The effect of different surface treatment on shear bond strength of soft and hard liners to CAD-CAM and conventional denture base resins: in vitro comparative study

Purpose: To evaluate the impact of different surface treatments on shear bond strength (SBS) of hard and soft denture liners bonded to CAD-CAM and conventional denture base resins. Methods: A total of 300 acrylic denture base specimens were fabricated with dimensions of 10 × 10 × 3 mm, with five different denture base materials: two milled (AvaDent and IvoCad), two printed (NexDent and FormLabs), and one heat-processed acrylic resin. The specimens underwent 5,000 thermal cycles both before and after the reline procedures, and each specimen was treated using one of three surface treatment methods: sandblasting, bur roughening, or no treatment (control). The reline procedure was performed with either a soft liner or a hard liner (n = 10). Shear bond strength was tested using a universal testing machine with a crosshead speed of 1 mm/min until failure. Data were analyzed by two-way ANOVA (α = 0.05). Results: Sandblasting significantly increases the SBS of hard liners to AvaDent, IvoCad, NextDent, and conventional resins compared to both the control and bur roughening groups (p ≤ 0.0001). For FormLabs, sandblasting significantly improved SBS compared to the control group only (p ≤ 0.01). In the case of soft liners, bur roughening significantly enhanced SBS for AvaDent, IvoCad, and conventional resins, while no significant improvement was observed for NextDent and FormLabs. Conclusion: Sandblasting is recommended to enhance the shear bond strength of hard liners across various denture base resins, whereas bur roughening is more effective when using soft liners.