Microtensile dentin adhesive bond strength under different positive pulpal pressures

Abstract

Purpose: To measure the in vitro dentin microtensile bond strength of established adhesives under different hydrostatic pulpal pressures.

Methods: After IRB approval, 24 human extracted third molars were randomly distributed into four adhesive treatment groups: Clearfil-SE (self-etch, water-based), One-Step Plus (total-etch, acetone-based), Peak-SE (self-etch, ethanol-based) and PQ1 (total-etch, ethanol-based, Ultradent). Additionally each group was assigned to be restored under 0.0, 5.0 or 15.0 cm of water pressure. Coronal enamel was removed using 60, 240 & 320-grit wet sandpaper until only dentin was visible. After adhesive placement Filtek Z250 Universal Restorative was applied in five 1.0 mm increments. All teeth were tested at 24 hours for microtensile bond strength and examined for mode of failure under light microscopy (x40).

Results: A two-factor ANOVA found a statistically significant effect for adhesives, water pressures and their interaction (P < or = 0.001). Post hoc pairwise comparisons of simple effects using the Ryan-Einot-Gabriel-Welsch Range procedure showed Clearfil-SE stronger than the other adhesives at 5.0 and at 15.0 cm water pressure (P < 0.07). One-Step Plus was weaker than PQ1 and Peak-SE at 5.0 and at 15.0 cm water pressure (P < 0.07). PQ1 and Peak-SE at 0.0, 5.0 and 15.0 cm were not significantly different from each other (P > 0.07). For water pressure comparisons, Clearfil-SE was stronger at 0.0 vs. 5.0 cm water pressure (P < 0.07), while there was no difference for Clearfil-SE between 5.0 and 15.0 cm water pressure (P > 0.07). One-Step Plus was significantly stronger at 0.0 cm water pressure than at 5.0 and 15.0 cm water pressure (P < 0.07), and at 5.0 cm water pressure it was stronger than at 15.0 cm pressure (P < 0.07). Both Peak-SE and PQ1 at 0.0 water pressure were significantly stronger than at 5.0 and 15.0 cm water pressure. There was no difference in strength between 5.0 and 15.0 cm water pressure for either of the two adhesives (P > 0.07).

Fig. 1

Clearfil-SE at x5000 shows fracture through the hybrid layer. The microtensile bond strength was 65.0 MPa. Water pressure was 5.0 cm.

Fig. 2

PQ1 at x5000 shows fracture through the adhesive-hybrid layer interface. The microtensile bond strength was 7.8 MPa. Water pressure was 5.0 cm. Note inability of adhesive to completely cover dentin due to water pressure from tubules.