A crestal sinus lift is conservative approach to access sinus and to augment it.  With this technique the sinus can be accessed through the root socket of an extracted tooth or it can be drilled with a series of special instruments. An opening is made until the sinus is exposed but the sinus membrane remains intact. Once the membrane is lifted,  bone grafting material is inserted between the sinus membrane and the sinus floor, thus lifting the sinus. The sinus floor will naturally lay back down on the new graft and heal into place. Once completely healed, bone graft material will become solid bone. An implant can be placed at the same time or latter depends on the individuals condition.  Because of its conservative approach the recovery period is shorter.