The Early Stability of Short vs. Standard Dental Implants with Identical Shallow-Thread in the Posterior Region of the Mandible: A Prospective Pilot Study.

BACKGROUND: Short dental implants are a less invasive alternative for the limited posterior mandible, but their early stability dynamics remain unclear compared to standard implants. PURPOSE: This prospective, non-randomized observational pilot study aimed to explore and descriptively compare early stability patterns (primary stability, stability dip, and recovery) between 7 mm short implants and 11 mm standard shallow-thread implants in the posterior mandible, treating implant length as the only design variable. MATERIALS AND METHODS: Ten patients received 20 implants (10 short, 10 standard) based on anatomical feasibility. Implant stability quotient (ISQ) was measured immediately post-implant placement (T0) and at the end weeks 1, 2, 3, and 5 (T1-T4). Insertion torque (ITV) was recorded. Linear mixed models (LMM) with patient random intercepts were the primary analysis. Bonferroni correction (α=0.005) was applied for 10 post-hoc comparisons. Bone density (D2/D3) by calibrated CBCT-HU. RESULTS: Primary stability (ITV and ISQ at T0) was similar between groups. Short implants showed nominal trends toward a larger dip magnitude (9.2±4.4 vs 5.9±2.3 ISQ units) and greater recovery (4.8±2.4 vs 2.6±2.2), but after Bonferroni correction none of the between-group comparisons at individual time points or intervals remained statistically significant (all p > 0.005). Bone density (D2 vs D3) had a statistically significant and clinically dominant effect on absolute ISQ at all times (LMM p<0.001). In the short-implant group, a moderate negative correlation between baseline ISQ and dip magnitude (r≈0.54) had wide confidence intervals that crossed zero and did not reach conventional statistical significance, and is therefore considered exploratory. CONCLUSIONS: Within the constraints of this small, nonrandomized pilot, 7-mm shallow-thread implants in D2-D3 bone demonstrated primary stability that was descriptively similar to 11-mm implants. Apparent differences in dip and recovery did not remain statistically significant after correction for multiple comparisons and should be interpreted as hypothesis-generating only. However, bone density exerted a greater influence on early ISQ than implant length. These observations provide effect-size estimates and testable hypotheses for future adequately powered randomized trials rather than practice-changing guidance.