hand, implants may have a slightly higher rate of initial failure. Conclusions on this topic are difficult to draw, however, because few studies have compared immediate and delayed implants in a scientifically rigorous manner. One versus two-stage surgery After an implant is placed, the internal components are covered with either a healing abutment, or a cover screw. A healing abutment passes through the mucosa, and the surrounding mucosa is adapted around it. A cover screw is flush with the surface of the dental implant, and is designed to be completely covered by mucosa. After an integration period, a second surgery is required to reflect the mucosa and place a healing abutment. In the early stages of implant development (1970−1990), implant systems used a two-stage approach, believing that it improved the odds of initial implant survival. Subsequent research suggests that no difference in implant survival existed between one-stage and two-stage surgeries, and the choice of whether or not to "bury" the implant in the first stage of surgery became a concern of soft tissue (gingiva) management When tissue is deficient or mutilated by the loss of teeth, implants are placed and allowed to osseointegrate, then the gingiva is surgically moved around the healing abutments. The down-side of a two-stage technique is the need for additional surgery and compromise of circulation to the tissue due to repeated surgeries. The choice of one or two-stages, now centers around how best to reconstruct the soft tissues around lost teeth. Additional surgical procedures For an implant to osseointegrate, it needs to be surrounded by a healthy quantity of bone. In order for it to survive long-term, it needs to have a thick healthy soft tissue (gingiva) envelope around it. It is common for either the bone or soft tissue to be so deficient that the surgeon needs to reconstruct it either before or during implant placement. Xenogeneic collagen matrices are used for gingival augmentation after dental implantation. Hard tissue (bone) reconstruction Bone grafting is necessary when there is a lack of bone. Also, it helps to stabilize the implant by increasing survival of the implant and decreasing marginal bone level loss. While there are always new implant types, such as short implants, and techniques to allow compromise, a general treatment goal is to have a minimum of 10 mm in bone height, and 6 mm in width. Alternatively, bone defects are graded from A to