PERMEABILITY CHARACTERISTICS OF DENTIN

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Dentin represents the living, sensitive, porous mineralized compartment that separates cavities prepared in teeth from the underlying dental pulp. The permeability characteristics of dentin are central to understanding dentin sensitivity and pulpal reactions to dental procedures or materials. Much of the pulpal irritation of cavity preparation is probably due to fluid shifts across dentin caused by thermal or evaporation stimuli during cutting. The proposed experiments are designed to measure the magnitude of these fluid shifts and reduce them to a common denominator, a physical force (cm H2O). Once identified, these forces will be applied to cavities to determine the critical physical force (negative hydrostatic pressure) necessary to produce odontoblast displacement in normal dog dentin and in dentin treated with a drug which disrupts odontoblast microtubules. As part of the reaction to cavity preparation may be due to neurogenic inflammation, we also plan to measure the spontaneous rate of dentinal fluid flow, pulpal pressure (PP) and pulpal blood flow (PBF) in innervated versus denervated dog teeth following normal cavity preparation to examine the influence of nerve stimulation on these variables. In another set of experiments, PP and PBF will be manipulated pharmacologically using both vasodilators and vasconstrictors, to determine how they influence fluid shifts across dentin. Finally, dentinal fluid will be physically forced across dentin (as may occur when crowns are seated) to determine what that does to PP and PBF. Some of the pulpal irritation seen following cavity preparation may be due to capillary forces acting on dry dentin. We will compare pulpal reactions to normal cavity preparations in dog teeth, to that done atraumatically in teeth were the dentin remains under saline solution that will prevent the expression of capillary forces. Other teeth will be subjected to mild thermal and chemical irritation for comparative purposes. A series of experiments will be done in vitro in an attempt to seal dentin with superior smear layers or adhesive resins to prevent fluid shifts from occurring. The best method of sealing will then be used in dog teeth in vivo to prevent fluid-induced pulpal irritation. Throughout the grant period, the data we collect will be used to develop a series of mathematical expressions of hydraulic conductance, diffusion and the interaction of outward convective fluid movement on inward diffusion in the presence or absence of smear layers. This will permit the development of computer simulations of dentin and the pulpodentin complex which should be extremely useful to many laboratories around the world. Overall, these experiments should provide much needed information regarding the effects of cavity preparation on the pulpodentin complex. The results will permit us to make a series of recommendations regarding how clinicians can protect the pulp and avoid pulpal irritation.