Siebert has classified residual ridge deformities into 3 categories:
Class I defects-faciolingual loss of tissue width with normal ridge height
Class II defects-loss of ridge height with normal ridge width
Class III defects-a combination of loss in both dimensions
The high incidence (91%) of residual ridge deformity following Ant. tooth loss
the majority of these are Class III defects, Because patients with Class II and III defects are frequently dissatisfied with the esthetics of their FPDs
preprosthetic surgery to augment the residual ridge should be carefully considered.
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