Bertram Mallia

Investigation of the physical properties of tricalcium silicate cement-based root-end filling materials

OBJECTIVE Tricalcium silicate-based cements have been displayed as suitable root-end filling materials. The physical properties of prototype radiopacified tricalcium silicate cement, Bioaggregate and Biodentine were investigated. Intermediate restorative material was used as a control. METHODS The physical properties of a prototype zirconium oxide replaced tricalcium silicate cement and two proprietary cements composed of tricalcium silicate namely Bioaggregate and Biodentine were investigated. Intermediate restorative material (IRM) was used as a control. Radiopacity assessment was undertaken and expressed in thickness of aluminum. In addition the anti-washout resistance was investigated using a novel basket-drop method and the fluid uptake, sorption and solubility were investigated using a gravimetric method. The setting time was assessed using an indentation technique and compressive strength and micro-hardness of the test materials were investigated. All the testing was performed with the test materials immersed in Hanks balanced salt solution. RESULTS All the materials tested had a radiopacity value higher than 3mm thickness of aluminum. IRM exhibited the highest radiopacity. Biodentine demonstrated a high washout, low fluid uptake and sorption values, low setting time and superior mechanical properties. The fluid uptake and setting time was the highest for Bioaggregate. SIGNIFICANCE The addition of admixtures to tricalcium silicate-based cements affects the physical properties of the materials.

Characterization of set Intermediate Restorative Material, Biodentine, Bioaggregate and a prototype calcium silicate cement for use as root-end filling materials

AIM To investigate the composition of materials and leachate of a hydrated prototype cement composed of tricalcium silicate and radiopacifier and compare this to other tricalcium silicate-based cements (Biodentine and Bioaggregate) to assess whether the additives in the proprietary brand cements affect the hydration of the materials, using Intermediate Restorative Material (IRM), a standard root-end filling material as a control. METHODOLOGY The materials investigated included a prototype-radiopacified tricalcium silicate cement, Biodentine, Bioaggregate and Intermediate Restorative Material (IRM). The pH and calcium ion concentration of the leachate were investigated. The hydrated cements were characterized using scanning electron microscopy (SEM) and X-ray energy dispersive analysis (EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). RESULTS All the cements tested were alkaline. The tricalcium silicate-based cements leached calcium in solution. Scanning electron microscopy of the prototype-radiopacified tricalcium silicate cement, Biodentine and Bioaggregate displayed hydrating cement grains, surrounded by a matrix composed of calcium silicate hydrate and calcium hydroxide. The presence of calcium hydroxide was evident from the XRD plots. FT-IR indicated the occurrence of a poorly crystalline calcium silicate hydrate. Biodentine displayed the presence of calcium carbonate. Bioaggregate incorporated a phosphate-containing phase. IRM consisted of zinc oxide interspersed in an organic matrix. CONCLUSIONS The hydration of prototype-radiopacified tricalcium silicate cement, Biodentine and Bioaggregate resulted in the formation of calcium silicate hydrate and calcium hydroxide, which was leached in solution. The hydrated materials were composed of a cementitous phase that was rich in calcium and silicon and a radiopacifying material. Biodentine included calcium carbonate, and Bioaggregate included silica and calcium phosphate in the powders. IRM was composed of zinc oxide interspersed in a matrix of organic 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 Hanks 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.

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 Hanks 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.

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 Hanks 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.

Evaluation of the dimensional changes of mineral trioxide aggregate sealer.

AIM To evaluate the setting time, early age restrained dimensional stability, fluid uptake, microstructure and porosity of a root canal sealer based on mineral trioxide aggregate (MTAS). METHODOLOGY The MTAS, mineral trioxide aggregate (MTA) and a commercially available sealer pulp canal sealer (PCS) were investigated. The setting time of the materials was determined according to ISO 6876; 2002. The dimensional change in the vertical direction was measured over a period of 7 days from setting time using a linear variable differential transducer. The test samples were restrained in lateral directions by the metal mould. The fluid uptake of the cements was evaluated in Hanks balanced salt solution (HBSS), and their porosity was investigated using light optical microscopy. RESULTS The addition of a water-soluble polymer to MTA reduced its setting time but PCS displayed the shortest setting time (P < 0.05). The dimensional stability of the materials was not affected by the test environmental conditions (P > 0.05). PCS exhibited a much higher degree of shrinkage than MTA (P = 0.997, 0.640, 0.449, 0.191) and MTAS (P = 0.952, 0.523, 0.380, 0.149) at 3 h and 1, 3, 7 days, respectively, when allowed to set at 100% humidity. An increase in weight and expansion was recorded for MTA when immersed in HBSS. Microscope investigation of test specimens revealed the highest degree of porosity in MTA followed by MTAS and PCS. CONCLUSIONS The novel sealer based on MTA demonstrated adequate setting time and was dimensionally stable. It has the potential to be used as root canal sealer cement in clinical practice.

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 Hanks 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.

Post-deposition heat treatment of co-deposited Cr3C2 and AISI 410 stainless steel using the coaxial laser deposition technique

Cr3C2 ceramic powder is added in varying amounts to AISI 410 stainless steel powder to develop AISI 400 based alloys with varying chromium and carbon content using the coaxial laser deposition technique operating at parameter sets which guarantee full melting of the constituent powder particles. Theoretical isothermal curves for the in situ generated alloys are correlated with the as-deposited and heat-treated microstructures using electron microscopy, X-ray and electron backscatter diffraction techniques. It is concluded that with an increased carbon loading in the mixture, post-deposition heat treatment involving full re-austenitising and tempering is necessary in order to reduce the effect of solute trapping which negatively affects the material mechanical properties.

Analytical, Numerical and Experimental Study of a Horizontal Electrothermal MEMS Microgripper for the Deformability Characterisation of Human Red Blood Cells

Microgrippers are typical microelectromechanical systems (MEMS) that are widely used for micromanipulation and microassembly in both biological and micromanufacturing fields. This paper presents the design, modelling, fabrication and experimental testing of an electrothermal microgripper based on a ‘hot and cold arm’ actuator design that is suitable for the deformability characterisation of human red blood cells (RBCs). The analysis of the mechanical properties of human RBCs is of great interest in the field of medicine as pathological alterations in the deformability characteristics of RBCs have been linked to a number of diseases. The study of the microgripper’s steady-state performance is initially carried out by the development of a lumped analytical model, followed by a numerical model established in CoventorWare® (Coventor, Inc., Cary, NC, USA) using multiphysics finite element analysis. Both analytical and numerical models are based on an electothermomechanical analysis, and take into account the internal heat generation due to the applied potential, as well as conduction heat losses through both the anchor pads and the air gap to the substrate. The models are used to investigate key factors of the actuator’s performance including temperature distribution, deflection and stresses based on an elastic analysis of structures. Results show that analytical and numerical values for temperature and deflection are in good agreement. The analytical and computational models are then validated experimentally using a polysilicon microgripper fabricated by the standard surface micromachining process, PolyMUMPs™ (Durham, NC, USA). The microgripper’s actuation is characterised at atmospheric pressure by optical microscopy studies. Experimental results for the deflection of the microgripper arm tips are found to be in good agreement with the analytical and numerical results, with process-induced variations and the non-linear temperature dependence of the material properties accounting for the slight discrepancies observed. The microgripper is shown to actuate to a maximum opening displacement of 9 μm at an applied voltage of 3 V, thus being in line with the design requirement of an approximate opening of 8 μm for securing and characterising a RBC.