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
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.
Selective removal of dental composite with high precision is best accomplished using lasers operating at
high pulse repetition rates focused to a small spot size. 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 compare the ablation rates and selectivity of
enamel and composite for a 30 W diode-pumped Er:YAG laser operating with a pulse duration of 30-50-μs
and evaluate it's suitability for the selective removal of composite from tooth surfaces. The depth of
ablation and changes in surface morphology were assessed using digital microscopy. The fluence range
of 30-50 J/cm2 appeared optimal for the removal of composite, and damage to sound enamel was limited to
less than 100-μm after the removal of composite as thick as 700-800-μm. Future studies will focus on the
use of methods of feedback to further increase selectivity.
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.
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.
In vivo and in vitro studies have shown that high contrast images of tooth demineralization can be acquired in the near-IR due to the high transparency of dental enamel. The purpose of this study is to compare the lesion contrast in reflectance at near-IR wavelengths coincident with high water absorption with those in the visible, the near-IR at 1300-nm and with fluorescence measurements for early lesions in occlusal surfaces. Twenty-four human molars were used in this in vitro study. Teeth were painted with an acidresistant varnish, leaving a 4×4 mm window in the occlusal surface of each tooth exposed for demineralization. Artificial lesions were produced in the exposed windows after 1 and 2-day exposure to a demineralizing solution at pH 4.5. Lesions were imaged using NIR reflectance at 3 wavelengths, 1310, 1460 and 1600-nm using a high definition InGaAs camera. Visible light reflectance, and fluorescence with 405-nm excitation and detection at wavelengths greater than 500-nm were also used to acquire images for comparison. Crossed polarizers were used for reflectance measurements to reduce interference from specular reflectance. The contrast of both the 24 hr and 48 hr lesions were significantly higher (P<0.05) for NIR reflectance imaging at 1460-nm and 1600-nm than it was for NIR reflectance imaging at 1300-nm, visible reflectance imaging, and fluorescence. The results of this study suggest that NIR reflectance measurements at longer near-IR wavelengths coincident with higher water absorption are better suited for imaging early caries lesions.
Near-IR (NIR) imaging can be used to view the formation of ablation craters during laser ablation since the enamel of the tooth is almost completely transparent near 1310-nm1. Laser ablation craters can be monitored under varying irradiation conditions to assess peripheral thermal and transient-stress induced damage, measure the rate and efficiency of ablation and provide insight into the ablation mechanism. There are fundamental differences in the mechanism of enamel ablation using erbium lasers versus carbon dioxide laser systems due to the nature of the primary absorber and it is necessary to have water present on the tooth surface for efficient ablation at erbium laser wavelengths. In this study, sound human tooth sections of approximately 2-3-mm thickness were irradiated by free running and Q-switched Er:YAG & Er:YSGG lasers under varying conditions with and without a water spray. The incision area in the interior of each sample was imaged using a tungsten-halogen lamp with a band-pass filter centered at 1310-nm combined with an InGaAs area camera with a NIR zoom microscope. Obvious differences in the crater evolution were observed between CO2 and erbium lasers. Ablation stalled after a few laser pulses without a water spray as anticipated. Efficient ablation was re-initiated by resuming the water spray. Micro-fractures were continuously produced apparently driven along prism lines during multi-pulse ablation. These fractures or fissures appeared to merge together as the crater evolved to form the leading edge of the ablation crater. These observations support the proposed thermo-mechanical mechanisms of erbium laser involving the strong mechanical forces generated by selective absorption by water.