Effects of the crown-to-implant ratio on the peri-implant marginal bone loss in a single Astra implant

Abstract

The aim of this study was to evaluate the long-term influence of the C/I ratio on the crestal bone loss around Astra single dental implants placed in the premolar and molar regions. The same definition of the C/I ratio (i.e., the ratio of the clinical crown length to the clinical implant length), implant design, surface texture, and configuration were used in all comparisons. Seventy-six subjects(40 males and 36 females; age range:39 to 71 years; mean age: 55 SD:8.5) were selected from patients who were treated with single Astra implants(AstraTech STTM , Astra Techs Dental Implant System; Astra Tech AB, Mölndal, Sweden) for replacement of missing premolars and molars at the Department of Periodontology, Gangnam Severance Dental Hospital between January 2003 and May 2005. All implants demonstrated at least 6 years of follow up.Peri-implant marginal bone loss were assessed one year after functional loading and six years after functional loading.The peri-implant marginal bone level change and gingival parameters (modified plaque index and modified sulcus bleeding index) of the peri-implant soft tissue were assessed one year after functional loading and six years after functional loading. The implant sample was divided into three groups according to the ratios of the implant restorations(percentile). A “higher C/I ratio” was defined as implants having a C/I ratio 1.12-2.38(1.10= 66.7 percentile). “medium C/I ratio” and “lower C/I ratio” was defined as implants having a C/I ratio 0.95-1.10 and 0.60-0.94 respectively.ANOVA analysis was used to statistically evaluate peri-implant marginal bone loss among three groups; no statistically significant relationship was found among the groups(p=0.82). No statistically significant difference were found between C/I ratio and crestal bone loss. (Pearson correlation analysis ; p=0.58).The Chi-squared trend test was used to analyze difference in technical complications among higher, medium and lower C/I group(p=0.162).Peri-implant soft tissues were clinically healthy and revealed low modified plaque index (mPI) and modified sulcus bleeding index (mSBI). mPI around higher C/I ratio group >mPI around medium and lower C/I ratio group. mSBI around higher C/I ratio group >mSBI around medium and lower C/I ratio group(p <0.05).From this study, we conclude that a higher C/I ratio does not increase the risk of peri-implant marginal bone loss during 6 years of functional loading.