The Early Stability of Short versus Standard Shallow-Threaded Dental Implants in the Posterior Region of the Mandible: A Prospective Clinical Pilot Study

Abstract

Short dental implants (≤ 8 mm) are increasingly used in the posterior region of the mandible with limited bony height; however, their early stability dynamics, particularly stability dip and recovery, remain unclear compared to standard implants. This prospective, non-randomized pilot study aimed to descriptively compare the early stability patterns (primary stability, stability dip, and recovery) between 7 mm short implants and 11 mm standard implants in the posterior region of the mandible. Ten patients received 20 implants (10 short, 10 standard) based on anatomical feasibility. The implant stability quotient (ISQ) was measured immediately after implant insertion (T0) and at the end of weeks 1, 2, 4, and 5 (T1–T4). The insertion torque value (ITV) was also recorded. Linear mixed models (LMM) were used to account for implant clustering within a single patient, confirming the primary t-test results. Bonferroni post-hoc correction ( α = 0.005) was applied to ten interval-time comparisons. Bone density (D2/D3) was assessed using Hounsfield (HU) units derived from CBCT (calibrated using a mock model and confirmed intraoperatively). The results revealed that initial stability (ITV, baseline ISQ) was comparable (P > 0.05). Before correction, short implants showed nominal trends toward greater reduction at T0-T1/T0-T2 (uncorrected P-values 0.049, 0.048) and stronger recovery at T1-T4 (P = 0.049). After Bonferroni correction, none of these differences remained statistically significant (all P-values > 0.005). Bone density had a dominant effect (D2 > D3, P < 0.008 by t-test and P < 0.001 by LMM). A moderate negative correlation was also observed in the short implant group (r = -0.54, wide confidence interval), which is an exploratory correlation. Based on these results, the study concluded that short implants achieved primary stability descriptively similar to standard implants. The difference in stability dip and recovery magnitude was not statistically significant after correction and is considered to be a hypothetical generation. However, bone density dominated the absolute stability. Therefore, correlation between mechanical stability and dip magnitude requires validation.