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.
