Effect of diode laser on micro-tensile bond strength of hybrid ceramic restorations to dentin using one-step and...

This study aimed to evaluate the effect of diode laser irradiation on the micro-tensile bond strength (µTBS) of hybrid ceramic restorations bonded to dentin using one-step and two-step self-etch adhesives.

An in vitro study was conducted using 20 freshly extracted human permanent molars. Standardized Class I inlay cavity preparations were performed, and hybrid ceramic inlays were fabricated using Shofu Block HC (Shofu Inc.). Specimens were randomly divided into four experimental groups (n = 5 per group) according to the adhesive strategy and laser treatment protocol. Two adhesive systems were evaluated: Clearfil S3 Bond Universal (Kurary Noritake Dental Inc.), applied in the self-etch mode (SE1), and Clearfil SE Bond 2 (Kurary Noritake Dental Inc.), a conventional two-step self-etch adhesive (SE2). Each adhesive group was further subdivided intolaser-irradiated (SE1-L, SE2-L) and non-irradiated control (SE1-NL, SE2-NL) subgroups. Laser irradiation was applied using a 940 nm diode laser after adhesive placement and before light polymerization in the SE1-L and SE2-L groups. The inlays were bonded using a light-cure flowable composite resin under static load. Following storage and accelerated aging by immersion in 10% sodium hypochlorite for one hour, specimens were sectioned into 0.9 mm microtensile beams. Microtensile bond strength (µTBS) was measured using a universal testing machine. Failure modes were analyzed using stereomicroscopy, and representative fractured specimens from each griuo were qualitatively examined by scanning electron microscopy (SEM). Data were analyzed using the Mann-Whitney U and Fisher's exact tests (α = 0.05). Randomization and assessor blinding were implemented.

Laser irradiation significantly increased the µTBS of both one-step (SE-1) and two-step (SE-2) self-etch adhesives. For SE-1, laser-treated specimens showed a median µTBS of 13.7 MPa (mean ± SD: 16.3 ± 5.6) compared to 7.7 MPa (8.8 ± 5.6) without laser (P=.047). Similarly, SE-2 groups exhibited median µTBS values of 22 MPa (21.3 ± 3.1) with laser and 12 MPa (12.5 ± 5.4) without laser (P=.028). However, no statistically significant difference in µTBS was observed between the two adhesive types, regardless of laser application (P>.05). Failure mode analysis revealed no significant differences among groups (P=.167).

Diode laser irradiation enhanced the µTBS of both one-step and two-step self-etch adhesive strategies when bonding hybrid ceramic restorations to dentin. No statistically significant difference was observed between the two adhesive strategies following laser irradiation. Further studies are needed to evaluate the long-term durability and clinical relevance of this approach.