A Predictive Bioengineering Model of Dental Implant Instability in Systemic Bone Disorders: A Periotest-Based Analysis

(1) Background: Dental implant instability represents a dynamic biomechanical process influenced by functional loading, peri-implant bone stiffness, and systemic conditions affecting bone metabolism. In patients with systemic bone disorders, altered material properties and impaired remodeling may reduce effective implant–bone interface stiffness, potentially increasing micromotion beyond what is detectable by conventional clinical indicators. The aim of this study was to develop and evaluate a predictive bioengineering model of implant instability based on Periotest-derived dynamic measurements. (2) Methods: A retrospective analysis was performed on 79 dental implants placed in patients with and without systemic bone disorders. Implant micromotion was quantified using Periotest values (PTVs). Linear and logistic regression analyses were applied to model the relationship between systemic bone status, implant location, and biomechanical instability (defined as PTV > +2.0). A load–stiffness–micromotion framework was used to provide mechanical interpretation of the findings. (3) Results: Implants placed in patients with systemic bone disorders exhibited significantly higher Periotest values compared to controls (+2.1 ± 1.3 vs. −0.4 ± 1.1; mean difference 2.5 PTV units, 95% CI 1.97–3.04; p < 0.001). High-risk biomechanical instability (PTV > +2.0) was observed in 46% of implants in the systemic group compared to 9% in controls. Multivariable logistic regression demonstrated that systemic bone disorders were independently associated with a 2.6-fold increase in the odds of high-risk instability after adjustment for implant location. The observed instability pattern was consistent with reduced effective peri-implant stiffness in systemically compromised bone. (4) Conclusions: Dental implant instability in systemically compromised patients can be interpreted as a load–stiffness imbalance at the implant–bone interface. The proposed predictive bioengineering framework links dynamic Periotest measurements with mechanical modeling and systemic bone status, enabling quantitative risk stratification beyond static stability assessments.