ObjectiveThis study was performed to determine whether the distance between an implant and a tooth present in an inter-proximal unit influenced the amount of marginal bone loss that occurred at the two facing (adjacent) surfaces. Materials and methodsOne hundred and eighty patients with a total of 278 inter-proximal units were included. Radiographs of implants that also included adjacent (facing) natural tooth/teeth were digitalized, and various linear measurements were performed using a software program. The marginal bone level and the bone level change that had occurred during a mean of 5.8years were assessed as well as distance between the implant and the adjacent tooth/teeth. ResultsThe mean amount of additional marginal bone loss that took place during the observation period was about 0.4mm at both implants and adjacent tooth surfaces. The horizontal distance between an implant and the facing tooth did not influence the amount of marginal bone loss that had occurred. In most inter-proximal units, more advanced bone loss (>1mm, >2mm) had ensued either at the implant or at the facing tooth surface. Advanced additional bone loss occurred at both the implant and the tooth in only about 3% of the examined subjects. ConclusionBone loss at implants and teeth appears to be a site-specific phenomenon and not dependent on the inter-proximal distance.