Contact-Driven Crack Formation in Dental Ceramic Materials Wei Li 1,a , Qing Li 1,2,b , Jeffery Loughran 2,c , Michael Swain 3,4,d , Ionut Ichim 4,e , Naoki Fujisawa 3,f 1 School of Aerospace and Mechanical Engineering, University of Sydney, NSW 2006, Australia 2 School of Engineering, James Cook University, Townsville, QLD 4811, Australia 3 Faculty of Dentistry, University of Sydney, NSW 2006, Australia 4 Department of Oral Science, Faculty of Dentistry, University of Otago, New Zealand a wei@aeromech.usyd.edu.au, b Qing.Li@aeromech.usyd.edu.au, c jeffrey.loughran@jcu.edu.au, d mswain@mail.usyd.edu.au, e ionut.ichim@stonebow.otago.ac.nz, f n.fujisawa@usyd.edu.au Keywords: Dental ceramics, contact damage, finite and discrete element, fracture mechanics. Abstract. Natural human tooth consists of multiple layered quasi-brittle biomaterials, which make dental restorations experience a complex stress state under masticatory contact loading. As such, many restorations are prone to failure and a constant effort is made to improve the mechanical characteristics of the restorative materials. Clinical observations have shown that improved strengths and fracture toughness in ceramic materials do not necessarily lead to an anticipated higher functional longevity of the restoration. While substantial experimental investigations have been carried out to identify the contact induced fracture in such multi-layer material systems, numerical modelling of this event was largely unexplored. This paper presents a new numerical method to account for micro-damage driven fracture in various multi-layered biomaterial structures. In this study, a Rankine constitutive model is adopted and the crack initiation and propagation are automatically implemented in an explicit finite element (FE) framework. The effects of indenter radius, surface curvature and thickness of layered biomaterials on the cracking patterns are investigated. The results show good agreement with the experimental studies in literature. Introduction Promoted by its excellent aesthetics and biocompatibility, ceramics are routinely and extensively used for dental restoration like inlays, crowns and bridges. However, the use of ceramics as restorative materials is limited mainly by their reduced loading capability due to inherent low fracture toughness. This shortcoming becomes particularly obvious when the ceramics are used in the layers, above the remaining enamel and/or dentine, and hence significantly affecting the functional longevity of dental restoration. More importantly due to complex mechanical interaction of these different materials an improvement of ceramic material properties may not necessarily guarantee a better restorative performance if it mismatched to other host dental materials [1]. For this reason, a new attention has been re-attracted to this topic in recent years [1-6]. A considerable experimental work was conducted by using an arrangement of glass (enamel) layer that was bonded with transparent epoxy (cement) to polycarbonate (dentine) [1], which allows one to observe the damage and fracture development across several layers of materials. Indeed, visible experiments reveal some important stages of the indentation test. The effects of indenter radius [1], surface curvature [2], coated thickness [3] have been explored. However, it is difficult to fully understand the damage and fracture mechanism without knowing the correlation of stress state with cracking. In this context, the existing numerical studies [1, 3] have been restricted to mainly a linear framework of stress analysis. It is therefore warranted to examine how the contact damage is accumulated and developed into fracture over the indentation. The paper aims at demonstrating the capability of a nonlinear explicit method in simulating crack nucleation and propagation so as to provide some new understanding how the geometrical parameters affect fracture patterns. Key Engineering Materials Vols. 324-325 (2006) pp. 1257-1260 online at http://www.scientific.net © (2006) Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net . (ID: 129.78.208.4-29/09/06,10:54:26)