This prospective double-blinded randomized controlled clinical trial was conducted in accordance with the ethical standards outline in the 1964 Declaration of Helsinki, as revised in 2008. Ethical clearance was attained, and the study was registered with the clinical trials registry.
Surgical technique for buccally displaced flap (supplementary video)
The surgical procedure was carried out during the implant uncovering stage 12 weeks after implant placement. Under local anaesthesia, bone sounding was performed on the crest of the ridge (Fig. 1a) using a UNC-15 probe (Hu-Friedy, USA), and the soft tissue thickness over the previously placed implant was found to be within the range of 2–4 mm. Two parallel vertical incisions were placed, extending 3–4 mm on the palatal/lingual surface of the edentulous crest. The parallel incisions were connected by a perpendicular incision on the palatal/lingual side (Fig. 1b). Partial thickness tissue dissection was then performed underneath the incisions extending till the mucogingival junction on the buccal side, and a partial thickness flap was reflected (Fig. 1c, d). The connective tissue over the implant was removed, and the implant was exposed using a curette (Hu-Friedy, USA) (Fig. 1e). The partial thickness flap was then displaced buccally and adapted over the surface (Fig. 1f). A 3-mm tissue punch was made in the displaced flap over the implant surface (Fig. 1g). To secure the flap in its new position, a 3–5-mm high healing abutment was placed through the punched flap into the implant (Fig. 1h).
Surgical technique for sub-epithelial connective tissue graft
Twelve weeks after implant placement, under local anaesthesia, a crestal incision was placed at the implant site. A full thickness mucoperiosteal flap was reflected to expose the implant. A 3–5-mm high healing abutment was placed into the implant. SCTG was harvested from the palate with a single incision technique and tucked buccally underneath the reflected flap. The graft and the flap were then stabilized using interrupted sutures.
Study design
Subjects were recruited for the study with the inclusion criteria: (1) > 21 years of age, (2) no medical contraindications and generally healthy patients, (3) missing teeth in the posterior region (premolar/molar), (4) no bone augmentation procedures required before or during implant placement, and (5) signed informed consent form for participation and permission to use obtained data for research purposes. Patients were excluded if they had (1) poor oral hygiene, (2) smoking or tobacco chewing habit, and (3) diabetes mellitus.
A standard sample size calculation determined that a minimum of 10 subjects per group with a total of 20 subjects were required for the difference between WKM and TKM values to be statistically significant when α = 0.05, the power of the study set at 80%, as determined by a study done by Temmerman et al. in 2018 [13]. Two-stage bone-level endosseous implants (Osstem TSIII, Osstem Implant Co., Busan, Korea) were placed in 20 subjects included for the study. Twelve weeks after the implant placement surgery, subjects were randomly divided into two groups, by envelope drawing, for soft tissue augmentation. Subjects of group A received augmentation using the buccally displaced flap (Fig. 2), and subjects of group B received augmentation using SCTG (Fig. 3) respectively. Treatment assignment was noted in the registration by the study monitor (N.Y.). Allocation concealment was performed using sequentially numbered sealed envelopes that were made by the study monitor using computer-generated random permuted block. The randomization envelope was opened prior to the surgical procedure. All the surgical procedures were carried out by a single operator (N.P.). Post-operatively, 400 mg ibuprofen was prescribed to all the participants on an as-needed basis.
The width (WKM) and thickness (TKM) of the KM were the clinical parameters assessed for the included subjects. WKM was measured on the buccal aspect from the gingival margin to the mucogingival junction using a UNC-15 probe (Hu-Friedy, USA). The TKM was measured 2 mm apical to the free gingival margin on the buccal aspect using an endodontic reamer file. The parameters were assessed prior to the implant uncovering (baseline), 4 weeks and 1 year after implant loading. Post-operative pain assessment was performed 1 week following the implant uncovering using the Numeric Rating Scale [14, 15]. The participants were instructed to select a number from 0 through 10 that best reflected the intensity of pain, with 0 equalling no pain and 10 the worst pain. All the clinical assessments were done by a second operator (L.M.) who was blinded to the surgical procedure performed.
Statistical analysis
The recorded data was entered in Microsoft Excel (MS office version 2010) and tabulated. Data analysis was done using the Windows PC based software “MedCalc Statistical Software” version 13.3.1 (MedCalc Software bvba, Ostend, Belgium; http://www.medcalc.org; 2014). All testing was done at alpha 0.05 (95% confidence limits). Intra- and inter-group comparison was performed using the paired and unpaired student t test, respectively, considering normality assumption and homoscedasticity. Differences above the 95% confidence intervals were regarded as statistically significant.