The primary aim of this randomized clinical trial is to evaluate the influence of subcrestal implant placement depth (-2 mm vs -4 mm) on peri-implant marginal bone level changes, including marginal bone loss and bone remodeling. Secondary outcomes include implant success, peri-implant probing depth (PPD), and bleeding on probing (BoP).
Partially edentulous patients requiring fixed implant-supported prosthetic rehabilitation with two implants in posterior maxillary or mandibular regions will be included. Implants will be placed subcrestally at either -2 mm or -4 mm from the bone crest, following a submerged healing protocol. Allocation to insertion depth will be randomized. Marginal bone level changes will be assessed using standardized periapical radiographs at second-stage surgery, prosthesis placement, and at 1, 3, 6, and 12 months after functional loading. PPD and BoP will be recorded at the same time points.
Patients ≥18 years old with partial edentulism.
Need for rehabilitation with fixed implant-supported prostheses in posterior regions.
Availability of minimum bone height for implants ≥6 mm in length.
Minimum bone width without the need for guided bone regeneration.
Systemic diseases contraindicating implant surgery.
Treatment with intravenous bisphosphonates.
Head and neck radiotherapy.
Uncontrolled diabetes.
Parallel
Subcrestal Implant Placement with Transmucosal Abutment and One Abutment-One Time Protocol
Procedure/SurgeryParticipants will receive bone-level dental implants placed subcrestally at either -2 mm or -4 mm below the bone crest in healed posterior sites of the maxilla or mandible, according to randomization. Implant placement will follow the manufacturer's drilling protocol, achieving a final insertion torque of at least 35 Ncm. A transmucosal abutment will be connected at the time of surgery, with height selected based on implant placement depth (2-3 mm for -2 mm placement and 4-5 mm for -4 mm placement). The abutment will be tightened to a final torque of at least 30 Ncm following a one abutment-one time protocol.
Changes in peri-implant marginal bone level (mm)
Parallelized periapical radiographs will be obtained and a calibrated digital tool will be used to determine the vertical distance from the implant-abutment junction to the most coronal bone-to-implant contact on the mesial and distal sides. Unit of measure: Milimeters (mm)
Peri-implant probing depth (mm)
Peri-implant soft tissue condition will be assessed by recording PPD using a periodontal probe at six surfaces per implant (mesiobuccal, midbuccal, distobuccal, and the corresponding lingual/palatal sites) to calculate the mean of every implant. Unit of measure: Milimeters (mm)
Bleeding on probing (presence/absence)
Bleeding on probing will be measured by gently passing a periodontal probe (using \~20-25g of force) to the base of the sulcus/pocket of the prosthesis at six surfaces per implant (mesiobuccal, midbuccal, distobuccal, and the corresponding lingual/palatal sites), then waiting 30 seconds to observe bleeding. It will be recorded as a dichotomous score (yes/no). Unit of measure: Percentage of sites showing bleeding per implant.
Implant success
Assessment of the implants will be performed by categorizing them into: success (optimal health), satisfactory survival, compromised survival, or failure.
Baseline characteristics
Baseline variables will be collected for descriptive purposes and will not be combined into a single outcome measure. These include: age (years); sex (male/female); smoking habit (non-smoker or ≤10 cigarettes/day); brushing frequency (0, 1-2, or 3 times/day); edentulism type (interdental or free end); periodontal phenotype (thin or thick); antagonist type (natural teeth, tooth-supported bridge, implant-supported prosthesis, or removable prosthesis); cause of tooth loss (caries, periodontitis, or fracture); implant location (arch and quadrant); and soft tissue thickness (mm).
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