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 aware of lower TBS value and possible cohesive failures, and the detachment of the reliner from the denture base.