This retrospective analysis aimed at assessing the 3D changes in tissue thickness at implant sites that underwent soft-tissue grafting procedures to increase KT width using an apically positioned flap with either CM or FGG. Volumetric tissue thickness changes occurring after 12 and 24 months were compared to the tissue thicknesses assessed 1 month after the healing.
Overall, the findings of the present analysis pointed toward a comparable reduction in tissue thickness within 1 and 24 months in both groups, which at the patient-level analysis in the CM group amounted to –0.31 mm, and –0.22 mm in the FGG group. Between 1 and 12 months, a decrease in tissue thickness tended to be higher in the FGG group (–0.23 mm versus –0.025 mm; patient-level analysis), whereas between 12 and 24 months, a greater tissue thickness loss was measured in the CM group (–0.32 mm versus –0.02 mm; patient-level analysis). In corroboration are the estimations of the implant-level analysis that, between 12- and 24 months, revealed a higher tissue thickness loss in the CM group compared to the FGG group (–0.09 mm versus –0.36 mm). Between 1 and 12 months, a decrease in tissue thickness was higher in the FGG group (–0.18 mm versus –0.04 mm), whereas within 12 and 24 months, a higher reduction was registered in the CM group (–0.37 mm versus 0.008 mm), without significant differences detected between the groups at any investigation time point. The initial analysis of the same patient sample reported the 3D tissue changes occurring over a 6-month period in the FGG and CM groups [13]. In particular, within 1 and 6 months, implant sites in both the FGG and CM groups showed a reduction in tissue thickness, with a slightly higher tissue thickness decrease between 1 and 3 months documented in the CM group [13]. Between 3 and 6 months, comparable tissue thickness shrinkage was registered in both groups [13]. To the author’s best knowledge, to date, this is the only clinical analysis assessing and comparing the 3D tissue thickness changes at implant sites treated with FGG or CM.
As advocated in one previous RCT, which assessed one-dimensional tissue thickness changes based on the measurements obtained in the CBCT scans, compared to the preoperative tissue thickness, after 6 months, implant sites treated with FGG showed an increase in tissue thickness of 0.11 ± 0.06 mm, whereas reduction in tissue thickness was documented in the CM group (–0.19 ± 0.12 mm; intra-group comparison: p = 0.002) [15]. On the other hand side, another RCT, which measured one-dimensional tissue thickness by using an endodontic file with a rubber stop, reported on the gain in tissue thickness at implants treated with CM and FGG, which after 2 and 6 months significantly favored implant sites in the FGG group compared to the baseline (i.e., preoperative tissue thickness; preoperative – 2 months: FGG: 1.0 ± 0.3 mm, CM: 0.1 ± 0.4 mm, p < 0.001; preoperative – 6 months: FGG: 0.9 ± 0.5 mm, CM: 0.1 ± 0.5 mm; p = 0.003) [16]. Between 2 and 6 months, a slight tissue thickness decrease of 0.1 mm occurred in the FGG group, whereas tissue thickness remained stable in the CM group [16]. Contrary to this are the results addressed by another RCT, which used a probe with a rubber stop to assess tissue thickness alterations at implant sites augmented either with CM or FGG [17]. In particular, within 1 and 6 months, the CM group displayed a significantly higher decrease in tissue thickness compared to the FGG group (−0.53 mm versus −0.36 mm, respectively; p < 0.001) [17]. Nonetheless, it must be highlighted that the aforementioned studies were limited to a 6-month follow-up period and assessed one-dimensional assessments, which subsequently prevent any direct comparison with the present findings.
Upon further analysis of the present data set, a significantly higher mean KT gain after 12 and 24 months was obtained in the FGG group. Specifically, after 12 and 24 months, the mean KT gain in the CM group amounted to 1.52 and 1.50 mm at the patient-level analysis, and to 1.53 mm 1.21 mm at the implant-level analysis. In the FGG groups, after 12 and 24 months the mean gain in KT was 4.22 and 4.04 mm at patient level, as well as 3.98 and 3.79 mm at the implant-level, respectively. Keeping in mind the recent recommendations that define the width of < 2 mm of KT as insufficient, it appears that the use of CM may not allow to obtain the desired endpoint of establishing at least 2 mm of KT [3]. Based on the results of the initial analysis of the same patient sample, after 6 months, the mean KT gain in the CM and FGG groups was 1.47 ± 1.25 mm and 3.94 ± 4.90 mm at implant-level analysis, as well as 1.45 ± 1.13 mm and 4.52 ± 1.46 mm at patient-level analysis, respectively, significantly favoring the FGG group [13]. The aforementioned outcomes basically suggest that the KT width established after 6 months could be maintained throughout the 24-month period. It must be acknowledged that, to date, a majority of the existing clinical studies comparing the FGG and CM groups for KT establishment at dental implant sites are limited to a 6-month follow-up period and reported upon the mean KT gain of 3.73 to 4.47 mm at the implant sites treated with FGG, as well as 2.51 to 3.23 mm at the implant sites treated with CM [17, 18]. In contrast to our findings, after 12 months, one retrospective analysis indicated comparable KT gain in the FGG and CM groups (4.10 ± 1.16 mm and 3.37 ± 0.97 mm, prospectively) [19]. Furthermore, within 6 to 12 months, a significant decrease in KT width was documented in the CM group, whereas insignificant changes were measured in the FGG groups [19]. In the present analysis, between 12 and 24 months, tissue thickness reduction was documented in the CM and FGG groups, without significant differences noted between the two groups. In line with this are the results of another retrospective analysis that revealed a constant decrease in KT width in both the FGG and CM groups throughout a mean follow-up period of 2.3 years (FGG group) to 2.6 years (CM group), with a greater graft contraction observed in the CM group [20].
According to the current findings, it is important to note that, after 24 months, three implants in two patients in the CM group displayed no gain in KT width compared to the preoperative KT measurements, whereas all implant sites possessed an increase in KT width in the FGG group. The latter finding underlines the importance of the case selection for the decision on the surgical approach, as autogenous grafts may be favored at sites with complete absence of KT, and soft-tissue substitutes could be considered when a limited amount of KT is needed [3]
When interpreting the present findings, it must be acknowledged that due to the fact that the software estimated the sutures present in the postoperative scan to the surface thickness calculation, an intraoral scan taken after 1 month was used as a baseline. The latter did not permit assessment of the overall tissue thickness changes, including those occurring within the first 4 weeks. In addition, for the volumetric and clinical measurements, loaded and unloaded implants have been pooled, which might have relevantly altered the accuracy of the ROI as well as the clinical measurements, particularly at implant sites treated during the second-stage surgery. Furthermore, implant sites with either a complete absence of KT and those with a reduced width (< 2 mm) were merged into the analysis, which might have considerably affected the dimensional alterations and changes in KT width at dental implant sites treated with FGG and CM. It is worth noticing that in the present analysis, we did not investigate the surface shrinkage of the grafted site during the investigation period due to the similarities of the grafted area in terms of tissue structure and color in the CM group compared to the surrounding tissues, which subsequently led to difficulties in demarcating the grafted site in the respective group. Finally, a A relatively small sample size enrolled in the analysis might have further affected the obtained outcomes. Finally, it is important to underline that one of the major limitations of the present analysis is the lack of the assessment of the clinical parameters defining peri-implant tissue health status, such as plaque values, bleeding on probing, and probing pocket depth. The latter did not permit to relate the surgical procedure implemented for the KT establishment and the maintenance of peri-implant tissue health
Within the limitations of the present study, it was concluded that CM and FGG were associated with comparable 3D thickness changes over a period of 24 months. A significantly wider KT band could be established in the FGG group.