Mahidol Dental Journal

Bond strength of a universal adhesive with different etching strategies to irradiated dentin

2026-05-11T12:09:49+07:00

Objectives: To evaluate the effects of irradiation and etching strategies on the microtensile bond strength (μTBS) of a universal adhesive to dentin.

Materials and methods: Extracted human molars (n = 10) were divided into irradiated and non-irradiated groups. Five teeth received a single dose of 60 Gy, while the others served as controls. Mid-coronal dentin surfaces were prepared and bonded with a universal adhesive using etch-and-rinse (ER) and self-etch (SE) strategies. Resin composite build-ups were sectioned to obtain resin–dentin sticks. Three sticks per tooth were tested for μTBS at a crosshead speed of 1 mm/min. The mean value per tooth was used as the statistical unit. Data were analyzed using two-way ANOVA and Duncan test (p < 0.05). Failure modes were examined using scanning electron microscopy (SEM).

Results: Two-way ANOVA showed no significant effect of irradiation (p = 0.529) and no significant interaction between irradiation and etching strategy (p = 0.884). A significant effect of etching strategy was found, with higher μTBS in the ER groups compared with the SE groups (p = 0.021). However, one-way ANOVA with Duncan test showed no significant differences among the four groups (p > 0.05). The control and ER groups showed slightly higher mean values. Mixed failure predominated, followed by adhesive and cohesive failure within the resin composite, whereas cohesive failure in dentin was rare.

Conclusion: The etch-and-rinse approach provided higher bond strength than the self-etch approach regardless of irradiation.

The effects of cyclic loading on flexural strength and wear resistance of injectable and conventional resin composites

2026-04-29T14:02:47+07:00

Objective: To evaluate the flexural strength and wear resistance of injectable and conventional resin composites after cyclic loading.

Materials and Methods: Three resin composites were evaluated: Filtek Z350XT (FZX), Beautifil Injectable X (BIX), and G-aenial Universal Injectable (GUI). Mini-flexural bar specimens (12 × 2 × 2 mm) were fabricated using Teflon molds and light-cured with a polywave LED unit. After 24 hours storage in a light-proof container, half of the specimens were tested directly, while the remaining half underwent cyclic loading (2.25 N, 60 Hz, 250,000 cycles) in distilled water. Flexural strength was determined using a three-point bending test with a 10-mm span at a crosshead speed of 0.5 mm/min. Wear resistance was assessed by wear volume loss measurement after cyclic loading.

Results: FZX showed the highest flexural strength under both non-cyclic and cyclic conditions (159.30 ± 5.66 MPa and 147.50 ± 9.12 MPa, respectively). The injectable composites demonstrated lower flexural strength values, with GUI showing slightly higher values than BIX. Cyclic loading reduced the flexural strength of all tested materials. For wear resistance, FZX exhibited the lowest wear volume loss (0.009±0.001 mm³), whereas BIX and GUI showed higher values (0.028 ± 0.008 mm³ and 0.033 ± 0.011 mm³, respectively), with no significant difference between the two injectable composites. The correlation analysis demonstrated a moderate negative relationship between wear volume loss and cyclic flexural strength (R²=0.487), indicating that materials with lower wear tended to exhibit higher flexural strength.

Conclusion: Cyclic loading reduced the flexural strength of all tested composites. The conventional composite, FZX, demonstrated superior flexural strength and wear resistance compared with the injectable composites. Higher cyclic flexural strength was associated with lower wear volume loss.

Effect of translucency and thickness of lithium disilicate ceramic on light transmission and composite cement polymerization

2026-05-01T23:30:56+07:00

Objective: To evaluate the effect of translucency and thickness of lithium disilicate ceramic on the light irradiance (LI) and the degree of conversion (DC) of a dual-cure and a light-cure composite cement under two LED lightcuring units (LCUs).

Materials and Methods: IPS e.max CAD discs were prepared in two translucencies (HT-A3, LT-A3) and four thicknesses (2, 3, 4, 5 mm), with no-ceramic controls. Two LED LCUs (Bluephase N G4, polywave; Elipar DeepCure-S, monowave) were used, both delivering ~1100 mW/cm² for 40 s. LI was measured with a light spectrometer (n = 2 per cell). DC of a dual-cure resin cement (Variolink Esthetic DC) and a light-cure restorative composite (Clearfil AP-X) was measured by micro-Raman spectroscopy at six time points (1 min, 5 min, 15 min, 1 h, 24 h, 1 week; n = 3 per cell). Non-parametric tests were used (α = 0.05).

Results: LI decreased with increasing ceramic thickness and lower translucency (Spearman’s ρ = −0.94 to −0.98, p ≤ 0.001) and fell below the detection limit at LT-A3 5 mm under both LCUs. DC increased over time, reaching a pooled mean of ~78% at one week; but the response depended on both cement chemistry and LCU spectrum. Variolink reached the 90% threshold in 6/8 ceramic groups under Bluephase N G4 and 5/8 under Elipar DeepCure-S, while Clearfil AP-X reached it in only 2/8 and 5/8, respectively. The worst-performing condition was Clearfil/LT-A3 5 mm (fitted plateau A = 66.27% under Elipar DeepCure-S).

Conclusion: Within the limitations of this in vitro study, lithium disilicate translucency and thickness markedly reduced LI and modulated DC in a cement- and LCU-dependent manner. Clinicians may consider a dual-cure cement combined with a polywave LCU when cementing thick or low-translucency lithium disilicate restorations.

Push-out bond strength of two universal resin cements on fiber post

2026-04-28T09:56:46+07:00

To evaluate the effect of different universal resin cements under self-adhesive mode on the push-out bond strength of cemented glass fiber posts. Ten extracted mandibular premolar teeth were randomly assigned into 2 groups based on cement types (n = 5): RelyX Universal in self-adhesive mode (RXU) and Panavia SA Luting Multi cement in self-adhesive mode (PSA). Push-out bond strength testing was performed on coronal, middle, and apical root sections. Failure mode was classified under stereomicroscope. Data were statistically analyzed using two-way ANOVA with Tukey HSD post-hoc test (α=0.05). RXU demonstrated a significantly higher pushout bond strength over PSA. RXU failed predominantly at the cement-post interface and as mixed failures, while PSA failed mainly at the cement-dentin interface. However, no statistically significant difference was observed in different root sections. RXU showed significantly better performance over PSA for the cementation of glass fiber post.