Synthesis of low-wear and high strength nano-scale leucite glass-ceramics for dentistry

Abstract

Leucite glass-ceramics serve Restorative Dentistry needs for aesthetic replacement of lost or removed teeth or tooth substance. Their brittle fracture and the wear of the antagonistic enamel are however their main disadvantages. The aim of this thesis was to synthesize high strength, low-wear nano-sized leucite glass-ceramics for dental applications. Aluminosilicate glasses were experimentally synthesized using Appen models, characterised (DSC, CTE, XRD) and milled to powders using various milling routes. Leucite glass-ceramic materials were produced from the milled glass powders. Microstructural and physico-mechanical property control was pursued via compositional modifications, processing and heat treatment optimisation. All final materials where characterised using SEM and XRD. The experimental materials were tested using the biaxial flexural strength (BFS) test against commercial leucite glassceramic materials. A wear testing protocol was adapted on an MTS-Bionix 858 system. Human enamel pins were wear tested against disc samples of two experimental and one commercial material. Wear quantification was performed by superimposition of digitised test surfaces before and after wear testing by white light profilometry and the dedicated software using a novel protocol. All results were processed by applying appropriate statistics. Nanoscale tetragonal leucite median (Q1,Q3) crystal areas of up to 0.048 (0.030, 0.070) μm2 were achieved for the experimentally synthesized materials. Microstructural control was achieved with varying morphologies (sphere-shaped, fibres) and minimal or no microcracking in all glassceramics. The BFS results showed that the experimental groups tested were significantly (p < 0.05) stronger than the commercial materials. The mean (SD) BFS of the experimental materials ranged from 192.5 (44.0) to 255.0 (35.0) MPa compared to a range of values of 75.7 (6.8) - 165.5 (30.6) MPa for commercial leucite glassceramic products. The experimental glass-ceramic groups tested in wear produced significantly (p < 0.05) lower antagonistic enamel wear than the commercial material, quantified both as tooth volume and mean-height loss. Further development and optimisation of the high strength nanosized materials synthesized may therefore help to address problems with brittle fracture of dental all-ceramic restorations and support their use to achieve reduced rates of enamel loss.