Biomedical subjects

Robert S Jones

Publications and source records attributed to Robert S Jones.

5 recordsLinked to original sources

PubMed2005

Early caries imaging and monitoring with near-infrared light.

Enamel is highly transparent in the near infrared (NIR); therefore, this region of the electromagnetic spectrum is suited ideally for the development of new optical diagnostic tools for the detection and imaging of early dental caries. This article discusses the NIR optical properties of sound and demineralized dental enamel and the potential use of polarization sensitive optical coherence tomography and NIR transillumination for the imaging of dental caries.

Dental Caries↗

PubMed2004

Peripheral thermal and mechanical damage to dentin with microsecond and sub-microsecond 9.6 microm, 2.79 microm, and 0.355 microm laser pulses.

BACKGROUND AND OBJECTIVES: It is desirable to minimize peripheral thermal damage during laser irradiation, since thermal damage to collagen and mineral compromises the bond strength to restorative materials in dentin and inhibits healing and osteointegration in bone. There were two primary objectives of this study. The first objective was to measure the degree of thermal damage peripheral to incisions in dentin produced with lasers resonant to the specific absorption bands of water, collagen, and hydroxyapatite with varying pulse duration using polarized-light microscopy (PLM). The second objective was to use synchrotron radiation infrared spectromicroscopy (SR-FTIR) to identify the specific chemical nature of the optical changes observed under PLM in the respective zones of thermal damage peripheral to the laser incisions. STUDY DESIGN/MATERIALS AND METHODS: Precise incisions were produced in 3 x 3 mm2 blocks of human dentin using CO2 (9.6 microm), Er:YSGG (2.79 microm), and Nd:YAG (355 nm) lasers with and without a computer controlled water-spray. Optical coherence tomography (OCT) was used to obtain optical cross-sections of each incision to determine the rate of ablation. The peripheral thermal damage zone around each incision was analyzed using PLM and SR-FTIR. RESULTS: Thermally induced chemical changes to both mineral and the collagen matrix were observed with SR-FTIR with a 10 microm spatial resolution and those changes were correlated with optical changes observed with PLM. Minimal (<10 microm) thermal damage was observed for pulse durations less than the thermal relaxation time (Tr) of the deposited laser energy, with and without applied water at 9.6 microm and with only applied water at 2.79 microm. For pulse durations greater than Tr, greater peripheral thermal damage was observed for both IR laser wavelengths with and without the water-spray. There was minimal thermal damage for 355 nm laser pulses less than Tr with and without applied water; however, extensive mechanical damage (cracks) was observed. CONCLUSIONS: High resolution SR-FTIR is well suited for characterization of the chemical changes that occur due to thermal damage peripheral to laser incisions in proteinaceous hard tissues. Sub-microsecond pulsed IR lasers resonant with water and mineral absorption bands ablate dentin efficiently with minimal thermal damage. Similar laser parameters are expected to apply to the ablation of alveolar bone.

Collagen↗

PubMedDate not supplied

Imaging artificial caries under composite sealants and restorations.

Polarization-sensitive optical coherence tomography (PS-OCT) is used to monitor the progression of simulated caries lesions on occlusal surfaces and image the lesions underneath composite sealants. The polarization-sensitive system, recording images in both the parallel and perpendicular axes, is useful for enhancing the image contrast of the artificial caries and minimizing the interference of the strong reflections at surface interfaces. Using the perpendicular-axis signal, the mean reflectivity increase from day 0 to day 14 is 5.1 dB (p<0.01, repeated-measures analysis of variation, Tukey-Kramer). For imaging lesions underneath the sealants, the mean reflectivity of the enamel underneath 250, 500, 750, and 1000 microm of composite is calculated for demineralized and control samples. The artificial lesions can be detected under 750 microm of visibly opaque sealant, with a 5.0-dB difference from the control samples (t-test, p<0.001). Tooth colored sealants allow deeper imaging depth. The artificial lesions could be detected under 1000 microm of sealant, with a 6.6-dB difference from the control samples (t-test, p<0.001). This study demonstrates that PS-OCT can be used to track lesion progression on occlusal surfaces nondestructively with or without sealants.

Artifacts↗

PubMedDate not supplied

Selective removal of composite sealants with near-ultraviolet laser pulses of nanosecond duration.

It is often necessary to replace pit and fissure sealants and composite restorations. This task is complicated by the necessity for complete removal of the remaining composite to enable suitable adhesion of new composite. Previous studies have shown that 355-nm laser pulses from a frequency-tripled Nd:YAG laser can selectively remove residual composite after orthodontic bracket removal on enamel surfaces. Our objective is to determine if such laser pulses are suitable for selective removal of composite pit and fissure sealants and restorations. Optical coherence tomography is used to acquire optical cross sections of the occlusal topography nondestructively before sealant application, after sealant application, and after sealant removal. Thermocouples are used to monitor the temperature in the pulp chamber during composite removal under clinically relevant ablation rates, i.e., 30 Hz and 30 mJ/pulse. At an irradiation intensity of 1.3 J/cm2, pit and fissure sealants are completely removed without visible damage to the underlying enamel. At intensities above 1.5 J/cm2, incident laser pulses remove the resin layer while at the same time preferentially etching the surface of the enamel. Temperature excursions in the pulp chamber of extracted teeth are limited to less than 5 degrees C if air-cooling is used during the rapid removal (1 to 2 min) of sealants, water-cooling is not necessary. Selective removal of composite restorative materials is possible without damage to the underlying sound tooth structure.

Animals↗

PubMedDate not supplied

Remineralization of in vitro dental caries assessed with polarization-sensitive optical coherence tomography.

Polarization-sensitive optical coherence tomography (PS-OCT) is potentially useful for imaging the nonsurgical remineralization of dental enamel. This study uses an all-fiber-based PS-OCT system operating at 1310 nm to image demineralized and fluoride-enhanced remineralized artificial lesions. PS-OCT images of lesions before and after remineralization are compared with the relative mineral loss DeltaZ (%vol x microm), obtained from high resolution digital microradiography (DM), and chemical composition changes by infrared spectroscopy. Severe early artificial caries show a significant increase in perpendicular-axis integrated reflectivity after remineralization. After sectioning the samples, DM demonstrates that the lesions remineralized with new mineral and the lesion surface zone show significant restoration of mineral volume. PS-OCT and DM both do not show a major change in lesion depth. For less severe artificial caries, the perpendicular-axis image resolves the scattering and depolarization of an outer growth layer after remineralization. This outer layer has a mineral volume close to that of sound enamel, and spectroscopic analysis indicates that the layer is a highly crystalline phase of apatite, without carbonate substitutions that increase the solubility of sound enamel. This study determines that PS-OCT can image the effects of fluoride-enhanced remineralization of mild and severe early artificial in vitro caries.

Bone Density↗