Table 1. Chiapasco's classification of the posterior maxilla.

Class	Height of the residual ridge	Thickness of the residual ridge	Interarch distance
A	>5 mm <8 mm	≥6 mm	Normal
B	>5 mm <8 mm	<6 mm	Normal
C	<5 mm	≥6 mm	Normal
D	<5 mm	<6 mm	Normal
E	>5 mm <8 mm	≥6 mm	Increased
F	>5 mm <8mm	<6 mm	Increased
G	<5 mm	≥6 mm	Increased
H	<5 mm	<6 mm	Increased
I	Completely resorbed alveolar ridge with increased distance interarch and Class III skeletal relationships