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A method is described which permits the quantitation of the rate of permeation of 131I through dog dentin, both in vivo and in vitro. The results demonstrate the rapidity of the systemic appearance of substances placed on intact dentin. Comparison of the rate of permeation of 131I made in vivo and in vitro, on the same teeth, indicates the rates are very similar.
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The diffusion of fluoride (F) from sodium fluoride, sodium fluorosilicate, and sodium monoflurophosphate solutions (containing 0.1 per cent F in physiological saline) was studied using a two-chamber diffusion cell separated by enamel membrane. The diffusion coefficient, D in cm2s-1, of F was determined under steady-state conditions over 3 weeks. The D value of F for NaF was significantly higher than for Na2SiF6 and Na2PO3F (p less than 0.001; unpaired t-test). F for acidic Na2SiF6 diffused more rapidly than for Na2PO3F (p less than or equal to 0.001), presumably as HF molecule. Despite the F in the tested solutions being in different forms, i.e. simple ion in NaF or mainly complex ions as in Na2SiF6 and Na2PO3F, the diffusivity of the F in enamel for these compounds was of the same order of magnitude (D = 10(-9)cm2s-1). The findings support the concept that enamel can behave as an ion-selective membrane with certain molecular-sieve effects.
The iodide permeability (Ip) of abraded bovine enamel increased after short exposure to an acid buffer and decreased after short exposure to a mineralizing solution. Intraoral exposure gave a marked decrease in Ip after one h and a continued lesser decrease after two and three h. In vitro exposure to fresh and dialyzed saliva and various undersaturated solutions indicated that the intraoral decrease was due to mineralization rather than to pellicle formation. Analysis of the data also indicated that part of the mineral formed intraorally was more loosely bound to the enamel than that formed from an inorganic mineralizing solution. The rapid rate of the initial phase of intraoral mineralization shown in this study reveals a powerful mechanism for protecting the dentition against demineralization.
Permselectivity of teeth was studied by membrane potential measurements. The enamel was found to have a preferential affinity for calcium and hydrogen ions. Its permselectivity could be modified by anionic compounds, such as phytate and alginate; by cationic compounds, such as protamine, polyarginine, and polylysine; or by an alternating coating of the above compounds.
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The active or passive mechanisms regulating the various movements of dentinal fluid have not yet been sufficiently studied. For this reason different "in vivo" factors that may modulate the kinetics of transdentinal flow were investigated. After systemic administration of a radiotracer in rats, the kinetics were examined with a push-pull perfusion device fixed to the incisor dentin. The drugs chosen, i.e. ouabain and colchicine, were for their respective effects on microtubules and on the ATPase-dependent Na+ K+ pump, since these two factors are involved in the transport process. Anesthetized animals were prepared to allow intravenous injection of iodine 125 (0,5 to 0,7 mCi), carotid sampling, and perfusion of upper incisors. Ouabain induced a very significant decrease in transdentinal flow, which was particularly evident in younger animals (2,81 x 10(-2) % vs 0,04 x 10(-2)%, p less than 0,05). However, colchicine produced two different kinds of results : at low doses (3,5 to 5 mg/100 g) the pulsatile pattern of the curves was partially inhibited, whereas, at higher doses (6 to 7 mg/100 g), the transdentinal flow of radioactivity increased. These results suggest that a combination of active and passive transport may be involved in the various movements of this fluid.
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Aliphatic amines with chain lengths from C2 to C18 were investigated for their effect on the diffusion of [3H]-sorbitol, [14C]-glycerol, 36Cl- and 86Rb+. Before amine application, enamel was pretreated with a phytate solution. C12-C18 amines reduced the rate of diffusion to values of about 20-30 per cent of the values found before treatment. Amines with chain lengths below C12 were less effective. The presence of an unsaturated carbon-carbon bond (C18:1) seems to promote the absorbance of the amine to enamel.
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Thin sections of newborn rat incisors were examined by tracer experiments and freeze-fracture replication in order to clarify the morphology and permeability of ameloblast junctional complexes in the maturation stage. Ameloblast junctional complexes consisted of gaps and tight junctions at the proximal and distal ends. Whereas the proximal junctional complexes sealed extracellular spaces incompletely, the distal ones formed complete, belt-like barriers around the cell. Tight junctions of these junctional complexes, however, were composed of both continuous and discontinuous rows of particles with various spaces among them. Intravenously injected horseradish peroxidase (HRP) reached the enamel surface through the extracellular spaces among ameloblasts and was absorbed by ameloblasts of the ruffled borders. Pinocytosis and transcellular migration of HRP could not be demonstrated in maturing ameloblasts except in the ruffled border zone.
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