The goal of this clinical trial is to understand how different implant neck designs and placement depths affect the surrounding bone and peri-implant tissue (the tissue around a dental implant) in adults who need implants in the back areas of the mouth (molars and premolars). The main questions it aims to answer are:

Does placing implants deeper under the bone crest (subcrestally) help preserve more bone and peri-implant tissue over time? Do implants with longer, conical necks and micro-threaded surfaces result in more stable peri-implant tissue than implants with shorter necks? Researchers will compare three types of one-piece dental implants with different neck heights (short, standard, and long), placed at different depths in the jawbone, to determine which combination better maintains bone and peri-implant tissue levels.

Participants will:

Receive two dental implants in the posterior upper or lower jaw Be randomly assigned to one of three groups depending on implant neck design and placement depth Undergo implant surgery using a digital workflow, with healing over three months Be rehabilitated with custom zirconia bridges Return for regular clinical and imaging checkups over a period of at least 3 years This study aims to generate evidence that helps clinicians choose implant designs and techniques that promote long-term peri-implant tissue health.

This randomized controlled clinical trial investigates the impact of different transmucosal neck configurations and vertical placement levels of one-piece dental implants on peri-implant hard and soft tissue stability over time. The trial specifically focuses on the PRAMA implant system (Sweden & Martina, Italy), which incorporates a ZirTi surface and a convergent neck design with an Ultrathin Threaded Microsurface (UTM). These implants are designed to optimize tissue integration and minimize marginal bone loss.

The study explores how subcrestal versus crestal placement of the rough-to-smooth transition, combined with variable neck lengths, influences peri-implant tissue outcomes under functional loading in posterior edentulous sites. Three types of PRAMA implants will be compared:

Short neck (1.8 mm total length with hyperbolic convergent shape)

Standard neck (0.8 mm cylindrical plus 2.0 mm convergent portion)

Long neck (0.8 mm cylindrical plus 3.0 mm convergent portion)

Each patient will receive two implants to support a 2- or 3-unit prosthetic bridge. The neck design determines the depth of implant placement:

Short group: coronal rough surface margin placed at bone crest (crestal placement)

Standard group: 1 mm subcrestal placement

Long group: 2 mm subcrestal placement

The trial adopts a parallel design, with a sample size of 30 patients (10 per group), allowing for adequate power while considering possible dropouts. Randomization will be performed electronically and concealed in opaque envelopes until surgery. Blinding is partially feasible, especially for radiographic and digital analysis where treatment allocation is masked.

Surgical procedures will be standardized using a fully digital workflow. Implants will be placed in healed sites without the need for bone grafting. Healing will be non-submerged using appropriate healing abutments. After three months, definitive zirconia bridges will be installed, and patients will be enrolled in a maintenance protocol.

In addition to comparing the impact of different neck designs and placement depths, the prosthetic crowns will be designed with two distinct emergence profiles: one simulating a natural root form extending apically, and the other adapted to the mucosal margin. This design will allow for the assessment of volumetric tissue adaptation based on prosthetic contour.

Primary outcomes will include longitudinal changes in marginal bone height evaluated through standardized periapical radiographs, CBCT, and digital scans. Secondary outcomes include:

Volumetric soft tissue changes assessed using superimposed 3D models derived from intraoral scans.

Comparison of tissue responses between the two crown designs (root-form vs. standard emergence).

Clinical parameters such as probing depth, plaque index, and bleeding on probing at designated follow-ups.

Radiographic and volumetric measurements will be performed by calibrated, blinded examiners. Imaging will be taken at baseline (prosthesis delivery), 6 months, and annually up to 3 years. Analytical methods include ANOVA or Kruskal-Wallis tests based on data distribution, with appropriate post-hoc comparisons and a significance level set at p < 0.05.

This study is expected to contribute relevant clinical data to the ongoing discussion around subcrestal implant placement and the role of implant macro- and micro-geometry in maintaining peri-implant tissue health.

Inclusion Criteria:

• Adults aged 21 years or older.
• Presence of an edentulous area in the posterior maxilla or mandible (premolar or molar region) that allows the placement of two dental implants.
• Alveolar bone height sufficient to permit implant insertion with a minimum depth of 6 mm, and total implant length of at least 10 mm.
• Indication for implant-supported prosthetic restoration (2- or 3-unit fixed dental bridge).
• Good general health with no contraindications for oral surgical procedures.
• Not pregnant at the time of screening.
• Willingness and ability to sign written informed consent and comply with study procedures.

Exclusion Criteria:

• Presence of uncontrolled systemic disease (e.g., diabetes, cardiovascular disorders, immunosuppression).
• History of chemotherapy or radiotherapy to the head or neck region.
• Heavy smokers (defined as >10 cigarettes per day)
• Previous bone regeneration or grafting procedures at the target implant site.
• Use of medications known to interfere with bone metabolism (e.g., bisphosphonates, corticosteroids).
• Poor oral hygiene or active periodontal disease that may compromise implant success.

-Known allergy or hypersensitivity to implant materials used in the study-

Individual participant data (IPD) will not be shared due to institutional policy and ethical considerations regarding patient confidentiality. Only aggregate-level results will be made publicly available through publications and study reports.

Allocation concealment is ensured via sealed opaque envelopes opened at the time of surgery. The surgeon is blinded to group assignment until after flap elevation, and the prosthetic team is unaware of crown design assignment until delivery. The outcomes assessor responsible for radiographic, CBCT, and 3D volumetric evaluations remains blinded to treatment allocation throughout the study.