The liquid movement in desiccated and rehydrated dentine in vitro

Assessment of pain in cervical dentinal sensitivity studies. A review

Traditionally cervical dentinal sensitivity (CDS) has been evaluated mainly subjectively on the basis of the individual patient's subjective response, e.g., in the form of verbal rating and visual analogue scales and questionnaires. The stimuli used for evaluating this response can be grouped into 4 main categories: mechanical, chemical, electrical and thermal. This review of the literature, however, indicates that there are problems in evaluating patient subjective response to these various test stimuli used in the assessment and treatment of CDS. Opinions also vary as to the reliability of some of these methods of assessment, although recently, efforts have been made to develop controlled reproducible stimuli more suited to the evaluation of CDS. Currently no single method of eliciting and assessing CDS may be considered ideal. Further research is required to evaluate suitable methodology for the quantification of realistic test stimuli under controlled clinical conditions, whereby the subjective response may be objectively measured by the investigator.

Evaporative water loss from human dentine in vitro

The rate of spontaneous evaporation of water from dentine was measured in extracted human teeth in vitro. Spontaneous water loss was the same with or without a smear layer. When air was blown on the dentine, the rate of evaporation increased significantly. After removal of the smear layer, the air blast-induced evaporative loss was twice as great as before its removal. Thus, with a smear layer present, evaporation is the major route by which fluid is lost from dentine rather than by filtration of dentinal fluid. After smear layer removal, fluid filtration sometimes may exceed the spontaneous rate of fluid evaporation.

Effects of air-drying in vitro on human dentine permeability

The effects of evaporation produced by air blasts of 0, 0.5, 2 or 5 min to dentine in vitro were evaluated by measuring dentine hydraulic conductance before and after each trial. When the tubules were filled with water, even prolonged evaporation had no effect on dentine permeability. Tubules filled with physiological salt solution produced a time-dependent decrease in dentine permeability. Tubules filled with 1.5 per cent albumin in water gave the largest reductions in dentine permeability. These effects were more marked in unetched as opposed to acid-etched dentine. The results suggest that part of the reduction in dentine sensitivity produced clinically by prolonged air blasts may be due to precipitation of organic and inorganic constituents of dentinal fluid at the surface.

Responses of intradental nerve fibres to stimulation of dentine and pulp

In the present work responses of intradental nerve fibres to stimuli that induce fluid flow in dentinal tubules as well as to direct mechanical irritation of the exposed pulp were studied on 9 young adult beagle dogs. Under pentobarbitone anesthesia 31 single functional intradental fibre units were dissected from the mandibular nerve. Stimuli were applied to the lower left canine tooth. Exposed dentine surface was irritated by scraping, air blasts and dry absorbent paper and the pulp mechanically with a von Frey hair. Ten fibre units responded to stimulation of dentine. Six of them were also tested with mechanical irritation of the pulp and were all responsive. Fifteen of twenty fibres responded to mechanical stimulation of the pulp. The mechanosensitive nerve fibres were all A-type according to conduction velocities (mean 25.6 +/- 8.1 (SD) m/s). It is concluded that there exist mechanosensitive intradental A-nerve fibres in the dog which are activated by stimuli that induce fluid flow in dentinal tubules. Nerve fibres of this type could be responsible for dentine sensitivity in man. Consequently, the present study gives support to the hydrodynamic hypothesis of dentine sensitivity. Moreover, mechanosensitive nerve fibres could also be responsible for the pain symptoms of pulpal inflammation, because pulpitis may also create suitable circumstances for their activation.

Dentin permeability: determinants of hydraulic conductance

A technique is described which permits measurements of the ease with which fluid permeates dentin. This value, the hydraulic conductance of dentin, increased as surface area increases and/or as dentin thickness decreases. It increased 32-fold when dentin was acid etched due to removal of surface debris occluding the tubules.