Introduction: the repeated connection and disconnection of healing abutments during dental implants´ osseointegration has been associated with significant increased peri-implant bone loss, when compared with placing the final prosthetic abutment during implant placement surgery and non-removing it ever again. Previous data from animal studies suggests that the higher the number of removals of the healing abutments, the greater the bone resorption around implants, however the evidence in humans is scarce and heterogeneous. Furthermore, this greater bone resorption has been claimed to be associated to the inflammatory status of the peri-implant soft tissues, which would be greater as a consequence of the repeated disruption of the soft-tissues attachment to the prosthetic abutment, and the hypothetical microbial contamination of the implant-abutment interphase, induced by the repeated manipulation of the prosthetic components.

Objective: to evaluate the changes in peri-implant crestal bone levels between two prosthetic protocols, the control being the conventional protocol where healing abutments are placed during surgery and removed four times before the delivery of the final abutment and prostheses, and the test protocol where definitive abutments are placed immediately after implant placement and are not removed ever again.

Material and methods: 80 platform switched implants will be placed in the posterior maxilla or mandible of 40 partial edentulous patients. Immediately after implant placement, patients will be randomized to receive the definitive abutment at the moment of implant placement (one abutment-one time protocol), or 12 weeks later, after removing the healing abutment four times during the confection of the final prostheses, following the conventional protocol for implant supported restorations. The day of prostheses delivery, a mucosal biopsy from the implant surrounding tissues will be taken for histomorphometric and immunohistochemical analyses of the inflammatory response of the peri-implant soft tissues. Radiographic assessment of vertical bone level changes (primary outcome), clinical status of peri-implant tissues, changes in soft tissues margin, patient related outcomes and adverse events will be assessed at 6, 12, 24 and 36 months after loading.

Inclusion Criteria:

• At least two adjacent missing teeth in the posterior maxilla or mandible (positions 4 to 7)
• Willing to receive implant supported fixed partial dentures
• There must be a natural tooth mesial to the most proximal implant site, however free end situations will be allowed for the distal implants
• Healed sites (minimum 12 weeks post-extraction)
• In the case of prior bone augmentation, a minimum of 6 months of healing is required
• Simultaneous bone augmentation will be allowed only for close sinus lifting

Exclusion Criteria:

Systemic exclusion criteria:

• Medical conditions requiring prolonged use of steroids and/or medications that can interfere with bone metabolism
• History of leukocyte dysfunction and deficiencies
• History of neoplastic disease requiring the use of radiation or chemotherapy
• History of renal failure
• Metabolic disorders such as osteoporosis
• History of uncontrolled endocrine disorders
• Physical handicaps that would interfere with the ability to perform adequate oral hygiene
• Alcoholism or drug abuse
• History of immunodeficiency syndromes
• Smokers of >10 cigarettes per day, cigar equivalents or tobacco chewers
• Any other condition or circumstance that, in the opinion of the investigator, would prevent completion of the study participation or interfere with the analysis of the study results, such as history of non-compliance or unreliability

Local exclusion criteria:

• Any kind of bone augmentation performed on the implant site, with a healing period of <6 months
• Local inflammation (including untreated periodontitis)
• Mucosal diseases such as erosive liquen planus
• Less than 2mm of keratinized mucosa in the intended implant sites
• History of local irradiation therapy
• Presence of osseous lesions
• History of implant failure
• Post-extraction sites with <12 weeks of healing
• Severe bruxism or clenching habits
• Persistent intraoral infection

Exclusion criteria at surgery: in any of the following circumstances, the patient will not be randomized and will be excluded from the analysis

• Lack of primary stability at surgery
• Need for crestal augmentation procedures during implant surgery
• Inability to place the implants according to the prosthetic requirements