The effect of subcrestal placement of the polished surface of implants on marginal soft and hard tissues-a retrospective clinical study

Introduction: In order to improve the longevity of implants and to achieve esthetically more satisfying results, it has been proposed to place implants with their border between the rough and smooth surfaces below the level of the alveolar crest, thereby obtaining a submucosally located implant shoulder following healing. The aim of the present retrospective clinical study was to clinically and radiographically evaluate the tissue response to the placement of one-stage transmucosal implants with the border between the rough and the smooth surfaces sunk into a subcrestal location. Material and methods: In total, 84 ITI, 13 Brånemark and 5 Type Frialit-2 (n = 102) implants were included in the study. Probing bone levels (DIB), gingival inflammation (GI) and plaque index (PI) were recorded at 2 years, at 3-4 years, and at 5-7 years. Periodontal probing depth (PPD), "attachment" levels, width of keratinised mucosa, distance from the implant shoulder to the marginal mucosa (DIM), the sulcus fluid flow rate (Periotron, Harco, Winnipeg, Canada), and radiologic bone loss over time were measured at the same time intervals. All parameters were assessed at 4 sites around each implant. The mean for each implant was calculated and used for analysis. The Wilcoxon matched pairs signed rank test and the Student t-test were applied to detect differences over time. Results: Results showed an overall success-rate of 97.1%. Expected correlations between GI and PI, the sulcus fluid flow and the amount of gingival inflammation (GI), PPD and the amount of angular bone-loss were found to be significant. All implants lost a significant amount of clinical bone height during the first 2 years (1.57 mm, p = 1. Keratinised mucosa was found to decrease over time. Tendencies to increased PPD could be seen when only a small amount of keratinised mucosa was present. This could be associated with the formation of the biological width around dental implants. Conclusion: In addition to the crestal bone resorption occurring at implants placed under standard conditions, the bone adjacent to the polished surface is also lost over time. From a biological point of view, the placement of the border between the rough and the smooth surfaces into a subcrestal location should not be recommended. Keywords: longevity of implants, retrospective clinical study, periodontal tissue response, radiologic bone, one-stage transmucosal implants loss, subcrestal placement of implants