AIM: To explore the views of patients, caregivers, and dental professionals on the factors that influence implementation, processes, and effectiveness of a guided self-help cognitive behavioural therapy (CBT) intervention, 'Your teeth, you are in control' (YTYAIC), in the CALM trial. METHODS: Semi-structured interviews were conducted as part of this qualitative component of the process evaluation, and data were analysed using a framework approach based on the Consolidated Framework for Implementation Research (CFIR) and the Five Areas Model of CBT. RESULTS: Thirty-seven participants were recruited. Potential mechanisms of action were identified using the Five Areas Model of CBT. Participants felt the intervention may exert change through targeting unhelpful thoughts and feelings (e.g., building trust and perceptions of control) and behaviours (e.g., encouraging effective communication and coping strategies) and facilitating a more positive situational context (e.g., developing more supportive relationships). Enablers (e.g., adaptability, design and delivery) and barriers (e.g., time/resource constraints, cost) to implementation were identified using the CFIR. CONCLUSIONS: This study revealed multiple potential mechanisms of action which could reduce dental anxiety and examined how implementation and contextual factors may influence this change process. The results of the research revealed that the intervention could be implemented in primary dental care and identified the potential barriers which should be addressed to aid successful implementation of the intervention in real world contexts. TRIAL REGISTRATION: This clinical trial has been registered with an international registry and has been allocated an International Standard Randomised Controlled Trial Number (ISRCTN27579420).