It is widely accepted that the uptake of research findings by practitionersis unpredictable, yet until they are adopted, advances intechnology and clinical research cannot improve health outcomesin patients. Despite extensive research there is limited knowledgeof the processes by which changes occur and ways of measuringthe effectiveness of change of practice. The overall aim of this thesiswas to investigate aspects of an educational intervention in clinicalendodontic routines and new instrumentation techniques in aSwedish County Public Dental Service. Special reference was madeto the establishment of changed behaviour in practice, the process ofchange, and the clinical effects.Although a high level of competence in root canal treatment proceduresis required in general dental practice, a number of Swedishstudies have revealed inadequate root-fillings quality and associatedperiapical inflammation in general populations. It is suggested thatthe adoption of the nickel-titanium rotary instrumentation (NiTiR)technique would improve the cleaning and shaping of root canalsand the quality of the root-filling. However, there is limited knowledgeof the effectiveness of the technique when applied in generaldental practice.In two of four consecutive studies, the subjects were employees of acounty Public Dental Service. The aim was to investigate the rate ofadoption of clinical routines and the NiTiR technique: the output,and the qualitative meaning of successful change in clinical practice.In the other two studies the aim was to investigate treatment effectand the cost-effectiveness of root canal treatment in a general population:the outcome.Four hundred employees (dentists, dental assistants, administrativeassistants and clinical managers) of a Swedish County Public DentalService were mandatorily enrolled in an educational and trainingprogram over two years. Change of practice was investigated in apost-education survey. The NiTiR technique was adopted by significantlymore dentists in the intervention county compared to acontrol county (77% and 6% respectively). Dentists in the interventioncounty completed root canal instrumentation in significantlyfewer sessions than the dentists in the control county.Eight in-depth interviews, two with each participant, (dentist, dentalassistant, receptionist, clinical manager), were strategically selectedfor a phenomenological analysis. Four factors were identified asnecessary for successful change: 1) disclosed motivation, 2) allowancefor individual learning processes, 3) continuous professionalcollaboration, and 4) a facilitating educator.A random sample of 850 performed root canal treatments was usedfor a study of treatment outcome; 425 before and 425 after the educationand adoption of the NiTiR technique. Root-filling quality,periapical status and tooth survival were assessed on radiographstaken at treatment and at follow-up, ≥4 years later. Apical periodontitiswas found in 34% of the teeth root-filled before the educationcompared to 33%, after. After the education, root-filling qualityimproved significantly, tooth survival was significantly higher,however, without a subsequent improvement in success rate posteducation;68% vs. 67%.A micro-costing model was used to calculate the costs of root canalinstrumentation, pre- and post-education, in the same sample usedin the study of treatment outcome. Costs were lower post-education:by SEK 264 for teeth with one canal and SEK 564 for teeth withthree or more canals. A reason for lower costs was that the NiTiRtechnique dominated after the education and required significantlyfewer instrumentation sessions. A cost-minimization analysis disclosedthat root canal treatments undertaken post-education weremore cost-effective.In conclusion, there was only a partial relationship between outputand outcome. Although root-filling quality improved significantly,the study did not show any association between the more frequentuse of NiTiR and an improvement in remaining teeth with normalperiapical status or success rate. However, the use of NiTiR wasmore cost-effective. These results are in accordance with previousfindings of the so called efficacy-effectiveness gap in clinical practice:a high output is not predictive of a high outcome. The overallconclusion to be drawn from these studies is that further researchis warranted to identify factors associated with improvement of thequality of endodontic care.The general interpretation of the findings of these implementationstudies is as important as the effects of the change in endodonticinstrumentation: a clinically relevant and applicable intervention,introduced by experienced expertise under allowing learning and collaboratingcircumstances, disclosed clinicians’ motivation and facilitatedimplementation. The finding of qualitative differences betweenthe questionnaire responses and the in-depth interviews suggestthat a critical approach is warranted when comparing surveys andqualitative methods aimed at investigating qualitative experiences ofchange, due to their different epistemological premises.