It has been well established that CO2 laser irradiation can be used to transform the mineral phase of dental enamel to make it more resistant to acid dissolution. The purpose of this study was to investigate if carbon dioxide laser irradiation and topical fluoride can be used to treat incipient caries lesions to inhibit further progression, i.e. treat active lesion surfaces as opposed to sound surfaces prior to subjecting them to an acid challenge. Simulated active caries lesions were produced on twenty eight bovine enamel samples using a pH cycling model and those surfaces were irradiated by a 9.4 μm CO2 laser and treated with topical fluoride. Changes in the surface morphology, acid resistance, and permeability were measured using digital microscopy, optical coherence tomography (OCT), and SWIR reflectance surface dehydration rate measurements at 1950 nm after exposure to a further acid challenge. There was a significant reduction (P < 0.05) of further lesion progression for lesion windows treated with CO2 laser irradiation followed by the application of an acidulated phosphate fluoride gel compared to the untreated lesion windows on each sample. Treatment by laser irradiation alone was not effective. The degree of lesion inhibition was not as high as has been previously observed for laser irradiated sound enamel surfaces exposed to an acid challenge.
Dental fluorosis is an increasing problem in the U.S. due to excessive exposure to fluoride from the environment. Fluorosis causes hypomineralization of the enamel during tooth development and mild fluorosis is visible as faint white lines on the tooth surface while the most severe fluorosis can result in pitted surfaces. It is difficult to quantify the severity of fluorosis and assessments are limited to subjective visual assessments. Dental fluorosis appears with very high contrast at short wavelength infrared (SWIR) wavelengths beyond 1400-nm and we hypothesize that these wavelengths may be better suited for detecting mild fluorosis and for estimating the severity. In this study the contrast of fluorosis of varying severity on extracted human permanent teeth was measured at SWIR wavelengths ranging from 1300-2000-nm using an extended range InGaAs camera and broadband light sources. Cross polarization optical coherence tomography was used to measure the depth of hypomineralization.
We have developed a clinical probe capable of acquiring simultaneous short wavelength infrared (SWIR) cross-polarized reflectance and occlusal transillumination images of lesions on tooth proximal and occlusal surfaces. We hypothesize that the dual SWIR reflectance and transillumination probe will improve the diagnostic accuracy of the device by reducing false positives since it is unlikely that confounding structural features or specular reflection are going to be present in both reflectance and transillumination images. In addition, the dual probe will provide complementary diagnostic information about lesion severity to help discriminate early superficial lesions on tooth surfaces from deeply penetrating lesions. The dual probe was 3D printed and equipped with a compact InGaAs camera and broadband superluminescent diode light sources that emit broadband light at 1300 nm for occlusal transillumination and 1600 nm light for cross-polarization reflectance measurements. The first clinical images acquired using this novel probe are presented.
Intraoral imaging of teeth with near-IR light provides increased contrast of dental caries and restorative materials compared to visible inspection and digital radiography. The objective of this study was to investigate the near-IR optical properties of the dental pulp-chamber floor, walls and canal orifices. We imaged in vitro extracted human posterior teeth at 1300-nm and 1500-1700-nm in reflectance and transillumination and compared the tissues properties with visible light images and quantitative light fluorescence. Transillumination of posterior teeth at both 1300-nm and 1500-1700-nm yielded significantly higher contrast between the pulp-chamber floor and walls than all other methods.
Significance: We have developed a clinical probe capable of acquiring near-simultaneous short-wavelength infrared (SWIR) reflectance and occlusal transillumination images of lesions on tooth proximal and occlusal surfaces. We hypothesize that dual images will aid in differentiating between shallow and deep occlusal lesions and reduce the potential of false positives (FPs).
Aim: The aim of this study was to test the performance of the dual reflectance and occlusal transillumination probe on extracted teeth prior to commencing clinical studies.
Approach: The dual probe was 3D printed and the imaging system uses an InGaAs camera and broadband superluminescent diode light sources that emit broadband light at 1300 nm for occlusal transillumination and 1600-nm light for cross-polarization reflectance. The diagnostic performance of the dual probe was assessed using 120 extracted teeth with approximal and occlusal lesions. Reflectance and transillumination images were fused into single images to enhance the contrast between sound and lesion areas. The lesion contrast in both modes did not increase significantly with either the lesion depth or the distance from the occlusal surface for approximal lesions. In addition, the diagnostic performance of radiography, the individual reflectance and transillumination images, dual images, and fused images were compared using micro-computed tomography as the gold standard.
Results: Reflectance imaging at 1600 nm yielded the highest diagnostic accuracy for lesions on both occlusal and proximal surfaces while radiography yielded the lowest number of FPs.
Conclusion: This study demonstrates that simultaneous acquisition of both reflectance and transillumination SWIR images is possible with a single clinical device.
New imaging technologies are needed for the clinical assessment of lesions on root surfaces. It is not sufficient to simply detect caries lesions; methods are needed to assess lesion depth, structural composition and activity to determine if chemical intervention has the potential to be effective and if remineralization has occurred. Lesions were monitored using CP-OCT during lesion dehydration to assess the lesion structure and any shrinkage. Thermal imaging at 6-10 μm wavelengths and short wavelength-IR imaging at 1450-1750-nm were used to monitor thermal emission during lesion dehydration to assess lesion activity. Imaging probes were custom fabricated for clinical use. We present the first clinical results of a small feasibility study employing CP-OCT, thermal and SWIR imaging to assess lesion activity in vivo on thirty test subjects with suspected root caries lesions.
Dental composites are used as restorative materials to replace tooth structure after the removal of caries, shaping, covering teeth for esthetic purposes and as adhesives. Dentists spend more time replacing existing restorations that fail than they do placing new restorations. Tooth colored restorations are difficult to differentiate from the surrounding tooth structure making them challenging to remove completely without incidental removal of healthy tooth structure. Previous studies have demonstrated that CO2 lasers in conjunction with spectral feedback can be used to selectively remove composite from tooth surfaces. In addition, we assembled a system feasible for clinical use that incorporates a spectral feedback system, scanning system, articulating arm and a clinical handpiece and subsequently evaluated the performance of that system on extracted teeth. The purpose of this study was to test this system in vivo to demonstrate its efficacy relative to dental clinicians. Eight test subjects with premolar teeth scheduled for extraction for orthodontic reasons had bilateral premolars prepared with small occlusal cavity preparations and filled with dental composite. The laser scanning system was used to remove the composite from one of the preparations and a dental handpiece was used to remove the composite from the other. Cross polarization optical coherence tomography was used to measure the volume of the preparation before and after composite placement and removal. There was no significant difference in the loss of enamel and residual composite between the laser and the handpiece. This study demonstrated that a computer controlled spectral guided CO2 laser scanning system can be used in vivo to selectively remove composite from tooth surfaces.
Most new caries lesions are found in the pits and fissures of the occlusal surface. Radiographs have extremely low sensitivity for early occlusal decay, and by the time the lesion is severe enough to appear on a radiograph, it typically has penetrated well into the dentin and surgical intervention is required. The occlusal surfaces are often heavily stained, and visual and tactile detection have poor sensitivity and specificity. Previous near-infrared imaging studies at wavelengths beyond 1300 nm have demonstrated that stains are not visible and demineralization on the occlusal surfaces can be viewed without interference from stains. The objective of our study is to determine how the contrast between sound and lesion areas on occlusal surfaces varies with wavelength from the visible to 2350 nm and determine to what degree stains interfere with that contrast. The lesion contrast for reflectance is measured in 55 extracted teeth with suspected occlusal lesions from 400 to 2350 nm employing silicon and indium gallium arsenide imaging arrays. In addition, the lesion contrast is measured on 25 extracted teeth with suspected occlusal lesions from 400 to 1600 nm in reflectance and from 830 to 1400 nm in transillumination before and after stains are removed using a ultrasonic scaler. The highest lesion contrast in reflectance is measured at wavelengths >1700 nm. Stains interfere significantly at wavelengths <1150 nm (400 to 1150) for both reflectance and transillumination measurements. Our study suggests that the optimum wavelengths for imaging decay in the occlusal surfaces are >1700 nm for reflectance (1700 to 2350 nm) and near 1300 nm (1250 to 1350 nm) for transillumination.
In vivo and in vitro studies have demonstrated that near-infrared (NIR) light at λ=1300-1700-nm can be used to acquire high contrast images of enamel demineralization without interference of stains. The objective of this study was to determine if a relationship exists between the NIR image contrast of occlusal lesions and the depth of the lesion. Extracted teeth with varying amounts of natural occlusal decay were measured using a multispectral-multimodal NIR imaging system which captures λ=1300-nm occlusal transillumination, and λ=1500-1700-nm cross-polarized reflectance images. Image analysis software was used to calculate the lesion contrast detected in both images from matched positions of each imaging modality. Samples were serially sectioned across the lesion with a precision saw, and polarized light microscopy was used to measure the respective lesion depth relative to the dentinoenamel junction. Lesion contrast measured from NIR crosspolarized reflectance images positively correlated (p<0.05) with increasing lesion depth and a statistically significant difference between inner enamel and dentin lesions was observed. The lateral width of pit and fissures lesions measured in both NIR cross-polarized reflectance and NIR transillumination positively correlated with lesion depth.
Most new lesions are found in the pits and fissures of the occlusal surface. Radiographs have extremely low sensitivity for early occlusal decay and by the time the lesion is severe enough on a radiograph it typically has penetrated well into the dentin and surgical intervention is required. The occlusal surfaces are heavily stained and visual and tactile methods for their detection also have poor sensitivity and specificity. Previous studies at wavelengths beyond 1300-nm have demonstrated that stains are not visible and demineralization on the occlusal surfaces can be viewed without interference from stains. New extended range InGaAs near- IR cameras allow access to wavelengths beyond 1700-nm. The objective of this study was to determine how the contrast of occlusal lesions varies with wavelength from the visible to 2350-nm. The lesion contrast was measured in 55 extracted teeth with suspected occlusal lesions using reflectance measurements from 400- 2350-nm using Si and InGaAs imaging arrays. The highest lesion contrast in reflectance was measured at wavelengths greater than 1700-nm. Stains interfered significantly at wavelengths shorter than 1150-nm. This study indicates that the optimum wavelengths for reflectance imaging decay in the occlusal surfaces are greater than 1700-nm.
Recent studies have shown that near-IR (NIR) imaging methods such as NIR reflectance can be used to image lesions on proximal surfaces, and optical coherence tomography (OCT) can be used to measure the depth of those lesions below the tooth surface. These imaging modalities can be used to acquire high contrast images of demineralized tooth surfaces, and 2-D and 3-D images can be extracted from this data. At NIR wavelengths longer than 1200-nm, there is no interference from stains and the contrast is only due to the increased light scattering of the demineralization. Previous studies have shown that image-guided laser ablation can be used to remove occlusal lesions, but its use for the removal of subsurface lesions on proximal surfaces has not been investigated. The objective of this study is to demonstrate that simultaneously scanned NIR and CO2 lasers can be used to selectively remove natural and artificial interproximal caries lesions with minimal damage to sound tooth structure. In this study, images of simulated and natural interproximal lesions on extracted teeth were imaged using a digital microscope, a scanned 1460-nm superluminescent laser diode with an InGaAs detector and a cross polarization OCT system operating at 1300-nm. The lesions were subsequently removed with a CO2 laser operating at 9.3-μm and the dental handpiece and the volume of sound tissue removed was compared.
The optical properties of human dentin can change markedly due to aging, friction from opposing teeth,
and acute trauma, resulting in the formation of transparent or sclerotic dentin with increased mineral
density. The objective of this study was to determine the optical attenuation coefficient of human dentin
tissues with different mineral densities in the near-infrared (NIR) spectral regions from 1300-2200 nm
using NIR transillumination and optical coherence tomography (OCT). N=50 dentin samples of varying
opacities were obtained by sectioning whole extracted teeth into ~ 150 μm transverse sections at the
cemento-enamel junction or the apical root. Transillumination images were acquired with a NIR camera
and attenuation measurements were acquired at various NIR wavelengths using a NIR sensitive
photodiode. Samples were imaged with transverse microradiography (gold standard) in order to determine
the mineral density of each sample.
A major advantage of composite restoration materials is that they can be color matched to the tooth.
However, this presents a challenge when composites fail and they need to be replaced. Dentists typically
spend more time repairing and replacing composites than placing new restorations. We have shown in
previous studies that high-contrast images of composite can be acquired in occlusal transmission mode at
near-IR wavelengths coincident with higher water absorption. The purpose of this study was to determine if
similar high-contrast images can be acquired in reflectance mode at longer wavelengths where water
absorption is even higher. Extracted human teeth with existing composite restoration (n=14) were imaged at
wavelengths from 900-2300 using an extended range InGaAs camera. Our results indicate that NIR
wavelengths longer than 1400-nm coincident with higher water absorption yield the highest contrast between
dental composites and tooth structure in reflectance.
Both laser irradiation and fluoride treatment alone are known to provide increased resistance to acid dissolution. CO2 lasers tuned to a wavelength of 9.3 μm can be used to efficiently convert the carbonated hydroxyapatite of enamel to a much more acid resistant purer phase hydroxyapatite (HAP). Further studies have shown that fluoride application to HAP yields fluoroapatite (FAP) which is even more resistant against acid dissolution. Previous studies show that CO2 lasers and fluoride treatments interact synergistically to provide significantly higher protection than either method alone, but the mechanism of interaction has not been elucidated. We recently observed the formation of microcracks or a “crazed” zone in the irradiated region that is resistant to demineralization using high-resolution microscopy. The microcracks are formed due to the slight contraction of enamel due to transformation of carbonated hydroxyapatite to the more acid resistant pure phase hydroxyapatite (HAP) that has a smaller lattice. In this study, we test the hypothesis that these small cracks will provide greater adhesion for topical fluoride for greater protection against acid demineralization.
Bitewing radiography is still considered state-of-the-art diagnostic technology for assessing cavitation within
approximal carious dental lesions, even though radiographs cannot resolve cavitated surfaces but instead are
used to measure lesion depth in order to predict cavitation. Clinicians need new technologies capable of
determining whether approximal carious lesions have become cavitated because not all lesions progress to
cavitation. Assessing lesion cavitation from near-infrared (NIR) imaging methods holds great potential due to
the high transparency of enamel in the NIR region from λ=1300-1700-nm, which allows direct visualization
and quantified measurements of enamel demineralization. The objective of this study was to measure the
change in lesion appearance between non-cavitated and cavitated lesions in artificially generated lesions
using NIR imaging modalities (two-dimensional) at λ=1300-nm and λ=1450-nm and cross-polarization
optical coherence tomography (CP-OCT) (thee-dimensional) λ=1300-nm. Extracted human posterior teeth
with sound proximal surfaces were chosen for this study and imaged before and after artificial lesions were
made. A high speed dental hand piece was used to create artificial cavitated proximal lesions in sound
samples and imaged. The cavitated artificial lesions were then filled with hydroxyapatite powder to simulate
non-cavitated proximal lesions.
UV and IR lasers can be used to specifically target protein, water, and the mineral phase of dental hard
tissues to produce varying changes in surface morphology. In this study, we irradiated enamel and dentin
surfaces with various combinations of lasers operating at 0.355, 2.94, and 9.4 μm, exposed those surfaces
to topical fluoride, and subsequently evaluated the influence of these changes on surface morphology and
permeability. Digital microscopy and surface dehydration rate measurements were used to monitor changes
in the samples overtime. The surface morphology and permeability (dehydration rate) varied markedly with
the different laser treatments on enamel. On dentin, fluoride was most effective in reducing the
permeability.
Clinicians need technologies to improve the diagnosis of questionable occlusal carious lesions (QOC’s) and
determine if decay has penetrated to the underlying dentin. Assessing lesion depth from near-infrared (NIR) images
holds great potential due to the high transparency of enamel and stain to NIR light at λ=1300-1700-nm, which
allows direct visualization and quantified measurements of enamel demineralization. Unfortunately, NIR reflectance
measurements alone are limited in utility for approximating occlusal lesion depth >200-μm due to light attenuation
from the lesion body. Previous studies sought to combine NIR reflectance and transillumination measurements taken
at λ=1300-nm in order to estimate QOC depth and severity. The objective of this study was to quantify the change in
lesion contrast and size measured from multispectral NIR reflectance and transillumination images of natural
occlusal carious lesions with increasing lesion depth and severity in order to determine the optimal multimodal
wavelength combinations for estimating QOC depth. Extracted teeth with varying amounts of natural occlusal
decay were measured using a multispectral-multimodal NIR imaging system at prominent wavelengths within the
λ=1300-1700-nm spectral region. Image analysis software was used to calculate lesion contrast and area values
between sound and carious enamel regions.
For over one hundred years, x-rays have served as a cornerstone of dentistry. Dental radiographic imaging
technologies have constantly improved, however, detecting occlusal lesions remains as one of the greatest
challenges due to the low sensitivity of radiographs and the overlap of enamel. Once detected, occlusal lesions have
penetrated far into the dentin, necessitating invasive restorative treatment. The adoption of near-infrared (NIR)
systems in dentistry introduces the potential for early detection of occlusal lesions. Commercially available NIR
systems for intra-oral applications currently operate near 800-nm; however, extrinsic stains may interfere with the
detection of demineralization of the underlying enamel surface. Higher wavelengths such as 1300-nm render stains
nearly transparent and enhances the contrast of sound enamel to demineralized enamel. This novel finding promotes
minimally invasive dentistry and allows oral health professionals the ability to detect, image, track, and monitor
early lesions without repeated exposure to ionizing radiation nor invasive treatment.
Previous studies have demonstrated that the structural changes on enamel due to demineralization and
remineralization can be exploited through optical imaging methods such as QLF, thermal and NIR imaging. The
purpose of this study is to investigate whether PS-OCT and NIR reflectance imaging can be utilized to assess lesion
structure in artificial enamel lesions on the smooth surfaces of primary teeth exposed to fluoride. The smooth
coronal surfaces of primary teeth (n=25) were divided into 4 windows: sound, demineralization, demineralization
with remineralization and APF with demineralization. Windows were treated with either acidulated phosphate
fluoride (APF) for 1 minute, a demineralization solution for 4 days, and/or an acidic remineralization solution for 12
days. The samples were imaged using PS-OCT, QLF and NIR reflectance at 1400–1700 nm wavelengths. This study
demonstrated that both PS-OCT and NIR reflectance imaging were suitable for assessing lesion structure in the
smooth surfaces of primary dentition.
Secondary caries stands as the leading reason for the failure of composite restorations and dentists spend more time replacing existing restorations than placing new ones. Current clinical strategies, and even modern visible light methods designed to detect decay, lack the sensitivity to distinguish incipient lesions, are confounded by staining on the surface and within the tooth, or are limited to detecting decay on the tooth surface. Near-IR (NIR) imaging methods, such as NIR reflectance and transillumination imaging, and optical coherence tomography are promising strategies for imaging secondary caries. Wavelengths longer than 1300-nm avoid interference from stain and exploit the greater transparency of sound enamel and dental composites, to provide increased contrast with demineralized tissues and improved imaging depth. The purpose of this study was to determine whether NIR transillumination (λ=1300-nm) and NIR crosspolarized reflectance (λ=1500-1700-nm) images can serve as reliable indicators of demineralization surrounding composite restorations. Twelve composite margins (n=12) consisting of class I, II and V restorations were chosen from ten extracted teeth. The samples were imaged in vitro using NIR transillumination and reflectance, polarization sensitive optical coherence tomography (PS-OCT) and a high-magnification digital visible light microscope. Samples were serially sectioned into 200–μm slices for histological analysis using polarized light microscopy (PLM) and transverse microradiography (TMR). The results presented demonstrate the utility of NIR light for detecting recurrent decay and suggest that NIR images could be a reliable screening tool used in conjunction with PS-OCT for the detection and diagnosis of secondary caries.
Previous studies have shown that near-IR transillumination is well suited for imaging deep occlusal lesions. The purpose of this study was to determine if near-IR images can be used to guide a CO2 laser for the selective removal of natural occlusal lesions on extracted teeth. Near-IR occlusal transillumination images of extracted human teeth with natural occlusal caries lesions were acquired using an InGaAs camera and near-IR light at wavelengths from 1290 to 1470-nm from a filtered tungsten halogen source. A CO2 laser operating at 9.3-μm with a pulse duration of 10-15-μs and a pulse repetition rate of 100-300-Hz was used for caries removal. Optical Coherence tomography was used to confirm lesion presence and serial scans were used to assess selective removal. Teeth were also sectioned for histological examination using polarized light microscopy. This study suggests that near-infrared transillumination is a promising method for the image guided laser ablation of occlusal caries lesions but the use of serial near-IR transillumination imaging for monitoring lesion removal was limited.
Selective removal of caries lesions with high precision is best accomplished using lasers operating at high pulse repetition rates utilizing small spot sizes. Conventional flash-lamp pumped Er:YAG lasers are poorly suited for this purpose, but new diode-pumped Er:YAG lasers have become available operating at high pulse repetition rates. The purpose of this study was to measure the ablation rate and selectivity of sound and demineralized enamel and dentin for a 30 W diode-pumped Er:YAG laser operating with a pulse duration of 20-30-μs and evaluate it's potential for the selective removal of natural occlusal lesions on extracted teeth. Microradiography was used to determine the mineral content of the demineralized enamel and dentin of 300-μm thick sections with natural caries lesions prior to laser ablation. The ablation rate was calculated for varying mineral content. In addition, near-IR reflectance measurements at 1500-1700- nm were used to guide the laser for the selective ablation of natural occlusal caries lesions on extracted teeth.
Previous studies have shown that near-infrared (NIR) reflectance and transillumination imaging can be used to acquire high contrast images of early caries lesions and composite restorative materials. The aim of the study was to determine the optimum NIR wavelengths for imaging demineralized areas under dental sealants. Fifteen natural human premolars and molars with occlusal lesions were used in this in vitro study. Images before and after application of sealants were acquired using NIR reflectance and NIR transillumination at wavelengths of 1300, 1460, and 1500 to 1700 nm. Images were also acquired using polarization sensitive optical coherence tomography (OCT) for comparison. The highest contrast for NIR reflectance was at 1460 nm and 1500 to 1700 nm. These NIR wavelengths are coincident with higher water absorption. The clear Delton sealant investigated was not visible in either copolarization or cross-polarization OCT images. The wavelength region between 1500 and 1700 nm yielded the highest contrast of lesions under sealants for NIR reflectance measurements.
One major advantage of composite restoration materials is that they can be color matched to the
tooth. However, this presents a challenge when composites fail and they need to be replaced. Dentists
typically spend more time repairing and replacing composites than placing new restorations. Previous
studies have shown that near-infrared imaging can be used to distinguish between sound enamel and decay
due to the differences in light scattering. The purpose of this study was to use a similar approach and
exploit differences in light scattering to attain high contrast between composite and tooth structure.
Extracted human teeth with composites (n=16) were imaged in occlusal transmission mode at wavelengths
of 1300-nm, 1460-nm and 1550-nm using an InGaAs image sensor with a tungsten halogen light source
with spectral filters. All samples were also imaged in the visible range using a high definition 3D digital
microscope. Our results indicate that NIR wavelengths at 1460-nm and 1550-nm, coincident with higher
water absorption yield the highest contrast between dental composites and tooth structure.
Previous studies have demonstrated the utility of near infrared (NIR) imaging for caries detection employing
transillumination and reflectance imaging geometries. Three intra-oral NIR imaging probes were fabricated for the
acquisition of in vivo, real time videos using a high definition InGaAs SWIR camera and near-IR broadband light
sources. Two transillumination probes provide occlusal and interproximal images using 1300-nm light where water
absorption is low and enamel manifests the highest transparency. A third reflectance probe utilizes cross polarization
and operates at >1500-nm, where water absorption is higher which reduces the reflectivity of sound tissues,
significantly increasing lesion contrast. These probes are being used in an ongoing clinical study to assess the
diagnostic performance of NIR imaging for the detection of caries lesions in teeth scheduled for extraction for
orthodontic reasons.
Laser based methods are well suited for automation and can be used to selectively remove dental caries to
minimize the loss of healthy tissues and render the underlying enamel more resistant to acid dissolution.
The purpose of this study was to determine which imaging methods are best suited for image-guided
ablation of natural non-cavitated carious lesions on occlusal surfaces. Multiple caries imaging methods
were compared including near-IR and visible reflectance and quantitative light fluorescence (QLF). In
order for image-guided laser ablation to be feasible, chemical and physical modification of tooth surfaces
due to laser irradiation cannot greatly reduce the contrast between sound and demineralized dental hard
tissues. Sound and demineralized surfaces of 48 extracted human molar teeth with non-cavitated lesions
were examined. Images were acquired before and after laser irradiation using visible and near-IR
reflectance and QLF at several wavelengths. Polarization sensitive-optical coherence tomography was
used to confirm that lesions were present. The highest contrast was attained at 1460-nm and 1500-1700-nm,
wavelengths coincident with higher water absorption. The reflectance did not decrease significantly after
laser irradiation for those wavelengths.
Dental enamel is highly transparent at near-IR wavelengths and several studies have shown that these
wavelengths are well suited for optical transillumination for the detection and imaging of tooth decay. We
hypothesize that these wavelengths are also well suited for imaging cracks in teeth. Extracted teeth with
suspected cracks were imaged at several wavelengths in the near-IR from 1300-1700-nm. Extracted teeth
were also examined with optical coherence tomography to confirm the existence of suspected cracks.
Several teeth of volunteers were also imaged in vivo at 1300-nm to demonstrate clinical potential. In
addition we induced cracks in teeth using a carbon dioxide laser and imaged crack formation and
propagation in real time using near-IR transillumination. Cracks were clearly visible using near-IR imaging
at 1300-nm in both in vitro and in vivo images. Cracks and fractures also interfered with light propagation
in the tooth aiding in crack identification and assessment of depth and severity.
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