People with severe mental Illness (SMI) bear an excessive burden of periodontal disease, which can exacerbate their mental and physical multimorbidity. Therefore, improving and sustaining good oral hygiene is key.

To co-create a theory-driven oral hygiene intervention for people with SMI.

A two-stage, eight-step method was followed drawing on the Behaviour Change Wheel. Stage 1, understanding the problem, involved evidence review and stakeholder consultations. Stage 2 focused on identifying theoretical barriers and facilitators through semi-structured interviews (n = 20) and co-designing the intervention content alongside people with SMI, carers, primary care, mental health and dental professionals and clinical leads. Interview data were analysed using framework analysis. Identified barriers and facilitators were mapped to the Capability, Opportunity, Motivation–Behaviour model and Theoretical Domain Framework. Intervention functions, policy categories and behaviour change techniques were identified and mapped accordingly.

The target behaviour of twice-daily toothbrushing was addressed through understanding the consequences of improving oral health and brushing, forming a brushing habit, brushing instructions and demonstration with consideration of cognitive capacity and exploring the need for financial and social support. Recommendations for intervention delivery included integrating it into the SMI physical health checks, training and remunerating primary care and mental health professionals to deliver it as part of a personalised and integrated care approach to rebuilding broader lifestyle routines; and maintaining engagement through follow-up appointments.

This is the first study to co-create a theory-driven toothbrushing intervention for people with SMI, delivered by primary care and mental health professionals.