Objective: To evaluate the effect of numbers of applications of a multi-mode adhesive in self-etch mode on micro-tensile bond strength to human dentin with and without simulated pulpal pressure.
Methods: A multi-mode adhesive system (Scotchbond Universal, 3M ESPE) was applied to flat mid coronal dentin surfaces of recently extracted third molars in self-etch mode. The bonding protocol comprised of a 20 s long application with different numbers of coats of the adhesive (1, 2, or 4) under agitation with a microbrush. Half of the samples were bonded either under simulated pulpal pressure at 15 cm H2O or under absence of pulpal pressure (0 cm H2O). Subsequently, all teeth were restored with a micro-hybrid resin composite (Filtek Z250, 3M ESPE) and stored for 24 hours in distilled water before cutting into sticks (cross sectional area 0.8±0.2 mm2). All sticks were tested for microtensile bond strength (µTBS) using a universal testing machine under tension load (1 mm/min) until failure. Statistical analysis was performed by means of a two-way ANOVA followed by Bonferroni post-hoc tests (α=0.05). Representative samples were subjected to ultramorphological evaluation under CLSM.
Results: (number of specimens/pre-testing failure) Mean±SD in MPa:
Number of coats
| Pulpal Pressure
| |
0 cm
| 15 cm
| |
1
| (42/0) 56.45±16.0aA
| (39/0) 41.95±17.5aB
|
2
| (37/0) 48.19±14.7aA
| (48/0) 48.85±23.2aA
|
4
| (40/0) 47.45±20.0aA
| (41/0) 52.44±22.4aA
|
Mean values with identical superscript lower-case letters within the same column (comparing number of coats) and identical superscript upper-case letters within the same row (comparing pulpal pressure) are not statistically different (p>0.05).
Conclusion: Pulpal pressure affected negatively bond strengths of a multi-mode adhesive when a single coat is applied. Multi-mode adhesive provide adequate bond strengths to dentin.