Objective: To compare, retrospectively, the influence of different types of restorative materials on caries in vivo. Method and Materials: Twenty-three primary teeth restored by a single operator with amalgam and 2 polyacid-modified resin composites, and with a band of tooth structure beyond the floor of the cervical box, were selected for microscopic evaluation. The teeth were sectioned mesiodistally with the aid of a hard tissue microtome, polished, and cleaned. A confocal laser scanning microscope was used to measure caries-related autofluorescence in the tooth tissue adjacent to the restorative material. A band of about 400 µm along the interface between the restoration and the tooth structure was observed. The extent of the fluorescent regions was recorded in relation to the total interface length. The specimens were then categorized according to the restorative material used: group A: amalgam (Spherodon, Silmet, n = 11); group D: polyacid-modified resin composite (Dyract, Dentsply DeTrey, n = 6); and group C: polyacid-modified composite (Compoglass, Ivoclar Vivadent, n = 6. The data were analyzed using a one-way analysis of variance (ANOVA) model (a = .05) and Pearson correlation coefficient. Results: No significant differences were found between the materials (P > .05). Conclusion: Within the limits of this clinical study, the data obtained using a small sample size suggests that the effect of the restorative material in primary molars does not have a predominant influence on secondary or residual caries. Keywords: amalgam, caries, confocal laser scanning microscope, in vivo, polyacid-modified resin composite, residual caries, restorative materials, secondary caries