A Five‐Year Follow‐Up Study on the Removal of Dental Amalgam Restorations (Bergen Amalgam Trial): Examining Potential Confounding Factors and Effect Modification

Background This government‐funded project comprised experimental treatment aimed at improving health and quality of life for individuals with health complaints attributed to dental amalgam. Objectives The objective was to evaluate long‐term changes in health complaints and health‐related quality of life (HRQoL) after amalgam removal in individuals attributing health issues to dental amalgam, while also assessing effect modification and confounding factors. Methods The project was designed as a prospective cohort study. Three cohorts were followed over time: an Amalgam cohort (treatment group, n = 32), a cohort of patients with medically unexplained physical symptoms (MUPS cohort, n = 28) and a cohort of healthy volunteers (Healthy cohort, n = 19). The Amalgam cohort included patients with MUPS attributed to amalgam seeking amalgam removal, while the MUPS cohort had no such symptom attribution. Amalgam cohort participants had their fillings replaced with alternative materials. Questionnaires were completed at baseline (Q1), 1‐year follow‐up (Q2) and 4 years later (Q3). Changes over time were analysed using linear mixed‐effects models. Results In the Amalgam cohort, general health complaints significantly decreased after amalgam removal, while HRQoL significantly improved. No major changes were observed over time in the other cohorts. The differences in change scores between the Amalgam and MUPS cohorts were statistically significant, indicating better health outcomes in the Amalgam cohort. Adjusting for potential confounders did not substantially alter the effect estimates. Stratified analyses suggested that baseline indicators of health might act as effect modifiers. Conclusion Improvement of health was consistent over time even after adjustment for potential confounders. Baseline indicators of health could be effect modifiers.