Particularly, atrophies within class IV, also known as knife-edge” ridges, present a serious horizontal defect, making challenging the placement of regular implants.** To clinically and radiographically evaluate bone regeneration of severe horizontal bone defects with three years of follow-up.**This study was designed as a single cohort, prospective clinical trial. Patients, having less then 4 mm of residual horizontal bone width were treated with resorbable collagen membranes and a 1-1 mixture of anorganic bovine bone and autogenous bone. Implants were inserted and loaded 7 months later. Outcomes- were- implant survival rate, any biological and prosthetic complications, horizontal bone dimensional changes measured on CBCT, peri-implant marginal bone level changes measured on periapical radiographs, plaque index (PI), and bleeding on probing (BOP).**Eighteen patients received 55 implants. No patient dropped-out, no implants failed and no prosthetic or biological complications were recorded. Supraimposition of pre- and 7-month post-operative CBCT scans revealed an average horizontal bone gain of of 5.03±2.15 mm (95% CI- 4.13–5.92 mm). After three years, mean marginal bone loss was 1.15±0.28 mm (95% CI 0.84–1.22mm), PI was 11.6% and BOP was 5.2%.**Within the limitations of the present study, high implant survival rate and high average bone augmentation seem to validate the use of collagen resorbable membranes with a 1-1 mixture of particulated anorganic bovine bone and autogenous bone, for the reconstruction of Cawood & Howell class IV atrophies.