Fluid flow through cat dentine in vivo

Simulated Hydrostatic Pulpal Pressure Effect on Microleakage-An Initial Study

PURPOSE

This study's purpose was to evaluate the effect of simulated in vitro hydrostatic pulpal pressure (HPP) on microleakage.

METHODS AND MATERIALS

Extracted third molars (n=12) were sectioned 5 mm below the cementoenamel junction, pulp tissue removed, and the sectioned crowns mounted on a Plexiglas plate penetrated by an 18-gauge stainless steel tube. The mounted specimen mesial surface received a 2×4×6 mm Class V preparation followed by restoration with a strongly acidic, one-step dental adhesive and a flowable microfilled resin, following all manufacturers' instructions. Restorations were finished to contour, and tubing was attached to a 20-cm elevated, 0.2% rhodamine G reservoir to the specimen steel tube for 48 hours. Specimens then received a nail polish coating to within 1 mm of the restoration margins and were placed in 2% methylene blue (MB) dye for 24 hours, followed by rinsing, embedding in epoxy resin, and sectioning into 1 mm slices using a diamond saw. Controls were intact molars (n=12) processed as above but without HPP. Specimen slices were evaluated using laser confocal microscopy with images exported to ImageJ software with microleakage assessed as the MB linear penetration as a percentage of the total interfacial wall length. Mean values were evaluated with the Kruskal Wallis/Dunn test at a 95% confidence level.

RESULTS

The control specimens demonstrated significantly greater (p<0.0001) MB penetration than experimental specimens with simulated HPP. Under this study's conditions, simulated HPP significantly decreased MB dye penetration.

CONCLUSION

Studies accomplished without simulated HPP may overestimate microleakage results.

A Correlation between Clinical Classification of Dental Pulp and Periapical Diseases with its Patho Physiology and Pain Pathway

Background

Dental pain due to pulpal involvement is difficult to diagnose due to the apparent inaccessibility of pulp to the clinical tests, indistinct symptoms, and referred toothache originating from the periodontal tissues. Though we have various clinical classification systems to categorize pulpal diseases, we are yet biased about the exact pathophysiology and pain pathway associated with it. Dental pulp has a complex physiology, and so is its pathophysiology.

Aims & objectives

To concisely reviews the basic understanding of the pathophysiology of pulp, pain pathway, and its correlation with the classification of various clinical conditions of pulpal inflammation and periapical diseases.

Methodology

Literature search on pulpal diseases and pathophysiology from the sources: MEDLINE, PubMed, Web of Science and Cochrane Databases dated from 1965 till December 2020 was carried on to collect 163 articles.

Results

Filtered search on the pathophysiology of pulp, pain pathway, and classification of various clinical conditions of pulpal inflammation resulted us to precise 36 articles required for our understanding and demystifying the correlation.

Conclusion

The emphasis should be laid on understanding the minute changes occurring inside the pulp in due course of inflammation to aid its diagnosis and a treatment plan accordingly.

How to cite this article

Samir PV, Mahapatra N, Dutta B, et al. A Correlation between Clinical Classification of Dental Pulp and Periapical Diseases with its Patho Physiology and Pain Pathway. Int J Clin Pediatr Dent 2023;16(4):639-644.

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.

ISP Good Clinical Practice Recommendations for the management of Dentin Hypersensitivity

Dentin hypersensitivity (DH) is a rising concern in clinical dentistry that causes pain and discomfort and negatively affects the quality of life of patients. Indian Society of Periodontology conducted a nationwide survey, involving 3000 dentists in December 2020, which revealed significant knowledge gaps regarding DH, viz., under-diagnosis, incorrect differential diagnosis, and treatment strategies/recommendations for the management of DH patients in daily clinical practice. The current paper has been envisioned and conceptualized to update the practicing Indian dentists regarding the so-called enigma of dentistry "Dentin Hypersensitivity," based on the best available contemporary evidence. An expert panel was constituted comprising 30 subject experts from across the country, which after extensive literature review and group discussions formulated these recommendations. The panel advocated routine screening of all dentate patients for exposed dentin areas and DH to avoid under-diagnosis of the condition and suggested an early preventive management. Consensus guidelines/recommendations for the use of desensitizing agents (DAs) at home, including the use of herbal agents, are also provided within the backdrop of the Indian context. The guidelines recommend that active management of DH shall be accomplished by a combination of at home and in-office therapies, starting with the simplest and cost-effective home use of desensitizing toothpastes. A diagnostic decision tree and a flowchart for application in daily practice are designed to manage the patients suffering from DH or presenting with exposed dentin areas in dentition. Various treatment methods to manage DH have been discussed in the paper, including the insights from previously published treatment guidelines. Further, a novel system of classification of DH patients based on specific case definitions has been developed for the first time. Explicit charts regarding the available treatment options and the chronology of institution of the agent, for the management in different case categories of DH, have been provided for quick reference. The management strategy takes into account a decision algorithm based on hierarchy of complexity of treatment options and intends to improve the quality of life of the patient by long-term maintenance with an innovatively defined triple C's or 3Cs approach.

The effect of fluoride iontophoresis on seal ability of self-etch adhesive in human dentin in vitro

Background

Fluoride iontophoresis (FI) is a non-invasive method for the transfer of fluoride ions under electrical pressure into dental hard tissue. This study aimed to determine the effect of FI on the seal ability of self-etch adhesive in human dentin using dentin permeability test and scanning electron microscopy (SEM).

Methods

The experiments were divided into 2 series: series 1 was performed on 28 extracted intact third molars and series 2 was performed on 28 extracted carious third molars (ICDAS 4 and 5). In each series, 20 teeth were used for dentin permeability test and 8 teeth were used for SEM study. For dentin permeability test, the specimens were divided into dentin without FI (control) and dentin with FI (experimental) subgroups. Hydraulic conductance (HD) of dentin was measured before and after adhesive treatment, and calculated for the percentage decrease of HD in each subgroup. Two-way ANOVA and Tukey test were used for statistical analysis. SEM study was used to assess the seal ability of self-etch adhesive and penetration of fluoride ions into dentinal tubules.

Results

HD after self-etch adhesive treatment reduced by 57.75 ± 17.99% in intact dentin with FI, 46.60 ± 17.03% in intact dentin without FI, 45.00 ± 15.30% in caries affected dentin without FI, and 37.28 ± 14.72% in caries affected dentin with FI. There was no significant difference in percentage decrease of HD between dentin without FI and dentin with FI (P = 0.742); meanwhile, intact dentin with FI had significant greater percentage decrease than caries affected dentin with FI (P < 0.05). SEM findings showed FI produced more particle formation and deeper precipitation in intact dentin than those in caries affected dentin.

Conclusions

FI did not affect the seal ability of self-etch adhesive in human dentin when compared to without FI. However, FI could augment the seal ability of the self-etch adhesive in intact dentin better than that in caries affected dentin.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02146-w.

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.

Influence of povidone-iodine on micro-tensile bonding strength to dentin under simulated pulpal pressure

Background

Previous studies had reported that bond strength deteriorate over time following the dentin surface pretreatment with chlorhexidine. Therefore, further investigations are needed to evaluate the effect of other materials such as povidone iodine.

The purpose of this study was to investigate the effects of 10% povidone-iodine pretreatment on the resin-dentin micro-tensile bond strength of a single bond adhesive system in permanent teeth over time, and compare it with 2% chlorhexidine.

Methods

Flat dentin surfaces were prepared in 63 extracted permanent teeth. Teeth were randomly assigned to a 10% povidone-iodine pretreatment, a 2% chlorhexidine pretreatment, or a control group. Composite resin blocks were built up over treated surfaces under pulp pressure simulation. The prepared specimens were assigned to three storage time, 24 h, 1 week, and 2 months. Samples were vertically sectioned to obtain specimens of 0.7 to 1.2 mm² cross-sectional area.

Results

No significant reduction of bond strength of povidone iodine group was found among the three storage times (p = 0.477). A significant reduction of bond strength for both chlorhexidine and control groups was found in the three storage times (p <  0.001).

Conclusion

Povidone iodine pretreatment of etched dentin was effective in reducing the loss of bond strength over time, while the chlorhexidine pretreatment and negative control showed significant deterioration in micro-tensile bond strength over time in permanent teeth.

Iontophoretic Drug Delivery in the Oral Cavity

Iontophoresis is a noninvasive method to enhance systemic and local drug delivery by the application of an electric field. For systemic drug delivery in the oral cavity, iontophoresis was studied primarily for transbuccal delivery. Significant enhancement of drug delivery was observed in buccal iontophoresis compared to passive transport for different drugs. For local drug delivery in the oral cavity, iontophoresis could enhance drug penetration into the enamel, dentin, and other oral tissues for the treatment of oral diseases. Iontophoresis was evaluated in dentistry such as to produce local anesthesia and treat tooth decalcification and hypersensitivity, but this technology has not been fully utilized. The most common drugs in these evaluations were fluoride and lidocaine. In general, there is limited knowledge of the mechanisms of iontophoresis in the oral tissues. In vivo animal and human studies have suggested that iontophoresis is safe in the oral cavity under the conditions investigated. The present review covers the topics of iontophoretic drug delivery in the oral cavity for both systemic and local treatments. The anatomy and diseases in the oral cavity for iontophoretic drug delivery are also briefly reviewed, and the challenges for this drug delivery method are discussed.

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 Marginal Leakage and Shear Bond Strength of Bonded Restorations in Primary Teeth after Caries Removal by Conventional and Chemomechanical Techniques

Background/Purpose. To evaluate and compare the marginal leakage and shear bond strength between conventional and Papacarie techniques of caries removal in primary molars. Materials and Methods. Sixty freshly extracted human carious primary molars were randomly divided into two groups: group I—caries removal by conventional method and group II—caries removal using Papacarie. After bonded restorations, both groups were further randomly subdivided into four subgroups for marginal leakage and shear bond strength evaluation. Results. Papacarie treated teeth (46.70%) showed less marginal leakage when compared to conventionally treated teeth (86.70%) for caries removal. The mean shear bond strength was found more in Papacarie treated teeth (12.91 MPa) than in those treated conventionally (9.64 MPa) for caries removal. Conclusion. Papacarie showed less marginal leakage and more shear bond strength when compared to those treated conventionally for caries removal.

Scaffold-free microtissues: differences from monolayer cultures and their potential in bone tissue engineering

OBJECTIVES

Cell-based therapies for bone augmentation after tooth loss and for the treatment of periodontal defects improve healing defects. Usually, osteogenic cells or stem cells are cultivated in 2D primary cultures, before they are combined with scaffold materials, even though this means a loss of the endogenous 3D microenvironment for the cells. Moreover, the use of single-cell suspensions for the inoculation of scaffolds or for the direct application into an area of interest has the disadvantages of low initial cell numbers and susceptibility to unwanted cellular distribution, respectively.

MATERIALS AND METHODS

We addressed the question whether an alternative to monolayer cultures, namely 3D microtissues, has the potential to improve osteogenic tissue engineering and its clinical outcome.

RESULTS

By contrast, to monolayer cultures, osteogenic differentiation of 3D microtissues is enhanced by mimicking in vivo conditions. It seems that the osteogenic differentiation in microtissues is enhanced by strong integrin-extracellular matrix interaction and by stronger autocrine BMP2 signaling. Moreover, microtissues are less prone to wash out by body fluids and allow the precise administration of large cell numbers.

CONCLUSION

Microtissue cultures have closer characteristics with cells in vivo and their enhanced osteogenic differentiation makes scaffold-free microtissues a promising concept in osteogenic tissue engineering.

CLINICAL RELEVANCE

Microtissues are particularly suitable for tissue engineering because they improve seeding efficiency of biomaterials by increasing the cell load of a scaffold. This results in accelerated osteogenic tissue formation and could contribute to earlier implant stability in mandibular bone augmentation.

Scaffold-free microtissues: differences from monolayer cultures and their potential in bone tissue engineering

Objectives

The paper’s aim is to review dentin hypersensitivity (DHS), discussing pain mechanisms and aetiology.

Materials and methods

Literature was reviewed using search engines with MESH terms, DH pain mechanisms and aetiology (including abrasion, erosion and periodontal disease).

Results

The many hypotheses proposed for DHS attest to our lack of knowledge in understanding neurophysiologic mechanisms, the most widely accepted being the hydrodynamic theory. Dentin tubules must be patent from the oral environment to the pulp. Dentin exposure, usually at the cervical margin, is due to a variety of processes involving gingival recession or loss of enamel, predisposing factors being periodontal disease and treatment, limited alveolar bone, thin biotype, erosion and abrasion.

Conclusions

The current pain mechanism of DHS is thought to be the hydrodynamic theory. The initiation and progression of DHS are influenced by characteristics of the teeth and periodontium as well as the oral environment and external influences. Risk factors are numerous often acting synergistically and always influenced by individual susceptibility.

Clinical relevance

Whilst the pain mechanism of DHS is not well understood, clinicians need to be mindful of the aetiology and risk factors in order to manage patients’ pain and expectations and prevent further dentin exposure with subsequent sensitivity.

Influence of femtosecond laser treatment on shear bond strength of composite resin bonding to human dentin under simulated pulpal pressure

This in vitro study evaluated the influence of femtosecond laser (fs-laser)-generated patterns on shear bond strength (SBS) of composite resin bonded to human dentin under simulated pulpal pressure. Laser treatment was used to produce two different patterns on dentin surfaces. Three test groups and a control group without laser treatment under pulpal pressure were investigated. Dentin discs of 800 nm thickness were cut from 60 extracted caries-free human molars. Using a perfusion machine, the discs were exposed to Ringer solution on their basal surfaces. Clearfil SE Bond/Herculite XRV system was used. The samples were stored in distilled water and thermocycled. Bonding failures caused by a test set-up to challenge SBS were analyzed by scanning electron microscope (SEM). An 80 μm-sized cube-shaped pattern caused more cohesive failures in dentin or resin compared with the 160 μm-sized cube-shaped pattern. Weibull statistics demonstrated a significant difference between the two laser patterns, but only the test group with small-sized laser pattern was significantly different from the control group. The Weibull moduli ranged from 4.3 to 9.6 (control group). The 160 μm-sized pattern enhanced the bonding quality and avoided dentin weakening. It was concluded that fs-laser treatment in a 160 μm-sized cube-shaped pattern enabled a simplified bonding procedure by dispensing the primer without affecting SBS, compared with the control group.

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.

Real-time measurement of dentinal fluid flow during amalgam and composite restoration

OBJECTIVES

This study examined changes in the dentinal fluid flow (DFF) during restorative procedures and compared permeability after restoration among restorative materials and adhesives.

METHODS

A class 1 cavity was prepared and restored with either amalgam (Bestaloy), or composite (Z-250) with one of two etch-and-rinse adhesives (Scotchbond MultiPurpose: MP and Single Bond 2: SB) or one of two self-etch adhesives (Clearfil SE Bond: CE and Easy Bond: EB) on an extracted human third molar which was connected to a sub-nanoliter fluid flow measuring device (NFMD) under 20 cm water pressure. DFF was measured from the intact tooth state through the restoration procedures to 30 min after restoration, and re-measured at 3 and 7 days post-restoration.

RESULTS

Inward flow during cavity preparation was followed by outward flow after preparation. In amalgam restoration, the outward flow changed into an inward flow during amalgam filling, which was followed by a slight outward flow after finishing. In composite restoration, MP and SB showed an inward flow and outward flow for the rinsing and drying steps, respectively. Application of a hydrophobic bonding resin in the MP and CE systems caused a decrease in the flow rate. Air-drying of solvent for the CE and EB systems caused a sudden outward flow, whereas light-curing of the adhesive and composite caused an abrupt inward flow.

CONCLUSIONS

Each restorative step clearly changed the direction and the rate of the DFF during restoration, which could be well identified with NFMD.

Effect of placement agitation and drying time on dentin shear bond strength: an in vivo study

The current study measured the bond strength of a self-etch system to dentin with and without agitation and with varying drying times of primer in vital dentin. The null hypotheses tested were that primer agitation and primer drying time did not affect the dentin shear bond strength. Sixty human maxillary and mandibular premolars scheduled to be extracted for orthodontic reasons were selected. The adhesive/resin combination used was Clearfil SE (Kuraray, Osaka, Japan)/TPH Spectrum (Dentsply DeTrey, Konstanz, Germany). The occlusal surfaces of the teeth were flattened using straight fissure diamond abrasive points ISO-012. Samples were divided into six groups of 10 teeth each. Primer was applied following the manufacturer's instructions with and without agitation followed by air-drying time of 0 (without air drying), five and 10 seconds. Clearfil SE Bond was applied and cured for 10 seconds. TPH Spectrum composite, shade A2 (Dentsply DeTrey), was placed over cured adhesive and was cured for 40 seconds. The teeth were restored to their original anatomy. The teeth were extracted after one week and the samples were kept in distilled water until testing at room temperature. The samples were tested in shear at a 1 mm/minute crosshead speed using an LR100 Universal Testing Machine. The data was analyzed using ANOVA and Tukey post-hoc tests (p < 0.05). Varying the drying time of the primer from zero (0) to 10 seconds did not significantly affect the bond strength values in vivo. At five seconds drying time, agitation significantly improved the shear bond strength to dentin. Agitation showed no effect when primer was not dried or it was dried for 10 seconds.

Morphological characterization and permeability of attrited human dentine

OBJECTIVE

Dentine is a vital tissue that can be changed by physiological and pathological condition. The purpose of this study was to clarify the morphology and permeability of dentine that changed by wearing process.

METHODS

Twenty extracted human molars with enamel attrition and dentine was exposed and 20 intact human extracted third molars that had not reached occlusion were used. Ten teeth per each group were observed under light microscope (LM) and transmission electron microscope (TEM). Remaining 10 teeth per each group were subjected for evaluation of dentine permeability.

RESULTS

Under LM, the transparent dentine and reactionary dentine were found in the attrition group but were not found in the group unaffected by attrition. When the transparent dentine were examined under the TEM, it was found that dentinal tubules were partially or completely occluded by growth of peritubular dentine or by precipitation of needle-like or rhombohedral crystals in transparent dentine. In reactionary dentine, tubular dentine structures that were comparable to those in secondary physiologic dentine were observed whereas atubular dentine demonstrated occlusion of tubules by high mineral substances or by peritubular dentine under the TEM. Permeability of dentine from worn teeth was less than those from unoccluded teeth significantly.

CONCLUSION

Change in dentine by wear resulted in the formation of reactionary dentine and transparent dentine that illustrated various types and degrees of tubular occlusion. These decrease the dentine permeability.

Effects of potassium ions on dentine sensitivity in man

OBJECTIVE

To determine the effect of applying 500 mmol/l KCl at a pressure of 150 mm Hg above atmospheric to exposed dentine on pain sensation evoked by probing and air blast stimuli in human subjects.

DESIGN

The experiments were carried out on 14 pairs of premolars in 14 human subjects (aged 17-30 years). Dentine was exposed at the tip of the buccal cusp, etched with acid and covered with saline, then 500 mmol/l KCl in Ringer's was applied at a pressure of 150 mm Hg for 4 min. Mechanical probing and air-drying stimuli were performed before and 2, 10, 20, 30 min after applying the KCl solution. The subject indicated the intensity of any pain produced on a visual analogue scale (VAS). Pulpal blood flow was recorded with a laser Doppler flow meter. Exactly the same procedure was carried out on the contralateral tooth except that 500 mmol/l NaCl in Ringer's was used in place of the KCl solution.

RESULTS

The pain responses to mechanical probing and air blast stimuli were significantly reduced during the first 10 min after applying the KCl but not the NaCl solution. Pulpal blood flow did not change significantly after either treatment.

CONCLUSION

Potassium ions, when applied to exposed dentine at a pressure of 150 mm Hg above atmospheric, produced temporary block of impulse conduction in sensory nerve endings in the dentine or pulp.

The relationship between the discharge of intradental nerves and the rate of fluid flow through dentine in the cat

OBJECTIVE

To investigate further the relationship between dentinal tubular flow and the discharge evoked in intradental nerves.

DESIGN

In anaesthetised cats, recordings were made of fluid flow through dentine during the application of hydrostatic pressure stimuli of 5 s duration in the range +500 to -500 mm Hg to exposed dentine and of the nerve impulses evoked by these stimuli. Single unit recordings were obtained from filaments dissected from the inferior alveolar nerve and multi-unit recordings, from the exposed dentine.

RESULTS

Of 20 single units tested, 10 (conduction velocities: 2.4-36.2 m s(-1)) responded to negative pressures and four of these, also to positive pressures. None responded to only positive pressures. The pressure thresholds of the units (single and multi-unit preparations) ranged from -100 to -500 and +100 to +500. In terms of flow (measured 1 s after the start of a stimulus) the thresholds ranged from 0.4 to 2.2 nl s(-1) mm(-2) exposed dentine with outward flow, and 0.4-2.1 nl s(-1) mm(-2) with inward flow. The outward flow per tubule at the threshold of the most sensitive units was estimated to be 21 fl s(-1) and the corresponding mean velocity of the contents of the dentinal tubules at their pulpal ends, 27 microm s(-1). Although the thresholds to outward and inward flow were similar, with outward flow the mean discharge rate increased with stimulus intensity; whereas with inward flow few impulses were evoked and the number was little affected by the stimulus intensity.

CONCLUSION

The transduction mechanism that generates impulses in hydrodynamic intradental afferents is much more responsive to outward than inward flow through the dentinal tubules, although the thresholds in both directions are similar.

An overview of the dental pulp: its functions and responses to injury

The dental pulp is a unique tissue and its importance in the long-term prognosis of the tooth is often ignored by clinicians. It is unique in that it resides in a rigid chamber which provides strong mechanical support and protection from the microbial rich oral environment. If this rigid shell loses its structural integrity, the pulp is under the threat of the adverse stimuli from the mouth, such as caries, cracks, fractures and open restoration margins, all of which provide pathways for micro-organisms and their toxins to enter the pulp. The pulp initially responds to irritation by becoming inflamed and, if left untreated, this will progress to pulp necrosis and infection. The inflammation will also spread to the surrounding alveolar bone and cause periapical pathosis. The magnitude of pulp-related problems should not be underestimated since their most serious consequence is oral sepsis, which can be life threatening, and hence correct diagnosis and management are essential. Clinicians must have a thorough understanding of the physiological and pathological features of the dental pulp as well as the biological consequences of treatment interventions.

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

OBJECTIVE

To determine the relationship between pain intensity and the rate of fluid flow through dentine in human subjects.

DESIGN

The experiments were carried out on 16 premolars in 13 human subjects (aged 15-25 years). Dentine was exposed at the tip of the buccal cusp, etched with acid and covered with saline. A series of 5 s hydrostatic pressure stimuli between 400 mmHg above and 400 mmHg below atmospheric were applied to the dentine, in steps of 50 mmHg. The subject indicated the intensity of any pain produced on a visual analogue scale (VAS). The fluid flow through dentine during application of the same stimuli was measured in vitro within 3 h after tooth extraction.

RESULTS

The median pain threshold with negative (subatmospheric) stimuli was -125 mmHg and, with positive pressure stimuli, 200 mmHg, which corresponded to dentinal fluid flow rates of 3.29 nL/(s mm(2)) exposed dentine and 5.75 nL/(s mm(2)), respectively. Both the median pressure and the mean rate of flow at threshold with negative pressures were significantly lower than with positive pressures. The curves relating VAS score to stimulus intensity were similar with both negative and positive pressures.

CONCLUSION

The sensory transduction mechanism for pain in human teeth is more sensitive to outward than inward flow through dentinal tubules. The difference in sensitivity was however much less than that of the hydrodynamic receptors in the cat, which respond very much more strongly to negative than positive pressure stimuli.

Sensory transduction mechanisms responsible for pain caused by cold stimulation of dentine in man

OBJECTIVE

To determine the effects on the sensitivity of exposed dentine to cold that are produced when dentine is etched to remove the smear layer and when the tubules are blocked again with calcium oxalate. Separate in vitro observations were made on the effects of these procedures on fluid flow through the dentine.

DESIGN

The experiments were carried out on 24 premolars in 17 subjects. Dentine was exposed at the tip of the buccal cusp and cold stimuli were applied by placing the tip of an ice stick on the cavity floor for 5s under the following conditions: before etching the dentine, after etching, and after oxalate treatment. The subject indicated the intensity of any pain produced on a visual analogue scale (VAS). Fluid flow through the dentine was recorded under similar conditions in eight of the teeth in vitro.

RESULTS

The mean VAS score produced by the ice before etching was 21.3+/-19.5mm (S.D.). This increased significantly to 85.4+/-15.6mm after etching (P<0.01). After oxalate treatment, it decreased significantly to 8.5+/-13.3mm. The corresponding mean rates of fluid flow through dentine were 2.15+/-1.02, 1.55+/-0.84, and 2.29+/-1.28nL/smm(2) exposed dentine, respectively. The mean after etching was significantly less than the other two values (P<0.05).

CONCLUSION

If the pain was due to hydrodynamic receptors, their sensitivity to dentinal fluid flow changed when the tubules were opened or closed. Alternatively the pain was produced by receptors sensitive to some other change produced by the cold stimuli, such as specific cold receptors.

An investigation of thermal stimulation in intact teeth

OBJECTIVES

To investigate the response of extracted intact teeth to thermal stimulation in terms of fluid movement, in relation to temperature change within tooth structure.

METHODS

Dentinal fluid movement was measured in response to thermal stimuli applied to enamel. Freshly extracted teeth with intact crowns were investigated for the effects of thermal stimulation; namely, hot water (80 degrees C), iced water (2 degrees C) and carbon dioxide dry ice (-72 degrees C) for 5s application. Two capillary-based methods were used to measure fluid flow. To measure temperature changes at the dentino-enamel junction (DEJ) and pulpal wall in response to the same stimuli, fine J type thermocouples were used.

RESULTS

Thermal stimuli caused fluid movement, which occurred before the temperature changed at the pulp wall. Sealing the dentinal tubules resulted in a delayed response time. In general, fluid movement occurred coincident with the temperature change detected at the DEJ. However, many teeth showed a "bidirectional" response to thermal stimulation. The initial fluid movement in the bidirectional response was detected before the earliest temperature change observed at the DEJ, and was in the opposite direction to the main fluid movement.

CONCLUSION

Our results imply that thermal contraction and expansion of dentinal fluid may not be the complete explanation for dentinal fluid movement in intact teeth. Enamel may serve not only as a temperature transfer medium but may also expand or contract when subjected to thermal stimulation.

Pressure transmission across dentine in response to an external pressure: A laboratory study

PURPOSE

To determine whether transducers could provide a convenient method of measuring dentine permeability and to investigate the effects of removal of pulp tissue and perfusion time on the pressure increase across human dentine after low-pressure perfusion.

METHOD

Human premolar teeth that had been stored for 1-2 months were prepared for full crown preparations. The pulp tissue was removed from half the samples and all the coronal segments perfused with saline at 1.3kPa for varying times. An external pressure was then applied and the response within the pulp chambers recorded with transducers.

RESULTS

Extirpation of pulp tissue reduced the rate of rise of pressure inside the pulp chamber by approximately 50%. Perfusion at 1.3kPa for up to 1h had no effect on pressure rise, but 6h of perfusion produced a very significant increase.

CONCLUSION

Transducers can provide a relatively simple, convenient and clinically relevant measurement of dentine permeability. For stored coronal segments that have been perfused at physiological pressures, extirpation of pulp tissue and perfusion time have significant effects on pressure transmission across dentine.

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.

Outward fluid flow reduces inward diffusion of bacterial lipopolysaccharide across intact and demineralised dentine

OBJECTIVE

To examine the ability of outward fluid flow (OF) on resisting the inward diffusion of bacterial lipopolysaccharide (LPS) across the demineralised dentine (DD) in comparison with that across the intact dentine (ID).

DESIGN

Twenty ID discs were prepared from freshly extracted human third molars. After etching both dentine surfaces, hydraulic conductance (L(p)) of the dentine was measured. Ten dentine discs were then completely demineralised using 10% EDTA, and L(p) was re-measured. The diffusion of LPS through ID and DD was measured against the OF and compared to the non-outward flow (NF) (n = 5 for each group) at 0, 1, 4 and 8h. Longitudinal sections of ID and DD surfaces were observed under a scanning electron microscope (SEM).

RESULTS

The L(p) of DD was significantly higher than that of ID (independent t-test, p < 0.001). The application of OF and demineralisation significantly affected LPS diffusion (two-way ANOVA, p < 0.05). In addition, the effect of OF depended on dentine demineralisation. SEM images of ID showed intact dentinal tubules, whereas those of DD showed expanded collagen fibres and enlarged dentinal tubules.

CONCLUSIONS

The inward diffusion of LPS across DD differed from that of ID and the OF affected the inward diffusion of LPS. In the presence of the OF, the inward diffusion of LPS was reduced to near zero in both ID and DD. Nevertheless, when compared to that in the ID group, the OF produced the slightly greater effect to resist the inward LPS diffusion in the DD group.

The effects of phosphoric acid, sodium hypochlorite, ferric oxalate and Scotchbond Multipurpose on the rate of pressure change across dentine: a laboratory study

The aim of this study was to investigate the consequences of dentine treatment on dentine permeability of crown preparations treated with phosphoric acid, sodium hypochlorite (NaOCl), and then ferric oxalate (Sensodyne sealant) or bis-phenol-A-diglycidyldimethacrylate (BIS-GMA) and hydroxyethylmethacrylate (HEMA) resin combination (Scotchbond Multipurpose). Thirty human premolars received full crown preparations (stage A), were then acid etched (stage B) and subsequently the pulp chamber flushed with NaOCl (stage C). They were then randomly assigned to two groups: group 1 was treated with Scotchbond Multipurpose and group 2 with 6% ferric oxalate (Sensodyne sealant) (stage D). Both groups were acid etched a second time (stage E) as the final step in the sequence. The rise in pressure in the pulp chamber because of the transmission of saline from the pressure chamber through cut dentine was recorded by a pressure transducer after each of the stages described (A to E). The mean rate of pressure change across dentine (Pa s(-1)) for each measurement point (A to E) (n = 30) were A = 2.3; B = 9.8; C = 16; D = 2.1; E = 3.1. Acid etching and NaOCl were both effective in producing significant increases in the rate of pressure change across dentine (P < 0.05). Sensodyne sealant and Scotchbond Multipurpose are both effective dentine sealants and there is no significant difference (P > 0.05) in their abilities in sealing dentine. Acid etching-sealed dentine produced a significant increase in the rate of pressure change across dentine (P < 0.05). The sealing of dentine appears to be a sensible consideration following crown preparations on vital teeth.

The use of the replica technique to record fluid emerging from exposed dentine

The effect of pulpal cavity pressure on structures present on etched and unetched dentine was determined in 24 human premolars in vitro. The dentine was exposed in vivo. After extraction, the pulp was removed and the crown stored in 2.5 N sodium hydroxide for 3 days to remove the odontoblasts. The pulp cavity was filled with Ringer's solution at atmospheric pressure, +30 or -5 mmHg. After 30s-5 min a silicone-rubber impression was taken of the cavity floor and a resin cast prepared and examined in a SEM. The replicas reproduced the dentine surface accurately when there was no outward flow through dentine. With a pressure of + 30 mmHg in the pulp cavity, but not at the lower pressures, droplets were present on unetched dentine after 30s. Droplets accumulated less rapidly on etched dentine, indicating that it may act as a sponge.