In Vitro Shear Bond Strength of Additively Manufactured Denture Base Resins to Hard Chairside Reline Materials

Abstract

Introduction and aims: Reliable bonding between additively manufactured denture base resins and hard chairside reline materials is essential for long-term clinical performance, yet evidence under simulated aging conditions remains limited. This in vitro study evaluated the shear bond strength (SBS) of two hard chairside reline materials to conventional polymethyl methacrylate (PMMA) and two additively manufactured denture base resins under thermocycling conditions simulating relining at denture delivery and after clinical service. Methods: One heat-polymerized PMMA resin and two additively manufactured denture base resins composed of urethane dimethacrylate (UDMA) and methacrylate ester monomer (MA) were bonded to Tokuyama Rebase II (R) or Ufi Gel Hard (U), forming six material combinations. Specimens were assigned to three conditions: non-thermocycling (NT), thermocycling before relining (TB), or thermocycling after relining (TA). Ten specimens were prepared per subgroup (n = 180). Specimens that exhibited complete debonding during thermocycling were assigned an SBS value of 0 MPa and included in the analysis. SBS was measured using a universal testing machine, and failure modes were classified. Data were analysed using appropriate statistical tests (alpha = 0.05). Results: SBS was significantly influenced by denture base resin type, reline material, and thermocycling condition (P < .05). U demonstrated higher SBS than R across all denture base resins. Under NT conditions, the MA-U group showed the highest SBS (6.78 +/- 1.57 MPa), and the UDMA-R group showed the lowest (1.41 +/- 0.49 MPa). After thermocycling, 80% of UDMA-R and 20% of MA-R specimens debonded, whereas no failures occurred in the U groups. R predominantly exhibited adhesive failures, while U mainly showed cohesive or mixed failures. Conclusion: Within the limitations of this in vitro study, bonding performance between denture base resins and hard chairside reline materials was influenced by material compatibility and thermal aging. U demonstrated greater resistance to thermally induced debonding than R.