Sally J. Marshall

Research Interests

Biomaterials, structure-property relationships in calcified tissues, implnat materials

Research Summary

My research interests have always centered on understanding the relationship between structures, properties and mechanisms in materials, both artificial materials and naturally occurring biomaterials. My expertise is in x-ray scattering, particularly diffraction, and scanning microscopy. My current research efforts are mainly focused on dentin: the analysis of dentin as a material; how it behaves in clinically related situations; how it can be modified to enhance bonding to it; and how the junction between dentin and the stronger, more brittle enamel can be used as a model for bonding two dissimilar materials.

Much of current dental materials research involves attempts to bond materials to teeth. Enamel has a structure such that good mechanical retention is possible, but dentin does not, and most restorations have dentin as their substrate. We have developed ties with materials scientist at LLNL and LBNL who have access to cutting edge materials analytical instrumentation. Through this collaborative effort we are characterizing the structure, chemistry, and mechanical properties at the nanoscale. We began by analyzing normal coronal dentin and have moved on to the dentin most likely to be the substrate for restorative dental procedures, that is, dentin modified by disease (caries), mechanical damage, or age. We have an NIH program project grant to study dentin and, in addition to characterizing its structure and properties, we are developing a model that will be used to predict the behavior of dentin under varying conditions. In addition to traditional techniques, we use x-ray tomogrphic microscopy, a technique developed by a colleague at LLNL, to study the mineral density variations in dentin, as a function of intratooth position, disease staus, and treatment. The technique operates on the same principle as CT scanning, but uses at high energy source (SSRL) and gives a resolution of 1-2 micrometers. The technique has also been used to study other calcified tissues. We use atomic force microscopy to study the morphology and nanoscale mechanical properties of dentin in its various states. Both these techniques offer advantages over the more traditional materials analytical methods in that the samples can remain in water or other biologically relevant solution.

A second project, funded by an NIH R01 grant, is investigating the demineralization characteristics of dentin, along with the associated dimensional changes. Demineralization is important because it occurs during the restoration process, as well as in caries. Another project, one of the first to be funded in response to the NIH tissue engineering and biommetics initiative, is trying to understand the fracture characteristics of the dentin-enamel junction so that it can be used as a model for interfaces between dissimilar materials. We are using traditional fracture mechanics methods on a microscale and AFM based nanoscale methods.

Another area of research interest is again a collaborative effort, as a subcontract on an NIH grant to LBNL, working to develop an adherent bioactive coating for Ti and Ti alloy implants. One of the problems with commercially available calcium phosphate coated implants is that the adherence of the coating to the implant fails over time.

Selected Publications

GW Marshall, M Balooch, JH Kinney, SJ Marshall. Atomic force microscopy of conditioning agents on dentin. J Biomed Mater Res 1995, 29, 1381-1387.

SJ Marshall, M Balooch, T Breunig, JH Kinney, AP Tomsia, N Inai, LG Watanabe, IC Wu-Magiidi, GW Marshall. Human Dentin and the Dentin-Resin Adhesive Interface. Acta Mater 1998, 46, 2529-2539.