The effect of horizontal microgap location on the bone loss around 2-piece implants

Abstract

The long-term success of endosseous implants depends mainly on integration between implant components and oral tissues, including hard and soft tissues. Maintenance of osseointegration and a steady state in marginal bone level are therefore imperative. However, initial breakdown of the implant-tissue interface generally begins at the crestal region even in successfully osseointegrated endosseous implants.1-4 In particular, after the first year of function, crestal bone loss to or beyond the first thread of titanium screw implants, characterized by saucerization, is often observed radiographically around 2-piece implants. In 1981, Adell et al.1 reported an average of 1.2 mm marginal bone loss after loading. Thereafter, many investigations2-4 have shown that 2-piece titanium implants had 0.9 mm to 1.6 mm marginal bone loss from the first thread by the end of first year in function. There is a lack of agreement as to why greater bone loss occurred during healing and the first year of implant function than following years. Microgap in 2-piece implant and biologic width formation around endosseous implants seem to play an important role in marginal bone resorption. The influence of the microgap on the peri-implant tissue formation during healing was studied in dogs by Hermann et al.25-28 The results indicated that the crestal bone level is dependent on the location of the microgap in all 2-piece implants. The study suggested that epithelial proliferation to establish a biologic width could be responsible for the crestal bone loss about 2mm below the microgap. Recently, there are some attempts to reduce marginal bone loss by supracrestal positioning of the implant collar.25-28,30,37 However, there is lack of data concerning the effect of horizontal change of microgap location on the bone loss around 2-piece implant. The aim of present study was to examine the effect on the marginal bone loss around 2-piece implants when the microgap shifts centrally to the