Which statement about calculus is true?

The statement about calculus that reflects the correct understanding is that it can only be removed by a dentist or hygienist. Calculus, which is hardened plaque that has mineralized on the tooth surface, adheres strongly to the enamel and requires specialized instruments to effectively remove it. Dental professionals utilize hand scalers or ultrasonic instruments to break it away from the teeth because its strong adherence cannot be addressed through methods like coronal polishing.

In contrast to the other options, which either misinterpret the nature of calculus or downplay its significance, it's crucial to understand that ignoring calculus can lead to serious dental issues, such as gum disease. Calculus is not the same as plaque, as plaque is a soft deposit that can be easily removed with regular brushing and flossing, but calculus requires professional intervention. Therefore, acknowledging that only a dental professional can remove calculus highlights the need for regular dental check-ups and cleanings to maintain oral health.