Influence of Crestal Implant Position and Smooth Collar on Marginal Bone Level: A 2-Year Retrospective Radiographic Analysis.

Abstract

The aim of this retrospective study was to establish the survival rate and the clinical outcome of a an endoosseous implant system and to evaluate the marginal bone level and the impact of the positioning of the machined collar neck on crestal bone level changes up to two years follow-up. 96 implants were placed in 57 patients and loaded with final restoration after at least three months of healing time. 15 of these implants were immediately placed into fresh extraction sockets while 81 implants were inserted in healed ridges. Marginal Bone Loss around implants were determined radiographically after a mean observation time ranging between twelve and twenty-four months after loading. The effect of location (mandible v/s maxilla, anterior v/s posterior), immediate implant v/s native bone, smoking habit, gender, implant length and diameter, the type of prosthesis (screw-retained/cemented) and the positioning of the machined collar on the marginal bone loss was evaluated. Survival rates were evaluated based on the criteria as determined by Misch et al. in 2008. The Survival Rate at the implant level was 98, 96% at 1 year follow-up period. The mean marginal bone level has significantly changed over time in the overall sample after a follow-up period of one year (-p-value<0.001); it (average) decreased significantly by 0.238 mm between baseline and loading (-p-value<0.001; post-hoc test). It also decreased by 0.154 mm between loading and 1 year, however the decline was not significant (-p-value=0.085; post-hoc tests). After a follow-up period of two years, the mean marginal bone level has significantly changed over time in the overall sample (-p-value<0.001); it has decreased significantly by 0.263 mm between baseline and loading. It (Average) has also decreased by 0.111 mm between loading and 1 year and by 0.199 mm between loading and 2 years, but these declines were not significant (-p-value>0.05; post-hoc tests). The mean bone loss after 1-year and 2 years was not significantly associated with implants type, implant site (maxilla/mandible or anterior/posterior implants), smoking habits and type of implant's surgery (-p-value=0.792).However, it was significantly associated with the type of prosthesis; it was significantly elevated with cemented prosthesis compared to screw-retained prosthesis. A supracrestal positioning of the machined collar (tissue level placement) was associated with no bone loss, while placing the smooth part of the implant below the alveolar crest has led to bone loss over 2 years. Marginal bone loss after 1 and 2 years was not significantly associated with implants type, implant site (maxilla/mandible or anterior/posterior implants), smoking habits and type of surgery. However, it was significantly elevated with cemented prosthesis compared to screw-retained prosthesis. It was dependent also on the positioning of the machined collar.