Fluid flow through cat dentine in vivo

Facilitation of iontophoretic drug delivery through intact and caries-affected dentine

AIM

To investigate the facilitative role of iontophoresis in drug delivery through intact and caries-affected dentine into the pulp.

METHODOLOGY

Forty-eight intact dentine or caries-affected dentine discs were prepared from freshly extracted human third molars. The hydraulic conductance was measured before and after the experiments. Drug diffusion with and without iontophoresis (0.05 mA, 10 min) was evaluated using a split-chamber device. The enamel side chamber was filled with metronidazole (MN), sodium salicylate (SS) or naproxen sodium (NA), while the pulpal side was circulated with phosphate buffered saline (PBS) and pressurized (15 cmH2O). Samples were collected after 1 h. Drug concentrations of the pulpal side solution were determined using a spectrophotometer. Then, electrical impedance of each dentine disc was measured. Finally, the dentine disc surfaces were observed by scanning electron microscopy.

RESULTS

Drug diffusion was significantly influenced by iontophoresis, caries-induced changes in dentine and the drugs used (three-way anova, P < 0.05). The diffusion of all the drugs through caries-affected dentine was significantly less than that through intact dentine (independent t-test, P < 0.05). Also, iontophoresis facilitated the diffusion of all the drugs through intact and caries-affected dentine. The drug diffusion of SS was significantly higher than MN and NA (one-way anova, P < 0.05), independent of iontophoresis.

CONCLUSIONS

Presence of dental caries may inhibit drug diffusion through dentine into the pulp. However, iontophoresis could enhance the delivery of ionized drugs through both intact and caries-affected dentine.

Patterns of fluoro-gold entry into rat molar enamel, dentin, and pulp

Permeabilities of enamel and dentin are not fully understood despite their importance for caries, restorative materials, and pulp-dentin-enamel interactions. We have found that Fluoro-Gold is useful for examining tooth permeability, and we designed studies to test the effects of aging, injury, neural function, and dentinal repair on its influx into vital rat teeth. We used fluorescence microscopy and immunocytochemistry to show that Fluoro-Gold rapidly penetrates enamel, the dentin-enamel junction, and outer dentinal acellular tubules, and then concentrates in odontoblasts, where it remains for weeks. As predicted, influx was greatest in immature teeth, and formation of reparative dentin impeded it. We expected that denervation would disrupt influx, because of neural regulation of dentinal fluid movement, but it did not. Damage to odontoblasts under injured dentin caused increased influx and efflux of Fluoro-Gold. Analysis of our data suggests that permeabilities of enamel and dentin to Fluoro-Gold are age-related, inter-dependent, and regulated by odontoblasts.

In vivo influence of residual moisture on microtensile bond strengths of one-bottle adhesives

PURPOSE

This study evaluated the microtensile bond strengths of three dentin adhesives applied on clinically moist dentin or on dentin that was dried with air for 5 seconds. The null hypothesis to test was that the level of residual moisture does not influence bond strengths when restorations are placed in vivo.

MATERIALS AND METHODS

Twenty-four premolars scheduled to be extracted for orthodontic reasons from patients between the ages of 15 and 23 years were restored with one of the following adhesive systems followed by a mini hybrid composite resin: Excite (Ivoclar/Vivadent), an ethanol-based dentin adhesive; Prime & Bond NT (Dentsply/Caulk), an acetone-based dentin adhesive; and Single Bond (3M ESPE), an ethanol and water-based dentin adhesive. After extraction, the specimens were sectioned with a slow-speed diamond saw in two perpendicular directions to obtain sticks with a cross-section of 0.7 +/- 0.2 mm2. The specimens were attached to a Geraldeli device and fractured using a universal testing machine at a crosshead speed of 1 mm per minute.

RESULTS

For each dentin adhesive, there were no statistical differences between means for dry dentin versus moist dentin. Single Bond and Prime & Bond NT ranked in the same statistical subset regardless of the moisture condition of the substrate. Both Excite, dry, and Excite, moist, resulted in statistically lower bond strengths than Single Bond, moist, but similar to those of Single Bond, dry, Prime & Bond NT, moist, and Prime & Bond NT, dry.

CLINICAL SIGNIFICANCE

In this study, the level of residual moisture did not influence microtensile bond strengths. Clinically, the degree of moisture left on the dentin surface upon rinsing off the etching gel may not be as relevant as previously reported in laboratory studies.

The effects of dentin permeability on restorative dentistry

The permeability properties of dentin determine its sensitivity and the degree of pulpal response to restorative procedure materials and microleakage. Most pulpal reactions are due to bacteria or bacterial products that permeate across dentin. These reactions can be prevented if dentin is sealed with resins as soon as it is exposed. In the future, restorative dentists may employ topical application of biologic growth factors to permeate across dentin to modify the formation of reactionary or reparative dentin, thereby lowering dentin permeability and protecting the pulp.

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

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

Chemical and topographical analyses of dentine surfaces after Carisolv treatment

OBJECTIVES

The aim of this study was to characterise the surface chemistry of cavities after chemomechanical caries excavation, and also to measure the surface topography after caries removal with Carisolv or burs, followed by acid etching.

METHODS

Fourier transform (FT)-Raman spectroscopy was used to study the relative amounts of organic material and minerals of sound enamel, dentine, and cavities, after caries excavation. Fourier transform infrared spectroscopy (FTIR) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were used for detection of Carisolv substances (i.e. mainly sodium hypochlorite, amino acids, and the gelling agent carboxymethyl cellulose). In total, 19 carious and 11 sound extracted teeth were used for the chemical analyses. Topographic examination of 30 carious extracted teeth was performed with a contact profilometer.

RESULTS

The relative amounts of organic material and minerals did not significantly differ between sound dentine and the cavities after caries removal with burs or Carisolv. The FTIR analyses indicated extremely small amounts of Carisolv substances at the cavity surface, but the LA-ICP-MS analyses did not confirm those findings. Furthermore, the topographical parameters did not significantly differ between etched cavities after caries removal using burs or Carisolv.

CONCLUSIONS

The chemical and topographical analyses in the present study imply that any differences between the cavities after caries excavation with burs or with Carisolv are insignificant.

Effect of dietary carbamyl phosphate on dentine apposition in rat molars

In rats, sucrose increases dental caries and impairs odontoblastic function by reducing dentine apposition during primary dentinogenesis. A high-sucrose diet also affects negatively a pulp or dentine function that appears to regulate solute or fluid movement within rat dentinal tissue. In earlier work it was found that carbamyl phosphate could significantly reverse sucrose-induced cariogenesis and also stimulate sucrose-depressed movement of dentinal fluid through a mechanism involving parotid function(s). In the current study, the possibility that carbamyl phosphate could overcome the sucrose-induced reduction in dentine apposition was examined. Weanling rats were fed a high-sucrose diet supplemented or not with carbamyl phosphate for 5 weeks. Dentine apposition was measured planimetrically in sagittal sections of the molars. The effect of carbamyl phosphate was similarly tested in parotidectomized animals. Carbamyl phosphate significantly reduced the deleterious effect of sucrose on dentine apposition by 58% in the first molars. However, the reduction in dentine apposition that followed parotidectomy was not altered by carbamyl phosphate supplementation. The possibility that the beneficial effect of carbamyl phosphate on dentinogenesis involves a parotid function is entertained.

Comparison of the in vitro permeability of human dentine according to the dentinal region and the composition of the simulated dentinal fluid

OBJECTIVE

To compare the permeability of the occlusal and the cervical dentinal regions within the same tooth, which represent the bottom of Class I and V cavities, respectively, with two different compositions of perfusion fluid, in vitro.

METHODS

An occlusal and a buccal disc were cut from each extracted third molar at a level close to the pulp chamber. The convective permeability of the discs was measured in a fluid transport model using de-ionised water or 1:3 diluted bovine serum and the hydraulic conductance was determined.

RESULTS

The mean hydraulic conductance values of the occlusal and the buccal cervical human dentine to water were 0.069 and 0.047 microl min(-1) cm(-2) cm H(2)O(-1), respectively. When diluted bovine serum was used, the corresponding values were 0.036 and 0.012 microl min(-1) cm(-2) cm H(2)O(-1), respectively. Statistical analysis revealed no significant difference between the permeability of these two regions. The composition of the perfusion fluid significantly influenced the permeability of dentine.

CONCLUSIONS

The occlusal and the buccal cervical regions of human dentine have similar permeability characteristics in vitro. There is a strong reverse correlation between the viscosity of the perfusion fluid and the perfusion through the dentine.

Comparative investigations of the desensitising efficacy of a new dentifrice

OBJECTIVES

In two clinical trials of 8 weeks duration, the ability of a new dentifrice, containing potassium nitrate, stannous fluoride and sodium fluoride to reduce dentine hypersensitivity was compared with either a non-desensitising fluoride dentifrice or a commercially available desensitising dentifrice (Sensodyne F) to reduce dentine hypersensitivity.

METHOD

In both studies, the participants had to have at least two sensitive root surfaces. Subjects were stratified by baseline tactile and air blast sensitivity scores and the number of sensitive teeth and randomly allocated to 2 balanced groups. In the first study (N=81) the new dentifrice was compared with a fluoride dentifrice and in the second study (N=105) with Sensodyne F. Participants were requested to brush with their assigned dentifrice twice a day for one minute. At 4 and 8 weeks the sensitive teeth were again examined and their tactile and air blast sensitivity scores recorded.

RESULTS

In study 1, the group using the new dentifrice tolerated greater pressure after 4 (34.9 g) and 8 weeks (38.4 g) than the group using the fluoride dentifrice (22.9 g and 19.0 g, respectively). These differences were statistically significant (p<0.001). At 4 and 8 weeks, the mean air blast scores for the group using the new dentifrice (1.39 and 0.83) were lower than for the group using fluoride dentifrice (1.78 and 1.76) and were significantly different at 8 weeks (p<0.001). In study 2 the group using the new dentifrice tolerated greater pressure after 4 (40.5 g) and 8 weeks (43.7 g) than the group using Sensodyne F (27.8 g and 33.2 g, respectively). These differences were statistically significant (p<0.001). At 4 and 8 weeks, the mean air blast scores for the group using the new dentifrice (1.10 and 0.67) were significantly lower than the group using Sensodyne F (1.90 and 1.57) (p<0.001).

CONCLUSIONS

These studies demonstrate that the new dentifrice, containing potassium nitrate, stannous fluoride and sodium fluoride is significantly better at reducing dentine hypersensitivity than both the dentifrice containing sodium fluoride and the one containing potassium chloride, triclosan and sodium fluoride (Sensodyne F).

The in vitro cytotoxicity of eluates from dentin bonding resins and their effect on tyrosine phosphorylation of L929 cells

OBJECTIVES

The aim of this study was to examine the relationship between the monomers eluted from dentin-bonding systems and their cytotoxicities, and to investigate the biochemical effect of the monomers on tyrosine phosphorylation, especially relating to the cell growth activity, of L929 cells in vitro.

METHODS

The primers, uncured or cured adhesives (3M and Kuraray) were tested to determine the cytotoxicity of confluent L929 cells cultured by Eagle's MEM medium supplemented with 10% FCS. The area of cells affected by the eluted monomers were evaluated with an image analyzer and the concentrations of monomers eluted into the medium were measured with high performance liquid chromatography (HPLC) after 24h incubation. The protein composition of the stimulated cells was compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tyrosine phosphorylation was detected by Western blot.

RESULTS

The primer and uncured adhesives revealed variable cytotoxicities. 2-hydroxyethyl-methacrylate (HEMA) was the major component eluted from uncured primers and adhesives. Small amounts of triethylene glycol dimethacrylate (TEGDMA) were also detected from the uncured adhesives. The cytotoxicities of the adhesives decreased as photo activation time increased. The amount of monomers eluted from the cured adhesives was almost undetectable and did not reach a sufficient concentration to suppress cell viability or cell growth. The cytotoxicities of the primers and adhesives correlated well with the amounts of either HEMA or TEGDMA eluted. Moreover, a high concentration of HEMA (4 mg/ml medium) affected intracellular tyrosine phosphorylation, which is related to cellular activities.

SIGNIFICANCE

Although the monomers present in dentin bonding resins are cytotoxic to L929 cells, the amount from cured bonding resin is very small and does not provide a cytotoxic dose. This data does however suggest that clinical exposure to the uncured primers and adhesives of dentin bonding resins should be minimized.

Effect of removal of the smear layer on apical microleakage

It has been shown previously that the smear layer created during instrumentation of the root canal promotes apical microleakage. The purpose of the present study was to investigate the effect of removal of the smear layer on apical microleakage, using the fluid filtration method. Thirty-six single-rooted human premolar teeth were used. Six of the teeth were selected randomly as controls, and the remaining 30 teeth were randomly divided into two groups of 15 teeth each. For the first group (group 1) teeth were irrigated with NaOCl only (smear layer not removed). In the second group (group 2) the teeth were irrigated with 15% EDTA, followed by NaOCl to remove the smear layer. Both groups were filled with thermoplasticized gutta-percha (Obtura II) using glass-ionomer cement as sealer. All teeth were stored at 37 degrees C and 100% humidity for 2 days. Apical microleakage of the filled root canal was measured by the fluid filtration technique. Hydraulic conductance was measured by the movement of an air bubble in a capillary tube after a pressure of 200 mm Hg was applied to the system. The mean microleakage rate of group 1 and group 2 were 13.0 (SD +/- 5.1) and 16.9 (SD +/- 15.3) nl/s, respectively. Removal of the smear layer caused significantly more apical microleakage (p < 0.05, Student's t test) than when the smear layer was left intact.

Sealing and dentin bond strength of adhesive systems in selected areas of perfused teeth

OBJECTIVES

(1) Test the sealing capacity and tensile strength of various adhesive systems: Scotch Bond 1 (Single Bond in USA)(SB1)+Z100, Syntac Sprint (SYN)+Tetric Ceram, Prime and Bond 2.1 (PB21)+TPH Spectrum, F2000 (Adhesive+Compomer) (F2000) and Optibond Solo (OPT)+Prodigy, to perfused teeth (30 cm distilled H2O), in select areas. (2) Determine the relationship between sealing ability and size of adhesive area (BA) with tensile strength (TS).

METHODS

Segments of human third molars (n=67) sealed with amalgam on their coronal side were connected to a perfusion system (30 cm distilled H2O), to measure the basal permeability. Access cavities were drilled through the amalgam to expose dentin (area range: 8.7-20.8 mm2) and measure the permeability of that area. Cavities were sealed with one of the test materials and permeability measured prior to tensile testing. The percentage of decrease in permeability (PPD) that occurred with the different combinations of materials was also measured. RESULTS. TENSILE STRENGTH: there were no statistically significant differences among groups. PERMEABILITY: ANOVA showed that there were statistically significant differences in the mean % decrease in permeability (PPD) among groups (p=0.018). Student-Newman-Keuls test (p<0.05) detected that the mean PPD of F2000 ranked statistically higher than that of SB1. Relationship among variables: a linear correlation was found defined by the formula TS=7.47+0.008 x PPD-0.23 x BA, with a significance of the model p=0.0097.

SIGNIFICANCE

None of the materials studied reduced permeability up to 100%. They all produced low tensile bond strengths (maximum mean value of groups: 5.51 MPa (OPT)).

Response of feline intradental nerve fibers to tooth cutting by Er:YAG laser

BACKGROUND AND OBJECTIVE

The aim of this study was to investigate the response of intradental A- and C-fibers during tooth cutting by Er:YAG laser.

STUDY DESIGN/MATERIALS AND METHODS

Bipolar electrical stimulation was applied to the cat's canine to identify functional single nerve fibers of the inferior alveolar nerve. The tip of the canine tooth was cut in 0.5-mm steps until the pulp was exposed. Teeth were alternately cut by using Er:YAG laser (50 mJ, 5 pps) and micromotor under water cooling. The nerve response recorded from the single nerve fibers during laser cutting was compared with that during micromotor cutting.

RESULTS

All 26 A-fibers responded to laser cutting with high frequency of nerve firings. The nerve firing rate was significantly higher during laser cutting compared with that during micromotor cutting of superficial dentin (Chi(2) test, P < 0.05) but was not significantly different at deep dentin (P > or = 0. 05). Nine of 11 C-fibers responded to laser cutting when the deep dentin was cut. Among those nine nerve fibers, three also showed a low frequency response to laser cutting of the superficial dentin.

CONCLUSION

During the tooth cutting, Er:YAG laser was more effective in activating intradental A-fibers compared with micromotor and also caused the activation of intradental C-fibers.

Permeability characteristics of bovine and human dentin under different pretreatment conditions

In order to use bovine dentin instead of human dentin for in vitro adhesion and cytotoxicity tests the permeability characteristics of human and bovine dentin should be similar. In the present study hydraulic conductance (Lp) and diffusional water flux (J5) of human and bovine dentin slices were compared. The permeability experiments were performed in a split chamber using tritiated water in physiological saline. Lp and Js of bovine dentin were 0.7- to 2.4-fold and 1.1- to 3.5-fold that of human dentin (not statistically significant). For human and bovine dentin Lp and Js increased with etching and showed an inverse linear relationship (r > or = 0.7) with dentin thickness. The variability of bovine data was low (perfusion = 30%, diffusion = 22%) and about half that of the human data. In conclusion bovine dentin near the cementoenamel junction seems to be a suitable alternative for coronal human dentin for in vitro tests with respect to transdentinal permeability characteristics.

Displacement of the contents of dentinal tubules and sensory transduction in intradental nerves of the cat

Experiments were performed on anaesthetized cats to test the hypothesis that fluid flow through dentinal tubules is part of the mechanism involved in the transduction of pain-producing stimuli in teeth. In 11 animals, fluid flow through dentine and single- and multi-unit activity in intradental nerves were recorded simultaneously during the application of changes in hydrostatic pressure (-500 to +500 mm Hg) to exposed dentine. Seventeen A-fibres (conduction velocity (CV), 10.6-55.1 m s(-1)) were isolated that were pressure sensitive. The thresholds of these units in terms of dentinal fluid flow were in the range 0.3-2.1 nl s(-1) mm(-2) during outward flow from the pulp and 2.0-3.5 nl s(-1) mm(-2) during inward flow. All the units were more sensitive to outward than inward flow. Twenty-eight units (CV, 0.6-48.8 m s-1) were not pressure sensitive, and 12 of these had conduction velocities in the C-fibre range (< 2.5 m s(-1)). The velocities of the tubular contents were calculated by estimating the number and diameters of dentinal tubules exposed. At the threshold of single-fibre responses these velocities were in the range 31.7-222.9 microm s(-1) during outward flow 211.4-369.6 microm s-1 during inward flow. Repetitive pressure stimulation of dentine resulted in a progressive reduction in the evoked discharge, which was probably due to pulp damage. In seven animals, 10 single intradental nerve fibres were selected that responded to hydrostatic pressure stimuli and their responses to the application of hot, cold, osmotic, mechanical and drying stimuli to exposed dentine were investigated. With these stimuli dentinal fluid flow could not be recorded in vivo for technical reasons and was therefore recorded in vitro after completion of the electrophysiological recordings. With each form of stimulus, the discharge evoked in vivo was closely related to the flow predicted from the in vitro measurements. The results were therefore consistent with the hypothesis that the stimuli act through a common transduction mechanism that involves fluid flow through dentine.

The effect of normal occlusal forces on fluid movement through human dentine in vitro

Receptors inside human incisors appear to respond to stress (comparable to pressure as opposed to force) on the crown. This ability may be used to limit the stress applied to teeth or to discriminate between the hardness of objects clenched between upper and lower teeth. Here the hypothesis that these receptors are activated by fluid squeezed out of dentinal tubules when the loaded tooth is stressed was tested. Vertically compressing the crowns of extracted human teeth with loads of from 20 to 120 N, similar to those used in other studies and during natural chewing, did indeed displace fluid into the pulp. The fluid was displaced away from the crown immediately after the tooth had been loaded and moved back into the crown when the load was removed. The volume ranged from 3.5 to 22.2x10(3) pl, similar to that known to stimulate single pulpal nerve fibres. Thus, normal chewing forces could displace sufficient fluid out of dentine to excite putative mechanoreceptors somewhere inside the dentine/pulp complex.

The permeability of the dentine and other tissues that are exposed at the tip of a rat incisor

The tissues that form the incisal surface of a rat incisor include dentine, an atubular calcified tissue which lines the last-formed dentine, and calcified pulp remnants. The permeability of these tissues was investigated in vitro and in vivo using Evans blue dye. The incisal surface was prepared by etching it with acid or removing 1 mm by fracturing or with a diamond disc followed by etching. In some cases, 1.5-3.0 mm was removed to expose the soft tissue of the pulp. The dye was applied for 30 min, then longitudinal sections of the crown were cut and examined microscopically to determine the extent to which the dye had diffused into the underlying tissues. In only those teeth in which the dye had been applied direct to the pulpal soft tissue could any be detected below the exposed tooth surface. In previous experiments, it was found that both cat and human dentines were freely permeable to Evans blue when they were tested in vitro. It is concluded that the dentine and other tissues that form the incisal surface of a rat incisor are less permeable than cat or human dentine.

The permeability of human dentine in vitro and in vivo

Experiments in cats have shown that Evans blue dye diffuses at a greater rate into dentine in recently extracted teeth than in vivo. These experiments have now been repeated in man and similar results were obtained except that, after applications in vivo, visible concentrations of the dye were present in the dentine, and in a few cases, even in the pulp. It is concluded that, as in the cat, the diffusion in vivo was impaired by outward flow of fluid in the dentinal tubules but the mean velocity of flow in the human dentine was less than that in the cat.

In vitro penetration of the pulp chamber by three brands of carbamide peroxide

PURPOSE

Vital tooth bleaching has become a popular procedure for whitening teeth. Most home bleaching products contain 10% carbamide peroxide. The purpose of this in vitro study was to measure the quantity of hydrogen peroxide that reaches the pulp chamber from three carbamide peroxide products: Opalescence, Sparkle, and Rembrandt.

MATERIALS AND METHODS

Seventy roots of extracted premolars were amputated approximately 3 mm apical to the cementoenamel junction, and the pulp tissues were removed. They were divided into three experimental groups (n = 20) and a control group of 10 teeth. An acetate buffer solution was placed in the pulp chamber before the crown was exposed to the bleaching agent at 37 degrees C for 25 minutes. The buffer solution was removed and reacted with leukocrystal violet and horseradish peroxidase. The optical density of blue color that developed was measured at a wavelength of 596 nm and read from a standard curve for hydrogen peroxide quantity.

RESULTS

The measured amounts of hydrogen peroxide were 3.605 +/- 1.405, 1.282 +/- 0.762, and 0.339 +/- 0.251 micrograms for the Opalescence, Sparkle, and Rembrandt groups, respectively. A statistically significant difference in the hydrogen peroxide levels was observed by analysis of variance (p < .05) among the three groups. It was concluded that the penetration of commercial bleaching products was different even though the products were labeled as having the same 10% carbamide peroxide.

CLINICAL SIGNIFICANCE

Carbamide peroxide penetration to the pulp varies significantly for various commercial bleaching products. This may result in different levels of tooth sensitivity or bleaching efficacy.

Interstitial fluid pressure in normal and inflamed pulp

Tissue pressure is the hydrostatic pressure in the interstitial fluid which surrounds the pulpal cells. This pressure outside the vessels is normally considerably lower than the blood pressure inside the vessels. The dental pulp has a relatively low interstitial compliance due to its enclosure between rigid dentin walls. Accordingly, even a modest increase in pulpal fluid volume will raise the tissue pressure, which may compress blood vessels, leading to ischemia and necrosis. Inflammation may lead to an increase in both interstitial fluid volume and blood volume in the low-compliant pulp and thereby increase the tissue pressure. However, the increased tissue pressure may, in turn, initiate increased lymph flow and absorption of fluid into capillaries in nearby non-inflamed tissue. Both of these latter factors will transport fluid out of the affected area and subsequently out of the tooth and consequently lower the tissue pressure. Increased tissue pressure, whether caused by increased blood volume or increased capillary filtration, will promote outward flow of fluid through exposed dentin tubules and thereby help to protect the pulp against entry of harmful substances. It seems physiologically beneficial, therefore, for the pulp to have a high tissue pressure, which promptly increases when blood flow increases due to its low compliance.

Crown cementation and pulpal health

LITERATURE REVIEW

A direct result of the liquid continuum within the pulpo-dentine complex is the effect of restorative dentistry on the health of the dental pulp. Better understanding of the role of the complex in relation to restorative dentistry enables strategies to be devised in preserving pulp vitality. A review of the literature produced good laboratory evidence to support the prophylactic sealing of crown preparations with dentine bonding agents.

Dentine permeability and tracer tests

OBJECTIVES

This paper reviews the evidence for dentine's permeability in order to clarify and emphasize its confounding effect on leakage test measurements, and hence the need to use special test designs to avoid its effects.

METHODS

The literature on the subject between 1887 and 1997, including 249 articles.

CONCLUSIONS

The prerequisite condition for any tracer penetration test is that unflawed specimens are themselves impermeable to tracer. Entry of tracer then can be used to indicate correctly the location or severity of flaws. The relative impermeability of intact dental enamel permits such testing of the enamel-restoration interface seal, but the same is not true when using dentine, which is usually frankly porous to most tracers through its tubules. False positive results are very likely. Recent intense interest in dentine bonding agents has increased the need and frequency of these tests with dentine, but this serious confounding factor has so far generally remained unstated, and has only been controlled adequately in one study. If tracer penetration test results are to be meaningful, then adequate control is required.

Responses of macrophage-associated antigen-expressing cells in the dental pulp of rat molars to experimental tooth replantation

Bacterial infection of the dental pulp is a major hindrance to successful pulp regeneration after tooth replantation. This study examined how macrophages and class II molecule-expressing cells of the pulp respond to tooth replantation, on the hypothesis that they contribute to the defence and repair of the traumatized pulp. Upper right first molars of 5-week-old male Wistar rats were replanted immediately after extraction; contralateral untreated teeth served as controls. Pulpal cells expressing macrophage-associated antigens were immunohistochemically demonstrated at 0 h (immediately after the replantation) to 84 days postoperatively using antirat monoclonal antibodies OX6 (anti-class II molecules), ED1 (pan-macrophage antibody, reactive also with dendritic cells) and ED2 (anti-resident macrophages). Between 3 and 7 days postoperatively, ED1+ and OX6+ cells, but not ED2+ cells, were concentrated in areas of degeneration formed in the coronal pulp, and frequently showed a marked accumulation along the pulp-dentine border of the cuspal area. Confocal laser scanning microscopy revealed that some of the OX6+ cells with a dendritic profile extended several cytoplasmic processes into the dentinal tubules communicating with the enamel-free area at the tip of the cusp. From 14-84 days, approx. two-thirds of specimens exhibited pulp-tissue regeneration with increasing formation of reparative dentine. Following the formation of sound reparative dentine, cells positive to each antibody were distributed more centrally in the pulp than in the controls, and thus did not show any accumulation along the pulp-dentine border. However, in the other specimens where a bone-like hard tissue had formed in the pulp chamber, many ED1+ and OX6+ cells were still concentrated in the remaining pulp tissue and showed a marked accumulation along the pulp dentine border. Few ED2+ cells were observed in these specimens. These findings suggest that, following tooth replantation, exudative macrophages are actively engaged in eliminating dentinal tubule-derived infectious stimuli and that class II molecule-expressing cells, most probably containing dendritic cells, are positioned strategically at the outermost portion of the injured pulp to monitor incoming antigens. The intensity of the pulpal defence reaction may be dependent on the status of hard-tissue formation, which influences the amount of incoming antigens.

Relationship between dentine hydraulic conductance and the cytotoxicity of four dentine bonding resins in vitro

OBJECTIVES

Dentine modifies pulpward diffusion of monomers leaching from restorative materials. Thus, remaining dentine thickness must be taken into account during in vitro cytotoxicity tests. This in vitro study was designed to determine the influence of dentine permeability on the outcome of a cytotoxicity test.

METHODS

Dentine slices were made from 36 human third permanent molar teeth. The 36 dentine slices were divided into two groups according to their hydraulic conductance: high or low hydraulic conductance. The cytotoxicity of four dentine bonding agents of similar cytotoxicity was tested on dentine slices from each group. Four dilutions of the experimental culture medium were tested: undiluted, 1:2, 1:10 and 1:100. An analysis of variance was used to compare the cytotoxicity of the dentine bonding agents tested on high versus low hydraulic conductance.

RESULTS

The cytotoxicity of the high hydraulic conductance (Lp) group was higher than that of low Lp group when tested with the undiluted test culture medium (p = 0.001). No difference was obtained with the 1:2, 1:10, 1:100 dilutions.

CONCLUSIONS

Under the conditions of the study, the dentine bonding resins were more cytotoxic when applied onto dentine slices of high hydraulic conductance.

The effect of dentine surface treatment on pulpward pressure transmission during crown cementation: a laboratory study

Thirty extracted human premolars received standardised full crown preparations. The teeth were randomly assigned into three groups: smeared (control), etched (phosphoric acid gel), and bonded (Scotchbond MP). Each tooth was perfused with saline to establish perfusion rates at baseline for all groups, and the post-etching stage for etched and bonded groups, post-bonding stage for bonded group, and post-cementation stage for all groups. Crowns made with four layers of die-spacing were cemented with zinc phosphate cement at 100N. Pulpal pressures were measured with a pressure transducer. It was concluded that dentine bonding agents may have the potential to reduce pulpal damage caused by pressure transmission from cementation.

Immune defense mechanisms of the dental pulp

Defense reactions of the dentin/pulp complex involve a variety of biological systems, in which the immune system plays a pivotal role. The knowledge of the organization and function of pulpal immunocompetent cells has been sparse, but in recent years a significant body of information of immune mechanisms in general has provided a footing for substantial new knowledge of the immune mechanisms of the dental pulp. The identification of pulpal dendritic cells (DCs) has generated research activities which have led to a concept of how an antigenic challenge may evoke a pulpal inflammatory response. Although DCs are not able to identify foreign antigens specifically, they provide necessary signals to activate T-lymphocytes which in turn will orchestrate other immunocompetent cells to mount the local immune defense of the dental pulp. The purpose of this review is to accent the organization and function of pulpal DCs and other tissue and cellular components and to provide a basis for how they may interact to instigate pulpal defense mechanisms.

The effects of immunoglobulins on the convective permeability of human dentine in vitro

Immunoglobulin molecules are localized in the dentinal tubules of non-carious and carious teeth, but their possible role in caries invasion is not understood. This study sought to examine the effects of immunoglobulin molecules on dentine permeability using a fluid-filtration method. Crown segments cut from impacted human third molars were treated by filtration with 100 micrograms/ml IgG, 100 micrograms/ml IgA or 30 micrograms/ml IgM under a constant pressure. Flow rates were recorded and percent changes in flow rate analysed over time. Filtrates collected at various times were tested for changes in immunoglobulin concentrations by an enzyme-linked immunosorbent assay, and the percent retention of immunoglobulins to dentine was calculated. There was a decreasing non-linear exponential relation between the percent changes in flow rate and filtration time for all three immunoglobulins. The percentage of retained immunoglobulins was significantly related to the filtration time for all three classes of immunoglobulins. Immunoglobulin retention contributed to significant changes in flow rate with time. These in vitro results indicate the potential mechanism of immunoglobulins in decreasing tabular permeability.

The Dentin Disc surface: a plausible model for dentin physiology and dentin sensitivity evaluation

Dentin sensitivity (DS) is a painful clinical condition which may affect 8-35% of the population. Various treatment modalities have claimed success in relieving DS, although at present there does not appear to be a universally accepted desensitizing agent. Current opinion based on Brännström's Hydrodynamic Theory would suggest that following exposure of the dentin surface (through attrition, abrasion, or erosion), the presence of open dentinal tubules, patent to the pulp, may be a prerequisite for DS. The concept of tubule occlusion as a method of dentin desensitization, therefore, is a logical conclusion from the hydrodynamic theory. The fact that many of the agents used clinically to desensitize dentin are also effective in reducing dentin permeability tends to support the hydrodynamic theory. This paper reviews the in vitro evaluation of desensitizing agents, the techniques used to characterize their effects on the prepared dentin surface, and the ability of these agents to reduce permeability through tubule occlusion, and presents recent findings from ongoing research based on the Pashley Dentin Disc model. It can be concluded that the use of this model to determine surface characteristics, and reductions in dentin permeability through tubule narrowing or occlusion, provides a useful screening method for evaluating potential desensitizing agents. Interpreting changes observed in vitro is difficult, and extrapolation to the clinical situation must be tempered with caution.

The dentin substrate: structure and properties related to bonding

OBJECTIVES

Dentin is a vital, hydrated composite material with structural components and properties that vary with location. These variations are reviewed along with alterations by physiological and pathological changes that allow classification into various forms of dentin. Structural characteristics and mechanical properties are reviewed and the limitations of our understanding of structure-property relationships for normal and modified forms of dentin are discussed with respect to their impact on dentin bonding. Recent progress in methods available to study dentin and its demineralization are emphasized with their promise to increase our understanding of dentin properties and structure.

DATA SOURCES

Recent microstructural studies, focusing on scanning electron microscopy, atomic force microscopy and X-ray tomographic microscopy are included. A review of fundamental studies with emphasis on microstructurally sensitive methods, and prior reviews of basic mechanical properties are included with discussion of their correlation to composition and structure.

STUDY SELECTION AND CONCLUSIONS

Emphasis in this work was placed on the major structural components of the tissue, including the collagen based organic matrix and its mineral reinforcement, the distribution of these components and their microstructural organization as related to mechanical properties and response to demineralization. Little information is included on biochemical and developmental studies or on non-collagenous proteins and other organic components for which limited understanding is available with respect to their role in structure-property relations and influence on bonding. In spite of the fact that the complexity of dentin precluded a comprehensive review, it is clear that local structural variations influence properties and impact nearly all preventive and restorative dental treatments. Much more work is needed in order to understand differences between vital and non-vital dentin, and dentin from extracted teeth. Although our knowledge is rudimentary in certain areas, increasingly sophisticated methods of studying dentin should provide the necessary information to model structure-property relations, optimize dentin bonding, and improve many aspects of preventive and restorative dentistry.

An evaluation of after-office-hour dental trauma in Singapore

The purpose of this study was to assess the post-traumatic sequelae and treatment outcome and the corresponding prognostic factors at the initial emergency visit. Over a 5-year period, the authors collected case records from 129 dental trauma patients. These patients had been referred subsequent to receiving emergency treatment after office hours at the Accident and Emergency Department of Singapore General Hospital. After the exclusion of 31 cases with concomitant fracture of maxilla and/or mandible and cases with insufficient documentation, the final study sample consisted of 98 patients (41 males, 57 females) who had sustained injuries to 264 permanent teeth. The main cause of dental trauma was falls (56%), and the main type of injuries was periodontal tissue injuries with or without concomitant injuries to hard tissue, including root fracture (73%). For the final evaluation, teeth with insufficient recall period were excluded before univariate and multivariate stepwise logistic regression analysis. It was found that for 100 teeth with luxation type of injuries, the presence of concomitant hard tissue injuries retained prognostic significance for pulpal outcome (p < 0.001) after adjusting for severity of luxation, while the severity of luxation was the only significant factor for periodontal outcome (p < 0.001). For 34 avulsed teeth, the stage of root development was the major factor associated with the pulpal outcome (p = 0.003), while extra-alveolar storage media were found to be significantly related to the periodontal outcome (p < 0.001). For 72 teeth with hard tissue injuries, first-visit interval played a significant role in the outcome (p = 0.03). Although the sample size in the root fracture group was too small for such statistical analysis, the results indicated that patient education on dental trauma was an important factor. Thorough standardized documentation was also recommended to facilitate optimal follow-up management and future research as well as medico-legal purposes.

Pulp interstitial fluid pressure and blood flow after denervation and electrical tooth stimulation in the ferret

The effects of sensory and sympathetic denervation on simultaneously measured interstitial fluid pressure and blood flow in the canine pulp before, during and after electrical tooth stimulation were investigated in 25 ferrets. The micropuncture technique was used to measure interstitial fluid pressure and laser-Doppler flowmetry was used to record pulpal blood flow. Animals with an intact innervation (group 1) served as controls. Sensory denervation was by axotomy of the left inferior alveolar nerve 10 days before the experiment (group 2) and sympathectomy by removal of the left cervical ganglion 5 days before the experiments (group 3). The study was designed to verify whether denervation affected basal pulp blood flow and interstitial fluid pressures during control conditions and/or after tooth stimulation. During control conditions the interstitial fluid pressure averaged 1.32 +/- 0.07 kPa in group 1, whereas the mean was only 0.51 +/- 0.13 kPa in the axotomized animals (group 2). The difference was highly significant, indicating decreased blood or interstitial fluid volume in the pulp after inferior alveolar nerve axotomy. In the sympathectomized group neither the interstitial fluid pressure nor the pulp blood flow was significantly different from those of group 1. Electrical tooth stimulation caused an almost simultaneous increase in interstitial fluid pressure and pulp blood flow in groups 1 and 3, whereas stimulation did not significantly change either variable in the axotomized animals (group 2). It is concluded that a resting nervous vasodilator tone of sensory origin exists in the ferret dental pulp, and that the sensory nerves are responsible for the increased interstitial fluid pressure and pulp blood flow during tooth stimulation.

Low versus high pressure for in vitro determination of hydraulic conductance of human dentine

The purpose of this study was to evaluate the effect of applied pressure and measurement time on the in vitro measurement of hydraulic conductance of human dentine. Dentine slices were prepared from 50 third molars. Water was forced through the slices under a constant hydrostatic pressure. Five pressures were tested: 1.3 kPa (n = 10), 13.3 kPa (n = 10), 26.6 kPa (n = 10), 40 kPa (n = 10) and 53.3 kPa (n = 10). The volume that went through the slices was recorded every 10 min for 3 h. The volume, the fluid flow rate and the hydraulic conductance under the five pressures were compared. The volume increased with time and pressure. The fluid flow and hydraulic conductance decreased with time under 13.3, 26.6 and 40 kPa, but remained constant under 1.3 and 53.3 kPa. Used of a low pressure (1.3 kPa) may permit water to pass through dentinal tubules without disturbing intratubular contents. Medium pressures (13.3, 26.6, 40 kPa) seemed to disturb tubule contents progressively, resulting in decreased fluid flow and therefore a decreased hydraulic conductance with time. Under these pressures, the calculated values of hydraulic conductance may be unreliable because they are time-dependent. High pressure (53.3 kPa) seemed to pack the tubule contents against intratubular resistances immediately, resulting in low fluid flows and low hydraulic conductances.

The effect of seating force and die spacing on pulpward cementation pressure transmission: a laboratory study

Pulpward pressure transmission during crown cementation occurs via the dentinal tubules. The present study investigated the effect of crown seating forces and the effect of increasing the die spacing on pulpward pressure transmission. Twenty upper premolars were prepared with 1 mm shoulder margins for non-precious metal full crowns. A 0-104 kPa pressure transducer (Mediamate EA, Data Instruments, Baltimore, MD, USA) was connected, via the sectioned root of the premolar, to the pulp chamber which was perfused with saline at 83 kPa driven by nitrogen gas, for two hours prior to cementation. Crowns with 2 or 6 layers of die-spacing were seated with 25 N or 100 N force using zinc-phosphate cement. The pressure transducer was connected to a Wheatstone bridge (Measurements Group, Instruments Division) and the extent of crown seating and output from the pressure transducer was recorded. Results indicate that 25 N seating force produced a lower mean pulpward pressure (41 +/- 54 Pa) compared to the 100 N seating force (251 +/- 276 Pa). Seating was significantly improved with 6 layers of die-spacing (seating discrepancy 18 +/- 12 mm) compared with 2 layers (139 +/- 111 mm). It is concluded that a higher seating force increases pulpward pressure transmission. Increasing die spacing improved crown seating but did not affect the amount of pressure transmitted.

The enigma of potassium ion in the management of dentine hypersensitivity: is nitric oxide the elusive second messenger?

We report the development of a 'second-messenger' model in an attempt to re-evaluate the role of K+ as a desensitising agent. Despite unequivocal validation of the effectiveness of potassium-based dentifrices in the management of dentine hypersensitivity, the mechanism(s) of action of K+ remains unclear. Although experimental paradigms of the Nernst equation demonstrate a direct inhibitory effect of K+ ion upon nerve conduction, in vivo considerable constraints can be argued to preclude this mechanism of action. Indeed, measurements of solution velocity within individual dentinal tubules obtained by scanning electrochemical microscopy indicate that outward movement of tubular fluid may represent a far greater barrier to the inward diffusion of K+ ions than previously estimated from measurements of hydraulic conductance across bulk dentine. Despite such probable limited penetration of dentine tubules, K+ ions may desensitise deeply-located nerve terminals through activation of a second-messenger transduction pathway that is capable of controlling the gain of K+-evoked effects which remain physically restricted to the more superficial aspects of the tubule. In addition to a direct effect upon transmembrane potential K+ can also indirectly attenuate neural activity through effects upon levels of the endogenously-synthesised free radical, nitric oxide (NO). Stimulation of the release of NO by K+ has been observed using a variety of cell preparations, which include endothelium, smooth muscle, adrenal medulla, hypothalamus and cerebellum. Importantly, a growing number of studies now report that an increase in the production of NO is associated with analgesia through a modulation of nociceptive input and a downregulation of sensitised nociceptors, most likely achieved through an increase in intraneural content of cGMP. The clinical role of a K+-evoked liberation of NO as a principal mechanism in the management of dentine hypersensitivity is supported by recent findings which include: (1) the localisation of NADPH-diaphorase activity and inducible nitric oxide synthase (iNOS) immunoreactivity within odontoblasts, their processes in dentine, and the subodontoblast layer of the pulp; (2) iNOS causes a sustained release of large (nanomolar) amounts of NO; (3) NO is freely diffusible and capable of displaying remarkably potent effector actions at distant target cells; (4) the actions of NO may be enhanced by endogenous carrier molecules such as S-nitrosothiols; (5) the synthesis of NO can be evoked by concentrations of K+ ion far less (i.e. <1 mM) than those required for direct inhibitory effects upon neural activity.

Efficacy of a potassium nitrate mouthwash in alleviating cervical dentine sensitivity (CDS)

Potassium nitrate (KNO3) has been used previously in a dentifrice or gel to alleviate cervical dentine sensitivity (CDS). The aim of this study was to compare a 3% KNO3 Silica/NaF mouthwash with a NaF/silica mouthwash in a 6-week multi-centre double-blind study. 47 subjects (12M; 35F, mean age 36.2 (SD 11.46) years) participated in the study. Subjects were evaluated for tactile (Yeaple probe) and air sensitivity (dental air syringe) together with subjective perception of pain (0-10 scale) at 0, 2 and 6 weeks. Results for Yeaple probe (gm wt) (Wilcoxon paired rank test) between 6 weeks and baseline, were highly significant for both groups. Differences between groups at 6 weeks were statistically significant. Subjective Yeaple probe scores (paired t-tests) between 6 weeks and baseline were significant for both groups. There were no significant differences (unpaired t-tests) between groups over 6 weeks for subjective Yeaple probe scores. Subjective air scores (paired t-tests) between 6 weeks and baseline were significant for both groups. There were significant differences (unpaired t-tests) between groups in favour of the 3% KNO3/Silica/NaF group at 6 weeks. The 2 weeks and baseline results for both groups were the same as reported for 6 weeks and baseline. The results demonstrated that a 3% KNO3/Silica/NaF mouthwash compared to a Silica/NaF control significantly reduced CDS when evaluated by tactile and thermal stimuli. A 3% KNO3/silica/NaF mouthwash would, therefore appear to have therapeutic potential to alleviate CDS.

Effects of pulsatile versus non-pulsatile pulpal pressure simulations on diffusional transport across human dentine in vitro

The influence of a simulated pulsatile pulpal pressure on the diffusion of NaCl through slices of human dentine (n = 12) was evaluated in vitro. The average hydraulic conductance of the slices of dentine was 0.0131 +/- 0.0031 microliter/cm2 per min per cmH2O(x +/- SD). A 1 mol/l NaCl solution was placed on one side of the slices of dentine and deionized water on the other side. The time needed to reach a steady state and the quantity of NaCl that diffused through the slice were successively measured on the same slice of dentine, under three conditions: without pressure simulation, with a static pressure of 1.5 kPa, and with a pulsatile pressure varying from 1.2 to 1.8 kPa. The pressure was applied to the deionized water. When a static pressure was applied, the time required to reach a steady state increased from 24 to 30 h. When a pulsatile pressure was applied the time required to reach a steady state decreased from 24 to 12 h. No statistically significant difference was found between the quantity of NaCl that had diffused when the steady state was reached.

A mathematical model of potassium ion diffusion in dentinal tubules

Desensitizing agents containing potassium ions (K+) are believed to inactivate intradental nerves by raising extracellular [K+]. A mathematical model was used to investigate factors affecting [K+] in dentinal tubules. The most important factors affecting the steady-state tubular [K+] were the tubular fluid-flow velocity, salivary [K+] and the permeability to potassium (k) of the barrier between the tubule and the pulp. Tubular [K+] decreased with increasing outward flow velocity and increasing k. whereas the dimensions of the tubule and odontoblast process had little effect. Following a 1 min simulated application of 500 mmol/1 K+ to the dentine surface, [K+] at the inner end of the tubule increased above steady-state levels for 20-30 min. The maximum [K+] attained at the inner end of the tubule was around 30 mmol/l for an impermeable barrier (k = 0) and flow velocity of 1.4 microns/s, but lower maximum tubular [K+] were achieved when either the outward flow velocity or k was increased. The model suggests that applying potassium-containing preparations to dentine may increase [K+] at the inner ends of dentinal tubules to levels sufficient to inactivate intradental nerves. However, the localized increase in [K+] is transient, and the concentration change will be lessened by conditions that increase the tubular fluid-flow velocity or the permeability of the barrier between the tubule and pulp.

Dynamics of the pulpo-dentin complex

Dentin has a relatively high water content due to its tubular structure. Once dentin is exposed, this intratubular water is free to move in response to thermal, osmotic, evaporative, or tactile stimuli. Fluid shifts across dentin are thought to cause sufficient shear forces on odontoblasts, nerve endings, nearby fibroblasts, and blood vessels to cause significant mechanical irritation, disruption, or damage, depending on the magnitude of the fluid shift. Even in the absence of fluid shifts, the water-filled tubules provide diffusion channels for noxious (i.e., bacterial products) substances which diffuse inward toward the pulp, where they can activate the immune system, provide chemotactic stimuli, cytokine production, and produce pain and pulpal inflammation. Viewed from this perspective, dentin is a poor barrier to external irritants. However, pulpal tissues react to these challenges by increasing the activity of nerves, blood vessels, the immune system, and interstitial fluid turnover, to make the exposed dentin less permeable either physiologically, via increased outward fluid flow, or microscopically, by lining tubules with proteins, mineral deposits, or tertiary dentin, thereby enhancing the barrier properties of dentin, and providing additional protection to pulpal tissues. These reactions involve dentin and pulp, both in the initiation of the processes and in their resolution. These responses of the dental pulp to irritation of dentin demonstrate the dynamic nature of the pulpo-dentin complex.

Dentinal fluid dynamics in human teeth, in vivo

Cavities were prepared in human premolars scheduled for extraction for orthodontic reasons. The smear layer was removed from the dentin surface by acid etching, and the cavity was sealed using a hollow chamber. The chamber was filled with sterile saline solution and connected via tubing to a hydraulic circuit featuring an adjustable pressure reservoir and a device that measures fluid movement across dentin. In the absence of any exogenous pressure, all cavities exhibited an outward fluid flow rate of 0.36 microliters min-1 cm-2. As exogenous pressure was applied to the cavity, the outward flow slowed. The exogenous pressure that stopped outward fluid flow was taken to be equal to normal pulpal tissue pressure. The mean value was 14.1 cm H2O in five teeth. This simple method permits measurement of dentinal fluid flux, the hydraulic conductance of dentin, and estimates pulpal tissue pressure.

Adhesion testing of dentin bonding agents: a review

Adhesion testing of dentin bonding agents was reviewed starting with the adhesion substrate, dentin, the variables involved in etching, priming and bonding, storage variables and testing variables. Several recent reports attempting to standardize many of these variables were discussed. Recent advances in the development of new bonding systems have resulted in bond strengths on the order of 20-30 MPa. At these high bond strengths, most of the bond failure modes have been cohesive in dentin. As this precludes measurement of interfacial bond strength, new testing methods must be developed. One such new method, a microtensile method, was described along with preliminary results that have been obtained. The last decade has produced major advances in dentin bonding. The next decade should prove to be even more exciting.

Effects of potassium ions on action potential conduction in A- and C-fibers of rat spinal nerves

Potassium ions in dentifrices for treating 'hypersensitive' dentin are believed to act directly on intradental nerves by raising extracellular potassium ion concentration ([K+]o) sufficiently to prevent action potential generation by axonal accommodation. However, the [K+]o necessary to block nerve conduction is not precisely known, nor is it certain that K+ can diffuse from a dentifrice in sufficient amounts to inactivate intradental nerves. To establish more accurately the [K+]o required to block nerve conduction under controlled conditions, we studied the effects of increased [K+]o on the sizes of compound action potentials (CAP) recorded from rat spinal nerves in vitro. [K+]o was increased by the addition of either KCl or KNO3 to Krebs' solutions applied to the central portion of the nerves. CAP attenuation increased in a dose-dependent manner as [K+]o was raised in the 8 to 64 mmol/L range, and complete block was generally produced with solutions containing at least 32 mmol/L K+. CAP attenuation was reversible, and recovery times increased with increasing [K+]o. The effects of KCl and KNO3 solutions were the same for all [K+]o tested. Half-maximal (50%) reduction in the A beta-fiber component of the CAP occurred with 17.4 mmol/L K+, and with 17.8 mmol/L and 19.3 mmol/L K+, respectively, for the A delta- and C-fiber components. Control experiments with glucose and choline chloride confirmed that the conduction block observed with increased [K+]o was not due to increased solution osmolarity or ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative study of three dental adhesives

The shear bond strengths of three dental adhesives to dentine and a NiCrBe alloy were determined. Forty human third permanent molar teeth were ground to expose superficial dentine, to 20 of which P50 composite was bonded, using All-Bond 2 (n = 10) or Scotchbond 2 (n = 10). Alloy discs were bonded to the remaining 20 specimens, using either All-Bond 2 (n = 10) or Panavia Ex (n = 10). All specimens were stored at 37 degrees C. 100% RH, for 24 h. Testing was carried out using a shear jig at a cross-head speed of 1 mm min-1, following which a 0.5 mm increment was removed to expose middle dentine for further bond tests (n = 10 for each adhesive). Removal of a further 0.5 mm increment exposed 'deep' dentine for final dentine bond strength tests. Results were then aggregated for each substrate/adhesive combination (n = 30). Alloy/alloy bond strengths were determined after bonding alloy discs together using Panavia Ex (n = 30) or All-Bond 2 (n = 30). Results were analysed using ANOVA and Weibull analysis. All-Bond 2 produced significantly greater and more reliable bond strengths to dentine than did either Scotchbond 2 or Panavia Ex. The bond strength of Scotchbond 2 and Panavia Ex to dentine was dependent upon the dentine depth whereas the bond strength of All-Bond 2 to dentine was independent of dentine depth. Alloy/alloy bond strengths were significantly greater when using Panavia Ex compared with All-Bond 2.

Effect of hydrostatic pressure on the diffusion of monomers through dentin in vitro

In previous work, the diffusion of monomers from composite and bonding resins through dentin was demonstrated in vitro. The monomers triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) were identified in samples from the pulp space. In the current study, we examined the effects of two levels of positive hydrostatic pressure on the passage of resin monomers through dentin in vitro from a composite-resin/bonding-resin combination to test the hypothesis that monomer diffusion is prevented by such pressure. An occlusal cavity prepared in the tooth crown was restored with the resins. Distilled water samples from the pulpal space were removed over time and analyzed for monomer content by high-performance liquid chromatography and mass spectrometry. Positive pulpal pressure reduced but did not prevent pulpward movement of diluent monomers that leach from bonding agents and from resin composites through dentin in vitro. The degree of reduction of diffusion was greater with TEGDMA than with the lower-molecular-weight monomer HEMA.

The micromorphology in vivo of the buccocervical region of premolar teeth in young adults. A replica study by scanning electron microscopy

The buccal surfaces of premolar teeth are common sites of gingival recession, generally attributed to overzealous oral hygiene. Scanning electron microscopy (SEM) of replicas made from dental impressions was applied to document the micromorphology of the buccocervical region of all premolar teeth in 27 dentally healthy, young adults. The SEM observations were correlated with clinical examination. Of the 216 sites, one-third, predominantly the maxillary first premolars, had gingival recession, but fewer than 50% were clinically discernible. The exposed roots were devoid of cementum, and the dentinal surface was smear-like or dotted with tubular apertures from which droplets of fluid extruded. SEM of replicas of gingiva, recorded as clinically healthy, frequently showed signs of inflammation: fluid exudate and distortion of gingival contour by swelling. The cervical enamel of healthy and affected sites showed characteristic periodic fissure-like cracks, probably enamel tufts. The high frequency of subclinical gingival recession, exposed cervical dentin, and gingival inflammation in dentally healthy young adults, in the absence of abrasion of hard or soft tissues, indicates the need to review conventional concepts of initiation of buccal recession and root exposure.

An investigation into the pressure transmitted to the pulp chamber on crown cementation: a laboratory study

Pressure changes in the pulp chamber resulting from crown cementation have not been previously quantified. An experiment was designed to investigate the effect of smear layer removal on the peak pressure transmitted to the pulp chamber with crown cementation. Ten matched pairs of single-rooted premolar teeth were collected from adolescents and prepared for full-coverage crowns. The pulp tissue from each tooth was removed. One tooth from each pair had the smear layer removed with the application of 37% phosphoric acid for 30 s. The null hypothesis states that the removal of the dentinal smear layer will not change pressure in the pulp chamber resulting from the cementation. Before cementation, a hydrostatic head of pressure was used to perfuse the tooth, and the perfusion rate was recorded. Crowns were cemented with zinc phosphate cement with a seating force of 100 N. The mean peak pressures recorded were 85 Pa (SE 12 Pa) with the smear layer intact, and 194 Pa (SE 49 Pa) when the dentin was etched. The difference in the peak pressures transmitted to the pulp chamber with the two groups was significant (p < or = 0.05). A significant negative correlation was found between dentin thickness and the peak pressure transmitted to the pulp chamber (r = -0.5531, p < or = 0.01). We have shown that the pressure transmission to the pulp chamber during crown cementation can be measured. Since smear layer removal significantly influences the peak pressure, it is concluded that the pressure detected is at least partially dependent on the fluid flow through the dentin.

Site-related streptococcal attachment to buccocervical tooth surfaces. A correlative micromorphologic and microbiologic study

Scanning electron (SEM) microscopy of epoxy replicas made from dental impressions has shown that in buccal gingival recession the root surfaces are devoid of cementum, leaving the dentin exposed. In this study replication techniques were applied to correlate the micromorphology of the buccocervical region with early streptococcal attachment. The subjects were 27 healthy young adults. The buccocervical surfaces of all the premolars were meticulously cleaned. The subjects fasted for 2 h before impression-taking. Replicas were made from impressions in hydrophilic A-silicone, and streptococcal attachment was visualized by light microscopy of mitis-salivarius agar replicas incubated anaerobically for 48 h. The surface micromorphology was documented by SEM of corresponding epoxy replicas. Colonization only 2 h after cleaning was very sparse. Sites with healthy or inflamed gingivae had markedly different colonization patterns in the sulcular region. In 4 subjects with a total of 12 sites where gingival recession, undetected clinically, was disclosed by SEM, representative colonies were retrieved and identified microbiologically to species level. Two healthy sites per subject were also sampled. Streptococcus mutans and S. sobrinus were identified from eight sites with exposed root dentin. S. oralis predominated on the enamel surfaces. The method offers a valuable complement to in situ and in vitro microbiologic studies of exposed dentin and a novel technique for sampling clinical isolates of streptococci.

Determination of plasma proteins in dentinal fluid from cavities prepared in healthy young human teeth

The discharge of albumin, IgG and fibrinogen in dentinal fluid released from freshly exposed dentine was determined by enzyme-linked immunosorbent assay. Data were compared with the relative concentrations of these proteins in the interstitial fluid of the pulp. The sampling procedure involved retrieval of phosphate-buffered saline placed in cavities exposing the dentine or pulp of young human premolars for a period of 15 min. Albumin and IgG were found in all dentine samples. The relative occurrence of these two proteins was similar in fluid samples from the exposed pulp. While fibrinogen was detected in all pulp samples only four of a total of 16 dentine samples displayed this protein. Shortly after a mechanical exposure, the exposed ends of the dentinal tubules will therefore release plasma proteins, although to a varying extent. The amount and quality appear related to the amount in which they are present in the interstitial fluid of the pulp.

Factors affecting nerve excitability and conduction as a basis for desensitizing dentine

Nerve excitability is principally determined by the state of membrane sodium channels, which can be influenced by factors such as drugs or the ionic composition of the extracellular fluids. The excitability of isolated nerves is increased by lowered extracellular calcium and hydrogen ion concentrations, and similar effects are seen on intradental nerve excitability. This is of interest as some agents used to desensitize hypersensitive dentine are believed to act by reducing intradental nerve excitability. A variety of ions, including potassium and divalent cations, have been shown to reduce intradental nerve excitability when applied in relatively high concentrations to dentine close to the pulp. However, these conditions do not mimic the clinical situation, where agents are applied to outer dentine, up to 2 mm from the pulp. Also, when agents are applied to dentine it is difficult to quantify the precise changes in extracellular fluid composition, and there is the additional complication of possible interactions between the agents and dentine. These problems can be minimized by using isolated nerves, which allow better control over the conditions and ionic concentrations necessary to achieve nerve conduction block. Such methods can provide a convenient way to screen potential desensitizing agents before evaluation in vivo or in clinical trials.

Morphological features of dentine and pulp related to dentine sensitivity

This review considers those structural features of the pulp and dentine relevant to an understanding of dentine sensitivity. It does not discuss innervation, or microvasculature, which are covered in other contributions. The sensitivity of dentine is directly related to the size and patency of the dentinal tubules. Tubular occlusion by peritubular dentine deposition or the formation of other intratubular material would reduce the flow of fluid and diffusion of molecules through dentine. Irregular (reparative) secondary dentine would, because its tubules are not continuous with those of primary dentine, be expected to reduce permeability and fluid flow and decrease sensitivity. Regular secondary dentine would have little or no effect other than by increasing diffusion distances. The odontoblast layer is of limited permeability and could restrict the access of materials diffusing through the dentinal tubules to pulpal axons. Odontoblasts are not involved in the sensory process as special sensory receptors but may, by modifying the local ionic environment, alter the threshold of intradentinal nerves.