Objectives. To evaluate if calcium supplementation during pregnancy could have any influence on primary dentition measured as the reduction of dental caries of the child. Design. Individual randomized controlled trial. Setting. One hospital in Rosario, Argentina. Population. Random sample of 195 12-year-old children from a follow-up study of 614 women who were randomized during pregnancy to calcium supplementation or placebo. Methods. An independent researcher blinded to the group where the mothers were assigned performed a dental examination of the children. Main outcome measures. Proportion of children with at least one decayed, missing or filled teeth (DMFT/dmft) and mean number of decayed, missing or filled surfaces (DMFS/dmfs) per children. Results. Ninety-eight children were assessed in the calcium supplementation group and 97 in the placebo group. 63.3% of the children whose mother took calcium supplementation had at least one DMFT/dmft compared to 86.6% in the placebo group (<0.001). The children whose mother received the intervention had a 27% reduction in the risk of developing at least one DMFT/dmft (RR: 0.73, CI 95%: [0.62; 0.87]). Conclusions. This study shows a modeling effect of calcium intake during pregnancy on dental caries of the offspring. At around 12 years of age children whose mothers received calcium supplementation when pregnant showed a significant reduction in dental caries.