Dentin matrix component solubilization by solutions of pH relevant to self-etching dental adhesives.

PURPOSE: To evaluate the potential for phosphoric acid solutions - common constituents of dental adhesive systems - of varying pH to solubilize dentin matrix components (DMCs) from human dentin. MATERIALS AND METHODS: Human dentin chips were ground under liquid nitrogen to a powder (ca 100 µm) and incubated at 4°C with agitation in phosphoric acid of pH 1, 2, 3, 4, 5, and 6 (1 g/4 ml; n = 4) for six days with solution changes each day. Estimates of daily protein release were made by UV spectrophotometry at 280 nm. Extract solutions were dialyzed for 7 days in reverse osmosis water, lyophilized, and weighed. Non-collagenous proteins (NCPs) and glycosaminoglycans (GAGs) were quantitated by dye-binding assays. 1D-PAGE for preliminary protein characterization and sandwich ELISA for presence of TGF-ß1 were performed. The results were analyzed by ANOVA and regression (α <= 0.05). RESULTS: Protein release was drastically reduced after the first few days, with the highest amounts obtained from pH 1. There was no significant difference in the quantity of DMCs solubilized by the different pH levels, but there was a significant logarithmic relation between release and pH, suggesting that greater DMC solubilization occurs with higher hydrogen ion concentrations. Dye binding assays confirmed the release of NCPs and GAGs at all pH levels. There were only subtle differences in protein bands observed between the different pH levels (1D-PAGE). Significant levels of TGF-ß1 were identified from extraction at all pHs. CONCLUSION: Acids at pH levels relevant to those used in commercial dentin adhesives are capable of solubilizing human DMCs, with release being related to hydrogen ion concentration.

Effects of a novel fluoride-containing aluminocalciumsilicate-based tooth coating material (Nanoseal) on enamel and dentin.

PURPOSE: To investigate the effect of a fluoride-containing aluminocalciumsilicate nanoparticle glass dispersed aqueous solution (Nanoseal) on enamel and dentin, under the hypothesis that this material can form insoluble mineral deposits that confer acid resistance to the tooth structure and occlude open dentin tubules. METHODS: Labial enamel and dentin of human extracted incisors were used. Morphology of the enamel and dentin artificially demineralized with a lactic acid solution that before and/or after coated with the test material were analyzed with a wavelength-dispersive X-ray spectroscopy electron probe microanalyzer with an image observation function (SEM-EPMA). Moreover, incorporation of the calcium and silicon by enamel and dentin were also detected with SEM-EPMA. RESULTS: Application of the fluoroaluminocalciumsilicate-based tooth coating material resulted in the deposition of substances (nanoparticles) onto the enamel surface porosities and open dentin tubules on the artificial lesions. Prior coating with the test material reduced the demineralization-induced loss of enamel and dentin. Moreover, Ca and Si incorporation into superficial enamel and dentin was detected.

Mineral ions in the fluid of biofilms formed on enamel and dentine shortly after sugar challenge.

To test the effect of distinct solubilities of dentine and enamel on mineral ion concentration in the biofilm fluid during a sugar-induced pH drop, dental biofilms were formed in situ for 4 days on acrylic (control), dentine or enamel. On the 5th day, they were treated with water (control) or 20% glucose and collected 5 min later. Significantly lower pH values and higher calcium concentrations were found in the biofilm fluid after glucose exposure, without significant differences among the three substrates. During pH drop, biofilm reservoirs release calcium to the fluid, masking the differential solubility between enamel and dentine.

The impact of root dentine conditioning on sealing ability and push-out bond strength of an epoxy resin root canal sealer.

AIM: To investigate the impact of dentine conditioning on sealing ability and dentine bond strength of an epoxy resin sealer. METHODOLOGY: Root canals in 90 single-rooted teeth were instrumented using a rotary Ni-Ti system. Fifty canals were irrigated with water during instrumentation, 40 with 3% NaOCl. A final flush was performed in the water-irrigated specimens with water (negative control), 3% NaOCl, 17% EDTA, 7% maleic acid (MA) or 2% chlorhexidine. The hypochlorite irrigated specimens received a final flush with a decalcifying agent (EDTA or MA) and then 3% NaOCl or 3% NaOCl and then the decalcifying agent (n = 10, each). Canals were all filled with AH Plus. Fluid transport was measured on day 3 and 30. Roots were then sectioned, and push-out tests were performed in coronal, middle and apical root thirds. Results were analysed using analysis of variance (anova) with Bonferroni's adjustment. Spearman's rank correlation was computed between fluid transport and push-out bond strength. RESULTS: Leakage decreased over time (P < 0.05). Push-out bond strength was highest in coronal and lowest in apical root thirds (P < 0.05). Irrigating protocols with final application of a decalcifying agent greatly decreased the leakage and increased push-out bond strength values, in contrast to groups where NaOCl was applied last (P < 0.05), wherein the effect of the decalcifying agent was abolished. Chlorhexidine had no impact on the outcomes. Fluid transport and push-out bond strength correlated strongly (ρ = -0.83). CONCLUSIONS: AH Plus appears to bond to the organic phase of dentine. This bond influences its sealing ability.

Smear layer dissolution by peracetic acid of low concentration.

AIM: To test the effect of a noncaustic concentration of peracetic acid (PAA) in a standardized smear layer model. METHODOLOGY: The smear layer dissolution kinetics of 0.5% PAA on human dentine were compared to those of 2.25% PAA and 17% ethylenediaminetetraacetic acid (EDTA) solutions. Coronal dentine discs were prepared from six human maxillary molars. A standardized smear layer was produced on the pulpal side of each disc. The smear layer-covered surface was divided into three similar areas and then exposed to one of the three solutions tested. Co-site image sequences (around 40, 500 ×) of the specific areas were obtained after four cumulative demineralisation times (15, 30, 60 and 180 s). An image processing and analysis sequence measured sets of images, providing data of area fraction (AF, dentine-free area in % of total analysis area). A general linear model for repeated measures was used to verify the influence of time and solution type over the change in AF from baseline (ΔAF). RESULTS: Overall, EDTA and 2.25% PAA produced higher ΔAF values than the 0.5% PAA solution (P < 0.05). No significant difference was observed in ΔAF between 15 s and 30 s (P > 0.05). After 60 s of etching, all tested solutions produced similar ΔAF (P > 0.05), whereas at 180 s, ΔAF of both EDTA and 2.25% PAA continued to increase (P > 0.05). CONCLUSIONS: After 60 s of contact, the 0.5% PAA solution dissolved smear layer as well as 2.25% PAA and 17% EDTA.

Influence of five home whitening gels and a remineralizing gel on the enamel and dentin ultrastructure and hardness.

PURPOSE: To investigate the influence of calcium phosphate enhanced home whitening agents on human enamel and dentin surface microhardness and ultramorphology. METHODS: Five intact molars crowns were used for ultrastructural analysis and five for microhardness test. Each resulting coronal structure was cut in slices. After measuring baseline Knoop Hardness Number (KHN) of the enamel and dentin, the slices were divided into six experimental groups and one control (n= 5). G1= 15% carbamide peroxide (CP); G2= 16% CP; G3= Ca and PO4 (remineralizing agent); G4= 16% CP with Ca and PO4; G5= 7.5% hydrogen peroxide (HP) with Ca and PO4; G6=7.5% HP with Ca. After each daily session of treatment, specimens were stored in distilled water (37 degrees C) until the next session. Products were applied for 2 weeks, according to manufacturers' instructions. Additional KHN weredetermined. RESULTS: Conventional whitening agents (G1; G2) and the gel with Ca (G6), caused KHN decrease (P< 0.05).The remineralizing and whitening agents with Ca and PO4 (G3; G4; G5) did not change KHN. A change of morphology was observed on enamel and dentin surfaces in G1; G2; G5.

Calcium phosphate-based solutions promote dentin tubule occlusions less susceptible to acid dissolution.

PURPOSE: To determine the efficacy supersaturated calcium phosphate (CaP) solutions containing fluoride (F) and zinc (Zn) ions in occluding dentin tubules with precipitates less susceptible to acid dissolution and to compare the performance of these solutions with the oxalate solutions containing calcium (Ca) or phosphate (P) ions. METHODS: Dentin sections from human molars divided into groups: Group A - control (treated with double distilled H2O), Groups A1, A2 and A3 were treated with experimental solutions supersaturated with respect to F and Zn-substituted calcium phosphates. Solutions A1 and A2 were similar in composition but differed in pH values (A1, pH 7; A2, pH 5.5). Solutions A2 and A3 were similar in pH (pH 5.5) but the A3 solution had twice the concentrations of F and Zn2+ ions compared to A2. Another group of dentin sections were treated with A3 solution, oxalate solution containing Ca (OX/Ca) and OX solution containing P (OX/P). The control and treated dentin sections were characterized using scanning electron microscopy. RESULTS: All treated dentin sections showed occluded dentin tubules; with the group A3 showing the highest percent of occluded dentin tubules. The precipitates in the dentin tubules treated with A3 remained while those treated with OX/Ca or OX/P dissolved after exposure to an acidic buffer.

Development of an acid challenge-based in vitro dentin disc occlusion model.

OBJECTIVE: The objective of this study was to evaluate the utility of a novel acid challenge-based dentin disc occlusion model, and to compare the occluding effect and acid resistance exhibited by currently marketed occlusion dentifrices in vitro. METHODS: Ninety-six bovine dentin discs were polished and etched in citric acid (6% w/w) for two minutes to provide a smooth dentin surface with patent tubules. The discs were divided into three treatment groups. Each treatment group was brushed (Oral-B Vitality Precision Clean/EB 17 FlexiSoft head) twice a day, for up to four days, with either a strontium acetate dentifrice (Sensodyne Rapid Relief), an arginine-based dentifrice (Colgate Sensitive Pro-Relief), or water. Prior to and between treatments, the dentin samples were stored in human saliva. On days 3 and 4, following dentifrice treatment and incubation in saliva (60 minutes), the samples were subjected to a grapefruit juice challenge. Eight samples from each treatment group were removed from the study on each day and analyzed by scanning electron microscopy (SEM). The SEM images were graded according to a categorical occlusion scale, and the data were analyzed by ANOVA. RESULTS: The strontium acetate dentifrice occluded dentin tubules significantly better than the negative control (water) on days 1 through 4 (day 4 p < or = 0.0001). The marketed occlusion-based dentifrices demonstrated various degrees of dentin tubule occlusion over the four days. The strontium acetate dentifrice demonstrated significantly better occlusion than a currently marketed arginine-based occlusion dentifrice on day 1 (p = 0.0337), day 2 (p = 0.0021 ), and day 4 (p < or = 0.0001). CONCLUSION: An in vitro model has been developed that can differentiate the dentin tubular occlusive effects of currently marketed occlusion dentifrices. Surface analysis reveals that the occluding deposits vary according to product, and that some are more susceptible to acid mediated dissolution.

Impact of irrigant sequence on mechanical properties of human root dentin.

To get the root canal system free of organic debris and the smear layer, it has been recommended to irrigate with a NaOCl solution during instrumentation, followed by a rinse with a chelating agent such as ethylenediaminetetraacetic acid (EDTA) and a final irrigation with NaOCl. However, both hypochlorite and EDTA weaken dentin through dissolution of its organic and inorganic components, respectively. EDTA exposes the organic dentin matrix, which could then be attacked more easily by hypochlorite. It was the aim of this study to assess the impact of different irrigation sequences of NaOCl (2.5% w/v; total exposure time, 24 minutes) and EDTA (17%; 3 minutes) on the elastic modulus and flexure strength of standardized human root dentin bars (n = 11 per group). Exposures to solely EDTA (3 minutes), NaOCl (24 minutes), and water were used as control treatments. Specimens were subjected to 3-point bending tests; modulus of elasticity and flexure strength values were compared between groups with one-way analysis of variance followed by Fisher probable least-squares difference test. The alpha-type error was set at .05. The 24-minute exposure to the hypochlorite solution caused a significant drop in flexure strength compared with water- or EDTA-treated controls (P < .05), whereas the elastic modulus remained unaffected. In contrast, the short exposure to EDTA as is clinically recommended did not affect the mechanical dentin parameters under investigation, regardless of the irrigant sequence that was used.

The efficacy of techniques for the disinfection of artificial sub-surface dentinal caries lesions and their effect on demineralization and remineralization in vitro.

OBJECTIVES: The efficacy of three techniques for the disinfection of artificial sub-surface root caries lesions and their response to subsequent episodes of de- and remineralization was investigated quantitatively in vitro. METHODS: Sub-surface dentinal lesions (n=20), cut into four experimental blocks and deliberately contaminated with Streptococcus mutans, were subject to either steam autoclaving (121 degrees C, 5min), gamma irradiation (4100Gy), immersion in 0.1% (w/v) thymol-distilled water solution (24h) or reserved as a control. Next, the lesions were incubated aerobically in sterile nutrient broth for 24h at 37 degrees C and resultant cultures plated onto blood agar and neutralisation agar. Ten blocks from each experimental group were then immersed in an acidic buffer solution or exposed to artificial saliva for 5 days. Baseline changes in the mineral content and distribution of the lesions were assessed by transverse microradiography (TMR). RESULTS: Micro-organisms were recovered from each control block and one block treated by gamma irradiation. Steam autoclaving and immersion in a thymol solution significantly decreased (p<0.05) the amount of mineral lost from the body of lesions subject to a further acid challenge. Mineral ion uptake by lesions exposed to artificial saliva was significantly increased (p<0.05) through disinfection by steam autoclaving. CONCLUSIONS: Gamma irradiation proved the most acceptable method for the disinfection of sub-surface root dentine lesions having the least adverse effect on demineralization and remineralization.

Dissolution of bio-active dentine matrix components by mineral trioxide aggregate.

OBJECTIVES: To analyze the soluble components of setting and set mineral trioxide aggregate (MTA), assess the abilities of two varieties of MTA and Ca(OH)(2) solutions to solubilise dentine matrix proteins (DMPs) and determine if these extracts contain signalling molecules important to pulpal repair and regeneration. METHODS: The metallic ion composition of solutions of white and grey MTA (pH 11.7), 0.02M Ca(OH)(2) (pH 11.9) and 10% EDTA (pH 7.2) was determined using atomic absorption spectroscopy. Extracellular dentine matrix components from powdered human dentine were extracted using all solutions over 14 days. Extracts were analysed for concentrations of non-collagenous proteins (NCPs) and glycosaminoglycans (GAGs), and protein profiles were examined using 1D-polyacrylamide gel electrophoresis (1D-PAGE). ELISAs for TGF-beta1 and adrenomedullin (ADM) were also performed. RESULTS: Aluminium, calcium, potassium, and sodium ions were detected in both white and grey MTA solutions. MTA and Ca(OH)(2) solutions liberated similar amounts of GAGs and NCPs although yields were considerably lower than those obtained using the EDTA solution. 1D-PAGE analysis demonstrated differences in protein profiles solubilised from dentine for all solutions. All extracts contained TGF-beta1 and ADM, EDTA solution liberated significantly greater amounts of TGF-beta1, and Ca(OH)(2) and grey MTA solutions released more ADM. CONCLUSIONS: These data imply that when placed clinically soluble components of set and setting MTA may release dentine matrix components that potentially influence cellular events for dentine repair and regeneration.

Stannous fluoride/sodium hexametaphosphate dentifrice increases dentin resistance to tubule exposure in vitro.

OBJECTIVE: The purpose of this study was to compare the reactivity of three dentifrice formulations on smear layer-covered root dentin surfaces, and the effects of the formulation treatments on resistance to acid softening and dentinal tubuli disclosure. METHODOLOGY: Commercial dentifrices, including Crest Cavity Protection Regular, Colgate Total, and a new dentifrice comprised of stannous fluoride/sodium hexametaphosphate (SnF2/HMP: Crest Pro-Health), were cycled through a pre-treatment period on smear layer-covered dentin surfaces, including intermittent soaking in dentifrice slurries and whole human saliva immersion. Following pre-treatments, the cycling treatments were modified to include dietary acid exposure, including soaks in an acidic soft drink. Vickers surface microhardness, variable pressure scanning electron microscopy (VP-SEM), and confocal laser scanning microscopy in reflection mode (CLSM) were used to characterize dentin reactivity and smear layer protection. RESULTS: CLSM and SEM analyses showed that specimens treated with SnF2/HMP appeared to resist acid solubilization, evidenced by the absence of disclosed dentinal tubuli. The histo-tomographic observations in this study were in agreement with the hardness measurements. The superior surface protection of dentin with SnF2/HMP would suggest potential benefits in ameliorating dentinal hypersensitivity in the clinical situation. CONCLUSION: A stannous fluoride/sodium hexametaphosphate dentifrice prevents dietary acid softening and tubule exposure of smear layer dentin surfaces.

Effect of sodium hypochlorite on primary dentin--a scanning electron microscopy (SEM) evaluation.

OBJECTIVE: The aim of this study was to evaluate the alterations of etched deciduous dentin when submitted to different time and concentrations of sodium hypochlorite (NaOCl), using scanning electron microscopy (SEM). MATERIAL AND METHODS: Forty deciduous anterior teeth were selected, cleaned and ground until expose a flat dentin area on the buccal surface. The specimens were randomly distributed into eight groups (n=5), according to dentin surface treatment (35% phosphoric acid etching for 7s--AE and/or NaOCl application), NaOCl solution concentration (5% or 10%), and time of application (0, 30, 60, and 120 s), as follows: G1: control (without AE and NaOCl); G2: only AE; G3, G4, and G5: AE+5% NaOCl for 30, 60, and 120 s, respectively; G6, G7, and G8: AE+10% NaOCl for 30, 60, and 120 s, respectively. All specimens were prepared for SEM analysis and the photomicrographs (three for each specimen) were classified according to a score as follow: 0: presence of smear layer (SL); 1: absence of SL+non-altered collagen fibrils; 2: absence of SL+collagen fibrils slightly altered; 3: absence of SL+collagen fibrils severely altered; and 4: absence of SL and absence of collagen fibrils. Data were submitted to Kruskal-Wallis and Mann-Whitney tests (p<0.05). RESULTS: All groups treated with NaOCl solution were significant different from G1 and G2, and showed alterations on the collagen fibrils network. Collagen complete removal was only observed when a 5% NaOCl solution was applied for 120 s and 10% NaOCl solution for 30, 60, and 120 s. CONCLUSIONS: The NaOCl action produced significant changes in the etched deciduous dentin. The higher NaOCl concentration, the lower the time required to completely removing the collagen fibrils network in deciduous dentin.

Dentin matrix components extracted with phosphoric acid enhance cell proliferation and mineralization.

OBJECTIVE: Acids, such as those used in adhesive dentistry, have been shown to solubilize bioactive molecules from dentin. These dentin matrix components (DMC) may promote cell proliferation and differentiation, and ultimately contribute to dentin regeneration. The objective of this study was to evaluate the potential for varying concentrations of DMC extracted from human dentin by phosphoric acid of a range of pHs to stimulate proliferation and mineralization of two different cultured pulp cell populations. METHODS: DMC were solubilized from powdered human dentin (7 days - 4°C) by phosphoric acid of pH 1, 3, and 5 and also, EDTA. Extracts were dialyzed for 7 days against distilled water and lyophilized. Undifferentiated mouse dental pulp cells (OD-21) and cells of the odontoblast-like cell line (MDPC-23) were seeded in six-well plates (1×10(5)) and cultured for 24h in DMEM (Dulbecco's modified Eagle's medium) containing 10% (v/v) FBS (fetal bovine serum). The cells were washed with serum-free medium and then treated with different concentrations of DMC (0.01, 0.1, 1.0 and 10.0µg/ml) daily in serum free medium for 7 days. After 3, 5 (MDPC-23 only), and 7 days of treatment, cell proliferation was measured using 10vol% Alamar blue solution, which was added to each well for 1h. Cell numbers were first measured by cell counting (Trypan blue; n=5) and Alamar blue fluorescence to validate the assay, which was then used for the subsequent assessments of proliferation. Mineralization was assessed by Alizarin Red S assay after 12 days exposure to DMC (n=5). Controls were media-only (DMEM) and dexamethasone (DEX; positive control). Results were analysed by ANOVA/Tukey's (p≤0.05). RESULTS: There was a linear correlation between cell counts and Alamar blue fluorescence (R(2)>0.96 for both cell types) , verifying the validity of the Alamar blue assay for these cell types. In general, there was a dose-dependent trend for enhanced cell proliferation with higher concentration of DMC for both cell lines, especially at 10.0µg/ml. DEX exposure resulted in significantly higher mineralization, but did not affect cell proliferation. DMC exposure demonstrated significantly greater mineralization than media-only control for 10µg/ml for all extracts, and at lower concentrations for EDTA and pH 5 extracts. SIGNIFICANCE: Human dentin matrix components solubilized by acids at pH levels found in commercial dentin adhesives enhanced cell proliferation and mineralization of mouse and rat undifferentiated dental pulp cells when presented in adequate concentration.

Influence of pulse frequency Er:YAG laser on the tensile bond strength of a composite to dentin.

PURPOSE: To evaluate the influence of different pulse frequencies of Er:YAG laser on the tensile bond strength of a composite to dentin. METHODS: The dentin surface treatment was performed by Er:YAG laser at 1, 2, 3 and 4Hz pulse frequencies and 80 mJ, for 20 seconds, followed by etching. The control group was etched by phosphoric acid solely. The Single Bond/Z250 system was used. The specimens were subjected to tensile strength tests in a testing machine (0.5mm/minute) after water storage (37 degrees C/24 hours). RESULTS: The averages in MPa were: 1Hz: 13.45 (+/- 5.31); 2Hz: 9.54 (+/- 2.13); 3Hz: 7.29 (+/- 1.26); 4Hz: 7.41 (+/- 2.44) and control group: 16.95 (+/- 2.57). The Kruskal-Wallis test revealed statistically significant difference. The increased frequency of the Er:YAG laser decreased the composite bond strength.

Evaluation of the effect of endodontic irrigation solutions on the microhardness and the roughness of root canal dentin.

The purpose of this study was to evaluate the effect of 0.2% chlorhexidine gluconate on the microhardness and roughness of root canal dentin compared with widely used irrigation solutions. Ninety, mandibular, anterior teeth extracted for periodontal reasons were used. The crowns of the teeth were removed at the CEJ. The roots were separated longitudinally into two segments, embedded in acrylic resin, and polished. A total of 180 specimens were divided into 6 groups of 30 teeth at random according to the irrigation solution used: group 1: 5.25% NaOCl for 15 min; group 2: 2.5% NaOCl for 15 min; group 3: 3% H2O2 for 15 min; group 4: 17% EDTA for 15 min; group 5: 0.2% chlorhexidine gluconate for 15 min; and group 6: distilled water (control). Each group was then divided into 2 subgroups of 15 specimens: groups 1a, 2a, 3a, 4a, 5a, and 6a were submitted to Vickers microhardness indentation tests; groups 1b, 2b, 3b, 4b, 5b, and 6b were used for determination of the roughness of root dentin. The data were recorded as Vickers numbers and Ra, microm for roughness test. The results were analyzed statistically by using one-way ANOVA and Tukey tests. The results indicated that all the irrigation solutions except chlorhexidine significantly decreased microhardness of root canal dentin (p < 0.05); 3% H2O2 and 0.2% chlorhexidine gluconate had no effect on roughness of the root canal dentin (p > 0.05). Although there are many other factors for irrigation solution preference, according to the results of this study, 0.2% chlorhexidine gluconate seems to be an appropriate endodontic irrigation solutions because of its harmless effect on the microhardness and roughness of root canal dentin.

Quantitative analysis of the solubilizing action of MTAD, sodium hypochlorite, and EDTA on bovine pulp and dentin.

Necrotic bovine pulp and dentin were used in this study as model tissues to represent the organic and inorganic components of the smear layer present in instrumented root canals. The capabilities of endodontic irrigants to dissolve pulverized forms of these tissues were compared. Lyophilized tissue samples were mixed for 2 h at 37 degrees C with MTAD, three concentrations of sodium hypochlorite (NaOCl), 17% EDTA, or isotonic saline. Undissolved tissues were rinsed with water and lyophilized. The change in tissue weight after exposure to an irrigant was measured to quantify solubilization. The results showed that various concentrations of NaOCl removed organic components of pulp and dentin effectively. As pulp solubilizers 5.25% and 2.60% NaOCl were equal (>90%), and 5.25% NaOCl was capable of dissolving virtually the entire organic component of dentin. EDTA was capable of solubilizing inorganic material in dentin and organic material in pulp and likely also in dentin. It dissolved >70% of the dentin and >51% of the pulp. The solubilizing effects of MTAD on pulp and dentin were somewhat similar to those of EDTA. The major difference between the actions of these solutions was a high binding affinity of doxycycline present in MTAD for the dentin.

A comparative profilometric in vitro study of the susceptibility of polished and natural human enamel and dentine surfaces to erosive demineralization.

This study sought to compare the depths of erosive lesions in samples from different tooth sides as well as from enamel, dentine and root surfaces, and to examine the effect of preparation and polishing of specimens on erosive demineralization. From 30 impacted human third molars, two enamel samples from the mesial, distal, buccal and oral aspects, and similar samples from the radicular dentine, were prepared. One of each pair of samples was polished whereas the other was left untreated. Four samples were also prepared from the coronal dentine. For erosive demineralization, all samples were immersed in 0.05 M citric acid for 3 h and the erosion depth was calculated profilometrically. In general, natural surfaces showed significantly smaller erosion depths than polished surfaces (p< or =0.001) and enamel samples showed greater depths than coronal dentine (not significant) and root dentine (p< or =0.001). The erosion depths of the four tooth sides correlated significantly for polished enamel and coronal dentine samples but not for natural enamel specimens. There was no correlation between erosion depths for enamel and coronal dentine, and only a weak correlation between enamel and root dentine.

Effects of water and water-free polar solvents on the tensile properties of demineralized dentin.

OBJECTIVES: The aim of this study was to test the null hypothesis that the tensile properties of demineralized dentin are not influenced by the hydrogen bonding ability of anhydrous polar solvents. METHODS: Dentin disks 0.5mm thick were prepared from mid-coronal dentin of extracted, unerupted, human third molars. 'I' beam and hour-glass shaped specimens were prepared from the disks, the ends protected with nail varnish and the central regions completely demineralized in 0.5M EDTA for 5 days. Ultimate tensile stress (UTS) and low-strain apparent modulus of elasticity (E) were determined with the specimens immersed for 60 min in water, methanol, HEMA, acetone or air prior to testing in those same media. Apparent moduli of elasticity were measured on the same specimens in a repeated measures experimental design. The results were analyzed with a one-way ANOVA on ranks, followed by Dunn's test at alpha=0.05. Regression analysis examined the relationship between UTS or E and Hansen's solubility parameter for hydrogen bonding (delta(h)) of each solvent. RESULTS: The UTS of demineralized dentin in water, methanol, HEMA, acetone and air was 18(7), 29(7), 31(6), 41(13) and 146(27)MPa, x(SD), n=10. Low-strain E for the same media were 11(7), 43(12), 79(21), 132(31) and 253(115)MPa. Regression analysis of UTS vs delta(h) revealed a significant (p<0.0005, r=-0.69, R(2)=0.48) inverse, exponential relationship. A similar inverse relationship was obtained between low-strain E vs delta(h) (p<0.0001, r=-0.93, R(2)=0.86). SIGNIFICANCE: The tensile properties of demineralized dentin are dependent on the hydrogen bonding ability of polar solvents (delta(h)). Solvents with low delta(h) values may permit new interpeptide H-bonding in collagen that increases its tensile properties. Solvents with high delta(h) values prevent the development of these new interpeptide H-bonds.

Tissue-dissolution capacity and dentin-disinfecting potential of calcium hydroxide mixed with irrigating solutions.

OBJECTIVE: The goal of this study was to compare the tissue-dissolution potential and antibacterial effectiveness of a conventional Ca(OH)(2)/saline paste with equivalent Ca(OH)(2)/NaOCl and Ca(OH)(2)/chlorhexidine digluconate medications. STUDY DESIGN: Tissue specimens were obtained from freshly dissected pig palates. Tissue pieces of similar form and weight were incubated in air-tight containers with Ca(OH)(2) pastes or solutions proper for up to 7 days. Antimicrobial testing was performed in dentin blocks infected with Enterococcus faecalis. Medicated, sealed dentin specimens were incubated for 1 and 5 days, and bacterial growth was tested at different dentin depths. RESULTS: Up to day 4, the Ca(OH)(2)/irrigating solution mixtures dissolved tissue more effectively than the conventional Ca(OH)(2)/saline paste. After 7 days, however, no statistically significant differences were found between the saline and hypochlorite mixtures, but the Ca(OH)(2)/chlorhexidine medication was significantly less effective. Dentin block disinfection was quicker and more thorough with the Ca(OH)(2)/chlorhexidine or the Ca(OH)(2)/NaOCl than with the Ca(OH)(2)/saline paste. CONCLUSION: Ca(OH)(2)/irrigant mixtures under investigation appear more advantageous than the conventional Ca(OH)(2)/saline mixture, and merit further investigation in a clinical study.