no treatment (control) (n=20 each). Each group was then randomly divided into 2 chemical surface pretreatment subgroups: application of a universal adhesive (Clearfil Universal Bond Quick) or no treatment (control) (n=10 each) and then composite resin (Clearfil Majesty ES-2 Classic) was bonded in the center of the surface-treated area. SBS was assessed using a universal testing machine at a crosshead speed of 1 mm/minute. Failure modes were analyzed under a microscope at ×12.5 magnification. Statistical analysis included a 3-way ANOVA and chi-squared test to evaluate the effects of material, mechanical pretreatment, and adhesive on SBS (α=.05).Results The application of an adhesive substantially increased the SBS (Mean difference (MD): 6.91 ±3.30 MPa; P<.001). When adhesive was used, no differences were observed between resin materials or mechanical surface pretreatments (airborne-particle abrasion or grinding) in either SBS or failure mode (chi-squared test). In contrast, in the absence of adhesive, significant differences were found between materials (P<.001) and mechanical pretreatment (P=.001) for both outcomes.Conclusions Repair bond strength depended on the application of an adhesive. When applied, the impact of resin material and mechanical pretreatment remained minimal.