Objective A novel implant design, the rectangular block implant (RBI), was investigated as a possible solution to the restoration of the posterior resorbed ridge. Aim To maximally load test the osseo‐integrated RBI in shear and tensile loads and relate these findings to known human masticatory loads as biomechanical proof of the study concept. Materials and methods Twelve RBIs were design‐manufactured and placed into posterior mandibular saddles in 3 mature greyhound dogs.—2 per left and right. After 12 weeks of healing, osseo‐integration was confirmed using resonance frequency analysis (RFA) and wrench torque tests. Three bone blocks each with two RBIs were dissected and mounted in acrylic. Micro‐computerized tomography (μ‐CT) was performed to assess bone to implant contact (BIC), and load analysis was performed using a Universal Test System. Three force applications were conducted until failure: pull‐out (tensile), buccal push from the lingual (shear) and distal push from the mesial (shear). The osteotomy sites were examined using light magnification and scanning electron microscopy (SEM). Results Pull‐out, buccal and distal force failures occurred at differing levels. Post‐detachment sites showed complex patterns of bone failure, including trabecular and cortical fracture, as well as shearing at varying distances from the BIC. Interfacial shear strength was calculated at 14.4 MPa. Conclusion The osseo‐integrated RBIs were able to withstand simulations of the demanding axially, bucco‐lingually and mesio‐distally oriented biomechanical challenges of the posterior saddle, under conditions of reduced bone volume. These values exceeded equivalent force components of maximal masticatory loads in humans.