Impact of Tooth Age and Adhesive Application Period on Dentin Microtensile Bond Strengths of Two Different Adhesive Systems: An In Vitro Comparative Study

Objectives: The current research assessed the impact of dentin age and adhesive application period on the microtensile bond strength (µTBS) of two different adhesive systems. Materials and Methods: A total of 96 human teeth were initially split into main groups (n=48) according to the age categories: young dentin (18–30 years) and aged dentin (≥55 years). Then, each main group was randomly split into two equal subgroups (n=24) based on the used adhesive system: a total-etch, 2-step system (Adper Single Bond 2) or a self-etch, 1-step system (Clearfil S³ Bond). Each subgroup was split into two divisions (n=12) based on the application time: the manufacturer’s recommended time or an extended time (double the recommended duration). Following adhesive application, a nanohybrid resin composite (Filtek Z350 XT, 3M ESPE) was placed incrementally in 2-mm layers over the bonded dentin surface via a specially-made Teflon split disc (4×4 mm). Following 24 hours of immersion in distilled water, the samples were cut into sticks and subjected to µTBS testing by the universal testing machine. Results: The results revealed that neither dentin age nor adhesive application time produced significant main effects. There was no statistically significant relationship between dentin age and application time. However, the total-etch adhesive demonstrated significantly greater µTBS values than the self-etch adhesive across all conditions. Conclusions: The performance of adhesive systems was primarily determined by the bonding strategy rather than dentin age or extended application time. The total-etch, 2-step adhesive system consistently outperformed the self-etch adhesive irrespective of substrate aging or application protocol.