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 Hank’s 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). 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.peer-reviewe

The effects of cold arm width and metal deposition on the performance of a U-Beam electrothermal MEMS microgripper for biomedical applications

Microelectromechanical systems (MEMS) have established themselves within various fields dominated by high-precision micromanipulation, with the most distinguished sectors being the microassembly, micromanufacturing and biomedical ones. This paper presents a horizontal electrothermally actuated 'hot and cold arm' microgripper design to be used for the deformability study of human red blood cells (RBCs). In this study, the width and layer composition of the cold arm are varied to investigate the effects of dimensional and material variation of the cold arm on the resulting temperature distribution, and ultimately on the achieved lateral displacement at the microgripper arm tips. The cold arm widths investigated are 14 μm, 30 μm, 55 μm, 70 μm and 100 μm. A gold layer with a thin chromium adhesion promoter layer is deposited on the top surface of each of these cold arms to study its effect on the performance of the microgripper. The resultant ten microgripper design variants are fabricated using a commercially available MEMS fabrication technology known as a silicon-on-insulator multi-user MEMS process (SOIMUMPs)TM. This process results in an overhanging 25 μm thick single crystal silicon microgripper structure having a low aspect ratio (width:thickness) value compared to surface micromachined structures where structural thicknesses are of the order of 2 μm. Finite element analysis was used to numerically model the microgripper structures and coupled electrothermomechanical simulations were implemented in CoventorWare ®. The numerical simulations took into account the temperature dependency of the coefficient of thermal expansion, the thermal conductivity and the electrical conductivity properties in order to achieve more reliable results. The fabricated microgrippers were actuated under atmospheric pressure and the experimental results achieved through optical microscopy studies conformed with those predicted by the numerical models. The gap opening and the temperature rise at the cell gripping zone were also compared for the different microgripper structures in this work, with the aim of identifying an optimal microgripper design for the deformability characterisation of RBCs.peer-reviewe

The corrosion–wear response of Cr–Ti coatings

Titanium alloys display problematic behaviour in environments where wear and corrosion take place either simultaneously or sequentially. While various surface treatments have been proposed for the alleviation of corrosion and wear of Ti-6Al-4V, there is still scope for new and novel approaches. In the work reported here, three coating compositions: Cr–13 at.%Ti, Cr–33 at.%Ti and Cr–48 at.%Ti, were synthesised by unbalanced magnetron sputter deposition and applied to Ti-6Al-4V substrates. In the as deposited state the coatings were single phased, while subsequent vacuum heat treatment at 800 ◦C resulted in the formation of the Laves phase (-TiCr2). Coated Ti-6Al-4V test pieces were subjected to reciprocation sliding corrosion–wear tests in 0.9% NaCl solution at 37 ◦C. All the coated variants tested showed a reduction in corrosion–wear compared to uncoated Ti-6Al-4V. The most effective coatings were those that contained the Laves phase (-TiCr2). It is proposed that the passive film formed on the Laves phase had greater mechanical integrity than any others formed during corrosion–wear testing and this phenomenon was a key factor in providing the observed enhanced surface durability.peer-reviewe

The chemical wear (corrosion-wear) of novel Cr based hard coated 316L austenitic stainless steels in aqueous saline solution

Austenitic stainless steels are prone to galling and seizure in sliding contacts and display poor resistance to corrosion-wear. The purpose of this paper was to discover if the surface engineering of austenitic stainless steel via the application of Cr based hard coatings can alleviate this problem. Corrosion-wear tests using an aluminium oxide ball (pin) to slide against coated and uncoated AISI 316L in 0.9% NaCl solution under a normal force 1 N revealed degradation, under open circuit potential conditions, to be dominated by mechanically antagonized corrosion (Type I corrosion-wear) for all the test materials. A minor contribution to degradation was caused through superficial plastic deformation (micro-asperity shearing) of the contact surfaces took place but this was due to running-in and would have ceased after a short time once the asperities were flattened. It was accidentally discovered that pre-oxidation of the coated 316L steels, via vacuum heat treatment, resulted in an important and major improvement in corrosion-wear resistance.peer-reviewe

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 Hank’s 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.peer-reviewe

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.peer-reviewe

Character and chemical-wear response of high alloy austenitic stainless steel (Ortron 90) surface engineered with magnetron sputtered Cr–B–N ternary alloy coatings

Many transition metal borides, in particular CrB2, show high inherent hardness, corrosion resistance and chemical stability. Appropriate additions of nitrogen to the Cr–B material system could in principle allow the synthesis of multi-phase materials containing hard, corrosion resistant (Cr–B, Cr–N) and lubricious (h-BN) phases providing a combination of good corrosion–wear resistance and in-situ lubrication. This factor has stimulated interest in the development of Cr–B–(N) magnetron sputtered thin tribological coatings. In the present reported work, several Cr–B–(N) coatings were produced by reactively sputtering a CrB2 target in an argon atmosphere containing increasing amounts of nitrogen. They were mostly applied to Ortron 90 (Fe–20Cr–10Ni–2Mo–0.4N) austenitic stainless steel substrates. The coating structure changed from crystalline to largely amorphous with increasing nitrogen content, this was accompanied by a fall in nano-indentation hardness from 40 GPa at 0 at.% to 18 GPa at 21 at.%. N. The corrosion–wear performance of Cr–B–(N) coated Ortron 90 stainless steel when sliding against aluminium oxide in 0.9% saline solution, was worse than uncoated Ortron 90, due to their propensity to undergo chemical (dissolution) based wear. In these tests, no friction reduction was noted for the Cr–B–N coated materials. However, the CrB1.87 coated Ortron 90 displayed superior corrosion–wear resistance and a slightly lower friction coefficient.peer-reviewe

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 wash-out 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.peer-reviewe

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 min1). 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.peer-reviewe

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.peer-reviewe