Data from available literature indicate that if submerged/nonsubmerged techniques do affect CBL, this effect could be associated with the post-operative healing period [9, 23, 24]. In the present study, at the end of the follow-up period (3 years), no significant difference was detected in CBL around submerged and nonsubmerged implants. A possible explanation for this observation could be that stimuli at the bone-implant interface led to the functional adaptation of the bone and connective tissue to the loading situation and to a similar differentiation, resulting in an equal CBL between submerged and nonsubmerged implants.

Few comparative studies between submerged and nonsubmerged implants reported data on PD. At the end of the 3-year follow-up, Sanz et al. [25] in a randomized controlled clinical trial found a similar mean PD value of 2.5 mm around both implants. Similar values have been reported also by the RCT of Flores-Guillen et al. [14] who, after 5 years of loading, founded a mean PD value of 2.40 (SD 0.7) mm for submerged implants and 2.31 (SD 0.40) mm for nonsubmerged implants. In the present study, after 3 years of function, the mean PD value for submerged implants was 0.7 ± 0.4 mm, while for nonsubmerged implants was 0.8 ± 0.1 mm. Differences in PD, compared with overmentioned RCTs, could be related to the presence of a laser-produced microgrooved collar surface on the investigated implants. Histological results in humans documented that the application of this technology allows to obtain a physical attachment of connective tissues to the microgrooved collar. The high mechanical stability and functional orientation of the connective fibers may allow the formation of a soft-tissue seal, which counteract the junctional epithelium downgrowth, the peri-implant marginal bone remodeling, and the PD [26]. Based on the study by Nevins et al. [27], in which connective tissue reattachment to the laser-microgrooved surface was documented, it is possible to hypothesize that the same functional peri-implant soft tissue apparatus may have formed around submerged and non-submerged implants with laser-microgrooved surface to protect the underlying bone. This hypothesis is supported also by the fact that, after the initial greater MBL occurred around the submerged implants, probably connected to the second surgery, during the 3 years of function both implants have showed similar changes of MBL (Δ = 0.12 ± 0.06 mm for submerged implants, and 0.15 ± 0.09 mm for nonsubmerged implants).