Er:YAG laser for superior endodontic treatment
Dr Igor Križnar, Slovenia

In the field of endodontics, practitioners routinely face the challenge of removing biofilm and debris from difficult-to-reach areas in the root canals. Anatomically complex root canal systems with lateral canals, canal branches, isthmuses and tubules represent a significant challenge for successful endodontic treatment. Irrigation is a general method for cleaning areas that are inaccessible to mechanical instruments.1

The Er:YAG photoacoustic technique has been a successful method of removing biofilm and debris from the dental root system for many years. The mechanism of cleaning and disinfection by photoacoustic irrigation is based on the mechanical removal of biofilm and debris via the turbulent movement of liquid (the irrigant) and simultaneously by the chemical reaction of the irrigant itself. Turbulent fluid motion results from the formation of cavitation vapour bubbles and their implosion, which releases a large amount of energy and consequently triggers fluid motion.2–4

There are several methods of Er:YAG photoacoustic irri-gation.5, 6 The pioneering single-super-short pulse (SSP) method is very successful in generating photoacoustic and shock waves in an infinite irrigation space, but in tight spaces such as a root canal, the cavitation  dynamic is significantly slowed down owing to friction  on the dentinal walls and the limited space available for rapid fluid movement during expansion and con-traction of the bubbles. A modified method, known as SWEEPS (shock wave enhanced emission photo-acoustic streaming),5, 6 has been developed as an up-grade of the SSP technique and is particularly suitable for very confined spaces.

Unlike the SSP technique, the SWEEPS technique delivers pulses in pairs. The second pulse exerts pressure on the initial bubble, which is generated by the first pulse, and accelerates its collapse and the emergence of a new generation of bubbles. In this way, even in very narrow geometries, shock waves are formed that travel faster than sound (acoustic waves). The optimal time difference between pulses in a pair depends on the volume and anatomy of the confined space.

When the correlation between tooth anatomy and the time between pulses in a pair cannot be defined exactly, a special modality of the method, known as AutoSWEEPS, is used, whereby the time separation between laser pulses in a pair varies continuously be-tween 250 and 650 microseconds, in increments of 10 microseconds. This ensures that during each cleaning cycle there is always an optimal time distance between the pulses, which is necessary for the emission of shock waves and thus for the maximum possible flow efficiency according to the dimensions of the irrigation system.5, 6 The efficiency of either SSP or SWEEPS in removing bio-film and debris can be enhanced with chemical irrigants. In endodontics, the two most commonly used irrigants are sodium hypochlorite and EDTA.

Endodontically treated teeth are often more prone to crown or root fracture compared with vital teeth. Several factors contribute to this, the most important being that non-vital teeth often have less sound tooth structure owing to progressive carious lesions, trauma or previous restorations. Certain clinical procedures may also lead to a higher incidence of tooth fracture in endodontically treated teeth, such as creation of large access cavities, excessive mechanical shaping of the roots, prolonged use of different irrigating solutions (sodium hypochlorite, EDTA) and medications (calcium hydroxide) during endodontic treatment, improper restorative treatment without cuspal coverage in the posterior region, and high masticatory forces in certain individuals. Once the tooth has broken off below the gingival margin, it is often very difficult to restore it properly, and additional clinical procedures such surgical lengthening of the clinical crown or orthodontic extrusion are needed. When placing a new restoration, the biologic width of the tooth has to be respected and the margin of the restoration should be at least 2.15–2.30 mm (preferably around 3.0 mm) from the crestal bone, to allow for a normal epithelial junction and connective tissue attachment to avoid chronic  inflammation and periodontal tissue loss.

Case presentation

A 28-year-old male patient was referred to our clinic for endodontic treatment of a mandibular molar owing to chronic periapical periodontitis. He stated that a few weeks before the appointment, a large part of the tooth had broken off. The patient was healthy, took no medication and reported no allergies. There was no trauma to the dentition in the patient’s dental history.

Intraoral examination revealed moderate plaque control and oral hygiene. All third molars had been removed in the past, and teeth #16, 24, 26 and 36 had already been endodonti-cally treated. The gingiva was quite healthy, pink in colour, and did not bleed on probing. Probing depth was normal around all teeth. There were no pathological conditions on the tongue, mucosa, or hard or soft palate, or in the oropharynx. The occlusion was Angle Class I. The intra-oral clinical examination showed that tooth #36 had a large mesioocclusal-distal (MOD) composite filling and that the buccal wall was intact, whereas the lingual wall of the tooth crown had broken off about 2 mm below the gingival margin. The tooth was slightly tender to percussion and sensitive to palpation adjacent to the apex of the tooth. The mobility of the tooth had not increased. Probing depth was normal, but there was slight bleeding on probing on the lingual side (Figs. 1 & 2).

Analysis of a radiograph showed the large MOD filling and the broken lingual wall of the tooth (Fig. 3). The tooth had been endodontically treated in the past; the root fillings were porous and short in the mesial root. There were bone lesions (chronic periapical periodontitis) under both the mesial and distal roots.

Diagnosis 

The diagnosis was chronic periapical periodontitis and a broken lingual wall of the tooth crown.

Treatment plan

Healing after surgical crown lengthening may be painful, and the sutures may interfere with good oral hygiene, in addition to being unpleasant for the patient. An alternative approach is the use of Er:YAG laser irradiation, which is readily absorbed in the water component of the collagen of the gingiva and bone, causing instantaneous vaporisation and enabling a precise and superficial cutting action with-out the risk of damage to the surrounding bone. Therefore the clinical crown lengthening procedure of gingivectomy and osteoplasty should be performed with an Er:YAG laser using shorter pulse modes (short pulse and micro-short modes, respectively), since there are almost no unwanted thermal effects on the surrounding tissue. The procedure can be finished with longer pulses (long pulse [LP] and very long pulse [VLP]) for coagulation of the blood vessels, thus reducing bleeding and enabling smoothing of the gingiva. In this way, the crown length of the tooth can be increased and a temporary filling can be performed, which enables further endodontic treatment of the tooth.

Treatment procedures

Before the clinical crown lengthening procedure, the periodontal tissue around tooth #36 was analysed. The gingiva was inspected to confirm that the height of the keratinised gingiva was sufficient and that there would be at least 3 mm of keratinised gingiva left after the repositioning of the gingival margin. The gingiva surrounding tooth #36 was locally anaesthetised using Ubistesin (1:100,000 adrenaline; 3M ESPE). The level to which the lingual wall had broken off was marked on the gingiva covering it, and 3 mm was subtracted from this level to mark where the new margin of the crestal bone should be.

For the gingivectomy, an Er:YAG laser was used with the Varian tip positioned perpendicularly in non-contact mode 0.5 mm from the gingiva. Air and water spray were set to 3 and 2, respectively (Table 1). For the osteoplasty, slightly different parameters were used. The Varian tip was inserted parallel to the tooth surface in non-contact mode, and water and air levels were set to 3 and 2, respectively (Table 2). During the treatment, a periodontal probe was used to check the exact level to which the crestal bone had to be osteomised. The procedure was finished with longer pulses (LP and VLP) for coagulation of the blood vessels in the gingiva, thus decreasing the bleeding, and for smoothing of the gingiva (Tables 3 & 4). After the procedures, there was minimal bleeding, and the wound was left to heal for 14 days (Fig. 4).

At the second appointment after 14 days, a temporary composite filling was used to recreate the lingual wall, thus preparing the tooth for endodontic treatment (Figs. 5–8).

A dental dam was placed on the tooth and the working field isolated. An endodontic access cavity was prepared and the root canals were negotiated to the apex with a size 8 hand C-file. Sequentially larger rotary files (HyFlex CM and EDM, COLTENE) were used to working length up to size 30 for the mesial canals and size 40 for the distal canal. Between each filing, the AutoSWEEPS irrigation protocol was used with 2.5% sodium hypochlorite for 30 seconds, followed by a 30-second rest phase, and no water or air. The access cavity was filled with irrigant constantly during the procedure. After the final shaping of the canals, the final irrigation protocol was performed. This consisted of a single 30-second irrigation cycle with EDTA, followed by a single cycle with distilled water and three 30-second cycles with 2.5% sodium hypochlorite, using the laser parameters stated in Table 5. After drying, a calcium hydroxide dressing was placed in the canals and the endodontic access cavity was temporarily sealed.

At the third clinical appointment, the calcium hydroxide was rinsed out of the canals. For the irrigation, a single 30-second EDTA cycle, followed by a single 30-second distilled water cycle and three cycles of 30-second AutoSWEEPS irrigation with 2.5% sodium hypochlorite were repeated, using the same energy setting as at the first clinical appointment. The canals were dried and filled with gutta-percha cones and a bioceramic sealer (Biodentine, Septodont) using the cold lateral compaction technique. A stronger temporary filling made of composite material was placed at the end of the procedure. The patient was referred back to his general practitioner with instructions for a final restoration of the tooth with an endocrown after six months, once the periodontal tissue and the periapical lesions had healed completely.

In the first week of healing, the patient rated his pain one on a scale of one to ten. Fourteen days after the crown lengthening procedure, the gingival margin looked healthy and had reattached at the new level with no observable bleeding on slight probing. It was possible to perform the composite build-up as an endodontic pretreatment with minimal effort. The endodontic treatment was finished without any complications, and the three-month radio-graphic follow-up showed excellent healing of the periapical lesions (Figs. 9 & 10). For the final restoration, the level of the gingival margin might have had to have been slightly adjusted further using the same procedure.

Conclusion

Our clinical case shows that the Er:YAG laser can be used with great ease and predictability when crown lengthening is indicated. This procedure can be performed as a pre-treatment of the tooth for endodontic treatment or before placing the final restoration. It is easy to perform, but just as important—or even more so—is that it causes minimal to no pain and discomfort for the patient and promotes excellent healing of the periodontal tissue.

Moreover, this case demonstrates the successful use of the SWEEPS mode to increase the fluid dynamics of the irrigant and thereby to improve the cleaning efficacy of the root canals in the treatment of chronic periapical periodontitis. As the sodium hypochlorite reaches even the most apical parts of the root canal system and provides sufficient disinfection, it is not necessary to prepare the canals to larger apical sizes or tapers, which is the case when only conventional irrigation methods are used. This technique truly represents a paradigm shift in the way that endodontic treatment is performed.