(1) This systematic review examined the effect of crowns in primary teeth on periodontal health. (2) The review found that teeth restored with stainless steel crowns have poorer periodontal health compared to conventional restorations, with the main risk factor being non-ideal marginal adaptation. (3) While some studies found no difference in periodontal health between ideal and non-ideal crowns, the majority of evidence indicates that non-ideal crowns are associated with increased gingivitis and bone resorption.