1) Kidney essence deficiency is caused by congenital endowment deficiency, improper nursed back to health, excessive atrioventricular, kidney injury caused by long-term illness or kidney deficiency in old age. The kidney dominates the bone, the teeth are outside the bone, the kidney essence is insufficient, and the teeth are not solid at all, so the teeth are yellow and black, loose and prone to dental caries. For example, the General Record of the Holy Records says: "The kidney governs the bones, and the teeth remove the bones. The kidney is strong and the bone marrow is strong, and the teeth are white and bright; Today, the kidney is weak and not proud of the bone marrow, so the teeth are yellow and black. "

2) Due to chronic illness, insufficient endowment, excessive consumption of atria and ventricles, excessive consumption of warm and dry products that rob yin, kidney yin is damaged, yin deficiency is flourishing, teeth are sparse, shaken and exposed, and gums fester and shrink. Zhi Zhi Fang says, "Kidney deficiency leads to tooth opening, exuberance leads to tooth firmness, and deficiency heat leads to tooth movement". If you feel heat evil and consume body fluid, your teeth will turn yellow and dry.

3) Long-term illness, lack of qi and blood, qi deficiency can't produce blood, or blood deficiency turns into qi, qi and blood deficiency, essence can't be transferred to gums, and gums are dystrophy, so teeth are pale; I think common cold will shrink again. "The General Record of Raw Muscle" said: "Deficiency of Qi and blood, improper management, common cold's attack on deficiency, and guests between teeth will make muscles cold, qi and blood weak, teeth atrophy, gradually exposed, and never attach teeth."

4) Pathogens invade Yangming meridians (hand Yangming and foot Yangming), and the blood circulation of meridians is blocked, so the teeth are yellow, black, dry and shaken. "Etiology" said: "Wind-cold takes advantage of its meridians, so the medullary bone is damaged, so it can't stick to the teeth, so the teeth are dark." "common cold's cold is confined to the meridians, and the weak blood can't be raised on the bones, so the teeth are yellow and black." In addition, eating spicy and greasy food turns heat into fire, or emotional failure, qi stagnation into fire, or invasion of heat evil leads to excessive stomach heat, but along the stomach meridian, stomach fire is smoked along the meridian, blood stasis, gingival swelling and pain, and even ulceration; When heat hurts blood vessels, teeth will bleed. 5) Tooth and heel diseases such as tooth and gum diseases, dental caries and tooth carbuncle can also lead to abnormal tooth color and shape.

In addition, long-term smoking, drinking a lot of strong tea, chronic lead poisoning or fluorosis, taking some drugs such as tetracycline and chronic diseases can also cause changes in tooth color and morphology.