The effect of veneering and heat treatment on the flexural strength of Empress® 2 ceramics

Cattell, M.J.; Palumbo, R.P.; Knowles, J.C.; Clarke, R.L.; Samarawickrama, D.Y.D.

« Previous Next »Journal of Dentistry
Volume 30, Issue 4 , Pages 161-169, May 2002

The effect of veneering and heat treatment on the flexural strength of Empress^® 2 ceramics

M.J. Cattell
- Department of Conservative Dentistry, St Bartholomew's and The Royal London School of Medicine and Dentistry, QM, Turner Street, London E1 2AD, UK
- Corresponding author. Tel.: +44-207-777000x2160; fax: +44-207-3777375
R.P. Palumbo
- Department of Conservative Dentistry, St Bartholomew's and The Royal London School of Medicine and Dentistry, QM, Turner Street, London E1 2AD, UK
J.C. Knowles
- Department of Biomaterials, Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WC1 8LD, UK
R.L. Clarke
- Department of Conservative Dentistry, St Bartholomew's and The Royal London School of Medicine and Dentistry, QM, Turner Street, London E1 2AD, UK
D.Y.D. Samarawickrama
- Department of Conservative Dentistry, St Bartholomew's and The Royal London School of Medicine and Dentistry, QM, Turner Street, London E1 2AD, UK

Received 30 November 2001; received in revised form 24 July 2002; accepted 26 July 2002.

Abstract

Objectives. The aims of the study were to test and compare the biaxial flexural strength and reliability of Empress 2 ceramics after heat treatment and the addition of the veneering material and to characterise their microstructures.

Methods. Forty disc specimens (2×14mm) and forty disc specimens (1×14mm) were produced by heat pressing in the EP 500 press furnace. Group 1 (2×14mm Empress 2 core) was as heat pressed and group 2 (2×14mm Empress 2 core) was subjected to the recommended firing cycles. Groups 3 and 4 (1×14mm Empress 2 core) were veneered with the dentine material and heat-treated as per group 2. Groups 1, 2 and 3 were lapped to 800 grit silicon carbide paper on the compressive surface only and group 4 on both the compressive and tensile test surfaces. Twenty disc specimens per group were tested using the biaxial flexure test at a crosshead speed of 0.15mm/min. Specimens were characterised using X-ray diffraction (XRD) and secondary electron imaging (SEM).

Results. Mean biaxial flexural strengths (MPa±SD) were group 1: 265.5±25.7; group 2: 251.3±30.2; group 3: 258.6±21.4 and group 4: 308.6±37.7. There was no statistical difference between groups 1, 2 and 3 (p>0.05), but differences for group 4 (p<0.05). XRD and SEM revealed lithium disilicate and lithium orthophosphate in the Empress 2 core material and an amorphous glass and some evidence of a crystalline phase in the dentine material.

Conclusions. Veneering or heat treatment of Empress 2 ceramics did not significantly affect the mean biaxial flexural strength (p>0.05) or reliability. Surface modification of the Empress 2 core material increased the mean biaxial flexural strength (p<0.05).

Keywords: Ceramics, Flexural strength, Microscopy, X-ray diffraction