The purpose of this study was to determine whether a nanosecond-pulsed, frequency-doubled Nd:YAG ... more The purpose of this study was to determine whether a nanosecond-pulsed, frequency-doubled Nd:YAG laser emitting at 532 nm can be used as an alternative to mechanical methods of root canal treatment or as an adjunct to conventional endodontic preparation. Laser parameters whose thermal effects did not exceed safety thresholds for adjacent periodontal tissues were selected in a preliminary study. In 27 extracted human teeth, root canals were irradiated for 30 to 60 s at fluences of 2 to 2.2 J/cm2, and 10 Hz. Samples were observed using SEM. Laser irradiation could achieve smear layer removal after minimal manual preparation. However, results were inhomogeneous, and at higher energy densities thermal damage was observed, especially in the fully manually prepared samples. Nanosecond-pulsed irradiation at 532 nm can achieve complete smear layer removal. However, mechanisms must be developed to monitor laser effects and avoid potential damage to collateral structures.
The interaction of a short pulse XeCl excimer laser radiation with human dentin was investigated.... more The interaction of a short pulse XeCl excimer laser radiation with human dentin was investigated. The dependence of surface temperatures and temperature gradients into the treated teeth on laser parameters such as fluence (0.5J/cm2-7J/cm2), pulse repetition rate (1Hz-35Hz), and spot size (0.004cm2-0.12cm2) was studied. Additionally, the effect of fluence and pulse repetition rate on dentin microstructure was studied using scanning electron microscopy (SEM). It is demonstrated that this "cold ablation" excimer laser can result in significant thermal modification in the dentin surfaces. Changes include the formation of melted dentin grains, which uniformly cover the surface and the exposed dentin tubules. Maximum temperatures of the ablated surfaces, however, remained relatively low at most laser parameters used. Also, the immediate neighborhood of the root canal was essentially undisturbed at most laser parameters. These observations suggest that with the appropriate choice of parameters XeCl lasers can be effective in producing surface structures that may prove useful in enhancing bond strength or other applications in dentistry, without exposing tooth pulp to significant temperature elevation.
To understand the pathophysiology of late Ahmed Glaucoma Valve failures and devise strategies to ... more To understand the pathophysiology of late Ahmed Glaucoma Valve failures and devise strategies to minimize this problem. One hundred sixty eyes that had undergone Ahmed Glaucoma Valve implants by one surgeon were retrospectively reviewed. Six eyes with late (greater than 3 months) Ahmed Glaucoma Valve occlusion requiring operative intervention were identified. Two of these eyes underwent initial successful transcameral drainage tube irrigation and four initially required Ahmed Glaucoma Valve exchange. Intraoperative images, postoperative histologic analysis, and Ahmed Glaucoma Valve handling experiments were performed. Two eyes with late occlusion (33%; 1.25% of total implants) were initially successfully treated with irrigation alone. A gap between the valve cover and valve body junction allowed fibrovascular ingrowth and produced valve failure ultimately in five of six eyes (83%; 3.1% of total implants). This gap could be produced by grasping the device along the center line, indenting the valve cover, and damaging the plastic rivets attaching the valve cover to the valve body. Handling the Ahmed Glaucoma Valve outside this "no touch zone" eliminated this problem. Leaflet adhesion has a low incidence and may be treated by transcameral drainage tube irrigation. Late onset distal occlusion is best treated by Ahmed Glaucoma Valve exchange with respect for the "no touch zone." Respecting the "no touch zone over the valve mechanism should avoid creation of gaps between the valve cover and valve body junction, which allow secondary fibrovascular ingrowth.
The chick chorioallantoic membrane (CAM) model allows direct observation of vascularization acute... more The chick chorioallantoic membrane (CAM) model allows direct observation of vascularization acutely in explanted or cultured tissues in an immunologically isolated environment. In vivo, angioinvasion of the tissue matrix does not occur in viable cartilage tissue, whereas denatured or nonviable grafts are readily vascularized and/or resorbed. To determine, using the CAM model, whether angioinvasion of thermally altered cartilage explants occurs acutely. Porcine septal cartilage specimens were removed from freshly killed animals and divided into 3 groups (n = 10): an untreated control group, a group in which cartilage was boiled in isotonic sodium chloride solution (normal saline) for 1 hour, and a laser-irradiated group (Nd:YAG, lambda = 1.32 microm, 30.8 W/cm2, irradiation time = 10 seconds). Tissue specimens were then washed in antibiotic solutions, cut into small cubes (approximately 1.5 mm3), placed on the surface of 30 CAMs (7 days after fertilization), and allowed to incubate f...
To determine the human corneal threshold ablation energy density for the 193-nm ArF excimer laser... more To determine the human corneal threshold ablation energy density for the 193-nm ArF excimer laser, approximating clinical conditions. The VISX Star (Santa Clara, CA) 193-nm argon fluoride excimer laser was used to ablate the cornea in human eye bank eyes under clinical conditions. Corneas were exposed to energy densities of 10, 20, 30, 35, 40, 45, and 140 to 160 mJ/cm2. Corneas were fixed for light and transmission electron microscopy immediately after laser exposure. Different ablation thresholds for various corneal structural elements were observed. The ablation threshold for the collagen in the corneal stroma was determined to be 30 mJ/cm2. Keratocytes had ablation thresholds of 40 mJ/cm2. These different ablation thresholds accounted for the production of stromal peaks and valleys, with the keratocytes atop the peaks. Different corneal structural elements have different ablation threshold energy densities.
Thermal and microstructural events resulting from KTP laser use during root canal preparation wer... more Thermal and microstructural events resulting from KTP laser use during root canal preparation were investigated in 30 extracted single-rooted human teeth. In the first section of this study, thermal events occurring on the root surfaces of 18 teeth during and after exposure of the root canal were measured using thermography. A variety of parameters were used to determine settings that would be effective without causing thermal damage to the periodontal ligament. In the second section of the study, root canals of 12 teeth exposed to KTP laser irradiation at parameters derived from section 1 were evaluated using Scanning electron microscopy. KTP laser application at a power setting of 3 W, an exposure time of 2 s, and a frequency of 5 Hz, applied five times, removed smear layer and debris from the root canal surface at temperatures below the thermal injury threshold for periodontal tissue.
Irradiation of the kinetochore region of PtK2 chromosomes by laser light of 532 nm was used to st... more Irradiation of the kinetochore region of PtK2 chromosomes by laser light of 532 nm was used to study the function of the kinetochore region in chromosome movement and to create an artificial micronuclei in cells. When the sister kinetochores of a chromosome were irradiated at prometaphase, the affected chromosome detached from the spindle and exhibited no further directed movements for the duration of mitosis. The chromatids of the chromosome remained attached to one another until anaphase, at which point they separated. No poleward movement of the chromatids was observed, and at telophase they passively moved to one of the daughter cells and were enclosed in a micronucleus. The daughter cell containing the micronucleus was then isolated by micromanipulation and followed through subsequent mitoses. At the next mitosis, two chromosomes, each with two chromatids, condensed in the micronucleus. These chromosomes did not attach to the spindle and showed chromatid separation, but no pole...
Initial hyperplasia is major cause of restenosis after vascular interventions for arterial occlus... more Initial hyperplasia is major cause of restenosis after vascular interventions for arterial occlusive disease. We reported that a fluorescent probe, Texas Red, conjugated to the scavenger-receptor ligand, maleylated bovine serum albumin accumulated almost exclusively in the injured, hyperplastic sites. The purpose of this study is to test the feasibility of enhanced drug delivery to the hyperplastic lesion by targeting the
ABSTRACT Photoacoustic microscopy (PAM) utilizes short laser pulses to deposit energy into light ... more ABSTRACT Photoacoustic microscopy (PAM) utilizes short laser pulses to deposit energy into light absorbers and sensitively detects the ultrasonic waves the absorbers generate in response. PAM directly renders a three-dimensional spatial distribution of sub-surface optical absorbers. Unlike other optical imaging technologies, PAM features label-free optical absorption contrast and excellent imaging depths. Standard dental imaging instruments are limited to X-ray and CCD cameras. Subsurface optical dental imaging is difficult due to the highly-scattering enamel and dentin tissue. Thus, very few imaging methods can detect dental decay or diagnose dental pulp, which is the innermost part of the tooth, containing the nerves, blood vessels, and other cells. Here, we conducted a feasibility study on imaging dental decay and dental pulp with PAM. Our results showed that PAM is sensitive to the color change associated with dental decay. Although the relative PA signal distribution may be affected by surface contours and subsurface reflections from deeper dental tissue, monitoring changes in the PA signals (at the same site) over time is necessary to identify the progress of dental decay. Our results also showed that deep-imaging, near-infrared (NIR) PAM can sensitively image blood in the dental pulp of an in vitro tooth. In conclusion, PAM is a promising tool for imaging both dental decay and dental pulp.
The purpose of this study was to evaluate the effects of the ArF-193 nm excimer laser on the dent... more The purpose of this study was to evaluate the effects of the ArF-193 nm excimer laser on the dentinal tubules of extracted human teeth under a scanning electron microscope. Fifteen 3 mm thick slices were cut with an electric saw at the cementoenamel junction from 15 extracted human teeth. A diamond bur was used to remove the cementum layer and expose the dentinal tubules. Each slice was scored by a permanent marker into four equal quadrants. The ArF excimer laser was applied for 5 seconds on three of the quadrants with fluences that ranged from 0.2 J/cm2 to 15 J/cm2 and pulse repetition of 25 Hz. The untouched quadrant served as a control. The specimens were mounted on stubs, sputter coated by gold, and examined by a scanning electron microscope. The effects of the ArF excimer laser irradiation varied. Laser fluences of 0.2, 0.5, and 1.0 J/cm2 had no effect. Although fluence of 15 J/cm2 caused significant removal of peritubular dentin, melting and resolidification of the dentinal smear layer was also observed under the scanning electron microscope with a laser fluence of 5 J/cm2.
Root hypersensitivity occurs as a result of exposed dentinal tubules. Various methods and materia... more Root hypersensitivity occurs as a result of exposed dentinal tubules. Various methods and materials have been tried in an attempt to occlude these tubules. The purpose of this investigation was to study by scanning electron microscope the effects of XeCl excimer laser on exposed dentinal tubules of human extracted teeth. Fifteen 3-mm-thick slices were cut at the cementoenamel junction from 15 extracted human teeth by an electric saw. By using a diamond bur to remove the cementum layer the dentinal tubules were exposed. Each slice was scored by a permanent marker into four equal quadrants. Three of the quadrants were lased for 4 s by XeCl excimer laser with fluences ranging from 0.5 to 7.0 J/cm2 and pulse repetition of 25 Hz. The unlased quadrant served as control. The specimens were mounted on a stub, sputter coated by gold, and examined by scanning electron microscope. Nonlased surfaces showed numerous exposed dentinal tubules. In contrast, all specimens lased at fluences of up to 1 J/cm2 showed the presence of melted dentin which closed the dentinal tubules. At fluences of 4 J/cm2 and higher, rupture of molten materials and exposure of dentinal tubules were noted. The results indicate the application of XeCl excimer laser at specific fluences can cause melting of dentin and closure of exposed dentinal tubules.
The early approximal caries lesion in enamel is observed clinically as a white spot and is diffic... more The early approximal caries lesion in enamel is observed clinically as a white spot and is difficult to detect and/or monitor with current methods available to dentists. New methods with high sensitivity and specificity are required to enable improved early dental caries diagnosis. Using unpolarized Raman spectroscopy to examine unsectioned teeth, peak intensity changes in the phosphate (PO43-) vibrations (nu2, nu3 and nu4) were observed between spectra of sound and carious enamel. However, there is little change in the nu1 vibration with this approach. In contrast, when tooth sections were examined by unpolarized Raman spectroscopy, marked changes in the nu1 peak at 959 cm-1 were noted between healthy and carious enamel. These differences suggest that sampling orientation play a role in understanding the spectral changes. Using polarized Raman spectroscopy to examine unsectioned samples, cross polarized measurements from sound enamel exhibited significant reduction of the nu1 peak compared with parallel polarized measurements. A similar reduction was observed with carious enamel, however, the reduction was not as prominent. By calculating the depolarization ratio of the area under the nu1 peak, sound enamel can be clearly distinguished from demineralized regions. The spectral changes observed are attributed to changes in the structure and/or orientation of the apatite crystals as a result of the acid demineralization process.
Journal of Clinical Laser Medicine <html_ent glyph="@amp;" ascii="&"/> Surgery, 2000
The purpose of this study was to investigate the effects of dentin ablation using a carbon dioxid... more The purpose of this study was to investigate the effects of dentin ablation using a carbon dioxide (CO2) laser emitted at 9.3 microm by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). There have been no reports on effects of CO2 laser irradiation emitted at 9.3 microm on dentin by SEM and CLSM. Thirty extracted human teeth showing no clinical signs of caries were used. All teeth were horizontally sectioned to approximately 200 microm thickness and sections were irradiated using a 9.3 microm CO2 laser at different parameters as follows: 26 mJ [energy density (ED) 53.0 J/cm2] and 30 mJ (ED 61.1 J/cm2). After laser irradiation, samples were treated with sodium hypochlorite, stained using rhodamine-123, and observed with CLSM followed by SEM procedures. No craters or cracks were observed, but many small molten and rehardened particles were documented on the sample surface using SEM. Some small cracks were seen in the subsurface layer, and some patent dentinal tubules were detected using CLSM. These results suggest that laser irradiation at these parameters affected the sample surface only (less than 20 microm) and would be less harmful to thermal damage of dental pulp for dentin ablation.
To characterize tissue destruction after CO(2) laser-ablation of the vocal cords with the use of ... more To characterize tissue destruction after CO(2) laser-ablation of the vocal cords with the use of optical coherence tomography (OCT). OCT was used to image fresh porcine vocal cords after laser ablation. OCT and histology estimates of the ablation crater dimensions and the depth of thermal injury were obtained. The vocal cord substructures up to 2.29 mm in depth at 10 microm resolution, and the thermal disruption after laser ablation were identified by OCT. OCT and histology estimates of the lesion dimensions showed no significant differences. Crater depth is directly proportional to laser power, whereas crater width and the zone of thermal injury appear to be unrelated to laser power. OCT may be used to accurately characterize the native states and the laser-induced thermal injury of laryngeal mucosa, within the inherent limitation in its depth of penetration. OCT may be a useful diagnostic and monitoring tool in an otolaryngology practice.
The purpose of this study was to determine whether a nanosecond-pulsed, frequency-doubled Nd:YAG ... more The purpose of this study was to determine whether a nanosecond-pulsed, frequency-doubled Nd:YAG laser emitting at 532 nm can be used as an alternative to mechanical methods of root canal treatment or as an adjunct to conventional endodontic preparation. Laser parameters whose thermal effects did not exceed safety thresholds for adjacent periodontal tissues were selected in a preliminary study. In 27 extracted human teeth, root canals were irradiated for 30 to 60 s at fluences of 2 to 2.2 J/cm2, and 10 Hz. Samples were observed using SEM. Laser irradiation could achieve smear layer removal after minimal manual preparation. However, results were inhomogeneous, and at higher energy densities thermal damage was observed, especially in the fully manually prepared samples. Nanosecond-pulsed irradiation at 532 nm can achieve complete smear layer removal. However, mechanisms must be developed to monitor laser effects and avoid potential damage to collateral structures.
The interaction of a short pulse XeCl excimer laser radiation with human dentin was investigated.... more The interaction of a short pulse XeCl excimer laser radiation with human dentin was investigated. The dependence of surface temperatures and temperature gradients into the treated teeth on laser parameters such as fluence (0.5J/cm2-7J/cm2), pulse repetition rate (1Hz-35Hz), and spot size (0.004cm2-0.12cm2) was studied. Additionally, the effect of fluence and pulse repetition rate on dentin microstructure was studied using scanning electron microscopy (SEM). It is demonstrated that this &quot;cold ablation&quot; excimer laser can result in significant thermal modification in the dentin surfaces. Changes include the formation of melted dentin grains, which uniformly cover the surface and the exposed dentin tubules. Maximum temperatures of the ablated surfaces, however, remained relatively low at most laser parameters used. Also, the immediate neighborhood of the root canal was essentially undisturbed at most laser parameters. These observations suggest that with the appropriate choice of parameters XeCl lasers can be effective in producing surface structures that may prove useful in enhancing bond strength or other applications in dentistry, without exposing tooth pulp to significant temperature elevation.
To understand the pathophysiology of late Ahmed Glaucoma Valve failures and devise strategies to ... more To understand the pathophysiology of late Ahmed Glaucoma Valve failures and devise strategies to minimize this problem. One hundred sixty eyes that had undergone Ahmed Glaucoma Valve implants by one surgeon were retrospectively reviewed. Six eyes with late (greater than 3 months) Ahmed Glaucoma Valve occlusion requiring operative intervention were identified. Two of these eyes underwent initial successful transcameral drainage tube irrigation and four initially required Ahmed Glaucoma Valve exchange. Intraoperative images, postoperative histologic analysis, and Ahmed Glaucoma Valve handling experiments were performed. Two eyes with late occlusion (33%; 1.25% of total implants) were initially successfully treated with irrigation alone. A gap between the valve cover and valve body junction allowed fibrovascular ingrowth and produced valve failure ultimately in five of six eyes (83%; 3.1% of total implants). This gap could be produced by grasping the device along the center line, indenting the valve cover, and damaging the plastic rivets attaching the valve cover to the valve body. Handling the Ahmed Glaucoma Valve outside this &quot;no touch zone&quot; eliminated this problem. Leaflet adhesion has a low incidence and may be treated by transcameral drainage tube irrigation. Late onset distal occlusion is best treated by Ahmed Glaucoma Valve exchange with respect for the &quot;no touch zone.&quot; Respecting the &quot;no touch zone over the valve mechanism should avoid creation of gaps between the valve cover and valve body junction, which allow secondary fibrovascular ingrowth.
The chick chorioallantoic membrane (CAM) model allows direct observation of vascularization acute... more The chick chorioallantoic membrane (CAM) model allows direct observation of vascularization acutely in explanted or cultured tissues in an immunologically isolated environment. In vivo, angioinvasion of the tissue matrix does not occur in viable cartilage tissue, whereas denatured or nonviable grafts are readily vascularized and/or resorbed. To determine, using the CAM model, whether angioinvasion of thermally altered cartilage explants occurs acutely. Porcine septal cartilage specimens were removed from freshly killed animals and divided into 3 groups (n = 10): an untreated control group, a group in which cartilage was boiled in isotonic sodium chloride solution (normal saline) for 1 hour, and a laser-irradiated group (Nd:YAG, lambda = 1.32 microm, 30.8 W/cm2, irradiation time = 10 seconds). Tissue specimens were then washed in antibiotic solutions, cut into small cubes (approximately 1.5 mm3), placed on the surface of 30 CAMs (7 days after fertilization), and allowed to incubate f...
To determine the human corneal threshold ablation energy density for the 193-nm ArF excimer laser... more To determine the human corneal threshold ablation energy density for the 193-nm ArF excimer laser, approximating clinical conditions. The VISX Star (Santa Clara, CA) 193-nm argon fluoride excimer laser was used to ablate the cornea in human eye bank eyes under clinical conditions. Corneas were exposed to energy densities of 10, 20, 30, 35, 40, 45, and 140 to 160 mJ/cm2. Corneas were fixed for light and transmission electron microscopy immediately after laser exposure. Different ablation thresholds for various corneal structural elements were observed. The ablation threshold for the collagen in the corneal stroma was determined to be 30 mJ/cm2. Keratocytes had ablation thresholds of 40 mJ/cm2. These different ablation thresholds accounted for the production of stromal peaks and valleys, with the keratocytes atop the peaks. Different corneal structural elements have different ablation threshold energy densities.
Thermal and microstructural events resulting from KTP laser use during root canal preparation wer... more Thermal and microstructural events resulting from KTP laser use during root canal preparation were investigated in 30 extracted single-rooted human teeth. In the first section of this study, thermal events occurring on the root surfaces of 18 teeth during and after exposure of the root canal were measured using thermography. A variety of parameters were used to determine settings that would be effective without causing thermal damage to the periodontal ligament. In the second section of the study, root canals of 12 teeth exposed to KTP laser irradiation at parameters derived from section 1 were evaluated using Scanning electron microscopy. KTP laser application at a power setting of 3 W, an exposure time of 2 s, and a frequency of 5 Hz, applied five times, removed smear layer and debris from the root canal surface at temperatures below the thermal injury threshold for periodontal tissue.
Irradiation of the kinetochore region of PtK2 chromosomes by laser light of 532 nm was used to st... more Irradiation of the kinetochore region of PtK2 chromosomes by laser light of 532 nm was used to study the function of the kinetochore region in chromosome movement and to create an artificial micronuclei in cells. When the sister kinetochores of a chromosome were irradiated at prometaphase, the affected chromosome detached from the spindle and exhibited no further directed movements for the duration of mitosis. The chromatids of the chromosome remained attached to one another until anaphase, at which point they separated. No poleward movement of the chromatids was observed, and at telophase they passively moved to one of the daughter cells and were enclosed in a micronucleus. The daughter cell containing the micronucleus was then isolated by micromanipulation and followed through subsequent mitoses. At the next mitosis, two chromosomes, each with two chromatids, condensed in the micronucleus. These chromosomes did not attach to the spindle and showed chromatid separation, but no pole...
Initial hyperplasia is major cause of restenosis after vascular interventions for arterial occlus... more Initial hyperplasia is major cause of restenosis after vascular interventions for arterial occlusive disease. We reported that a fluorescent probe, Texas Red, conjugated to the scavenger-receptor ligand, maleylated bovine serum albumin accumulated almost exclusively in the injured, hyperplastic sites. The purpose of this study is to test the feasibility of enhanced drug delivery to the hyperplastic lesion by targeting the
ABSTRACT Photoacoustic microscopy (PAM) utilizes short laser pulses to deposit energy into light ... more ABSTRACT Photoacoustic microscopy (PAM) utilizes short laser pulses to deposit energy into light absorbers and sensitively detects the ultrasonic waves the absorbers generate in response. PAM directly renders a three-dimensional spatial distribution of sub-surface optical absorbers. Unlike other optical imaging technologies, PAM features label-free optical absorption contrast and excellent imaging depths. Standard dental imaging instruments are limited to X-ray and CCD cameras. Subsurface optical dental imaging is difficult due to the highly-scattering enamel and dentin tissue. Thus, very few imaging methods can detect dental decay or diagnose dental pulp, which is the innermost part of the tooth, containing the nerves, blood vessels, and other cells. Here, we conducted a feasibility study on imaging dental decay and dental pulp with PAM. Our results showed that PAM is sensitive to the color change associated with dental decay. Although the relative PA signal distribution may be affected by surface contours and subsurface reflections from deeper dental tissue, monitoring changes in the PA signals (at the same site) over time is necessary to identify the progress of dental decay. Our results also showed that deep-imaging, near-infrared (NIR) PAM can sensitively image blood in the dental pulp of an in vitro tooth. In conclusion, PAM is a promising tool for imaging both dental decay and dental pulp.
The purpose of this study was to evaluate the effects of the ArF-193 nm excimer laser on the dent... more The purpose of this study was to evaluate the effects of the ArF-193 nm excimer laser on the dentinal tubules of extracted human teeth under a scanning electron microscope. Fifteen 3 mm thick slices were cut with an electric saw at the cementoenamel junction from 15 extracted human teeth. A diamond bur was used to remove the cementum layer and expose the dentinal tubules. Each slice was scored by a permanent marker into four equal quadrants. The ArF excimer laser was applied for 5 seconds on three of the quadrants with fluences that ranged from 0.2 J/cm2 to 15 J/cm2 and pulse repetition of 25 Hz. The untouched quadrant served as a control. The specimens were mounted on stubs, sputter coated by gold, and examined by a scanning electron microscope. The effects of the ArF excimer laser irradiation varied. Laser fluences of 0.2, 0.5, and 1.0 J/cm2 had no effect. Although fluence of 15 J/cm2 caused significant removal of peritubular dentin, melting and resolidification of the dentinal smear layer was also observed under the scanning electron microscope with a laser fluence of 5 J/cm2.
Root hypersensitivity occurs as a result of exposed dentinal tubules. Various methods and materia... more Root hypersensitivity occurs as a result of exposed dentinal tubules. Various methods and materials have been tried in an attempt to occlude these tubules. The purpose of this investigation was to study by scanning electron microscope the effects of XeCl excimer laser on exposed dentinal tubules of human extracted teeth. Fifteen 3-mm-thick slices were cut at the cementoenamel junction from 15 extracted human teeth by an electric saw. By using a diamond bur to remove the cementum layer the dentinal tubules were exposed. Each slice was scored by a permanent marker into four equal quadrants. Three of the quadrants were lased for 4 s by XeCl excimer laser with fluences ranging from 0.5 to 7.0 J/cm2 and pulse repetition of 25 Hz. The unlased quadrant served as control. The specimens were mounted on a stub, sputter coated by gold, and examined by scanning electron microscope. Nonlased surfaces showed numerous exposed dentinal tubules. In contrast, all specimens lased at fluences of up to 1 J/cm2 showed the presence of melted dentin which closed the dentinal tubules. At fluences of 4 J/cm2 and higher, rupture of molten materials and exposure of dentinal tubules were noted. The results indicate the application of XeCl excimer laser at specific fluences can cause melting of dentin and closure of exposed dentinal tubules.
The early approximal caries lesion in enamel is observed clinically as a white spot and is diffic... more The early approximal caries lesion in enamel is observed clinically as a white spot and is difficult to detect and/or monitor with current methods available to dentists. New methods with high sensitivity and specificity are required to enable improved early dental caries diagnosis. Using unpolarized Raman spectroscopy to examine unsectioned teeth, peak intensity changes in the phosphate (PO43-) vibrations (nu2, nu3 and nu4) were observed between spectra of sound and carious enamel. However, there is little change in the nu1 vibration with this approach. In contrast, when tooth sections were examined by unpolarized Raman spectroscopy, marked changes in the nu1 peak at 959 cm-1 were noted between healthy and carious enamel. These differences suggest that sampling orientation play a role in understanding the spectral changes. Using polarized Raman spectroscopy to examine unsectioned samples, cross polarized measurements from sound enamel exhibited significant reduction of the nu1 peak compared with parallel polarized measurements. A similar reduction was observed with carious enamel, however, the reduction was not as prominent. By calculating the depolarization ratio of the area under the nu1 peak, sound enamel can be clearly distinguished from demineralized regions. The spectral changes observed are attributed to changes in the structure and/or orientation of the apatite crystals as a result of the acid demineralization process.
Journal of Clinical Laser Medicine <html_ent glyph="@amp;" ascii="&"/> Surgery, 2000
The purpose of this study was to investigate the effects of dentin ablation using a carbon dioxid... more The purpose of this study was to investigate the effects of dentin ablation using a carbon dioxide (CO2) laser emitted at 9.3 microm by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). There have been no reports on effects of CO2 laser irradiation emitted at 9.3 microm on dentin by SEM and CLSM. Thirty extracted human teeth showing no clinical signs of caries were used. All teeth were horizontally sectioned to approximately 200 microm thickness and sections were irradiated using a 9.3 microm CO2 laser at different parameters as follows: 26 mJ [energy density (ED) 53.0 J/cm2] and 30 mJ (ED 61.1 J/cm2). After laser irradiation, samples were treated with sodium hypochlorite, stained using rhodamine-123, and observed with CLSM followed by SEM procedures. No craters or cracks were observed, but many small molten and rehardened particles were documented on the sample surface using SEM. Some small cracks were seen in the subsurface layer, and some patent dentinal tubules were detected using CLSM. These results suggest that laser irradiation at these parameters affected the sample surface only (less than 20 microm) and would be less harmful to thermal damage of dental pulp for dentin ablation.
To characterize tissue destruction after CO(2) laser-ablation of the vocal cords with the use of ... more To characterize tissue destruction after CO(2) laser-ablation of the vocal cords with the use of optical coherence tomography (OCT). OCT was used to image fresh porcine vocal cords after laser ablation. OCT and histology estimates of the ablation crater dimensions and the depth of thermal injury were obtained. The vocal cord substructures up to 2.29 mm in depth at 10 microm resolution, and the thermal disruption after laser ablation were identified by OCT. OCT and histology estimates of the lesion dimensions showed no significant differences. Crater depth is directly proportional to laser power, whereas crater width and the zone of thermal injury appear to be unrelated to laser power. OCT may be used to accurately characterize the native states and the laser-induced thermal injury of laryngeal mucosa, within the inherent limitation in its depth of penetration. OCT may be a useful diagnostic and monitoring tool in an otolaryngology practice.
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