Near-IR imaging of erbium laser ablation with a water spray

Abstract

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-nm 1 . 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 CO 2 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 thermomechanical mechanisms of erbium laser involving the strong mechanical forces generated by selective absorption by water.

Fracture Forces of Dentin after Surface Treatment with High Speed Drill Compared to Er:YAG and Er,Cr:YSGG Laser Irradiation

“…In the present study, constant water spray was used during the whole laser irradiation process for both Er:YAG and Er,Cr:YSGG lasers, as it is also used in clinical treatments of enamel and dentin, either for cavity preparation or for other surface modifications. The importance of continuous spray application is also confirmed by Darling et al who observed “very clean without large cracks” ablation craters and no accompanying thermal side effects [ 19 ]. The water spray acts as a mediator for efficient ablation and minimizes the risk of adverse thermal effects in the pulp tissue.…”

Effects of lasers on titanium dental implant surfaces: a narrative review

“…The currently accepted theory for the mechanism of erbium laser ablation of dental hard tissues (enamel, dentine, cementum and bone) is a photo-mechanical action based on micro-explosions of water within the target. Conversion of the water to steam generates an increase in pressure, leading to micro-explosions [104,105]. These same mechanisms also apply to the ablation of dental plaque biofilms and dental calculus.…”

Near-IR imaging of thermal changes in enamel during laser ablation

“…Over the past two years we have presented work showing that near-IR (NIR) imaging can be used to image the formation of craters during IR laser ablation since the enamel of the tooth is almost completely transparent near 1310-nm (1)(2)(3). These studies showed that there is great potential for NIR imaging to monitor laser-ablation events in real-time to assess safe laser operating parameters by imaging thermal and stress-induced damage, elaborate the mechanisms involved in ablation such as dehydration, monitor removal of demineralized enamel and investigate the dynamic changes in the transparency of enamel with water loss.…”