Brown and Shaw classification of maxillectomy defects:

Vertical classification: 

I, Maxillectomy not causing an oronasal fistula
II, not involving the orbit
III, involving the orbital adnexa with orbital retention
IV, with orbital enucleation or exenteration
V, orbitomaxillary defect
VI, nasomaxillary defect.

Horizontal classification: 

a, Palatal defect only, not involving the dental alveolus
b, less than or equal to 12 unilateral
c, less than or equal to 12 bilateral or transverse anterior
d, greater than 12 maxillectomy.

Letters refer to the increasing complexity of the dentoalveolar and palatal defect, and qualify the vertical dimension