Time-course of the effect of potassium oxalate in the treatment of hypersensitive dentine in man

OBJECTIVE

Investigate the cause of hypersensitive dentine (HD) by recording the time course of changes in dentine sensitivity, sensory threshold to electrical stimulation (ET) and pulpal blood flow (PBF) following tubular occlusion using in vitro and clinical experiments.

DESIGN

Nineteen teeth with HD and 13 with normal dentine from 8 participants were evaluated, and the intensity of any pain produced by various stimuli was recorded at different times after oxalate treatment. The participants used a visual-analogue scale (VAS) to indicate the intensity of any pain. The ET and PBF were recorded at the same times.

RESULTS

Preliminary in vitro experiments showed that oxalate treatment had no effect on the method used to record PBF, and blocked the treated tubules immediately after application. Considering teeth with HD, a decrease in the median VAS evoked by all forms of stimulation was observed at all post-treatment times, except immediately after treatment (p < 0.05), while the treatment produced no significant effect in teeth with normal dentine. No significant changes in ET or PBF was observed in any of the groups.

CONCLUSIONS

The effect of oxalate in relieving the symptoms of HD is not only due to a reduction in the intensity of stimulation of sensory receptors sensitive to fluid flow in the dentinal tubules, but also to a reduce in the sensitivity of the receptors that respond to dentine stimulation. There was no evidence that acute pulpitis or central sensitization to pain, which would be associated with changes in PBF or ET, contributes to HD.

Odontoblast TRPC5 channels signal cold pain in teeth

Teeth are composed of many tissues, covered by an inflexible and obdurate enamel. Unlike most other tissues, teeth become extremely cold sensitive when inflamed. The mechanisms of this cold sensation are not understood. Here, we clarify the molecular and cellular components of the dental cold sensing system and show that sensory transduction of cold stimuli in teeth requires odontoblasts. TRPC5 is a cold sensor in healthy teeth and, with TRPA1, is sufficient for cold sensing. The odontoblast appears as the direct site of TRPC5 cold transduction and provides a mechanism for prolonged cold sensing via TRPC5's relative sensitivity to intracellular calcium and lack of desensitization. Our data provide concrete functional evidence that equipping odontoblasts with the cold-sensor TRPC5 expands traditional odontoblast functions and renders it a previously unknown integral cellular component of the dental cold sensing system.

The iontophoresis of lignocaine with epinephrine into carious dentine for pain control during cavity preparation in human molars

OBJECTIVE

To determine the effectiveness of the iontophoretic delivery of lignocaine with epinephrine through carious dentine for pain control during cavity preparation.

DESIGN

The experiments were carried out on 56 carious molars that required class I restorations in 42 subjects (aged 15-20 years). The overhanging enamel and soft caries were removed then the sensitivity of the exposed dentine was tested with drilling, probing and air blast stimuli. The subject indicated the intensity of any pain produced by marking a visual analogue scale (VAS). The cavity was then filled with 20% w/v lidocaine with 0.1% w/v epinephrine and a 200 μA iontophoretic current applied for 2 min after which the sensitivity of the dentine was re-tested. If the dentine was not anaesthetized, the treatment and testing were repeated up to 6 times.

RESULTS

The total duration (min) of iontophoresis required to anaesthetize the dentine was: 2 in 7 teeth, 4 in 17 teeth, 6 in 14 teeth, 8 in 4 teeth, and 10 in 7 teeth. The remaining 7 teeth were not anaesthetized even after 14 min of iontophoresis.

CONCLUSIONS

The iontophoretic delivery of lignocaine with epinephrine anaesthetized dentine for cavity preparation in 49 of 56 (87.5%) of carious molars.

Dentin and pulp sense cold stimulus

Dentin hypersensitivity is a common symptom, and recent convergent evidences have reported transient receptor potential (TRP) channels in odontoblasts act as mechanical and thermal molecular sensor, which detect stimulation applied on the exposed dentin surface, to drive multiple odontoblastic cellular functions, such as sensory transduction and/or dentin formation. In the present study, we confirmed expression of TRP melastatin subfamily member-8 (TRPM8) channels in primary cultured cells derived from human dental pulp cells (HPCs) and mouse odontoblast-lineage cells (OLCs) as well as in dentin matrix protein-1 (DMP-1) and dentin sialoprotein (DSP) positive acutely isolated rat odontoblasts from dental pulp tissue slice culture by immunohistochemical analyses. In addition, we detected TRPM8 channel expression on HPCs and OLCs by RT-PCR and Western blotting analyses. These results indicated that both odontoblasts and dental pulp cells express TRPM8 channels in rat, mouse and human, and therefore we hypothesize they may contribute as cold sensor in tooth.

Functional expression of TRPM8 and TRPA1 channels in rat odontoblasts

Odontoblasts produce dentin during development, throughout life, and in response to pathological conditions by sensing stimulation of exposed dentin. The functional properties and localization patterns of transient receptor potential (TRP) melastatin subfamily member 8 (TRPM8) and ankyrin subfamily member 1 (TRPA1) channels in odontoblasts remain to be clarified. We investigated the localization and the pharmacological, biophysical, and mechano-sensitive properties of TRPM8 and TRPA1 channels in rat odontoblasts. Menthol and icilin increased the intracellular free Ca(2+) concentration ([Ca(2+)]i). Icilin-, WS3-, or WS12-induced [Ca(2+)]i increases were inhibited by capsazepine or 5-benzyloxytriptamine. The increase in [Ca(2+)]i elicited by allyl isothiocyanate (AITC) was inhibited by HC030031. WS12 and AITC exerted a desensitizing effect on [Ca(2+)]i increase. Low-temperature stimuli elicited [Ca(2+)]i increases that are sensitive to both 5-benzyloxytriptamine and HC030031. Hypotonic stimulation-induced membrane stretch increased [Ca(2+)]i; HC030031 but not 5-benzyloxytriptamine inhibited the effect. The results suggest that TRPM8 channels in rat odontoblasts play a role in detecting low-temperature stimulation of the dentin surface and that TRPA1 channels are involved in sensing membrane stretching and low-temperature stimulation. The results also indicate that odontoblasts act as mechanical and thermal receptor cells, detecting the stimulation of exposed dentin to drive multiple cellular functions, such as sensory transduction.

Expression of ecto-ATPase NTPDase2 in human dental pulp

Dental pulpal nerve fibers express ionotropic adenosine triphosphate (ATP) receptors, suggesting that ATP signaling participates in the process of dental nociception. In this study, we investigated if the principal enzymes responsible for extracellular ATP hydrolysis, namely, nucleoside triphosphate diphosphohydrolases (NTPDases), are present in human dental pulp. Immunohistochemical and immunofluorescence experiments showed that NTPDase2 was predominantly expressed in pulpal nerve bundles, Raschkow's nerve plexus, and in the odontoblast layer. NTPDase2 was expressed in pulpal Schwann cells, with processes accompanying the nerve fibers and projecting into the odontoblast layer. Odontoblasts expressed the gap junction protein, connexin43, which can form transmembrane hemichannels for ATP release. NTPDase2 was localized close to connexin43 within the odontoblast layer. These findings provide evidence for the existence of an apparatus for ATP release and degradation in human dental pulp, consistent with the involvement of ATP signaling in the process of dentin sensitivity and dental pain.