Denture base fracture is one of the most annoying problems for both prosthodontists and patients. Denture repair is considered to be an appropriate solution rather than fabricating a new denture. Digital denture fabrication is widely spreading nowadays. However, the repair strength of CAD-CAM milled and 3D-printed resins is lacking. This study aimed to evaluate the effect of surface treatment on the shear bond strength (SBS) of conventionally and digitally fabricated denture base resins. One l heat-polymerized (Major base20), two milled (IvoCad, AvaDent), and three 3D-printed (ASIGA, NextDent, FormLabs) denture base resins were used to fabricate 10 × 10 × 3.3 acrylic specimens (N = 180, 30/resin, n = 10). Specimens were divided into three groups according to surface treatment; no treatment (control), monomer application (MMA), or sandblasting (SB) surface treatments were performed. Repair resin was bonded to the resin surface followed by thermocycling (5000 cycles). SBS was tested using a universal testing machine where a load was applied at the resin interface (0.5 mm/min). Data were collected and analyzed using ANOVA and a post hoc Tukey test (α = 0.05). SEM was used for failure type and topography of fractured surfaces analysis. The heat-polymerized and CAD-CAM milled groups showed close SBS values without significance (p > 0.05), while the 3D-printed resin groups showed a significant decrease in SBS (p < 0.0001). SBS increased significantly with monomer application (p < 0.0001) except for the ASIGA and NextDent groups, which showed no significant difference compared to the control groups (p > 0.05). All materials with SB surface treatment showed a significant increase in SBS when compared with the controls and MMA application (p < 0.0001). Adhesive failure type was observed in the control groups, which dramatically changed to cohesive or mixed in groups with surface treatment. The SBS of 3D-printed resin was decreased when compared with the conventional and CAD-CAM milled resin. Regardless of the material type, SB and MMA applications increased the SBS of the repaired resin and SB showed high performance.

Statement of Problem. Novel polymethyl methacrylate (PMMA) containing zirconium dioxide nanoparticles (nano-ZrO₂) was suggested as a denture base material but there is a lack of information regarding denture cleanser effects. Objectives. This study aimed to evaluate denture cleanser effects on color stability, surface roughness, and hardness of PMMA denture base resin reinforced with nano-ZrO₂. Materials and Methods. A total of 420 specimens were fabricated of unreinforced and nano-ZrO₂ reinforced acrylic resin at 2.5% and 5%, resulting in 3 main groups. These groups were further subdivided (n = 10) according to immersion solution (distilled water, Corega, sodium hypochlorite, and Renew) and immersion duration. Surface roughness, hardness, and color were measured at baseline (2 days-T₀) in distilled water and then after 180 and 365 days of immersion (T₁ & T₂) in water or denture cleansing solutions. Data was collected and analyzed using two-way ANOVA followed by Bonferroni post hoc test (α = 0.05). Results. Surface roughness increased significantly after denture cleanser immersion of unmodified and nano-ZrO₂-modified PMMA materials while hardness decreased ( ). The denture cleansers significantly affected the color of both PMMA denture bases ( ). The immersion time in denture cleansers significantly affected all tested properties ( ). Within denture cleansers, NaOCl showed the highest adverse effects ( ) while Renew showed the least adverse effects. Conclusion. Denture cleansers can significantly result in color change and alter the surface roughness and hardness of denture base resin even with ZrO₂ nanoparticles addition. Therefore, they should be carefully used.