Clinical question. In primary and permanent teeth, does the use of glass ionomer restorations result in fewer carious lesions at the margins across time compared with the use of amalgam restorations? Review methods. The reviewers searched seven databases for randomized or quasi-randomized controlled studies written in English, Portuguese or Spanish. The reviewers included articles reporting on clinical trials published through Jan. 5, 2008. Two reviewers independently extracted data from six articles that included reports of eight studies. The methodological quality of these studies varied. The reviewers categorized the studies into clinically homogenous groups of patients characterized by the type of the dentition (primary or permanent), type of cavity (single- or multiple-surface) and number of years of follow-up. The results are presented in three separate fixed-effect meta-analyses. Main results. The eight studies were conducted in Syria, Tanzania, Sweden, the United Kingdom and Denmark. The investigators followed up with the participants from almost two years to eight years in parallel group and split-mouth study designs. The investigators in some of the studies reported using hand excavation and others reported using drilling before placing the glass ionomer restoration. The investigators in these studies evaluated a total of 2,341 teeth with glass ionomer restorations and 1,998 teeth with amalgam restorations. The quality of the studies was diverse. The investigators observed significantly fewer carious lesions on single-surface glass ionomer restorations in permanent teeth after six years than they did in amalgam restorations (odds ratio = 2.64, 95 percent confidence interval = 1.39-5.03). The reviewers did not identify any studies that investigated multiple-surface restorations on permanent teeth. The results of studies that investigated carious lesions' at the margins of restorations in primary teeth showed no differences between the restoration materials after three and eight years. Conclusion. There is limited evidence that, in permanent teeth, less recurrent caries occurs at the margins of single-surface glass ionomer restorations than at the margins of single-surface amalgam restorations. There also is limited evidence showing that there is no difference in carious lesions on the margins in primary teeth with multiple-surface restorations.