The density and branching of dentinal tubules in human teeth.

Detailed knowledge of dentine structure, and especially that of the dentinal tubules, is essential in order to understand dentine permeability and to interpret data from investigations on dentine adhesive materials. The aim here was to examine the density and branching of dentinal tubules in human teeth by light and scanning electron microscopy. Stained and unstained demineralized sections and undemineralized fractured specimens were studied. Statistically significant differences in the density of tubules were found depending on location. Differences in density of tubules between the peripheral and inner aspects were more marked in the crown than in root. The mean number of dentinal tubules in the middle part of the root was significantly lower than in the middle part of the crown. The density of the tubules in the outer dentine at the cusp location was also significantly different from that subjacent to the occlusal fissure. The number of branches of dentinal tubules was particularly abundant in locations where the density of tubules was low. The branching patterns revealed an intricate and profuse canalicular, anastomosing system, criss-crossing the intertubular dentine. Three types of branches, major, fine and microbranches, were identified on the basis of size, direction and location. Major branches, 0.5-1.0 micron dia., were the typical delta branchings found peripherally. Fine branches, 300-700 nm dia., forked off at 45 degrees and were abundant in areas such as in the root where the density of the tubules was relatively low. Microbranches, 25-200 nm dia., extended at right angles from the tubules in all parts of the dentine. The findings emphasize the need for detailed characterization of dentine substrates for adhesive testing and of samples used in permeability studies.

Dimensional change following setting of root canal sealer materials.

OBJECTIVE: The study was designed to evaluate a method proposed for measuring dimensional changes of endodontic sealers, and to assess the dimensional changes of 11 commercial sealers after prolonged storage in water. METHODS: The method for linear dimensional change described in the draft standard for endodontic sealers was applied to 11 different types of endodontic sealers. One material (Sealapex) could not be tested by the method. The other 10 materials were followed for dimensional change over 48 weeks. RESULTS: The sealers showed markedly different dimensional properties. For most materials, the greatest dimensional changes took place within the first 4 weeks. Zinc-oxide-eugenol based sealers generally showed shrinkage ranging from 0.3 to 1%, while one product (Proco-Sol) exhibited expansion exceeding 6% after prolonged storage. The epoxy-based materials, AH 26 and AH 26 silverfree, exhibited a large, initial expansion of 4-5%. AH Plus expanded from 0.4% after 4 weeks up to 0.9%. Apexit, a Ca(OH)2-based material, showed only minor variation round baseline value, -0.14 to +0.19%. Roeko-Seal expanded to 0.2% within 4 weeks, but was stable thereafter. SIGNIFICANCE: The test methodology adequately assessed dimensional changes exceeding +/-0.2%, but some brands of material either could not be made into adequate test specimens or showed surface changes which interfered with dimensional change measurements. Theoretical approaches to the consequences of expansion by materials of low bulk strength question the necessity of a strict requirement against expansion, whereas bacterial penetration may be a real threat from sealers shrinking as little as 1%.

Glass ionomer cements and dental pulp.

Only slight pulp reactions to glass ionomer cements occurred when inserted in Class V cavities of dog teeth. Most inflammatory reactions were due to bacteria at the tooth/filling interface. Special dentin reactions were noted in almost half the teeth, including hematoxyphilic bands in the dentin and a disturbance of the mineralization pattern of predentin. The clinical significance of these dentin reactions is not known.