To evaluate dimensional bone alterations following horizontal ridge augmentation using guided bone regeneration (GBR) with or without autogenous block graft (ABG) for the rehabilitation of atrophic jaws with dental implants.

Forty-two patients with 42 severe horizontal bone atrophy sites in the maxilla or mandible will be randomly assigned to two groups: ABG or GBR.

In the ABG group, a combination of ABG with particulate xenograft, covered with collagen membrane, will be used, while only a combination of particulate xenograft and collagen membrane alone will be in the GBR group. After 6-9 months of healing, implants were inserted. All implants will be definitively restored 6 months after implant placement. Radiographic examination (cone beam computed tomograms, CBCT) will be performed to evaluate the amount of horizontal bone width (HBW) gain immediately after bone grafting procedure (T0), at 6 months (T6), and at 18 months (T18). Patient demographic information, amount of width augmentation, implant survival, complications, and contributing factors will be gathered and analyzed.

Inclusion Criteria:

• 18 years old, who required an implant supported restoration in at least one site, with severe atrophy of the alveolar ridge in the horizontal plane (class III-IV atrophy according to Cawood and Howell classification),
• adequate oral hygiene
• no history of previous bone augmentation procedures at the implant site, and
• able to understand and sign an informed consent form.

Exclusion Criteria:

• uncontrolled systemic conditions, irradiation in the head and neck area, - immunosuppressed or immunocompromised,
• presented with oral disorders (such as lichen planus),
• treated or under treatment with intravenous amino-bisphosphonates,
• untreated periodontitis, poor oral hygiene and motivation,
• parafunctional habits,
• pregnant or lactating,
• drug or alcohol abuse,
• psychiatric disorders,
• a history (within the last 3 months) of using (at least weekly or more frequently) smokeless chewing tobacco, smoking a pipe, cigar or cigarette (at a rate of more than 10 cigarettes per day),
• acute/chronic infection/inflammation in the area, or
• an extraction with less than 3 months of healing

Outcome measurements will be recorded by an examiner, who will not participate in any study procedure, and will be blind to the allocated treatment. This blinded examiner will be trained and calibrated to perform measurements. A dentist who is blinded to the treatment protocol will performe all radiographic measurements.