Relationship Between Caries-affected-dentin Mineral Density and Microtensile Bond Strength

Objective: Preliminary investigation of the relationship between mineral density and microtensile bond strength (uTBS) of caries-affected-dentin (CAD). Methods: Eighteen extracted human carious molars were collected and flattened to expose the dentin. Caries was removed using Caries Detector (Kuraray Medical, Tokyo, Japan) leaving a firm light pink stained dentin and then bonded with resin-based composite (Z100, shade T, 3M ESPE, Germany) using an etch-and-rinse 3-step adhesive system (Adper ScotchBond Multi-Purpose Plus, 3M ESPE, St. Paul, MN). The bonded teeth were stored overnight at 37ºC before vertically sectioning into sticks using diamond saw blades (IsoMet 1000, Buehler Ltd., Lake Bluff, IL, USA). The sticks were then trimmed into dumbbell-shaped specimens with a cross-sectional area of 0.5 mm2 and a gauge length of 1 mm. Tensile testing was performed at a crosshead speed of 1 mm/min (Zwick Materials Testing Machine Z2.5/TN1S, Zwick, Ulm, Germany). X-ray microtomography was used to examine the fractured specimens (Micro-CAT II, Siemens Preclinical Solutions, Knoxville, TN) at maximum resolution of 27 microns. The mean mineral densities at the resin-dentin interface of the bonded specimens were calculated independently by two of the authors using a custom BMD (bone mineral density) analyzer software (Iowa City, IA, USA). Mineral density (image intensity) was plotted against uTBS (MPa) to determine correlation based on Spearman rank correlation test at 0.05 level of statistical significance.

Results: No statistically significant relationship between uTBS and mineral density (p=0.4888) was observed. Intra- and inter-examiner reliability was 0.99 and 0.98, respectively, for mineral density measurements.

Conclusion: Within the limitations of this preliminary study, the uTBS of CAD has no direct relationship with mineral density. Continued studies regarding the validity of mineral density measurements of specimens with interfacial and mixed failure mode specimens is ongoing.

Acknowledgements: Funded by the Academy of Operative Dentistry's 2009 George C Paffenbarger Student Research Award.