Introduction & Objective: Due to the patients' growing interest in the use of dental implants, medical staff should be completely aware of treatment success and prognostic factors to prevent failures. The purpose of this study was to evaluate the effect of different crown to implant ratio (C / I Ratio) in the posterior areas of the maxilla and mandible as one of the most important principles of biomechanics on marginal bone loss around the implant neck (MBL). Material & Methods: This study was

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... onducted as a prospective cohort study. In this study, patients treated at a private dental implants office during the years 2013-2014 were selected. Parallel digital radiographs 6 months and 12 months after loading the implants were measured to evaluate the effects of prosthetic implants on posterior areas of the maxillary and mandibular crowns by a digital caliper. All patients were evaluated radiographically and data were collected and analyzed by SPSS 16 with non parametrical tests. Results: A total of 48 fixtures of SIC Implant System in 18 patients, including 28 pcs in maxilla and 20 pcs in mandible were evaluated. Statistical analysis of marginal bone level around the implant neck in radiograpy taken showed no significant difference in the effect of different C/I Ratio of marginal bone loss around implants (P=0.094). Comparison of posterior areas of the maxilla and mandible also showed no difference between the effects of different amounts of C/I Ratio of the marginal bone. Conclusion: The present study showed that the marginal bone loss was not statistically significant after the placement of implants in the posterior region of the jaw with a different range of crown – to- implant ratio from 0.87 to 2.55. Thus, it seems that there is no relationship between marginal bone loss around the implant neck with different proportions of crown - implant and with the location of the treatment (P>0.05). (Sci J Hamadan Univ Med Sci 2016; 23 (1):5-16)