Date of Degree
MS (Master of Science)
Steven R. Armstrong
Objective: To determine the relationship between mineral density and microtensile bond strength of caries-affected dentin (CAD).
Methods: Sixty-three extracted human molars with carious lesions and nine extracted sound human molars are collected and flattened to expose the dentin. Caries is removed using Caries Detector (Kuraray Medical, Tokyo, Japan) leaving a firm light pink stained dentin and then bonded with RBC (Z100, shade T, 3M ESPE, Germany) using an etch-and-rinse 3-step adhesive system (Optibond FL,Kerr, Orange, CA, USA). The bonded teeth are stored overnight at 37ºC before vertically sectioned with diamond saw blades (IsoMet 1000, Buehler Ltd., Lake Bluff, IL, USA). The sticks are then trimmed into dumbbell-shaped specimens with a cross-sectional area of 0.5 mm2 and a gauge length of 1 mm. Tensile testing is 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 are calculated using a custom BMD (bone mineral density) analyzer software (Iowa City, IA, USA). Mineral density (image intensity) will be plotted against uTBS (MPa) to determine correlation between these two properties based on Spearman rank correlation test at 0.05 level of statistical significance.
Results:There was a statistically significant relationship between µTBS and image intensity (p< 0.0001). However, the correlation coefficient was weak (0.31). Significant effect of the failure mode on the image intensity and the µTBS were observed (p < 0.0001). No significant difference in the mean image intensity was found between the 2 levels (p = 0.6519) and 3 levels of dye staining (p = 0.2531). Intra- and inter-examiner reliability was near perfect (0.99; 0.98) for mineral density measurements.
Conclusion: Within the limits imposed in the experimental design, we concluded that the degree of mineralzation of CAD has an influence on its failure mode and µTBS. Positive increasing relationship was also found between CAD's failure mode and its µTBS. Additionally, no significant relationship was found between levels of dye staining and the degree of mineralization.
Copyright 2011 Savitri Vaseenon