Lasers in Dentistry Part 3: Erbium Lasers

Laser Dentistry

Dr Ilay Maden BDS MSc PhD

Part 3

Erbium lasers

There are two different kinds of erbium lasers used in dentistry; Erbium-doped yttrium aluminium garnet (Er:YAG ) with a wavelength of 2940 nm and erbium, chromium: yttrium-scandium-gallium garnet (Er,Cr:YSGG) with a wavelength of 2790 nm. The absorbance of these wavelengths in water makes them the most appropriate lasers for dentistry. These lasers remove hard tissues like enamel, dentin, cement, bone and soft tissues through thermo-mechanical ablation. The energy is absorbed in water, causing micro-explosions and removal of surface material either through the water in the tissue (soft tissues) or the water spray accompanying the laser beam if there is not enough water in the tissue (hard tissues). One essential thing is that they are also absorbed in hydroxyapatite, making it possible to damage hard tissues with heat accumulation if there is not enough water on the hard tissue's surface. This interaction is especially important for Er,Cr:YSGG’s wavelength as it is less absorbed in water and more absorbed in hydroxyapatite compared to Er:YAG’s wavelength. Both wavelengths do not cause too much temperature rise on the soft tissues. They are not absorbed by haemoglobin or melanin, making them weaker soft tissue coagulators than the other lasers.

Lasers have been blamed for being too slow in removing hard tissues. However, technology has improved immensely compared to earlier days. Now dental laser devices are reaching up to 20Watts of power and 1000mJ of energy per pulse, removing enamel and dentine at least as fast as drills. Energy and power are essential parameters in effectivity, but pulse duration is an important variable for efficiency. Pulse duration is the time that the laser is transferred onto the tissue. The shorter the pulse duration, the more powerful the energy will be, and longer pulse durations cause more heat. Short pulses deliver several kilowatts of power in one pulse. One more crucial physical property is the speed of increase and decrease of the power for each pulse. Ideally, the quicker it reaches the peak power and drops down to zero at the end of the pulse, the better for maximum efficiency. Having the possibility to choose from more different pulse durations delivers flexibility for the practitioner to manipulate laser-tissue interaction. Short pulses (50-100µs) cause very little or no heat accumulation, creating very high peak powers, which can remove hard tissues. Longer pulses (250-1000µ) are better for soft tissue removal as they are less effective and create a certain level of temperature rise, causing the tissue to coagulate without any carbonisation. The pulse durations between these two groups can be used for both hard and soft tissues with short-comings for both kinds of tissue treatments. Currently, the number of pulse durations practitioners can choose from can be from 1 to 6 depending on the brand and model of erbium lasers. To increase the coagulation effect, we can turn the water spray down to shift the laser-tissue interaction (heat creation) to the inside of the tissue rather than the surface. Turning down the water flow can cause a rise in pain perception.

Erbium lasers have a wide range of applications. For example, Er:YAG laser has long been shown to be used without anaesthesia at 8Hz frequency with pulse energy 250mJ while restoring class V cavities with 80% of individuals (Matsumoto et al., 1996). Keller studied patients’ responses to conservative treatment by treating them with laser or traditional mechanical management for cavities (Keller et al., 1998). Over 80% of patients reported less discomfort with the laser procedure and expressed a preference for laser management of caries in future. While modern erbium lasers can remove tooth material very fast, the main idea is to be more selective through the tissue's content. Caries, in addition to being softer than sound dentine, also has significantly more water content. Both of these properties make it easier to remove caries with low powers selectively. Erbium laser is also known to disinfect the underlying healthy dentine layers and dentine tubules (Schoop et al. 2004).

Some Er:YAG studies show more desensitisation over the longer term than dentine bonding agents (Schwarz et al., 2002).

The absence of vibrations, faster healing of soft and bone tissues and relatively pain-free recovery, in addition to bactericidal and bio-stimulatory effects, make the Er:YAG laser an important surgical instrument. Studies where Er:YAG laser was used to treat osteonecrosis of the jaws in patients under bisphosphonate therapy show how atraumatic this tool can be. (Vescovi et al. 2010) Incisions, excisions and removal of any soft tissue and overgrowths like granulomas, fibromas, and epulis or lesions are possible with erbium laser except for vascular lesions.

In root canal treatments, the laser should be involved in the two critical steps needed for successful treatment: cleaning the smear layer in the root canal and removing bacteria from all parts of the root canal system [6]. Classically, the complete removal of the smear layer is impossible, especially from the side canals. The Er:YAG laser wavelength is used for non-thermal, photoacoustic cleaning and debridement of the complex root canal system. Hypocloride, saline solution or 17% EDTA and a specially shaped Er:YAG fiber tip are used for the effect of laser-induced photoacoustics. A combination of 6% sodium hypochlorite with an Er:YAG fiber tip effectively eliminates bacteria from the root canal (DiVito et al. 2012, Ando et al. 1996).

Modern periodontal therapy deals with the effective removal of infected soft and hard tissue during surgical or non-surgical therapy. There are various benefits of the combined use of laser-assisted and classical methods of periodontal treatments. The Er:YAG laser with an appropriate fiber tip is used for concrement and calculus ablation while removing bacteria, endotoxins and lipopolysaccharide on the hard root surface and the elimination of granulomatous tissue on the soft gingival side (Aoki et al. 2000, Folwaczny et al. 2002 & 2003,  Akiyama et al. 2011) improving the treatment outcomes and patient comfort (Schwarz et al. 2001 & 2003, Badran et al. 2012 . Lopes et al. 2010, Dominguez et al. 2010, Tomasi et al. 2006, Crespi et al. 2007, Braun et al. 2010) Many surgical periodontal procedures like gingivectomy, gingivoplasty, or operculectomy can be performed by erbium lasers in an elegant way (Ishikawa et al. 2004).

Implants are placed surgically, which may have some drawbacks during the initial phase. Possible complications include pain, swelling and infection. There are many roles that dental lasers can play to alleviate these issues and increase the success rate. (Romanos et al. 2009)

After raising the flap, if the procedure will be immediate implantation, the teeth should be extracted, causing as little trauma as possible, and that can be achieved by ablating the root/ bone with a very thin fiber tip, making space for the elevator between the bone and the root. Usually, extraction is indicated because of extensive infection. The Er:YAG laser is a perfect tool to remove the granulation tissue neighbouring the bone because it does not cause mechanical or thermal trauma to the bone while disinfecting the surface. Conventionally, when a curette is used, there is a risk of traumatising the bone, especially the socket's thin vestibular wall. Any present infection is a problem for osseointegration and even more so if bone augmentation is planned. The Er:YAG laser can also be used to level the bone around the implant bed. When this is done with burs, there is a high chance the bone will become heated. If it is cortical bone, then there will be resorption around the neck of the implant. If it is cancellous bone, then the ground bone will be pushed into the trabeculae, and that will cause oedema. The patient feels discomfort during the procedure because of the pressure and vibration caused by the bur in both cases.

Ablating the bone with Er:YAG (Pourzarandian et al. 2004) laser to have the desired coronal bone thickness, such as by removing a knife-edge thin portion to shape a plateau, or an osteotomy for a sinus lift, or to obtain a bone block, or bone splitting is advantageous. Also, marking the first drilling site's location with an Er:YAG laser is more straightforward, especially for new implantologists, because the laser beam cannot slip and cause iatrogenic damage like an implant drill.

The Er:YAG laser is used in particular indications relating to the implant bed preparation, such as when the bone is very thin and fragile. It is beneficial to prepare the implant bed with a laser to disinfect the site, remove the smear layer, activate osteoblastic activity and achieve more bone-to-implant contact during the early healing (Kesler et al. 2006). Another use for the Er:YAG laser is uncovering the implant in a two-stage surgery (Arnabat-Dominguez et al. 2003). With the help of Er:YAG, no anaesthesia is needed for this procedure. The impression can be made during the same session, as the tissue is not heated and will not retract later. Again, as the ablation is “cold for the tissue”, there is no risk of damaging the bone surrounding the implant or the implant itself.

A very successful indication for the Er:YAG laser is the treatment of peri-implantitis. As microorganisms are present in the implant's microporous surface in a case of peri-implant infection, the photons of a laser have a suitable antimicrobial effect. (Leja et al. 2013, Kim et al. 2011)

After removing the granulation tissue around the implant and disinfecting both bone and implant surfaces with Er:YAG, bony walls are perforated to induce bleeding for better augmentation success without any adverse side effects.

Crown lengthening or gingival levelling can be a routine procedure for laser-assisted aesthetic interventions. When Er:YAG is used, almost no anaesthesia is needed as it does not cause thermal damage to the tissue. The result is a stable gingival height after the procedure. When required, the bone level may be corrected with an Er:YAG laser equipped with adjustable pulse duration (referred to as VSP technology in Fotona lasers) in a non-invasive way without raising a flap (McGuire et al. 2011).

The gingival depigmentation treatment (Hegde et al. 2012) is very safe with the Er:YAG laser due to its superficial absorption. De-epithelisation of the basal layer with pigmentation is achieved with longer Er:YAG pulses. If a small amount of water spray is used, there can be mild bleeding during the operation, but the tissue heals faster, and the need for anaesthesia is decreased.

The activation of the bleaching gel for tooth whitening is very successful with the Er:YAG laser (Gutknecht et al. 2011) with very long pulses. The overall treatment time, as well as post-operative sensitivity, is decreased. The reduction in sensitivity is most probably due to the shortened time of gel-teeth contact time as sub-ablative energy of the Er:YAG laser activates the bleaching gel in a short time.

References

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