A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs

Background: It is claimed that bone remodeling is limited when the implant neck has microthreads and an internal abutment connection. However, comparative studies, excluding confounding factors, are scarce. Aim: This RCT aims to assess whether a coronal microthreaded design and an internal abutment connection affects crestal bone loss, up to one year of function. Materials and Methods: Twenty-one maxillary edentulous patients were consecutively treated for a bar supported maxillary overdenture on four different implants with respectively: internal connection and microthreads on the implant neck (I MT); internal connection, no microthreads (I NMT), external connection, with microthreads (E MT), and external connection, without microthreads (E NMT). Other design features, s.a. width, surface topography, platform switch as well as surgical placement and prosthetic protocol were consistent. Implant survival and crestal bone loss in relation to the implant type were considered the main variables and a Friedman test for ordered alternatives was used to assess the difference in crestal bone loss between the different study implants. Results: Twenty-one patients received 83 study implants. Three implants failed within three months and required replacement. The total survival rate was 96.39% after one year and based on 21 patients and 80 implants a mean crestal bone loss of 0.25 mm (SD: 0.38; range: 0-1.48) was measured. After a follow-up of 3, 6, 12, and 21 months no statistically significant differences in crestal bone loss between the different study implants or the different time intervals could be identified. Conclusions: From this RCT, it is concluded that the implant-abutment connection and a microthreaded external thread configuration have limited influence on crestal bone remodeling. The latter can be considered a multifactorial process and is more dependent on other factors such as biologic considerations than on implant design.