The primary purpose of this study is to

1. determine whether dental implant engaging both the alveolar crest cortical bone and sinus floor using vertical stopper drill and self-threading concept (bi-cortical fixation) increases initial implant stability compared to the short implants engaging only alveolar crest cortical bone (uni-cortical fixation) and/or ones engaging both crest and sinus floor but with green stick fracture (indirect sinus lift technique),
2. study whether different surgical techniques, residual bone height, bone density, and length and width of the implants used affect initial implant stability in posterior maxilla. In addition, this study will continue to
3. compare secondary implant stability of implants fixed bi-cortically, uni-cortically and with indirect sinus lift technique at 2nd stage surgery/6 month healing and 1 year follow-up from the restoration and
4. measure amount of endo-sinus bone formation from the 1- year follow up CT (computer tomogram) scan and evaluate safety and potential post-operative complications of bi-cortical fixation and indirect sinus lift technique reported throughout the follow up periods.

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)

Inclusion Criteria:

• Eligible volunteers must be at least 18 years old, partially edentulous in maxillary posterior region with 7-11 mm residual bone height under the sinus floor and be indicated for CBCT scan for diagnosis and treatment planning, and of a medical risk of ASA I or II classification to participate.

Exclusion Criteria:

• Patients with bone pathology, sinus infection, and who are pregnant will be excluded. Implants requiring tapping, site of an implant replacement, and implant with dehiscence and/or fenestration will be excluded.

Eligible volunteers must be at least 18 years old, partially edentulous in maxillary posterior region with 7-11 mm residual bone height under the sinus floor and be indicated for CBCT scan for diagnosis and treatment planning, and of a medical risk of ASA I or II classification to participate. Patients with bone pathology, sinus infection, and who are pregnant will be excluded.

Implants requiring tapping, site of an implant replacement, and implant with dehiscence and/or fenestration will be excluded.