Abstract
Over the years, the use of the laser within health fieldand more particularly dentistry has been increasing andimproving. The application of laser in the periodontaltreatment takes part of a non-surgical and surgicalapproaches, is used for the decontamination of perio-dontal pockets due to its bactericidal effect, and theremoval of granulation tissues, inflamed and diseasede pithelium lining, bacterial deposits and subgingivalcalculus. However in spite of all the marketing surround-ing, the use of laser highlighting its beneficial effect, thecapacity of laser to replace the conventional treatmentfor chronic periodontitis is still debatable. In fact thereis no evidence that any laser system adds substantialc linical value above conventional treatments of chronicp eriodontitis. Some studies showed a significant positiveeffect on clinical attachment level gain and probingdepth reduction. In the other hand, several articlesdemonstrated no evidence of the superior effectivenessof laser therapy compared to root planing and scaling.Our aims is to review the literature on the capacityof erbium:Yttrium-aluminum-garnet and neodymium:Y ttrium-aluminium-garnet laser to either replace orcomplete conventional mechanical/surgical periodontaltreatments.

NTRODUCTION
Chronic periodontitis is defined as inflammation of the gingiva extending into the adjacent attachment apparatus. The disease is characterized by loss of clinical attachment due to destruction of the periodontal ligament and loss of the adjacent supporting bone
[1].Clinical findings include attachment loss, gingival recession, alveolar bone loss and pocket formation.Although chronic periodontitis is the most common form of destructive periodontal disease in adults, it can occur over a wide range of ages. It usually has slow to moderate rates of progression, but may have periods of rapid progression. Clinical features may include combinations of the following signs and symptoms: Edema, erythema, gingival bleeding upon probing, and/or suppuration
[1]. The development ofperiodontitis appears to be associated with a shift from a predominantly Gram-positive flora to a predominance of anaerobic Gram-negative rods
[2].Several characteristics can be observed in contami-nated periodontal pockets. Usually, biofilm deposits,calculus and bacterial endotoxins infiltration into the cementum of root surfaces are reported. Mechanical scaling and root planning with manual and/or ultrasonic instruments represents the initial phase of periodontal non-surgical therapy. However, this therapy is not always effective for complete removal of bacterial and their endotoxins deposits. In fact, complex root anatomy makes access to areas such grooves and furcations difficult
[3]. Although systemic and local administration of antibiotics into periodontal pockets is occasionally effective for disinfection, but risk of producing resistant microorganisms limits this approach.

Furthermore, conventional mechanical therapy is often uncomfortable for both patients and operators.Indeed, this time - consuming technique depends on the operator’s dexterity. The power and the curette’s angulation vary form one operator to another and can give totally different results. In addition, noises and vibrations of ultrasonic instruments are often source of stress and fear in some patients. All these constraints led searchers to explore other therapeutic approach to replace or complete the conventional periodontal mechanical therapy, such as lasers. Recently, the appli-cation of laser - assisted treatments for removal of granulation tissues, inflamed and diseased epithelium lining, bacterial deposits and calculus has been proposed as alternative or as adjunctive treatment to the more conventional periodontal mechanical therapy The word Laser is the acronym for light amplification by stimulated emission of radiation. Lasers can be distin-guished from other light sources by their coherence,allowing lasers to be focused to a tight spot.
Since Albert Einstein’s theory of stimulated emission of electromag-netic radionation and Maiman’s first functioning laser using a synthetic ruby crystal in 1960, laser research has produced a variety of improved and specialized laser types, optimized for different application such as dentistry. In fact dental lasers are recognized today for their ability to ablate hard and soft tissues, to reduce bacteria counts and even to provide hemostasis of soft tissues during their use with minimal anesthesia Lasers used in dentistry emit wavelengths between 377 nm and 10.6 µm. The most common types are CO2,diode, erbium:Yttrium-aluminium-garnet (Er:YAG) and neodymium:Yttrium-aluminium-garnet (Nd:YAG) lasers.
The use of lasers in periodontal therapy has evolved since a laser for periodontal applications was first introduced in 1985. Initially, most articles that advo-cated the use of lasers for soft tissue surgery were anecdotal. Nowadays, it appears that research in soft tissue applications is increasing exponentially, and the claims of decreased bleeding, swelling, pain, and bacterial populations are being referenced in several publications
Four types of interactions may occur when biologi-cal tissue is irradiated with laser light: Reflection,scattering, absorption, or transmission. Basically, the reflection, scattering and transmission decrease, as the absorption increases. The type of interaction that takes place depends on the wavelength of the laser.For most biological tissues, higher absorption occurs in wavelengths with greater absorbance in water. The lasers with greater absorbance in water are the Er:YAG lasers. Erbium radiation is readily absorbed by most tissues, and this translates into less penetration and a shallower layer of laser-affected tissue.
Laser irradiation exhibits strong ablation, hemostasis,detoxification and bactericidal effects on the human body.These effects can be useful during periodontal treatment,especially for handling of the soft tissue as well as for the debridement of diseased tissues. Thus laser treatmentmay serve as an alternative or adjunctive therapy to mechanical approaches, in periodontal therapy. However,the high cost of laser equipment and the lack of reliable clinical research are a significant barrier for the laser utilization by the dentist. Also, each laser has different characteristics because of their different wavelengths.
Thus the operator must be aware of the possible risks involved in clinical applications, and precaution must be exercised to minimize these risks when performing laser therapy. The most important precaution in laser surgery is the use of glasses to protect the eyes of the patient,the operator and the assistants. Protection of the tissues surrounding the target is also recommended. Second,thermogenesis during the interaction of the laser with the tissues must be addressed and well controlled
.In lasers that exhibit deep-tissue penetration, such as the Nd:YAG, the thermal injury to the pulp tissue and underlying bone tissue can be a concern during treatment. Also, a root surface that has received major thermal damage could render the tissue incompatible for cell attachment and healing. During treatment of hard tissue, the use of water spray can minimizes heat generation by cooling the irradiated area and absorb-ing excessive laser energy. Therefore, thermal injury must be prevented by using irradiation conditions and techniques that are appropriate for the lasers used. In addition, in periodontal applications, there exists the risk of excessive tissue destruction as a result of direct ablation and the possibility of thermal side effects in periodontal tissues during irradiation of periodontal pockets. Improper use of lasers could cause further destruction of the intact attachment apparatus at the bottom of the pocket wall as well as excessive ablation of root surfaces and the lining of the gingival crevice dental laser tips
[4].Damage of the tooth surface should also be avoided during irradiation with Er:YAG lasers, as the enamel and dentin easily undergo melting, carbonization or ablation by these types of lasers. Thus, in order to use lasers safely in clinical practice, the practitioner should haveprecise knowledge of the characteristics and effects of each laser system and their performance during application, and should exercise appropriate caution during their use
[4].The aim of this study is to review the literature on the effectiveness of Er:YAG and Nd:YAG lasers in periodontics, as either a complete treatment or as an adjunctive treatment. We performed a review of the recent literature in Pubmed and Mesh databases.
Despite of all the potential beneficial effect of lasers in periodontics, the ability to replace or even add on to our conventional periodontal treatment is still doub-tful. Further studies are needed to determine laser effectiveness for root scaling and planing, calculus removal, bacterial decontamination and specially,randomized clinical trials performed by independent researches are essential to demonstrated the real role that lasers can play in the management of ours periodontal patients.