Thomas M. Breunig

Imaging caries lesions and lesion progression with polarization sensitive optical coherence tomography

New diagnostic tools are needed for the characterization of dental caries in the early stages of development. If carious lesions are detected early enough, they can be arrested without the need for surgical intervention. The objective of this study was to demonstrate that polarization sensitive optical coherence tomography (PS-OCT) can be used for the imaging of early caries lesions and for the monitoring of lesion progression over time. High-resolution polarization resolved images were acquired of natural caries lesions and simulated caries lesions of varying severity created over time periods of 1 to 14 days. Linearly polarized light was incident on the tooth samples and the reflected intensity in both orthogonal polarizations was measured. PS-OCT was invaluable for removing the confounding influence of surface reflections and native birefringence necessary for the enhanced resolution of the surface structure of caries lesions. This study demonstrated that PS-OCT is well suited for the imaging of interproximal and occlusal caries, early root caries, and for imaging decay under composite fillings. Longitudinal measurements of the reflected light intensity in the orthogonal polarization state from the area of simulated caries lesions linearly correlated with the square root of time of demineralization indicating that PS-OCT is well suited for monitoring changes in enamel mineralization over time.

Direct observation of crack opening as a function of applied load in the interior of a notched tensile sample of AlLi 2090

Abstract Results of in situ high resolution X-ray computed tomography are reported for a notched tensile sample of AlLi 2090 T841. The fatigue crack within the interior of the sample is imaged with 6 μm voxels as a function of applied load, and the crack face morphology is found to be similar to that observed in compact tension samples of this alloy. The loads and approximate stress intensities at which the tomography data were obtained were 82, 50, 25 and 5 kg and 7.1, 4.3, 2.2 and 0.4 MPa√m, respectively. Crack openings measured during unloading as a function of position show that physical closure at portions of the crack tip and at positions behind the crack tip precedes (during unloading) the bend in the samples load-displacement curve. The three-dimensional pattern of crack opening shows substantial mixed mode I–III contact on the faces of asperities behind the crack tip, even at the maximum load of the fatigue cycle. Mixed mode I–II contact is also observed at loads above the bend in the load-displacement curve. The fraction of voxels open remains nearly constant for the loads immediately above and below the nominal closure load, as determined from the load-displacement curve, of 41 kg; and this suggests that these mixed mode I–III surfaces begin to carry significant load at the point where the load-displacement curve starts to deflect, and is the source of the apparent stiffening of the sample at loads below the nominal closure load.

Human dentin and the dentin-resin adhesive interface

Dentin, the inner hard tissue of teeth, is a complex hydrated composite and forms the substrate for much of restorative dentistry. Current efforts to improve restorative and preventive dentistry involve the development of effective bonds to this tissue. Modern bonding techniques involve etching the dentin to remove the mineral portion, leaving a collagen network that can be infiltrated with a monomer and polymerized in place to form a mechanical bond. The objective of this study was to investigate the nature of the interfacial zone, called the resin-dentin interdiffusion zone, using scanning electron microscopy for characterization and thickness measurements, X-ray tomographic microscopy for fracture characteristics and atomic force microscopy for the local modulus and hardness variations.

Infrared spectroscopy of laser-irradiated dental hard tissues using the Advanced Light Source

FTIR spectroscopy used in the specular reflectance mode is well suited for resolving thermally induced changes in dental hard tissue as a result of laser irradiation. High spatial resolution is achievable with a high brightness synchrotron radiation source such as the ALS at Lawrence Berkeley National Laboratory. IR spectra of modified enamel were acquired after laser ablation using several laser wavelengths from the UV to the mid-IR. Specific areas of laser ablation craters were probed non-destructively with 10-micrometers spatial resolution. The chemical composition of the crater walls deviates markedly from that of hydroxyapatite after Er:YAG and CO2 laser irradiation without added water. New mineral phases were resolved that have not been previously observed using conventional IR spectroscopy.

Nondestructive Imaging of Materials Microstructures Using X-Ray Tomographic Microscopy

A technique for nondestructively imaging microstructures of materials in situ, especially a technique capable of delineating the time evolution of chemical changes or damage, will greatly benefit studies of materials processing and failure. X-ray tomographic microscopy (XTM) is a high resolution, three-dimensional inspection method which is capable of imaging composite materials microstructures with a resolution of a few micrometers. Because XTM is nondestructive, it will be possible to examine materials under load or during processing, and obtain three-dimensional images of fiber positions, microcracks, and pores. This will allow direct imaging of microstructural evolution, and will provide time-dependent data for comparison to fracture mechanics and processing models. 23 refs., 8 figs.

Imaging caries lesions and lesion progression with polarization-sensitive optical coherence tomography

New diagnostic tools are needed for the characterization of dental caries in the early stages of development. If carious lesions are detected early enough, they can be arrested without the need for surgical intervention. The objective of this study was to demonstrate that polarization sensitive optical coherence tomography (PS-OCT) can be used for the imaging of early caries lesions and for the monitoring of lesion progression over time. High-resolution polarization resolved images were acquired of natural caries lesions and simulated caries lesions of varying severity created over time periods of 1 to 14 days. Linearly polarized light was incident on the tooth samples and the reflected intensity in both orthogonal polarizations was measured. PS-OCT was invaluable for removing the confounding influence of surface reflections and native birefringence and for resolving the surface structure of caries lesions. This study demonstrated that PS-OCT is well suited for the resolution of interproximal and occlusal caries, early root caries, and secondary caries around composite fillings. Longitudinal measurements of lesion progression established a strong correlation (p<0.001) between the reflected light from the lesion area and the square root of time indicating that PS-OCT is well suited for monitoring changes in enamel mineralization over time.