Objective: To evaluate the bond strength of self-adhesive resin cement under three alterable conditions: (1) liquid activation time, (2) mixing time and (3) mode of curing.
Methods: Encapsulated self-adhesive resin cement (RelyX Unicem, 3M ESPE) was used in the evaluation of how liquid activation time (at 2, 3, 4 or 5s), mixing time (10 or 15s), and mode of curing (with/without photopolymerization) affect bond strength. Extracted molars were flattened to expose the dentin and divided into 16 groups according to mixing protocols and mode of curing (n=8/gp). Ceramic disks were fabricated, surface treated with hydrofluoric acid and silanized prior to being cemented onto the prepared dentin under various mixing protocols. Each prepared specimen was loaded to failure in shear mode (Instron) at a crosshead speed of 0.05 mm/min. The data was statistically analyzed using three-way ANOVA, followed by Tukey's test. A Raman spectroscopy and a scanning electron microscope were used to evaluate the microstructure of the cement.
Results: Liquid activation time, mixing time and mode of curing significantly affected shear bond strength (p<0.01). The prepared specimens with photopolymerization had significantly higher bond strengths than those without (p<0.01). The highest bond strength was obtained at 5s liquid activation time, 15s mixing time and with photopolymerization. The specimen tested at 2s liquid activation time, 10s mixing time and without photopolymerized showed the lowest bond strength. At a 10s mixing time, Raman spectra revealed the greatest difference in excitation energy and wavelength intensity between the specimens with and without photopolymerization. Cement mixed at 2s liquid-activation time and 10s mixing time was shown by SEM micrographs to develop the most internal porosities.
Conclusion: Mixing protocols and mode of curing affect self-adhesive resin cement's bond strength to dentin. When photopolymerization is restricted, bond strength improves with increases in both liquid-activation time and mixing time.
| With Photopolymerized | Without Photopolymerized | |
Mixing at 10 seconds
| |||
Liquid activation time
| 2 seconds
| 8.96 (1.59) | 5.29 (1.66) |
3 seconds
| 9.74 (2.48) | 5.74 (2.23) | |
4 seconds
| 11.25 (2.17) | 5.63 (1.96) | |
5 seconds
| 11.88 (1.64) | 6.04 (1.58) | |
Mixing at 15 seconds
| |||
Liquid activation time
| 2 seconds
| 10.82 (1.72) | 6.26 (2.07) |
3 seconds
| 11.31 (1.24) | 6.44 (2.20) | |
4 seconds
| 13.91 (3.41) | 7.88 (1.46) | |
5 seconds
| 14.74 (2.89) | 9.71 (1.56) | |