Loss-of-function mutations in stromal interaction molecule 1 (STIM1) impair the activation of Ca release-activated Ca (CRAC) channels and store-operated Ca entry (SOCE), resulting in a disease syndrome called CRAC channelopathy that is characterized by severe dental enamel defects. The cause of these enamel defects has remained unclear given a lack of animal models. We generated mice to delete STIM1 and its homolog STIM2 in enamel cells. These mice showed impaired SOCE in enamel cells. Enamel in mice was hypomineralized with decreased Ca content, mechanically weak, and thinner. The morphology of SOCE-deficient ameloblasts was altered, showing loss of the typical ruffled border, resulting in mislocalized mitochondria. Global gene expression analysis of SOCE-deficient ameloblasts revealed strong dysregulation of several pathways. ER stress genes associated with the unfolded protein response were increased in -deficient cells, whereas the expression of components of the glutathione system were decreased. Consistent with increased oxidative stress, we found increased ROS production, decreased mitochondrial function, and abnormal mitochondrial morphology in ameloblasts of mice. Collectively, these data show that loss of SOCE in enamel cells has substantial detrimental effects on gene expression, cell function, and the mineralization of dental enamel.