Over the past decade, implant research has focused on maintaining the health and stability of peri-implant tissues. A key factor is platform switching at the bone level, where a narrower abutment than the implant is used. This technique increases the implant's horizontal surface area for biological width establishment and reduces stress on the crestal bone.

Studies showed that repeated disconnection and reconnection of prosthetic components could compromise the mucosal barrier around implants, leading to an apical shift in the connective tissue junction and vertical tissue loss. This led to the "one abutment, one time" protocol, advocating the placement of the definitive abutment during initial implant surgery to avoid its removal during healing.

A recent meta-analysis indicated bone loss at the marginal level due to abutment connection and disconnection, despite different treatment protocols. Thus, a standardized abutment between the fixed prosthesis and the implant has been recommended to preserve marginal bone levels. This approach moves the biological width apically, protecting the bone from irritation and improving marginal bone isolation.

However, comparative evidence between direct implant-connected prostheses and trans-epithelial abutments is lacking. This study aims to evaluate the "one abutment, one time" protocol's effect on bone loss 12 months after prosthesis placement.

Secondary objectives include assessing patient satisfaction using Patient-Reported Outcome Measures (PROM) during prosthesis fabrication and placement, and obtaining information on the diversity and function of microorganisms on the implant using metagenomic techniques 12 months post-prosthesis placement.

Throughout the prosthesis fabrication and the first 12 months, various evaluations will be conducted in both abutment and Ti-base groups:

• **Bleeding:** Recorded during various prosthetic stages.
• **Pain:** Assessed using a visual analog scale after each stage.
• **Anesthesia:** Recorded if used at each stage.
• **Radiographs:** Number taken to check the fit.
• **Time:** Measured for each prosthetic phase.
• **Repetitions:** Number of repeated procedures quantified.
• **Metagenomic tests:** Samples collected following the Human Microbiome Project protocol to analyze microbial diversity and function.

Inclusion Criteria:

• Healthy partially edentulous adult patients needing at least two implants for the placement of single or consecutive crowns in the posterior mandible or maxilla will be recruited.
• These patients should exhibit a plaque index and gingival bleeding index of less than 25%, and have sufficient bone height and width for the placement of dental implants measuring 8 or 10 mm in length and 3.5 or 4 mm in diameter.
• Additionally, they must have at least 2 mm of keratinized vestibular gingiva, stable occlusion, and a periodontium in good health

Exclusion Criteria:

• Edentulous areas requiring bone grafts will be excluded.
• Patients with medical conditions contraindicating implant surgery, such as severe bruxism or inadequate oral hygiene.
• Pregnant or lactating women, patients undergoing bisphosphonate therapy, those receiving chemotherapy or radiotherapy in the head and neck area, non-compliant patients with incomplete data records, and those who do not attend regular follow-up appointments will also be excluded.