Tensile bond strength of auto‐polymerizing and heat‐polymerizing denture reliners on the conventional and CAD–CAM denture base materials

Purpose The study aimed to compare the tensile bond strength (TBS) of auto‐polymerizing and heat‐polymerizing denture reliners on the conventional (compression‐molding and injection‐molding) and computer‐aided design and computer‐aided manufacturing (milled and 3D‐printed) denture base materials. Materials and methods Eighty standard dogbone‐shaped specimens were fabricated from four materials: compression‐molding, injection‐molding, milled, and 3D‐printed denture base materials. A 3‐mm cutoff was removed from each specimen at the midsection, and all specimens were reattached with either auto‐polymerizing (n = 10) or heat‐polymerizing (n = 10) reliner. The TBS was measured on the universal testing machine. A scanning electron microscope (SEM) was used to examine the fractured surfaces at cross sections to determine the dominant failure mode in each group. Two‐way ANOVA was used to examine the effects of denture base material and reliner on the TBS (α = 0.05). Weibull survival analysis was also used to determine the survival probability curves. Results Heat‐polymerizing reliner led to a higher TBS than the auto‐polymerizing reliner, except in the compression‐molding (p = 0.573) groups. Compression‐molding denture base material connected with a heat‐polymerizing reliner showed the highest TBS (29.8 ± 6.9 MPa), whereas 3D‐printed denture base material connected with an auto‐polymerizing reliner showed the lowest TBS (7.2 ± 0.9 MPa). The survival probability based on the Weibull model demonstrated that the compression‐molding denture base material connected with either auto‐polymerizing or heat‐polymerizing reliners had the longest survival time to failure, whereas 3D‐printed denture base material relined with auto‐polymerizing reline material showed the shortest survival time to failure. Under the SEM, the compression‐molding groups demonstrated that the failure modes were mixed but predominantly cohesive. The injection‐molding and milled groups showed predominantly adhesive failures at the denture base‐reline material interfaces. The dominant mode of failure in the 3D‐printed groups was cohesive failures within the bonding adhesive. Conclusions Although the heat‐polymerizing reliner led to a higher TBS than the auto‐polymerizing reliner in most denture base materials, the compression‐molding denture base material can achieve high TBS with both reliners. When the auto‐polymerizing reliner is used with 3D‐printed denture base material, clinicians should be awa