Few studies evaluated the influence of vertical KTT on CBL at the time of implant placement [28,29,30]. Linkevicius et al. [30] investigated the influence of vertical KTT on CBL around implants placed 2 mm supracrestally (non-submerged/test) and implants placed at bone level (submerged connected with healing abutments/control), after 1 year of loading. In sites with vertical KTT ≤ 2 mm, all implants underwent additional CBL, regardless of crestal or supracrestal location of the microgap/interface. In sites with vertical KTT > 2 mm, test implants had significantly less CBL compared with control implants. In addition, there was no statistically significant difference between test and control implants with thin tissues. Contradicting the assumption that placement of a microgap/interface above bone level can prevent CBL [31,32,33,34], results by Linkevicius et al. showed that crestal bone was maintained only if vertical KTT was > 2 mm.

In the current study, the vertical gingival thickness was measured at the time of surgery in the center of the osteotomy. A mean value of 1.74 ± 0.9 mm was recorded with no statistical difference between sites with vertical KTT > 2 mm and ≤ 2 mm. A possible explanation for the difference in findings compared with Linkevicius et al. could be related to the method used for measuring the vertical KTT. Linkevicius et al. performed the measurements using a periodontal probe after partial flap deflection. However, this method presents possible bias as a result of non-standardized periodontal probe inclination, flap incision line angulation, and flap mobility.

One limitation of the present study may lie in the fact that the sites compared were not the same (for example molar vs. premolar areas). However, each contralateral implant site was in the same arch (mandible or maxilla) and intercalated between mesial and distal teeth with similar hard and soft tissue conditions. Other limitations of the present study include the use of two different abutments (full titanium and hybrid zirconia), the small sample size, and lack of histological data. Therefore, further studies with an increased number of samples, longer follow-up, and histological data on laser-microgrooved submerged vs. non-submerged implants are still necessary to confirm the reported findings.