‘ Pain free ’ and ‘ simple procedure ’ are two of the most attractive phrases to patients who are otherwise reluctant to accept any dental treatment (138). Mini- mally invasive dental therapy (81) could satisfy the demands of such patients. The procedures can be comfortable, although not necessarily without any pain; and be effective for disease control whilst pre- serving more healthy dental tissue. Scaling and root planing is an example of a mini- mally invasive procedure because it is a conservative, cause-related therapy that attempts to eliminate etio- logic factors from the root surface (26). Scaling and root planing can result in improved clinical outcomes such as reduced bleeding on probing and decreased periodontal pocket depth. However, some calculus occasionally remains on the ‘ scaled ’ and ‘ planed ’ root surface. Moreover, treatment outcomes may not always be successful for moderate and deep peri- odontal pockets (95). In those cases, and after further evaluation, surgical procedures may be performed in an attempt to eliminate the remaining etiological fac- tors, as well as to achieve regeneration of lost peri- odontal tissue. Although periodontal surgery is not minimally invasive, it will produce better results if preceded by scaling and root planing (47). Clearly, if predictable treatment could be estab- lished for moderate periodontitis without surgery or with minimally invasive fl apless surgery, it would pro- vide a signi fi cant bene fi t to many patients with chronic periodontal disease, as well as to dentists providing their care. Thus far, conventional mechani- cal therapy has not resulted in such an ideal treat- ment  outcome,  even  when  using  power-driven devices.  Moreover,  antimicrobial  therapy  using systemic or locally delivered antibiotics has only occasionally   demonstrated   some   effectiveness. Recent evidence demonstrates that laser treatment has the potential to improve therapeutic outcomes and therefore be a valuable addition to conventional treatments (55). Currently, high-power-output lasers are used adjunctively with scaling and root planing or as minimally invasive surgery. Also, very-low-power- output lasers are employed for cellular stimulation and/or activation of antimicrobial agents following scaling and root planing. Both of these laser applica- tions  can  be  considered  as  minimally  invasive approaches to periodontal disease treatment. The aim of the present review was to survey the rele- vant literature of the clinical application of lasers as minimally  invasive  treatment  in  periodontal  and implant therapy for periodontists, general practition- ers and dental hygienists who are the primary provi- ders of initial treatment of these periodontal diseases and conditions. This paper will focus on the potential therapeutic bene fi ts of photonic energy produced by laser instruments and exclude discussions of other nonlaser optical devices, such as light-emitting diodes.
Laser applications for periodontal and implant therapy have gradually expanded as a result of the increase in published basic and clinical investigations using diode, carbon  dioxide  (CO 2 ),  neodymium-doped  yttrium aluminium garnet (Nd:YAG), erbium-doped yttrium aluminium garnet (Er:YAG) and erbium, chromium- doped: yttrium, scandium, gallium, garnet (Er,Cr: YSGG) lasers. All of these wavelengths with moderatepower output can be used adjunctively for initial peri- odontal therapy, not only to debride connective tissue and epithelium within periodontal pockets, but also to inactivate bacteria that invade the periodontal tissues. In addition, erbium lasers can ablate calculus with ef fi - ciency comparable with that of hand or ultrasonic instruments, preserving the root cementum under- neath the calculus (8, 11, 46, 51, 55). The delivery of laser power through a fi ne laser tip enables the practi- tioner to perform precise and small procedures with minimal damage around the treated site. Such a pre- cise treatment modality is essential for performing minimally invasive periodontal treatments. In contrast to the laser approaches discussed above, another treatment modality has emerged, named pho- totherapy, which is better known as low-level laser therapy (76). An important principle of phototherapy is that the power parameters employed are at a lower dose than those used for surgery (5, 12). Low-level laser therapy was often termed ‘ soft laser therapy ’ or ‘ cold laser therapy ’ , which created some confusion. The cur- rent  term,  photobiomodulation,  more  accurately describes the intended process, that is, the reduction of in fl ammation along with the stimulation of cell pro- liferation. Another application of phototherapy is antimicrobial photodynamic therapy, which aims to destroy pathogens in the pocket with reactive oxygen species produced by the combination of a low-level visible light laser and a photosensitizer. This protocol has attracted attention as a novel, minimally invasive approach for the treatment of pockets around teeth and dental implants (130). For a proper understanding of the basic principles of the applications of lasers in minimally invasive periodontal therapy, it is essential to discuss the characteristics of each laser and their applications based on their particular wavelengths.

Characteristics of each wavelength in periodontal and peri-implant therapy
Lasers used for periodontal and peri-implant therapy can be divided into three groups.
Lasers for soft-tissue ablation only Diode and Nd:YAG laser
he photonic energy from diode and Nd:YAG lasers is in the near-infrared spectrum (approximately 800 – 1,100 nm) and is readily and selectively absorbed in areas of in fl ammation by blood components and tissue pigment. Wavelengths of 800 – 1,100 nm are essentially transmitted through water, which explains their deep penetration into healthy soft tissue. As most subgingival calculus is dark in color, to avoid thermal damage, care should be taken to avoid pro- longed contact of these types of laser on the root structure. Similarly, the same precautions must be taken around osseous tissue. On the other hand, there is minimal to no interaction of these types of laser with healthy dental hard tissue. This property of diode and NdYAG lasers makes them suitable for soft- tissue procedures. The laser beam is conducted through an optical fi ber, which is used ‘ in contact ’ with the target tissue. However, a noncontact mode may be employed when attempting any hemostasis. Although diode and Nd:YAG lasers have similar interactions with hard and soft tissues, they differ in their emission mode. The Nd:YAG is a free-running pulsed laser, with very-short-duration pulses and an emission cycle (ratio of ‘ on ’ time to total treatment time) of < 1% and correspondingly very high peak power per pulse (in the order of 100 – 1,000 W). All diode lasers can be used in a continuous-wave mode, in which there is a constant emission of laser energy. In addition, they can operate by producing pulses, although with larger emission cycles and signi fi cantly less peak power than the Nd:YAG laser. Thus, the clinician must be aware of the heat that could be pro- duced in the target tissue by each of these types of laser. For initial periodontal therapy, these lasers are used for inactivation of bacteria and removal of in fl amed soft tissue from the periodontal pocket or from around the implant sulcus, as well as for achiev- ing hemostasis in acutely in fl amed tissue. These pro- cedures employ relatively low average power, which are usually below that used for surgery. Regarding use of the Nd:YAG laser in implant ther- apy, two studies suggest that the free-running pulsed Nd:YAG laser is contraindicated for treatment of tita- nium implant surfaces because the high peak power, as well as the moderate re fl ection rate of this laser from titanium metal, easily causes melting of the metal surface, as reported by Romanos et al. (99) and Schwarz et al. (108). However, Gonc ß alves et al. (41), in an in vitro study, used an Nd:YAG laser in noncon- tact mode with a longer pulse duration and demon- strated no damage to these titanium surfaces. The difference in the results of these studies was caused by the irradiation parameters. Romanos et al. (99) employed a contact mode with a very short pulse duration of 100 microseconds and higher average power, and Giannelli et al. (39) used a pulse duration approximately 10 times longer (1 millisecond). This latter study demonstrated the ability of low-energy Nd:YAG laser irradiation to suppress experimentally induced in fl ammation from contaminated implant surfaces without affecting the surface morphology of those implant fi xtures. In general, an Nd:YAG laser must be used with caution, and attention must be given to the irradiation parameters and to the laser beam placement.
CO 2 laser
CO 2 lasers employ photonic energy in the far-infrared spectrum (wavelength 9,300 – 10,600 nm). Compared to any other dental wavelengths, they have the high- est absorption in dental minerals, such as hydroxyap- atite and calcium phosphate, and must be used with some care during periodontal soft-tissue procedures in order to avoid direct contact with hard tissue. The penetration depth into soft tissue is relatively shallow (approximately 0.2 mm) (77). In an identical manner to diode lasers, CO 2 lasers can be used in a continuous wave or pulsed. Their peak powers can approach 200 W, so they are very ef fi cient at soft-tissue removal. The laser beam is focused on the tissue without direct contact, which differs from the approach of the fi ber optic system of a diode. Some accessory tips are employed to direct the energy into the periodontal pocket. CO 2 lasers have similar soft tissue applications for periodontal therapy as the diode and Nd:YAG wavelengths. These applications include bacterial reduction, debride- ment of diseased soft tissue in pockets and around implants, and coagulation.