Effect of Potassium Oxalate on Dentin Adhesive Microtensile Bond Strength

A previous pilot study found when the adhesives OneStep (pH 4.6) and PQ1 (pH 1.7) were bonded to acid etched dentin under a positive pulpal pressure of 5.0 cm water that the microtensile bond strength was 20.6 (10.6) MPa and 35.2 (9.6) MPa, respectively. Objectives: The purpose of this in-vitro pilot study was to compare the microtensile bond strength of two total etch two-step adhesive systems under a positive pulpal pressure of 5.0 cm of water after the dentin was treated with potassium oxalate. Methods: After IRB approval, extracted human 3^rd molar teeth were stored in a phosphate buffered solution with 0.002 % sodium azide and randomly distributed into two treatment groups, PQ1 (ethanol-based, Ultradent^TM) and OneStep (acetone-based, Bisco^TM). Each tooth had its enamel removed using 60, 240 & 320 grit wet sandpaper until only dentin was visible. After acid etching, potassium oxalate (Bisblock^TM, Bisco) was applied to the dentin surface before application of the adhesive. 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 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
PQ1	33	16.3 (5.8)	9	0
Onestep	37	33.4 (12.7)	1	2

A t-test found a statistically significant difference (p≤0.001). Conclusion: A more acidic dentin adhesive had lower dentin microtensile bond strengths when used in the presence of potassium oxalate. Supported by USPHS Grant K23-DE016324.   purkj@umkc.edu