Influence of the apical limit of instrumentation and photodynamic therapy on the postoperative pain of lower molars with asymptomatic apical periodontitis

•The apical limit of instrumentation does not have influence in the postoperative pain.•The PDT does not have influence in the postoperative pain.•The foraminal enlargement associated with PDT does not induces severe postoperative pain. The aim of present study was to evaluate the influence of apical limit of instrumentation and PDT on the postoperative pain of lower molars with asymptomatic apical periodontitis. Forty patients were included in the present study and were divided into 4 groups (n=10), according to apical limit of instrumentation and use of PDT: instrumentation at 0.0 measurement; instrumentation at 0.0 measurement+PDT; instrumentation 1mm beyond 0.0 measurement; instrumentation 1mm beyond 0.0 measurement+PDT. In the PDT, the root canals were filled with 0.01% methylene blue, remaining for 5 min. The low-intensity laser was used with 100 mW, 660–690 nm wavelength), using intra-canal fibre. Root canals were irradiated for 90 s, delivering total dose of 9 J and energy density of 320 J/cm2. After root canal preparation and PDT protocols, root canals were filled with gutta-percha and AH Plus endodontic sealer, being sealed with composite resin.The evaluation of postoperative pain was performed by visual analog scale after 24, 48, 72 hours and 7 days. Data were analysed by specific statistical tests, at level of 5%. No statistical significant difference was observed among experimental groups in all evaluation periods, as well as in the intragroup analysis over time, regarding postoperative pain and analgesic medication consumption (p>0.05). Apical limit of instrumentation and PDT have no influence on the postoperative pain of lower molars with asymptomatic apical periodontitis.