| research Use of carbon dioxide lasers in dentistry Dr Kenneth Luk, Irene Shuping Zhao, China; Prof. Norbert Gutknecht, Germany & Prof. Chun Hung Chu, China “Laser” is an acronym that stands for “light amplification by stimulated emission of radiation”.1 The photons that make up a laser beam are coherent, amplified in phase (standing wave) and of a specific wavelength (monochro- matic). Laser has been used in dentistry for over two de- cades.2 Dental lasers are categorised according to their active medium and wavelengths. The currently available dental lasers are diode lasers (445, 635 and 810–980 nm), potassium titanyl phosphate lasers (532 nm, green), neo- dymium-doped yttrium aluminium garnet (Nd:YAG) la- Model Manufacturer Location Miran CYMA Dental Surgical CO2 laser 2015 Korea fractional CO2 laser DENTA 2 LightScalpel OPELASER PRO Smart US20D Mediclase BISON MEDICAL DOCTOR MED Daeshin Enterprise GPT Dental LightScalpel YOSHIDA DENTAL DEKA Tel Aviv, Israel Seoul, South Korea Seoul, South Korea Seoul, South Korea Fairfield, Neb., USA Bothell, Wash, USA Tokyo, Japan Calenzano, Italy Table 1: Several 10,600 nm carbon dioxide lasers on the market. 1 - m c / ) a i ( t n e c i f f e o C n o i t p r o s b A 105 104 103 102 101 100 10-1 10-2 10-3 10-4 100 0 8 9 - 0 1 8 4 6 0 , 1 5 4 4 2 3 5 5 3 6 0 8 7 , 2 0 4 9 , 2 Melanin Water CO2 laser 0 0 3 , 9 0 0 6 , 9 0 0 3 , 0 1 0 0 6 , 0 1 Haemoglobin Hydroxyapatite 500 1,000 3,000 10,000 Wavelength ()/nm Fig. 1: Absorption spectra (log scale) of several biological materials and laser wavelengths (adapted from Zuerlein et al.15). 06 2 2019 sers (1,064 nm), erbium lasers (2,780 and 2,940 nm) and carbon dioxide (CO2) lasers (9,300 and 10,600 nm). Each laser wavelength has a specific thermal output and a particular tissue interaction. Dental lasers of different wavelengths are used to perform different procedures. Blue lasers, diode lasers, Nd:YAG lasers and CO2 lasers are primarily used in soft-tissue sur- gery to provide good coagulation.3–6 Because CO2 laser energy is well absorbed by water, it is absorbed on the surface of the soft tissue. The visible lasers (445–660 nm) are absorbed within the first centimetre of the soft tissue because they are best absorbed by pigmented chromo- phores such as melanin and haemoglobin. Lasers with 810 to 1,064 nm wavelengths in the near-infrared spec- trum can penetrate into the soft tissue by a few centime- tres because they are comparatively less well absorbed by melanin and haemoglobin. Erbium lasers, operating in free-running pulse mode, are highest in water absorp- tion, enabling their use for soft-tissue ablation, as well as for dental hard tissue and osseous preparation. The two erbium wavelengths commonly used in dentistry are er- bium, chromium-doped yttrium, scandium, gallium and garnet (Er,Cr:YSGG) lasers (2,780 nm) and erbium-doped yttrium aluminium garnet (Er:YAG; 2,940 nm) lasers. Al- though erbium lasers can be used for soft-tissue proce- dures, bleeding control is less effective than with diode and CO2 lasers, which offer better visualisation of the sur- gical site.6 A CO2 laser is a useful and efficient gas laser for use in clinical dentistry. It is available in 10,600 nm on the market (Table 1). CO2 lasers are often used in soft-tissue surgery because their wavelengths are well absorbed by water, which makes up 70 % of biological tissue. They penetrate less than a millimetre and can produce excellent coagulation, along with a very precise cut.7, 8 The optical property of the wavelength in tissue is important to determine the use of lasers to perform dental hard-tissue preparation. Enamel and dentine are mainly composed of hydroxy- apatite, which has a high absorption coefficient to the wavelengths of CO2 lasers. Nevertheless, it takes time for a CO2 laser to ablate dental hard tissue, which contains mainly hydroxyapatite, with a melting point over 1,600 °C.