Imaging mechanical properties of dentin with Brillouin microscopy
Résumé
The structure of teeth can be altered by diet, age or diseases such as caries or sclerosis. It is very important to characterize the mechanical properties to predict and understand tooth decay, to design restorative dental procedure, and to investigate the tribological behavior of teeth. Yet, existing imaging techniques are not well suited to the investigation of the micromechanics of the tooth, in particular at tissue interfaces. Here we developed a microscope based on Brillouin light scattering (BLS) to probe mechanical changes in tooth tissues. BLS is an inelastic process that uses the scattering of light by acoustic waves in the GHz range. Our microscope thus reveals the mechanical properties at a micrometer scale without contact to the sample. BLS signals show significant differences between sound tissues and pathological lesions, and allow delineating precisely carious dentin. We also show maps of the sagittal and transversal planes of sound tubular dentin that reveal its anisotropic microstructure with a 1 \mum resolution. Our observations indicate that the collagen-based matrix of dentine is the main load-bearing structure, which can be thought of as a fiber-reinforced composite. In the vicinity of polymeric tooth-filling materials, we observed infiltration of the adhesive complex into the opened tubules of sound dentine. The ability to probe the quality of this interfacial layer could lead to innovative designs of biomaterials used for dental restorations in contemporary adhesive dentistry, and would have direct repercussions on the decision-making during clinical work.