According to the International Organization for Standards (ISO) refinements 3950 to the FDI system, 05 refers to:

International Organization for Standards (ISO) has added refinements (ISO 3950) to the FDI system to designate areas of the oral cavity and to provide 'sextants' as with the CPITN.  00 whole oral cavity  01 maxillary area  02 mandibular area  03 upper right sextant  04 upper anterior sextant  05 upper left sextant  06 lower left sextant  07 lower anterior sextant  08 lower right sextant  09 additional document