Clinical Investigation of the Effectiveness of Laser-activated Photoacoustic Flow in One-visit Revision of Teeth With Apical Periodontitis

Introduction:

Endodontic treatment of teeth involves thorough mechanical removal of microorganisms, necrotic and infected pulp tissue, and chemical disinfection of the endodontic space. Due to the complex morphology of the endodontic space, which includes lateral canals, isthmuses, and apical bifurcations, more than a third of the root canal remains untreated after mechanical treatment, so chemical disinfection is an indispensable addition to mechanical treatment. The work of instruments in the root canal creates a residual layer on the canal walls, and dentin debris created by instrumentation accumulates in the irregularities of the canal and serves as an ideal refuge for remaining bacteria. In addition, the residual layer on the dentin walls can prevent the penetration of irrigant and filler into the dentinal tubules. Therefore, abundant irrigation with irrigant is essential for removing dentin chips from the root canal, but also the residual layer from its walls.

Ultrasonic and laser-activated disinfection are increasingly used to improve the depth of penetration of the irrigant used and thus reduce persistent periradicular inflammation. However a systematic review from 2023 that laser-activated disinfection is significantly better at reducing the number of microorganisms and removing residual layer and dentine debris compared to ultrasonically activated disinfection. It is believed that laser-activated disinfection improves the effectiveness of irrigant in disinfecting the endodontic space by creating secondary cavitations through expansion and subsequent implosion of the liquid. Er:YAG lasers use laser energy to create acoustic waves that move the irrigant and thus improve its flow inside the root canal, which is especially true for the PIPS technique (photon-induced photoacoustic streaming). It is shown that laser-activated disinfection, in vitro, can reduce the number of bacteria in infected canals by 99.5%. Modalities of the Er:YAG laser, such as SWEEPS (shock wave enhanced emission photoacoustic streaming) and SSP (super short pulse), create a precise concentration of shock waves during irrigation, which enable the washing agent to penetrate deeper into the lateral canals and microscopic tubules, thereby increasing the effectiveness of disinfection. Because of the above, SWEEPS/SSP modalities have significant advantages during endodontic treatment, especially in teeth with complicated root canal morphology.

However, although in vitro studies show that laser-activated irrigation (LAI) is superior to other methods in removing intracanal microorganisms, there are still very few clinical studies. Clinical studies show that the healing of periapical lesions after one year on single-rooted teeth and premolars is the same for all irrigation techniques. However, a higher percentage of healing has also been reported when using the SWEEPS modality. It is also emphasized the need for additional research that would study the effectiveness of LAI in multi-rooted teeth, considering their more pronounced morphology of the endodontic space, on which pulsed laser modalities could be more effective.

There is also increasing emphasis on the use of cone-beam computed tomography (CBCT) in future studies to assess prognostic factors affecting the outcome of root canal treatment. Periapical radiographs show a more favorable outcome of healing of periapical lesions compared to CBCT, which significantly affects the correct assessment of treatment success. The ESE guidelines recommend clinical and radiographic follow-up for at least one year after endodontic treatment, with the patient's radiation dose as low as possible to achieve the desired level of diagnosis. The use of CBCT with ethical approval is justified in the clinical use of small CBCT scans for research purposes: to evaluate treatment with new protocols, disinfection techniques, which will provide a more objective treatment outcome.