Background/Objectives: The aim of this study is to examine the relationship between cervical spine and jaw bone mineral density (BMD) and assess how cortical thickness and BMD influence primary implant stability (PIS) across different bone health conditions. Methods: The study included 29 patients (mean age: 63.7 ± 13.7 years; 13 women) and 15 healthy controls (mean age: 25.3 ± 3.0 years; seven women). Cervical spine (C2–C4) and mandibular BMD were evaluated using asynchronous calibration and manual segmentation. Cortical thickness was measured, and primary implant stability was assessed via insertion torque in Newton centimeters (Ncm). Results: Cervical spine BMD was significantly lower in the patient group compared to controls (203.0 ± 51.0 vs. 252.0 ± 21.7 mg/dL, p < 0.0001). No significant correlation was found between mandibular BMD and cervical spine BMD in both groups (patients: ρ = 0.1287; p = 0.506, controls r = −0.1214; p = 0.667). Linear regression analysis revealed that cortical thickness alone, not implant site BMD, significantly influenced PIS (F(2.74) = 5.597, p = 0.005). Conclusions: Asynchronous calibration accurately quantifies cervical and mandibular BMD. Cortical thickness rather than overall bone density emerges as a critical factor in determining implant stability. These findings suggest that clinicians should prioritize cortical thickness assessment when planning dental implant procedures, potentially improving outcomes across diverse patient bone health profiles.