Computed tomography has been used in dentistry as a complement to two-dimensional (2D) imaging since the 1980s. The advent of cone beam computed tomography (CBCT), a more modern computed tomog-raphy technique, meant a revolution in dento-maxillofacial imaging due to sharper images, with less radiation and at a lower cost than with mul-ti-slice computed tomography (MSCT), i.e., conventional medical com-puted tomography. However, CBCT still uses higher radiation doses and is more expensive for the patient than conventional 2D methods. CBCT is generally reported as more accurate than intra-oral radiographs to diagnose pathologies orconditions of interest in endodontics. The diagnostic process is, nevertheless, not only about radiographs and it is not certain that the use of CBCT will provide a different chain of actions, and ultimately result in a health benefit for the patient. There is thus a need to establish whether the added information of computed tomography has an impact on diagnosis and therapy choice in endodontics. Guidelines based on the best available evidence have been issued to as-sist clinicians in how to use CBCT. However, little is known about the decision process that drives dentists to request computed tomography and there is a need for more insight into this process. The aims of this thesis were to assess the influence of CBCT in diagno-ses and treatments choices and to gain insight into dentists’ decision process when requesting CBCT examinations. Study I Cases used were of a fictive standardised clinical history of asympto-matic root-filled maxillary molars from 34 consecutively included pa-tients in which MSCT and intra-oral radiographs taken simultaneously. All cases were analysed by five decision makers. Before and after MSCT assessments were 1-3 months apart. The results showed that MSCT does not improve therapy planning agreement among decision makers but it influences therapy changes within each decision maker, often to more aggressive therapies (e.g. more teeth extractions) Studies II and III The studies were prospective observational studies. The cases were au-thentic clinical scenarios presented to the decision makers who also were the actual caregivers. The same cases were used in both studies II and III involving 53 consecutive patients referred for CBCT using the the evidence based European Commission (EC) guidelines. Seven deci-sion makers in two different clinics participated and made before and after CBCT assessments during normal clinical praxis. The results showed that CBCT significantly influenced changes in diagnoses and therapy plans. The changes in therapies were often towards more ag-gressive therapies and are strongly correlated with changes in diagnoses. CBCT also improved statistically decision makers’ confidence in the assessments. The decision makers felt that CBCT had a positive impact on the patient’s health in a large number of patients, but this could not be controlled, and the assessment was not blinded. Study IV Fourteen strategically selected dentists (informants) that use CBCT for endodontic purposes were interviewed. The interviews were semi-structured. The informants narrated on their last three self-reported CBCT cases. The interviews’ transcripts were analysed by qualitative content analysis. The interpretation of the phenomenon of the decision of using CBCT examinations for endodontic purposes was made at two different levels: the explicit and the implicit content. The explicit con-tent revealed three categories as follows: “visualization as a desire”, “fa-cilitating tough decisions” and “allocation of responsibility”. The im-plict content was interpreted as: dentists working in Sweden seemed to have a clinical common sense that compensates for the unfamiliarity of the guidelines. On the other hand, a “safer than sorry” attitude counter-balanced (e.g when tackling difficult patients) the restriction induced by the common sense approach. There was a belief that the national regula-tory system worked as a gate-keeper for over usage.