structure of nerves in the dentinal-pulp border zone after sensory and autonomic nerve transection in the cat. Acta Odont. Scand. 31, 273-281, 1973. In order to investigate the origin of intradentinal nerve-like structures, unilateral transection of the sensory (inferior alveolar nerve) and/or the autonomic (cranial cervical sympathetic ganglion) supply was performed in 6 cats. After 2 -4 weeks, when degenerative change was expected in the cut nerves, electrophysiological recordings from the dentin showed total absence of impulse activity in teeth subjected to sensory denervation regardless of whether or not the autonomic innervation was intact. Control teeth, on the other hand, responded to different local pain stimuli. Electron microscopic study of predentin and inner dentin in control teeth showed intratubular nerve-like structures similar to ,associate cells)) earlier described in human teeth. In teeth subjected to sensory nerve resection, however, the intradentinal ))associate cells)) showed advanced degenerative change or were absent. Resection of the sympathetic nerve supply did not influence the appearance of these intratubular structures. The present results indicate that intratubular nerves are present in predentin and the inner dentin in the cat and that these nerves are of sensory origin. It is further suggested that the intradentinal nassociate cells)) earlier described in human teeth are sensory neurons.

It has been known for a long time that the organic matrix of the enamel could be histologically studied only if the preservation through a sufficiently long fixation could be established.' The penetration of the fixative is likely to be mediated by the more-or-less hydrated organic stroma, which, it is suggested, exists in a non-fibrous form,2 possibly a gel.3 An increasing number of publications report that the water phase in enamel seems to occupy a larger part than had previously been supposed.4 A diffusion of liquid through the enamel was microscopically demonstrated by Bergman.5'6It was thought that there might be a difference in the permeability between freshly obtained untreated and intentionally coagulated dental hard tissues and that sodium ions (Na22) would be a suitable test substance. Materials and MethodsThe material of this study comprises sixteen pairs of intact, homologous premolars, from boys and girls eleven to thirteen years old, which were removed for orthodontic indications. Four of these pairs were used for the first part of the experiment, which was performed as follows.Immediately after the extraction, the teeth were placed in Ringer's solution. One tooth in each pair was boiled for 5 minutes in this solution in order to coagulate the organic substances. The apical part of the root was cut with a diamond disk at a level 2-3 mm. from the enamel-cementum border.The remaining part of the root was covered with Tenax wax, which formed a funnel to the root pulp (Fig. 1). These preparations of the teeth were made immediately after the extractions with great care, so that the crown was never allowed to dry. The crown was submerged in a vessel containing Ringer's solution of known volume. With a fineglass pipette, a certain amount of Na22-labeled saturated NaCl solution (specific activity, 1 mc/ml) was injected into the pulp cavity of the tooth. At various time intervals, samples of the surrounding Ringer's solution were analyzed for activity in welltype and solid-crystal detectors operating with a single-channel analyzer.For the second part of the experiment, four pairs of intact homologous premolars were used. In an attempt to limit the effect to the enamel, the crown of one tooth in each pair was submerged down to the enamel-cementum border in the boiling Ringer's solution for 2 minutes. The rest of the tooth was protected by a shield of aluminum foil. The control tooth was left untreated. As in the first part of the experiment, the roots were cut off and Na22 injected into the pulp chamber. The activities in the surrounding Ringer's solution were measured as before.In order to check some variables, the following test experiments were made:1. The concentration of the Na22Cl solution was lowered to 0.5 per cent.2. The boiling time was varied from 1 to 10 minutes.3. Identical experiments were performed in which the amount of injected Na22 was varied.4. To elucidate the effect of boiling on the size of the hydroxyapatite crystals, two glass capillary tubes inner diameter 2 mm. 1299 permission. at U...

Chlorhexidine solutions have been tested to determine their usefulness as media for the transport of biopsy specimens for diagnosis in order to facilitate the use of cold microtome sectioning and enzyme histochemical techniques in routine histopathological diagnostic practice. The drug was chosen for its antibacterial and protein "preserving" capacities. Tissue morphology, chemical components and enzyme activities were found to be retained well in specimens from human gingiva when stored in a cold solution, pH 7.2, containing 2.2 mM chlorhexidine gluconate, 0.19 M cacodylate buffer and 7.5 % polyvinylpyrrolidone. The procedure allowed reliable enzyme activity evaluations to be performed under the light microscope within 48 hours after excision of the tissues. Fresh frozen tissues served as controls. In an additional electron microscopic study, morphology of the cells was found to be reasonably well preserved after transport in the solution.

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