| case report Without this guidance, even the most experienced cli- nicians should be cautious and take several radiographs to ensure the correct insertion position of the instrument used to achieve the canal.2, 7 The reduction in the number of radiographs with this approach is also of benefit and compensates for the patient’s radiation exposure in CBCT scanning.7 Still, periodic intraoperative radiographs should be taken to control the drill path.18 Also, stepwise control is suggested using a microscope, and as soon as a canal can be negotiated, conventional instrumentation can be carried out.18 The planning of guided endodontics is very time- consuming compared with conventional root canal therapy because of CBCT acquisition, intraoral scanning, virtual planning and printing8 (Figs. 25–27). When the root ca- nal disease is symptomatic, usually prompt treatment is needed and the patient and dentist do not want to wait.16 However, the time that it takes for an endodontic specialist with or without an operating microscope to localise calci- fied root canals can be more time-consuming than with the help of a 3D guide, as the chair time with this technique is minimal.8, 20 The additional cost, including a CBCT scan, intraoral scan, software and fabrication of templates, may be jus- tified by the reduction of iatrogenic errors and the better prognosis of the tooth, compared with the costs for an implant.15, 19 Isolation by rubber dam is essential for the success of endodontic treatment. In guided endodontics, the adap- tation of the guide is fundamental for the outcome, and so initial access without a rubber dam may be necessary. Once the canal is located, it is mandatory to place a rubber dam before instrumentation of the root canal.20–22 Another disadvantage, as mentioned by Van der Meer et al., is the restricted visualisation of the treatment when the guide is used despite its transparent nature.10 The in- termittent removal of the guide may be needed to ensure that the proper path is still being followed.20 In the field of endodontics, the use of guided templates assisted by CBCT images has been described not only for treating teeth with PCO, but also for development anomalies that affect the root canal system, apical microsurgery, selective canal retreatment and fiber post removal.17 Conclusion Negotiation of obliterated root canals is a tremendous challenge for clinicians. The use of new technologies, knowl- edge of pulp anatomy and interpretation of radiographs are the keys to achieving success in the treatment of PCO. use of endodontic guides may facilitate the localisation of the canal and allow a more predicable approach to these cases. However, it is still necessary to develop burs with smaller diameters and different lengths to allow access to calcified canals in longer and narrow teeth, such as canines and mandibular incisors. Further improvements are also necessary to allow this technique to be used in the treatment of posterior teeth and curved canals, the guidance of retreatment of selective canals and the re- moval of fiber posts. Editorial note: This article originally appeared in Clinical Master Magazine 1/2019. A list of references is available from the publisher. about Dr Hugo Sousa Dias graduated with a DDS from University Fernando Pessoa, Porto, Portugal, and completed the postgraduate programme in endodontics at the University of Lisbon, Portugal. Besides running a practice limited to endodontics in Porto, he is Director of the Master in Endodontics clinical residency programme at Foramen Dental Education. Dr Dias is the founder of the Portuguese Group for Endodontic Study (study club). He is a member of the European Society of Endodontology and the Sociedade Portuguesa de Endodontologia (Portuguese endodontic society). He has given more than 20 lectures around the world and is co-author of a chapter in the book The Root Canal Anatomy in Permanent Dentition (Springer, 2018). Dr Inês Pampulha graduated with a DDS from the University of Lisbon, Portugal, in 2014. She has taken modular courses in the field of endodontics and completed the Master in Endodontics Clinical Residency programme, at Foramen Dental Education in 2018. She obtained a master’s degree in Endodontics from the Miguel de Cervantes European University, Valladolid, Spain, in 2018. She is a member of the Portuguese endodontic society. Dr Maria João Valadas graduated with a DDS from the University of Lisbon, Portugal, in 2014. She has taken modular courses in the field of endodontics and completed the Master in Endodontics clinical residency programme at Foramen Dental Education in 2018. She obtained a master’s degree in Endodontics from Guided endodontics appears to be a safe, reliable and clinically useful method for treating teeth with PCO. The the Miguel de Cervantes European University, Valladolid, Spain, in 2018. She is a member of the Portuguese endodontic society. 20 roots 1 2019