Fracture Resistance of Thermal-Mechanical Aged Resin Composite-Restored Premolars: Effect of Different Application Protocols of a Universal Adhesive.

Abstract

Objectives: This research investigated the effect of different applications of Universal bonding on the fracture resistance (FR) of maxillary premolars restored with mesio-occluso-distal resin composite.

Materials and methods: One-hundred and eight extracted maxillary premolars were randomly assigned into nine groups (n = 12): (1) ST, sound teeth; (2) nonrestored teeth; (3) SEE, selective enamel etching; (4) E&R, etch-and-rinse; (5) SDE, selective dentin etching; (6) SEE+resin layer; (7) E&R+resin layer; (8) SDE+resin layer/precuring; (9) SDE+resin layer/co-curing. Following restoration, mechanical loading (100,000 cycles, 50 N), 6-month water storage, and thermocycling (1000 cycles), FR was tested. Failure mode was evaluated. Data were analyzed using one-way ANOVA and Tukey test (α = 0.05).

Results: SDE+resin layer/precuring showed the highest mean fracture load (1222.0 ± 58.7 N), with a significant difference with all groups (p < 0.001), except SDE+resin layer/co-curing (1166.5 ± 50.3 N). FR of SEE with the lowest value (894.50 ± 70.41 N) was lower than SDE (p < 0.001) but comparable with E&R. Resin layer significantly improved FR in all etching conditions, except the E&R group (p = 0.272). The highest number of restorable fractures was in two SDE with resin layer groups.

Conclusion: Adhesive application protocols affected FR. Combining short-time dentin etching with a HEMA-free hydrophobic resin may be suggested to increase the stable reinforcement potential of universal adhesive-resin composite restorations in premolars and preserve teeth under high loading.

Clinical relevance: The adhesive application protocol considerably affected the fracture resistance of MOD resin composite-restored premolars. A short time dentin etching using an ultra-mild universal adhesive, along with increasing hydrophobicity of the adhesive interface, may enhance the mechanical reinforcement of resin composite-restored premolars during simulated thermal-mechanical intraoral conditions. This approach also possibly prevents the risk of catastrophic failure under unexpectedly high loads.