Influence of in-office whitening gel pH on hydrogen peroxide diffusion through enamel and color changes in bovine teeth.

PURPOSE: To assess the influence of in-office whitening gel pH on whitening efficiency. METHODS: Hydrogen peroxide diffusion and color changes on bovine teeth were assessed. Three gels with close hydrogen peroxide concentrations but with various pH levels were tested: Zoom 2 (Discus Dental), Opalescence Endo and Opalescence Boost (Ultradent). The pH levels were respectively: 3.0, 5.0 and 7.0. Thirty enamel slices and tooth crowns were used for both studies (n = 10 per group per study). Hydrogen peroxide diffusion through the enamel slices and the tooth crowns was spectrophotometrically recorded every 10 minutes for 1 hour to calculate the diffusion coefficients. Color changes were spectrophotometrically recorded every 10 minutes for 1 hour and quantified in term of CIE-Lab. RESULTS: The hydrogen peroxide diffusion coefficient through enamel ranged from 5.12 +/- 0.82 x 10(-9) cm2 s(-1) for pH 3 to 5.19 +/- 0.92 x 10(-9) cm2 S(-1) for pH 7. Through tooth crowns it ranged from 4.80 +/- 1.75 x 10(-10) cm2 s(-1) for pH 5 to 4.85 +/- 1.82 x 10(-10) cm2 s(-1) for pH 3. After 1 hour, the deltaE varied from 5.6 +/- 4.0 for pH 7 to 7.0 +/- 5.0 for pH 3 on enamel slices and from 3.9 +/- 2.5 for pH 5 to 4.9 +/- 3.5 for pH 7 on tooth crowns. There was no statistically significant difference between groups for both parameters.

Influence of acid etching on hydrogen peroxide diffusion through human dentin.

PURPOSE: To evaluate the influence of dentin etching with phosphoric acid on hydrogen peroxide diffusion through human dentin in internal bleaching. METHODS: 46 human premolars were extracted for orthodontic reasons from adolescents. The teeth were endodontically treated and a flat defect was created at the enamel-cementum junction. The teeth were divided into two groups: the access cavity was etched for 30 seconds with 35% H3PO4 in the first group and left intact in the second group. The teeth were filled with 20 microL of 35% hydrogen peroxide gel. The receiving medium on the other side was renewed at Day 1, Day 2 and Day 7 to quantify the diffusing hydrogen peroxide. An analysis of variance was performed to compare the diffusion between the two groups. RESULTS: This work demonstrated a higher hydrogen peroxide diffusion when the access cavity was etched (P < 0.01).

Why Molière most likely did write his plays.

As for Shakespeare, a hard-fought debate has emerged about Molière, a supposedly uneducated actor who, according to some, could not have written the masterpieces attributed to him. In the past decades, the century-old thesis according to which Pierre Corneille would be their actual author has become popular, mostly because of new works in computational linguistics. These results are reassessed here through state-of-the-art attribution methods. We study a corpus of comedies in verse by major authors of Molière and Corneille's time. Analysis of lexicon, rhymes, word forms, affixes, morphosyntactic sequences, and function words do not give any clue that another author among the major playwrights of the time would have written the plays signed under the name Molière.

Gingival contour assessment: clinical parameters useful for esthetic diagnosis and treatment.

BACKGROUND: The purposes of this study were to quantify some clinical parameters that are useful as esthetic guidelines when the gingival contour is modified and to compare the left and right sides of the six maxillary anterior teeth. METHODS: Maxillary casts mounted on an articulator according to the axis orbital plane were photographed from 103 young adults. The angle formed between the gingival line and the maxillary midline (GLA) and the distance between the gingival zenith of the lateral incisor and the gingival line (LID) were measured. The asymmetry was evaluated using a paired t test for the left versus right measurements of GLA and LID. The descriptive statistics for GLA and LID were calculated. RESULTS: The GLA measurements of the left side (86.5 degrees +/- 5.1 degrees ) were significantly greater than those of the right side (85.2 degrees +/- 4.9 degrees ), and the mean absolute asymmetry for GLA was 4.1 degrees +/- 3.0 degrees . The mean LID measurement was 0.68 +/- 0.52 mm. CONCLUSIONS: The gingival zenith of the canine is apical to the gingival zenith of the incisors (GLA <90 degrees ), and the gingival zenith of the lateral incisor is below (81.1%) or on (15%) the gingival line when the head is oriented in the axis orbital plane. A directional asymmetry was shown, with the right side higher than the left side. Along with other parameters related to dental esthetics, these clinical parameters applied to the gingival contours may serve as esthetic guidelines and may enable us to obtain a more predictable esthetic outcome.

Induction of specific cell responses to a Ca(3)SiO(5)-based posterior restorative material.

OBJECTIVES: A Ca(3)SiO(5)-based cement has been developed to circumvent the shortcomings of traditional filling materials. The purpose of this work was to evaluate its genotoxicity, cytotoxicity and effects on the target cells' specific functions. METHODS: Ames' test was applied on four Salmonella typhimurium strains. The micronuclei test was studied on human lymphocytes. The cytotoxicity (MTT test), the Comet assay and the effects on the specific functions by immunohistochemistry were performed on human pulp fibroblasts. RESULTS: Ames' test did not show any evidence of mutagenicity. The incidence of lymphocytes with micronuclei and the percentage of tail DNA in the Comet assay were similar to the negative control. The percentage of cell mortality with the new cement as performed with the MTT test was similar to that of biocompatible materials such as mineral trioxide aggregate (MTA) and was less than that obtained with Dycal. The new material does not affect the target cells' specific functions such as mineralization, as well as expression of collagen I, dentin sialoprotein and Nestin. SIGNIFICANCE: The new cement is biocompatible and does not affect the specific functions of target cells. It can be used safely in the clinic as a single bulk restorative material without any conditioning treatment. It can be used as a potential alternative to traditionally used posterior restorative materials.

Evaluation of a natural resin-based new material (Shellac F) as a potential desensitizing agent.

OBJECTIVES: To evaluate the cytotoxicity of Shellac F, a new fluoride varnish, and its effects on human dentin hydraulic conductance. METHODS: Shellac F was compared to another fluoride varnish (Duraphat) and a fluoride containing desensitizing agent (Isodan). The cytotoxicity test was performed on human gingival fibroblasts and through dentin slice on human pulp fibroblasts. The hydraulic conductance (Lp) was recorded by fluid filtration with a Flodec device under a constant pressure (15 cm H2O). The treated surface of the dentin disks and their sections were also investigated with SEM. RESULTS: The cytotoxicity test on gingival fibroblasts revealed that Duraphat was the least cytotoxic material, followed by Shellac F then Isodan. With dentin slice interposition, a lower level of cytotoxicity was obtained. All of them showed a lower cytotoxicity decreasing on further dilutions (p<0.001). The measurement of hydraulic conductance showed that all materials resulted in a significant decrease in dentin permeability after 24h comprising between 60 and 76%, but there was no statistically significant difference among the materials. This decrease was still over 50% of the initial values after 7 days for all three materials. SEM investigation showed dentin tubules covered with a thick layer of Shellac F or Duraphat whilst no material was observed on dentin surfaces treated with Isodan. SIGNIFICANCE: Shellac F showed an adequate cellular compatibility and a significant effect on human dentin hydraulic conductance. This indicates that the new material is safe and seems to be effective as a potential desensitizing agent.

Time-course diffusion of hydrogen peroxide through human dentin: clinical significance for young tooth internal bleaching.

The purpose of this study was to record the time-course diffusion of hydrogen peroxide through human dentin from a peroxide carbamide gel designed for the walking bleach technique in order to determine its optimal renewal time. It was considered that the optimal renewal rate corresponded to the time necessary to achieve 80% of the maximal diffusion because a much longer time does not involve further significant diffusion. Thirty-six freshly extracted human premolars were used for this study. Eighteen were extracted for orthodontic reasons on patients under 20 years old (young-teeth group). Eighteen were extracted for periodontal reasons on patients between 40 and 60 years old (old-teeth group). The teeth were endodontically treated, and a flat defect was created at the enamel-cementum junction. The teeth were suspended in vials containing water, and the access cavities were filled with 20 microL of 20% hydrogen peroxide gel. The amount of diffusing hydrogen peroxide was assessed at 1 hour, 24 hours, 48 hours, and 120 hours. The diffusive flux and the maximal diffusion were calculated as well as the optimal renewal time. Hydrogen peroxide diffusion through young teeth lasted 352 hours but lasted 291 hours through old teeth. Diffusive flux and maximal diffusion were higher through young teeth than through old teeth. The optimal renewal time for young teeth was 33 hours and for old teeth was 18 hours.

Activation of human dental pulp progenitor/stem cells in response to odontoblast injury.

In restorative dentistry, whilst moderate carious lesion treatment does not significantly compromise odontoblast cell survival, deep cavity preparation may lead to a partial death of these cells. However, newly formed odontoblast-like cells can replace the necrotic odontoblasts and secrete a reparative dentine matrix. Although several lines of evidence strongly suggest the presence of resting progenitor or stem cells in the dental pulp, little is known about the activation and migration of these cells in response to injury. Human immature third molars extracted for orthodontic reasons were used in this work to study the activation of progenitor/stem cells and their migration after deep cavity preparation involving in pulpal exposure using 5-bromo-2'-deoxyuridine labelling (BrdU). After incubation for 1 day, the BrdU was localised to the nuclei of cells in the perivascular area. The BrdU-immunolabelling exhibited a gradient. It was strong in the blood vessels surrounding the pulpal cavity and decreased in those away from the cavity. After incubation for 2 weeks, labelled cells were seen in the vicinity of the cavity. At 4 weeks, the immunolabelling was localised to the cavity area only. Control teeth without cavities or with shallow dentine cavities did not show any perivascular labelling after culture. These results clearly demonstrate that perivascular progenitor/stem cells can proliferate in response to odontoblast injury. They also show that these proliferating cells can migrate to the pulpal injury site in their tissue of origin simulating the situation in vivo.

Polymerized bonding agents and the differentiation in vitro of human pulp cells into odontoblast-like cells.

OBJECTIVES: Odontoblasts are highly differentiated post-mitotic cells, which under pathological conditions such as carious lesions and dental injuries may degenerate and be replaced by other pulp cells. We have recently shown that this physiological event can be reproduced in an in vitro assay system, but is highly modified by the presence of unpolymerized resinous monomers. Our hypothesis was that the photopolymerization of the monomers in the bonding agents might abolish these negative effects. The purpose of this study was to evaluate the effects of polymerized dentin bonding agents, through dentin slices, on odontoblast differentiation in vitro. METHODS: Pulp cells were obtained from human third molars. They were used to study the effects of four dentin bonding agents through 0.7 mm dentin slices which served as a barrier between the bonding agents and the culture medium. The media containing the bonding agents' extracts were added at non-toxic concentrations onto the cultured cells. Immunohistochemistry was performed to study the differentiation of pulp fibroblasts into odontoblasts under these conditions by evaluating the expression of several odontoblast specific genes. RESULTS: Pulp fibroblasts cultivated under these conditions synthesized type I collagen, osteonectin, dentin sialoprotein and nestin at the same level as in control cultures. Moreover, pulp cells synthesized a mineralized nodular extracellular matrix. Expression of these proteins was higher in the cells contributing to the nodule formation. In addition, except nestin, all these proteins were expressed in the mineral nodules. SIGNIFICANCE: This work shows the lack of effects of photopolymerized bonding agents, through dentin slices, on cytodifferentiation of secondary odontoblasts.

Bioactivity of a Calcium Silicate-based Endodontic Cement (BioRoot RCS): Interactions with Human Periodontal Ligament Cells In Vitro.

INTRODUCTION: Tricalcium silicate-based materials are recognized as bioactive materials through their capacity to induce hard tissue formation both in the dental pulp and bone. Sealing the apex implies that the root canal filling materials interact with the periapical tissues. This work was designed to study the interactions of newly developed tricalcium silicate cement (BioRoot RCS; Septodont, Saint Maur Des Fosses, France) with apical tissue compared with a standard zinc oxide-eugenol sealer (Pulp Canal Sealer [PCS]; SybronEndo, Orange, CA). METHODS: Cell viability was assessed by direct contact between human periodontal ligament (PDL) cells and BioRoot RCS or PCS. In addition, an in vitro tooth model was used to study the interactions between these materials and PDL cells. For this purpose, human extracted incisors were sectioned at the enamel-cementum junction; root canals were prepared, sterilized, and filled with lateral condensation with both materials. The root apices were dipped in the culture medium for 24 hours. These conditioned media were used to investigate their effects on human PDL cells. Cell proliferation was investigated with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and the secretion of angiogenic and osteogenic growth factors was quantified using an enzyme-linked immunosorbent assay. RESULTS: BioRoot RCS has less toxic effects on PDL cells than PCS and induced a higher secretion of angiogenic and osteogenic growth factors than PCS. CONCLUSIONS: Taken together, these preclinical results suggest that the calcium silicate cement (BioRoot RCS) has a higher bioactivity than the zinc oxide-eugenol sealer (PCS) on human PDL cells.

Implications of endodontic-related sinus aspergillosis in a patient treated by infliximab: a case report.

INTRODUCTION: Sinus aspergillosis is a potential complication after root canal therapy of antral teeth. Indeed, zinc oxide-eugenol cement overfilling in the sinus may promote fungal infection. Moreover, if sinus aspergillosis triggers chronic sinusitis with aspergilloma, it may also lead to invasive phenomena, especially for immunocompromised patients. METHODS: We reported a sinus aspergillosis case of a patient treated with infliximab (Remicade; Janssen Biologics BV, Leiden, Netherlands). The purpose of this article was to explore the mechanisms of this pathosis, especially the impact of the root canal sealer overextension, which is a contributing factor for fungal infection. The surgical management and the follow-up are also described. RESULTS: Six months after surgery, the patient showed no clinical signs and presented with a healthy and airy right maxillary sinus on the computed tomography scan. CONCLUSIONS: In conclusion, prevention and screening of aspergillosis of maxillary sinus may be considered before starting an anti-tumor necrosis factor alpha therapy.

Do cell phones affect establishing electronic working length?

INTRODUCTION: Patients often keep their cell phones on and nearby during root canal therapy. Cell phones release electromagnetic interference, which might disturb electronic working length measurements. The purpose of this ex vivo study was to determine the effect of a cell phone (Apple iPhone 5 [Apple, Cupertino, CA] or KP100 [LG, Seoul, Korea]) placed into direct contact with an electronic apex locator (EAL) (Dentaport Root ZX module [J Morita Corp, Tokyo, Japan] or Propex II [Dentsply Maillefer, Ballaigues, Switzerland]) on working length determination. METHODS: Twenty-six human premolars without fractures or carious lesions were used; previously cleaned; and observed under magnification (×15) in order to check for the presence of only 1 apical foramen, the absence of apical resorption, an "open" apex, and accessory canals. The working length measurement was performed with a #15 K-file in the presence of 2.6% sodium hypochlorite under 4 conditions: (1) visually, under the microscope until the file tip reached the canal terminus; (2) electronically, without the cell phone in proximity; (3) electronically, with the cell phone in standby mode placed in physical contact with the EAL; and (4) electronically, with the cell phone activated by a call in the same position. The experimental model for electronic working length determination was a screw top plastic container filled with a saline solution. The measurements were repeated 3 times per canal under each condition. Scores of 1 to 3 categorized the stability of the readings as follows: (1) good stability; (2) unstable reading with minor difficulties determining the working length; and (3) major difficulties or impossible to determine the working length. A 2-way repeated measures analysis of variance (way 1: cell phone type and way 2: EAL model) was performed, and a second repeated measures analysis of variance was performed to seek a difference among the 4 working length determination conditions. RESULTS: Neither the cell phone type nor the EAL affected the measurements (not significant). The electronic working length measurements gave the same results as the visual examination, and this length was not influenced by direct contact with a cell phone (not significant). It was also possible to determine the electronic working length under all the experimental conditions. CONCLUSIONS: Within the limitations of the present study, it can be concluded that patients can keep their cell phones on during root canal therapy without any adverse effect on electronic working length determination.

In vivo sensitivity of human root dentin to air blast and scratching.

BACKGROUND: The present study evaluated the prevalence of radicular sensitivity to scratching as well as the effects of a common oxalate desensitizing agent on sensitivity to air blast and scratching. METHODS: Eighty-seven patients self-reporting dentin hypersensitivity, with at least two hypersensitive teeth, were included. Prior to any treatment, their sensitivity to air blast was recorded and rated as absent or present, and the force necessary to trigger pain when scratching was measured with a scratchometer in cN. For each patient one sensitive tooth was treated with an oxalate desensitizing agent and the other one with a placebo solution. The same measurements were carried out after treatment. RESULTS: Following treatment with a placebo solution, 70% of the teeth remained sensitive to air blast while only 38% of the desensitizing agent-treated teeth remained sensitive to air blast (P < 0.01). The mean force required to elicit pain prior to any treatment was 44 +/- 17 cN. This force statistically increased significantly after application of the placebo (53 +/- 17 cN) (P < 0.05). After using the desensitizing agent, the force was even higher (95 +/- 24 cN) (P < 0.01). Only 8% of the teeth treated with the desensitizing agent did not respond to treatment compared to 37% of the teeth treated with the placebo solution. CONCLUSIONS: The placebo solution had a significant effect on sensitivity to air blast and to scratching (P < 0.05). The oxalate desensitizing agent was more effective than the placebo solution at decreasing the sensitivity both to air blast and to scratching (P < 0.01). The sensitivity to air blast seems to be overestimated because, after using the desensitizing agent, 38% of the teeth remained sensitive to air blast but only 8% remained sensitive to scratching. Pulpal inflammation may be involved in those teeth that did not respond to treatment.

Cytotoxicity testing of endodontic sealers: a new method.

The purpose of this study was to compare ISO standards versus a new technique for in vitro evaluation of cytotoxicity of root canal sealers. The cytotoxicity of AH Plus, Cortisomol, and Sealapex was first recorded according to ISO standards on L 929 fibroblasts by the MTT assay. In parallel, 30 single-rooted teeth were cut at the cementum enamel junction (CEJ), and the roots were prepared and sterilized before filling with the lateral condensation using one of three sealers (n = 10). The apexes of the roots were dipped into 1 ml of minimum essential medium for 1, 2, and 30 days renewing the medium every other day. After 24-h contact between the medium and the filled roots, the medium was used to measure the cytotoxicity on L 929 with the MTT assay. ISO standards always gave a statistically higher cytotoxicity than the root-dipping technique (p < 0.0001), whatever the sealer and the exposure time. The ISO standards showed statistically significant differences among the sealers (p < 0.0001). AH Plus was noncytotoxic, Cortisomol showed a high cytotoxicity decreasing over time (p < 0.001), and Sealapex displayed a high cytotoxicity that did not decrease over time (NS). The new technique showed statistically significant differences among the sealers (p = 0.001), but the differences were so small that they were likely not clinically relevant. The high cytotoxicity of Sealapex decreased over time but the cytotoxicity of AH Plus and Cortisomol did not. The results show that the ISO standards may strongly over-evaluate the cytotoxicity of the endodontic sealers, emphasize the difference among the sealers, and may clinically correspond to a large overfilling. The new technique reduces the discrimination of the test and may clinically correspond to a classical filling. Therefore, both methods might be considered as clinically relevant, corresponding to classical and overfilling conditions.

Reliability of the dye penetration studies.

The purpose of this study was to compare the classical dye-penetration method to a dye-extraction method, with a fluid-filtration method as control. Forty teeth were prepared with a ProFile device and divided into four groups (n = 10 per group) according to the sealer used for the lateral condensation: Pulp Canal Sealer, Sealapex, AH Plus, and Ketac-Endo. The apical seal was evaluated on the same teeth with all three methods, successively: a fluid-filtration method, a dye-penetration method with 2% methylene blue, and a new method where the roots were dissolved in 65% nitric acid to extract the methylene blue before reading the absorbance of the solution. The classical dye penetration did not show any difference among the sealers and showed no correlation with the two other techniques. The fluid filtration (p < 0.01) and the dye extraction (p < 0.01) showed that Sealapex displayed the highest apical leakage. The correlation between the results obtained with these two methods was significant (p = 0.001 and r = 0.7). This study showed the limitation of the classical dye-penetration studies and that the dye-extraction, i.e. dissolution, method gave the same results as fluid filtration but saved much laboratory time.

Evaluation of periapical lesion healing by correction of gray values.

The purpose of this study was to compare two methods for evaluating periapical healing in humans: the periapical index (PAI) and a gray value correction method. Fifty human teeth with a periapical lesion were endodontically treated. Radiographs, with a special aluminum device, were taken postoperatively, after 3 months and after 6 months. The PAI was recorded at each period of time, and a Kruskall and Wallis test was performed to compare the three groups. After scanning, the size of the lesion and its gray value were recorded. The aluminum device allowed the gray values to be equalized. An analysis of variance followed by a Duncan test was performed to compare the three groups. The teeth that showed no sign of healing according to the PAI were separately analyzed by an analysis of variance and a Duncan test. The PAI (n = 50) showed signs of periapical healing over time (p < 0.01). The analysis of variance, based on gray value evaluation (n = 50), also showed signs of periapical healing over time (p < 0.002). The analysis of variance of teeth with the same PAI over time (n = 15 at 3 months, and n = 5 at 6 months), based on gray value evaluation showed statistically significant differences among the 3 groups (p < 0.02). These results show that the gray level correction method is powerful and may reduce the risks of false negative responses during assessment of treatment results or epidemiological studies.

Apical leakage of four endodontic sealers.

The purpose of this study was to evaluate the sealing properties of four root canal sealers. Forty-eight maxillary central incisors were instrumented with Profile rotary instruments. They were randomly divided into four groups (n = 12) and filled using lateral condensation with one of the four sealers: Sealapex, Pulp Canal Sealer, AH 26, and Ketac-Endo. The apical leakage was measured with a fluid filtration method and expressed as L s(-1) KPa(-1). The teeth filled with Sealapex displayed a higher apical leakage (8.42 +/- 4.2 10(-11) L s(-1) KPa(-1)) than those filled with AH 26 (2.10 +/- 1.39 10(-11) L s(-1) KPa(-1)), Pulp Canal Sealer (0.17 +/- 0.09 10(-11) L s(-1) KPa(-1)) or Ketac-Endo (0.32 +/- 0.24 10(-1) L s(-1) KPa(-1)) (p < 0.01). No statistically significant difference was found among AH 26, Pulp Canal Sealer, and Ketac-Endo. No correlation was found between the sealing efficiency of the four sealers and their adhesive properties recorded in a previous study.

Adhesion of endodontic sealers to dentin and gutta-percha.

Adhesion of endodontic sealers to dentin and gutta-percha offers clues into their interaction with the wall of the root canal and the filling material. In this in vitro study, four classes of endodontic sealers (Kerr, a ZOE-based sealer; Sealapex, a calcium hydroxide-based sealer; AH 26, an epoxy resin-based system; and Ketac-Endo, a glass-ionomer based sealer) were compared for their ability to bond to dentin or gutta-percha. Flat coronal dentin or gutta-percha surfaces were created by using a diamond-impregnated saw blade. Aluminum cylinders (ca. 5-mm diameter) were stabilized on the substrates with small amounts of wax and then filled with one of the sealers. After setting in 100% humidity for 24 h, their tensile bond strengths were measured. Controls were the unfilled cylinders stabilized with wax. The bond strengths and modes of failure were measured. The results were statistically analyzed by using a two-way ANOVA (materials versus substrates) and Student-Newman-Keuls test at alpha = 0.05. The results indicated that sealant bond strengths to dentin (from lowest to highest mean +/- SD, n = 10) were: Kerr 0.13 +/- 0.02; Sealapex 0.30 +/- 0.08; Ketac-Endo 0.80 +/- 0.24; AH 26 2.06 +/- 0.53 MPa. The latter two were significantly different (p < 0.05) from the first two sealers and from themselves. The sealant bond strength to gutta-percha (from lowest to highest mean +/- SD, n = 10) were: Ketac-Endo 0.19 +/- 0.01; Sealapex 0.22 +/- 0.01; Kerr 1.07 +/- 0.19; AH 26 2.93 +/- 0.29 MPa. AH 26 gave the significantly highest bonds to gutta-percha.

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.

Efficiency and cytotoxicity of resin-based desensitizing agents.

PURPOSE: To compare in vitro the efficacy of five resin-based desensitizing agents at reducing human dentin permeability and to compare their cytotoxicity. The tested hypothesis was that their different curing techniques cause variations in efficiency and cytotoxicity. MATERIALS AND METHODS: Dentin slices (0.5 +/- 0.05 mm thick) were prepared from human third molars (10 per group) and their hydraulic conductance was recorded before and after application of one of the desensitizing agents with a Flodec device. Six desensitizing agents were studied: one light curing agent (Seal and Protect); one self-curing agent (Pain Free); the resin-based agents without any polymerization initiator (Health-Dent, Gluma Desensitizer, Isodan); one oxalate-based agent served as a control (Protect). A MTT assay on L 929 fibroblasts was performed to measure the cytotoxicity of the six desensitizing agents applied onto additional dentin slices (10 per group). RESULTS: All the desensitizing agents resulted in a large decrease in dentin permeability. The best results were obtained with Gluma Desensitizer, Isodan, Pain Free and Protect. A statistically significant difference was found among the materials (P = 0.001). All the materials were non-cytotoxic. Cell viability ranged from 88% for Seal and Protect to 100% for Isodan. No difference was found among their cytotoxicity.