Laser Fundamentals

LASER is an acronym, meaning Light Amplification by Stimulated Emission of Radiation. The first laser was demonstrated in 1960 (The Nobel Prize for the first laser was awarded to both Russians and Americans), and their first use in dentistry was in 1964 by Leon Goldman but was not successful. As time has passed, the laser-tissue interactions have been studied at greater depth and with greater understanding, to the degree nowadays, that lasers in dentistry are starting to be used both more safely and effectively.

A laser is generally named after the active ions or active media; for example, an Nd:YAG laser has an active ion of Neodynium and the host material is Yttrium Aluminium Garnet. The active media can be gaseous, as in CO2 lasers; solid states, such as an Erbium: Yttrium Aluminium Garnet crystal; or semi-conductor structures, as is the case with diode lasers. . Dental lasers can be classified in many ways. They are sometimes referred to as soft tissue lasers, incorporating those that can only ‘cut’ soft tissue, and hard tissue laser, but these in fact are able to cut both soft and hard tissues very well. Another term used is hot and cold lasers, the latter having a water spray and therefore being effective and safe to use on teeth and bone as well as soft tissue. Another different classification of cold lasers is in Low Level Laser Therapy (LLLT) devices used for various bio-stimulatory applications within or outside of dentistry.

Laser tissue interactions

Each laser has a different wavelength. This is one aspect of a laser that generally cannot be altered, and is instrumental in giving the laser its unique properties in terms of tissue interactions. Laser wavelengths used in dentistry range from the visible to the far infrared in the electromagnetic spectrum (500um to 10600nm). Each laser wavelength will be absorbed by certain chromophores in tissues, and it is the peaks in absorption that translate to the clinical properties we can then achieve with each wavelength. So, for example, Erbium lasers (which generate at 3 micrometers wavelength range) have a high absorption in water (the chromophore), which is present in both soft and hard dental tissues – this translates clinically as the erbium lasers having the ability to ‘cut’ or ablate these tissues. Conversely, Argon or diode lasers in visible spectrum have low absorption in water and no effect on hydroxyapatite, and are therefore ineffective on hard tissues, other than being able to heat them. However, they are very effective in haemostasis and on soft tissue due to their high absorption by pigment and haemoglobin. There is no one laser wavelength that is able to achieve all desired clinical effects, and therefore often multiple wavelength therapy is more the ideal.

Absorption is the most relevant laser tissue interaction effect. Along with absorption by chromophores within the tissues, and the depth of penetration through the tissue, we see different changes according to the temperature rise that ensues. These can be referred to as photo-thermal laser tissue interactions. As tissues warm up, but no visible change occurs, laser energy can be working at a cellular level, stimulating cell proliferation and increasing vasodilatation. This is a term known as low lever laser therapy, or photo-biomodulation, and is discussed more on the diode page. As temperatures continue to rise, bacteria are killed (most over 50º) and at 60º, proteins denature and coagulation occurs. With further rises in temperature (>100º) vaporisation occurs, which manifests as seeing tissues ablate (”cut”). Ablation is a two-step process of the removal of tissue through vaporisation and mechanical disruption. At 200º, tissues carbonise (Coluzzi 2004), which causes a delay in healing and increased post-op discomfort.

Absorption is the most relevant laser tissue interaction effect. Along with absorption by chromophores within the tissues, and the depth of penetration through the tissue, we see different changes according to the temperature rise that ensues. These can be referred to as photo-thermal laser tissue interactions. As tissues warm up, but no visible change occurs, laser energy can be working at a cellular level, stimulating cell proliferation and increasing vasodilatation. This is a term known as low lever laser therapy, or photo-biomodulation, and is discussed more on the diode page. As temperatures continue to rise, bacteria are killed (most over 50º) and at 60º, proteins denature and coagulation occurs. With further rises in temperature (>100º) vaporisation occurs, which manifests as seeing tissues ablate (”cut”). Ablation is a two-step process of the removal of tissue through vaporisation and mechanical disruption. At 200º, tissues carbonise (Coluzzi 2004), which causes a delay in healing and increased post-op discomfort.

Other effects of laser light on coming into contact with tissue include transmission – where the laser energy is not absorbed by the target tissue, and passes through. One use of this phenomenon may be caries detection. Laser light can be reflected if not absorbed – this has safety implications when using diodes for example, which are not absorbed by enamel, and so the laser energy is partially reflected back. The same applies to all dental laser wavelengths on amalgam, where they are not effective. Another effect is scattering, where the laser energy scatters into the tissues in all direction (including back scattering), and again, this can be useful in photo bio-modulation.

Laser Safety:

There are a few aspects to laser safety to be aware of. Firstly, all surgical dental lasers are classified as class IV, which means there is potential harm to the eyes which could cause corneal or retinal damage depending on the wavelength used and its penetration depth. It is therefore vital that all in the room – patients and operators, wear the correct protective eyewear for the chosen laser wavelength. A laser plume is produced when interacting with the target tissue. The composition of a laser plume can include steam, carbonised tissue, blood, potential viruses and bacteria, polycyclic aromatic hydrocarbons, benzene, toluene and formaldehydes. Therefore high volume aspiration should be used, and masks worn. There is a potential fire risk, so the laser should not be kept in close proximity to flammable gases. Lastly, but certainly not least, an important rule of laser safety is to use the lowest energy to achieve the desired outcome. In other words, avoid any collateral damage, and so with that, it is vital to be trained accordingly with whichever laser you choose to use, so that it is safe for your patients, yourself and your team.

Laser use in periodontics: wavelenghts, chormophores and classification

Laser Wavelength Chromophore Classification
Diode 810-1064nm Melanin, Haemoglobin Hot; soft tissue
Nd:YAG 1064nm Melanin, Haemoglobin Hot; soft tissue
Er,Cr:YSGG 2790nm Water, Hydroxyapatite Cold; hard  or all tissue
Er:YAG 2940nm Water, Hydroxyapatite Cold; hard or all tissue
CO2 9300 – 10600nm Water, Hydroxyapatite Hot or Cold; soft or all tissue

Benefits of using lasers for surgical procedures (as supported by the literature)

  • Changes tissue response pattern
  • Lack of traditional post-surgical effects and seals blood and lymphatic vessels
  • Laser will also decontaminate the surgical site both on tissue surface and to depth in target tissue (soft and hard tissue)
  • Biostimulation occurs, which speeds up mitochondrial metabolism resulting in faster tissue regrowth
  • Dry and bloodless surgery (good haemostasis)
  • Disinfection of surgical site
  • Reduced bacteraemia
  • Reduced mechanical trauma
  • Minimal postoperative swelling & scarring
  • Minimal post-operative pain

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