Lead apatites, distinguished and compelling bulk materials with the stoichiometric arrangement as Pb10(POx)6Oy, are renowned for their structural complexity. Recently, the discovery of possible room-temperature superconductivity under ambient pressure in copper-substituted lead apatites has engendered considerable interest within both the physics community and beyond. Nevertheless, exploration of pristine Pb10(POx)6Oy parent structures has hitherto remained elusive. In this study, we employ density functional theory (DFT) calculations to investigate the effects of oxygen defects on the electronic structures of Pb10(POx)6Oy and Pb9Cu(POx)6Oy. We scrutinize two distinct categories of defects: oxygen atoms enmeshed within POx groups (Ox) and solitary oxygen atoms (Oy). Our investigation uncovers a profound influence of these defects on the band structure. Specifically, the introduction of Oy defects prompts a remarkable transition in Pb10(PO4)6Oy from a metal to semiconductor to metal state, accompanied by pivotal shifts in the principal electronic contributors from p orbitals of Oy to those of Pb atoms. Furthermore, the introduction of Ox defects in Pb10(POx)6O1 engenders metamorphosis in the band structure, transmuting it from a semiconductor to a metallic state. Significantly, our findings pinpoint the suitable range of x in the Pb10(POx)6O1 configuration as lying between 2 and 4. Additionally, our study also demonstrates that the oxygen defects (Ox/Oy) do not affect the metallic properties of copper-substituted lead apatites. This study elucidates the significant role of oxygen defects in modulating the electronic properties of apatite materials, offering insights into potential interdisciplinary applications. This establishes a crucial link between material composition and electronic behavior, revealing key mechanisms for engineering functionality in lead apatites and other advanced materials.