Bioceramic Dental Inserts Based on Calcium Phosphate Nano-particles

Dental inserts are perceived as a potential solution to reduce polymerization shrinkage and the associated stress in direct composite restorations. Inserts are designed to be placed inside the unpolymerized composite resin, thereby reducing the amount of resin in the restoration. Experimental inserts have been recently manufactured from hydroxyapatite (HAp) based nano-particles with an idea to combine their bioactive potential with aesthetic restorative materials. Controlled porous biphasic hydroxyapatite/tricalcium phosphate, monophasic dense hydroxyapatite and composite hydroxyapatite/zirconia dental inserts were processed and tested in the last few years for application as dentine substitutes. Obtained bioceramic inserts were of satisfied hardness and fracture toughness in the range of values for human dentine. These inserts have been shown in vitro to reduce polymerization shrinkage of insert-containing restorations and change shrinkage vectors of surrounding resin-based composite acting as a possible central stress reducer. When adhesively bonded to composites following a total-etch or self-etch protocol, controlled porous HAp-based inserts have shown certainly higher bond strengths than when bonded to glass-ionomer or self-adhesive resin cements. Optical properties (colour and translucency), considerably differ from tooth tissues, and may be masked with a 2 mm capping layer of a microhybrid or nanohybrid composite.