Microtensile Dentin Adhesive Bond Strength Under Different Positive Pulpal Pressures

Objectives: The purpose of this in-vitro pilot study was to compare the dentin microtensile bond strength of adhesives under different pulpal pressures.  Methods: After IRB approval, human 3^rd-molars were randomly distributed into four treatment groups: Clearfil-SE (self-etch, water-based, Kuraray Medical^TM), OneStep (total-etch, acetone-based, Bisco^TM), Peak-SE (self-etch, ethanol-based, Ultradent^TM) and PQ1 (total-etch, ethanol-based, Ultradent^TM).  Additionally each group was assigned to be restored under 0.0, 5.0 or 15.0 cm of water pressure. Teeth had their enamel removed using 60, 240 & 320-grit wet sandpaper until only dentin was visible.  After acid etching and adhesive placement 3M^TMESPE^TMFlitek^TMZ250 Universal Restorative was applied/cured with a quartz halogen light in five 1.0 mm increments.  Manufacturer's directions were followed.  24-hours later teeth were sectioned to obtain rectangular specimens with a surface area ~0.5 mm². Samples were tested on a Bisco Microtensile-Tester until failure at a crosshead speed of 2.0mm/min. Light Microscopy (10X) was used to characterize modes of failure as either adhesive or cohesive.

Results:

Adhesive	Cm water	N	Mean-(StD) in MPa	Cohesive Failures	Debonds
Clearfil-SE	0.0	13	53.7-(21.4)	3
	5.0	37	54.1-(10.6)	5
	15.0	31	57.9-(15.7)	14
OneStep	0.0	14	53.9-(18.1)		1
	5.0	43	20.6-(10.6)		11
	15.0	25	12.9-(6.6)		8
Peak-SE	0.0	17	50.8-(17.0)	3
	5.0	37	33.4-(9.9)
	15.0	29	30.5-(15.3)	1
PQ1	0.0	22	53.3-(21.1)	1
	5.0	37	35.2-(9.6)	1	3
	15.0	30	33.0-(15.1)	1

A two-way ANOVA found a statistically significant difference for adhesives and pulpal pressures (p ≤ 0.001). Post-hoc testing using the Bonferroni procedure showed ClearfilSE stronger than the other adhesives (p< 0.001) and 0.0 cm of pressure stronger than both 5.0 and 15.0 cm (p ≤ 0.001). There was no difference between 5.0 and 15.0 cm of water pressure (p≤ 0.05). Conclusion: Dentin adhesive microtensile bond strength can be affected by positive pulpal pressure. Supported by USPHS Grant K23-DE016324.   purkj@umkc.edu