"Biomer" : a new type of dental material obtained through hybridization between calcium aluminates and glass ionomer cements

Abstract: About half of the restorations made on teeth today are restorations of old fillings, which explain the need for a better dental material. Recently Calcium aluminates as dental materials, CACs, entered the market and have shown good potentials. However their main disadvantage is slow development of mechanical properties. By combining CACs with Glass ionomer cements, GICs, that obtain most of their material properties during the first couple of hours after placement, into a hybrid, this problem could be solved. The main reason for believing in a successful hybridization is the similar ion release taking place during the hydration and hardening processes in both GICs and CACs. CACs dissolve into Ca and aluminate ions when mixed with water, an analogue to the dissolution of glass in GICs into calcium and aluminum ions when mixed with a Polyelectrolyte, most commonly Poly(acrylic acid), PAA. With both a cross linking of the PAA and a hydrate precipitation that contribute to the strength development, a rapid initial strength would be obtained that continues to improve with time. The aim of this thesis work was to explore the possibilities of manufacturing this hybrid, a "Biomer", to optimize candidate compositions and to evaluate the mechanical properties of the "Biomer"-candidates.The work was divided into two parts: a pre-study was performed in order to find suitable constituents for the Biomer and to determine whether the CAC and the GIC reactions were compatible, and part two was the actual manufacturing of the Biomer. During the pre-study it was concluded that the two systems could co-react and that the hybrid should besides CA also contain the commercial GIC ChemFlex, manufactured by Dentsply. As reactive agent ChemFlex liquid, major constituent PAA, and distilled water containing Li+ (accelerator) was used. Two candidates with different GIC-CA compositions were tested in terms of mechanical properties and the microstructure was imaged using scanning electron microscopy (SEM). The conclusion made from the results obtained was that hybridization between CAC- and GIC-systems was possible. The microstructure of the hybrid was dense and showed well distributed grains The short term mechanical properties were improved compared to the two systems by themselves, this due to the dual hardening process, with the cross linking of PAA giving initial strength and hydration supplying the material with long-term strength.