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Responses of intradental nerve fibres to stimulation of dentine and pulp.

In the present work responses of intradental nerve fibres to stimuli that induce fluid flow in dentinal tubules as well as to direct mechanical irritation of the exposed pulp were studied on 9 young adult beagle dogs. Under pentobarbitone anesthesia 31 single functional intradental fibre units were dissected from the mandibular nerve. Stimuli were applied to the lower left canine tooth. Exposed dentine surface was irritated by scraping, air blasts and dry absorbent paper and the pulp mechanically with a von Frey hair. Ten fibre units responded to stimulation of dentine. Six of them were also tested with mechanical irritation of the pulp and were all responsive. Fifteen of twenty fibres responded to mechanical stimulation of the pulp. The mechanosensitive nerve fibres were all A-type according to conduction velocities (mean 25.6 +/- 8.1 (SD) m/s). It is concluded that there exist mechanosensitive intradental A-nerve fibres in the dog which are activated by stimuli that induce fluid flow in dentinal tubules. Nerve fibres of this type could be responsible for dentine sensitivity in man. Consequently, the present study gives support to the hydrodynamic hypothesis of dentine sensitivity. Moreover, mechanosensitive nerve fibres could also be responsible for the pain symptoms of pulpal inflammation, because pulpitis may also create suitable circumstances for their activation.

Animals↗

Treating hypersensitivity with fluoride varnish.

Dentinal hypersensitivity results when stimulation causes the fluid in open dentinal tubules to undergo pressure changes, which activates mechanoreceptor nerves and results in pain. Treatment with fluoride varnish forms a protective layer of calcium fluoride that prevents this fluid flow, thereby reducing dentinal sensitivity.

Calcium Fluoride↗

Dentin deformation after scratching with clinically-relevant forces.

OBJECTIVE: In order to understand the mechanism of dentin sensitivity to tactile stimuli, the purpose of this study was to evaluate possible permanent deformation of dentin produced by scratching dentin surfaces with clinically-relevant forces. METHODS: Midcoronal dentin was prepared from twenty human teeth and polished to 4000-grit and ultrasonicated. The dentin surface of each specimen was scratched under forces ranging from 30 to 100 centi-Newtons (cN). The depth of the grooves were measured with a profilometer and the overall hardness of dentin in the vicinity of the grooves was measured. Additional dentin specimens were prepared for SEM evaluation. RESULTS: Dentin hardness was constant and no statistical difference was found among the specimens. Statistically significant differences in groove width and depth were found when increasing force was applied to the dental explorer tip. The depth of the groove ranged from 0.21+/-0.09 microm for the 30 cN group to 1.27+/-0.39 microm for the 100 cN group. The width of the groove ranged from 19.3+/-4.0 microm for the 30 cN group to 43.0 microm for the 10 0 cN group. CONCLUSIONS: (1). The threshold force necessary to create scratches in dentin with a dental explorer was 30 cN or a compressive stress of 1003 MPa. As this exceeds the crushing strength of dentin, this force produces plastic deformation of dentin; (2). Theoretical calculations indicated that even the highest scratching forces (100 cN) could not induce sufficient fluid flow to activate pulpal mechanoreceptors, although it could induce sufficient elastic deformation to theoretically shift dentinal fluid at a rate sufficient to activate mechanoreceptors; (3). The results of this work may lend support the hydrodynamic theory in that scratching of dentin surfaces causes both elastic and plastic deformation of dentin that may displace dentinal fluid toward the pulp where it could activate mechanoreceptors.

Dentin↗

An investigation of potential desensitizing agents in the dentine disc model: a scanning electron microscopy study.

Cervical dentine sensitivity (CDS) may be defined as pain arising from exposed dentine. The prefix cervical indicates the location of the sensitivity and/or its subsequent treatment. Currently the most accepted mechanism of intradental nerve activation associated with dentine sensitivity appears to be hydrodynamic in nature. The concept of tubule occlusion as a method of dentine desensitization is a logical conclusion of the hydrodynamic theory. The authors employed the dentine disc model, qualitative scanning electron microscopy (SEM) and X-ray microanalysis to investigate whether selected desensitizing agents occlude dentinal tubule orifices. Strict control procedures have been used together with various methods of application to apply these agents to human dentine discs. SEM was used to examine the degree of deposit left by the various agents on disc surfaces and X-ray microanalysis was employed to characterize the elemental composition of the deposit. Analysis of selected agents, both prior to and after application on dentine discs was performed for comparative purposes. The degree of retention of the surface deposit upon rotation with saliva supernatant for 6 h was also studied. The results of this study indicated that ferric oxalate, the active ingredient of Sensodyne Sealant, which produced initial crystal-like structures, occluding almost all the tubule orifices was superior to potassium oxalate (Butler Protect). Of the over-the-counter (OTC) desensitizing products tested, both silica- and calcium-based abrasive components were observed both on the surface and within the tubules, indicating a certain degree of therapeutic potential for these two components. These findings suggest that certain desensitizing agents have tubule occluding properties as observed in this in vitro system which, in turn, may indicate a therapeutic potential in vivo.

Calcium↗

Effect of desensitizing agents on dentin permeability and dentin tubule occlusion.

PURPOSE: The aim of this study was to evaluate: 1) the effect of five dentin desensitizing agents (DDAs) on permeability using hydraulic conductance, and 2) morphological tubule changes with scanning electron microscopy (SEM). MATERIALS AND METHODS: The agents tested were Seal & Protect, Gluma Desensitizer, HurriSeal, D/Sense 2, and Super Seal. Thirty extracted human molars were sectioned into 1-mm mid-coronal dentin disks. Dentin permeability was measured at baseline and after treatment using bovine serum and phosphate-buffered saline at 10 psi. Treatments were applied to the occlusal surfaces of dentin according to the manufacturer's instructions. Representatives from each group were selected for SEM observation. Kruskal-Wallis ANOVA and Tukey's post-hoc comparisons were used to evaluate differences between groups. RESULTS: Mean percent reduction in dentin permeability for each group: SuperSeal = 97.5 +/- 4.0, HurriSeal = 54.2 +/- 35.3, D/Sense 2 = 46.6 +/- 20.4, Gluma Desensitizer = 39.6 +/- 26.7, and Seal & Protect = 33.8 +/- 19.4. The data provided strong evidence of differences in permeability reduction among the agents (p < 0.01). Pairwise comparisons of means demonstrated that the effects of SuperSeal differed significantly from the reductions achieved using Seal & Protect, Gluma Desensitizer, and D/Sense 2. Differences in the degree and content of dentinal tubule occlusion were seen among all DDAs under SEM. CONCLUSION: Of the materials included in this in vitro study, SuperSeal may be the most beneficial when treating dentin sensitivity. The wide range of results may reflect the various approaches and chemistries used to occlude tubules.

Analysis of Variance↗

Fluid shifts across human dentine in vitro in response to hydrodynamic stimuli.

Most authorities agree that the hydrodynamic theory of dentine sensitivity best explains the stimulus-response relations of most painful stimuli. However, as the usual hydrodynamic stimuli are so different, it has been impossible to compare them. The equivalency of hydrodynamic stimuli can be evaluated from measurements of the fluid movement induced in vitro and relating this to the hydraulic conductance (Lp) of the same dentine specimen. From this determination, a common denominator is obtained which is equivalent to the hydrostatic pressure that would be required to cause the same magnitude of fluid movement. The purpose of this study was to measure the direction and magnitude of fluid shifts across dentine in extracted human crown segments with a flat, dentine occlusal surface in response to the following hydrodynamic stimuli; air blast, 56 degrees C water, 2 degrees C water, tactile and osmotic. In acid-etched superficial dentine, which simulates hypersensitive dentine, the largest to the smallest fluid flows obtained were: hot > cold > air blast > osmotic > tactile. When these were converted to equivalency units, the ranking of stimuli from strongest to weakest was hot > cold > air blast > osmotic > tactile. This new approach to comparing hydrodynamic stimuli should be verified in vivo.

Acid Etching, Dental↗

The Effectiveness of Systemp.desensitizer in the treatment of dentine hypersensitivity.

PURPOSE: This study reports the effectiveness of Systemp.desensitizer (Ivoclar Vivadent, Schaan, Liechtenstein), when used both with and without an acid-etch step, in the treatment of patients with dentine hypersensitivity in UK dental practices. MATERIALS AND METHODS: Ten general dental practitioners (GDPs) were selected from two practice-based research groups. The GDPs were each requested to use Systemp.desensitizer in the treatment of at least ten patients who presented with pain due to dentine hypersensitivity. Systemp.desensitizer was applied to the sensitive dentine area in strict accordance with the manufacturer's handling instructions, except that the patients were divided into two groups. For the first, group NE, the procedure was to isolate the tooth, gently blot it dry with cotton wool pellets, rub Systemp.desensitizer into the tooth for 20 seconds, then gently air-dry it. For the second, group E, the procedure was identical except that after isolation, the treatment area was etched for 15 seconds with 35% phosphoric acid. Patients were asked to complete a pro forma using a 10 cm visual analogue scale designed to provide details of the extent of their pain before treatment, 24 hours post-treatment, one week post-treatment, one month post-treatment, and three months post-treatment. The zero end of the scale was marked 'no pain' and the 10 cm end was marked 'extreme pain'. The percentage change in the patients' perception of their pain, relative to pretreatment, was calculated using repeated measures analysis and suitable follow-up confidence intervals for the mean changes in perceived pain. Comparisons were then made between the treatment groups NE and E. RESULTS: Ninety-one patients completed the first pro forma and 77 completed all the pro formas. Overall, there was a significant reduction in pain at each of the time points after treatment but the pattern of pain reduction across the two groups was different. In general, the non-etched group (group NE) saw an 'immediate' reduction in pain which was then fairly consistent across the longer term, whilst, in general, the etched group (group E) saw less reduction in pain 24 hours after treatment, and then further reduction in pain at both one week and one month after treatment. Thus the non-etched group experienced an early reduction whilst the etched group took longer to perceive a reduction in pain; however, there were no statistically significant differences between the reductions in pain scores between the two groups at any of the time points after treatment. CONCLUSION: It is concluded that Systemp.desensitizer was effective in reducing pain from dentine hypersensitivity in the patients treated, and this finding was unaffected by whether or not the tooth was acid-etched prior to application of the reagent.

Acid Etching, Dental↗

An update on the physiology of the dentine-pulp complex.

The properties of dentine and pulp are closely related and from a functional standpoint these tissues are often referred to as the dentine-pulp complex. In recent years there has been considerable progress in our understanding of the physiology of the dentine-pulp complex. This review describes some of the advances that are relevant to clinical dentistry, including dentine permeability, dentine bonding, dentine sensitivity, the properties of pulpal nerves and blood vessels and the reactions of the dentine-pulp complex to operative dental procedures.

Dental Bonding↗

Technique sensitivity of dentin bonding: effect of application mistakes on bond strength and marginal adaptation.

This in vitro study evaluated dentin bond strength and marginal adaptation of direct resin composites according to the manufacturers' instructions and with simulated application errors. One hundred and forty cavities were prepared into disks of freshly extracted human third molars and filled with one resin composite. Dentin adhesives of the third (with self-etching primer: Syntac Classic), fourth (with total etching: Scotchbond Multi-Purpose Plus) and fifth generation (one-bottle adhesive: Prime&Bond 2.1) were used for bonding. Simulated application mistakes were as follows: 1) prolonged etching; 2) excessive drying after conditioning; 3) drying primers immediately after application and 4) drying primers excessively. After 21 days of storage and 24 hours thermocycling (1150 cycles), replicas were made and push-out testing was performed. Replicas were examined for marginal adaptation using SEM (X200 magnification). Compared with values of the control groups, application errors resulted in dramatically decreased bond strengths and reduced percentages of gap-free margins for all products tested (p < 0.05). Excessive drying after conditioning exhibited significantly less effect for the third generation adhesive than for products requiring total etching/wet bonding.

Acid Etching, Dental↗

Closing of dentinal tubules by Gluma desensitizer.

Gluma Dentin Bond is an adhesive system, where the primer contains 5% glutaraldehyde and 35% hydroxyethyl methacrylate. Practitioners have reported a strong desensitizing effect of the Gluma system on dentin. This study, thus, sought to evaluate the effect of this system on dentin using various microscopic techniques. 12 non-restored human molars extracted for prosthodontic reasons were used. Prior to extraction the buccal cusps were removed such that a 2 mm x 2 mm wide dentin surface was exposed. The surfaces were treated in 6 ways: (1) application of Gluma 2 cleanser, Gluma 3 primer to which 0.1% w/v fluorescein was added, and Gluma 4 sealer; (2) as in (1) but treatment with H2O/0.1% w/v fluorescein instead of the Gluma 3; (3) as in (1) but without Gluma 2; (4) as in (1) but with application of 5% glutaraldehyde instead of Gluma 3; (5) as in (1) but without Gluma 4; (6) as in (1) but with application of 35% HEMA/0.1% w/v fluorescein instead of Gluma 3. Following extraction, 1 tooth per procedure was prepared for confocal laser scanning microscopy. The remaining teeth were fixed and prepared for SEM and TEM evaluation. In specimens of procedures (1) and (5), tubular occlusions could be seen to a depth of 200 microm. In specimens of procedure (4) tubular occlusions were found only to a depth of 50 microm. Such occlusions were not seen in control specimens (2), in specimens where the smear-layer had not been removed (3), or following application of HEMA alone (6). It is concluded that glutaraldehyde can intrinsically block dentinal tubules. The septa in the tubules may counteract the hydrodynamic mechanism for dentinal sensitivity.

Adhesives↗

ESR investigation of joint use of dentin and tooth enamel to estimate photon and neutron dose components of a mixed field.

In the case of mixed photon and neutron field, estimation of photon and neutron dose components from the ESR signal of tooth enamel alone is impossible. To differentiate neutron and photon components using the method described in ICRU 26 for twin chambers, enamel and dentin sensitivities to photon and to neutron were investigated. Enamel and dentin relative sensitivities were, respectively, estimated at 0.03 +/- 0.02 and 0.14 +/- 0.10 for fission neutrons. Basing on this result, calculation of neutron and photon doses was performed in realistic case of criticality accident. Estimation of neutron and photon dose components was found in good agreement with reference dosimetry.

Artifacts↗

Clinical effectiveness of a Class V flowable composite resin system.

This clinical study evaluated a Class V flowable composite resin restoration system and its ability to reduce dentin sensitivity. Twenty-one patients required Class V restorations because of erosion, abrasion, or decay at the cervical area. Each patient exhibited moderate or severe sensitivity and required replacement of tooth structure. The degree of sensitivity was determined by either tactile scraping of the tip of an explorer over the surface of the tooth or by an air blast from a syringe for 5 seconds. A total of 52 restorations were performed. According to phone conversations and questionnaires, 1 patient experienced continued sensitivity on 1 treated tooth for a duration of 1 week, but this sensitivity was gone at 1-month, 3-month, 6-month, and 1-year recalls. None of the other patients exhibited sensitivity at any phone checks or during recall visits.

Composite Resins↗