Darkening of the gap between the lower teeth may be the result of pigmentation caused by poor diet and lifestyle habits, and the patient should correct the bad habits. It may also be caused by caries, periodontitis and other diseases, patients can take medication, surgical treatment and other therapeutic measures. 1. Bad diet and lifestyle habits lead to hyperpigmentation: if patients often drink tea, coffee, etc. in their daily diet, as well as smoking, it will lead to hyperpigmentation, and if patients do not brush their teeth in time for a long period of time, they will have blackened crevices in their lower teeth. Patients should correct their habits in time and develop the habit of brushing. 2. caries: caries can also lead to the phenomenon of blackening of the gap between the lower teeth, patients can follow the medical advice to use silver fluoride ammonia solution, tin fluoride solution, such as containing solution. Patients can also take surgical treatment, the main surgical methods include composite resin direct bonding restoration, amalgam filling. 3. Periodontitis: Periodontitis can lead to the phenomenon of root surface caries, but also lead to patients with large gaps in the lower teeth or blackened tartar. Patients should take surgical treatment, such as scaling, scraping, serious flap surgery, bone grafting, dental implants. When the patient has the symptom of blackening of the gap between the lower teeth, if it is caused by bad habits, no special treatment is needed. If it is caused by a disease, patients should consult a doctor in time and follow the doctor’s instructions for treatment.