Diode lasers (wavelengths 500- 1064) are probably the least expensive lasers and most commonly used in several different capacities. Therapeutic use in periodontology is dependent on wavelength used and how it is used, but there are essentially four fundamental actions. Firstly, they can be used as a’ cutting tool’; secondly, as a bactericidal device; thirdly in photodynamic therapy, where the diodes affinity to pigment activates an antibacterial agent; and lastly in the administration of low level laser therapy. Because diodes can be used in several different ways, reading the literature can be misleading unless you have a basic understanding of mechanisms and doses. For the purposes of this summary, we’ll divide the diode wavelengths into a sub-classification of low level lasers (500-700nm), and surgical diodes (800-1064nm.)
Diodes are essentially soft tissue lasers, with an effect on hard tissues in their ability to desensitise and penetrate into dentinal tubules to kill bacteria. These lasers do no emit energy as a free running pulse; they work through a continuous wave of laser energy, and dependent on the machine, this wave of energy can be turned on and off (or pulsed), with different intervals (duty cycles). The advantage of pulsing is to allow tissues a cool down period. For example, the diode may be set at 2W with a duty cycle of 50% – this translates as being able to cut the tissue using a peak power of 2W, but the average power is in fact 1W, thus potentially avoiding overheating and carbonising tissues. However, if the average power is too low, the cutting time needed becomes too long, and heat build-up is an inevitability. When used as a ‘cutting tool’ on non-pigmented (pale) or vascular tissue, the tip needs to be initiated. This is a process of placing the tip in contact with pigment, such as on articulating paper or through a cork. If the tip is initiated effectively and efficiently, then the wavelength being used is not actually so relevant; the cutting occurs due to a photo-thermal interaction, and from a very hot tip. The temperatures they are able to reach are so high, that care must be taken around delicate anatomical structures such as salivary glands, bone, tooth and implant surfaces. Also, if too much heat is accumulated in the target tissue, then post-operative shrinkage can be a problem, as well as delayed and more painful healing.
The primary chromophores for diodes are melanin and haemoglobin. Absorption in melanin decreases with longer wavelengths, while absorption in haemoglobin increases. That means that an 810nm may work faster on pigmented tissue, and a 980nm diode may work faster in vascularised tissue. 940nm diodes are in the middle of these two. Also as wavelength increases towards 980nm, so does the absorption in water. This can have several implications: tissue vaporisation is more effective resulting in a faster excision, but at the same time, this can lead to quicker dehydration and then carbonisation; as absorption in water increases, then penetration depth through tissue decreases, which may mean that the higher wavelengths may not be as bactericidal at greater depths and the low lever laser effects at a distance from the point of contact may not penetrate as far. Penetration depths can be as high as 4-6mm. It is essential to understand these tissue interactions and the capabilities of the machine and tip initiation to get the best out of your diode laser in the safest way.
Safety aspects to be aware of are the potential to damage the eyes up to a distance of 4.6m, so it is essential to wear the correct protective eyewear for the wavelength used. Due to the heat produced, there is a risk of burning soft tissues, bone necrosis, and damage to root surfaces and pulp. Implant surfaces, unlike with Nd:YAG lasers, are not actually damaged by diodes, but the heat build-up would lead to increased bone temperatures over the critical temperature of 47ºC, and can therefore lead to necrosis. Potential risks if used incorrectly therefore include laser-induced oral mucositis, bone sequestration, loss of vitality and burns. Training in their safe and effective use is essential.
Diode use for periodontal disease can have several actions. Firstly, they are bactericidal with the ability to penetrate deeply into tissues, and disinfect pockets. At the same time their affinity for pigment, makes them particularly useful in killing pigmented periodontal pathogens within the pocket. The low lever laser energy has an anti-inflammatory effect, where studies have demonstrated faster healing and reduced bleeding on probing through just the application of low level laser energy after treatment. They are all helpful tools in the management of hypersensitivity. The low level energy may have an effect on pulpal nerve endings, reducing their reactiveness. At higher levels of power, the heat produced will melt the dentinal tubules and seal them off. All this can and should be done with uninitiated tips. Diodes can be used for implant surface decontamination in the management of peri-implantitis, but care is needed particularly in a flapless environment due to the increased risks of overheating. Once flapped, granulation tissue and mechanical debridement of the implant surface needs to be carried out by other means. Erbium lasers can be useful here. Diodes are not suitable to raise flaps for the management of periodontal pockets, but can be used for additional decontamination of the surgical site, with or without a photosensitizer (dye).
Once a tip is initiated, it can be used to remove the diseased pocket lining as well as outer epithelium. Obviously great care is needed in this process to direct the tip away from the root surface, and not to spend too long in the pocket to avoid overheating. Using cooling air and high volume aspiration are also helpful. Also, it is worth pointing out here, that once in contact with blood, a tip will initiate so regular removal from the pocket and cleaning of the tip to remove coagulated tissue also helps to control the environment.
Other uses on soft tissues
The bloodless cut produced by diode lasers can be carried out with minimal anaesthesia. They are effective for any kind of excisions, including but not limited to gingivectomies, gingivoplasty, soft tissue crown lengthening (as long as biological width is not violated, or bone removal can be carried out using erbium lasers), vestibular deepening, fibroma and granuloma removal, operculectomy, hyperplastic tissue removal. Due to their affinity to pigment, gingival depigmentation works very well with diodes, as does the shrinkage or removal of haemangiomas in a much safer way than conventional surgical removal which would lead to considerable bleeding. Speed of cut is considered acceptable, but a diode should not be compared directly with a scalpel blade due to the additional benefits a blade cannot provide, such as coagulation, less pain, simultaneous disinfection of the wound site to name but a few advantages. Sutures are not required for any of these procedures. Healing is through an initial inflammation associated with surgery, followed by a rapid resolution, and typically takes 1-2 weeks. If used for biopsy, the histo-pathology form should be filled in indicating that the tissue was removed using laser.
Diodes are not suitable to raise flaps, full or partial thickness, and not ideal in grafting procedures to harvest grafts or preparing the recipient bed or tunnel as blood is essential here. However, they can be used to coagulate the palate when tissue is taken for a free gingival graft, and in a photo-biomodulatory way to accelerate healing of the donor site and integration of the grafted tissue through the use of low level laser therapy. They are also very helpful in accelerating the healing of and pain relief from oral ulceration, herpetic lesions, angular chelitis and Lichen Planus.
They are relatively cheap in comparison to other lasers, as well as being inexpensive to run and very reliable, but this can depend on manufacturer. The learning curve is considered moderate, patient acceptance good, and it can be an indispensable tool.
A few final personal comments from our contributor, Mark Cronshaw:
Can you comment on how you as a clinician have found the use of this laser wavelength to be an advantage to your clinical practice:
- Many clinical procedures are easy to carry out and I can do more of them
- Time taken to carry out procedures reduces complexity, better outcome= saves time
- The results obtained by incorporating lasers are very good indeed
- Increased practice revenue – if so – how/ why? Additional procedures, enhances prestige of practice = added value product
Low Level laser Therapy (LLLT)
The other group of diodes, also referred to as low level lasers, have wavelengths that fall generally between 500-700nm. They are used with very low powers and are used for photo-biomodulation (PBM) or activation of photo-sensitizers such as toluidine blue, methylene blue, or indocyanine green. These photosensitizers attach to micro-organisms and release singlet oxygen atoms which are toxic and kill the bacteria. They can therefore be useful in both periodontal pockets and in the management of peri-implantitis.
The process of photo-biomodulation occurs through the absorption of low levels of penetrating energy by the organelles of cells, particularly the mitochondria, the power house of the cell, which produces adenosine tri-phosphate (ATP). This has an up-regulation effect on the intracellular metabolism, so cellular effects include increased cell proliferation, increased phagocytosis and chemotaxis, increased cytokine production, increased vasodilation, blood flow and lymphatic drainage, with the promotion of healing. Studies in periodontology have demonstrated at the correct doses, LLLT can stimulate the proliferation of periodontal fibroblasts and differentiation of periodontal ligament stem cells, and in vivo have been tested for their possible use in promoting periodontal regeneration. (Choi et al 2010 35; Soares et al 201336, Sadighi 201237, Emrem Dogan et al 2014 38)
Studies by Qadri et al(39) and Aykol et al(40) measured a statistically significant improvement in PPD, CAL and gingival inflammation in test groups treated with the low level Diode laser at a dose in the range 2-5J/cm2 In vitro and in vivo animal studies demonstrate that there are effects on the expression of IL-1, IL-6, IL-8 and TNF-α all of which are suppressed by PBM. In consequence PBM could prove of value in promoting healing and reducing inflammation as well as alleviating post-operative pain. The clinical studies of Aykol and Qadri however show only a small improvement in clinical parameters and the adjunctive value of this interesting treatment strategy have yet to be proven.
Low level laser effects on cells
Transformation into myofibroblasts
Reduced secretion of PGE2 and IL-1
Enhanced secretion of BFGF
Secretion of fibroblast growth factors
Increased granulation tissue
Relaxation of vascular smooth muscle
Reduced synthesis of inflammatory mediators
Maturation and regeneration
Depigmentation with uninitiated tip – before, immediate post-op and 3 weeks later (Dr Bassam)
Before and one month after surgical depigmentation using 940nm diode (Walid Al-Tayeb)
Crown lengthening and depigmentation using 980nm diode with 5 year follow up (Walid AlTayeb)
Gingival recontouring and depigmentation using diode with 3 year follow up (Walid Al-Tayeb)
Crown lengthening and veneer placement using 940nm diode and chisels for the bone removal (Walid Altayeb)
Periodontal Pocket Decontamination using 810 diode, uninitiated tip (Ilay Maden)
Periodontal pocket decontamination using 940nm diode with uninitiated tip (Mark Croshaw)
Aphthous ulcer before and 24 hours after LLLT with diode (Ilay Maden)
Coagulation of wound site (Ilay Maden)