Root exposure is a serious symptom of gingival atrophy. The specific symptoms include alveolar bone absorption and degeneration, obvious decline of gingival level, weakness of teeth chewing, biting pain, tooth allergy to cold and hot stimuli, tooth loosening and so on. The root of the tooth does not grow directly on the alveolar bone (gum), and there is a thick layer of gum tissue between them. This part of the gum is called "periodontal tissue" by modern stomatology (perhaps called the inner gum is more vivid), and the periodontal tissue and alveolar bone are tightly wrapped by the peripheral gum. Therefore, the combination of teeth and alveolar bone is actually a kind of joint relationship, which belongs to the micro-motion joint in the human body (the range of motion is small), so even strong and healthy teeth will feel slightly active when touched by hand. Alveolar bone is the only special part of human skeletal system, because it is a prominent part without bone marrow. When the human skeletal system develops and takes shape, alveolar bone is basically supported by the surrounding gingival tissue. When the gums age and shrink, the ability to deliver nutrition to the alveolar bone decreases day by day, and the alveolar bone shrinks and shortens, which is called "bone absorption phenomenon" in stomatology. Gingival atrophy causes the wrapping strength of this "fretting joint" to decrease, and the teeth begin to loosen. At the same time, the alveolar bone is absorbed, which makes the tooth root shallower and the teeth longer. With more and more bone absorption, teeth naturally fall off. References:

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