A 1 year follow-up investigation of salivary acidic proline-rich proteins (aPRPs) in preterm and at-term newborns using HPLC-ESI-IT-MS showed that (i) this class of proteins is constitutive rather than inducible, as it is still found in the oral cavity of preterm newborns from 180 days of postconception age (PCA); (ii) the expression of PRH-2 locus anticipates that of PRH-1, since Db isoforms are expressed some months after the PRP-1 and PRP-2 isoforms. The evaluation of the relative abundances of the different aPRPs isoforms and derivatives (differently phosphorylated and cleaved) as a function of PCA showed that (iii) the proteolytic enzymes generating truncated isoforms are also constitutive because they are fully active since 180 days of PCA; (iv) the kinase involved in aPRP phosphorylation is not fully mature in preterm newborns, but its activity increases with PCA, synchronizing with that of at-term newborns and reaching the adult levels at about 500-600 days of PCA, in concomitance with the beginning of deciduous dentition.