Purpose: To assess the social cognitive constructs of the Health Action Process Approach (HAPA) of parents of high caries risk children to be treated under intravenous sedation (IVS) or with behavioural guidance techniques (BGT), and to assess the changes in these constructs for each treatment group after treatment. Design: In this cohort study, 160 children aged 3–10 years were allocated by their paediatric dentist to either IVS (77.4%) or BGT. Their parents filled out a HAPA questionnaire, before (T1, n = 160), immediately (T2, n = 108) and three months (T3, n = 71) after their children's dental rehabilitation. Results: Before treatment, all parents had high scores on all social cognitive constructs. There were no differences in mean HAPA scores between the treatment groups (p > 0.05). After treatment, mean scores changed in both groups. In the BGT group, action self-efficacy changed from 3.64 (T1) to 3.36(T2) (p = 0.027) and to 3.13 (T3) (p = 0.021) and coping self-efficacy changed from 3.63 (T1) to 3.23 (T2) (p = 0.015). In the IVS group, action planning changed from 3.25 (T1) to 3.05(T3) (p = 0.036) and action control changed from 2.58 (T1) to 2.82 (T2) (p = 0.012) and to 2.87 (T3) (p = 0.006). Conclusions: High scores on social cognitive constructs of parents of children referred to a paediatric dentist showed that they seem to be motivated to brush their children’s teeth, irrespective of the treatment group. Small changes were observed in the HAPA constructs, however, these are not considered clinically relevant.