Early Stability of Short vs. Standard Dental Implants in the Posterior Mandible

This study compares how well short dental implants (7mm) work compared to standard-length implants (11mm) when placed in the back part of the lower jaw. Both types of implants have special shallow threads designed to reduce stress on the bone. The main goal is to see how stable they are during the first 4 weeks after placement-a critical time for healing.

• Short implants may be a good option for patients with limited jawbone height, avoiding the need for bone grafting.
• Understanding their early stability helps dentists decide when it's safe to place teeth on them.
• This study uses advanced tools like 3D scans (CBCT) and implant stability measurements (ISQ) to track healing.

What will happen in the study?

1. Screening: A dental exam and 3D scan to check bone quality.

2. Implant Placement:

   • Short (7mm) or standard (11mm) implant, depending on your bone height.
   • Minimally invasive surgery with local anesthesia.

3. Follow-ups: Painless stability checks at end of 1, 2, 3, and 4 weeks using a small device (RFA).

Who can participate?

Adults (18-60 years) missing posterior teeth in the lower jaw, with:

• Enough bone width (≥6.5mm).
• No uncontrolled health conditions (e.g., severe diabetes).
• Non-smokers or light smokers (<10 cigarettes/day).
• Benefits: Free implant placement and monitoring; contributes to better dental care.
• Risks: Typical surgery risks (swelling, infection); rare nerve injury (<5% chance).

How long is the study?

• Active participation: 4 weeks (with optional long-term follow-up).
• Total study duration: ~12 months (including data analysis). Mohammad Abdulwahab Al-Jonaid University of Science and Technology, Sana'a.
• Supervisor: Dr. Ali Al-Hudaied, Oral and Maxillofacial Surgery Specialist.

A prospective, controlled, parallel-group pilot clinical trial comparing 7mm short implants (SHI) versus 11mm standard implants (SDI) with identical shallow-thread macrodesign (depth <0.5mm) and 4.2mm diameter. Implant allocation is anatomically driven based on CBCT-measured vertical bone height (7mm group: 8.5-9mm residual bone; 11mm group: ≥12.5mm).

Technical Innovations

1. Thread Geometry: Dual shallow-thread reverse-buttress design (0.2-0.5mm depth) with progressive pitch to optimize cortical engagement while minimizing shear stress (Ao et al. 2010).

2. Surgical Protocol: Standardized osteotomy using under-drilling for D2 bone (final drill diameter reduced by 0.2mm) and non-condensing drilling for D3 bone to prevent over-compression.

3. Stability Metrics:

   • Primary Stability: ITV (last quarter-turn torque) + ISQ (Penguin RFA, mean of 4-directional measurements).
   • Dynamic Stability: ISQ tracked at T0 (baseline), T1 (7d), T2 (14d), T3 (21d), T4 (28d) to capture dip magnitude (ΔISQ) and recovery onset (start of biological stability).

Bone Density Integration

• Pre-op CBCT: Hounsfield Unit (HU) stratification (D2: 800-1250 HU; D3: 350-850 HU) with 2mm² ROI analysis at coronal/middle/apical levels.
• Intra-op Validation: Tactile assessment using Lekholm & Zarb scale (D2: "white pine" resistance; D3: "balsa wood").

Quality Controls

• Operator Standardization: Single experienced surgeon performs all placements.
• RFA Calibration: Pre-measurement checks with reference block and standardized SmartPeg torque (5-10 Ncm).
• Blinding: ISQ measurements by research assistant masked to implant type.

Rationale for 4-Week Endpoint

Focuses on the critical early healing phase where:

1. Primary stability (mechanical) transitions to secondary stability (biological).
2. The "stability dip" (week 2-4) predicts osseointegration failure risk.

Technical Constraints

• Limited Sample Size (n=20): Pilot study design prioritizes feasibility over powered comparisons.
• Bone Density Homogeneity: Excludes D1/D4 bone to reduce confounding.

Innovative Aspects

First clinical study to combine:

1. Shallow threads + short length in posterior mandible.
2. Weekly RFA tracking during the dip phase.
3. HU-quantified bone density correlation with ISQ trends.

Inclusion Criteria:

• 1. Adults ≥18 years with partial posterior mandibular edentulism. 2. Bone height ≥7 mm and width >6 mm (CBCT-confirmed). 3. D2/D3 bone density (HU: 350-1250). 4. Healed posterior mandibular sites (3-6 months post-extraction). 5. Good oral hygiene (plaque index ≤1). 6. Willingness to adhere to study protocols.

Exclusion Criteria:

• 1. Uncontrolled systemic diseases (e.g., diabetes with HbA1c >7%, liver disease) or medications affecting bone healing (e.g., corticosteroids, bisphosphonates).

  2. History of head/neck radiotherapy (with in past year). 3. Heavy smoking (>10 cigarettes/day). 4. Absolute contraindications for oral surgery (e.g., recent MI/CVA < 6months, bleeding disorders).

  5. Active periodontal disease, parafunctional habits as bruxism, or prior bone grafting at the site.

Anonymized data available upon request after publication

6 months from 21/07/2025

De-identified individual participant data will be made available upon reasonable request to corresponding author . Requests require a methodology sound proposal and a signed data access agreement.

This clinical trial employs partial masking (blinding) to minimize bias in outcome assessments:

1. Blinded Parties

   • Outcome Assessors:
   • The researcher performing resonance frequency analysis (RFA) measurements (ISQ values at T0-T4) is masked to:
   • Implant length (7mm vs. 11mm)
   • Insertion torque value (ITV) Rationale: Prevents measurement bias in stability tracking.
   • Data Analysts:
   • Statisticians processing ISQ trends are blinded to group allocation until analysis completion.

2. Non-Blinded Parties

   • Surgeon: Cannot be masked due to visual/tactile differences during osteotomy preparation.
   • Patients: Aware of implant type due to post-operative healing abutment visibility.

3. Blinding Methods

   • RFA Protocol:
   • SmartPeg placement/readings performed by a separate researcher not involved in surgery.
   • ISQ values recorded using coded forms without implant length details.