The microbial contamination of the matrix barrier during exposure could be another important factor that might hamper bone formation within the underlying graft. This factor has not been investigated in the present study. However, it has been reported by other groups that the resorbable matrix barrier per se might be less prone to bacterial contamination and can be better cleaned using disinfectant agents such as chlorhexidine rinse than PTFE membranes [35]. Matrix membrane presents an outer and inner surface. The external surface is more occlusive (the pore sizes are bigger than those of internal surface) to allow gingival tissue penetration. The internal layer, smaller pores, prevents further penetration of the gingival tissue through the barrier, thus protecting new bone formation underneath the barrier. From clinical observation, the space between the two layers seemed already occupied by connective tissue protecting the inner layer and leaving only the outer layer of the matrix exposed to the oral cavity and subsequent degradation. Still, this clinical observation has to be confirmed in further studies.

The results from this study suggest that primary flap closure over the matrix barrier is preferable leading to better ridge width gain than when the matrix is left exposed or early exposures happen. However, exposures were not completely detrimental to the lateral ridge augmentation and sufficient ridge width gain could be achieved allowing for successful implant placement. In critical cases, where 1 or 2 mm less bone would affect the esthetic results, the matrix barrier should not be left exposed and due care should be taken to avoid any exposures during healing after primary closure was achieved.