Lasers in Dentistry: Overview and Perspectives

Biostimulation and Healing Effect of Laser Radiation

Low-level laser therapy is defined by specific characteristic parameters of the laser source, a value of power within the range of 10⁻³–10⁻¹ W, and a wavelength in the interval where the radiation is not absorbed by the water. Therefore, laser systems such as helium-neon, argon, and krypton, and mainly semiconductor laser diodes, including gallium arsenide and gallium aluminum arsenide, can be used in this case. The main applications are wound healing after tooth extraction, temporomandibular joint rehabilitation, soft-tissue healing, herpes labialis, glossodynia, and angular cheilitis. Laser radiation directly influences healing stimulation and pain reduction. The anti-inflammatory, analgesic, and biostimulative effects were also confirmed. ^1,2

Lasers in Periodontal Procedures

Lasers have the potential advantages of producing a bactericidal and detoxification effect, and also of removing the epithelium lining and granulation tissue, which are desirable properties for the treatment of periodontal pockets. ³ Some lasers may be capable of effective removal not only of dental plaque but also of calculus from the root surface. This causes extremely low mechanical stress, and, therefore, a smear layer is not formed on the treated root surface. ⁴ The Er:YAG laser is a useful tool for debriding safely and effectively both the root surface and gingival tissue of the periodontal pockets, and the Nd:YAG, diode, and argon lasers have a potential for soft tissue curettage and disinfection of periodontal pockets. The alexandrite and Er:YAG laser has also shown highly promising results for use in selective calculus removal. ³

Bone and Soft Tissue Laser Therapy

The radiations of some lasers reduce bleeding intra-operatively and lead to the patient feeling less pain postoperatively. ⁵ Visible wavelengths generated by argon or KTP lasers are absorbed and scattered in the same proportion at the peak value of the hemoglobin absorption curve; therefore, these lasers have superficial penetration from 0.1 μm to 1 mm, and very good hemostatic effect on treating vascular lesions (i.e., hemangiomas). The absorption in water is minimal. Such lasers as the semiconductor, Nd:YAG or Nd:YAP are commonly used for cutting, vaporization, and decontamination of soft tissue. The laser indications are: papilloma, fibroma, hemangioma, venous lake, cysts, ulcers, herpes labialis, epulis, pyogenic granuloma, gingivectomy, and frenectomy. ⁶ Laser radiation can also be of assistance in treating dental trauma. The Er:Cr:YSGG, Cr:Tm:Er:YAG, or Er:YAG lasers, and the far-infrared CO₂ provide more efficient ablation whenever healthy or minimally pigmented and vascularized tissue is treated.

Treatment of Dentin Hypersensitivity by Laser Radiation

Dentin hypersensitivity is characterized by short, sharp pain arising from exposed dentin as a response to stimuli typically thermal, evaporative, tactile, osmotic, or chemical, which cannot be ascribed to any other form of dental defect or pathology. The lasers used for treating dentin hypersensitivity are divided into two groups: low-level continual lasers (such as He-Ne or GaAlAs lasers), and lasers with higher power (Nd:YAG or CO₂ lasers). Low output power laser therapy has an anti-inflammatory effect and stimulates nerve cells. The mechanism of Nd:YAG and CO₂ laser is the narrowing of dentinal tubules as well as direct nerve analgesia. ⁷

Photoactivated Dye Disinfection Using Laser Radiation

This technique is effective in killing bacteria in complex biofilms such as subgingival plaque and carious lesions, as visible red light transmits well across dentin. The photoactivated dye technique can be undertaken with a range of visible red and near infrared lasers and systems using low power (100 mW) He-Ne or visible red semiconductor diode lasers. The major clinical applications include disinfection of root canals, periodontal pockets, deep carious lesions, and sites of peri-implantitis without thermal effects. ⁸ The dye tolonium chloride can also be used in high concentrations for screening patients for malignancies of the oral mucosa and oropharynx.

Lasers in Endodontic Procedures

Endodontics deal with the treatment of root canals in teeth, in which, because of advanced decay, the tooth crown is destroyed. Laser radiation can reduce 99% of microbial pathogens during the endodontic treatment. ⁹ The organic substances are completely removed, and coagulation of proteins in the dentinal tubules is reached. ¹⁰ Laser radiation can remove the smear layer. Many types of laser radiation appeared to be useful for this procedure, namely Er: YAG, argon, KTP, Ho:YAG, and Nd:YAG laser irradiation. ¹¹ Dentin permeability was reduced after CO₂ laser irradiation. Root canal orifices are prepared by using an Er:YAG laser; the Er:YAG laser can cut hard dental tissues without significant thermal or structural damage. ¹²

Early Caries Diagnostics

Lasers with the low power and wavelength in the visible region can be used for early caries detection. The red radiation from the semiconductor diode laser or blue lights (488 nm) from the argon laser penetrate carious lesions where bacterial byproducts, including porphyries with a strong fluorescence signal, are accumulated. The lack of fluorescence from carious enamel and dentin demonstrates the presence of the caries lesion. ¹³

Laser Procedures on Hard Dental Tissues

The CO₂ laser can modify the fissure system to increase its resistance to future carious attack, for microdentistry preparation and fissure sealing, and to increase the preventive fluor content in enamel. ⁷

The Er:YAG, Er:YSGG, and Er:Cr:YSGG lasers ⁸ wavelengths correspond to the peak absorption range of water in the infrared spectrum, and can be used for effective caries removal and cavity preparation without significant thermal effects, collateral damage to tooth structure, or patient discomfort. Er-based dental lasers can also be used to remove composite resin and glass ionomer cement restorations, and to etch tooth structure. ¹⁴

Photodynamic Therapy in Soft Tissues

A more powerful and more efficient laser-initiated photochemical reaction is based on photodynamic therapy employed in the treatment of malignancies of the oral mucosa. Laser radiation absorbed in proper molecules causes the singlet oxygen generation that destroys the bulk of tumor cells, activates the host immune response, and promotes antitumor immunity through the activation of macrophages and T lymphocytes. The ulcerated lesions typically take up to 8 weeks to heal fully, and supportive analgesia is required in the first few weeks.

Other Photochemical Laser Effects

The argon laser produces high intensity visible blue light that can initiate photopolymerization of light-cured dental restorative materials. Argon laser radiation also reduces the probability of recurrent caries. ¹⁵

Laser Bleaching

The term “bleaching” signifies chemical destruction through groups of the chromophore compounds. Power bleaching has resulted in easy-to-use bleaching agents, essentially using highly concentrated hydrogen peroxide mixed with thickening agents or additional buffering agents, catalysts, or coloring agents. ¹⁶ The energy source can be derived from blue-colored halogen curing lamps, infrared CO₂ lasers, and blue-colored plasma arc lamps as well as the cool blue argon and GaA1As lasers.

Laser and Composite Resin Adhesion

Many studies have concluded that adhesion to laser-ablated or laser-conditioned dentin and enamel of permanent teeth is inferior to that of conventional rotary preparation and acid etching. ¹⁷ Microleakage in cavities prepared by laser is less than in mechanical bur-prepared cavities. ¹⁸ Porcelain veneers or bracket can also be removed using laser radiation (laser debonding). ^19,20

Laser Applications in the Dental Laboratory

Laser holographic imaging is a well-established method for storing topographic information, such as crown preparations, occlusal tables, and facial forms. Laser scanning of casts can be linked to computerized milling equipment for fabrication of restorations from porcelain and other materials. A variation on this theme is ultraviolet He-Cd (helium-cadmium 325 nm) laser-initiated polymerization of liquid resin in a chamber, to create surgical templates for implant surgery and major reconstructive oral surgery. These templates can be coupled with laser-based positioning for complex reconstructive and orthognathic surgical procedures. ²¹

Laser welding can be used in practice in prosthodontics and orthodontics. ²²

Advantages of Dental Laser

The use of a laser instead of a classical dental handpiece in dentistry has many advantages, including the absence of pressure, vibration, noise, or significant pain. The procedures can be performed without anesthesia. Various studies and clinical reports have shown how the laser, when used as an alternative to rotary instruments in dentistry, brings an added measure of safety when used in the treatment of patients. Moreover, the use of laser radiation offers a new possibility for minimally invasive tissue interventions and overall better patient acceptance than that found with traditional techniques.