Regarding the implant shoulder level, the average interproximal marginal bone level was − 0.49 ± 0.83 mm (range, 0 to − 3.3 mm) at the mesial aspect and − 0.51 ± 0.82 mm (range, 0 to − 3.9 mm) at the distal aspect of the implants.

When the marginal bone level was considered as a function of time, there was no strict correlation between the marginal bone status and the length of the follow-up period (r = 0.025, p = 0.764; Spearman rank correlation coefficient), suggesting that bone levels remained, by and large, stable during the observation period.

No relevant difference of marginal bone level was noticed for implants in the different risk factor groups (no RF − 0.53 ± 0.82, local RF − 0.50 ± 0.67, systemic RF − 0.63 ± 0.64, local and systemic RF − 0.17 ± 0.23).

The marginal bone level for implants inserted immediately (− 0.46 ± 0.68 mm) or delayed (− 0.52 ± 0.75 mm) did not show a difference (p = 0.676).