The most frequent aesthetic complication following single implant treatment seems to be a lack of buccal convexity. This 'alveolar process deficiency' is the result of buccal bone remodeling following tooth extraction.

A traditional approach to treat alveolar process deficiency is guided bone regeneration (GBR), however post-operative complications such as swelling, bleeding and pain are common and the aesthetic outcome may not be optimal.

An alternative to the traditional GBR approach could be soft tissue contour augmentation using a connective tissue graft (CTG) at the buccal aspect. Possible advantages over GBR include less morbidity at the implant site, a superior aesthetic outcome since there is no need for vertical releasing incisions and less costs since there are no biomaterials to be used.

The primary study objective is to compare the GBR and CTG group in terms of 2 and 3 dimensional tissue alterations, focusing on the amount of tissue gain and volume stability over time. The secondary study objectives are morbidity, overall radiographic, clinical and aesthetic outcomes.

Aim:

This study aims to compare guided bone regeneration (GBR) with connective tissue graft (CTG) to re-establish buccal convexity at single implants.

Sample size calculation:

The sample size calculation was based on the primary study outcome (BSP) and was performed in SAS Power using the Satterthwaite t-test (De Bruyckere et al., 2018). The calculation was based on finding a mean difference of at least 0.5 mm between these groups with a standard deviation of 0.5 mm. This standard deviation was arbitrarily chosen given the lack of comparative studies. Alpha was set at 0.05 and the power was set at 0.80. This resulted in the inclusion of at least 17 patients per group. To compensate for possible drop-outs, 21 patients were included in each group.

Randomization and allocation concealment:

Patients were randomly assigned to the control group (GBR) or test group (CTG). Simple randomization was performed using sealed envelopes with an equal number of envelopes for every treatment group. Group allocation was revealed just prior to surgery by the surgeon and remained concealed for the evaluating investigator during the analytical stage of the project.

Surgical procedure:

In brief, a mucoperiosteal flap was raised in the control group by means of a midcrestal incision, sulcular incisions at both neighbouring teeth and a vertical parapapillary releasing incision at the distal neighbouring tooth. Following implant installation (NobelActive®, Nobel Biocare, Gothenburg, Sweden), the buccal concavity was augmented with deproteinized bovine bone mineral (DBBM) (Bio-Oss®; 0.25 - 1mm; Geistlich Biomaterials, Wolhusen, Switserland) and a collagen membrane (Creos® xenoprotect; 15x20mm; Nobel Biocare, Gothenburg, Sweden). Following apical release of the tissues, a cover screw was installed and primary wound closure was achieved (Seralon® 5/0, Serag Weissner, Naila, Germany). Aftercare included the use of a chlorhexidine rinse, systemic antibiotics (amoxicillin 1g, two times a day) and anti-inflammatory medication (ibuprofen 600mg) as deemed necessary by the patient. After 3 months, the implant was uncovered by means of a pouch procedure. A screw-retained provisional crown was placed as described by De Rouck et al. (2008), which was replaced by the permanent restoration (Procera® on ASC® abutment, Nobel Biocare, Gothenburg, Sweden) 3 months later.

The flap design in the test group was identical to the one in the control group, yet without a vertical parapapillary releasing incision. Instead of augmenting with DBBM, an appropriately sized CTG harvested from the palatal flap or palatal mucosa in the premolar area was pulled into the envelope and immobilized (Seralon® 5/0, Serag Weissner, Naila, Germany). Non-submerged healing was respected. Aftercare and prosthetic procedures were identical in both groups. All surgical treatments and provisional restorations were performed by the same clinician. Referring dentists made permanent restorations.

Inclusion Criteria:

• At least 18 years old.
• Good oral hygiene defined as full-mouth plaque score ≤ 25% (O'Leary et al.1972
• Presence of a single tooth gap in the anterior maxilla (15 - 25) with both neighbouring teeth present
• Failing tooth at least 3 months earlier removed
• Class I defect at the single tooth gap as clinically assessed (buccopalatal loss of tissue with a normal apicocoronal ridge height) (Seibert, 1983)
• Signed informed consent
• Buccopalatal bone dimension of at least 6 mm at the central and crestal aspect of the single tooth gap to ensure complete embedding of an implant by bone

Exclusion Criteria:

• Systemic diseases
• Smoking
• (History of) periodontal disease
• Untreated caries lesions
• Need for horizontal bone augmentation at the time of implant placement

Patients will be randomly assigned to the control group (GBR) or test group (CTG). Simple randomization was performed using sealed envelopes with an equal number of envelopes for every treatment group. Group allocation was revealed just prior to surgery by the surgeon.

The measuring clinician will not be involved in the treatment of any of the patients and will be blinded to allow unbiased registrations.