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To estimate permeability properties of bovine dental enamel, complex impedance measurements and radioisotope diffusion experiments were carried out before and after X-ray irradiation (single dose, 72 Gy) of enamel specimens. Neither impedance measurements nor diffusion experiments showed significant changes in permeability.
A comparison was made between the rate of iodide permeation of dentin by diffusion and by filtration. Before acid etching, filtration only doubled the rate of iodide permeation relative to that obtained by diffusion. After acid etching, filtration produced a 32-fold increase in permeation. Acid etching, by removing occluding debris, facilitates filtration more than diffusion.
Iontophoretic currents (0--1.0 mA) were applied to dentin disks prepared from human third molars. A negative electrode increased 125I-permeation 10X, while a positive electrode increased 14C-lidocaine 8X. Iontophoresis appears promising as a method to increase the permeation of dentin by ionized substances of therapeutic interest.
Two independent techniques (filtration and surface tension) were developed to measure the functional tubular radii of 11 dentin and 2 glass discs. Anatomic radii were determined using SEM for comparative purposes. The functional radii of the dentin discs ranged from 5 to 40% of the anatomic radii. This differences was due to the fact that SEM visualizes only the surface while the functional techniques measure the radii within dentin tubules. It is concluded that the functional methods are preferred whenever the dynamics of fluid flow through dentin are under consideration.
Analysis of these results shows that complete hard tissue bridges, aside from occurring with great frequency, produce a satisfactory protection to the pulp. In a case in which the barrier is incomplete, some future clinical problems may result as an incomplete barrier does not offer adequate protection as shown by the chronic inflammatory reaction in the remaining pulp tissue.
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The permeability of coronal dentine was investigated by measuring the hydraulic conductance of dentine discs. Reductions in dentine thickness from the enamel side of disc resulted in a greater increase in permeability than reductions from the pulpal side. Scanning electron microscopy revealed fewer dentinal tubules with smaller diameters in superficial dentine than in deep dentine. The permeability of coronal incisor bovine dentine is six to eight times less than that of unerupted coronal human third molar dentine but similar to that of human root dentine.
Infiltration of a porous hard tissue with methyl methacrylate, followed by dissolution of the tissue provides a three-dimensional methacrylate cast of spaces within the tissue. Examination of such a cast by scanning electron microscopy provides information on the nature and extent of the pore system to a degree that cannot readily be visualized by the direct examination of fractured surfaces. The findings described concern human dentine but the technique may have a wider application in studies on the internal structure of other hard tissues.
A simple in vitro method has been described for quantitatively measuring the rate at which isotopically labeled substances permeate through dentin in occlusal cavity preparations. The presence or absence of pulp tissue had only a minor effect on the kinetics of permeation. As the dentin was made thinner there was a resulting increase in the rate of iodide permeation. The relative rates of permeation were 3H2O greater than 131I greater than 99mTc greater than 14C-urea, a sequence that follows the molecular dimensions of these substances.
The posteruptive maturation of enamel is an important factor in caries disposition. In an experimental study the demineralization of enamel as well as its permeability and its morphological features in dependence of eruption stage were examined on extracted premolars. Chemical analysis showed variations in the Ca/P molar ratio. It is possible, that the instability of Ca-ions in crystalline configuration decreased during the time of eruption. The permeability of enamel decreased between 5 and 11.8%. It appears to be useful to concentrate preventive measure on this phase of dentition development.
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The systemic distribution of 14C-labeled formaldehyde which had been placed in the root canals of the canines of cats following pulpectomies was studied using liquid scintillation counting and wholebody autoradiographic technique. Radioactive 14C which had been placed in the canals was found in the plasma 30 min after the root canal procedure. The recovery of systemic 14C radioactivity increased with time. In addition, it seemed that approximately 3% of the dose placed in the teeth was excreted in the urine within 36 h. Whole-body autoradiograms indicated extensive concentration of 14C radioactivity in tissues other than those analyzed with the liquid scintillation technique.
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