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

Short dental implants are a less invasive alternative for the limited posterior mandible, but their early stability dynamics remain unclear compared to standard implants.

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.

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.

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.

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.