ABH is important in achieving primary stability vertically and is measured from the crestal bone to the maxillary sinus floor through the radiograph. The result will determine the indication for socket lifting.(Fig. 1) Classification of ABH is as follows:
• Grade A: ABH>8.0 mm; sufficient to contain the fixture in the vertical dimension and does not require socket lifting.
• Grade B: 6.0 mm≤ABH≤8.0 mm; may or may not require socket lifting, socket lifting is required for a longer implant.
• Grade C: ABH<6.0 mm; insufficient ABH, socket lifting is mandatory.