[Hydrodynamics of dental dentinal fluid]. / Gidrodinamika dentinnoi zhidkosti zuba.

BACKGROUND: Dentinal fluid is very close in its physical and mechanical properties and composition to blood plasma, which makes it a potentially aggressive biological environment for modern adhesive systems. An in-depth study of the physiological processes of the functioning of tooth dentin remains relevant in order to solve problems associated with its artificial restoration. PURPOSE OF THE STUDY: Study using computer simulation speed of movement and pressure distribution of dentinal fluid in the dentinal tubule of the tooth to assess the possibilities of their regulation. MATERIAL AND METHODS: To model the distribution of flow velocity and pressure of dentinal fluid in the dentinal tubule, the finite element method (Fluent ANSYS computer program) was used. RESULTS: Immediately behind the spherical tip of the odontoblast, there is a rapid increase in the hydraulic diameter of the flow section of the dentinal tubule, and, accordingly, a decrease in capillary pressure, while the tip of the odontoblast creates a large local hydraulic resistance. The resulting distribution of pressure drop in the damaged dentinal tubule is consistent with the fact that fluid movement is due, to a greater extent, to the capillary effect rather than the inlet pressure into the dentinal tubule. CONCLUSION: By changing the length of the odontoblast process, it is possible to influence the parameters of the hydrodynamics of dentinal fluid in the space of the dentinal tubule.

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.

Evaluation of dentin tubule occlusion after laser irradiation and desensitizing agent application.

PURPOSE: To evaluate the effects of lasers (Nd:YAG and Er:YAG) and of topical desensitizing agents on dentin tubule occlusion by measuring real-time dentin fluid flow (DFF). METHODS: 32 molars were prepared with V-shape cavity at the cervical area, acid-etched, water rinsed, blotted dry, and treated with (1) Nd:YAG laser; (2) Er:YAG laser; (3) SuperSeal, a desensitizing agent; (4) ClinproXT, a resin-modified glass-ionomer (RMGI) varnish (n = 8 each). A real-time fluid flow measuring instrument (nano-Flow) was used to measure the DFF throughout the procedures. The DFF rates before and after the treatment were compared. Moreover, the surface topography of dentin tubules after each desensitizing method was examined using SEM. RESULTS: DFF varied among the groups. The DFF rate was significantly reduced after laser irradiation/application of the desensitizing agents (P < 0.05). ClinproXT showed the greatest reduction of DFF rate (71.9%), followed by the SuperSeal (34.8%) and laser groups (P< 0.05). However, there was no significant difference between the Nd:YAG (24.1%) and Er:YAG (20.6%) groups (P > 0.05). In SEM images, narrowed dentin tubules were observed in both lased groups and SuperSeal group. In the ClinproXT group, the occluded dentin tubules by the RMGI covering were observed.

Evaluation of the permeability of five desensitizing agents using computerized fluid filtration.

OBJECTIVE: The aim of this study was to evaluate the permeability of five desensitizing agents using computerized fluid filtration (CFF) test method. MATERIALS AND METHODS: Sixty dentin discs of 500 ± 200-mm-thick were prepared from middle dentin of bovine incisors without exposed the pulp and then randomly divided into five groups (n = 12). The permeability of the discs was measured using the CFF test method before and after application of the following desensitizers: Admira Protect (Voco, Cuxhaven, Germany), Seal and Protect (Dentsply, Konstanz, Germany), Sensi Kill (DFL, Brazil), Systemp Desensitizer (Ivoclar Vivadent, Liechtenstein), BisBlock (Bisco, USA). Fluid movement measurements were made at 2-min intervals for 8 min, and a mean of the values obtained was calculated for each specimen. The results were analyzed using Kruskal-Wallis test and Wilcoxon signed ranks tests with a significance threshold of P < 0.05. RESULTS: There were no significant differences in permeability among desensitizing agents (P > 0.05); however dentin permeability was reduced in all groups (P < 0.05). CONCLUSION: The in vitro fluid conductance of dentin discs were reduced by treating with these five desensitizing agents.

A photochemical method for in vitro evaluation of fluid flow in human dentine.

OBJECTIVE: To evaluate the flow dynamics of dentine fluid using a chemiluminescence method in vitro. MATERIALS AND METHODS: Horizontally sliced coronal dentine specimens with thicknesses of 1.4, 1.6, 1.8, and 2.0mm (n=10 each) were prepared from extracted human third molars. After cleaning with EDTA, a mounted specimen was clamped between 2 acrylic chambers attached to both the occlusal and pulpal sides. The occlusal chamber, which was closed with a glass coverslip, was filled with a chemiluminescent solution (0.02% luminol and 1% sodium hydroxide in water). A trigger solution of 1% hydrogen peroxide and 1% potassium ferricyanide was injected into the pulpal chamber at a constant pressure of 2.5 kPa, and allowed to immediately flow into the patent dentinal tubules. Four consecutive measurements (T1-T4) were performed on each sample by recording the emission of chemiluminescence with a photodetector. The relationship between the crossing time of the liquid through the slice and dentine thickness was examined. RESULTS: An apparent time delay was detected between the starting points of the trigger solution run and photochemical emission at T1. Dt (Dt, s) values of each thickness group were 13.6 ± 4.25 for 1.4mm, 18.1 ± 2.38 for 1.6mm, 28.0 ± 2.46 for 1.8mm, and 39.2 ± 8.61 for 2.0mm, respectively. Dt significantly decreased as dentine became thinner towards the pulp chamber (P<0.001). CONCLUSIONS: The velocity of fluid flow increased both with increasing dentine depth or reduction of remaining dentine thickness.

Effect of sonic application mode on the resin-dentin bond strength and dentin permeability of self-etching systems.

PURPOSE: To compare manual and sonic adhesive application modes in terms of the permeability and microtensile bond strength of a self-etching adhesive applied in the one-step or two-step protocol. MATERIALS AND METHODS: Self-etching All Bond SE (Bisco) was applied as a one- or a two-step adhesive under manual or sonic vibration modes on flat occlusal dentin surfaces of 64 human molars. Half of the teeth were used to measure the hydraulic conductance of dentin at 200 cm H2O hydrostatic pressure for 5 min immediately after the adhesive application. In the other half, composite buildups (Opallis) were constructed incrementally to create resin-dentin sticks with a cross-sectional area of 0.8 mm² to be tested in tension (0.5 mm/min) immediately after restoration placement. Data were analyzed using a two-way ANOVA and Tukey's test (α = 0.05). RESULTS: The fluid conductance of dentin was significantly reduced by the sonic vibration mode for both adhesives, but no effect on the bond strength values was observed for either adhesive. CONCLUSION: The sonic application mode at an oscillating frequency of 170 Hz can reduce the fluid conductance of the one- and two-step All Bond SE adhesive when applied on dentin.

Dentine hypersensitivity.

Dentine hypersensitivity is a common oral pain condition affecting many individuals. The aetiology is multifactorial; however, over recent years the importance of erosion has become more evident. For dentine hypersensitivity to occur, the lesion must first be localised on the tooth surface and then initiated to exposed dentine tubules which are patent to the pulp. The short, sharp pain symptom is thought to be derived from the hydrodynamic pain theory and, although transient, is arresting, affecting quality of life. This episodic pain condition is likely to become a more frequent dental complaint in the future due to the increase in longevity of the dentition and the rise in tooth wear, particularly amongst young adults. Many efficacious treatment regimens are now available, in particular a number of over-the-counter home use products. The basic principles of treatment are altering fluid flow in the dentinal tubules with tubule occlusion or modifying or chemically blocking the pulpal nerve.

Development and validation of an in vitro model for measurements of cervical root dentine permeability.

OBJECTIVES: The aim of this series of studies was the development and validation of a new model for evaluation of dentinal hypersensitivity (DH) therapies. MATERIALS AND METHODS: Roots from extracted human teeth were sealed with a flowable composite. In the cervical area, a 3-mm-wide circular window was ground through the seal 1 mm deep into dentine. The pulp lumen was connected to a reservoir of artificial dentinal fluid (ADF) containing protein, mineral salts and methylene blue. At increased pulpal pressure, the ADF released through the said window was collected in containers each with 20 ml of physiologic saline for a consecutive series of 30-min intervals and ADF concentration (absorption) was determined photometrically. The model was verified by three experiments. In experiment 1, the lower limit of quantification (LLoQ, coefficient of variation = 20 % and difference of 5 standard deviations (SD) from blank) of ADF in physiologic saline was determined by measuring the absorption of 15 dilutions of ADF in physiologic saline (containing 0.625 ng to 12.5 µg methylene blue/ml) photometrically for ten times. In experiment 2, long-term linearity of ADF perfusion/outflow was investigated using 11 specimens. The ADF released through the window was collected in the said containers separately for each consecutive interval of 30 min for up to 240 min. Absorption was determined and analysed by linear regression over time. In experiment 3, perfusion before (2×) and after single treatment according to the following three groups was measured: BisGMA-based sealant (Seal&Protect®), an acidic fluoride solution (elmex fluid®) and control (no treatment). RESULTS: In experiment 1, the LLoQ was 0.005 µg methylene blue/ml. In experiment 2, permeability was different within the specimens and decreased highly linearly with time, allowing the prediction of future values. In experiment 3, Seal&Protect® completely occluded dentinal tubules. elmex fluid® increased tubular permeability by about 30 % compared to control. CONCLUSIONS: A model comprising the use of artificial dentinal fluid was developed and validated allowing screening of therapeutic agents for the treatment of DH through reliable measurement of permeability of cervical root dentine. CLINICAL RELEVANCE: The described in vitro model allows evaluation of potential agents for the treatment of DH at the clinically relevant cervical region of human teeth.

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.

Dentina / Dentin

Si bien la dentina y la pulpa tienen marcadas diferencias en su composición y estructura, ambas están tan íntimamente ligadas por su origen embriológico, que cualquier cosa que afecte a la dentina lo hará sobre la pulpa y viceversa. El ejemplo más claro en ese sentido está dado por el líquido intersticial. Este líquido, semejante al plasma pero con menos proteínas, constituye una continuidad entre ambos tejidos y sus efectos hidrodinámicos son muy importantes, tanto en los estados fisiológicos como en los patológicos

Dentine hypersensitivity--guidelines for the management of a common oral health problem.

UNLABELLED: Dentine hypersensitivity (DHS) remains a worldwide under-reported and under-managed problem, despite making some dental treatments more stressful than necessary and having a negative impact on the patient's quality of life. This article is designed to build dental professionals' confidence and remove any confusion regarding the diagnosis, prevention and treatment of sensitive teeth caused by dentine hypersensitivity in those patients known to be at risk. There is a need for simple guidelines, which can be readily applied in general practice. However, it is also obvious that one strategy cannot suit all patients. This review describes a DHS management scheme for dental professionals that is linked to management strategies targeted at three different groups of patient. These patient groups are: 1) patients with gingival recession; 2) treatment patients with toothwear lesions; and 3) patients with periodontal disease and those receiving periodontal treatment. The authors also acknowledge the role of industry as well as dental professionals in a continuing role in educating the public on the topic of sensitive teeth. It is therefore important that educational activities and materials for both dental professionals and consumers use common terminology in order to reduce the possibility for confusion. CLINICAL RELEVANCE: This review article provides practical, evidence-based guidance on the management of dentine hypersensitivity for dental professionals covering diagnosis, prevention and treatment. Sensitivity associated with gingival recession, toothwear and periodontal disease and periodontal treatment are specifically addressed in the article.

How can sensitive dentine become hypersensitive and can it be reversed?

This paper reviews a number of studies in oral biology and endodontics that deal with the reactivity of the pulpo-dentine complex in response to mechanical and immunological stimuli. It can be hypothesized that these reactions could also apply to changes in dentine sensitivity following periodontal procedures. Some of these changes involve neurogenic inflammation of the pulp under exposed open tubules; this increases the rate of outward fluid flow through the tubules, making the overlying exposed dentine more sensitive. Other changes may be due to inflammation-related nerve sprouting of pulpal nerves, which can lead to innervation of more tubules than normal. Changes may also involve upregulation of new, more sensitive ion channels in the membranes of these nerves. The goal of the paper is to increase awareness of the complex issues involved in dentine sensitivity, so that future investigators may develop agents or techniques to stimulate mechanisms that mitigate dentine sensitivity, or to block mechanisms that aggravate the condition, for therapeutic effect.

Cellular and molecular mechanisms of dental nociception.

Due, in part, to the unique structure of the tooth, dental pain is initiated via distinct mechanisms. Here we review recent advances in our understanding of inflammatory tooth pain and discuss 3 hypotheses proposed to explain dentinal hypersensitivity: The first hypothesis, supported by functional expression of temperature-sensitive transient receptor potential channels, emphasizes the direct transduction of noxious temperatures by dental primary afferent neurons. The second hypothesis, known as hydrodynamic theory, attributes dental pain to fluid movement within dentinal tubules, and we discuss several candidate cellular mechanical transducers for the detection of fluid movement. The third hypothesis focuses on the potential sensory function of odontoblasts in the detection of thermal or mechanical stimuli, and we discuss the accumulating evidence that supports their excitability. We also briefly update on a novel strategy for local nociceptive anesthesia via nociceptive transducer molecules in dental primary afferents with the potential to specifically silence pain fibers during dental treatment. Further understanding of the molecular mechanisms of dental pain would greatly enhance the development of therapeutics that target dental pain.

Physical and chemical characterization of the surface layers formed on dentin following treatment with an experimental anhydrous stannous fluoride dentifrice.

PURPOSE: To characterize, in vitro, the mode of action of stannous fluoride containing formulations in occluding dentin tubules, by means of high resolution microscopy techniques. METHODS: Focused ion beam scanning electron microscopy (FIB SEM) was used to site-specifically prepare cross sections for SEM and TEM imaging and analysis of dentin samples treated with either a stannous fluoride dispersion in glycerol or an experimental stannous fluoride dentifrice. RESULTS: An experimental stannous fluoride dentifrice formed a protective layer over the dentin surface and occluded dentin tubules. Additional supporting data derived from a stannous fluoride dispersion in glycerol suggest that stannous fluoride is a key component of this occluding system. Multiple SEM images obtained from sequential FIB cross-sections were reconstructed into 3-dimensional tomograms that showed a formed layer and tubule occlusion. Sections thinned by FIB techniques were observed by transmission electron microscopy (TEM) and related methods and showed that the coating, which was up to 3 microm-thick, consisted of a tin containing precipitate. Chemical analysis by energy dispersive x-ray spectroscopy (EDS) mapping that used scanning TEM (STEM) methods showed interdiffusion of tin up to 200 nm into the dentin structure.

The role of toothpaste in the aetiology and treatment of dentine hypersensitivity.

Dentine hypersensitivity (DH) is a common, painful dental condition with a multi-factorial aetiology. The hydrodynamic mechanism theory to explain dentine sensitivity also appears to fit DH: lesions exhibiting large numbers of open dentinal tubules at the surface and patent to the pulp. By definition, DH can only occur when dentine becomes exposed (lesion localisation) and tubules opened (lesion initiation), thus permitting increased fluid flow in tubules on stimulation. Erosion, particularly from dietary acids appears to play a dominant role in both processes. Toothbrushing with most toothpaste products alone cause clinically insignificant wear of enamel but are additive, even synergistic, to erosive enamel loss. Additionally, toothbrushing with toothpaste is implicated in 'healthy' gingival recession. Toothbrushing with most toothpastes removes the smear layer to expose tubules and again can exacerbate erosive loss of dentine. These findings thereby implicate toothbrushing with toothpaste in the aetiology of DH. Management of the condition should have secondary prevention at the core of treatment and therefore, must consider first and foremost the aetiology. Fluoride toothpaste at present appears to provide little primary or secondary preventive benefits to DH; additional ingredients can provide therapeutic benefits. Potassium-based products to block pulpal nerve response have caused much debate and are considered by many as unproven, which should not translate to ineffective. Several toothpaste technologies formulated to block tubules are from studies in vitro, in situ and controlled clinical trials considered proven for the treatment of DH.

Influence of different intrapulpal pressure simulation liquids on the microtensile bond strength of adhesive systems to dentin.

PURPOSE: To evaluate the effect of three different liquids used for intrapulpal pressure (IPP) simulation on the microtensile bond strength (µTBS) of three adhesive systems to dentin. MATERIALS AND METHODS: The occlusal surfaces of sound human molars were ground flat down to mid-dentin depth. The teeth were bonded under 15 mmHg simulated IPP using distilled water, phosphate buffered saline, or human plasma as a simulating liquid. Three adhesive systems were tested: a single-bottle etch-and-rinse adhesive (SingleBond, 3M ESPE), and two single-step self-etching adhesives (G-Bond, GC) and (iBond, Heraeus Kulzer). Resin composite (Tetric EvoCeram, Ivoclar Vivadent) buildups were made in 2 increments, each 2 mm in height. Specimens were stored in artificial saliva under 20 mmHg IPP at 37°C for 24 h prior to testing. µTBS (n = 15) was tested using a universal testing machine, and failure modes were determined. Data were statistically analyzed using ANOVA and Bonferroni post-hoc tests at p <= 0.05. RESULTS: With SingleBond adhesive, distilled water showed significantly higher µTBS compared to plasma and phosphate buffered saline. With G-Bond, no significant difference was found between distilled water and phosphate buffered saline, whereas plasma showed significantly lower µTBS values. In contrast, no significant difference was encountered between the three IPP liquids for iBond adhesive. Predominant modes of failure were adhesive and mixed. CONCLUSION: A difference in intrapulpal pressure simulating liquids influences the bonding of adhesives to dentin. Etch-and-rinse adhesives are more sensitive to intrapulpal simulating liquids than are self-etching adhesives. Adhesives containing protein-coagulating components perform better with plasma perfusion than those lacking such components.

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.

The effectiveness of current dentin desensitizing agents used to treat dental hypersensitivity: a systematic review.

OBJECTIVE: Dentin desensitizing agents are used in the treatment of dentin hypersensitivity, which is defined as a painful response in the exposed dentin to stimuli that are thermal, evaporative, tactile, osmotic, or chemical. A systematic review was conducted to analyze the clinical effectiveness of current desensitizer with at least 3 months of follow-up. METHOD AND MATERIALS: Eight electronic databases were searched: MedLine (PubMed), Embase, Lilacs, Ibecs, Web of Science, Scopus, Scielo, and The Cochrane Library. Only those clinical trials published from 2000 to 2012 were included. RESULTS: A total of 3,029 relevant records were identified. After title and abstract examination, 2,645 articles were excluded. A data extraction form was designed and completed by reviewers from the selected studies for a retrospective comparison. From the 99 studies retrieved for detailed review, only 17 had an evaluation time of at least 3-months follow-up and fulfilled the selection criteria. CONCLUSION: Cervitec Plus, SE Bond & Protect Liner F, laser, and iontophoresis have shown satisfactory posttreatment results between 3 and 6 months. However, additional clinical trials are warranted to better compare the different types of treatments and their effectiveness in the longer term.

The effect of dentinal fluid flow during loading in various directions--simulation of fluid-structure interaction.

OBJECTIVES: This study uses a fluid-structure interaction (FSI) simulation to evaluate the fluid flow in a dental intrapulpal chamber induced by the deformation of the tooth structure during loading in various directions. METHODS: The FSI is used for the biomechanics simulation of dental intrapulpal responses with the force loading gradually increasing from 0 to 100N at 0°, 30°, 45°, 60°, and 90° on the tooth surface in 1s, respectively. The effect of stress or deformation on tooth and fluid flow changes in the pulp chamber are evaluated. RESULTS: A horizontal loading force on a tooth may induce tooth structure deformation, which increases fluid flow velocity in the coronal pulp. Thus, horizontal loading on a tooth may easily induce tooth pain. CONCLUSION: This study suggests that experiments to investigate the relationship between loading in various directions and dental pain should avoid measuring the bulk pulpal fluid flow from radicular pulp, but rather should measure the dentinal fluid flow in the dentinal tubules or coronal pulp. The FSI analysis used here could provide a powerful tool for investigating problems with coupled solid and fluid structures in dental biomechanics.