This prospective, randomized pilot clinical trial will evaluate the effect of dental implant macro-design and surface treatment on insertion torque values (ITV) and early implant stability quotient (ISQ) trajectories in healed posterior mandibular bone. The study has been approved by the Vilnius University Regional Bioethics Committee (approval no. 2025/11-1722-1165) and will be conducted at a private dental clinic (Dantų implantologijos centras, Vilnius, Lithuania).

Fifty implants will be randomly allocated to five groups of ten implants each, comparing two implant macro-designs - Straumann Bone Level Tapered (BLT) and Megagen BlueDiamond (BD) - combined with different surface treatments: (1) BLT with a sandblasted, large-grit, acid-etched (SLA®) surface plus chairside vacuum plasma activation (XActive®); (2) BLT with a manufacturer-hydrophilic SLActive® surface; (3) BD with a nanostructured calcium-incorporated Xpeed® surface plus chairside plasma activation; (4) BD with the standard Xpeed® surface (no plasma activation); and (5) BLT with a standard SLA surface (control, no plasma activation). Randomization will be performed by drawing a sealed envelope indicating group assignment immediately after osteotomy preparation and before implant placement.

Eligible participants will be adults aged 18 years or older requiring a single dental implant in a healed mandibular molar site (at least 3 months post-extraction) suitable for a 4.1 × 10 mm implant.

Insertion torque will be recorded in Newton centimeters (Ncm) using a prosthetic torque wrench at the time of implant placement. Implant stability will be measured non-invasively by resonance frequency analysis (RFA) using a SmartPeg, with ISQ recorded at four timepoints: at implant placement (baseline) and at 2, 4, and 6 weeks after placement. The primary comparisons will be (1) insertion torque according to implant macro-design (BLT vs. BD) and (2) the trajectory of ISQ change from baseline through 6 weeks according to surface treatment/plasma activation status. Correlation between insertion torque and ISQ will also be assessed. Also marginal bone maintenance (loss) will be documented from periapical radiographs obtained during prosthetic and 1 year follow-up visits.

As a pilot study, this trial is designed to assess feasibility, estimate effect sizes, and inform sample-size calculations for a future, adequately powered randomized controlled trial comparing implant macro-design and surface activation strategies for early implant stability.