PubMed · 11225534
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J McIntyre. 2000. Dental root surface caries study.. https://pubmed.ncbi.nlm.nih.gov/11225534/
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OBJECTIVE: In order to understand the mechanism of dentin sensitivity to tactile stimuli, the purpose of this study was to evaluate possible permanent deformation of dentin produced by scratching dentin surfaces with clinically-relevant forces. METHODS: Midcoronal dentin was prepared from twenty human teeth and polished to 4000-grit and ultrasonicated. The dentin surface of each specimen was scratched under forces ranging from 30 to 100 centi-Newtons (cN). The depth of the grooves were measured with a profilometer and the overall hardness of dentin in the vicinity of the grooves was measured. Additional dentin specimens were prepared for SEM evaluation. RESULTS: Dentin hardness was constant and no statistical difference was found among the specimens. Statistically significant differences in groove width and depth were found when increasing force was applied to the dental explorer tip. The depth of the groove ranged from 0.21+/-0.09 microm for the 30 cN group to 1.27+/-0.39 microm for the 100 cN group. The width of the groove ranged from 19.3+/-4.0 microm for the 30 cN group to 43.0 microm for the 10 0 cN group. CONCLUSIONS: (1). The threshold force necessary to create scratches in dentin with a dental explorer was 30 cN or a compressive stress of 1003 MPa. As this exceeds the crushing strength of dentin, this force produces plastic deformation of dentin; (2). Theoretical calculations indicated that even the highest scratching forces (100 cN) could not induce sufficient fluid flow to activate pulpal mechanoreceptors, although it could induce sufficient elastic deformation to theoretically shift dentinal fluid at a rate sufficient to activate mechanoreceptors; (3). The results of this work may lend support the hydrodynamic theory in that scratching of dentin surfaces causes both elastic and plastic deformation of dentin that may displace dentinal fluid toward the pulp where it could activate mechanoreceptors.
OBJECTIVE: The purpose of this study was to investigate the changes of hardness and elastic modulus of human dentin after Nd:YAG laser irradiation. BACKGROUND DATA: The application of Nd:YAG laser in dental hard tissues has been widely studied. However, little information is available about the mechanical properties of teeth after Nd:YAG laser irradiation. METHODS: The human dentin was irradiated by Nd:YAG laser through a 400-microm optic bare fiber. The parameters in laser delivery were 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec. Both the hardness and elastic modulus were obtained using an Instron microhardness tester and Vickers indenter. The indentations were then examined under a scanning electron microscope. RESULTS: The hardness and elastic modulus of irradiated human dentin in the energy of 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec were 44.7 kg/mm(2) and 22.8 GPa, and 46.9 kg/mm(2) and 21.4 GPa, respectively. These values were significantly lower than that of non-irradiated dentin by the Student's t test. CONCLUSION: Our study demonstrated that Nd:YAG laser irradiation would reduce the hardness and elastic modulus of human dentin.
The purpose of the present study was to evaluate the bond strength of four adhesive systems to dentin. Twelve human third molars had their occlusal enamel removed in order to expose a flat dentinal surface, on which the adhesive procedures were carried out. The teeth were divided into four groups, according to the employed adhesive system and composite resin: Group 1 - Single Bond + P60 (SB); Group 2 - Bond 1 + Surefil (B1); Group 3 - Prime Bond NT + Alert (NT); and Group 4 - Prime Bond 2.1 + TPH (2.1). After 24 h in distilled water at 37 degrees C, the teeth were longitudinally sectioned in two perpendicular directions in order to obtain parallelogram-shaped specimens with a cross-sectional area of 0.8 mm2 and 10 mm of length, on the average. The test specimens were submitted to microtensile test. The data were submitted to ANOVA (alpha = 0.05), which revealed no differences between the groups, although the analysis of the specimens that presented early fracture evidenced the lower sensitivity of the SB system.