Transmitted-light plethysmography detects changes in human pulpal blood flow elicited by innocuous tooth cooling and foot heating.

OBJECTIVES: The present study aimed firstly, to investigate whether pulpal circulatory changes elicited by innocuous tooth cooling and foot heating can be monitored with transmitted-light plethysmography (TLP), which detects pulpal blood volume changes, and secondly, to assess the effect of autonomic nervous control on TLP values. DESIGN: Thirty sound permanent maxillary incisors in 30 healthy volunteers (age: 25-35 years) were examined. The photodiode and 525-nm light-emitting diode of a prototype TLP system (J. Morita) were fixed onto the palatal and labial side, respectively, of each tooth with a custom-made acrylic cap. The subjects were stimulated for 10 min by cold (0 °C) water application to the experimental tooth or 30 min by foot heating with a footbath (43 °C). TLP and finger plethysmography were simultaneously recorded before (baseline), during and after stimulation. TLP values and autonomic nerve activity were statistically analyzed using a repeated measures one-way ANOVA followed by Tukey post-hoc test and partial correlation analysis. RESULTS: TLP values decreased significantly after both innocuous stimuli (P < 0.05), and returned to their baseline levels shortly after the removal of the stimuli. There was no significant serial correlation between the autonomic nervous activity and TLP values (P > 0.05). CONCLUSION: TLP was able to monitor the pulpal circulatory changes evoked by innocuous stimuli. Systemic autonomic nervous control mechanisms were not associated with the pulpal circulatory changes, suggesting the involvement of other mechanisms, such as somatosensory-sympathetic nervous control.

Human pulpal blood flow in different root formation stages measured with transmitted-light plethysmography.

OBJECTIVES: To determine the pulp vitality after traumatic injury, dentists often use pulp sensitivity tests, which can be ambiguous in young permanent teeth with incomplete root formation. Transmitted-light plethysmography (TLP) is a non-invasive objective method that uses a 525-nm LED to detect blood volume change in the pulp. The present study aimed (1) to investigate pulpal blood flow with TLP and optical characteristics in healthy permanent maxillary incisors in different root formation stages, and (2) to assess the influences of body growth of the children and tooth color on the TLP amplitude. DESIGN: Seventy-eight fully erupted maxillary central incisors were divided into four groups, according to the root formation stages. Group 1: root with wide-open apex, Group 2: root completed in length with open apex, Group 3: root with half-closed apex, Group 4: root with complete formation. The TLP amplitude, optical density, electric pulp testing, and cervical tooth color measurements of each group were compared using a one-way analysis of variance followed by the Bonferroni method. The correlation between the weights/heights of children and TLP amplitudes was analyzed using Pearson coefficient. RESULTS: The TLP amplitude was significantly higher in Group 3 than in the other groups. The amplitude was correlated with the weights/heights of children, but not with the tooth color. Optical density and electric sensitivity increased with tooth maturation. CONCLUSION: The amplitude of TLP and optical density may be affected by growth and development in children and indicate changes in the vascular dynamics of the pulp and hard tissue maturation during root formation stages.

Transient receptor potential melastatin (TRPM) 8 is expressed in freshly isolated native human odontoblasts.

OBJECTIVE: Cold-sensitive ion channels, such as transient receptor potential melastatin (TRPM) 8 and transient receptor potential ankyrin (TRPA) 1, may play a crucial role in the nociceptive function of odontoblasts, whereas expression of these TRP channels in human native odontoblasts remains to be elucidated. This study aimed to analyze the expression of TRPM8 and TRPA1 in freshly isolated native human odontoblasts. DESIGN: Odontoblasts were isolated from freshly extracted healthy human teeth (n=4); after removing the inner pulp tissues from the pulp chambers, odontoblasts remaining on the dentin surface were washed out with phosphate buffered saline and collected. Reverse transcription-polymerase chain reaction was employed to compare the expression levels of TRPM8, TRPA1, and dentin matrix acidic phosphoprotein 1 (DMP1) mRNAs between the isolated odontoblasts and the inner pulp tissues. The isolated cells were subjected to immunolocalization of TRPM8 and nestin. Paraformaldehyde-fixed, EDTA-demineralized frozen sections obtained from freshly extracted healthy human teeth (n=4) were also analyzed immunohistochemically using anti-nestin, TRPM8, and TRPA1 antibodies. RESULTS: Expression levels of TRPM8 and DMP1 in the isolated odontoblasts were significantly higher than those in the inner pulp tissues (p<0.05). Expression of TRPM8 and nestin was observed in the odontoblastic layer of the dental pulp tissue and isolated odontoblasts, while expression of TRPA1 was not detected. CONCLUSIONS: TRPM8, but not TRPA1, was detected in freshly isolated native human odontoblasts at the protein and mRNA levels, suggesting that odontoblasts play an important role in detecting external cold stimulation via TRPM8 in healthy condition.

Sympathetic Regulation of Tertiary Dentinogenesis via Beta-2 Adrenergic Receptor on Rat Odontoblasts.

INTRODUCTION: Beta-2 adrenergic receptor has been found within the osteoblast membrane meditating bone remodeling. Propranolol is a sympatholytic beta antagonist commonly used as long-term medication for the management of many common diseases such as hypertension. This study was performed to verify the presence of this receptor on odontoblasts in rats and, if present, to investigate its possible association with tertiary dentinogenesis. METHODS: Twenty male Sprague-Dawley rats (9 weeks old) were randomly assigned to 4 groups: CP0.8 group, cavity preparation + propranolol treatment (0.8 mg/day, n = 5); CP4 group, cavity preparation + propranolol treatment (4.0 mg/day, n = 7); CON group, cavity preparation + saline treatment (0.2 mL/day, n = 5); and NT group, no treatment (n = 3). Cavity preparation was performed on the mesial aspect of the maxillary first molars bilaterally. After 2 weeks, the tertiary dentinogenesis (CP0.8, CP4, and CON) was examined by hematoxylin-eosin staining, and the localization of beta-2 adrenergic receptor (NT) was examined by immunohistochemistry. RESULTS: The beta-2 adrenergic receptor immunoreactivity was observed in the odontoblastic layer in normal rat molar dental pulp. The tertiary dentinogenesis beneath the prepared cavity was significantly higher in the rats receiving 2-week systemic administration of propranolol than in those without the propranolol treatment. The higher-dose treatment of propranolol (P < .001) presented more effective up-regulation of tertiary dentinogenesis than the lower-dose treatment (P < .01). CONCLUSIONS: These results indicate that the sympathetic nervous system decreases tertiary dentin formation via beta-2 adrenergic receptors located on rat odontoblasts. It suggests that adrenergic beta antagonist is expected to use in the treatment of inducing tertiary dentin formation to protect dental pulp.

Determination of the functional space for fluid movement in the rat dentinal tubules using fluorescent microsphere.

OBJECTIVES: The size of the functional space available for hydrodynamic fluid movement between cellular components and the walls of dentinal tubules has not yet been investigated. We attempted to measure the space using small diameter fluorescent microspheres. METHODS: The coronal enamel of 144 rat molars was removed to expose the dentine, which was acid-etched. Fluorescent microspheres of different diameters (0.02-4.0µm) were applied to the exposed dentine for 60min before the rat jaws were cut into cryostat sections. The distribution and fluorescent intensities of the fluorescent microspheres were examined with confocal laser scanning microscope and analyzed using image analysis software. RESULTS: Microspheres with a diameter of 2.0-4.0µm were detected only on the surface of the cavities. A small number of microspheres with a diameter of 1.0µm accumulated primarily in the outer third of the dentine. Microspheres with a diameter of 0.2-0.5µm were found in the outer and middle thirds of the dentine. Microspheres with a diameter of 0.02-0.1µm accumulated in the middle and occasionally inner thirds of the dentine. Some of the microspheres measuring 0.02-0.04µm in diameter reached the dental pulp. CONCLUSIONS: The dentinal tubules in the inner third of the rat coronal dentine may have a space less than 0.1µm through which dentinal fluid can move, despite outward tapering of the dentinal tubules. Retrograde tapering may increase the pressure in the inner third of the dentine layer, and this elevated pressure may contribute to mechanical deformation of the content in the dentinal tubules.

Facilitatory effect of AC-iontophoresis of lidocaine hydrochloride on the permeability of human enamel and dentine in extracted teeth.

OBJECTIVES: The objectives of the present study were to quantitatively evaluate chemical permeability through human enamel/dentine using conductometry and to clarify if alternating current (AC) iontophoresis facilitates such permeability. MATERIALS AND METHODS: Electrical impedance of different concentrations of lidocaine hydrochloride was measured using a bipolar platinum impedance probe. A quadratic curve closely fitted to the response functions between conductance and lidocaine hydrochloride. For analysis of the passage of lidocaine hydrochloride through human enamel/dentine, eight premolars that were extracted for orthodontic treatment were sectioned at the cemento-enamel junction. The tooth crowns were held between two chambers with a double O-ring. The enamel-side chamber was filled with lidocaine hydrochloride, and the pulp-side chamber was filled with extrapure water. Two platinum plate electrodes were set at the end of each chamber to pass alternating current. A simulated interstitial pulp pressure was applied to the pulp-side chamber. The change in the concentration of lidocaine hydrochloride in the pulp-side chamber was measured every 2min using a platinum recording probe positioned at the centre of the pulp-side chamber. Passive entry without iontophoresis was used as a control. RESULTS: The level of lidocaine hydrochloride that passed through enamel/dentine against the dentinal fluid flow increased with time. Electrical conductance (G, mho) correlated closely to the concentration (x, mmol/L) of lidocaine hydrochloride (G=2.16x(2)+0.0289x+0.000376, r(2)=0.999). CONCLUSIONS: Lidocaine hydrochloride can pass through enamel/dentine. Conductometry showed that the level of lidocaine hydrochloride that passed through enamel/dentine was increased by AC iontophoresis.

Rapid penetration of lucifer yellow into vital teeth and dye coupling between odontoblasts and neighbouring pulp cells in the cat.

The location and long process of odontoblasts appear well suited to detection of external stimuli. The odontoblasts may transmit the information not individually but as a syncytium via gap junction, which functions as a mechanism for intercellular linking cells and as the route for dye coupling. The aims of the present study were to examine dye penetration through enamel and dentin, and to confirm dye coupling between odontoblasts (OBs) or between odontoblasts and other pulpal cells beneath the odontoblastic layer (PCs). Either lucifer yellow (LY) or borate buffer (control) was applied to etched enamel surface of feline canines for 30 min at atmospheric pressure. In the decalcified sections, lucifer yellow positive cells were found not only in but also beneath the odontoblastic layer (experiment 1). In the isolated pulp cells, all OBs (27/27) and some PCs (6/9) that were immunocytochemically differentiated using two monoclonal antibodies were labelled with LY (experiment 2). These results indicate the remarkably quick movement of LYE through enamel and dentin into the superficial pulp. In experiment 3, fresh OBs and PCs were isolated from feline canines to which LY had not been applied. LY was iontophoretically injected into an OB-like cell that had an oval cell body and a long monopolar process. Some PCs and OBs identified immunocytochemically were labelled with LY, with the exception of a few LY-negative cells. These findings indicate that dye coupling exists not only between OBs but also between OBs and PCs. Thus, the coupling provides evidence for a functional link via which information is transmitted between OBs and PCs.

Sensory experiences in relation to pulpal nerve activation of human teeth in different age groups.

There are no data on the correlation of intradental nerve activity and sensation from intact human teeth. We used microneurography to examine this relation and to determine whether it changes with age. Fifteen informed and healthy male volunteers were divided into three age groups: group A (18.6+/-1.82 years, mean+/-standard deviation (S.D.)), group B (38.4+/-2.70 years) and group C (64.0+/-4.06 years). Ratings of perceived pain intensity to thermal stimulation were obtained using a visual analogue scale (VAS). In addition, each subject chose one or two words from the short-form McGill Pain Questionnaire to describe perceived pain. A total of 90 single pulpal axons were studied with microneurography at the same time as the sensory experiences were recorded. Mean conduction velocities and variance estimates correlated closely with age. With advancing age, first, the percentage of teeth from which the subjects did not perceive any sensations to thermal stimulation increased, second, units responding to heat stimulus decreased, and third, latencies of sensation induced by thermal stimulation increased. In addition, a burst of afterdischarges following thermal stimulation and neural discharges evoked by thermal stimulation produced no sensation only in some of group B and C units. In contrast, no significant difference was found among three groups in VAS scores and words to describe the perceived pain to thermal stimulation. These results suggest that pulpal afferents were activated by the same mechanism(s); the hydrodynamic mechanism works immediately after thermal stimulation and is possibly followed by direct activation of some nerves, especially slow conducting fibres. In older tooth pulps, the decrease in the number of fast conducting afferents and mineral apposition of dentinal tubules impaired the nerve activation, especially by heat, as per the hydrodynamic mechanism. Spike discharges without sensation in older individuals were suggested to be due to insufficient spatial and temporal summation and may be involved with abnormal uncomfortable sensations.

The effect of pulpward pressure on the response to 50% lidocaine (lignocaine) applied to exposed dentine in cats.

The responses of intradental nerves can be blocked by 50% lidocaine applied to exposed, etched dentine. The aim here was to analyse electrophysiologically the contribution of pulpward pressure to the anaesthetic effect of lidocaine applied to exposed dentine. In 17 adult cats with intact lower canines, approximately 1mm of the coronal tip of the canine was removed and the exposed dentine acid-etched. Pulpward pressure was applied to the exposed dentine through a chamber fixed to the tip of the tooth. Cervical and coronal electrodes of silver wire and Ag/AgCl mixture were placed, the cervical 2mm from the gingival margin of the canine and the coronal into the coronal pulp chamber. The inferior alveolar nerve was surgically exposed and single pulpal nerve fibres responding to electrical stimulation of the canine were identified. The chamber was filled with 50% lidocaine solution, and 0 (atmospheric pressure), 1.3, 5.0 or 10.0 kPa pressure was applied to the chamber for 20 min. Orthodromic and antidromic action potentials were compared before and after the lidocaine application. When lidocaine was applied at 0, 1.3 or 5.0 kPa (n=5 each) for 20 min, all the orthodromic responses to cathodal electrical stimulation with the coronal electrode were blocked. Almost all orthodromic responses (12/15) remained unblocked when the cathodal electrical stimulation was applied with the cervical electrode. Applying 10.0 kPa pressure to the lidocaine solution blocked all the pulpal nerve responses (n=5) to both stimulation modes. The amplitude of the antidromic compound action potential was significantly decreased when the applied pressure was increased. These results suggest that increased pulpward pressure may effectively force anaesthetic solution more rapidly through the dentinal tubules into the pulp.