ORIGINAL ARTICLE Efficacy of ultrasonic and Er:YAG laser activated EDTA irrigation in removing bacteria from ex vivo root canal system Sharonit Sahar-Helft 1 & Ayşe Sena Kabaş Sarp 2 & Murat Gulsoy 2 & Idan Redenski 1,3 & Adam Stabholtz 1 & David Keinan 4 & Doron Steinberg 3 Received: 1 May 2017 /Accepted: 25 October 2018 # Springer Nature Switzerland AG 2018 Abstract Purpose Due to the limited effectiveness of irrigation to reduce the bacterial load inside root canals, the efficacy of activated irrigation techniques was evaluated. Methods Sixty endodontically prepared single-rooted human teeth were sterilized, infected with Enterococcus faecalis, and divided into six groups: (A) endodontic treatment positive control, (B) irrigation with EDTA 17%, (C) Er:YAG laser activated irrigation with tip 1 mm from working length, (D) Er:YAG laser to the coronal third, (E) ultrasonic irrigation applied 1 mm from working length, (F) US irrigation to the coronal third. Results The positive control group had significantly more bacteria than all other groups. EDTA irrigation had low efficiency. US irrigation 1 mm from the working length was significantly more effective than controls. Laser treatment to the coronal third was the most efficient. Conclusions Laser activated irrigation caused the greatest bacterial reductions. Keywords Biofilm . Ultrasonic . Laser . Root canal . Irrigation Introduction The major goal of biomechanical cleaning of the root canal system is to eliminate bacteria and irritants which can cause periapical lesions [1]. Biomechanical instrumentation reduces the microbial load; however, complete bacterial eradication is difficult [2–4] because some areas of the canal wall are inac- cessible to the instruments, including advanced rotary systems [5]. Ethylenediaminetetraacetic acid (EDTA) is a widely used irrigant in endodontic treatment because it reacts with the cal- cium ions in dentin and forms soluble calcium chelates. The use of antimicrobial canal irrigation agents such as NaOCL with EDTA 17% in combination with mechanical instrumen- tation further reduces the bacterial content [6]. Nevertheless, some bacteria still persist [7, 8]. Endodontic instrumentation reduces bacteria on the root canal wall; however, a smear layer is created. This layer is amorphous and irregular, containing inorganic debris, pulp tissue, odontoblastic residue, necrotic debris, as well as microorganisms and their metabolic prod- ucts [9]. Furthermore, the smear layer itself may be infected, preventing efficient cleaning by irrigation [10–12]. Almost 700 bacterial species can be found in the oral cavity [13]. Once the root canal is infected coronally, infection pro- gresses apically until bacterial products or bacteria themselves stimulate the periapical tissues, leading to apical periodontitis. The dominant bacteria remaining following intra-canal disin- fection procedures and after root canal treatment is the gram- positive bacteria E. Faecalis. This bacterium has been identi- fied in cases of failed endodontic therapy and in canals with persistent infections [14]. E. Faecalis has many features which enable survival in the root canal. * Sharonit Sahar-Helft helft1@bezeqint.net 1 Department of Endodontics, Faculty of Dental Medicine, School of Dental Medicine, The Hebrew University–Hadassah, P.O.B. 12272, 91120 Jerusalem, Israel 2 Biophotonics Laboratory, Institute of Biomedical Engineering Çengelköy, Boğaziçi University, Kandilli Kampüs, Istanbul, Turkey 3 Biofilm Research Laboratory, Institute of Dental Sciences, Faculty of Dental Medicine, School of Dental Medicine, The Hebrew University–Hadassah, Jerusalem, Israel 4 Department of Endodontics, Sheba Medical Center, Israel Defense Force Medical Corps, Ramat Gan, Israel Lasers in Dental Science https://doi.org/10.1007/s41547-018-0046-z