Pain and the rate of dentinal fluid flow produced by hydrostatic pressure stimulation of exposed dentine in man

The effect of 2% chlorhexidine iontophoresis on dentin sealing ability of etch-and-rinse adhesive: An in vitro study

Background/purpose

Iontophoresis could enhance the delivery of chlorhexidine into oral tissue. This study aimed to determine the effect of 2% chlorhexidine iontophoresis (CHI) on the sealing ability of etch-and-rinse adhesive in human dentin using hydraulic conductance (HD) measurement, scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM-EDS).

Materials and methods

Thirty-nine sound dentin specimens were prepared from 39 extracted intact third molars. Thirty specimens were used for HD measurement and randomly divided into 3 equal-sized groups; (1) No chlorhexidine treatment (control), (2) passive chlorhexidine treatment (CHT) and (3) CHI on acid-etched dentin. Each dentin surface was treated with etch-and-rinse adhesive. HD of each specimen was measured before treatment, after immediate bonding and after 14 days. The other 9 specimens were subjected to SEM-EDS analysis of the acid-etched dentin and the dentin treated with CHT and CHI. ANOVA test and Student-Newman-Keuls method were used for statistical analysis.

Results

After bonding, there was no significant difference in percentage decrease of HD among the treatment groups (P > 0.05). After 14 days, CHI and CHT groups had greater percentage decrease of HD than the control (P < 0.001 and P = 0.009, respectively). Under SEM-EDS analysis, acid-etched dentin with CHI presented opened dentinal tubule orifices and more chlorhexidine precipitates on dentin than the dentin with CHT, which strongly related to a higher percentage of chloride ions on the CHI dentin surface (P < 0.001).

Conclusion

The use of CHI on acid-etched dentin had a positive effect on dentin sealing ability of etch-and-rinse adhesive.

The anatomy, neurophysiology, and cellular mechanisms of intradental sensation

Somatosensory innervation of the oral cavity enables the detection of a range of environmental stimuli including minute and noxious mechanical forces. The trigeminal sensory neurons underlie sensation originating from the tooth. Prior work has provided important physiological and molecular characterization of dental pulp sensory innervation. Clinical dental experiences have informed our conception of the consequence of activating these neurons. However, the biological role of sensory innervation within the tooth is yet to be defined. Recent transcriptomic data, combined with mouse genetic tools, have the capacity to provide important cell-type resolution for the physiological and behavioral function of pulp-innervating sensory neurons. Importantly, these tools can be applied to determine the neuronal origin of acute dental pain that coincides with tooth damage as well as pain stemming from tissue inflammation (i.e., pulpitis) toward developing treatment strategies aimed at relieving these distinct forms of pain.

Mechanobiology of Dental Pulp Cells

The dental pulp is the inner part of the tooth responsible for properly functioning during its lifespan. Apart from the very big biological heterogeneity of dental cells, tooth microenvironments differ a lot in the context of mechanical properties-ranging from 5.5 kPa for dental pulp to around 100 GPa for dentin and enamel. This physical heterogeneity and complexity plays a key role in tooth physiology and in turn, is a great target for a variety of therapeutic approaches. First of all, physical mechanisms are crucial for the pain propagation process from the tooth surface to the nerves inside the dental pulp. On the other hand, the modulation of the physical environment affects the functioning of dental pulp cells and thus is important for regenerative medicine. In the present review, we describe the physiological significance of biomechanical processes in the physiology and pathology of dental pulp. Moreover, we couple those phenomena with recent advances in the fields of bioengineering and pharmacology aiming to control the functioning of dental pulp cells, reduce pain, and enhance the differentiation of dental cells into desired lineages. The reviewed literature shows great progress in the topic of bioengineering of dental pulp-although mainly in vitro. Apart from a few positions, it leaves a gap for necessary filling with studies providing the mechanisms of the mechanical control of dental pulp functioning in vivo.

Using tissue clearing and light sheet fluorescence microscopy for the three-dimensional analysis of sensory and sympathetic nerve endings that innervate bone and dental tissue of mice

Bone and dental tissues are richly innervated by sensory and sympathetic neurons. However, the characterization of the morphology, molecular phenotype, and distribution of nerves that innervate hard tissue has so far mostly been limited to thin histological sections. This approach does not adequately capture dispersed neuronal projections due to the loss of important structural information during three-dimensional (3D) reconstruction. In this study, we modified the immunolabeling-enabled imaging of solvent-cleared organs (iDISCO/iDISCO+) clearing protocol to image high-resolution neuronal structures in whole femurs and mandibles collected from perfused C57Bl/6 mice. Axons and their nerve terminal endings were immunolabeled with antibodies directed against protein gene product 9.5 (pan-neuronal marker), calcitonin gene-related peptide (peptidergic nociceptor marker), or tyrosine hydroxylase (sympathetic neuron marker). Volume imaging was performed using light sheet fluorescence microscopy. We report high-quality immunolabeling of the axons and nerve terminal endings for both sensory and sympathetic neurons that innervate the mouse femur and mandible. Importantly, we are able to follow their projections through full 3D volumes, highlight how extensive their distribution is, and show regional differences in innervation patterns for different parts of each bone (and surrounding tissues). Mapping the distribution of sensory and sympathetic axons, and their nerve terminal endings, in different bony compartments may be important in further elucidating their roles in health and disease.

Self-propelled bioglass janus nanomotors for dentin hypersensitivity treatment

Dentin hypersensitivity treatment is not always successful owing to the exfoliation of the blocking layer. Therefore, efficiently delivering a desensitization agent into the dental tubule is critical. Nanomotors are widely used as in vivo drug delivery systems owing to their strong power and good biocompatibility. Herein, we report a kind of self-propelled bioglass Janus nanomotor with a Pt motion unit (nBGs@Pt) for application in dentin hypersensitivity that was prepared via a simple sol-gel method and magnetron sputtering method, with an average size of 290 nm. The Pt layer as the power unit provided the dynamics to deliver the bioglass (desensitization agent). Using hydrogen peroxide as a fuel, the nBGs@Pt could automatically move in different media. In addition, the nBGs@Pt with a mesoporous structure demonstrated good hydroxyapatite formation performance. An in vitro dentin pressure model was used to verify the blocking ability of the nBGs@Pt in dentin tubules. The dynamics of the nBGs@Pt was sufficient to resist the outflow of dentin fluid and movement into the dentin tubules, with a blocking rate of 58.05%. After remineralization, the blocking rate could reach 96.07% and the formation of hydroxyapatite of up to 10 μm or more occurred. It is expected that this study will provide a simple and feasible new strategy for the painless treatment of dentin sensitivity.

Piezo1-pannexin-1-P2X3 axis in odontoblasts and neurons mediates sensory transduction in dentinal sensitivity

According to the "hydrodynamic theory," dentinal pain or sensitivity is caused by dentinal fluid movement following the application of various stimuli to the dentin surface. Recent convergent evidence in Vitro has shown that plasma membrane deformation, mimicking dentinal fluid movement, activates mechanosensitive transient receptor potential (TRP)/Piezo channels in odontoblasts, with the Ca²⁺ signal eliciting the release of ATP from pannexin-1 (PANX-1). The released ATP activates the P2X₃ receptor, which generates and propagates action potentials in the intradental Aδ afferent neurons. Thus, odontoblasts act as sensory receptor cells, and odontoblast-neuron signal communication established by the TRP/Piezo channel-PANX-1-P2X₃ receptor complex may describe the mechanism of the sensory transduction sequence for dentinal sensitivity. To determine whether odontoblast-neuron communication and odontoblasts acting as sensory receptors are essential for generating dentinal pain, we evaluated nociceptive scores by analyzing behaviors evoked by dentinal sensitivity in conscious Wistar rats and Cre-mediated transgenic mouse models. In the dentin-exposed group, treatment with a bonding agent on the dentin surface, as well as systemic administration of A-317491 (P2X₃ receptor antagonist), mefloquine and ¹⁰PANX (non-selective and selective PANX-1 antagonists), GsMTx-4 (selective Piezo1 channel antagonist), and HC-030031 (selective TRPA1 channel antagonist), but not HC-070 (selective TRPC5 channel antagonist), significantly reduced nociceptive scores following cold water (0.1 ml) stimulation of the exposed dentin surface of the incisors compared to the scores of rats without local or systemic treatment. When we applied cold water stimulation to the exposed dentin surface of the lower first molar, nociceptive scores in the rats with systemic administration of A-317491, ¹⁰PANX, and GsMTx-4 were significantly reduced compared to those in the rats without systemic treatment. Dentin-exposed mice, with somatic odontoblast-specific depletion, also showed significant reduction in the nociceptive scores compared to those of Cre-mediated transgenic mice, which did not show any type of cell deletion, including odontoblasts. In the odontoblast-eliminated mice, P2X₃ receptor-positive A-neurons were morphologically intact. These results indicate that neurotransmission between odontoblasts and neurons mediated by the Piezo1/TRPA1-pannexin-1-P2X₃ receptor axis is necessary for the development of dentinal pain. In addition, odontoblasts are necessary for sensory transduction to generate dentinal sensitivity as mechanosensory receptor cells.

The effect of iontophoresis delivery of fluoride in stannous fluoride desensitizing toothpaste on dentin permeability in human extracted teeth

This study aimed to determine the effect of iontophoresis delivery of fluoride in stannous fluoride (SnF₂) toothpaste on dentin permeability in human extracted third molars. For dentin permeability test, 26 dentin specimens were randomly divided into 4 groups; SnF₂ without-iontophoresis (n = 10), SnF₂ with-iontophoresis (n = 10), no SnF₂ without-iontophoresis (n = 3), and no SnF₂ with-iontophoresis (n = 3). The hydraulic conductance of dentin (HD) was measured after smear layer removal, immediate treatment, 7 days, and acid challenge. The other 26 specimens were also prepared under these different conditions to assess degree of dentinal tubule occlusions using scanning electron microscopy (SEM). Percentage decrease of HD in SnF₂ without-iontophoresis after immediate treatment, 7 days and acid challenge were 38.38 ± 13.61, 56.92 ± 17.22 and 33.07 ± 23.57%. The corresponding values in SnF₂ with-iontophoresis were 42.16 ± 14.49, 62.35 ± 15.67 and 50.01 ± 12.60%, respectively. There was a significant difference between without- and with-iontophoresis groups after acid challenge (p < 0.05). For SEM, after 7 days, SnF₂ with-iontophoresis showed deeper dentinal tubule occlusion (p < 0.05) and more resistance to acid challenge than SnF₂ without-iontophoresis. No significant change was observed in groups of no SnF₂ treatment. Cathode iontophoresis could enhance the effect of SnF₂ toothpaste in decreasing dentin permeability and increasing resistance to acid challenge.

Expression of Piezo1 in the Trigeminal Neurons and in the Axons That Innervate the Dental Pulp

Information on the neurons and axons that express the mechanosensitive channel Piezo1 and its expression in axons innervating the dental pulp may help understand the nature of the Piezo1-mediated mechanosensation and the underlying mechanism of dentin sensitivity elicited by mechanical stimuli. For this, we here investigated the neurochemical properties of the neurons in the rat trigeminal ganglion (TG) and their axons in its sensory root that express Piezo1 and the expression of Piezo1 in the rat and human dental pulp by light and electron microscopic immunohistochemistry and quantitative analysis. Piezo1 was expressed mainly in medium-sized and large TG neurons. Piezo1-immunopositive (+) neurons frequently coexpressed the marker for neurons with myelinated axons, NF200, but rarely the markers for neurons with unmyelinated axons, CGRP or IB4. In the sensory root of TG, Piezo1 was expressed primarily in small myelinated axons (Aδ, 60.2%) but also in large myelinated (Aβ, 24.3%) and unmyelinated (C, 15.5%) axons. In the human dental pulp, Piezo1 was expressed in numerous NF200+ axons, which formed a network in the peripheral pulp and often “ascended” toward the dentin. Most Piezo1+ myelinated axons in the radicular pulp became unmyelinated in the peripheral pulp, where Piezo1 immunoreaction product was associated with the axonal plasma membrane, suggesting a functional role of Piezo1 in the peripheral pulp. These findings suggest that Piezo1 is involved primarily in mediating the acute pain elicited by high-threshold mechanical stimuli, and that the Piezo1-mediated dental mechanotransduction occurs primarily in the axons in the peripheral pulp.

Effects of desensitizing dentifrices on dentin tubule occlusion and resistance to erosive challenges

Background

Many studies have demonstrated efficacy of casein phosphopeptide (CPP) containing products for dentin tubule occlusion for treatment of dentin sensitivity, but their effectiveness under dynamic erosive challenges remains to be elucidated. The purpose of the present study was to investigate the effectiveness of a desensitizing dentifrice containing CPP in occluding dentin tubules and resisting erosive challenges in comparison to that containing polyvinyl methyl ether/maleic acid (PVM/MA) copolymers.

Methods

A total of 33 dentin discs were prepared from coronal sections of human third molars and divided into 3 groups: a toothpaste containing CPP; a toothpaste containing PVM/MA and submicron silica; and a regular toothpaste (Controls). A soft-bristle toothbrush was used to brush the dentin discs with the dentifrices for 45 strokes in 30 s at a force of approximately 200 g. The brushing cycle was repeated after immersion of the dentin discs in artificial saliva overnight. The dentin discs were then challenged in orange juice for 10 min in an incubator rocking at 120 rpm. Three fields were randomly selected on each dentin disk surface to assess dentin tubule occlusions after each brushing cycle and after orange juice challenge with a 3D laser scanning microscope. Specimen cross sections were examined with a scanning electron microscope equipped with energy dispersive spectroscopy (SEM/EDS).

Results

After the first and second cycles of brushing, dentin tubules were occluded on average by 56.3% and 85.7% in CPP group, 66.2% and 88.1% in PVM/MA group, and 0.0 and 13.0% in the controls, respectively. There were no statistically significant differences in dentin tubule occlusions between the CPP and PVM/MA groups after two cycles of brushing (p>0.05). After dynamic erosive challenges with orange juice, 20.3% of the dentin tubules in the CPP group, 79.1% in the PVM/MA group and none in the control remained occluded (P<0.05). SEM/EDS imaging showed that dentin tubules were blocked with plugs containing dentifrice substances in CPP and PVM/MA groups after treatments, but none in the controls.

Conclusions

Desensitizing dentifrices containing CPP or PVM/MA could effectively occlude dentin tubules after two cycles of brushing. PVM/MA in combination with submicron silicon dioxide exhibited stronger resistance to dynamic erosive challenges by acidic beverages. Inorganic fillers that can enter dentin tubules and resist erosive challenges may be key for desensitizing dentifrices.

Comparison between effectiveness of dentine desensitizer and one bottle self-etch adhesive on dentine hypersensitivity

BACKGROUND

Dentine hypersensitivity is one of the most common chief complaints of patients observed by dentists in their practice. However, there is a lack of universal consensus over the selection of reliable treatment modality.

OBJECTIVES

To compare the effectiveness between dentine desensitizer and self-etch adhesive in patients complaining of moderate to severe dentine hypersensitivity pain.

METHODS

A total of 254 patients with moderate to severe dentine hypersensitivity were randomly divided into Group A (Single Bond Universal Agent) and Group B (Seal & Protect Agent) according to the treatment provided. Sensitivity was assessed by means of mechanical (probing) and evaporative (air blast) stimuli. Discomfort Internal Scale (DIS) was explained to patients. DIS scores were recorded after one minute and one month following the application of both agents. Descriptive statistics were calculated. Stratification was done to control confounder and post stratification chi-square test was also applied.

RESULT

The statistically significant difference (p= 0.000) in effectiveness between the two groups was observed. The mean discomfort internal scale score at baseline, after 1 minute and after 1 month in Group A was 3.65 ± 0.60, 2.33 ± 0.64 and 0.41 ± 0.71 respectively, while in Group B, it was 3.55 ± 0.58, 2.40 ± 0.62 and 0.72 ± 0.92 respectively. Overall, 86.6% patients observed improvement in dentinal sensitivity in Group A while in Group B only 67.7% patients reported reduction in sensitivity.

CONCLUSION

Self-etch adhesive significantly reduces dentin hypersensitivity, immediately after one minute of its application and is effective for a period of one month compared to desensitizing agent.

Use of high- and low-intensity lasers in the treatment of dentin hypersensitivity: A literature review

Background

Dentin hypersensitivity (DH) is defined as an exaggerated sensitivity of vital dentin exposed to thermal, chemical and tactile stimuli. This study aimed to evaluate, through a literature review, the applicability of high- and low-intensity lasers in the treatment of DH for the past 10 years, as well as its therapeutic potential.

Material and Methods

The electronic databases MEDLINE/PubMed and LILACS were searched using the descriptors (“Dentin Sensitivity” OR “Dentin Hypersensitivity”) AND (“Low-Level Therapy” OR Laser), for articles published between 2010 and 2020. Only randomized clinical trials with full-text and full case resolution were included.

Results

We found 187 articles in total, among which 61 were pre-selected and 10 included in this literature review.

Conclusions

Considering the found results and their possible limitations, high- and low-intensity lasers, associated or not with other therapies, have demonstrated beneficial effects in the treatment of DH, being considered a promising, safe, easy, and effective field of research, reducing pain sensitivity and preserving pulp vitality.

Key words:Dentin sensitivity, dentistry, laser.

Dental Pain: Dentine Sensitivity, Hypersensitivity and Cracked Tooth Syndrome

Dentine hypersensitivity is a frequently encountered patient complaint that can present with a number of associated factors including erosion and abrasion. the hydrodynamic mechanism responsible for dentine hypersensitivity is intimately related to the anatomical and physiological composition of teeth. Alterations to the integrity of the enamel and dentine through processes of trauma, decay and toothwear can increase dentine permeability. This gives rise to symptoms of sensitivity as dentinal fluid movement in response to thermal, chemical and mechanical cues stimulate the pulpal Aδ fibres. Restorative procedures can also rapidly change the architecture of the protective enamel and dentine layers leading to pulpal inflammation and increased thermal sensitivity of the tooth.<br/> Patient-reported symptoms of dentine hypersensitivity can be attributed to a number of possible causes and a definitive diagnosis can therefore be difficult. A full history including social and medical factors such as occupation, diet and/or medication is likely to provide significant information to aid a diagnosis. Consideration of occlusal factors should not be overlooked as these may contribute to symptoms arising from a cracked tooth.<br/> Management strategies are linked to the diagnosis - from topically applied desensitising pastes and resin bonding agents to direct restorations and possibly more advanced restorative procedures such as root canal treatment. Management should, however, be staged to enable more conservative strategies to prevail prior to considering irreversible dental interventions.

TRPM8 and TRPA1 do not contribute to dental pulp sensitivity to cold

Sensory neurons innervating the dental pulp have unique morphological and functional characteristics compared to neurons innervating other tissues. Stimulation of dental pulp afferents whatever the modality or intensity of the stimulus, even light mechanical stimulation that would not activate nociceptors in other tissues, produces an intense pain. These specific sensory characteristics could involve receptors of the Transient Receptor Potential channels (TRP) family. In this study, we compared the expression of the cold sensitive receptors TRPM8 and TRPA1 in trigeminal ganglion neurons innervating the dental pulp, the skin of the cheek or the buccal mucosa and we evaluated the involvement of these receptors in dental pulp sensitivity to cold. We showed a similar expression of TRPM8, TRPA1 and CGRP in sensory neurons innervating the dental pulp, the skin or the mucosa. Moreover, we demonstrated that noxious cold stimulation of the tooth induced an overexpression of cFos in the trigeminal nucleus that was not prevented by the genetic deletion of TRPM8 or the administration of the TRPA1 antagonist HC030031. These data suggest that the unique sensory characteristics of the dental pulp are independent to TRPM8 and TRPA1 receptors expression and functionality.

Thermal analysis of the dentine tubule under hot and cold stimuli using fluid-structure interaction simulation

The objective of this study is to compare the thermal stress changes in the tooth microstructures and the hydrodynamic changes of the dental fluid under hot and cold stimuli. The dimension of the microstructures of eleven cats' teeth was measured by scanning electron microscopy, and the changes in thermal stress during cold and hot stimulation were calculated by 3D fluid-structure interaction modeling. Evaluation of results, following data validation, indicated that the maximum velocities in cold and hot stimuli were - 410.2 ± 17.6 and + 205.1 ± 8.7 µm/s, respectively. The corresponding data for maximum thermal stress were - 20.27 ± 0.79 and + 10.13 ± 0.24 cmHg, respectively. The thermal stress caused by cold stimulus could influence almost 2.9 times faster than that caused by hot stimulus, and the durability of the thermal stress caused by hot stimulus was 71% greater than that by cold stimulus under similar conditions. The maximum stress was on the tip of the odontoblast, while the stress in lateral walls of the odontoblast and terminal fibril was very weak. There is hence a higher possibility of pain transmission with activation of stress-sensitive ion channels at the tip of the odontoblast. The maximum thermal stress resulted from the cold stimulus is double that produced by the hot stimulus. There is a higher possibility of pain transmission in the lateral walls of the odontoblast and terminal fibril by releasing mediators during the cold stimulation than the hot stimulation. These two reasons can be associated with a greater pain sensation due to intake of cold liquids.

Activation of Mechanosensitive Transient Receptor Potential/Piezo Channels in Odontoblasts Generates Action Potentials in Cocultured Isolectin B4-negative Medium-sized Trigeminal Ganglion Neurons

INTRODUCTION

Various stimuli to the dentin surface elicit dentinal pain by inducing dentinal fluid movement causing cellular deformation in odontoblasts. Although odontoblasts detect deformation by the activation of mechanosensitive ionic channels, it is still unclear whether odontoblasts are capable of establishing neurotransmission with myelinated A delta (Aδ) neurons. Additionally, it is still unclear whether these neurons evoke action potentials by neurotransmitters from odontoblasts to mediate sensory transduction in dentin. Thus, we investigated evoked inward currents and evoked action potentials form trigeminal ganglion (TG) neurons after odontoblast mechanical stimulation.

METHODS

We used patch clamp recordings to identify electrophysiological properties and record evoked responses in TG neurons.

RESULTS

We classified TG cells into small-sized and medium-sized neurons. In both types of neurons, we observed voltage-dependent inward currents. The currents from medium-sized neurons showed fast inactivation kinetics. When mechanical stimuli were applied to odontoblasts, evoked inward currents were recorded from medium-sized neurons. Antagonists for the ionotropic adenosine triphosphate receptor (P2X₃), transient receptor potential channel subfamilies, and Piezo1 channel significantly inhibited these inward currents. Mechanical stimulation to odontoblasts also generated action potentials in the isolectin B₄-negative medium-sized neurons. Action potentials in these isolectin B₄-negative medium-sized neurons showed a short duration. Overall, electrophysiological properties of neurons indicate that the TG neurons with recorded evoked responses after odontoblast mechanical stimulation were myelinated Aδ neurons.

CONCLUSIONS

Odontoblasts established neurotransmission with myelinated Aδ neurons via P2X₃ receptor activation. The results also indicated that mechanosensitive TRP/Piezo1 channels were functionally expressed in odontoblasts. The activation of P2X₃ receptors induced an action potential in the Aδ neurons, underlying a sensory generation mechanism of dentinal pain.

TRPM7 Mediates Mechanosensitivity in Adult Rat Odontoblasts

Odontoblasts, with their strategic arrangement along the outermost compartment of the dentin-pulp complex, have been suggested to have sensory function. In addition to their primary role in dentin formation, growing evidence shows that odontoblasts are capable of sensing mechanical stimulation. Previously, we found that most odontoblasts express TRPM7, the nonselective mechanosensitive ion channel reported to be critical in Mg²⁺ homeostasis and dentin mineralization. In line with this finding, we sought to elucidate the functional expression of TRPM7 in odontoblasts by pharmacological approaches and mechanical stimulation. Naltriben, a TRPM7-specific agonist, induced calcium transient in the majority of odontoblasts, which was blocked by TRPM7 blockers such as extracellular Mg²⁺ and FTY720 in a dose-dependent manner. Mechanical stretch of the odontoblastic membrane with hypotonic solution also induced calcium transient, which was blocked by Gd³⁺, a nonselective mechanosensitive channel blocker. Calcium transient induced by hypotonic solution was also blocked by high extracellular Mg²⁺ or FTY720. When TRPM7-mediated calcium transients in odontoblasts were analyzed on the subcellular level, remarkably larger transients were detected in the distal odontoblastic process compared with the soma, which was further verified with comparable immunocytochemical analysis. Our results demonstrate that TRPM7 in odontoblasts can serve as a mechanical sensor, with its distribution to facilitate intracellular Ca²⁺ signaling in the odontoblastic process. These findings suggest TRPM7 as a mechanical transducer in odontoblasts to mediate intracellular calcium dynamics under diverse pathophysiological conditions of the dentin.

In vivo analyses of the effects of polyamidoamine dendrimer on dentin biomineralization and dentinal tubules occlusion

This study evaluated the biomineralization and dentinal tubules occlusion abilities of the carboxyl-terminated polyamidoamine dendrimer (PAMAM-COOH) on human demineralized dentin in vivo at different time points. Demineralization dentin model with and without treated with PAMAM-COOH were sutured to the interior side of the rat's cheeks, that was incubated in the rats' saliva for 2, 4 and 6 weeks respectively. Finally, the newly formed precipitates were characterized by SEM, EDS, XRD and microhardness test. The hydroxyapatite (HA) on the dentin treated with PAMAM-COOH were formed gradually with the time going by, and the regenerated HA has a similar crystal structure with natural dentin, whereas the crystallites did not exist on the control group. The microhardness of PAMAM-COOH-applied specimens had a significantly higher than those without application. These results suggest that the PAMAM-COOH promoted the biomineralization of demineralized dentin and displayed favourable effects on blocking the open dentinal tubules.

Effect of tropical fruit juices on dentine permeability and erosive ability in removing the smear layer: An in vitro study

Background/purpose

Acidic diet is one major cause of dentine hypersensitivity. The objective of this study was to determine the effects of different tropical fruit juices on dentine permeability and their erosive ability to remove the smear layer in extracted human teeth.

Materials and methods

Thirty-six noncarious human premolars were used, and the dentine was exposed at the tip of the buccal cusp by cutting a cavity (diameter 3 mm, depth 3 mm). Permeability of the dentine was tested under different conditions: with a smear layer and 5 minutes after the application of freshly squeezed green mango, lime, tamarind, and starfruit juices. The smear layer was created before each treatment by gently cutting the dentine with a diamond bur. In the final treatment, the dentine was etched with 37% phosphoric acid for 30 seconds. The erosive ability of these fruit juices to remove the smear layer was also examined using a scanning electron microscope.

Results

Results revealed that application of green mango, tamarind, lime, and starfruit juices for 5 minutes significantly increased dentine permeability by 128.2%, 73.4%, 80.6%, and 70.4%, respectively (P < 0.05, Friedman repeated measures analysis of variance on ranks). The corresponding value of 37% phosphoric acid was 125.1%. Scanning electron microscopy data showed that green mango and lime juices had very strong erosive ability to remove the smear layer, similar to 37% phosphoric acid.

Conclusion

We conclude that tropical fruit juices, especially green mango and lime, increase dentine permeability and have a strong erosive ability to remove the smear layer, which causes dentine hypersensitivity.

Intercellular Odontoblast Communication via ATP Mediated by Pannexin-1 Channel and Phospholipase C-coupled Receptor Activation

Extracellular ATP released via pannexin-1 channels, in response to the activation of mechanosensitive-TRP channels during odontoblast mechanical stimulation, mediates intercellular communication among odontoblasts in dental pulp slice preparation dissected from rat incisor. Recently, odontoblast cell lines, such as mouse odontoblast lineage cells, have been widely used to investigate physiological/pathological cellular functions. To clarify whether the odontoblast cell lines also communicate with each other by diffusible chemical substance(s), we investigated the chemical intercellular communication among cells from mouse odontoblast cell lines following mechanical stimulation. A single cell was stimulated using a glass pipette filled with standard extracellular solution. We measured intracellular free Ca(2+) concentration ([Ca(2+)]i) by fura-2 in stimulated cells, as well as in cells located nearby. Direct mechanical stimulation to a single odontoblast increased [Ca(2+)]i, which showed sensitivity to capsazepine. In addition, we observed increases in [Ca(2+)]i not only in the mechanically stimulated odontoblast, but also in nearby odontoblasts. We could observe mechanical stimulation-induced increase in [Ca(2+)]i in a stimulated human embryo kidney (HEK) 293 cell, but not in nearby HEK293 cells. The increase in [Ca(2+)]i in nearby odontoblasts, but not in the stimulated odontoblast, was inhibited by adenosine triphosphate (ATP) release channel (pannexin-1) inhibitor in a concentration- and spatial-dependent manner. Moreover, in the presence of phospholipase C (PLC) inhibitor, the increase in [Ca(2+)]i in nearby odontoblasts, following mechanical stimulation of a single odontoblast, was abolished. We could record some inward currents evoked from odontoblasts near the stimulated odontoblast, but the currents were observed in only 4.8% of the recorded odontoblasts. The results of this study showed that ATP is released via pannexin-1, from a mechanically stimulated odontoblast, which transmits a signal to nearby odontoblasts by predominant activation of PLC-coupled nucleotide receptors.

Intracanal molar barometric pressure differentials at simulated altitude conditions - proof of concept study

AIM

To evaluate whether objective data could be obtained regarding internal pressure conditions of a molar tooth with canals prepared but not filled exposed to reduced barometric pressures that could be experienced by aircrew.

METHODOLOGY

The root canals of five mandibular molars were prepared but not filled. Root apices were sealed with a resin-modified glass-ionomer liner and root surfaces sealed with a dental adhesive. The sealed root surfaces were then coated with a polyvinylsiloxane (PVS) adhesive and the teeth inserted into cylinders of PVS impression material to the level of the cervical enamel junction. Barometric pressure transducers were placed in the pulp chambers with the endodontic access sealed with cotton and a provisional restoration. The specimens were then subjected to a manually controlled, atmospheric altitude challenge consisting of a slow ascent and descent to a simulated 25 000 feet above sea level followed by a rapid altitude climb and descent. The real-time difference between intracanal and simulated atmospheric pressures were recorded and correlated (Pearson's, P = 0.05).

RESULTS

No tooth material fractured, and there was no failure of the provisional restorations. Barometric pressures inside the closed prepared molar canals and the ambient atmospheric pressure were found to correlate (r(2)  = 0.97-0.99; P < 0.0001), but pressure equalization lags were observed. However, no differences greater than six pounds per square inch (310 torr) were noted.

CONCLUSION

This pilot study established a protocol that demonstrated that objective data regarding barometric pressures within the prepared canals of molars can be obtained at simulated altitude conditions.

External Dentin Stimulation Induces ATP Release in Human Teeth

ATP is involved in neurosensory processing, including nociceptive transduction. Thus, ATP signaling may participate in dentin hypersensitivity and dental pain. In this study, we investigated whether pannexins, which can form mechanosensitive ATP-permeable channels, are present in human dental pulp. We also assessed the existence and functional activity of ecto-ATPase for extracellular ATP degradation. We further tested if ATP is released from dental pulp upon dentin mechanical or thermal stimulation that induces dentin hypersensitivity and dental pain and if pannexin or pannexin/gap junction channel blockers reduce stimulation-dependent ATP release. Using immunofluorescence staining, we demonstrated immunoreactivity of pannexin 1 and 2 in odontoblasts and their processes extending into the dentin tubules. Using enzymatic histochemistry staining, we also demonstrated functional ecto-ATPase activity within the odontoblast layer, subodontoblast layer, dental pulp nerve bundles, and blood vessels. Using an ATP bioluminescence assay, we found that mechanical or cold stimulation to the exposed dentin induced ATP release in an in vitro human tooth perfusion model. We further demonstrated that blocking pannexin/gap junction channels with probenecid or carbenoxolone significantly reduced external dentin stimulation-induced ATP release. Our results provide evidence for the existence of functional machinery required for ATP release and degradation in human dental pulp and that pannexin channels are involved in external dentin stimulation-induced ATP release. These findings support a plausible role for ATP signaling in dentin hypersensitivity and dental pain.

Odontoblasts as sensory receptors: transient receptor potential channels, pannexin-1, and ionotropic ATP receptors mediate intercellular odontoblast-neuron signal transduction

Various stimuli induce pain when applied to the surface of exposed dentin. However, the mechanisms underlying dentinal pain remain unclear. We investigated intercellular signal transduction between odontoblasts and trigeminal ganglion (TG) neurons following direct mechanical stimulation of odontoblasts. Mechanical stimulation of single odontoblasts increased the intracellular free calcium concentration ([Ca(2+)]i) by activating the mechanosensitive-transient receptor potential (TRP) channels TRPV1, TRPV2, TRPV4, and TRPA1, but not TRPM8 channels. In cocultures of odontoblasts and TG neurons, increases in [Ca(2+)]i were observed not only in mechanically stimulated odontoblasts, but also in neighboring odontoblasts and TG neurons. These increases in [Ca(2+)]i were abolished in the absence of extracellular Ca(2+) and in the presence of mechanosensitive TRP channel antagonists. A pannexin-1 (ATP-permeable channel) inhibitor and ATP-degrading enzyme abolished the increases in [Ca(2+)]i in neighboring odontoblasts and TG neurons, but not in the stimulated odontoblasts. G-protein-coupled P2Y nucleotide receptor antagonists also inhibited the increases in [Ca(2+)]i. An ionotropic ATP (P2X3) receptor antagonist inhibited the increase in [Ca(2+)]i in neighboring TG neurons, but not in stimulated or neighboring odontoblasts. During mechanical stimulation of single odontoblasts, a connexin-43 blocker did not have any effects on the [Ca(2+)]i responses observed in any of the cells. These results indicate that ATP, released from mechanically stimulated odontoblasts via pannexin-1 in response to TRP channel activation, transmits a signal to P2X3 receptors on TG neurons. We suggest that odontoblasts are sensory receptor cells and that ATP released from odontoblasts functions as a neurotransmitter in the sensory transduction sequence for dentinal pain.

Evaluation of a calcium phosphate desensitizer using an ultrasonic device

This study evaluated the effect of a calcium phosphate desensitizer on the demineralization of bovine dentin by measuring changes in transmitted ultrasonic velocity. Bovine dentin specimens with and without application of desensitizer were immersed in 0.1 M lactic-acid buffer solution (pH 4.75) 10 min twice daily throughout the test period, and stored in artificial saliva solution (pH 7.0) between treatments. The propagation time of longitudinal ultrasonic waves was measured by a pulser-receiver. Data were evaluated using one-way ANOVA followed by Tukey HSD test (α=0.05). The ultrasonic velocity decreased over time in specimens stored in demineralizing solution (3,785-3,462 m/s); however, desensitizer-applied specimens had a significantly higher sonic velocity (3,945-3,990 m/s) than those without application. The calcium phosphate desensitizer appeared to reduce the demineralization of dentin and occluded dentinal tubules.

Thermal Pain in Teeth: Electrophysiology Governed by Thermomechanics

Thermal pain arising from the teeth is unlike that arising from anywhere else in the body. The source of this peculiarity is a long-standing mystery that has begun to unravel with recent experimental measurements and, somewhat surprisingly, new thermomechanical models. Pain from excessive heating and cooling is typically sensed throughout the body through the action of specific, heat sensitive ion channels that reside on sensory neurons known as nociceptors. These ion channels are found on tooth nociceptors, but only in teeth does the pain of heating differ starkly from the pain of cooling, with cold stimuli producing more rapid and sharper pain. Here, we review the range of hypotheses and models for these phenomena, and focus on what is emerging as the most promising hypothesis: pain transduced by fluid flowing through the hierarchical structure of teeth. We summarize experimental evidence, and critically review the range of heat transfer, solid mechanics, fluid dynamics, and electrophysiological models that have been combined to support this hypothesis. While the results reviewed here are specific to teeth, this class of coupled thermomechanical and neurophysiological models has potential for informing design of a broad range of thermal therapies and understanding of a range of biophysical phenomena.

An investigation of dentinal fluid flow in dental pulp during food mastication: simulation of fluid-structure interaction

This study uses fluid-structure interaction (FSI) simulation to investigate the relationship between the dentinal fluid flow in the dental pulp of a tooth and the elastic modulus of masticated food particles and to investigate the effects of chewing rate on fluid flow in the dental pulp. Three-dimensional simulation models of a premolar tooth (enamel, dentine, pulp, periodontal ligament, cortical bone, and cancellous bone) and food particle were created. Food particles with elastic modulus of 2,000 and 10,000 MPa were used, respectively. The external displacement loading (5 μm) was gradually directed to the food particle surface for 1 and 0.1 s, respectively, to simulate the chewing of food particles. The displacement and stress on tooth structure and fluid flow in the dental pulp were selected as evaluation indices. The results show that masticating food with a high elastic modulus results in high stress and deformation in the tooth structure, causing faster dentinal fluid flow in the pulp in comparison with that obtained with soft food. In addition, fast chewing of hard food particles can induce faster fluid flow in the pulp, which may result in dental pain. FSI analysis is shown to be a useful tool for investigating dental biomechanics during food mastication. FSI simulation can be used to predict intrapulpal fluid flow in dental pulp; this information may provide the clinician with important concept in dental biomechanics during food mastication.

Evaluation of dentinal fluid flow behaviours: a fluid-structure interaction simulation

This study uses the fluid-structure interaction (FSI) method to investigate the fluid flow in dental pulp. First, the FSI method is used for the biomechanical simulation of dental intrapulpal responses during force loading (50, 100 and 150 N) on a tooth. The results are validated by comparison with experimental outcomes. Second, the FSI method is used to investigate an intact tooth subjected to a mechanical stimulus during loading at various loading rates. Force loading (0-100 N) is applied gradually to an intact tooth surface with loading rates of 125, 62.5, 25 and 12.5 N/s, respectively, and the fluid flow changes in the pulp are evaluated. FSI analysis is found to be suitable for examining intrapulpal biomechanics. An external force applied to a tooth with a low loading rate leads to a low fluid flow velocity in the pulp chamber, thus avoiding tooth pain.

MATHEMATICAL MODELING FOR THE PREDICTION AND IMPROVEMENT OF TOOTH THERMAL PAIN: A REVIEW

Tooth pain, especially tooth thermal pain, is one of the most important symptoms and signs in dental clinic and daily life. As a special sensation, pain has been studied extensively in both clinic and experimental research aimed at reducing or eliminating the possible negative effects of pain. Unfortunately, the full underlying mechanism of pain is still unclear, because the pain could be influenced by many factors, including physiological, psychological, physical, chemical, and biological factors and so on. Besides, most studies on pain mechanisms in the literature are based on skin pain sensation and only few are based on tooth pain. In this paper, we present a comprehensive review on both neurophysiology of tooth pain mechanism, and corresponding thermal, mechanical, and thermomechanical behaviors of teeth. We also describe a multiscale modeling approach for quantifying tooth thermal pain by integrating the mathematic methods of engineering into the neuroscience. The mathematical model of tooth thermal pain will enable better understanding of thermal pain mechanism and optimization of existing diagnosis and treatment in dental clinic.

FLUID DYNAMICS ANALYSIS OF SHEAR STRESS ON NERVE ENDINGS IN DENTINAL MICROTUBULE: A QUANTITATIVE INTERPRETATION OF HYDRODYNAMIC THEORY FOR DENTAL PAIN

Noxious thermal and/or mechanical stimuli applied to dentine can cause fluid flow in dentinal microtubules (DMTs). The fluid flow induces shear stress (SS) on intradental nerve endings and may excite pulpal mechanoreceptors to generate dental pain sensation. There exist numerous studies on dental thermal pain, but few are mathematical. For this, we developed a computational fluid dynamics (CFD) model of dentinal fluid flow (DFF) in innervated DMTs. Based on this model, we systematically investigated the effects of various parameters (e.g., biological structure, DFF velocity, and fluid properties) on the SS experienced by intradental nerve endings and thus provide a quantitative interpretation to the hydrodynamic theory. The dimensions of biological structures, odontoblastic process (OP) movement, dentinal fluid velocity, and viscosity were found to have significant influences on the SS while dentinal fluid density showed negligible influence under conditions studied. The results indicate that: (i) dental pain study of animal models may not be directly applied to human being and the results may even vary from one person to another and (ii) OP movement caused by DFF changes the dimension of the space for the fluid flow, affecting thus the SS on nerve endings. The present work enables better understanding of the mechanisms underlying dental pain sensation and quantification of dental pain intensity resulted from clinical procedures such as dentine sensitivity testing and dental restorative processes.

Inflammatory mediators in fluid extracted from the coronal occlusal dentine of trimmed teeth

BACKGROUND

Chemokines and cytokines may occur in dentinal fluids in response to local infection and inflammation. To test this hypothesis, we assessed the presence and concentration of inflammatory mediators in fluid extracted from the coronal occlusal dentine of trimmed teeth.

DESIGN

Freshly extracted sound, carious, and restored molars were trimmed through the enamel to expose the underlying dentine, etched with 35% phosphoric acid, and rinsed. Fluid was extracted from the coronal occlusal dentine of these trimmed teeth by centrifugation at 2750 × g for 30 min.

RESULTS

When assessed by MALDI-TOF, fluid extracted from the coronal occlusal dentine from 16 molars contained at least 117 peaks with different masses suggesting that this fluid was rich with molecules within the appropriate mass range of potential mediators. Indeed, when assessed for chemokines and cytokines, fluid extracted from the coronal occlusal dentine from 25 extracted molars with caries lesions, 10 extracted restored molars with occlusal amalgam, and 77 extracted sound molars contained IL-1β, TNF-α, IL-6, IL-8, IL-12(p70), and IL-10. A significant elevation was found for TNF-α (p=0.041) in extracted fluid from teeth restored with amalgam fillings.

CONCLUSIONS

Overall, fluid extracted from the coronal occlusal dentine of trimmed teeth may be useful in identifying proteins and other molecules in dentine and pulpal fluids and determining their role as mediators in the pathogenesis of oral infection and inflammation.

Fluid mechanics in dentinal microtubules provides mechanistic insights into the difference between hot and cold dental pain

Dental thermal pain is a significant health problem in daily life and dentistry. There is a long-standing question regarding the phenomenon that cold stimulation evokes sharper and more shooting pain sensations than hot stimulation. This phenomenon, however, outlives the well-known hydrodynamic theory used to explain dental thermal pain mechanism. Here, we present a mathematical model based on the hypothesis that hot or cold stimulation-induced different directions of dentinal fluid flow and the corresponding odontoblast movements in dentinal microtubules contribute to different dental pain responses. We coupled a computational fluid dynamics model, describing the fluid mechanics in dentinal microtubules, with a modified Hodgkin-Huxley model, describing the discharge behavior of intradental neuron. The simulated results agreed well with existing experimental measurements. We thence demonstrated theoretically that intradental mechano-sensitive nociceptors are not “equally sensitive” to inward (into the pulp) and outward (away from the pulp) fluid flows, providing mechanistic insights into the difference between hot and cold dental pain. The model developed here could enable better diagnosis in endodontics which requires an understanding of pulpal histology, neurology and physiology, as well as their dynamic response to the thermal stimulation used in dental practices.

Analysis of thermal-induced dentinal fluid flow and its implications in dental thermal pain

OBJECTIVES

The initiation of the pain sensation experienced following the thermal stimulation of dentine has been correlated with fluid flow in the dentinal tubules. There may be other mechanisms.

METHODS

This study examines this possibility using a mathematical model to simulate the temperature and thermal stress distribution in a tooth undergoing thermal stimulation. The results obtained were then used to predict the fluid flow in a single dentinal tubule by considering the deformation of the dentinal tubules and dentinal fluid.

RESULTS

Deformation of the pulp chamber was observed before a noticeable temperature change was recorded at the dentine-enamel junction. Tubule deformation leads to changes in fluid flow more rapidly than fluid expansion or contraction. This finding agreed with previously reported experimental observations. An initially high rate of outward fluid flow under cooling was found to correspond to short latency neural responses whilst heating was associated with long latency neural responses.

CONCLUSION

Rapid fluid flow caused by thermal deformation of dentinal tubules may account for the short latency (<1s) activation of mechano-sensitive receptors after of cooling. Long latency (>10s) neural responses could be associated with the activation of thermo-sensitive receptors.

Human dental pulp cells exhibit bone cell-like responsiveness to fluid shear stress

BACKGROUND AIMS

For engineering bone tissue to restore, for example, maxillofacial defects, mechanosensitive cells are needed that are able to conduct bone cell-specific functions, such as bone remodelling. Mechanical loading affects local bone mass and architecture in vivo by initiating a cellular response via loading-induced flow of interstitial fluid. After surgical removal of ectopically impacted third molars, human dental pulp tissue is an easily accessible and interesting source of cells for mineralized tissue engineering. The aim of this study was to determine whether human dental pulp-derived cells (DPC) are responsive to mechanical loading by pulsating fluid flow (PFF) upon stimulation of mineralization in vitro.

METHODS

Human DPC were incubated with or without mineralization medium containing differentiation factors for 3 weeks. Cells were subjected to 1-h PFF (0.7 ± 0.3 Pa, 5 Hz) and the response was quantified by measuring nitric oxide (NO) and prostaglandin E₂ (PGE₂) production, and gene expression of cyclooxygenase (COX)-1 and COX-2.

RESULTS

We found that DPC are intrinsically mechanosensitive and, like osteogenic cells, respond to PFF-induced fluid shear stress. PFF stimulated NO and PGE₂ production, and up-regulated COX-2 but not COX-1 gene expression. In DPC cultured under mineralizing conditions, the PFF-induced NO, but not PGE₂, production was significantly enhanced.

CONCLUSIONS

These data suggest that human DPC, like osteogenic cells, acquire responsiveness to pulsating fluid shear stress in mineralizing conditions. Thus DPC might be able to perform bone-like functions during mineralized tissue remodeling in vivo, and therefore provide a promising new tool for mineralized tissue engineering to restore, for example, maxillofacial defects.

Effect of a new desensitizing material on human dentin permeability

OBJECTIVES

Resin-modified glass ionomers (RMGI) have demonstrated clinical success providing immediate and long-term relief from root sensitivity. RMGIs have been recently introduced as paste-liquid systems for convenience of clinical usage. The objective of this study was to measure the ability of a new paste-liquid RMGI to reduce fluid flow through human dentin, compared to an established single-bottle nanofilled total etch resin adhesive indicated for root desensitization.

METHODS

Dentin permeability was measured on human crown sections on etched dentin, presenting a model for the exposed tubules typical of root sensitivity, and permitting measurement of the maximum permeability. In the first two groups, the etched dentin was coated with either the RMGI or adhesive, and permeability measured on the coated dentin. In a third group, a smear layer was created on the dentin with sandpaper, then the specimens were coated with the RMGI; permeability was measured on the smeared and coated dentin. Specimens from each group were sectioned and examined via scanning electron microscopy (SEM).

RESULTS

Both the resin adhesive and the new paste-liquid RMGI protective material significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either open tubules or smear-layer occluded tubules. The RMGI infiltrated the smear layer with resin during placement, penetrated dentin tubules, and formed resin tags.

SIGNIFICANCE

The RMGI was equivalent to the adhesive in its ability to reduce fluid flow and seal dentin. It is therefore concluded that the new RMGI and the adhesive show the potential to offer excellent sensitivity relief on exposed root dentin.

Effect of a new liner/base on human dentin permeability

OBJECTIVES

Resin-modified glass ionomers (RMGI) have demonstrated clinical success in their ability to minimize post-operative sensitivity of restorations. RMGIs have been recently introduced as paste-liquid systems for convenience of clinical usage. The objective of this study was to measure the ability of a new paste-liquid RMGI liner/base to reduce fluid flow through human dentin.

METHODS

Dentin permeability was measured on human crown sections on etched dentin, using etched dentin as a model for the exposed tubules typical of root sensitivity, and permitting measurement of the maximum permeability. In the one group, the etched dentin was coated with the RMGI, and pre- and post-treatment permeability was measured on the coated dentin. In the second group, a smear layer was created on the dentin with sandpaper, then the samples were coated with the RMGI; permeability was measured on the smeared and coated dentin. Samples from each group were sectioned and examined via scanning electron microscopy (SEM).

RESULTS

The new paste-liquid RMGI liner/base significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either a smear layer or open tubules. SEM images show evidence that the RMGI infiltrated the smear layer with resin during placement, penetrated dentin tubules, and formed resin tags in acid-etched dentin.

CONCLUSIONS

Based on these results, combined with previous research on adhesion and microleakage, it is concluded that the new RMGI liner/base should minimize post-operative sensitivity in restorations.