An evaluation of commercial and experimental resin-modified glass-ionomer cements

Glass-ionomer cement (GIG) has become widely accepted as a restorative material due to its bonding ability and sustained release of fluoride. The cement is, however, sensitive to moisture imbalance and lacks toughness. Recently, resin-modified glass-ionomer cements (RMGIC) have been introduced. These materials contain monomeric species, such as 2-hydroxyethyl methacrylate (HEMA) in addition to the components of the conventional glass-ionomer cements. Disadvantages of RMGICs include a relatively high contraction and exotherm on polymerisation. HEMA is known to be cytotoxic, leading to problems of biocompatibility, and polyHEMA swells on exposure to water, leading to dimensional instability of the cements. Addressing these problems is important in the development of the RMGICs. Using alternative monomers to replace or reduce the amount of HEMA used in the current RMGIC formulations would be appropriate. This study was divided into two parts. Initially certain properties such as water sorption, micro-hardness, flexural strength and polymerisation exotherm of commercially available RMGICs were evaluated. Long-term storage of RMGICs in aqueous solutions resulted in their high water uptakes and solubilities and large volumetric expansions. However, the surface hardness and strengths of the restorative grade RMGICs were not affected on storage in distilled water. When the materials were immersed in artificial saliva, significantly higher water uptake were obtained; the equilibrium water uptake were not reached after 20 months. As a consequence, plastic behaviour and reduced surface hardness were observed. The RMGICs also produced high exotherm during polymerisation. The second part of the study investigated the use of an experimental resin as an alternative to HEMA. The experimental resin has the advantage of low toxicity to the pulp and relatively low polymerisation shrinkage. This study compared the polymerisations of the resin and HEMA, and of mixtures of these two monomers with other dimethacrylates such as bis-GMA and UDMA. The experimental cements formulated with these resins were evaluated using similar tests to those performed in the first part and their properties were compared with those of the commercial materials. Strength and hardness of the experimental cements were higher than those using HEMA. These two parameters of all the cements increased over a period up to 30 days. Polymerisation exotherm of the cements formulated using the experimental resin combinations were similar but water sorption, solubility and volumetric expansion of these cements was lower than those of cements formulated using HEMA. This implies a higher degree of conversion of the experimental resins when compared to the HEMA model system

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

Flexural strength of dental composite restoratives: Comparison of biaxial and three-point bending test

10.1002/jbm.b.30103Journal of Biomedical Materials Research - Part B Applied Biomaterials712278-283JBMR