Improving durability of dental structures

How can dental restorations – such as fillings and crowns – be made to last longer? A new research group centered at Charité – Universitätsmedizin Berlin and Technische Universität (TU) Berlin plans to address this topic by utilizing approaches from both materials science and dentistry. The aim is to gain a better understanding of the composition and structure of the material-tissue interfaces and the stresses exerted on them. The interdisciplinary ‘InterDent’ research group is funded by the German Research Foundation (DFG). It will receive an initial funding of €2.1 million Euro over three years.

Restorative dentistry uses synthetic biomaterials such as ceramics, alloys and composites to restore damaged teeth. These materials must withstand heavy and repeated stresses in order to retain their ability to function for many years. Secure adhesion to the remaining healthy tooth tissue depends on the creation of ‘interface zones’, three-dimensional structures which consist of different connecting layers of varying composition, microstructure and properties. Interzones are never as resilient as their natural counterparts. This is one of the reasons why dental restorations often fail early and become detached. The new DFG research group – known as FOR2804 ‘InterDent’ – is a collaborative effort involving medical experts and materials scientists. Partners also include the Helmholtz-Zentrum Berlin (HZB), a research center for energy materials research, and the Max Planck Institute of Colloids and Interfaces (MPI-KG), which is located in Potsdam. The researchers hope that a better understanding of what causes tooth-related structural weaknesses will pave the way toward more resilient interzones.

“The research group is organized into four sub-projects and one overarching, coordinating project, which serves as the basis for close interaction between experts from materials science and dentistry in different institutes. The purpose of this interdisciplinary collaboration is to identify key parameters which can be used to predict the risk of degradation and which are capable of implementation into clinical practice,” explains the research group’s spokesperson, Dr. Paul Zaslansky, who is project leader at Charité’s Institute of Dental, Oral and Maxillary Medicine. He adds: “Thanks to the close proximity of ultra-modern materials laboratories and outstanding dental expertise, the Berlin-Brandenburg area offers an ideal growth environment for inspiring collaborations and innovative findings.”

The goal of the team is to create better dental materials by shedding light on the ways in which different materials interact with the surrounding tissues. One of the sub-projects aims at predicting the way in which dentine (the hard bony tissue that makes up the tooth´s core) changes over time, depending on the material used for the filling to which it is attached. Employing non-destructive, highly sensitive, high-resolution technology, the researchers will study the microstructure and chemical characteristics of dentine, tracking progressive changes over time as part of an aging process known as ‘sclerosis’. “We want to use this approach in order to develop a model of sclerotic dentine which will enable us to gain a better understanding of changes in its structure and composition,” says Dr. Ioanna Mantouvalou of the HZB, who leads the sub-project together with Dr. Zaslansky.

Another sub-project will focus on the structure and mechanical properties of a natural tooth interzone which is exposed to particularly severe stress: the junction between dentine and cementum surrounding it. While this structure is remarkably robust and resilient to cyclic loading, surprisingly little is known about its microstructure and mechanical properties. “We want to gain a better understanding of the structure and function of junction zones in farm mammals and human teeth, comparing younger and older teeth and teeth which have been subject to altered mechanical stresses. This will enable us to deduce general underlying principles which contribute to the long-term fatigue resistance of the dentino-cemental junction and which we will explore for bioinspired structures,” says Prof. Dr. Claudia Fleck, Head of Materials Engineering at TU Berlin and Deputy Spokesperson for the research group.

When oral bacteria colonize the surfaces of teeth and of the biomaterials used in restorative dentistry, they produce ‘biofilm’: a cohesive community of microorganisms which forms a slime layer. “We will explore and understand the formation and growth of biofilms by focusing on both composition and microstructure as well as the interzone areas where they interface with dental materials,” says Dr. Cécile Bidan, a group leader of the MPI-KG Biomaterials department and the third sub-project’s co-lead alongside Prof. Dr. Sebastian Paris, Director of Research at Charité’s Institute of Dental, Oral and Maxillary Medicine. “To do this, we will conduct quantitative and systematic analyses to determine the spatial and temporal development of specific bacteria in biofilms grown on different surfaces and in contact with dental restoratives.”

How the teeth may be better sealed against bacteria following root canal treatments forms the focus of the fourth InterDent sub-project. “By combining high-resolution imaging, digital image analysis and mechanical testing methods, we want to determine parameters which are critical to establishing a sealed interzone between biomaterials and the root. We have several new ideas how to lay the foundations for more durable root canal restorations,” explains PD Dr. Kerstin Bitter of the Department of Restorative and Preventive Dentistry, who shares the co-project lead role on this project with Prof. Fleck.

To overcome the existing deficiencies and limitations of dental biomaterials, it will be necessary to use available resources and samples in a coordinated manner, and raise a new generation of doctoral researchers integrating findings across all sub-projects. A key objective of the coordinating project is to create a culture of interdisciplinary collaboration – leading to a better understanding of dental interzones with the ultimate goal of improving dental treatment.

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