One-time Abutment Placement Versus 4 Times Abutment Removal Around Dental Implants

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 denturesThere must be a natural tooth mesial to the most proximal implant site, however free end situations will be allowed for the distal implantsHealed sites (minimum 12 weeks post-extraction)In the case of prior bone augmentation, a minimum of 6 months of healing is requiredSimultaneous bone augmentation will be allowed only for close sinus liftingExclusion Criteria:Systemic exclusion criteria:Medical conditions requiring prolonged use of steroids and/or medications that can interfere with bone metabolismHistory of leukocyte dysfunction and deficienciesHistory of neoplastic disease requiring the use of radiation or chemotherapyHistory of renal failureMetabolic disorders such as osteoporosisHistory of uncontrolled endocrine disordersPhysical handicaps that would interfere with the ability to perform adequate oral hygieneAlcoholism or drug abuseHistory of immunodeficiency syndromesSmokers of >10 cigarettes per day, cigar equivalents or tobacco chewersAny 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 unreliabilityLocal exclusion criteria:Any kind of bone augmentation performed on the implant site, with a healing period of <6 monthsLocal inflammation (including untreated periodontitis)Mucosal diseases such as erosive liquen planusLess than 2mm of keratinized mucosa in the intended implant sitesHistory of local irradiation therapyPresence of osseous lesionsHistory of implant failurePost-extraction sites with <12 weeks of healingSevere bruxism or clenching habitsPersistent intraoral infectionExclusion criteria at surgery: in any of the following circumstances, the patient will not be randomized and will be excluded from the analysisLack of primary stability at surgeryNeed for crestal augmentation procedures during implant surgeryInability to place the implants according to the prosthetic requirements