Six-Year Success Rates of Occlusal Amalgam and Glass-Ionomer Restorations Placed Using Three Minimal Intervention Approaches

The present randomised clinical trial was aimed at comparing three minimally invasive restorative treatment approaches for managing dental caries in occlusal surfaces using a non-gamma-2 amalgam and a low-viscosity glass-ionomer as the restorative material. The treatment approaches tested in parallel groups were: conventional in a university setting, modified-conventional and ultraconservative (Atraumatic Restorative Treatment, ART) approaches in a field setting. A split-mouth design was used in which the two restorative materials were randomly placed in 430 matched contralateral pairs of permanent molar teeth. A total of 152 children from five primary schools were recruited and treated by a dental therapist. The restorations were evaluated after 6 years by 2 calibrated independent examiners. The 6-year successes for all occlusal amalgam and glass-ionomer restorations were 72.6 and 72.3%, respectively. There were no statistically significant differences observed between the successes for both amalgam and glass-ionomer restorations placed either by the ART (68.6%, with 95% CI = 61–76%) approach or by the conventional (74.5%, with 95% CI = 65–82%) and the modified-conventional (75.8%, with 95% CI = 67–83%) approaches after 6 years. There was also no statistically significant difference observed between the successes of occlusal ART restorations with glass-ionomer (67.1%, with 95% CI = 56–77%) and occlusal conventional restorations with amalgam (74%, with 95% CI = 61–85%) after 6 years. ‘Restoration fracture/marginal defects’ and ‘loss of material’ were the most common causes for failure. The former was more often recorded in amalgam restorations and the latter in glass-ionomer restorations. Secondary caries was observed for 2% of glass-ionomer and for 10% of amalgam restorations. This difference was statistically significant (p = 0.001). The ART approach using glass-ionomer performed equally well as conventional restorative approaches using electrically driven equipment and amalgam for treating dentinal lesions in occlusal surfaces after 6 years.