Push-out bond strength of MTA with antiwashout gel or resins.

AIM: Assessment of the push-out bond strength of four MTA-based formulations for use as root-end filling materials. METHODOLOGY: MTA Plus mixed with (i) water ('MTA-W'); (ii) a proprietary water-based antiwashout gel ('MTA-AW'); (iii) Superbond C&B chemically curing resin ('MTA-Chem'); and (iv) Heliobond light-curing resin ('MTA-Light') was tested. Root slices 3 mm thick human had a 1.5 mm diameter hole drilled centrally and were treated with 17% EDTA for 60s. Forty specimens divided into groups 1-4 were prepared and filled with MTA-W, MTA-AW, MTA-Chem and MTA-Light, respectively. Groups 3 and 4 were etched with 37% phosphoric acid for 60s, and bonding agent was applied to the dentine surface. Specimens were stored for 28 days in Hanks' Balanced Salt Solution at 37 °C. Push-out strength was tested with a punch and die (punch diameter 1.3 mm, die diameter 2.0 mm, punch speed 1 mm min(-1)). Stereomicroscopy was used to classify failure mode (adhesive, cohesive or mixed type). RESULTS: The resulting push-out strengths were 5.1 MPa (MTA-W), 4.3 MPa (MTA-AW), 4.7 MPa (MTA-Chem) and 11.0 MPa (MTA-Light). MTA-W had higher push-out strength than MTA-AW (P = 0.022). The same was noted for MTA-Light relative to the other materials (P < 0.05). All materials exhibited adequate push-out strengths compared with MTA-W. Failure was predominantly mixed, except for MTA-Chem (predominantly adhesive). CONCLUSIONS: All materials exhibited adequate push-out strength. Previous studies have shown the new formulations have additional advantages including increased washout resistance and faster setting time, making them promising for future dental applications.

Porosity and root dentine to material interface assessment of calcium silicate-based root-end filling materials.

OBJECTIVES: The aim of this study was to evaluate the porosity and assess the root dentine to material interface of four root-end filling materials based on tricalcium silicate cement using two microscopy techniques. METHODS: The porosity of Bioaggregate, Biodentine, a prototype radiopacified tricalcium silicate cement (TCS-20-Zr) and intermediate restorative material (IRM) was evaluated after immersion for 28 days in Hank's balanced salt solution (HBSS) using mercury intrusion porosimetry. The root dentine to material interface of the cements when used as root-end filling materials in extracted human teeth was assessed after 28 days of dry storage and immersion in HBSS using a confocal microscope together with fluorescent tracers and also a field emission gun scanning electron microscope. RESULTS: Biodentine and IRM exhibited the lowest level or degree of porosity. The confocal microscopy used in conjunction to fluorescent tracers demonstrated that dry storage resulted in gaps at the root dentine to material interface and also cracks in the material with Biodentine being the most affected. Zinc was shown to be present in root dentine adjacent to the IRM restorations. CONCLUSIONS: Dry storage of Biodentine resulted in changes in the material microstructure and cracks at the root dentine to Biodentine interface. Furthermore, the gaps resulting from material shrinkage allowed the passage of the fluorescent microspheres thus indicating that these gaps are significant and can potentially allow the passage of micro-organisms.

The setting characteristics of MTA Plus in different environmental conditions.

AIM: Characterization and assessment of the hydration reaction of mineral trioxide aggregate (MTA) Plus exposed to different environmental conditions. METHODOLOGY: The specific surface area, surface morphology and characterization of un-hydrated MTA Plus (Avalon Biomed Inc. Bradenton, FL, USA) were investigated. The specific surface area was compared with that of ProRoot MTA (Dentsply International, Tulsa Dental Specialties, Johnson City, TN, USA). The reaction rate was determined using calorimetry, and the hydrated cement was assessed for setting time (determined using an indentation technique), and the set material was characterized using X-ray diffraction analysis, scanning electron microscopy and X-ray energy-dispersive analysis. Atomic ratio plots were drawn to establish the relationship of the hydration products. Three different environmental conditions namely dry or immersed in either water or Hank's balanced salt solution (HBSS) were used. RESULTS: Mineral trioxide aggregate Plus had a higher specific surface area than ProRoot MTA. The hydration reaction was exothermic. The setting time of MTA Plus was retarded when in contact with fluids (P < 0.001). The setting time was longer when MTA Plus was in contact with HBSS than when in contact with water (P < 0.001). Hydration of MTA Plus resulted in the formation of calcium silicate hydrate, calcium hydroxide, ettringite and monosulfate phases. Bismuth was incorporated in the calcium silicate hydrate structure. The hydration of the core material was not affected by contact with the different solutions but the periphery exhibited microcracking, leaching of calcium hydroxide, partial decalcification of calcium silicate hydrate, inhibition of hydration in contact with the physiological solution. CONCLUSIONS: The novel MTA Plus was finer than ProRoot MTA but had a similar chemical composition. MTA Plus in direct contact with fluids exhibited partial decalcification of calcium silicate hydrate in contact with the solution, microcracking and leaching of calcium hydroxide. Interaction with a physiological solution resulted in inhibition of hydration.

A quantitative method for determining the antiwashout characteristics of cement-based dental materials including mineral trioxide aggregate.

AIM: To introduce and assess a novel method for measuring washout resistance of cement-based dental materials, including mineral trioxide aggregate (MTA), to qualitatively verify the results with a clinical simulation and to evaluate the washout resistance of a new root-end filling material. METHODOLOGY: A method for assessment of washout resistance of root-end filling materials was developed by adapting the CRD-C 661-06 (a method for evaluating the resistance of freshly mixed concrete to washout in water), to permit testing of dental cements. White Portland cement (PC), MTA-Plus mixed with either water or a polymer-based antiwashout gel (MTA-AW), MTA-Angelus, IRM and amalgam were tested with either distilled water or HBSS as washout media. Additionally, the washout resistance was tested qualitatively by spraying the test materials at the terminus of simulated canals with a metered jet of water. RESULTS: A mass loss of 2-7% for PC, 0.4-4% for MTA-Plus, -0.9% for MTA-AW, 5-10% for MTA-Angelus and 0% for IRM and amalgam was recorded with the modified CRD-C 661-06 method. No significant difference was found between using water and HBSS as washout media for the same material. The results of the modified CRD-C 661-06 method were similar to those obtained on the simulated canals. CONCLUSIONS: The modified CRD-C 661-06 method provided repeatable results that were comparable to the simulated clinical method. The antiwashout gel used with MTA-Plus reduced the material washout and was similar to IRM and amalgam.

The effect of curing conditions on the physical properties of tricalcium silicate cement for use as a dental biomaterial.

AIM: To investigate the physical properties of tricalcium silicate (TCS) with and without the addition of a radiopacifier and compare them with that of Portland cement (PC) and radiopaque PC in an mineral trioxide aggregate-like system. METHODOLOGY: Tricalcium silicate, PC and radiopacified variants containing 20% bismuth oxide were tested for radiopacity, compressive strength, setting time and dimensional stability. All the testing was performed at 37 °C and under different environmental conditions namely at 100% humidity or immersed in either water or Hank's balanced salt solution (HBSS). Testing was performed after both 1 and 28 days. RESULTS: The cements exhibited radiopacity values equivalent to <3 mm. Addition of 20% bismuth oxide resulted in adequate radiopacity. The strength of TCS was independent of the curing conditions. The cements without radiopacifier had improved strength characteristics when immersed in HBSS, whilst the radiopacified cements exhibited higher strengths when soaked in water. Tricalcium silicate demonstrated the shortest setting time. Addition of bismuth oxide increased the setting time of the cements while HBSS inhibited the setting of bismuth oxide-replaced cements. The PC-based materials exhibited a net contraction higher than that recorded for TCS-based cements in all curing conditions. The dimensional change exhibited by the specimens was generally greater in the first few hours of setting, but then stabilized with time. CONCLUSIONS: Tricalcium silicate cement required the addition of a radiopacifying agent to make it suitable for use as a dental material. Tricalcium silicate exhibited adequate physical properties and thus was shown to be a suitable replacement for the PC component in MTA. Bismuth oxide drastically increased the setting time of the test cements in phosphate-containing solutions. Alternative radiopacifiers that do not retard the setting time need to be investigated.

Mercury intrusion porosimetry and assessment of cement-dentin interface of anti-washout-type mineral trioxide aggregate.

INTRODUCTION: One of the disadvantages of mineral trioxide aggregate (MTA) is washout (ie, the tendency of freshly prepared cement paste to disintegrate upon early contact with physiological fluids). A novel MTA (MTA Plus; Prevest Denpro, Jammu City, India) exhibits low washout and superior physical properties when mixed with a gel instead of water. When used as a root-end filler, MTA is in contact with both bone and root dentin. This study aimed to investigate the porosity and interfacial characteristics of the novel MTA mixed with water or antiwashout gel. METHODS: Porosity was evaluated after 1 or 28 days of immersion in Hank's balanced salt solution using mercury intrusion porosimetry. The root dentin to material interface was investigated using a scanning electron microscope and energy-dispersive X-ray spectroscopy complete with line scans and elemental maps. RESULTS: Anti-washout-type MTA Plus was found to have lower initial porosity than MTA Plus mixed with water although this trend was reversed after 28 days of immersion in physiological fluid. Both materials exhibited good marginal adaptation. The diffusion of silicon, calcium, and phosphorus across the cement/dentin interface was observed. CONCLUSIONS: MTA Plus mixed with antiwashout gel was found to have lower initial porosity than MTA Plus mixed with water. Both materials exhibited good marginal adaptation and the diffusion of silicon, calcium, and phosphorous across the cement/dentin interface. Thus, the anti-washout-type MTA can be considered to be a suitable substitute for ordinary MTA in all its indications.

The chemical properties of light- and chemical-curing composites with mineral trioxide aggregate filler.

OBJECTIVE: One of the challenges encountered with composite restorations is their inability to prevent secondary caries. Alternative fillers that initiate remineralization have been proposed but poor mechanical strength limits their use to lining and support materials. Mineral trioxide aggregate (MTA) is a material with many dental applications including root-end filling and pulp capping. MTA is capable of encouraging remineralization by leaching calcium in solution, and has the ability to form apatite in physiological solution. The aim of this study was to characterize and investigate the chemical properties of MTA-filled composite resins. METHODS: Composite resins composed of light-cured (Heliobond) and chemical-cured (Superbond) dental resins filled with MTA Plus (MTA-Light, MTA-Chem) respectively, and MTA Plus mixed with water (MTA-W), were investigated. Un-hydrated and set materials were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) analysis and Fourier transform infrared (FT-IR) spectroscopy after being stored dry or immersed in Hank's balanced salt solution (HBSS). The chemical properties of the set materials were then investigated. RESULTS: XRD and FT-IR analyses revealed that MTA powder remains unhydrated within the composite, even after 28 days of immersion in HBSS. Furthermore neither resin appeared to chemically react with the MTA. EDX revealed minimal diffusion of bismuth oxide through the polymer network. Apatite formation on the material surfaces was demonstrated by SEM. Significantly less apatite deposition was exhibited on the composites compared to MTA-W. All materials leached calcium and produced an alkaline pH in physiological solution. The pH at 28 days was: MTA-W 12.7, MTA-Light 11.4, and MTA-Chem 10.8. Calcium ion concentration followed the same trend, with MTA-W>MTA-Light>MTA-Chem. SIGNIFICANCE: The novel composites exhibited calcium ion release, alkalinizing pH and formation of apatite, although in each case not as strongly as the control (MTA-W). MTA-Chem fared less favorably than MTA-Light in these aspects. Thus they are recommended for applications where bioactivity is desirable but not critical, and only they have a significant advantage over ordinary MTA in some other aspect.

Mineral trioxide aggregate with anti-washout gel - properties and microstructure.

OBJECTIVE: One of the problems encountered clinically when using mineral trioxide aggregate (MTA) as a root-end filling material is washout immediately after placement. A novel MTA is supplied with an anti-washout gel that replaces the mixing water. The aim of this research was to characterize and assess the properties of a novel MTA mixed with an anti-washout liquid. METHODS: MTA Plus mixed with either water (MTA-W) or an anti-washout gel (MTA-AW) was investigated. Un-hydrated and set materials were characterized by scanning electron microscopy (SEM), energy X-ray dispersive analysis (EDX), X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy (FT-IR) after being stored dry or immersed in Hank's balanced salt solution (HBSS). The chemical and physical properties of the set materials were then investigated. RESULTS: The MTA Plus was composed of tricalcium silicate, dicalcium silicate and bismuth oxide. The anti-washout gel used was water-based and FT-IR plots showed the presence of an organic additive. Both materials immersed in HBSS displayed the presence of reaction by-product with MTA-W exhibiting a high-intensity calcium hydroxide peak on X-ray diffraction. The X-ray diffractograms of all materials following hydration demonstrated the reduction in peak intensity of the tri- and dicalcium silicate. Hydroxyapatite deposits were evident on the surfaces of both materials in contact with HBSS. The pH of the leachate was similar for both materials. MTA-AW exhibited lower levels of calcium ions in solution and reduced fluid uptake in the early stages of reaction. The anti-washout gel reduced the setting time of the cement and enhanced the compressive strength. The radiopacity of both materials was approximately 8mm aluminum. SIGNIFICANCE: The use of the water-based anti-washout material instead of the standard water with MTA affects the hydration and properties of the set material.

The microstructure and surface morphology of radiopaque tricalcium silicate cement exposed to different curing conditions.

OBJECTIVE: Tricalcium silicate is the major constituent phase in mineral trioxide aggregate (MTA). It is thus postulated that pure tricalcium silicate can replace the Portland cement component of MTA. The aim of this research was to evaluate the microstructure and surface characteristics of radiopaque tricalcium silicate cement exposed to different curing conditions namely at 100% humidity or immersed in either water or a simulated body fluid at 37°C. METHODS: The materials under study included tricalcium silicate and Portland cements with and without the addition of bismuth oxide radiopacifier. Material characterization was performed on hydrated cements using a combination of scanning electron microscopy (SEM) with X-ray energy dispersive (EDX) analyses and X-ray diffraction (XRD) analyses. Surface morphology was further investigated using optical profilometry. Testing was performed on cements cured at 100% humidity or immersed in either water or Hank's balanced salt solution (HBSS) for 1 and 28 days at 37°C. In addition leachate analysis was performed by X-ray fluorescence of the storage solution. The pH of the storage solution was assessed. RESULTS: All the cements produced calcium silicate hydrate and calcium hydroxide on hydration. Tricalcium silicate showed a higher reaction rate than Portland cement and addition of bismuth oxide seemed to also increase the rate of reaction with more calcium silicate hydrate and calcium hydroxide being produced as demonstrated by SEM and XRD analysis and also by surface deposits viewed by the optical profilometer. Cement immersion in HBSS resulted in the deposition of calcium phosphate during the early stages following immersion and extensive calcification after 28 days. The pH of all storage solutions was alkaline. The immersion in distilled water resulted in a higher pH of the solution than when the cements were immersed in HBSS. Leachate analysis demonstrated high calcium levels in all cements tested with higher levels in tricalcium silicate and bismuth replaced cements. SIGNIFICANCE: Tricalcium silicate cement is more bioactive than Portland cement as demonstrated by various characterization techniques. The bioactivity was monitored by measuring the production of calcium hydroxide and the formation of calcium phosphate when in contact with simulated body fluids.