Aim: The objective of this retrospective cohort study was to compare the amount of marginal bone loss (MBL) in a bone-level and a soft-tissue-level implant system, both of which have similar intra-bony shape and surface composition. A subgroup analysis was done to compare the amount of MBL of each implant type in relation to the different vertical placement within the respective groups of implants.
Materials and methods: Records of all patients who underwent implantation for replacement of teeth using comparable bone level (BL) and soft tissue level implants (TE) from 1st January 2006 to 31st December 2009 were scrutinized. Initial depth of implant placement (IDIP) was measured for all implants. Marginal bone loss was measured in patients whose records were available at time point corresponding to 12, 24 and 36 months post insertion.
Results: Out of a total of 384 implants, 337 implants were included for study. The mean MBL for the BL implants were 0.3, 0.38, 0.48 and for TE implant were 0.6, 0.54 and 0.93 for time periods 12, 24 and 36 months respectively. Although there was no statistically significant difference between the two groups at time periods at 6-12 months, in later time periods, there was a slightly greater amount of MBL around TE implants as compared to BL implants (p < 0.001). When comparing the IDIP and MBL in the same implant type, there was a statistically significant (p < 0.001) positive correlation between the depth of implant placement and the amount of MBL, with deeper placed implants having more bone loss.
Conclusion: Within the limitations of this retrospective cohort study design, one can conclude that BL implants had statistically significant lesser MBL as compared to TE in time periods above 12 months. Although the difference is statistically significant, the difference may not be clinically significant. The IDIP had an influence on the amount of MBL, with deeper placed implants and screw structure of the implant placed below the bone, having more MBL in the period of study.
Keywords: Bone level implant; Bone loss; Implant depth; Marginal bone level; Retrospective clinical study; Tissue level implant.