Comparison of Bond Strength Between Universal Adhesives and Zirconia Primer on Prefabricated Pediatric Zirconia Crowns: Influence of Functional Monomers and Thermocycling

This study compared the shear bond strength of two universal adhesives (Scotchbond Universal Plus, 3M ESPE, St. Paul, MN, USA, and Optibond Universal, Kerr, Orange, CA, USA) with a zirconia primer (Z-Prime Plus, Bisco, Schaumburg, IL, USA) on specimens replicating the internal surface of prefabricated pediatric zirconia crowns, and evaluated thermocycling’s influence on bond stability. Zirconia specimens were fabricated using 3mol% yttria-tetragonal zirconia polycrystal (3Y-TZP) with surface treatment matching the inner surface of prefabricated pediatric zirconia crowns. Specimens were divided into three adhesive groups and further subdivided based on thermocycling application (n = 10). Thermocycling consisted of 5,500 cycles between 5°C and 55°C. Shear bond strength was measured using a universal testing machine, and failure modes were analyzed with scanning electron microscopy. Before thermocycling, Scotchbond Universal Plus (23.86 ± 3.99 MPa) and Z-Prime Plus (20.13 ± 3.18 MPa) showed significantly higher bond strength than Optibond Universal (7.89 ± 1.56 MPa) (p < 0.0167). This trend continued after thermocycling, though bond strength decreased significantly in all groups (p < 0.05). Adhesives containing 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) demonstrated superior bond strength and hydrolytic stability compared to glycerol phosphate dimethacrylate (GPDM)-containing adhesives. Therefore, 10-MDP containing adhesive systems may provide more predictable and durable bonds for pediatric zirconia crowns.