PubMed · 14780660
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E J HIRSCHTICK. 1950. Hypersensitive dentine.. https://doi.org/10.1016/0030-4220(50)90007-7
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A thick oxygen-inhibited layer (OIL) on a cured adhesive layer (AL) is believed to result in both good adaptation of composite resin (CR) and high bond strength. A high degree of conversion (DC) of the AL is also needed for durable bonding. This study evaluated the hypothesis that increasing the DC by prolonging the light-curing time of adhesive bonding resin might decrease the bond strength of the adhesive to dentin because of the subsequent thinning of the OIL thickness. The OIL thickness and the DC of solvent-removed One Step and D/E bonding resin of All Bond 2 (Bisco, USA) were measured simultaneously with FT-NIR spectroscopy according to increasing light-cure times (10, 20, 30, and 60 s) so as to evaluate their effect on the microtensile bond strength. The bonded interfaces were evaluated using scanning electron microscopy. Excessive irradiation of light-curing adhesives increased the DC, but decreased the OIL thickness. When the OIL was significantly thin by curing the adhesives for 30 or 60 s, defects were observed at the interface between the AL and the CR, as well as at the interface between the AL and the hybrid layer. When the OIL was thick, free radicals from the overlying CR may have diffused into the unreacted monomer mixtures of the OIL, chemically connecting the cured AL and the newly curing composite. It was found that to obtain maximum dentin bond strength, light-curing adhesives should be cured for the irradiation time recommended by the manufacturer.
There is no quantitative description available that numerically relates any acoustic parameter pattern or the local elastic behaviour to any standardized geometrical positions within human teeth. However, the speed of ultrasound at 20MHz varies in different parts of teeth. Great differences occur between the values attributed to longitudinal waves that propagate in the three mineralized human hard tissues at identical relative tooth width portions [John, C., 2004. The corono-apically varying ultrasonic velocity in human hard dental tissues. Journal of the Acoustical Society of America 116, 545-556]. The aim of this work was to investigate the distribution of the longitudinal ultrasound velocity (LUV) at distinct relative tooth width portions and at a height level of 8mm relative to the coronal reference. Individual tooth widths w were accounted for, and a standardized, dimensionless radial distances variable X=|x/w-0.5| was utilized to express the radial position of measurements in a unified way. The observed lateral increase in LUV of 21 specimens along X was approximated. A Padé shape function predicts the lower contour of the envelope curve of all the individual LUV distributions. Individual residuals and coefficients are provided for LUV=a+b.ln(X).X.X, where a and b represent individual intercepts and slope factors (e.g. a=3206 m/s and b=-4184 m/s), respectively.
Dentine is a porous hydrated composite structure that forms the major bulk of the human tooth. The aim of this study was to investigate the role of free water on the in-plane, mechanical strain response in dentine structure. A digital moire interferometry was used for this purpose. It was observed from this experiment that structural dentine demonstrated distinct strain gradients in the axial (perpendicular to the dentinal tubules) and lateral (parallel to the dentinal tubules) directions. The hydrated dentine displayed significant increase in strain with stress in the direction perpendicular to the dentinal tubules, and this response was characteristic of a tough material. On the contrary, the dehydrated dentine, which was dehydrated at 24 degrees C, 55% relative humidity for 72 h showed a strain response characteristic of a brittle material. The strains formed in the direction parallel to the dentinal tubules for hydrated dentine were consistent and did not vary much with increase in applied loads. Upon dehydration, the outer dentine experienced higher strains, and the difference between the outer and inner dentine became more conspicuous with increase in loads. This experiment highlights hydration-induced, distinct in-plane strain gradients in the directions perpendicular and parallel to the dentinal tubules in the dentine structure.