PPT Slide

CONCLUSIONS

In an intact tooth, the enamel and the tight junctions between the odontoblasts form a relatively impermeable barrier to inward diffusion. Ions probably enter dentinal fluid via odontoblasts.
When dentine is exposed by caries or fracture, inward diffusion is opposed by outward flow in dentinal tubules. Odontoblast tight junctions open to allow outward diffusion of even large molecules e.g. antibodies.
Under these conditions, vasoconstrictors in local anaesthetic solutions may cause tubular flow to reverse, which will facilitate inward diffusion.
A smear layer does not necessarily reduce inward diffusion. It will reduce outward flow but will still allow inward diffusion of small molecules.
The results of experiments on dentine permeability and dentine bonding carried out on extracted teeth could be misleading.
Drugs should penetrate exposed dentine if applied at a pressure greater than that of the pulpal tissue fluid.