Dental Lasers (review)
In 1975 surgeons started to use a laser as a new addition to the scalpel and in some cases instead of the scalpel. In 1980-s the CO2 laser became a regular tool in the operating room. In 1989 the first laser for dentistry was developed and soon became affordable. Today, it’s one of the most thrilling achievements in dentistry with unique advantages for patients.
The laser radiates light with two important characteristics that distinguish it from ordinary light: monochromaticity and coherence, which means that all waves are identical in size and shape. This monochromatic, coherent light emerging from the laser device is a unique efficient source of energy. Lasers are classified by the active medium contained in the resonator. It consists of chemical elements, molecules or compounds and represents a gas, a crystal or a diode. Semiconductor lasers are called diode lasers, and the laser crystals are denoted by such abbreviations as Nd: YAG, Er, Cr: YSGG, or Er: YAG.
Laser Radiation Interaction with Tissue
Every special wavelength has a unique impact on a tooth structure due to the absorption of the laser energy by tissues. Some laser radiation is absorbed by blood and tissue pigments only, some by water and by hard tissues such as enamel, dentin and bones.
There are three groups of laser wavelength:
1. diode and Nd: YAG lasers: the wavelength is effective for target pigments in soft tissues and for pathogenic processes, as well as for inflammation and tissue vascularization.
2. (CO2) lasers easily interact with free molecules of water in soft tissues and vaporize intracellular water of pathogens.
3. Erbium lasers (Er, Cr: YSGG и Er: YAG) are universal tools for tissues; they have a short period of emittance and absorption by water in soft and hard tissues.
Laser radiation is absorbed by tissue, and this process activates in the tissue a thermal reaction. Depending on the tool parameters and the tissue optic properties, the temperature will rise stimulating various effects. Most of the nonspore-forming bacteria, anaerobic organisms included, are killed at the temperature of 50ºC, and the soft tissues inflammation due to periodontal diseases disappears at 60ºC. Besides, hemostasis can be achieved at the same temperature parameters. Soft tissue cutting is done at 100ºC; the intracellular and extracellular water evaporation causes ablation or biological tissue removal. The water component of the tooth and bone structure boils at this temperature. Thus, it is possible to continue the mouth cavity preparation and bone shape removal.
Laser operation modes
There are two main operation modes for dental lasers – continuous and pulse. The continuous wave means that the energy is generated without a pause while the laser is working. C2 and diode lasers work on the basis of this method. Mechanical and electrical control elements can produce short and strobe pulses at the output minimizing the loss of the laser energy. The autonomous pulse mode is produced with the help of a flash lamp generating pulses of decimilligrade of seconds. Nd: YAG, Er: YAG as well as Er, Cr:YSGG laser work in an autonomous pulse mode.
Modern dental lasers use various means to transfer laser energy to the place of application. Some of them, such as diode or Nd: YAG lasers, use flexible glass fibers of a small diameter to transfer laser radiation to the biological tissue. They are usually used in contact with the tissue.
Erbium and CO2 devices are placed inside a semi-stiff waveguide or in a jointed swinging construction; some erbium lasers have stiffer glass fibers. Some of these systems use stiffer glass fibers. Others use some additional quantities of quartz crystals or sapphire ends attached to its operational parts. Dental lasers remove micro-fissures and reduce the pulp temperature. They also eliminate bacteria and microorganisms in the surgical field.
Though the erbium laser is helpful for tooth preparation and caries treatment, it cannot remove the gold or glazed porcelain and is not very effective to interact with amalgam or enamel removal.
Types of Dental Lasers
Dental lasers have been used in modern practice for quite a long time. Laser devices significantly expand the abilities of traditional tools and make treatment less traumatic and less painful. The fields of application and efficiency of dental lasers depend on the laser beam parameters determined by the laser type.
The argon laser (488 nm and 514 nm wavelength). The laser radiation is well absorbed by melanin and hemoglobin. A wavelength of 488 nm is similar to that of polymerization lamps. At the same time, the rate and degree of polymerization of light-hardening materials are much higher. In surgery, the argon laser ensures perfect hemostasis.
The Nd: YAG (Neodymium) laser (1064 nm wavelength). The laser radiation is well absorbed in pigmented tissue and worse in water. Used to be very popular in dentistry but now is replaced by more multi-purpose erbium, diode and combined systems.
The He-Ne (Helium-neon) laser (610–630 nm wavelength). The laser radiation easily penetrates tissues and has a photo-stimulatory effect. This laser is widely used in physiotherapy and is the only one publicly available.
The CO2 (Dioxide carbon) laser (10600 nm wavelength). The laser radiation is well absorbed by water and moderately in hydroxyapatite. This laser is potentially dangerous for hard tissues because of possible bone and enamel overheating. It has excellent surgical characteristics. Today, CO2 lasers have given way to multi-purpose systems.
The diode (semiconductor) laser (792–1030 nm). The laser radiation is well absorbed in pigmented tissue, has a good hemostatic, anti-inflammatory and repair stimulating effects. Is used in endodontics and paradontology for conservative and surgical treatment of teeth and gums disorders, as well as for teeth whitening. Today, the diode laser is the most affordable in terms of price and functionality.
The erbium laser (2940 and 2780 nm wavelength). The laser radiation is well absorbed by water and hydroxyapatite. It’s the most prospective laser in dentistry. Suitable for work with hard and soft tissues. Does not have the drawbacks of its precursors. Has a wider range of application, fully in line with the list of dental disorders. Erbium systems have modifications. For example, the Er Cr: YSGG (erbium, chrome: yttrium-scandium-gallium garnet) with a wavelength of 2780 nm, patented by the American company Biolaser, allows treating practically any dental disorders with maximum comfort for the patient.
Erbium lasers are commonly used for:
• Preparation of cavities of all classes, caries treatment.
• Treatment of enamel.
• Root canal sterilization, treatment of the apical site of infection.
• Pulpotomy.Treatment of parodontal pockets.
• Exposition of implants. Gingivotomy and gingivoplasty.
• Mucosa treatment.
• Reconstructive and granulomatous lesions.
• Operative dentistry.
In dentistry, the СО2 laser is mostly used for soft tissues treatment, while the erbium laser is used to treat hard tissues.
Laser modes and parameters.
• pulse, power/pulse mJ/pulse.
• pulse (up to 50 mJ/мм2)
• continuous (1-10 W)
The mechanism of the СО2 laser effect on soft tissues is based on the laser light energy absorption by water and on tissues heating. This allows to remove soft tissues layer-by-layer and coagulate them with the minimal (0,1mm) zone of thermonecrosis and carbonization of the nearby tissues.
The mechanism of the erbium laser effect on hard tissues is based on «mini explosions» of the water inside enamel and dentin when heated by the laser beam. The absorption and heating process leads to water evaporation, mini destruction of hard tissues and removal of the solid fragments from the zone of exposure by the water vapor (fig.2). For tissue cooling, a water-air spray is used. Due to the minimal laser energy absorption by hyroxiapatite – a mineral component of chromophore – the nearby tissues heating does not exceed 2оС.
Two ways of laser application is used:
1. Small neoplasms (less than 0,3 cm) are removed using ablation (2 – 4 W, a continuous or repetitively pulsed mode with a 500-1000 ms pulse duration and a 100-500 ms pause duration.
2. Big neoplasms (bigger than 0,3 cm) are removed using laser excision ( 3-5 W, a continuous and repetitively pulsed mode with a 1000 – 2000 ms pulse duration and a 100-1000 ms pause duration.
The laser scalpel can be used to remove practically any kinds of benign tumors of the mouth cavity and lips, including tumor-like lesions (reticular cysts), to surgically treat patients with periodontal diseases, hypertrophic gingivitis, anatomical and topographical structure features of the oral cavity soft tissues, and with diseases of the oral mucosa.
Laser whitening procedure
The laser whitening procedure starts with professional teeth cleaning and removal of plagues. After that, a special whitening gel is applied to the enamel and the teeth are exposed to the diode laser beam. It activates the gel performance evolving active oxygen. It penetrates deep into the enamel and oxidizes the surface pigmentation, as well as neutralizes deep teeth staining. This procedure enables to lighten the teeth color by 8-12 tones. The result remains the same for many years. After laser whitening, it is recommended to refrain from consuming of “staining” food, as well as from too hot and too cold meals and drinks for a few days.
Advantages of laser teeth whitening
• No pain. The laser beam operates locally and by pulses, that is why thermal damage of gums and discomfort are excluded.
• Efficiency and comfort. The session of laser teeth whitening lasts about 30-40 minutes. This amount of time is enough to significantly lighten the enamel.
• Long-lasting result. The deep effect of active oxygen together with the unique splitting properties of the beam makes it possible to achieve persistent whitening that lasts for more than 10 years with proper dental care. A few years later, the enamel may darken, but the color of the teeth will not become the same as before the whitening procedure.
• Safety. The mechanism of the laser system operation provides an accurate selection of the intensity parameters and time of exposure. The dentist can precisely control the process. The soft laser effect neither increases the enamel sensitivity nor damages the integrity of its structure.
• Enamel strengthening. The laser beam has bactericidal properties, due to which it helps cope with caries and strengthen enamel. Patients’ reviews confirm this fact. Many of them mention the teeth sensitivity reduction after laser whitening.
Laser teeth restoration
The research center of Harvard’s Wyss Institute undertook a successful experiment in dentin restoration – the mineralized tooth tissue, which is the tooth basis. The scientists filled the holes drilled in mice’s and rats’ molars with a plugging material containing stem cells and exposed them to the laser light to activate the regeneration process.
With this laser therapy method tissue is treated with small doses of laser light (low-intensity laser therapy). Earlier, this kind of low-intensity light therapy was used to remove hair or stimulate its growth and for skin cells rejuvenation.
12 weeks later the research results confirmed that the laser treatment had stimulated dentin formation in the teeth holes out of the stem cells from the plugged material. It’s worthwhile mentioning that the dental treatment in rats is much more complicated than in humans.
The scientists say that this laser therapy will hardly help grow teeth, but it will suit to fill root canals and treat patients with sensitive teeth.