Improvement of the properties of mineral trioxide aggregate by mixing with hydration accelerators

Introduction

Mineral trioxide aggregate (MTA) is used widely in endodontic therapy. This study examined the setting time, compressive strength, and pH of MTA mixed with several hydration accelerators (calcium chloride, low-dose citric acid, calcium lactate gluconate solution).

Methods

Group 1 (control) was obtained by mixing MTA with distilled water. In group 2, MTA containing 10% calcium chloride was mixed with distilled water. In group 3, MTA was mixed with 0.1% citric acid. In group 4, MTA was mixed with a calcium lactate gluconate solution. The setting time, compressive strength, and pH were examined.

Results

The setting time of MTA mixed with hydration accelerators was significantly shorter than that of MTA mixed with water (P < .01). In particular, replacing distilled water with a calcium lactate gluconate solution provided a significant decrease in setting time. The compressive strengths of MTA mixed with hydration accelerators were significantly lower than that of MTA mixed with water (P < .01), but those values increased with time. The pH of MTA mixed with hydration accelerators was significantly lower than that of MTA mixed with water (P < .01) but stable at a high level (pH 11–12).

Conclusions

Hydration accelerators improved the setting time of MTA. Nevertheless, more study will be needed to improve MTA without impairing its preexisting advantages.     

Chemico-physical and mechanical evaluation of three calcium silicate-based pulp capping materials

AimThis study compared biointeractivity (pH of soaking water and calcium ions), porosity, water sorption, solubility, compressive strength, lap shear strength, as well as the apatite forming ability of three calcium silicate-based capping materials: Mineral trioxide aggregate (MTA), Biodentine (BD) and Tech Biosealer capping (BS).MethodsOne hundred and five discs of the tested materials were prepared in compliance with the manufacturer’s instructions. The materials' pastes were placed in Teflon molds and allowed to set before testing. The pH and Ca⁺² ions were measured by a potentiometric method. Porosity, water sorption, and solubility were calculated through the measurement of initial mass, mass, saturated mass and dry mass. Apatite forming ability was measured by an Environmental Scanning Electron Microscope that was connected to a secondary electron detector for energy dispersive X-ray analysis. Meanwhile compressive strength was measured by a computer controlled universal testing machine. Lap shear strength was measured by computer software on the testing machine. All data were statistically analyzed.ResultsThe tested materials showed Ca ions release and alkalization, which decreased with soaking time. The BD exhibited a very high Ca release at both short (3 h) and long times (28 days). Significant high values of open and apparent porosities, water sorption, and solubility were measured for BS, which was followed by the MTA then BD (P < .05). The BD had significant higher compressive and lap shear bond strength than the MTA and BS (P < .05).ConclusionMTA, BD and BS are biointeractive bioactive materials that possess the ability to release ions and form calcium phosphate deposits. Unlike BD, BS is incapable of alternating MTA in pulp capping due to its high porosities, water sorption and solubility, as well as poor compressive and lap shear bond strength.     

Impact of ZrO2 nanoparticles addition on flexural properties of denture base resin with different thickness

PURPOSEThis study aimed to evaluate the effect of incorporating zirconium oxide nanoparticles (nano-ZrO₂) in polymethylmethacrylate (PMMA) denture base resin on flexural properties at different material thicknesses.MATERIALS AND METHODSHeat polymerized acrylic resin specimens (N = 120) were fabricated and divided into 4 groups according to denture base thickness (2.5 mm, 2.0 mm, 1.5 mm, 1.0 mm). Each group was subdivided into 3 subgroups (n = 10) according to nano-ZrO₂ concentration (0%, 2.5%, and 5%). Flexural strength and elastic modulus were evaluated using a three-point bending test. One-way ANOVA, Tukey''s post hoc, and two-way ANOVA were used for data analysis (α = .05). Scanning electron microscopy (SEM) was used for fracture surface analysis and nanoparticles distributions.RESULTSGroups with 0% nano-ZrO₂ showed no significant difference in the flexural strength as thickness decreased (P = .153). The addition of nano-zirconia significantly increased the flexural strength (P < .001). The highest value was with 5% nano-ZrO₂ and 2 mm-thickness (125.4 ± 18.3 MPa), followed by 5% nano-ZrO₂ and 1.5 mm-thickness (110.3 ± 8.5 MPa). Moreover, the effect of various concentration levels on elastic modulus was statistically significant for 2 mm thickness (P = .001), but the combined effect of thickness and concentration on elastic modulus was insignificant (P = .10).CONCLUSIONReinforcement of denture base material with nano-ZrO₂ significantly increased flexural strength and modulus of elasticity. Reducing material thickness did not decrease flexural strength when nano-ZrO₂ was incorporated. In clinical practice, when low thickness of denture base material is indicated, PMMA/nano-ZrO₂ could be used with minimum acceptable thickness of 1.5 mm.     

Effect of Various Mixing and Placement Techniques on the Flexural Strength and Porosity of Mineral Trioxide Aggregate

Introduction

The aim of this study was to evaluate the effect of mechanical and manual mixing as well as the effect of ultrasonic agitation during placement on the flexural strength and porosity of mineral trioxide aggregate (MTA).

Methods

White ProRoot MTA and white MTA Angelus were used. One gram of each powder was mixed with a 0.34-g aliquot of distilled water. Specimens were mixed either by mechanical mixing of capsules for 30 seconds at 4500 rpm or by a saturation technique and application of a condensation pressure of 3.22 MPa for 1 minute. The mixed slurries of all materials were loaded into 2 × 2 × 25 mm molds for testing flexural strength and 3 × 4 mm molds for evaluation of porosity. Half of the specimens were placed in the stainless steel molds by using indirect ultrasonic activation. All specimens were incubated for 4 days. Micro–computed tomography was used to determine the porosity of each specimen, and a 3-point bending test was used to evaluate flexural strength. Tukey honestly significant difference and independent t tests were carried out to compare the means at a significance level of P < .05.

Results

Irrespective of mixing and placement techniques applied, the flexural strength values of ProRoot MTA were significantly greater than those of MTA Angelus (P < .05). A medium negative correlation was found between flexural strength values and total porosity percentage.

Conclusions

Although mechanical mixing of encapsulated cements was quicker and provided more consistent mixes, this technique along with ultrasonic agitation was not associated with a significant advantage in terms of flexural strength and total porosity over manual mixing.     

Evaluation of Compressive Strength of Hydraulic Silicate-based Root-end Filling Materials

Introduction

Hydraulic silicate cements such as mineral trioxide aggregate (MTA) have many clinical advantages. Newer hydraulic silicate materials have been developed that improve on the limitations of mineral trioxide aggregate such as the long setting time and difficult handling characteristics. The purpose of this study was to examine the effect of saline and fetal bovine serum (FBS) on the setting and compressive strength of the following hydraulic silicate cements: ProRoot MTA (white WMTA; Dentsply International, Tulsa Dental Specialties, Johnson City, TN), EndoSequence Root Repair Material (Brasseler USA, Savannah, GA), MTA Plus (MTAP; Avalon Biomed Inc, Bradenton, FL), and QuickSet (QS; Avalon Biomed Inc, Bradenton, FL).

Methods

Samples of root-end filling materials were compacted into polyethylene molds. Samples were exposed to FBS or saline for 7 days. A universal testing machine was used to determine the compressive strengths.

Results

QS had significantly lower compressive strength than all other materials (P < .001). White MTA and MTAP mixed with liquid had lower compressive strengths after exposure to FBS compared with saline (P = .003). ERRM, MTAP mixed with gel, and QS were not affected by the exposure to FBS.

Conclusions

New silicate-based root-end filling materials, other than QS, have compressive strength similar to MTA. Within the limits of this study, premixed materials and those mixed with antiwashout gel maintain their compressive strength when exposed to biological fluids.     

The shear bond strength of resin-based composite to white mineral trioxide aggregate

BackgroundIt is unknown if resin-based composite can be placed on top of mineral trioxide aggregate (MTA) immediately after placement of the MTA. The authors aimed to measure the bond strength of a resin-based composite to white MTA (WMTA) with different bonding strategies at different intervals.MethodsThe authors bonded resin-based composite to MTA with three bonding protocols (n = 45 per group) (group 1, total-etching adhesive; group 2, two-step self-etching adhesive; or group 3, one-step self-etching adhesive), immediately (subgroup A), 45 minutes (subgroup B) or 24 hours (subgroup C) after placement of the MTA. The authors measured shear bond strength by means of a universal testing machine and performed statistical analysis of the data by means of two-way and one-way analysis of variance (P < .05).ResultsIn all three groups, subgroup A demonstrated greater bond strengths than the other subgroups. Group/subgroup 3/A demonstrated the highest bond strength (mean [standard deviation] 49.2 [2.1] megapascals), which was significantly higher than that in all other groups (P < .05). This was followed by group/subgroup 1/A (40.2 [2.5] MPa), 2/A (38.4 [1.3] MPa) and 1/B (38.5 [1.91] MPa). The lowest bond strength was shown by group/subgroup 2/C (14.7 [1.90] MPa). There was a significant difference between the two-step and one-step self-etching adhesives at all three intervals (P < .05).ConclusionsWithin the limitations of this study, the representative one-step self-etching adhesive demonstrated the strongest bond to WMTA immediately after fabrication of MTA samples.Clinical ImplicationsOne-step self-etching adhesive may be used to bond resin-based composite to WMTA immediately after placement, thereby offsetting the need for a second appointment for permanent restoration.     

Effect of Diabetes on Tubular Density and Push-out Bond Strength of Mineral Trioxide Aggregate to Dentin

IntroductionThis study compared the tubular density and push-out bond strength of mineral trioxide aggregate (MTA) to dentin in diabetic and nondiabetic patients.MethodsTen extracted single-rooted human teeth from diabetic and nondiabetic patients (n = 5 in each group) were decoronated, prepared up to a #5 Gates-Glidden drill, and sectioned horizontally at the midroot area to prepare 3 dentin slices, each measuring 2 mm in thickness (1 slice for the push-out test and 2 slices for the tubular density test). MTA was prepared and packed into the root canal space followed by incubation for 3 days. The push-out bond strength values were determined using a universal testing machine. Specimens were viewed under a stereomicroscope and a scanning electron microscope to determine the failure types at the cement-dentin interface. Ten slice specimens in each group were evaluated under SEM at 3 different sites to determine the tubular density. Comparisons were performed using the Mann-Whitney U test (P < .05).ResultsDiabetic patients exhibited significantly lower push-out bond strength of MTA to root canal dentin (P < .05). The pattern of failure at the MTA-dentin interface was different between the 2 groups. The tubular density was significantly higher in diabetic patients (P < .05).ConclusionsThe dentin in diabetic patients exhibited different physicochemical properties. The failure patterns and modes in diabetic patients might be explained by the changes in the push-out bond strength, the calcification mechanism of the dentin-pulp complex, a higher dentinal tubule density, and less peritubular dentin. These differences could explain the higher failure rate of root canal treatment in these patients.     

Effect of Ultrasonic Activation of Endodontic Sealers on Intratubular Penetration and Bond Strength to Root Dentin

IntroductionThis study aimed to evaluate the effect of ultrasonic activation (UA) of endodontic sealers on dentin tubule penetration and the bond strength to root dentin.MethodOne hundred single-rooted teeth were prepared with 40.06 nickel-titanium instruments and divided into 2 groups: with or without UA. Three resin-based sealers (MTA Fillapex [Angelus Dental Solutions, Londrina, PR, Brazil], Sealer Plus [MK Life Medical and Dental Products, Porto Alegre, RS, Brazil], and AH Plus [Dentsply, DeTrey GmbH, Konstanz, Germany]; n = 20) and 2 calcium silicate–based sealers (Sealer Plus BC [MK Life Medical and Dental Products] and EndoSequence BC [Brasseler, Savannah, GA], n = 20) were used and subdivided (n = 10) according to the protocols. Fluo-3 (Thermo Fisher Scientific, Waltham, MA) and rhodamine B dyes were added to the calcium silicate- and resin-based sealers, respectively. In the UA groups, the activation was performed for 40 seconds followed by lateral compaction. Samples were transversely sectioned to evaluate the dentin tubule penetration and the bond strength to root dentin. The penetration data were analyzed with the Student t test, 1-factor analysis of variance, and Bonferroni tests. Bond strength was evaluated using the Student t test, Kruskal-Wallis, and Dunn post hoc test.ResultsResin-based sealers showed the highest tubule penetration without UA (P < .05). UA significantly enhanced MTA Fillapex and Endosequence BC dentin tubule penetration (P < .05). AH Plus and Sealer Plus BC improved their bond strength to root dentin after UA (P < .05). AH Plus/UA, Sealer Plus/UA, and Sealer Plus BC/UA presented the highest bond strength values (P < .05). Adhesive failures were predominant in all groups regardless of the use of ultrasound.ConclusionsUA interferes with tubule penetration and the bond strength to root dentin of resin- and calcium silicate–based sealers.     

Effect of Acid Etching Procedures on the Compressive Strength of 4 Calcium Silicate–based Endodontic Cements

Introduction

The purpose of this study was to evaluate the effect of acid etching on the compressive strength of 4 calcium silicate–based cements.

Methods

One gram of each corresponding powder of ProRoot MTA (Dentsply Tulsa Dental, Johnson City, TN), MTA Angelus (Angelus, Londrina, PR, Brazil), and CEM cement (BioniqueDent, Tehran, Iran) and a 0.33-g aliquot of liquid were placed in a plastic mixing capsule that was then mechanically mixed for 30 seconds at 4500 rpm in an amalgamator. For the preparation of Biodentine (Septodont, Saint Maur-des-Fossés, France), the liquid provided was added to the powder within the plastic capsule supplied by the manufacturer and then mechanically mixed for 30 seconds at 4500 rpm using the amalgamator. The resulting slurries were then placed incrementally into 40 cylindrical molds to give a total of 160 specimens that were incubated at 37°C for a week. Twenty specimens of each material were then subjected to the acid etch procedure. The compressive strength of the samples was then calculated in megapascals using a universal testing machine. The results were then subjected to 2-way analysis of variance analysis of variance followed by the Tukey post hoc test.

Results

The application of acid etch significantly reduced (P < .0001) the compressive strength of Angelus MTA and CEM cement; however, it did not reduce the compressive strength of ProRoot MTA or Biodentine. Regardless of the acid etch application, Biodentine showed significantly higher compressive strength values than the other materials (P < .0001), whereas CEM cement had the lowest compressive strength values. There was no significant difference between CEM cement and MTA Angelus. The compressive strength of ProRoot MTA was significantly lower (P < .0001) than Biodentine but significantly higher (P < .0001) than MTA Angelus and CEM cement in both the test and control groups.

Conclusions

When the application of acid etchants is required, Biodentine and ProRoot MTA seem to be better options than MTA Angelus or CEM cement.     

Physicochemical Properties of Calcium Silicate Cements for Endodontic Treatment

IntroductionThe purpose of this study was to examine the physicochemical properties of novel calcium silicate cements (CSCs) prepared by using a sol-gel method.MethodsThe compressive strength, morphology, and phase composition of various cements were evaluated after mixing with water, in addition to setting time and pH value.ResultsAs solid phases, the sol-gel–derived powders mainly consisted of β-dicalcium silicate. Setting times for cements mixed with water ranged from 12–42 minutes and were lower for cements with higher starting CaO content. The compressive strength of the CSCs ranged from 0.3–15.2 MPa; these values were significantly different (P < .05). Calcium silicate hydrate (C ? S?H) was the principal phase that formed in the hydration process. The CSCs' pH values changed from an initial 11 to a high of 13.ConclusionsCSCs display advantageously shortened setting times and might have potential for endodontic use, although further tests are necessary to confirm this.     

Mixing with Propylene Glycol Enhances the Bond Strength of Mineral Trioxide Aggregate to Dentin

IntroductionMixing mineral trioxide aggregate (MTA) with different proportions of propylene glycol (PG) improves its handling property. The aim of this study was to evaluate the effect of PG on MTA-dentin push-out bond strength.MethodsSeventy-five 2-mm-thick midroot sections were prepared from single-rooted human extracted teeth. The lumen of each slice was enlarged with Gates-Glidden burs. The slices were randomly divided into 3 groups (n = 25). In each group, 0.3 mL of the liquid was mixed with 1 g MTA (Angelus, Londrina, Brazil). The liquid vehicles used in groups 1–3 were 100% distilled water (DW), 20% PG–80% DW, and 100% PG, respectively. After incubation, the push-out strength of the samples was measured using a universal testing machine. The samples were then cut in halves and examined under a stereomicroscope to determine the failure pattern. One-way analysis of variance followed by the Tukey post hoc test was used to compare the push-out strength among groups.ResultsThere were statistically significant differences between groups (P < .001). The push-out strength in group 1 (DW) was significantly lower than groups 2 and 3 (P < .001 and P = .022, respectively). However, there was no significant difference between groups 2 (DW-PG) and 3 (PG).ConclusionsMixing MTA with PG increased its push-out bond strength to dentin. In the present study, the most suitable ratio was 80% DW–20% PG.     

Effect of silicon dioxide nanoparticles on the flexural strength of heat-polymerized acrylic denture base material: A systematic review and meta-analysis

ObjectiveThis study evaluated the influence of silicon dioxide (SiO₂) nanoparticles on the flexural strength of heat-polymerized denture base materials.BackgroundNanoparticles have been incorporated into the denture base materials in different proportions to enhance the mechanical properties. Recently, the incorporation of SiO₂ nanoparticles at low concentrations has shown promising outcomes.Materials and MethodsFollowing the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol, this study was designed with the following focused question: “Does the addition of SiO₂ nanoparticles improve the flexural strength of heat-polymerized acrylic resins?” The inclusion criteria included in-vitro studies that assessed the flexural strength of SiO₂ nanoparticle-reinforced heat-polymerized acrylic denture base resins tested according to American Dental Association specifications. The database search involved articles published from 2005 to 2020 on PubMed/MEDLINE, Web of Science, Google Scholar, and Scopus using the following keywords: SiO₂, nanosilica, silica oxide, nanoparticles, denture base resin, acrylic resin, polymethyl methacrylate, PMMA, flexural strength, and mechanical properties.ResultsAmong 167 studies, five papers fulfilled the inclusion criteria and were added for the data analysis and meta-analysis. Proportions of incorporated SiO₂ nanoparticles ranged from 0.25% to 15% and the reported flexural strength values for the reinforced acrylic resin ranged from 41.25 MPa to 124.56 MPa. The meta-analysis revealed no significant effect on the flexural strength between the unmodified and the SiO₂ nanoparticle-reinforced acrylic resin.ConclusionTherefore, No particular concentration of SiO₂ nanoparticles could be recommended for heat-polymerized denture base reinforcement.     

Flexural strength and Weibull characteristics of stereolithography additive manufactured versus milled zirconia

Statement of problemZirconia restorations can be processed by using stereolithography additive manufacturing (AM) technologies. However, whether additive manufactured zirconia could achieve flexural strength values comparable with those of milled zirconia is unclear.PurposeThe purpose of this in vitro study was to compare the flexural strength and Weibull characteristics of milled and additive manufactured zirconia.Material and methodsA total of 40 zirconia bars (25×4×1.2 mm) were obtained by using 2 manufacturing procedures, subtractive (CNC group) (IPS e.max ZirCAD; Ivoclar Vivadent AG) and additive manufacturing (AM group) (3DMix ZrO₂; 3DCeram) technologies and assigned to 2 subgroups according to accelerating artificial aging procedures (mastication simulation): nonaged and aged (n=10). Flexural strength was measured in all specimens by using 3-point bend tests according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501; Instron Corp). Two-parameter Weibull distribution values, including the Weibull modulus, scale (m), and shape (0) were calculated. Flexural strength values were analyzed by using 2-way ANOVA and Student t statistical tests (α=.05).ResultsThe manufacturing procedure (P<.001), the mastication simulating aging procedure (P<.001), and the interaction between them (P<.001) significantly affected flexural strength values. The CNC group exhibited statistically higher flexural strength values than those in the AM group when the specimens were tested before performing an aging procedure (P<.001) and after mastication simulation (P<.001). Moreover, mastication simulation produced a significant reduction in flexural strength for both the CNC group (P<.039) and the AM group (P<.001).ConclusionsThe manufacturing process reported a significant effect on the flexural strength of the zirconia material tested. Mastication simulation as a means of accelerating artificial aging resulted in the significantly decreased flexural strength values of milled and additively manufactured zirconia material, with the Weibull moduli being significantly higher for the milled groups versus the milled specimens.     

Effect of Different Concentrations of Sodium Hypochlorite on the Compressive Strength of Endodontically Treated Roots

IntroductionThe aim was to compare the compressive strength of dentin after irrigation with different concentrations of sodium hypochlorite (NaOCl).MethodsA total of 259 extracted human tooth roots with no root caries or previous endodontic treatment were collected. They were sorted by size and length, and assigned to 7 groups (n = 37): negative control (no instrumentation, no irrigant), positive control (saline irrigant), 1%, 2.5%, 4%, 5.25%, and 10% NaOCl. A total of 13 mL NaOCl or saline (in 1-mL increments) was used per canal while being instrumented to #35 files (approximately 13 minutes). EDTAC (15%) was then used to remove the smear layer (2 minutes), followed by NaOCl as a final rinse. The roots were sectioned into 2-mm-thick disks and subjected to compression testing.ResultsThere was a significant difference between the negative control group and all instrumented groups (P < .05). The positive control group was significantly different from the 5.25% group (P < .05) and had a low P value when compared with the 2.5% group and the other higher concentrations (P ? .1). When the NaOCl groups were compared with each other, there was a significant difference between 1% NaOCl and all higher concentrations (P < .05), but no significant difference when 2.5% NaOCl was compared with higher concentrations.ConclusionA concentration of 1% NaOCl had the least effect on the compressive strength of dentin and this was significantly different from all higher concentrations tested. Therefore, the use of concentrations of NaOCl above 1% should be reconsidered.     

Effect of build orientation on the manufacturing process and the properties of stereolithographic dental ceramics for crown frameworks

Statement of problemStereolithography (SLA) ceramic crown frameworks are suitable for clinical use, but the impact of SLA build orientation has not been identified.PurposeThe purpose of this in vitro study was to investigate the effect of 3 build orientations on the physical and mechanical properties and the microstructure of SLA alumina dental ceramics.Material and methodsThe physical and mechanical properties and microstructures of 3 different oriented SLA alumina ceramics (ZX, ZY, and XY) were evaluated by visual observation, hydrostatic weighing (n=10/group), Weibull analyses (n=30/group), scanning electron microscopy, 3-point flexural strength (n=30/group), fracture toughness (indentation, single-edge-V-notched-beam) (n=4/group), and Vickers hardness (n=15/group) testing. The hydrostatic weighing, 3-point flexural strength, fracture toughness, and Vickers hardness testing data were statistically analyzed (α=.05).ResultsThe minimum resting period of slurries between the polymerization of 2 layers was shorter for the ZY- and ZX-oriented specimens and increased with the layer surface. The density and Vickers hardness of the SLA-manufactured specimens were similar for all groups (P>.05). The 95% confidence intervals of the Weibull moduli of the ZX- and ZY-oriented specimens were higher than that of the XY-oriented specimens, with no overlap fraction. The ZY-oriented specimens displayed significantly higher 3-point flexural strength (P<.05) and fracture toughness as evaluated by the single-edge-V-notched-beam method than the ZX-oriented specimens (P<.05). They also displayed significantly higher 3-point flexural strength than the XY-oriented specimens (P<.05). The microstructural analysis showed that the texturing was heterogeneous and that the major axis of the large grains of alumina ran parallel to the orientation of the layers.ConclusionsThe ZY orientation produced a reliable dental ceramic by SLA, with the shortest general manufacturing time and the highest mechanical strength when the layers were perpendicular to the test load surface.     

Effect of setting conditions on mineral trioxide aggregate flexural strength

This study evaluated the effect of setting conditions (time and hydration) on mineral trioxide aggregate (MTA) flexural strength. MTA beam specimens were allowed to set for either 24 or 72 hours with specimens exposed to moisture on either one or two specimen surfaces. These moisture conditions were used to simulate MTA setting with only external tissue moisture (one-sided moisture) versus tissue moisture in combination with a moistened intracanal cotton pellet (two-sided moisture). Ten specimens were stored at 37 degrees C under each of the four experimental setting conditions (1) 24-hour/moist/2-sided; (2) 24-hour/moist/1-sided; (3) 72-hour/moist/2-sided; (4) 72-hour/moist/1-sided. After storage at respective setting conditions, MTA specimens were tested to failure with three-point bend test to measure flexural strength. Flexural strength of the 24h/moist/2-sided specimens, 14.27 +/- 1.96 MPa, was significantly higher (p < or = 0.05) than the flexural strength values associated with conditions two, three, and four, respectively, 10.77 +/- 1.44, 11.16 +/- 0.96, 11.18 +/- 0.99 MPa, which were not significantly different from each other (p > 0.05). Clinically, these results suggest that a moistened cotton pellet should be placed on the intracanal MTA surface under a temporary restoration; and if possible, to optimize flexural strength, the moistened pellet should only remain in place for 24 hours.     

Enhancing Effect of Elastinlike Polypeptide-based Matrix on the Physical Properties of Mineral Trioxide Aggregate

Introduction

Elastinlike polypeptide (ELP) is 1 of the genetically engineered, protein-based polypeptides, which offers outstanding advantages such as superior biocompatibility, long-term stability, elasticity, and cost-effectiveness. This study aimed to investigate the effect of an ELP-based matrix on the physical properties and biocompatibility of mineral trioxide aggregate (MTA).

The influence of different radiopacifying agents on the radiopacity,compressive strength,setting time,and porosity of Portland cement

Objectives

The aims of this study were to evaluate the radiopacity, compressive strength, setting time, and porosity of white Portland cement (PC) with the addition of bismuth oxide (Bi₂O₃), zirconium dioxide (ZrO₂), and ytterbium trifluoride (YbF₃) after immersion at 37 °C for 7 days in distilled water or phosphate buffer saline.

Materials and methods

Specimens measuring 8 mm in diameter and 1 mm in thickness were fabricated from PC with the addition of 10, 20, and 30 wt% Bi₂O_3, ZrO₂ or YbF₃. ProRoot MTA (Dentsply, Tulsa, OK, USA) and pure PC were used as controls. For radiopacity assessments, specimens were radiographed alongside a tooth slices and an aluminum stepwedge on Extraspeed occlusal dental films (Insight Kodak, Rochester, New York). Mean optical density of each specimen was calculated and used to express radiopacity of the material as an equivalent thickness of aluminum. Compressive strength was measured by using 4-mm diameter and 6-mm high specimens and Universal testing machine. High-pressure mercury intrusion porosimeter (Carlo Erba Porosimeter 2000) was employed to measure the porosity of the specimens. The setting time was measured by using a needle of 100 g in weight. The morphology of specimens was evaluated using a scanning electron microscope (TESCAN Mira3 XMU, USA Inc.). Data were analyzed by one-way ANOVA and post hoc Tukey test (P?<?0.05).

Results

The PC with the addition of at least 10 wt% Bi₂O₃ and 20 wt% ZrO₂ or YbF₃ demonstrated greater radiopacity value than the recommended 3 mmAl cut-off. ZrO₂ and YbF₃ increased the compressive strength of PC, but it was not statistically significant (P?>?0.05), while Bi₂O₃ decreased it (P?<?0.05). All radiopacifiers significantly increased the porosity of the experimental cements (P?<?0.05). Bi₂O₃ extended the setting time of PC (P?<?0.05), whilst ZrO₂ and YbF₃ did not significantly affect it (P?>?0.05).

Conclusions

ZrO₂ and YbF₃ may be used as a suitable alternative to replace Bi₂O₃ in MTA without influencing its physical properties.     

Effect of different surface treatments on the biaxial flexural strength of zirconia ceramics

Statement of problemDifferent surface treatments have been applied to zirconia restorations in clinical practice to increase the bond strength between zirconia and cement, but their effect on flexural strength is unknown.PurposeThe purpose of this in vitro study was to evaluate the effect of different surface treatments before and after sintering on the flexural strength of zirconia.Material and methodsSixty disk-shaped specimens with an initial diameter of 18.6 ±0.1 mm and thickness of 2 ±0.1 mm were prepared from preshaded presintered 3Y-TZP blocks. The specimens were randomly divided into 3 groups (n=20) according to surface treatments (Group Laser, Group APA, Group Rocatec), and the groups were then divided into 2 subgroups (n=10) according to surface treatment before and after sintering. The phase compositions of the groups were examined by using an X-ray diffractometer (XRD) with 3 randomly selected specimens from each group. Biaxial flexural strength testing was conducted using a universal testing machine to examine the flexural strength of the zirconia specimens. Two-way ANOVA and post hoc least significant difference tests were performed (α=.05).ResultsAccording to the XRD analysis, no monoclinic phases were determined on the surface of the presintered laser-treated specimens, but tetragonal phases were observed on the surface of the postsintered specimens. Surface treatment type and application stage (presintering to postsintering) have a significant effect on the biaxial flexural strength of the specimens (P<.05). The lowest biaxial flexural values were observed in the Laser group, and postsintered specimens showed higher biaxial flexural strength than presintered specimens (P<.05).ConclusionsPostsintered specimens showed higher monoclinic content than presintered specimens. Laser-treated specimens showed the lowest biaxial flexural strength for both presintered and postsintered specimens.     

Modification of mineral trioxide aggregate. Physical and mechanical properties

Aim To evaluate the physical and mechanical properties of two cements with a similar chemical composition to mineral trioxide aggregate and to attempt to improve their properties by producing a composite material. Methodology Two cement types were used: a mixture of calcium sulpho‐aluminate cement and Portland cement (CSA) and calcium fluoro‐aluminate cement (CFA) in conjunction with an admixture to improve the handling characteristics. Cements were mixed with an inert filler to produce cement composite. The setting time of the cements was evaluated using an indentation technique. The flexural and uni‐axial compressive strengths and solubility of the cements and cement composites were evaluated. The properties of the materials were compared with proprietary brand glass–ionomer cement. Results The setting time of the CSA and CFA cements was less than 6 min. The use of an admixture to improve the handling properties tended to retard setting. CSA was stronger then CFA in both compression and flexure (P < 0.001). Addition of granite increased the flexural strength of both cements but reduced the compressive strength (P < 0.01). CFA absorbed more water then CSA. Addition of granite reduced the water uptake of both cements. Conclusions Both CSA and CFA cements had adequate setting times and compressive strength values when compared with proprietary brand glass–ionomer cement. CSA was superior to CFA and had more promise as a prospective dental material.