Does ultraconservative access affect the efficacy of root canal treatment and the fracture resistance of two-rooted maxillary premolars? A. A. Silva 1 , F. G. Belladonna 2 , G. Rover 3 , R. T. Lopes 4 , E. J. L. Moreira 1 , G. De-Deus 2 & E. J. N. L. Silva 1,2 1 Department of Endodontics, Grande Rio University, Duque de Caxias, Rio de Janeiro; 2 Department of Endodontics, Fluminense Federal University, Niter oi, Rio de Janeiro; 3 Department of Dentistry, Federal University of Santa Catarina, Florian opolis, Santa Catarina; and 4 Nuclear Engineering Program, Federal University of Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil Abstract Silva AA, Belladonna FG, Rover G, Lopes RT, Moreira EJL, De-Deus G, Silva EJNL. Does ultraconservative access affect the efficacy of root canal treatment and the fracture resistance of two-rooted maxillary premolars? International Endodontic Journal, 53, 265–275, 2020. Aim To evaluate the influence of ultraconservative endodontic cavities (UEC) on canal shaping and filling ability, cleaning of the pulp chamber, time required to perform root canal treatment and fracture resistance of 2- rooted maxillary premolars in comparison with tradi- tional endodontic access cavities (TEC) in extracted teeth placed in a phantom head to simulate clinical conditions. Methodology Twenty extracted intact 2-rooted maxillary premolars were scanned in a micro-com- puted tomographic device, matched based on similar anatomical features of the canals and assigned to UEC or TEC groups (n = 10). Then, teeth were mounted on a mannequin head and their pulp chamber accessed. After canal preparation, filling and cavity restoration, the time required to perform root canal treatment was recorded and the specimens were loaded to fracture in a universal testing machine. The maximum load at fracture was recorded. The sample was scanned after root canal instrumentation, filling and restoration pro- cedures. Untouched canal areas, accumulation of hard-tissue debris (AHTD), voids in root fillings and cleaning of the pulp chamber were analysed. Data were analysed statistically using Shapiro–Wilk and Student’s t-tests with a significance level of 5%. Results The percentage of untouched canal area did not differ significantly between UEC and TEC groups (P > 0.05). However, UECs were associated with a greater percentage of AHTD after canal preparation (P < 0.05). No differences were observed in terms of voids in root fill- ings between the groups (P > 0.05). Nonetheless, UEC had a greater percentage of root filling remnants in the pulp chamber after cleaning procedures (P < 0.05). The time required to perform root canal treatment was significantly longer in the UEC group (P < 0.05). There was no differ- ence regarding the mean load at fracture between the groups (P > 0.05). Unrestorable fractures were observed in all specimens of both groups. Conclusions There was no true benefit associated with ultraconservative endodontic cavities. UEC resulted in more AHTD remaining inside the root canals. UEC did not influence the quality of root fillings; however, UEC made the cleaning procedure of the pulp chamber more difficult, thus increasing the total time required to perform root canal treatment. Moreover, UEC were not associated with an increase in fracture resistance of root filled 2-rooted maxillary premolars. Keywords: fracture resistance, maxillary premo- lars, micro-CT, root canal treatment, ultraconserva- tive endodontic cavity. Received 6 June 2019; accepted 9 September 2019 Correspondence: Emmanuel Jo~ ao Nogueira Leal da Silva, Rua Herotides de Oliveira, 61/902, Icara  ı, Niter oi, RJ 24220-000, Brazil (e-mail: nogueiraemmanuel@hotmail.com). International Endodontic Journal, 53, 265–275, 2020 © 2019 International Endodontic Journal. Published by John Wiley & Sons Ltd doi:10.1111/iej.13219 265