Initial Stability of Posterior Maxillary Implants With Bicortical Fixation

The clinical trial will evaluate initial implant stability as a primary outcome measured by resonance frequency analysis (RFA) employing dental implants surgically placed in posterior maxillary bone by engaging alveolar crest and the sinus floor using vertical stopper drill and self-threading concept (bi-cortical fixation), engaging only the alveolar crest (uni-cortical fixation), and engaging alveolar crest and the sinus floor using indirect sinus lift technique (indirect sinus lift technique). The surgical procedures compared in this experiment include 3 groups: * Group 1 (15 implants) Short implants placed in proximity of the sinus without sinus floor involvement (unicortical fixation) * Group 2 (15 implants) Implants placed using indirect sinus lift technique (indirect sinus lift technique) * Group 3 (15 implants) Bi-cortically fixed implants intentionally engaging sinus floor beyond up to 1-2mm without graft but using stopper drill and self-threading concept (bi-cortical fixation)