Adhesive Bond Strength Under Pulpal Pressure at the Gingival Wall

Clinically when teeth are restored they are restored under a slight positive pulpal pressure.  Objectives: The purpose of this in-vitro pilot study was to compare the dentin microtensile bond strength of four adhesive systems under a positive pulpal pressure of 5.0 cm of water at the gingival wall of class II posterior resin-composites. Methods: After IRB approval, extracted human 3^rd molar teeth were stored in phosphate buffered solution with 0.002 % sodium azide and randomly distributed into four treatment groups: PQ1 (total-etch, two-step, ethanol-based, Ultradent^TM), ClearfilSE (self-etch, two-step, water-based, Kuraray Medical^TM), Adper^TMPrompt-L-Pop^TM (self-etch, one-step, water-based, 3M^TM ESPE^TM) and Adper^TMSingleBondPlus (total-etch, two-step, ethanol-based, 3M^TM ESPE^TM).  Each tooth, from a pair of teeth from the same patient, received two class II box only preparations and was restored with one of the four adhesives above.  3M^TM ESPE^TM Flitek^TM Z250 Universal Restorative was then applied and cured with a quartz halogen light in five 1.0 mm increments.  Manufacturer's directions were followed.  24 hours later the teeth were sectioned to obtain rectangular specimens from the gingival wall with a surface area of ~0.5 mm². Samples were tested on a Bisco Microtensile-Tester until failure at a crosshead speed of 2.0 mm/min. Light Microscopy (10X) was used to characterize modes of failure as either adhesive or cohesive.

Results:

Adhesive	N	Mean (StD) in MPa	Number Debonds	Cohesive Failures
ClearfilSE	18	32.6 (14.8)	0	1
PQ1	21	45.4 (15.8)	0	2
Prompt-L-Pop	7	16.6 (8.2)	9	0
SingleBond+	13	40.1 (18.7)	7	0

A one-way ANOVA found a statistically significant difference among adhesives (p≤0.001). Post-hoc testing using the Bonferroni procedure showed significantly different means for PQ1 vs. Prompt-L-Pop and Prompt-L-Pop vs. SingleBondPlus (p< 0.05)  Conclusions: Dentin adhesive microtensile bond strength can be affected by positive pulpal pressure at the gingival wall. Supported by USPHS Grant K23-DE016324.   purkj@umkc.edu