Scanning ablation of root caries with acoustic feedback control

Abstract

It has been previously demonstrated that short &lgr;=355-nm laser pulses can be used for the selective removal of caries lesions and composite restorative materials from occlusal surfaces with minimal damage to the peripheral sound tooth structure. One advantage of laser-systems is they can be integrated with acoustic and optical feedback systems for the automated discrimination of dental caries and restorative materials. The objective of this study was to test the hypothesis that root caries could be selectively removed from tooth surfaces using a computer controlled laserscanning system coupled with an acoustic feedback system. Dental root caries surfaces on extracted teeth were scanned with &lgr;=355-nm laser pulses at irradiation intensities ranging from 0.6 to 0.8 J/cm². Acoustic feedback signals were acquired and used to control the laser output and scanning stages were used to position the laser over carious dentin until all the caries were removed to a fixed depth. Polarization optical coherence tomography (PSOCT) was used to acquire images of the root caries lesions before and after removal by the laser in order to assess if ablation was selective. The amplitude of the acoustic waves generated during the ablation of carious dentin was higher than for sound dentin allowing the acoustic feedback system to discriminate between sound and carious dentin. PS-OCT showed that caries were removed to a depth of up to 1.5-mm with minimal peripheral damage to peripheral sound dentin. The acoustic feedback was successfully used to distinguish between root caries and sound dentin, enabling the selective removal of caries from dentin surfaces using a &lgr;=355-nm, Nd:YAG Q-switched laser system.