The aim of this study was to analyze the primary stability of BoneTrust Sinus implants (BTSIs), which are intended to enable higher primary stability by their special design with reduced thread section in cases of reduced vertical bone availability, in comparison with standard BoneTrust implants (SBTIs) in vitro. A bone window 3 cm in length, 4 cm in width, and 3 cm in depth, resembling the maxillary bone window of the lateral sinus wall with 4 mm of residual bone height, was prepared at the dorsal side of freshly slaughtered bovine ribs. One single BTSI and a single SBTI with the same diameter (4 or 5 mm) were placed in each window. After implant placement, the implant stability quotient (ISQ) was measured by using resonance frequency analysis with an Osstell device. A total of 88 implants were placed. ISQ values varied between 63 and 84. Among the implants with 4-mm diameter, all BTSIs showed higher ISQ values compared with SBTIs. One-way analysis of variance showed a significant difference between BTSIs/SBTIs (P .05). BTSIs with 4-mm diameter showed statistically higher values compared to BTSIs with 5-mm diameter (P .05). Among the implants with 5-mm diameter, all SBTIs showed higher ISQ values compared to BTSIs but there was no significant difference. The use of 4-mm-diameter BTSIs could present higher ISQ values during simultaneous implant placement in conjunction with lateral sinus floor augmentation.