Bone Retention Without Osseointegration During Antiresorptive Therapy: A Rat Model of Immediate Implant Placement Following Prolonged Ligature-Induced Periodontitis

Background/Objectives: Immediate implant placement in sites with prolonged ligature-induced periodontal disease during antiresorptive therapy is poorly modeled. This study investigated whether zoledronic acid (ZA) could preserve peri-implant bone sufficiently to support osseointegration in a rat challenge model. Methods: Thirty-two adult male Wistar rats received saline (SAL) or ZA (ZOL). Ligature-induced periodontitis was maintained for seven weeks around the mandibular first molar, followed by extraction and immediate placement of a commercially pure titanium implant. Animals were euthanized after 28 days. Removal torque (RTQ), SEM-EDX, and micro-computed tomography were assessed alongside undecalcified histology, which underwent qualitative evaluation and blinded exploratory semiquantitative scoring. Results: Median RTQ and peri-implant bone volume fraction (BV/TV) were numerically higher in ZOL than SAL animals (RTQ: 4.0 vs. 2.5 N·cm, p = 0.104; BV/TV: 46.5% vs. 28.0%, p = 0.113), but neither difference reached statistical significance. Histology showed near-complete absence of new bone–implant contact, with median scores of 0 in both groups. Compared with SAL, ZOL specimens showed descriptively greater retention of alveolar architecture, while 4 of 8 specimens had no detectable viable bone in the assessed peri-implant region. Epithelial coverage scores were lower in ZOL than in SAL (median: 0 vs. 2; nominal p = 0.027). Conclusions: Under the combined experimental conditions, retention of peri-implant mineralized tissue did not correspond to meaningful regenerative osseointegration. The findings distinguish bone quantity and mechanical anchorage from direct biological integration and should not be extrapolated directly to routine clinical implant therapy.