As neonates transition from the protected fetal environment to the external world, their nascent immune system must swiftly adapt to the colonizing microbiota before establishing lifelong mucosal homeostasis. Our study sheds light on the role of maternal IgG (mIgG) antibodies and dendritic cells (DCs) in this early life process. We first demonstrate that mIgG transferred in utero are actively transported to the salivary glands and subsequently secreted into neonatal saliva. This mIgG notably diminishes the microbial load in the oral cavity and salivary glands of neonates. In the absence of maternal antibodies, neonatal DCs exhibit increased migration from the oral mucosa to the salivary glands. These migrating DCs then prompt heightened activation of IFN-γ-producing CD4+ and CD8+ T cells while suppressing T regulatory cells. Additionally, elevated B-cell expansion occurs in the salivary glands, leading to dysregulation in the IgG/IgA balance within the saliva. The absence of maternal antibodies also impacts adult gingival immunity, a crucial component of the oral barrier, exacerbating alveolar bone loss during experimental periodontitis. Our findings underscore the significance of the salivary-oral axis during neonatal development, wherein maternal antibodies and DCs collaborate to regulate local mucosal immunity, thereby safeguarding against pathological damage in adulthood.