To treat resorbed alveolar ridges, many surgical procedures are available in the literature such as ridge splitting, distraction osteogenesis, block grafting techniques and guided bone regeneration, which is the most documented technique. Various grafting materials are available but there is a lack of evidence on the superiority of a material or a combination of materials.

Bone width at the implant site is an important prerequisite for a predictable and long-term prognosis in implant dentistry. Different types of membranes and bone grafts are used in the GBR procedure. However, there is a lack of studies in the literature about the combination allograft/xenograft. The aim of the present trial is to compare two different bone graft combinations (autogenous-xenogeneic and allogeneic-xenogeneic) covered with a cross-linked collagen membrane in a horizontal alveolar ridge augmentation (without simultaneous implant placement).

Inclusion Criteria:

• Healthy patients, non-smokers or smokers <10 cigarettes/day.
• Age between 20 and 75.
• Full mouth bleeding score (FmBS) <20 %.
• Full mouth plaque score (FmPS) <15%.
• Residual bone width < 5 mm and adequate bone height in the maxilla and the mandible.
• Tooth extraction performed at least 6 weeks before surgery.
• Presence of enough teeth to support an occlusal stent/radiographic guide.

Exclusion Criteria:

• Systemic diseases.
• Heavy smokers (> 10 cigarettes/day).
• History of radiotherapy in the head and neck region in the last 5 years.
• Active periodontitis on the remaining teeth.
• Pregnancy.
• Intake of medications that may have an effect on bone turnover and mucosal healing (i.e., tetracycline within the last month, steroids within the last 6 months, bisphosphonates or fluorides at bone therapeutic levels, vitamin D and metabolites at therapeutic levels within the last 6 months).