Proper horizontal and vertical thickness of the gingival connective tissue has been proven to be one of the success criteria in dental implant and reconstructive surgery. When thin tissue is found, gingiva augmentation methods can be used to increase the quality and volume of the tissue. Many methods have been described, among them pedicle soft-tissue flaps or autogenic tissue grafts. As an alternative to patients' own tissue, xenogenic materials can be used for grafting. The fundamental issue is to choose a material that will ensure the maximum therapeutic effect, while also minimizing the negative influence on the patient's health. The aim of this study was to compare gingival augmentation procedures using a palatal connective tissue graft (CTG) and an xenogenic soft-tissue substitute, Geistlich Mucograft (xenogeneic collagen matrix; CMX), and assess whether the timing of the graft surgery influences the clinical outcomes. The original study was a randomized control trial with a total of 75 implants placed. The patients received the soft-tissue thickening 3 months before the implant placement or 3 months after the implant placement (depending on the group). A connective tissue graft (CTG) or Geistlich Mucograft were used (depending on the group). For both the CTG and Geistlich Mucograft, better clinical outcomes were observed for maintaining the alveolar bone level and the thickness of the attached gingiva compared to the control group with no gingival augmentation. The Geistlich Mucograft showed good clinical performance in comparison to the control. Soft-tissue augmentation with the CTG before the implant placement was found to be most efficient method in terms of a stable increase of the tissue thickness since, throughout the entire observation period, the greatest increase of 1.035 mm (SD = 0.73 mm) in thickness was observed. Statistically important differences in the tissue thickness baseline compared after 5 years were observed for groups G1 vs. G2b (no augmentation vs. CTG before), G1 vs. G3b (no augmentation vs. CTG after) and for groups G2b vs. G3a (CTG before vs. CMX after).
Keywords: dental implant; TKT; soft tissues; CTG; connective tissue; CMX; tissue graft
The proper width and thickness of the gingival connective tissue has been proven to be one of the success criteria in dental reconstructive surgery. Good quality soft tissue determines the possibility not only to obtain full primary wound closure during the bone defect reconstruction, but also assures effective implant treatment. Moreover, it is very important to assure the proper emergence profile of the implant supported restoration, which gives the opportunity to achieve the highest aesthetic appearance. In the long-term, the correct width and thickness of the attached keratinized tissue is the key point to ensure the stable position of the gumline around the implant's neck. Linkevicius [[
The aim of this study was to perform a long-term, 5-year observation follow-up study.
The hypotheses of this study were:
- The augmentation procedure of gingiva does not improve the thickness of the soft tissues in the aesthetic area in a 5-year observation.
- The non-inferiority of the Geistlich Mucograft (Geistlich Pharma AG, Wolhusen, Switzerland) to the connective tissue graft in a gingiva augmentation procedure in a 5-year observation.
The present study is a long-term observational study. The study was performed in the Wroclaw Medical University Dental Clinical and Teaching facility. The study protocol of the original randomized control trial (RCT) was approved by a local ethical committee (registration number No. KB-217.2012); the RCT was registered under the clinical trial registration number NCT04243460 (ClinicalTrials.gov). A total of 67 patients (42 women and 25 men) aged between 18 and 60 years participated in the original study; all the patients gave two written consents: the first was a general consent to have dental implants placed, and the other consent involved participation in the study. The study was conducted in full compliance with the Declaration of Helsinki. A protocol for this follow-up required a new bioethics committee approval that was granted (registration number 861/2021). The details on the specific inclusion and exclusion criteria, the exact clinical procedures and the 12-month data were reported in our previous publications [[
The details regarding the randomization and group allocation are outlined in the original study [[
G1—No gingival augmentation. Fifteen single implants in fifteen patients.
Groups 2 and 3 were divided into two subgroups, according to the material used:
Group 2—Thickening of the soft tissue 3 months before the implantation as a preliminary pre-implantation intervention before the implant placement. Total 30 implants in 27 patients.
Group 2 consisted of two subgroups:
- (a) G2a: CMX before Geistlich Mucograft, 15 implants in 13 patients (11 patients with single, 2 patients with double implants);
- (b) G2b: CTG before a connective tissue graft from the palate (CTG); 15 implants in 14 patients (13 patients with single and 1 patient with double implants).
Group 3 involved thickening the soft tissue 3 months after the implantation; a total of 30 implants in 25 patients.
Group 3 consisted of two subgroups:
- (a) G3a: CMX after Geistlich Mucograft; 15 implants in 12 patients (9 patients with single, 3 patients with double implants)
- (b) G3b: CTG with a connective tissue graft from the palate (CTG); 15 implants in 13 patients (11 patients with single, 2 patients with double implants).
A total of 75 tapered implants (Conelog, Camlog; CAMLOG Biotechnologies GmbH, Basel, Switzerland) were used in the study. The implant-loading took place after 6 months. All the implants were restored with metal-ceramic cemented crowns with semi-permanent cement (Implantlink, Detax, Ettlingen, Germany).
To qualify for the study, the patients had to be >18 years and have missing teeth in the aesthetic zone. The additional inclusion criteria were as follows:
- missing single or double teeth in the anterior area of their upper or lower jaw, with a proper interarch relationship (incisors, canines and first premolar), ridge width (bucco–lingual) greater than 5 mm at its narrowest point and minimum height of keratinized gingiva of 2 mm buccally;
- no previous soft-tissue augmentation procedure at the experimental site.
The exclusion criteria included previous grafting procedures performed in the area of interest and systemic or local diseases that could compromise healing or osteointegration. Smokers and patients with bruxism were also excluded from the study. The additional exclusion criteria were as follows:
- implants placed with an insertion torque of 35 Ncm or less;
- irradiation in the head and neck area; untreated periodontitis;
- poor oral hygiene (plaque score API 20%, bleeding score 10%);
- poor motivation;
- fresh post-extraction sockets.
The surgical procedures were conducted under local anesthesia and are described in detail in the previous study [[
Intraoral radiographs were taken using the straight-angle technique with a holder (Visualixe HD, Gendex, Hatfield, PA, USA). The radiologic evaluation and measurements were performed using the RVG (Gendex, Hatfield, PA, USA). Before the calculation of the crestal bone changes, an RVG image was calibrated using the calibration in the Gendex software. The diameter of the implants was used as a reference point for the calibration. The same device and software were used for the 12-month and 5-year follow-ups.
The TKT was measured using ultrasonography with a Pirop dental ultrasound device (Echoson Company, Puławy, Poland). For the purpose of this study, the results of the ultrasound examination conducted 12 months after the procedure were compared to the 5-year results. The measurements were made at two points (10 measurements at each point for each patient) with the use of ultrasound equipment (Pirop, Echoson), and the mean value for Points 1 and 2 was used for further calculations. Point 1 was considered to be in the middle of the line connecting the cemento-enamel junction (CEJ) to the adjacent teeth, and Point 2 was on the muco-gingival junction (MGJ).
The clinical evaluation included bleeding on probing (BOP). The probing depths (PD) at four sites (mesial, distal, buccal, lingual) were used to evaluate the presence of peri-implantitis, according to Derks et al. [[
After the original study had finished, most of the patients remained under regular maintenance in our clinic (Figure 2). Some of the patients had maintenance done in their place of residence for their convenience. No severe problems were reported by the patients during the 5-year period. All the patients were called for a free follow-up visit 5 years after the dental implant placement. A follow-up clinical appointment including clinical, radiological and USG evaluations was conducted by the same investigator (AB) who performed the postoperative measurements in the original study; this investigator was independent from the surgery team and did not know what material was used in each patient.
An assessment of the soft-tissue thickness was selected as the primary endpoint of the study. The data collected after 12 months was compared to the data collected after 5 years. As secondary endpoints, the implant survival rate, MBL and complications, including biological complications such as peri-implant mucositis and peri-implantitis, were evaluated.
The statistical analysis was performed using GraphPad Prism 9 software (GraphPad Software, Inc., Boston, MA, USA). For MBL, the Shapiro–Wilk test analysis was performed, and the distribution was not normal, so the Kruskal–Wallis test was used to check the existence of differences between the means. For the soft-tissue analysis, the Shapiro–Wilk test analysis was performed, and the distribution was normal, so a one-way ANOVA Tukey test was applied; each p value was adjusted to account for multiple comparisons, and the family-wise alpha threshold and confidence level was 0.05 (95% confidence interval). For the correlation between the MBL and TKT, the Shapiro–Wilk test was carried out and, since the distribution was not normal, the Spearman's r correlation was used. All the data were given as the means ± standard deviation (SD). p < 0.05 was considered statistically significant.
The overall survival rate of the 75 Conelog
The 12-month results are presented in a previous publication [[
Gradually, progressive bone loss was observed in all the groups throughout the observation period and can be observed on the simplified chart (Figure 4). The lowest MBL, 0.3 mm, was observed in G2b (CTG treatment performed 3 months prior to the implant treatment); the highest MBL, 0.80 mm, was observed in the G3a (CTG treatment performed 3 months after implantation). Nominally better parameters—lower MBL—were obtained for the groups where the soft-tissue surgery was performed 3 months before the implant insertion. However, the differences between the groups were not statistically significant.
An increase in soft-tissue thickness was observed in all the groups after 12 months, as previously reported [[
It was found that in Group G2b (CTG, before implant placement), a TKT of 2.43 mm was present at the end of the observation period; in the same group, the lowest bone loss, MBL 0.3 mm, was observed. Although this data could suggest that when a lower tissue thickness is present the more MBL around implants could be present, when analyzing all the groups together, considering the relationship of TKT and MBL, there was neither a statistically significant correlation nor inverse correlation found between the MBL and TKT (Figure 8).
The implant survival rate was 100%. A total number of four implants met the criteria of Derks for peri-implantitis (BOP+ and MBL > 2 mm [[
Aguido et al. [[
Various surgical approaches have been presented to increase the soft-tissue volume. Santamaria et al. [[
The objective of our study is a long-term perspective on patients treated in our facility comparing CTG to CMX Mucograft. Such long-term observations from an RCT study are lacking in the literature.
Huang et al. found that, despite the superiority of free gingival grafts (FFG) to restore keratinized gingiva, both Mucografts and FGGs can increase soft-tissue volume around dental implants to better maintain the peri-implant health and obtain comparable aesthetic outcomes [[
It is known that the volume of biomaterial changes over time. In the latest systematic review by Moraschini [[
Schmitt et al. compared the peri-implant keratinized mucosa regenerated with the Geistlich Mucograft and FGG. He found that most of the volume loss of the regenerated tissue occurred in the first 90 days post-surgery, and slowed down in both groups but did not completely stop until the end of the observation period (5 years) [[
Multiple factors might affect the changes in the MBL, such as smoking habits, diabetes and a history of periodontal disease, which is the reason that, in our study, patients with these conditions were excluded. A progressive MBL around the implant neck is the prelude to peri-implantitis development [[
Strong evidence exists that cemented restorations may influence MBL due to excessive cement. Therefore, it is advised to use screw-retained restorations that limit the influence of cement on MBL, instead [[
The meta-analysis of Suárez-López del Amo et al. [[
Many other factors are important for the well-being and stability of the tissues surrounding the implant; attention is paid to the materials of prosthetic components that contact the soft tissue [[
Regarding our research hypotheses:
- The first research hypothesis was rejected. In all the groups, a nominal gain of tissue thickness was observed comparing the baseline to 5 Y post-operation. Statistically significant differences in soft-tissue thickness gain were found between G1 vs. G2b (no gingival augmentation vs. CTG before), G1 vs. G3b (no augmentation vs. CTG after) and for G2b vs. G3a (CTG before vs. CMX after).
- The second hypothesis of the non-inferiority of the Geistlich Mucograft compared to the connective tissue grafts in the augmentation gingiva could not be verified. Although the CMX material showed good results in comparison to the control, a statistically significant difference to the CTG, in terms of thickness gain, was observed, with the CTG being superior. When comparing the baseline to the 5 Y thickness, the results were ranked in order of the smallest to the largest tissue gain: no augmentation (0.018 mm) < CMX after (0.226 mm) < CMX before (0.486 mm) < CTG after (0.76 mm) < CTG before (1.035 mm).
Despite the groups of 15 implants each, a large standard deviation was observed in the groups. Although nominal differences between the groups were observed, the large standard deviation significantly influenced the statistical analysis of the data and the difficulty in identifying statistically significant differences.
For both the CTG and Geistlich Mucograft, better clinical parameters were observed, both for maintaining the alveolar bone level and the thickness of the keratinized gingiva, compared to the control group with no gingival augmentation. Performing a gingival augmentation before the implant treatment resulted in an improvement of the clinical outcomes. In our study, we found a nominally lower increase in tissue thickness for the corresponding CMX groups compared to the CTG groups. Statistically important differences in soft-tissue thickness gain during the 5 years of observation were observed for groups G1 vs. G2b (no augmentation vs. CTG before), G1 vs. G3b (no augmentation vs. CTG after) and for groups G2b vs. G3a (CTG before vs. CMX after).
Graph: Figure 1 Flow chart, study schedule and timeline.
Graph: Figure 2 Study timeline, primary and secondary study endpoints [[
Graph: Figure 3 Marginal bone loss after 5 years.
Graph: Figure 4 MBL change in individual groups from baseline to 5 years. Simplified chart.
Graph: Figure 5 Soft-tissue thickness at 5-year follow-up.
Graph: Figure 6 Soft-tissue thickness change for individual groups at the 5-year follow-up. Simplified chart.
Graph: Figure 7 Change of the keratinized soft-tissue thickness (before treatment and at 5 years).
Graph: Figure 8 Correlation between MBL and TKT. Shapiro–Wilk test was carried out; since the distribution was not normal, the Spearman's r correlation was used. r = 0.02662.
Table 1 Marginal bone loss after 5 years. No statistically significant differences were found between the groups (p < 0.05).
Group Description No Gingiva Augmentation CMX Before CTG Before CMX After CTG After Group G1 G2a G2b G3a G3b MBL 5 years (in mm) Min 0 0 0 0 0 Max 3.5 2 1.2 2.6 3.7 Median: 0.60 0.60 0.3 0.80 0.67 25% Percentile: 0 0.29 0 0 0.2 75% Percentile: 1.35 0.85 0.65 1.15 1.6 Range 3.50 2.0 1.2 2.59 3.96
Table 2 TKT in mm. Mean T0—initial value, 12 M—12-month value, 60 M—5 year value. Mean change of the soft tissue (Mean T0–Mean 60 M) thickness between T0 and 5 Y in mm.
Group Description No Giginva Augmentation CMX Before CTG Before CMX After CTG After Group G1 G2a G2b G3a G3b TKT Mean T0 1.48 1.326 1.4 1.426 1.2 Mean 12 M 1.776 2.25 2.587 1.835 2.36 Mean 60 M 1.496 1.813 2.436 1.652 1.95 Mean change T0 vs. 60 M 0.018 0.486 1.035 0.226 0.76
Table 3 TKT 60 M. Tukey multiple comparison test between the groups. Differences were observed for groups G1 vs. G2b (no gingival augmentation vs. CTG before) and for groups G2b vs. G3a (CTG before vs. CMX after). ns, non sugificant; ** for a level of significance.
Tukey's Multiple Mean Diff. 95.00% CI of Diff. Significant Summary Adjusted G1 vs. G2a −0.3167 −0.9843 to 0.3510 No ns 0.6697 G1 vs. G3a −0.1560 −0.8237 to 0.5117 No ns 0.9643 G1 vs. G3b −0.4567 −1.092 to 0.2110 No ns 0.3149 G2a vs. G2b −0.6233 −1.292 to 0.01230 No ns 0.0782 G2a vs. G2a 0.1607 −0.5070 to 0.8283 No ns 0.9603 G2a vs. G3b −0.14 −0.8077 to 0.50277 No ns 0.9759 G2b vs. G3b 0.4833 −0.1843 to 1.151 No ns 0.2606 G3a vs. G3b −0.3007 −0.9683 to 0.3670 No ns 0.7108
Table 4 Mean change of TKK baseline compared to 60 M. Tukey multiple comparison test between the groups. Differences were observed for groups G1 vs. G2b (no augmentation vs. CTG before), G1 vs. G3b (no augmentation vs. CTG after) and for groups G2b vs. G3a (CTG before vs. CMX after). Ns, non sugificant; *, ** and *** for a level of significance.
Tukey's Multiple Mean Diff. 95.00% CI of Diff. Significant Summary Adjusted G1 vs. G2a −0.4693 −1.155 to 0.2161 No ns 0.3180 G1 vs. G3a −0.2087 −0.8941 to 0.4768 No ns 0.9130 G2a vs. G2b −0.5487 −1.234 to 0.1368 No ns 0.1769 G2a vs. G2a 0.2607 −0.4248 to 0.9461 No ns 0.8238 G2a vs. G3b −0.2693 −0.9548 to 0.4161 No ns 0.8058 G2b vs. G3b 0.2793 −0.4061 to 0.9648 No ns 0.7842 G3a vs. G3b −0.5300 −1.215 to 0.155 No ns 0.2052
Table 5 Number of implants affected with peri-implantitis in each group.
No Gingiva Augmentation CMX Before CTG Before CMX After CTG After G1 G2a G2b G3a G3b Number of implants 2 0 0 1 1 Percentage of implants 13% 0% 0% 6.6% 6.6%
Conceptualization, M.D. and J.H.; methodology, J.H.; software, J.H.; formal analysis, T.G.; investigation, J.H. and A.B.; data curation, A.B.; writing—original draft preparation, J.H.; writing—review, M.D.; visualization, J.H.; supervision, J.H. and M.D.; funding acquisition, M.D. All authors have read and agreed to the published version of the manuscript.
The protocol was approved by the Bioethics Committee of the Medical University of Wroclaw. The clinical study was registered on ClinicalTrials.gov. All the patients were informed of the planned treatment, its possible consequences and had given their written consent for the procedure.
All the patients gave two written consents: the first was a general consent to have dental implants placed, and the other consent involved the participation in the clinical study. The study was conducted in full compliance with the Declaration of Helsinki.
The data are available upon request from the corresponding author.
Geistlich Pharm AG, the manufacturer of the Mucograft used in the study, provided funding for the study. However, the data are the possession of the authors, and the sponsor did not interfere with the course of the trial or in the publication of its results whatsoever. The authors declare no other conflicts of interest that could have influenced the outcomes of this manuscript.
The authors thank Monika Puzio for her involvement and participation in the first 12 months of the study.
By Jakub Hadzik; Artur Błaszczyszyn; Tomasz Gedrange and Marzena Dominiak
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