Charles Q. Le

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.

Caries inhibition in vital teeth using 9.6-μm CO2-laser irradiation

The aim of this study was to test the hypothesis that in a short-term clinical pilot trial short-pulsed 9.6 μm CO(2)-laser irradiation significantly inhibits demineralization in vivo. Twenty-four subjects scheduled for extraction of bicuspids for orthodontic reasons (age 14.9 ± 2.2 years) were recruited. Orthodontic brackets were placed on bicuspids (Transbond XT, 3M). An area next to the bracket was irradiated with a CO(2)-laser (Pulse System Inc, Los Alamos, New Mexico), wavelength 9.6 μm, pulse duration 20 μs, pulse repetition rate 20 Hz, beam diameter 1100 μm, average fluence 4.1 ± 0.3J∕cm(2), 20 laser pulses per spot. An adjacent nonirradiated area served as control. Bicuspids were extracted after four and twelve weeks, respectively, for a quantitative assessment of demineralization by cross-sectional microhardness testing. For the 4-week arm the mean relative mineral loss ΔZ (vol% × μm) for the laser treated enamel was 402 ± 85 (mean ± SE), while the control showed significantly higher mineral loss (ΔZ 738 ± 131; P = 0.04, t-test). The difference was even larger after twelve weeks (laser arm ΔZ 135 ± 98; control 1067 ± 254; P = 0.002). The laser treatment produced 46% demineralization inhibition for the 4-week and a marked 87% inhibition for the 12-week arm. This study shows, for the first time in vivo, that the short-pulsed 9.6 μm CO(2)-laser irradiation successfully inhibits demineralization of tooth enamel in humans.

In-vivo occlusal caries prevention by pulsed CO2 -laser and fluoride varnish treatment--a clinical pilot study.

High caries prevalence in occlusal pits and fissures warrants novel prevention methods. An 86% reduction in dental enamel smooth surface demineralization in‐vivo following short‐pulsed 9.6 µm‐CO2‐laser irradiation was recently reported. The objective of this study was to conduct a blinded 12‐month‐pilot clinical trial of occlusal pit and fissure caries inhibition using the same CO2‐laser irradiation conditions.

An Automated Digital Microradiography System for Assessing Tooth Demineralization.

Digital Transverse microradiography (TMR) offers several advantages over film based methods including real-time image acquisition, excellent linearity with exposure, and it does not require expensive specialized film. The purpose of this work was to demonstrate that a high-resolution digital microradiography system can be used to measure the volume percent mineral loss for sound and demineralized enamel and dentin thin sections from 150-350-µm in thickness. A custom fabricated digital microradiography system with ~ 2-µm spatial resolution consisting of a digital x-ray imaging camera, a computerized high-speed motion control system and a high-intensity copper Kα x-ray source was used to determine the volume percent mineral content of sound and demineralized tooth sections. The volume percent mineral loss was compared with cross-sectional microhardness measurements on sound extracted human teeth. The correlation between microhardness and microradiography was excellent (Pr=0.99) for section thickness ranging from 59-319-µm (n=11). The attenuation was linear with varying exposure time from 1-10 seconds. Digital TMR is an effective and rapid method for the assessment of the mineral content of enamel and dentin thin sections.

Effects of CO2 laser irradiation on tooth enamel coated with biofilm

CO2 laser irradiation of tooth enamel can inhibit demineralization of tooth enamel, by changing enamel composition and resistance to acid attack. The aim of this work was to examine these effects of CO2 laser irradiation on enamel covered by biofilm.

Changes in Acid Resistance of Dentin Irradiated by a CW 10.6 μm CO2 Laser

The overall objective of our studies is to establish laser conditions that can be used clinically for the prevention or treatment of early carious lesions in dental enamel and dentin. Previous studies have shown that laser irradiation of dental enamel by specific carbon dioxide laser conditions can inhibit subsequent acid dissolution of the dental enamel surface. The purpose of this study was to determine whether irradiation of dentin by a continuous wave 10.6 µm carbon dioxide laser would inhibit acid dissolution. Blocks of human dentin roots (3x3 mm2) were irradiated at 10.6 µm wavelength with power settings of 0.5, 0.75, 1.0, 1.5 and 2.0 watts. A motion controller system was used to ensure uniform irradiation of the entire dentin surface. Surface acid dissolution profiles following irradiation were acquired for the irradiated groups and a non-irradiated control group. Dissolution rates for 0.5 and 0.75 watts were not statistically significant (p>0.05) from the control group, whereas irradiation at 1.0 watts and higher significantly (p<0.05) increased the acid dissolution rate. Considerable surface damage occurred at these higher powers. This study demonstrated that irradiation of dentin by a continuous wave 10.6 µm carbon dioxide but did not decrease the acid dissolution rate, and was detrimental at powers of 1.0 watts and above.

Lack of dentin acid resistance following 9.3 um CO2 laser irradiation

Previous studies have shown that laser irradiation of dental enamel by specific carbon dioxide laser conditions can inhibit subsequent acid dissolution of the dental enamel surface. The purpose of this study was to determine whether similar carbon dioxide laser conditions would have a protective effect on dentin. Blocks of human dentin roots (3x3 mm2) were irradiated at 9.3 µm wavelength with a 15-18 µs pulse duration laser and fluences of 0.50-1.50 J/cm2. A motion controller system was used to ensure uniform irradiation of the entire dentin surface. Surface acid dissolution profiles following irradiation were acquired for the five study groups, control group (Non-irradiated) and four laser-treated groups. Dissolution profiles of low fluence groups (0.50 and 0.75 J/cm2) exhibited similar profiles to the control group. Dissolution profiles of higher fluence groups (1.0 and 1.5 J/cm2) showed an increased dissolution rate over the control group, but these differences were not statistically significant (p>0.05). This study demonstrated that the application of carbon dioxide laser irradiation significantly alters the surface of dentin but did not decrease the acid dissolution rate.

The influence of pulse duration on the bond strength of dentin to composite after Er:YAG laser irradiation

Last year we demonstrated that thermal damage to dentin could be minimized by using Q-switched Er:YSGG laser pulses shorter than the thermal relaxation time of the deposited laser energy in conjunction with a layer of water added to the tissue surface before ablation. This resulted in significantly higher bond strengths of composite resin to laser treated dentin surfaces. Unfortunately, Q-switched erbium laser pulses cause strong acoustic effects and sound waves that are potentially irritating to the clinician and patient. The objective of this study was to investigate the influence of slightly longer Er:YAG laser pulses that avoid the undesirable acoustic effects on the bond strength of composite to laser prepared dentin surfaces. The surfaces of human dentin samples were irradiated by Er:YAG lasers operating with pulse durations of 0.5-μs, 20-μs, and 200-μs. A motion control system and a pressurized spray system incorporating a microprocessor controlled pulsed nozzle for water delivery, were used to ensure uniform treatment of the entire surface. Shear bond testing was used to evaluate the adhesive strength in order to assess the suitability of laser treated surfaces for bonding. High bond strengths with minimal peripheral thermal damage were achieved using 20-30μs Er:YAG laser pulses.

Laser all-ceramic crown removal-a laboratory proof-of-principle study-phase 1 material characteristics.

The removal of all‐ceramic crowns is a time consuming and destructive procedure in the dental office. The removal of all‐ceramic crowns using Er:YAG lasers has not been previously described in the scientific literature. The objective of this laboratory proof‐of‐principle study was to evaluate whether with regards to absorption and transmission characteristics of bonding cements and ceramics all‐ceramic crowns can be removed from natural teeth using an Erbium laser.

Caries inhibition with a CO2 9.3 μm laser: An in vitro study

The caries preventive effects of different laser wavelengths have been studied in the laboratory as well as in pilot clinical trials. The objective of this in vitro study was to evaluate whether irradiation with a new 9.3 μm microsecond short‐pulsed CO2‐laser could enhance enamel caries resistance with and without additional fluoride applications.