This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Calculus is detrimental to the gingival tissues because it is 
Select and explain. 
A. A mechanical irritant, B. Covered with bacterial plaque, C. Composed of calcium and phosphorous, D. Locked into surface irregularities
B: Covered with bacterial plaque
Answer: B: Covered with bacterial plaque 
Explanation: calculus is calcified dental plaque. It is always covered by a layer of uncalcified plaque, which is detrimental to the gingival tissues.