Effect of exposing dentine to sodium hypochlorite and calcium hydroxide on its flexural strength and elastic modulus

AIM: The aim of this study was to evaluate the effect of sodium hypochlorite (NaOCl) solutions (3%, 5%) and saturated calcium hydroxide (Ca(OH)2) solution, individually and consecutively, on the flexural strength and modulus of elasticity of standardized dentine bars. METHODOLOGY: Standardized plano-parallel dentine bars (n = 121) were divided into five test groups and one control group. The control group 1 consisted of dentine bars, stored in normal saline until testing. The dentine bars in the five test groups were treated by exposure to the following solutions; group 2--3% NaOCl, 2 h; group 3--5% NaOCl, 2 h; group 4--saturated Ca(OH)2 solution, 1 week; group 5--3% NaOCl, 2 h and then saturated Ca(OH)2 solution 1 week; group 6--5% NaOCl, 2 h and then saturated Ca(OH)2 solution 1 week. The dentine bars were then loaded to failure in a three-point bend test. RESULTS: The data revealed a significant (P < 0.001) decrease in the modulus of elasticity and flexural strength of the dentine bars treated with 3% and 5% NaOCl. There was no significant difference in the flexural strength and the modulus of elasticity between the 3% and 5% NaOCl groups. Exposure to Ca(OH)2 significantly (P < 0.001) reduced the flexural strength but had no significant effect on the modulus of elasticity. The groups treated with sodium hypochlorite followed by calcium hydroxide did not have moduli of elasticity and flexural strengths that were significantly different from those treated only with sodium hypochlorite. CONCLUSIONS: NaOCl (3 & 5%) reduced the modulus of elasticity and flexural strength of dentine. Saturated Ca(OH)2 reduced the flexural strength of dentine but not the modulus of elasticity. Sequential use of NaOCl and Ca(OH)2 has no additional weakening effect.     

Effect of MTAD on the bond strength to enamel and dentin

The purpose of this study was to compare the effect of MTAD (a mixture of a tetracycline isomer [doxycycline], an acid [citric acid], and a detergent [Tween 80]) and phosphoric acid on the bond strength to enamel and dentin using a conventional OptiBond Solo Plus dentin adhesive system. One hundred flat surfaces (50 enamel/50 dentin) were prepared for bonding. Specimens were embedded in acrylic with the flat surface exposed. One of the following surface treatments was applied before bonding composite with Optibond Solo Plus (Kerr Corp): 1 min NaOCl/1 min EDTA; 1 min NaOCl/1 min MTAD; 30 s etch with H3PO4 (positive control), 2 min saline (negative control), or 20 min NaOCl/5 min MTAD (clinical protocol for MTAD). Shear bond strength was tested 30 min after bonding. Data were analyzed using a one-way ANOVA followed by the Student-Newman-Keuls multiple comparison method. Surface pretreatment with acid etch resulted in the greatest enamel bond strengths (p < 0.05). All surface pretreatments were superior to saline for dentinal bonding (p < 0.05). On the basis of our findings, it appears that teeth endodontically treated with the MTAD protocol for clinical use (20 min 1.3% NaOCl/5 min MTAD) may not need any additional dentin conditioning before the application of the dental adhesive.     

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 effects of calcium hydroxide removal methods on bond strength of Epiphany SE with two irrigation protocols

Abstract

Objective: The purpose of this study was to compare the effects of five calcium hydroxide removal methods on the bond strength of Epiphany SE sealer after canal irrigation with NaOCl+EDTA or NaOCl+MTAD. Materials and methods: The 120 roots were instrumented by using the ProTaper rotary system under irrigation with 2.5% sodium hypochlorite and randomly divided into two major groups according to the final irrigation: 1.3% NaOCl + MTAD and 5% NaOCl + 17% EDTA. For controls, 10 roots from each of the final irrigations with NaOCl + MTAD and NaOCl + EDTA (20 roots) were not filled with Ca(OH)₂. The intra-canal paste, Ca(OH)₂ was applied to each of the 100 remaining roots and stored at 37°C for 7 days. Each group was sub-divided into five sub-groups (n = 10) according to the removal technique for the intra-canal dressing: Group-1: recapitulation with size 30 K file + 3 ml of saline solution, Group-2: recapitulation with size 30 K file + 3 ml of 5% NaOCl, Group-3: using 5% NaOCl + 17% EDTA, Group-4: using 5%NaOCl + 15% citric acid, and Group-5: using 1.3% NaOCl + 5 ml MTAD. The root canals were filled with Resilon and Epiphany SE sealer. The bond strength was measured. Results: The mean bond strength of Epiphany SE to root dentine irrigated with NaOCl + MTAD was lower than that of NaOCl + EDTA. The highest bond strengths were 3.31 ± 0.057 and 2.60 ± 0.054 in the NaOCl + citric acid group when Ca(OH)₂ was applied to roots treated with NaOCl + EDTA and NaOCl + MTAD, respectively (p < 0.05). Conclusion: For root canals treated with NaOCl + EDTA or NaOCl + MTAD, the use of NaOCl + chelating agent for Ca(OH)₂ removal does not adversely affect the bond strength of Epiphany SE to dentin.     

In vitro evaluation of effect of various endodontic solutions on selected physical properties of white mineral trioxide aggregate

During endodontic therapy various irrigating solutions at different concentrations and duration are used. These chemical solutions may affect the setting reaction of mineral trioxide aggregate (MTA). The aim of this study was to evaluate the effect of sodium hypochlorite (NaOCl) (5.25%), chlorhexidine gluconate (CHX) (2%), ethylenediaminetetraacetic acid (EDTA) solution (17%) and BioPure MTAD on surface micro-hardness and flexural strength of white MTA. Twenty-five disk-shaped and 25 bar-shaped specimens were divided into five groups and were stored under distilled water, NaOCl (5.25%), chlorhexidine CHX (2%), EDTA solution (17%) and BioPure MTAD for 7 days. The micro-hardness of disk specimens was measured while the flexural strength was tested on bar specimens. EDTA and BioPure MTAD significantly reduced the hardness and flexural strength as compared with other groups. Under distilled water strength remained high; therefore, a final flush with distilled water before placement of MTA is advocated, especially if decalcifying agents are used during the clinical procedure.     

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.     

Application of biologically-oriented dentin bonding principles to the use of endodontic irrigants

PURPOSE: To compare the removal of smear layer and the structure of the hybrid layer formed after the use of EDTA or MTAD solutions when used as a final flush. METHODS: Single-rooted extracted premolars (n=18) were collected and treated for root canal therapy using NaOCl irrigation followed by a final rinse of 17% EDTA, Biopure MTAD, or saline (negative control). The roots were obturated with gutta-percha and a hydrophilic HEMA-containing root canal sealer. The TEM specimens were impregnated with 50% silver nitrate to visualize sealing imperfections and nanoleakage. The structure of the coronal, middle and apical parts of root canal walls was examined using transmission electron microscopy. RESULTS: After NaOCl irrigation, a final rinse with BioPure MTAD or 17% EDTA completely removed the 2 microm-thick smear layer on mechanically instrumented root canal walls. The BioPure MTAD hybrid layer was thicker than the 17% EDTA hybrid layer. Both the BioPure MTAD and EDTA caused a collapse of the dentin matrix structure which impeded sealer infiltration and the formation of high quality hybrid layer bonding. The hybrid layers created in smear layer-covered dentin exhibited less potential for nanoleakage than the MTAD or EDTA hybrid layers.     

Effect of sodium hypochlorite on mechanical properties of dentine and tooth surface strain

AIM: The aim of this study was to test the null hypothesis that sodium hypochlorite irrigation of root canals does not alter the properties of dentine and contribute to the weakening of root-treated teeth. METHODOLOGY: The effect of two concentrations (0.5%, 5.25%) of sodium hypochlorite (NaOCl) and saline on (i) the elastic modulus and flexural strength of machined dentine bars, and (ii) changes in strain of 'whole' extracted human teeth were evaluated. One hundred standardized plano-parallel dentine bars (> 11.7 x 0.8 x 0.8 mm) were randomly divided into the three groups, immersed for 2 h in the respective solutions and then subjected to a three-point bend test. Changes in strain of each of 10 teeth on cyclical nondestructive occlusal loading were measured using electrical resistance strain gauges bonded to the cervical aspects. Each tooth had its crown and enamel reduced and root canal prepared. These were irrigated sequentially in a series of four separate, 30-minute regimes; initial-saline, 0.5% NaOCl, 5.25% NaOCl and final-saline. The changes in strains after each irrigation regime were compared. RESULTS: There was a significant decrease in elastic modulus of the dentine bars immersed in 5.25% NaOCl compared with the saline group (P < 0.01). There was also a significant decrease in flexural strength of the dentine bars in the 5.25% NaOCl group compared to both the saline and 0.5% NaOCl groups (P < 0.01). The strain data from the nondestructive tooth loading tests revealed significant increases in tensile strain between the initial-saline and the final-saline stages (P < 0.01). Significant increases in compressive strains were also found between initial-saline and 5.25% NaOCl; and between 0.5% NaOCl and 5.25% NaOCl stages (P < 0.01). CONCLUSIONS: The null hypothesis was rejected, 5.25% NaOCl reduced the elastic modulus and flexural strength of dentine. Irrigation of root canals of single, mature rooted premolars with 5.25% NaOCl affected their properties sufficiently to alter their strain characteristics when no enamel was present.     

Effect of endodontic irrigants on the shear bond strength of epiphany sealer to dentin

This study examined the effects of commonly employed endodontic irrigants on Epiphany-dentin bond strengths. Smear layers were created on dentin discs obtained from human third molars. Five groups of 10 discs each were treated with one of the following: (a) water; (b) 2% chlorhexidine; (c) 6% sodium hypochlorite (NaOCl); (d) 6% NaOCl followed by EDTA and water; or (e) 1.3% NaOCl followed by MTAD. The treated surfaces were air-dried and treated with Epiphany primer. Hollow steel tubes were placed on the dentin surfaces, and Epiphany sealer was applied to dentin inside the tubes. Samples were tested for shear bond strengths after 7 days of storage. Representative specimens were examined using scanning electron microscopy. One-way ANOVA and Tukey's test revealed significant differences among the groups (p<0.05). Using water or chlorhexidine as an irrigant resulted in significantly lower bond strengths when compared with NaOCl, NaOCl/EDTA, or NaOCl/MTAD. Neither EDTA nor MTAD significantly improved Epiphany-dentin bond strengths when compared with NaOCl used alone.     

The Effect of Endodontic Irrigants on the Microtensile Bond Strength of Dentin Adhesives

IntroductionThe purpose of this study was to evaluate the microtensile bond strength of a total etch (XP-Bond) and a self-etch (Clearfil SE Bond) adhesive system to dentine surfaces treated using endodontic irrigants.MethodsTwenty-four freshly extracted third molars were used. After creating a smear layer on the coronal midthird portion of the crowns, the teeth were divided into three groups and surfaces were irrigated with distilled water, 5.25% NaOCl + 17% EDTA, and 1.3% NaOCl + BioPure MTAD, respectively. Each group was divided into two subgroups, and a self-etching adhesive and an etch-and-rinse adhesive were applied respectively. The teeth were restored with a composite material and sectioned to produce sticks for microtensile bond testing.ResultsThe microtensile bond strength of the MTAD + Clearfil SE group was found to be significantly lower than the microtensile bond strength of the distilled water + Clearfil SE Bond group and the NaOCl, EDTA, + Clearfil SE Bond group (p = 0.0001, p = 0.009).ConclusionsBecause of the significant reduction of Clearfil SE Bond to coronal dentine after MTAD application, an etch-and rinse adhesive such as XP-Bond may be preferred if this irrigant has been chosen during endodontic treatment.     

Similar glucose leakage pattern on smear-covered, EDTA-treated and BioPure MTAD-treated dentin

This study assessed the effect of BioPure MTAD on the sealing ability on the basis of the filtration rate of glucose along the root fillings. Both 17% ethylenediaminetetraacetic acid (EDTA) and smear-covered dentin were used as reference patterns to compare the results. Sixty-four human upper incisors were prepared with different irrigation protocols (n = 18): G1, NaOCl; G2, NaOCl + EDTA; and G3, NaOCl + BioPure MTAD. The teeth were obturated and then prepared in a double-chamber apparatus to evaluate the glucose leakage along the root fillings. The amount of glucose leakage was quantified with spectrophotometry at 7, 14, 21, 28, 35, 42, 49, and 56 days. Leakage existed in every sample and was variable in all of the experimental groups, and Kruskal-Wallis H test results showed that there were no significant differences among the experimental groups (P > .05). The smear-covered dentin did not allow more glucose leakage than EDTA-treated and BioPure MTAD-treated dentin.     

Comparative assessment of time-related bioactive glass and calcium hydroxide effects on mechanical properties of human root dentin

Abstract – Suspensions of micro‐ or nanoparticulate SiO₂‐Na₂O‐CaO‐P₂O₅ bioactive glasses could potentially be used as dressings in traumatized front teeth with open apices as an alternative to Ca(OH)₂. These materials have a disinfecting capacity similar to Ca(OH)₂, but bear the advantage of bioactivity. However, because bioactive glasses initially act as alkaline biocides just as Ca(OH)₂ does, they may also negatively affect mechanical dentin properties over time. This was assessed in the current study using standardized human root dentin bars. Specimens were immersed in 1:20 (wt vol^?1) suspensions of nanometric bioactive glass 45S5 or calcium hydroxide for 1, 10, or 30 days. Control specimens were immersed in pure saline for 30 days (n = 20 per group). Subsequently, modulus of elasticity (E) and flexural strength (FS) of the specimens were determined. Results were compared between groups using one‐way anova and Scheffé’s post‐hoc test. Ca(OH)₂ caused a significant (P < 0.001) 35% drop in mean flexural strength values compared to the control treatment after 10 days. No further change was observed between 10 days and 30 days. Bioactive glass caused a 20% drop in mean flexural strength as compared to the control after 10 days. However, this difference did not reach statistical significance (P > 0.05). No effects of either material on dentin modulus of elasticity values were observed. It was concluded that the calcium hydroxide suspension affected the dentin more than the bioactive glass counterpart; however, the effect was self‐limiting and probably restricted to superficial dentin layers, as suggested by the mere decrease in flexural strength but not in modulus of elasticity values.     

Stabilizing sodium hypochlorite at high pH: effects on soft tissue and dentin

Introduction

When sodium hypochlorite solutions react with tissue, their pH drops and tissue sorption decreases. We studied whether stabilizing a NaOCl solution at a high pH would increase its soft-tissue dissolution capacity and effects on the dentin matrix compared with a standard NaOCl solution of the same concentration and similar initial pH.

Methods

NaOCl solutions were prepared by mixing (1:1) a 10% stock solution with water (standard) or 2 mol/L NaOH (stabilized). Physiological saline and 1 mol/L NaOH served as the controls. Chlorine content and alkaline capacity of NaOCl solutions were determined. Standardized porcine palatal soft-tissue specimens and human root dentin bars were exposed to test and control solutions. Weight loss percentage was assessed in the soft-tissue dissolution assay. Three-point bending tests were performed on the root dentin bars to determine the modulus of elasticity and flexural strength. Values between groups were compared using one-way analysis of variance with the Bonferroni correction for multiple testing (α < .05).

Results

Both solutions contained 5% NaOCl. One milliliter of the standard and the stabilized solution consumed 4.0 mL and 13.7 mL of a 0.1-mol/L HCl solution before they reached a pH level of 7.5, respectively. The stabilized NaOCl dissolved significantly more soft tissue than the standard solution, and the pH remained high. It also caused a higher loss in elastic modulus and flexure strength (P < .05) than the control solutions, whereas the standard solution did not.

Conclusions

NaOH-stabilized NaOCl solutions have a higher alkaline capacity and are thus more proteolytic than standard counterparts.     

Effect of MTAD on Enterococcus faecalis-contaminated root canals of extracted human teeth

The purpose of this investigation was to compare the antimicrobial effect of MTAD (a mixture of a tetracycline isomer, an acid, and a detergent) with that of NaOCl with and without EDTA. Eighty-five extracted human teeth were contaminated with Enterococcus faecalis for 4 weeks. After biomechanical instrumentation using 1.3% or 5.25% NaOCl as root canal irrigant, the root canal and the external surface of each tooth were exposed to a 5-min application of MTAD, 1.3% NaOCl, 5.25% NaOCl or a 1-min application of EDTA followed by irrigation with 5 ml of 1.3% NaOCl or 5.25% NaOCl. Teeth or dentin shavings were cultured to determine presence or absence of the test bacteria. Fisher's exact test showed that the combination of 1.3% NaOCl as a root canal irrigant and MTAD as a final rinse was significantly more effective against E. faecalis than the other regimens. The chi2 test showed no difference between the other regimens.     

Effect of sodium hypochlorite on human root dentine--mechanical, chemical and structural evaluation

AIM: To investigate the mechanical, chemical and structural alterations of human root dentine following exposure to ascending sodium hypochlorite concentrations. METHODOLOGY: Three-point bending tests were carried out on standardized root dentine bars (n = 8 per group, sectioned from sound extracted human third molar teeth) to evaluate their flexural strength and modulus of elasticity after immersion in 5 mL of water (control), 1% NaOCl, 5% NaOCl or 9% NaOCl at 37 degrees C for 1 h. Additional dentine specimens were studied using microelemental analysis, light microscopy following bulk staining with basic fuchsin, and scanning electron microscopy (SEM). Numerical data were compared using one-way ANOVA. Bonferroni's correction was applied for multiple testing. RESULTS: Immersion in 1% NaOCl did not cause a significant drop in elastic modulus or flexural strength values in comparison to water, whilst immersion in 5% and 9% hypochlorite reduced these values by half (P < 0.05). Both, carbon and nitrogen contents of the specimens were significantly (P < 0.05) reduced by 5% and 9% NaOCl, whilst 1% NaOCl had no such effect. Exposure to 5% NaOCl rendered the superficial 80-100 mum of the intertubular dentine permeable to basic fuchsin. Three-dimensional SEM reconstructions of partly demineralized specimens showed NaOCl concentration-dependent matrix deterioration. Backscattered electron micrographs revealed that hypochlorite at any of the tested concentrations left the inorganic dentine components intact. CONCLUSIONS: The current data link the concentration-dependent hypochlorite effect on the mechanical dentine properties with the dissolution of organic dentine components.     

Flexural Strength and Modulus Properties of Carbamide Peroxide–Treated Bovine Dentin

Background : The effects of carbamide peroxide bleach on tooth structure are uncertain.
Purpose : The purpose of this study was to investigate the effects of direct or indirect carbamide peroxide application on dentin flexural strength and modulus in vitro.
Materials and Methods : Dentin bars were machined from bovine incisors and treated with 10% carbamide peroxide for 6 h/d for 14 days. Four groups were created, with eight bars in each group: group 1–direct bleach application only; group 2–indirect bleach application only; group 3–direct bleach application followed by a 2–week storage in artificial saliva; group 4–direct bleach application followed by a 2-week storage in artificial saliva and daily topical fluoride treatments. The specimens' flexural strength and modulus were tested after 24 hours, and the results were compared with water controls using independent t -tests ( p < .05).
Results : Flexural strength results (in megapascals) for bleached versus control dentin (1 = 205 ± 26 vs 215 ± 14,2 = 257 ± 25 vs 261 ± 14,3 = 180 ± 22 vs 193 ± 36, 4 = 157 ± 18 vs 184 ± 11) were significantly lower in group 4 ( p = .005). Modulus results (in gigapascals) for bleached versus control dentin (1 = 10.7 ± 1.4 vs 12.2 ± 0.6, 2 = 14.2 ± 1.7 vs 14.4 ± 1.6, 3 = 10.0 ± 2.0 vs 10.9 ± 1.3, 4 = 9.0 ± 1.2 vs 11.1 ± 1.0) were significantly lower in groups 1 and 4 ( p = .013 and p = .003, respectively). There were no significant differences in strength and modulus results between the bleached and control dentin in groups 2 and 3. A direct application of carbamide peroxide to bovine dentin significantly decreased some dentin mechanical properties in vitro. An indirect application of carbamide peroxide to dentin did not significantly decrease dentin strength and stiffness.     

Comparison of the antimicrobial efficacy of 1.3% NaOCl/BioPure MTAD to 5.25% NaOCl/15% EDTA for root canal irrigation

The purpose of this study was to compare the antimicrobial efficacy of 1.3% NaOCl/BioPure MTAD to 5.25% NaOCl/15% EDTA for root canal irrigation. Twenty-six bilaterally matched pairs of human teeth were collected. The teeth were incubated with Enterococcus faecalis for 4 weeks. The teeth were divided into two experimental groups and one positive control group. The canals were instrumented and irrigated with either 5.25% NaOCl/15% EDTA or 1.3% NaOCl/BioPure MTAD. Bacterial samples were collected after instrumentation/irrigation and after additional canal enlargement. Statistical analysis of the data using the Wilcoxon Signed Rank test showed significant differences between the experimental groups. The first bacterial samples revealed growth in 0 of 20 samples with 5.25% NaOCl/15% EDTA irrigation and in 8 of 20 samples with 1.3% NaOCl/BioPure MTAD irrigation. Samples taken after additional canal enlargement revealed growth in 0 of 20 samples in 5.25% NaOCl/15% EDTA and in 10 of 20 samples in 1.3% NaOCl/BioPure MTAD group. This investigation showed consistent disinfection of infected root canals with 5.25% NaOCl/15% EDTA. The combination of 1.3% NaOCl/BioPure MTAD left nearly 50% of the canals contaminated with E. faecalis.     

Reduction in antimicrobial substantivity of MTAD after initial sodium hypochlorite irrigation

Potential intrinsic tetracycline staining of intraradicular dentin has been observed when BioPure MTAD was employed as the final irrigant after initial rinsing with NaOCl. This study examined the effect of NaOCl-MTAD interaction on the antimicrobial substantivity of MTAD in dentin. Dentin cores previously irrigated with either MTAD, or in conjunction with 1.3% NaOCl as an initial irrigant were placed on blood agar plates inoculated with Escherichia faecalis at 10(5) cfu/ml. Dentin cores irrigated with 1.3% NaOCl only, and autoclaved dentin disks were used as the respective positive and negative controls. After anaerobic incubation, the mean diameter of bacterial inhibition zones formed around the MTAD group was significantly larger than the NaOCl/MTAD group, which, in turn, was not significantly different from the NaOCl positive control. Oxidation of MTAD by NaOCl resulted in the partial loss of antimicrobial substantivity in a manner similar to the peroxidation of tetracycline by reactive oxygen species.     

Soft chelating irrigation protocol optimizes bonding quality of Resilon/Epiphany root fillings

This study was designed to test the impact of either a strong (MTAD) or a soft (1-hydroxyethylidene-1, 1-bisphosphonate [HEPB]) chelating solution on the bond strength of Resilon/Epiphany root fillings. Both 17% EDTA and the omission of a chelator in the irrigation protocol were used as reference treatments. Forty extracted human upper lateral incisors were prepared using different irrigation protocols (n = 10): G1: NaOCl, G2: NaOCl + 17% EDTA, G3: NaOCl + BioPure MTAD (Dentsply/Tulsa, Tulsa, OK), and G4: NaOCl + 18% HEPB. The teeth were obturated and then prepared for micropush-out assessment using root slices of 1 mm thickness. Loading was performed on a universal testing machine at a speed of 0.5 mm/min. One-way analysis of variance and Tukey multiple comparisons were used to compare the results among the experimental groups. EDTA- and MTAD-treated samples revealed intermediate bond strength (0.3-3.6 MPa). The lowest bond strengths were achieved in NaOCl-treated samples (0.3-1.2 MPa, p < 0.05). The highest bond strength was reached in the HEBP-treated samples (3.1-6.1 MPa, p < 0.05). Under the present in vitro conditions, the soft chelating irrigation protocol (18% HEBP) optimized the bonding quality of Resilon/Epiphany (Resilon Research LLC, Madison, CT) root fillings.     

Flexural properties of endodontic posts and human root dentin.

OBJECTIVES: To evaluate the flexural modulus and flexural strength of different types of endodontic post in comparison with human root dentin. METHODS: Three different types of fiber-reinforced composite (FRC) posts and three metal posts each comprising 10 specimens (n=10) and 20 dentin bars were loaded to failure in a three-point bending test to determine the flexural modulus (GPa) and the flexural strength (MPa). Three randomly selected fiber posts of each group were evaluated using a scanning electron microscope (SEM) to illustrate the differences in mode of fracture. Data were subjected to a one-way ANOVA to determine significant differences between groups and the Bonferroni t-test multiple comparison was applied to investigate which mean values differed from one another with significance levels of P<0.05. RESULTS: The flexural modulus recorded for the dentin bars was 17.5+/-3.8 GPa. The values for posts ranged from 24.4+/-3.8 GPa for silica fiber posts to 108.6+/-10.7 GPa for stainless steel posts. The flexural strength for dentin was 212.9+/-41.9 MPa, while the posts ranged from 879.1+/-66.2 MPa for silica fiber posts to 1545.3+/-135.9 MPa for cast gold posts. The ANOVA test analysis revealed significant differences between groups (P<0.05) for flexural modulus and flexural strength mean values. SIGNIFICANCE: FRC posts have an elastic modulus that more closely approaches that of dentin while that for metal posts was much higher. The flexural strength of fiber and metal posts was respectively four and seven times higher than root dentin.