## 3 Photonic Technologies
### Lasers
#### 3.3.2 Dental Applications  
Lasers have been used in dental applications for more than 30 years [74, 76]. The first dental lasers cleared by the Food and Drug Administration (FDA) were for oral, soft-tissue procedures and included the carbon dioxide; neodymium:YAG (Nd:YAG); argon; and diode lasers. Dental laser instruments have been widely employed in soft-tissue procedures, such as gingivectomy, gingivoplasty, ferenectomy, curettage, crown lengthening, for the removal of benign tumors in oral surgery, and periodontitis [76, 77]. The benefits of using lasers include hemostasis, precise cutting, bacterial reduction, and reduced pain. The argon laser has also has been cleared for hard-tissue use and for curing light-activated materials [77].  
Lasers have numerous tissue interactions, such as ablation or vaporization of dental hard tissue [78, 79, 80, 81], hemostasis [82], microbial inhibition and destruction, as well as biological effects, such as biostimulation (photo-bio-modulation), which induce various beneficial therapeutic effects and biological responses, like in bone regeneration in the midpalatal anterior suture [83, 84]. In a similar study, it was evaluated the histologic effects of CO\({}_{2}\) laser irradiation, during gingival surgery and the histologic effects on cortical bone following irradiation with increasing energy densities [85]. Other reports in literature relate the use of lasers for the treatment of periodontal and peri-implant infections, promoting the peri-implant healing [74, 86, 87, 88]. Additionally, morphological changes and thermal effects of Er:YAG lasers and CO\({}_{2}\) lasers on implants were studied, because they can be useful to remove submerged implants and to decontaminate their surfaces [89, 90].  
There are several reports in the literature about the effects of lasers in the dental pulp [91, 92] and the first one was made by [PERSON] _et al._[91] in 1971. The authors wanted to determine the histologic and morphologic changes that characterize the pulpal response to laser irradiation and to determine the relationship between the amount of energy deposited on the surface and the degree of pulpal response. Both the CO\({}_{2}\) and Nd:YAG lasers have a thermal effect on both soft and hard tissues. Yet, the Er:YAG  
Figure 4: Schematic representation of the classification of lasers, according to penetration depth in biological tissue and their effects (adapted from [74]).  
laser is more efficient in absorption, both in water and in hydroxyapatite and, for that, has been reported to have less of a thermal effect on dental hard tissue [93,94].  
Over the last few years the 9.6-\(\upmu\)m CO\({}_{2}\) laser was developed. It has been observed that this device can preserve tissue with almost no adverse effects. In contrast, modifications of approved CO\({}_{2}\) laser therapies of premalignant lesions resulted in higher recurrence rates than the conventional defocused laser technique. However, several studies indicate that other wavelengths such as Nd:YAG (\(\lambda=1064\) nm) or diode lasers (\(\lambda=810\) nm) may be also interesting in this field. Intraoperatively, the use of photodynamic therapy or peri-implant care of ailing implants, with the CO\({}_{2}\) laser, seems to be more appropriate than conventional methods [95]. Er:YAG laser was also used to investigate its effect as an antibacterial agent, to disinfect root canals, and enhance bond strengths of fiber posts [96].