Dental tissue ablation by means of a picoseconds laser
Laser technology has been extensively used for dental treatment since the 1990s . In particular hard tissue ablation is performed by Er: YAG lasers due to their affinity with water and hydroxipa tite, thus avoiding the formation of micro- and macro-cracks, and thermal damaged areas[2 - 5]. On the other hand Er: YAG lasers are affected by cumbersome instrumentation, and operation durations can be higher than the ones of traditional instruments. Records of dental surface treatment with ultra-short pulsed lasers, 150 - 500 fs, are also present, at such pulse duration remarkable results have been obtained, regardless to the laser emission wavelength [6,7]. In this work human extracted teeth have been exposed to 1064 nm, 500 ps, laser radiation (Helios IR 5W – Innolight GmbH). During exposures the temperature has been continuously monitored inside the tooth with a thermocouple, in this way it was possible to monitor the thermal increase ( ' T) where the dental pulp is. The exposed samples have been cooled by continuously flowing water on them. Fig. 1 represents optical microscope images of drilled holes. It is possible to observe the complete absence of cracks, and any thermal damage. The ' T has been measured as 7.1°C on average, when room temperature water was used for cooling, above the 5.5°C accepted, after which irreversible damage to the dental pulp is caused. When cold water (10°C) was used for cooling, an average ' T of 4.3°C has been measured, with a maximum measured temperature of 5°C, in this way it was possible to keep the ' T under 5.5°C.
Images of two different holes drilled, in two different teeth, are here reported. It is possible to observe the absence of cracks and smears. Exposures have been performed at the repetition rate of 30 kHz, and pulse duration of 500 ps.
The results demonstrate that the ablation of dental hard tissue by means of a solid state picoseconds laser, working in the near infrared region, is effective without damaging the tooth vitality, and for this it is fundamental to keep the 'T under the maximum value accepted. The use of this kind of laser can result as a good alternative to Er:YAG lasers, and it is also a cheaper solution compared to the costly fs lasers systems.
The authors would like to acknowledge the NEXPRESSO programme for purchasing the Helios laser on behalf of the working group.