Suitable subjects who were in need of implant placement were randomised between two groups; Group-A (NA=23) received crestal implant placement. In Group-B (NB=23) a CTG harvested from the palate was stabilised over the implant-neck. At the time of implant placement (T0), Groups were categorized as having thin mucosa ≤2.5mm at the surgical site, or thick mucosa >2.5mm. Mucosa thickness, width of keratinised tissue (WKT), crestal bone levels and bone thickness were determined at T0 and at the two-stage surgery (T1).

Initially, 48 patients were recruited from new referrals to the Lab of Preventive Dentistry, Periodontology and Implant Biology, Aristotle University of Thessaloniki (AUTh) for surgical placement of at least one implant located in the upper/lower jaw in the anterior/posterior segment.

Study design An initial screening visit included full-mouth periodontal assessment, radiographic examination, fulfillment of inclusion/exclusion criteria and suitable patients (n=48) were randomised into either treatment Group; in the control Group (Group-A), a conventional surgical protocol was followed for implant placement, while in the test Group (Group-B) implants were placed in conjunction with an autologous CTG. Each Group was further categorized as having thin mucosa (≤2.5mm for Subgroups-AI/-BI) or thick mucosa (>2.5mm for Subgroups-AII/-BII) at the implantation site before implant placement (baseline=T0). Implants were exposed 3-4 months later (T1).

Surgical procedures A single implant system (Osseotite, Certain, parallel wall, Biomet 3i, Florida, USA; implants of 3.25/4.0 mm in diameter) was used in all cases. At T0, following local anaesthesia (lidocaine hydrochloride 2%, epinephrine 1:100000, Lignospan standard, Septodont, France), crestal incisions were performed and full-thickness flaps were raised for implant placement. Implants were placed at the level of the alveolar crest following the manufacturer's surgical guidelines and a two-stage protocol. Flaps were repositioned using absorbable sutures (polygalactic acid 5/0 sutures; PGA, medipac, Greece). In Group-B, a similar protocol was followed as in Group-A, with the exception that following implant placement a CTG was harvested from the palate, between the maxillary canine and the first molar (Liu & Weisgold, 2002) and was stabilised onto the lingual flap using a horizontal mattress suture. Standardised dimensions of the CTG (11×6×1.5mm) were sought to cover the implant's shoulder and extend 3-5 mm on the buccal and the lingual aspect of the alveolar ridge (Fig. 1). Scoring of the periosteum for coronal advancement of the flaps was mainly performed in Group-B (16 of 23 cases).

Post-operative care Post-operative pain and oedema were controlled by Ibuprofen, 600 mg. All participants were prescribed antibiotics (Amoxicillin, 500 mg per 8 hours for 5 days) and were instructed to rinse twice daily with chlorhexidine digluconate (0.12%) and to abstain from oral hygiene in the test area for one week. Any post-operative adverse events (i.e. swelling, suppuration, flap dehiscence, persistent pain) were recorded upon suture removal ten days after surgery.

Clinical assessments

The following clinical assessments were performed at the implant site at T0 and were repeated at T1:

A periodontal probe (Hu-Friedy XP-23/QW) that had an endo-stop attached on it was used to determine the distances which were finally measured in millimetres by a digital calliper (Mitutoyo Europe GmbH) for precision.

Mucosa thickness (mm) was measured by bone sounding on the alveolar crest and at 2- and 4 mm apically, both on the buccal and the lingual aspects.

The WKT (mm) was measured on the mid-buccal aspect of the implant site. The Implant to Bone Crest (I-BC) distance (mm) was measured at four sites, mid-buccally, mid-lingually, mesially and distally and was determined as the distance of the osseous crest from the implant platform.

The Thickness of the buccal and lingual bone (mm) was measured at the level of the implant shoulder and at 3- and 6 mm apically, using a customised metallic calliper (Ustomed, Tuttlingen, Germany). The inner part of one jaw firmly touched the periphery of the screw hole within the implant fixture and the opposing jaw firmly touched the osseous surface of the alveolar ridge at the predetermined depth.

Radiographic assessment Intraoral digital radiography and the VixWin™ Platinum Gendex software (Hatfield, PA, USA) was utilised to linearly assess the I-BC distance on the mesial/distal aspect at T0 and T1. The long-cone paralleling technique was used at a distance of 10 cm between the x-ray head and the digital sensor which was attached to a custom-made silicone bite block for reproducible radiographs.

Inclusion Criteria:

• above 18 years of age
• no active periodontal disease (Plaque Index ≤15%, Gingival Index ≤20%, <20% of sites equal to or deeper than 5mm).

Exclusion Criteria:

• medical conditions that contraindicated surgical implant placement,
• medication that interfered with bone metabolism,
• pregnancy or lactation,
• inadequate dimensions of the alveolar ridge or grafted bone at the surgical site,
• tooth extraction 3 months prior to the study.