Characterization of sound human dentin particles of sub-millimeter size

Objectives: To obtain small dentin particles to provide material for the characterization of dentin. To study the interaction of etchants with dentin not covered by a smear layer and bonding agents. Methods: Sound human dentin particles of sub-millimeter sizes were obtained by room temperature high-pressure fragmentation. Smear-layer free particles of three different average sizes were obtained by sieving. Surface areas were measured by the BET method. Simultaneous thermogravimetric and differential thermal analysis was carried out on all specimens and etched samples. Densities were measured by helium pycnometry. Results: On average, the water, organic and mineral contents show the expected proportions. The more dense particles tend to be in the smaller sized fractions. Thus dentin particles of average size 100 μm have a density of 2.482(0.002) g/ml which is statistically different from the 300 μm average sized particles with 2.306(0.002) g/ml. However, the respective measured specific surface areas of 2.54(0.01) and 2.50(0.02) m2/g are not found to be statistically different. The specific surface areas of dentin particles increase upon etching, the increase being related to acid strength. Thermal analysis of acid-etched 200 μm diameter particles shows up to 75% loss of carbonate and only 30% loss of phosphate. Significance: Smear-layer free dentin particles which have not been exposed to heat by grinding can be obtained by room temperature high-pressure fragmentation. Such sub-millimeter sized dentin particles can be acid-etched to significantly increase their specific surface area. Thermogravimetry used to analyze carbonate and phosphate contents gives new insight to the buffering action of human dentin.