When you smile, your teeth may not show up because your upper lip is too long, the attachment of the labial band is too low, and the teeth are not properly aligned. 1. Excessive length of the upper lip: Excessive length of the upper lip refers to the vertical distance from the corner of the nasolabial angle to the highest point of the upper lip, that is, the length of the middle of the human body, and when the upper lip is too long, it may lead to the teeth not showing when smiling. 2. Low attachment of the labial tie: common in young children, rare in adults, the patient may also have the performance of the teeth do not come out when smiling, and if serious, it may also affect the speech. 3. Abnormal alignment of teeth: for example, teeth are tilted inward, if the patient has the manifestation of teeth not coming out when he smiles, the tilting situation is generally more serious, and it is recommended to carry out orthodontic treatment in time. In addition to the above, other possibilities cannot be ruled out, if it affects the daily life, it must be treated in time.