Physico-mechanical characterisation of polymeric CAD/CAM materials for aesthetic and prosthetic applications

Abstract

Polymer-based CAD/CAM blocks have been suggested as a viable metal-free alternative to meet the needs of aesthetics, biomimetics, and minimally invasive dentistry. Therefore, this research characterised various optical, surface, and mechanical aspects of new reinforced polymeric CAD/CAM materials, subdivided based on their clinical applications into aesthetic (Part I) and prosthetic (Part II) sections. The blocks investigated for Part I were three resin composites, one polymer-infiltrated ceramic network (PICN), and one feldspathic ceramic; for Part II, three high-performance polymer (HPP) composites, which included two fibre-reinforced composites (TRINIA, TR, and CarboCAD 3D Dream Frame, CC), and one ceramic-filled polyetherether ketone (DentoKeep, PK). For Part I, firstly, thickness-dependent apparent radiopacity and material composition were investigated for five aesthetic blocks versus that of direct resin-based substrates. PICN appeared relatively radiolucent even at 2.5 mm thickness, posing challenges for its identification from tooth structure and other substrate materials, such as luting cements. Secondly, material- and thickness-dependent translucency, blue-light transmittance, and its consequences on polymerising two IvocerinTM-containing luting cements (light-cured, LC, and dual-cured, DC) were investigated after 1 h of irradiation through four CAD/CAM substrates. PICN showed the least favourable optical features, resulting in significantly lower hardness of the underlying DC cements. Overall, LC cement exhibited greater early hardness compared to DC, irrespective of the substrate thickness. For Part II, the surface and mechanical stability of HPP composites were examined after 1 and 7 days of ageing in three food-simulating solvents (water, 70% ethanol/water, and MEK). Significant material variations in terms of microstructural composition have reflected on the properties investigated, such as roughness, hardness, flexural strength, and fracture toughness. In comparison to TR and CC, PK demonstrated relative stability after accelerated aging. CC and TR were sufficiently strong at sections as thin as 1 mm. However, their increased deterioration in FSLs requires full protection with a veneer material. This research concludes that although initial results were promising, more material enhancement and a review of the currently proposed clinical applications are necessary.