Background: The aim of this ex vivo study was to compare the resistance to lateral wall failure during sequential implant site preparation using osseodensification (OD) burs and conventional rotary drills in a standardized narrow ridge model. The primary outcome was the drill diameter at first lateral wall perforation. Secondary outcomes included paired perforation occurrence at a clinically relevant diameter (4.0 mm) and perforation morphology (length and width). Methods: Twenty standardized trabecular bone blocks were prepared in a paired within-specimen design, with each block receiving two osteotomies: one prepared using conventional rotary drills and the other using OD burs. Osteotomy diameter was sequentially increased according to the manufacturers’ protocols until lateral wall perforation occurred. The drill diameter at first perforation was recorded. Perforation morphology (length and width) was quantified using high-resolution extraoral digital scanning and software-based measurements. Statistical analysis was performed using paired non-parametric tests (α = 0.05). Results: OD burs significantly delayed lateral wall perforation compared with conventional drills (median 4.30 vs. 4.00 mm; p = 0.0000171). At the 4.0 mm drill step, perforation occurred in 16/20 (80%) conventional versus 2/20 (10%) OD preparations (p = 0.0013). Perforation length was significantly greater with conventional drilling (p = 0.000681), while no significant difference was observed for perforation width (p = 0.073). Conclusions: Within the limits of this decorticated trabecular ex vivo model, OD increased resistance to lateral wall failure, delayed perforation onset, and reduced perforation length compared with conventional drilling.