ThisstudyinvestigatedthehardnessandYoung'smodulusofcoronalandradicularintertubulardentin.Tenbovineteeth were each divided into coronal and radicular groups, and the flat surfaces of the coronal and radicular dentin were subsequentlyprocessedalongthetoothaxis.ThehardnessandYoung'smodulusofthecoronalandradicularintertubular dentinwereevaluatedusingnanoindentationtests,attwolocationspertooth.MeanhardnessandYoung'smodulusvalues werestatisticallycomparedbyone-wayANOVAandFisher'sPLSDtest.Thehardnessofcoronalintertubulardentinwas 0.81±0.05GPaandthatofradiculardentinwas0.55±0.02GPa.Additionally,theYoung'smodulusofcoronalintertubular dentin was 26.60±2.19 GPa and that of radicular dentin was 20.89±1.10 GPa. Findings of this study revealed that the hardnessandYoung'smodulusofcoronalintertubulardentinweregreaterthanthoseofradicularintertubulardentin.
Surprisingly little is known about how the structure and composition of tooth dentin varies between different areas of the tooth. This study was to investigate and compare the mineral density of coronal and radicular dentin using ten bovine incisor teeth. The mineral density of coronal and radicular dentin was quantifi ed at two locations per tooth using micro-computed tomography (micro-CT). The coronal area was 15.0 mm coronal to the cemento-enamel junction on the buccal side of the tooth, while the radicular area was 5.0 mm apical to the cemento-enamel junction, also on the buccal side. Mean mineral density value was compared statistically by the paired Student's t-test. The mineral density of coronal dentin was 1,628.8±34.0 mg/cm 3 , and that of radicular dentin was 1,406.1±38.7 mg/cm 3 , suggesting that the dentin mineral density is higher in the crown than in the root. Micro-CT intensity data is a useful method for quantitating dentin mineral density.
This study investigated the effects of thermal cycling on the tensile strength of dentin. Bovine dentin were divided into 10 groups, which were then subjected to various conditions: intact after preparation, thereby serving as a control; heating in boiling water for 45 minutes; 10,000 thermal cycles in water; 10,000 thermal cycles in PBS; storage in water at 5, 23, or 55℃ for two weeks; and storage in PBS at 5, 23, or 55℃ for two weeks. Subsequently, bovine dentin were trimmed into dumbbell-shaped specimens and the tensile test performed in distilled water at 37℃. Mean tensile strengths were compared statistically by one-way ANOVA and Fisher's PLTD test (p<0.05). Fracture surfaces were observed by scanning electron microscopy, and reliability of the results was analyzed with Weibull distribution. Tensile strength did not significantly change after thermal cycling or storage in water and PBS at all temperatures tested (71.2-77.0 MPa) but decreased after treatment with boiling water (65.5 MPa).
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