Structure and fatigue-behaviour of an endurable, highly loaded natural interzone: the cemento-dentine junction

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Mammal teeth are suspended within the jaw via the periodontal ligament and the dental cementum which covers dentine nearly all over the root. Dentine and cementum, two mineralised bony tissues of similar stiffness are connected by a thin, more compliant interzone, the cemento-dentine junction (CDJ). Over the human lifespan, millions of chewing cycles are transferred from dentine via the CDJ to the periodontal apparatus. Interestingly, the CDJ endures these millions of cyclic stresses, with no clinically reported cases of failure, even though it has no capacity of cellular re-modelling and thus repair. Maybe this clinical inconspicuousness is the reason why the CDJ has only sparsely been investigated, so far.Within the scope of the research group InterDent, we aim in project 2 at better understanding the relationship between microstructure and fatigue properties of this endurable interzone between dentine and cementum. We want to elucidate the design-principles leading to its long-lasting fatigue resistance. Further, we wish to understand whether the regionally different loading conditions are reflected in micro- and nano-structural local variations of the CDJ and whether temporal load changes lead to adaptive changes in the CDJ structure and characteristics.To achieve this, we plan i) to characterise the micro- and nanostructure as well as the micro- and nano-mechanical properties of the CDJ, and the influence of species, tooth type, sex and location along the root surface; ii) to analyse potential morpho-mechanical adaptations to different loading conditions, originating from tooth pathologies or age-related changes of the tooth; iii) to investigate the micro- and nano-fatigue properties of the CDJ in relation to locally varying in vivo loading conditions along the root surface.Thus, we will gain a better understanding of the structure/property-relationship and the function of the CDJ, which will allow us to derive general material science principles that constitute a durable and fatigue-resistant interzone between two stiffer materials. Ultimately, this way, the CDJ will serve as a role-model for bio-inspired design of such interzones, in dentistry and beyond.