Tribochemical silicoating of amalgam promotes effective amalgam-resin repairs.

The purpose of this study was to determine the most effective method for bonding composite resin to artificially aged amalgam. A spherical amalgam alloy was triturated and condensed by hand into cylindrical plastic molds (6 mm in diameter and 4 mm in height) to create 90 specimens, which were then aged for 2 weeks in closed plastic containers at 23°C. The amalgam surfaces underwent 1 of 3 surface treatments (n = 30 per treatment): (1) air particle abrasion (APA) with 50-µm aluminum oxide particles applied with a force of 45 psi from a 10-mm distance, followed by rinsing with deionized water for 60 seconds; (2) APA following the same protocol with subsequent application of a metal primer (Alloy Primer); or (3) coating with 30-µm silica (CoJet) at a force of 45 psi from a 10-mm distance until the surface turned black. Specimens were then treated with 1 of 3 adhesives (n = 10 per adhesive per surface treatment): (1) 2-step total-etch adhesive (OptiBond Solo Plus), (2) 1-step self-etching adhesive (Scotchbond Universal), or (3) dual-cured resin cement (Panavia F 2.0). Each adhesive was applied to the treated amalgam surfaces following its manufacturer's instructions. The specimens were placed in a bonding clamp, and nanocomposite resin columns, 2.38 mm in diameter and 2.00 mm in height, were photocured (40 seconds, 500 mW/cm2) against the treated amalgam surfaces. The specimens were stored for 24 hours in 37°C deionized water and underwent shear bond strength testing at a crosshead speed of 0.5 mm/min. Data were analyzed using 2-way analysis of variance and post hoc analysis with the Tukey test at 95% confidence. The mean (SD) shear bond strength values ranged from 12.3 (1.2) MPa for aluminum oxide-treated surfaces bonded with OptiBond Solo Plus to 25.9 (4.6) MPa for silicoated surfaces bonded with Panavia F 2.0. All bonding agents produced the highest shear bond strength when the amalgam surface was silicoated. These results indicate that composite can be effectively bonded to amalgam via silicoating.

Microshear bond strength of resin luting agents to monolithic zirconia.

The objective of this study was to evaluate the effects of different surface treatments on the microshear bond strength (µSBS) of resin cements to zirconia. Twenty-four zirconia wafers measuring 2.0 × 9.0 × 15.0 mm were sintered and randomly distributed into 3 groups based on the resin cement (n = 8): Panavia F 2.0, NX3, and RelyX Ultimate. The resin cement groups were divided into 4 subgroups based on the surface treatment: a control subgroup (air abrasion with 50-µm alumina particles) and 3 experimental surface treatments (Alloy Primer, Ea-Z-y Primer, and tribochemical silicoating using CoJet Sand). Each surface treatment was applied to the zirconia wafers according to its manufacturer's instructions. The resin cements were mixed and placed in thermoplastic tubes, producing cylinders measuring 0.8 mm in diameter × 2.0 mm in height. Five tubes containing the resin cements were placed on each of the pretreated zirconia wafers, resulting in a sample size of 10 specimens per treatment per resin cement. The luting agents were allowed to cure chemically for 4 minutes and then light cured for 30 seconds. The thermoplastic tubes were removed after 24 hours, and specimens were stored in deionized water (37°C) for 24 hours. A shear force was applied using a wire loop attached to a universal testing machine with a crosshead speed of 0.5 mm/min, and the microshear forces required for failure were recorded. The parametric data were analyzed with a 2-way analysis of variance with post hoc Tukey and Dunnett tests (P < 0.05). The mean (SD) µSBS values ranged from 3.6 (0.9) to 9.3 (2.4) MPa. Surface treatment with Alloy Primer and Ea-Z-y Primer increased the µSBS of the 3 cements compared to their controls, but the difference was not always statistically significant. CoJet Sand only increased the µSBS of Panavia F 2.0. The results suggest that the effects of different surface treatments may be specific for each cement.

Peracetic acid: a practical agent for sterilizing heat-labile polymeric tissue-engineering scaffolds.

Advanced biomaterials and sophisticated processing technologies aim at fabricating tissue-engineering scaffolds that can predictably interact within a biological environment at the cellular level. Sterilization of such scaffolds is at the core of patient safety and is an important regulatory issue that needs to be addressed before clinical translation. In addition, it is crucial that meticulously engineered micro- and nano- structures are preserved after sterilization. Conventional sterilization methods involving heat, steam, and radiation are not compatible with engineered polymeric systems because of scaffold degradation and loss of architecture. Using electrospun scaffolds made from polycaprolactone, a low melting polymer, and employing spores of Bacillus atrophaeus as biological indicators, we compared ethylene oxide, autoclaving and 80% ethanol to a known chemical sterilant, peracetic acid (PAA), for their ability to sterilize as well as their effects on scaffold properties. PAA diluted in 20% ethanol to 1000 ppm or above sterilized electrospun scaffolds in 15 min at room temperature while maintaining nano-architecture and mechanical properties. Scaffolds treated with PAA at 5000 ppm were rendered hydrophilic, with contact angles reduced to 0°. Therefore, PAA can provide economical, rapid, and effective sterilization of heat-sensitive polymeric electrospun scaffolds that are used in tissue engineering.

Mineralization Potential of Electrospun PDO-Hydroxyapatite-Fibrinogen Blended Scaffolds.

The current bone autograft procedure for cleft palate repair presents several disadvantages such as limited availability, additional invasive surgery, and donor site morbidity. The present preliminary study evaluates the mineralization potential of electrospun polydioxanone:nano-hydroxyapatite : fibrinogen (PDO : nHA : Fg) blended scaffolds in different simulated body fluids (SBF). Scaffolds were fabricated by blending PDO : nHA : Fg in the following percent by weight ratios: 100 : 0 : 0, 50 : 25 : 25, 50 : 50 : 0, 50 : 0 : 50, 0 : 0 : 100, and 0 : 50 : 50. Samples were immersed in (conventional (c), revised (r), ionic (i), and modified (m)) SBF for 5 and 14 days to induce mineralization. Scaffolds were characterized before and after mineralization via scanning electron microscopy, Alizarin Red-based assay, and modified burnout test. The addition of Fg resulted in scaffolds with smaller fiber diameters. Fg containing scaffolds also induced sheet-like mineralization while individual fiber mineralization was noticed in its absence. Mineralized electrospun Fg scaffolds without PDO were not mechanically stable after 5 days in SBF, but had superior mineralization capabilities which produced a thick bone-like mineral (BLM) layer throughout the scaffolds. 50 : 50 : 0 scaffolds incubated in either r-SBF for 5 days or c-SBF for 14 days produced scaffolds with high mineral content and individual-mineralized fibers. These mineralized scaffolds were still porous and will be further optimized as an effective bone substitute in future studies.

Evaluating EDTA as a substitute for phosphoric acid-etching of enamel and dentin.

Matrix metalloproteinases (MMPs) are proteolytic enzymes released when dentin is acid-etched. The enzymes are capable of destroying unprotected collagen fibrils that are not encapsulated by the dentin adhesive. Chlorhexidine applied after etching inhibits the activation of released MMPs, whereas neutral ethylenediamine tetra-acetic acid (EDTA) prevents the release of MMPs. The purpose of this study was to determine if conditioning enamel and dentin with EDTA can be a substitute for treating acid-etching enamel and dentin with chlorhexidine. A column of composite resin was bonded to enamel and dentin after conditioning. Shear bond strengths were evaluated after 48 hours and after accelerated aging for three hours in 12% sodium hypochlorite. Shear bond strengths ranged from 15.6 MP a for accelerated aged EDTA enamel specimens to 26.8 MPa for dentin conditioned with EDTA and tested after 48 hours. A three-way ANOVA and a Tukey HSD test found statistically significant differences among the eight groups and the three independent variables (P < 0.05). EDTA was successfully substituted for phosphoric acid-etched enamel and dentin treated with chlorhexidine. Interactions of conditioning agent and aging were significant for dentin but not for enamel. In an effort to reduce the detrimental effects of MMPs, conditioning enamel and dentin with EDTA is an alternative to treating acid-etched dentin and enamel with chlorhexidine.

Resistance of composite and amalgam core foundations retained with and without pins and bonding agents.

To compare the resistance of different amalgam and composite core foundations retained by pins, bonding agents, or both, 100 molars were mounted in acrylic resin and their occlusal surfaces were reduced to expose dentin. Pins were inserted at the four line angles of the teeth and matrices were placed. Bonding agents were applied according to the manufacturers' instructions. Amalgam was handcondensed and composite was incrementally added and photocured. Restorations were adjusted to produce specimens (n = 10) 5 mm in height with a 1 mm bevel at the axial-occlusal surface. After immersion in deionized water for 24 hours, specimens were loaded at a 45 degree angle on their beveled surfaces in a Universal Testing Machine at a crosshead speed of 0.02 in./minute. ANOVA and Tukey's tests indicated that FluoroCore 2 (with or without pins) was statistically stronger than all other combinations (p < 0.05).

Accuracy and dimensional stability of extended-pour and conventional alginate impression materials.

BACKGROUND: The authors conducted a study to determine if two irreversible hydrocolloid impression materials (Cavex ColorChange, Cavex Holland BV, Haarlem, Netherlands; Jeltrate Plus Antimicrobial Dustless Alginate Impression Material, Dentsply Caulk, Milford, Del.) stored for five days were dimensionally accurate. METHODS: The authors modified Ivorine teeth (Columbia Dentoform, Long Island City, N.Y.) on a Dentoform model (1560 series model, Columbia Dentoform) to allow measurements of tooth and arch width. They made impressions and generated casts immediately and at five additional times. They recorded tooth and arch widths on the casts and compared the measurements with those for the standard model. RESULTS: Compared with measurements for the model, the greatest measured difference in casts was 0.003 inches for Cavex ColorChange (extended-pour alginate) and 0.005 inches for Jeltrate Plus Antimicrobial Dustless Alginate Impression Material (conventional alginate). The percentage of dimensional change ranged from -0.496 to 0.161 percent for the extended-pour alginate and from -0.174 to 0.912 percent for the conventional alginate. CONCLUSIONS: Results of analysis of variance and paired t tests indicated that when generated immediately and at day 5, casts produced from both impression materials were not statistically different from the standard model (P < .05). CLINICAL IMPLICATIONS: When stored properly, both alginate materials can produce accurate impressions at day 5 for diagnostic casts and for fabrication of acrylic appliances.

Review of matrix metalloproteinases' effect on the hybrid dentin bond layer stability and chlorhexidine clinical use to prevent bond failure.

This review describes the relationship between dentin collagen hybrid bond layer degradation and the Matrix Metalloproteinases (MMPs) after their release by acid etch and rinse adhesives and self etching bonding adhesives that can reduce the bond stability over time. MMP-2, MMP-8 and MMP-9 are indicated as the active proteases that breakdown the collagen fibrils in the hybrid bond layer. Phosphoric acid in the acid etch and rinse bonding process and acid primers in the self etch process are implicated in the release of these proteases and their activation by several non-collagen proteins also released from dentin by the etching. MMPs are released in saliva by salivary glands, by cells in the gingival crevices to crevicular fluid and by pulpal odontoblasts cells to the dentinal fluids. These sources may affect the hybrid layer also. Evidence of the bond strength deterioration over time and the ability of Chlorhexidine to prevent bond deterioration by inhibiting MMP action are discussed. Dentin Bonding procedure utilizing Chlorhexidine for different application times and concentrations are being developed. The application of 2% Chlorhexidine to the phosphoric acid etch surface after rinsing off the acid is the only procedure that has been clinically tested for a longer period of time and shown to prevent bond strength degradation so far. The adoption of this procedure is recommended as means of improving bond stability at this time.

An evaluation of dentin conditioners for resin-modified glass ionomer cements.

This study sought to test the null hypothesis that there was no difference between three dentin conditioners in terms of how they affected the shear bond strength to dentin of three resin-modified glass ionomer (RMGI) cements. One hundred twenty caries-free third molars were mounted in acrylic resin and their occlusal surfaces were reduced to within 2 mm of their cemento-enamel junction (CEJ). Of the three cements tested, Rely-X Plus (22.7 MPa) and Fuji CEM (19.0 MPa) produced the highest bond strengths when dentin was treated with 37% phosphoric acid and followed by the application of Optibond Solo Plus and BondLink. Among the dentin conditioners tested, Fuji Plus Conditioner increased bond strengths for all three cements more than leaving the smear layer intact, although the increase was not statistically significant. Dentin treated with Cavity Conditioner demonstrated the weakest bond strengths.

Multiple factor interactions in biomimetic mineralization of electrospun scaffolds.

One of the major limitations in scaffold-based bone tissue engineering has been the inability to increase the loading of biologically active inorganic mineral. The present study introduces a novel two step strategy to increase overall mineral content of electrospun scaffolds and employs multiple factor interaction as a statistic to identify the combination of factors that yields maximal scaffold mineralization. Different amounts of nHA (0, 10, 25 and 50% by wt. of polymer) were electrospun in combination with polydioxanone (PDO) or poly(glycolide: lactide) to generate composite scaffolds. Successful incorporation of nHA within, on and in between nanofibers was confirmed by transmission and scanning electron microscopy. These scaffolds were immersed in different types (conventional, revised, ionic and modified) of simulated body fluid (SBF), prepared at 1x and 4x concentrations and the incubation was carried out either in static or dynamic setting at biomimetic conditions. At 2 weeks, the total amount of mineral within the scaffold was quantified using a modified Alizarin Red-based assay. Each of the five independent factors was analyzed independently and tested for interaction using random effects ANOVA. Statistics revealed significant higher order interactions among factors and the combination of PDO containing 50% nHA incubated in 1x revised SBF resulted in maximum mineralization.

Fracture resistance of extensive amalgam restorations retained by pins, amalgapins and amalgam bonding agents.

This in-vitro study compared the resistance of extensive amalgam restorations retained by either four Regular TMS Link Plus pins, four amalgapins, Amalgambond Plus, Amalgambond Plus with HPA, Scotchbond Multi-Purpose Plus, PQ Amalgam, Panavia F 2.0, All-Bond 2 or Resinomer. Ninety caries-free third molars were embedded in acrylic resin and their occlusal surfaces reduced to within 2 mm of their CEJ. Tytin amalgam alloy was hand-condensed into copper band matrices reinforced with modeling compound after placement of mechanical retention or application of the amalgam bonding agents. Modeling compound and copper bands were removed after 24 hours, and the restorations were adjusted to produce specimens 5 mm in height with a 1 mm bevel on the occlusal-axial surface. The specimens were stored in 100% humidity for one month followed by immersion in de-ionized water for 24 hours at 37 degrees C. The specimens were loaded in compression at a 45 degrees angle in an Instron Universal Testing Machine at a crosshead speed of 0.02 inches/minute. The mean failure loads and standard deviations recorded in Newtons were as follows: Amalgambond Plus with HPA 2160N (380), Scotchbond Multi-Purpose Plus 1900N (380), four Amalgapins 1770N (340), PQAmalgam 1660N (270), Panavia F 2.0 1620N (440), Amalgambond Plus 1570N (390), four Regular TMS Link Plus Pins 1325N (406), All-Bond 2 1300N (390) and Resinomer 1245N (310). A one-way ANOVA and Tukey post hoc analysis indicated all amalgam bonding agents were statistically equal to either four Regular TMS Link Plus pins orfour amalgapins.

Bonding properties of newly erupted and mature premolars.

INTRODUCTION: The purpose of this study was to determine whether there were differences in bond strength between mature and newly erupted teeth when using both conventional and self-etching primer techniques for bonding orthodontic appliances. The nature of adhesive bond failure among the groups was also compared by using the adhesive remnant index (ARI). METHODS: Premolars were collected, randomly divided, and bonded with either the conventional or the self-etching technique. Brackets were debonded on a testing machine with a shear-testing device. Bond strengths were compared with ANOVA and the Weibull analysis. RESULTS: There were no statistically significant differences in bond strength values between the conventional etching and the self-etching primer groups or between newly erupted and mature teeth. ARI scores differed between mature and newly erupted teeth. Newly erupted teeth had more adhesive failures, and mature teeth had more cohesive bond failures at the enamel-composite resin interface. CONCLUSIONS: Based on these results, bond strength does not appear to be affected by the posteruptive enamel maturation process.

The effect of operational speed on the fracture of nickel-titanium rotary instruments.

The purpose of this study was to compare the number of rotations to fracture of nickel-titanium (NiTi) rotary files operated at different speeds and different angles. We used 60 Profile NiTi rotary files, size 25 (30 each of 0.04 and 0.06 taper), operated at speeds of 350 or 600 rpm at angles of 25, 28, and 33.5 degrees. The time to fracture and number of rotations to fracture were recorded and calculated. A significant (p < 0.001) difference was found in the number of rotations to fracture according to taper and angle. Files of 0.06 taper fractured more readily than files of 0.04 taper. Increasing the angle at which the file was rotated decreased the number of rotations to fracture for both tapers; 0.04-taper files were more affected by an increase in the angle than the 0.06-taper files. However, the number of rotations to fracture was not related to the speed at which the files were operated.

A quantitative comparison of the fill density of MTA produced by two placement techniques.

This study compared the fill density of mineral trioxide aggregate (MTA) produced by hand condensation with that produced by hand condensation with indirect ultrasonic (US) activation. Sixty acrylic blocks with straight or curved canals were instrumented to an apical size 45, and weighed with a digital electronic balance. In 30 randomly chosen specimens, the canal was filled with MTA by hand condensation and weighed. The MTA was removed; the canal was rinsed and dried, and refilled using hand condensation with indirect US activation. In the other 30 specimens, the procedure was carried out identically but in reverse order. The blocks were then reweighed. The weight of the MTA fill produced by the two placement methods in the two canal configurations was analyzed by a two-way ANOVA. Hand condensation with indirect US activation resulted in an MTA fill that was statistically significantly heavier, and thus denser, than that accomplished by hand condensation alone in both curved and straight canals (p < 0.0001).

Influence of a 3-step tooth disinfection procedure on dentin bond strength.

STATEMENT OF PROBLEM: Clinicians have used disinfection materials to remove surface contaminants during cavity preparation. It has been postulated that disinfection materials may negatively affect shear bond strength of restorative materials. If so, large numbers of restorations may be predestined for early failure with the use of a disinfection protocol. PURPOSE: The purpose of this study was to determine whether there is a difference in the bond strength between dentin and resin composite with a 3-step disinfection technique compared to a conventional bonding technique without the additional disinfection protocol. MATERIAL AND METHODS: Sixty human molar teeth were sectioned parallel to the occlusal surface to expose mid-coronal dentin and mounted parallel to a bond shearing device on a universal testing machine and divided into 2 groups. In the 3-step disinfection group (n = 30), specimens were treated with chlorhexidine, Tubulicid red, and sodium hypochlorite before dentin bonding, following the manufacturer's instructions for All Bond 2. In the control group (n = 30), specimens were treated only with the bonding protocol of All Bond 2. To ensure a uniform bond surface area, core paste was syringed into a cylindrical mold (2.38-mm diameter and 2.00-mm height) that was in contact with the dentin bonding surface of each specimen and allowed to polymerize under constant force. All specimens were subjected to fracture by shear loading in a universal testing machine at a uniform crosshead speed of 0.05 mm per minute and expressed as MPa. Statistical analysis was performed using the Student t test (alpha = .05). The mode of failure was noted after a visual examination using a light microscope under x30 magnification. Failures were recorded as adhesive, cohesive or mixed, and statistical analysis was performed using a chi-square of homogeneity (alpha = .05). RESULTS: A significantly higher shear bond strength was found for the 3-step disinfection group (mean shear bond strength, 25.3 +/- 4.6 MPa) compared to the control group (mean shear bond strength, 20.5 +/- 3.4 MPa) (P < .0001). Most failures were adhesive for the control group, but the fracture modes were evenly divided for the 3-step disinfection protocol group. A chi-square test of homogeneity showed a value of 12.3, df = 2, P = .0012. CONCLUSIONS: The 3-step disinfection technique group showed a significantly stronger dentin shear bond strength compared to the conventional bonding technique without disinfection.

Comparative tensile strengths of preceramic and postceramic solder connectors using high-palladium alloy.

STATEMENT OF PROBLEM: It is not known whether different high-palladium alloys of similar composition possess comparable tensile strength properties associated with connector soldering. PURPOSE: The purpose of this study was to evaluate the tensile strength properties of 2 high-palladium alloys on soldered connectors under simulated pre-ceramic and post-ceramic soldering conditions. MATERIAL AND METHODS: Eighty cylindrical castings were fabricated (Rx Naturelle Plus alloy and Option alloy). The 40 castings for each alloy were subdivided into 2 groups of 20 each. In the first group, castings for each alloy were randomly paired and soldered with presolder (SMG2) to produce 10 preceramic test connector specimens for each alloy. In the second group, castings were similarly paired and soldered with postsolder (490 fine) to produce 10 postceramic test connector specimens for each alloy. Each soldered connector was subjected to tensile force until failure in a universal testing machine. Statistical analysis using a Wilcoxon rank sums test was performed (alpha=.05) RESULTS: No significant difference was found between the mean tensile failure stress for Rx Naturelle Plus preceramic solder (344.7 +/- 77.6 MPa) compared to Option preceramic solder (411.5 +/- 112.8 MPa) (P =.1202). However, the mean tensile failure stress for Rx Naturelle Plus postceramic solder (260.8 +/- 223.7 MPa) was significantly lower than the Option postceramic solder (312.6 +/- 120.8 MPa) (P =.0407). Not only did Rx Naturelle Plus postceramic solder connectors show evidence of lower strength, but also an increased variation among specimens. CONCLUSIONS: Rx Naturelle Plus solder connectors provided better strength with the preceramic as opposed with the postceramic connectors. For postsolder connectors, Rx Naturelle Plus alloy had less acceptable strength and a wider variation, suggesting it is more technique sensitive than Option alloy connectors.

The effect of endodontic solutions on resorcinol-formalin paste in teeth.

This study determined if any of six endodontic solutions would have a softening effect on resorcinol-formalin paste in extracted teeth, and if there were any differences in the solvent action between these solutions. Forty-nine single-rooted extracted teeth were decoronated 2 mm coronal to the CEJ, and the roots sectioned apically to a standard length of 15 mm. Canals were prepared to a 12 mm WL and a uniform size with a #7 Parapost drill. Teeth were then mounted in a cylinder ring with acrylic. The resorcinol-formalin mixture was placed into the canals and was allowed to set for 60 days in a humidor. The solutions tested were 0.9% sodium chloride, 5.25% sodium hypochlorite, chloroform, Endosolv R (Endosolv R), 3% hydrogen peroxide, and 70% isopropyl alcohol. Seven samples per solution were tested and seven samples using water served as controls. One drop of the solution was placed over the set mixture in the canal, and the depth of penetration of a 1.5-mm probe was measured at 2, 5, 10, and 20 min using a dial micrometer gauge. A repeated-measures ANOVA showed a difference in penetration between the solutions at 10 min (p = 0.04) and at 20 min (p = 0.0004). At 20 min, Endosolv R, had significantly greater penetration than 5.25% sodium hypochlorite (p = 0.0033) and chloroform (p = 0.0018); however, it was not significantly better than the control (p = 0.0812). Although Endosolv R, had statistically superior probe penetration at 20 min, the softening effect could not be detected clinically at this time.

Placement of mineral trioxide aggregate using two different techniques.

The purpose of this study was to determine if the adaptation of mineral trioxide aggregate (MTA) would differ when placed into simulated root canals of varying length when using two different placement and condensation methods. Hand condensation was compared to ultrasonic condensation. Eighty polyethylene tubes were divided into four groups of 20 tubes each. The tubes in the four groups were prepared to receive 3-, 5-, 7-, and 10-mm lengths of MTA respectively. Each group of 20 tubes was subdivided; 10 samples of each length had MTA placed and condensed by the hand method and the other 10 by the ultrasonic method. After condensation the samples were evaluated with a light microscope and radiographs for the degree of adaptation of the MTA to the tube walls and for the presence of voids within the MTA material itself. The results demonstrated an 80% agreement for findings between the light microscopy and radiographic evaluation. Hand condensation resulted in better adaptation to the tube walls and less voids than the ultrasonic method. There was no significant difference in the results for any of the four lengths of MTA placed by the hand method (p > 0.9). At this time hand condensation should be considered the preferred method for placement of MTA.

The effect of endodontic solutions on resorcinol-formalin paste.

This study determined if any of four endodontic solutions would have a softening effect on resorcinol-formalin paste and if there were any differences in the solvent action between these solutions. Resorcinol, formalin, and zinc oxide were mixed and allowed to set for 30 days. The solutions tested were 0.9% sodium chloride, 5.25% sodium hypochlorite, chloroform, and Endosolv R. Seven samples per solution were tested and an additional seven samples served as controls. Each sample was saturated with one of the solutions and the depth of penetration was tested at 1, 2, 5, 10, and 20 min using a dial strain gauge. At 2 min, sodium hypochlorite and sodium chloride had significantly greater penetration than the other groups (p < 0.0010). Sodium hypochlorite was superior to all other groups after 5 min. This study showed that both sodium chloride and sodium hypochlorite exhibited a significant softening effect within 2 min.