Final answer:
Plaque is the soft material that forms on the teeth and is the primary cause of gingival inflammation and other forms of periodontal disease.
Step-by-step explanation:
The soft material that forms on the teeth and is the primary cause of gingival inflammation and other forms of periodontal disease is plaque. When plaque accumulates on the teeth, it promotes the growth of bacteria that can cause gum inflammation and damage. If left untreated, this can progress to more severe periodontal disease.