Subcrestal versus Bone-Level One-Stage Implants: Early Bone and Soft Tissues Modification: One-Year Randomized Clinical Trial  
Magda [PERSON]  
future peri-implantitis development and implant failure [7]. Therefore, several strategies and protocols have been tested with the aim of limiting implant bone loss. Sub-crestal implant placement has been introduced with the rationale that anticipating the expected early bone loss by adjusting the apico-coronal position of the implant could prevent the exposure of the treated and threaded area of the fixture, lowering the risk of biological and esthetic complications [2; 13; 14; 15]. Sub-crestal placement seems to be particularly important for patients with thin, soft tissues at the time of implant placement: a thin biotype seems to lead to more bone loss, possibly due to the space required for the establishment of a supracrestal tissue attachment of appropriate dimension [2; 9; 13; 16]. Overall, the benefits of sub-crestal implant placement are still controversial, as recent publications found no significant difference in bone loss around sub-crestal and equi-crestal implants [2; 17; 18]. However, some authors have recently started arguing that not all bone loss bears the same clinical weight: bone resorption occurring below the implant neck increases the risk of thread exposure and complications, whilst bone resorption above the implant neck leaves the fixture safely covered. Therefore, [PERSON] et al. [19] and [PERSON] et al. [15] introduced the distinction between bone remodeling, observed above the implant collar, and bone loss, which instead exposes the implant neck and threads. It is worth mentioning that only implants placed sub-crestally present bone above the collar which could buffer the initial bone modification as bone remodeling, whilst equi-crestal implants inevitably fall into the bone loss category. With this distinction in mind, it seems that sub-crestal implant placement might not prevent bone modification, but it mostly occurs as bone remodeling, with minimal observed bone loss [19]. Sub-crestal implant placement is often used in conjunction with a one-time abutment (OTA). An OTA consists of an immediate abutment placement at time of implant placement, which will be left in situ for all the restorative procedures, avoiding the multiple disconnection and reconnection of regular abutments during traditional workflows [20; 21; 22]. The use of an OTA may reduce the risk of damaging the supra-crestal soft tissue complex and the implant-to-abutment connection wear and tear [20; 23; 24; 25]. Other factors that seem to positively influence the initial bone modification relate to the implant design, specifically the choice of an internal conical connection and the platform switching. An internal conical connection between the fixture and the abutment seems to be less prone to bacterial infiltration and more stable under static and dynamic loads when compared to flat-to-flat connection systems [4; 26; 27; 28; 29; 30]. Platform switching of the abutment diameter is thought to provide a horizontal space for soft tissue attachment during the formation of the supracrestal tissue attachment, therefore reducing bone modification [5; 31; 32]. Finally, the choice of a screw-retained restoration over a cemented one [33; 34; 35] and the careful positioning of the restorative margin through the correct prosthetic abutment height [36; 37; 38] are important considerations for peri-implant tissue stability. The aim of the present study was to compare the early bone changes around conical connection, platform-switched implants placed at bone level or 2 mm sub-crestally. These changes were measured as marginal bone modifications (MBMs), a term describing the apical repositioning of the peri-implant marginal bone, within which a distinction was made between bone remodeling (BR) above the implant neck and bone loss (BL) below it.