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P l a s m a e f f e c t o n a b u t m e n t s Introduction Periimplant soft- and hard-tissue stability is critical for the success of an implant-supported restoration, from a functional and esthetic point of view.1 It has been described that the relation- ship between the implant–abutment connection and surrounding hard and soft tissue plays an important role in establishing such mechanical and biological stability.2, 3 In fact, the literature has demonstrated that, when an implant is ex- posed to the oral environment after the connec- tion of a prosthetic component, periimplant hard-tissue level changes may occur4 and that the amount of bone remodeling, characterized by circumferential (horizontal and vertical) bone loss, should remain stable after one year.5 Sev- eral factors and, in particular, disruptions occur- ring after prosthetic connections may affect periimplant resorption,6 since the bacterial con- tamination of the implant–abutment junction from the oral cavity has been shown to trigger a hard-tissue response.7 Many strategies have been advocated to minimize the effect of this contamination clini- cally: mechanical improvement of the implant– abutment connection stability,8 implant– abutment microgap shifting from the vital bone,9–12 and reducing the number of abutment dis- and reconnections.6 Nevertheless, minimal bone resorption (0.5 mm) has been observed in longitudinal analysis.13 Bone resorption might be related to the con- taminants (bacteria, wear microparticles and pollution from laboratory procedures) present on the abutment at the time of implant– abutment connection. In fact, the presence of contaminants on the abutment surface can still be observed after the steam cleaning protocol after technical laboratory procedures.14 Since the abutment comes into contact with both bone and connective tissue, abutment cleanliness appears to be important. In fact, the presence of contaminants at the platform–abutment level has been suggested to cause associated tissue- damaging inflammation.14 Titanium wear micro- particles have been demonstrated to activate osteoclastogenesis.15 Additionally, it has been shown how interactions between cellular com- ponents and implant–abutment materials influ- ence the healing process around implants and how these interactions are regulated by the state of the surface.16 In order to protect abutments against such pollutants, plasma cleaning of customized abut- ments has recently been advocated.17 Plasma cleaning has been demonstrated in vitro to have a triple effect on titanium: cleaning, corrosion protection and increased surface energy.18, 19 However, there is a lack of evidence in the litera- ture regarding the clinical relevance of a plasma cleaning procedure performed on dental implant abutments. Although there are certain differences in the inflammatory response and in the bacterial popu lation, the beagle dog model has been ex- tensively used in experimental study because of its size and its extremely cooperative nature. Although some major differences exist between dogs and humans, all periodontal tissues and the size of the teeth are quite similar to those observed in humans. Furthermore, they are a very inbred type of animal with very limited ana- tomical differences between the various dogs. The aim of this animal study was to assess histologically soft- and hard-tissue adaptation after insertion of cleaned and activated titanium implant abutments. The null hypothesis was that argon plasma cleaning treatment of abut- ments does not have any positive or detrimental effect on periimplant bone remodeling and soft-tissue adhesion. Materials and methods S u b j e c t s This study followed the ARRIVE guidelines.20 The research protocol was approved by the local ethics committee for animal research at the Uni- versity of São Paulo, Ribeirão Preto, Brazil. Eight beagle dogs were used for the experi- ment. The animals were pre-anesthetized for all surgical procedures with Acepran 0.2% (0.05 mg/kg; Univet-vetnil, São Paulo, Brazil) and sedated with Zoletil (10 mg/kg; Virbac, St. Louis, Mo. U.S.), and the maintenance of the anesthesia was performed with inhalation of Forane (Baxter Hospitalar, São Paulo, Brazil). All mandibular premolars and the first molars were extracted bilaterally and after three months, a crestal incision was performed in the premolar–molar region of one randomly select- ed side of the mandible. Full-thickness muco- periosteal flaps were elevated, and four experi- mental sites were selected in the edentulous alveolar ridges of the mandible, two in the an- terior and two in the distal regions. The surgical preparation of the sites was performed accord- Journal of Oral Science & Rehabilitation Volume 3 | Issue 2/2017 09