Final answer:
Secondary union is the primary type of healing for a site of attachment loss after periodontal instrumentation, involving wound contraction and replacement of tissues to progressively close and heal the gap.
Step-by-step explanation:
The primary type of healing in a site of attachment loss after periodontal instrumentation is through a process known as secondary union. When periodontal instrumentation occurs, it can result in a gap between the tissues that cannot be closed immediately. Instead, healing happens progressively as the wound edges are gradually pulled closer through wound contraction. As the wound heals, granulation tissue forms. This tissue is rich in collagen and fibroblasts supplied by the growth of new blood vessels, a process called angiogenesis. If the gap was significant, the use of sutures might be employed to enhance healing, mimicking a primary union, which is faster and typically results in less scarring.
However, in the absence of primary closure, the site heals by filling in from the bottom and sides of the defect with new connective tissue and epithelium until the site is restored - a secondary union. Regeneration of tissues also contributes to healing, replacing the lost cells with new ones of the same type.