The reasons for the odor inside the teeth are: 1.The neighboring space of the teeth often occurs food embedment, which can produce sour odor under the fermentation of bacteria in the mouth. 2.The bad restoration will stimulate the gums to be red, swollen, bleeding, and even form deeper periodontal pockets, producing secretion, which makes the odor exist in the mouth. 3.The long-term accumulation of food residue, soft scale, plaque, etc. on the tooth surface, mineralized to form calculus, will cause the swelling of the gums and 4.When the teeth are not filled with deep cavities, the food residues can be decomposed by bacteria and produce bad odor.