periodontitis

例句：

1. 1. He was diagnosed with periodontitis and had to undergo treatment.
   他被诊断出患有牙周炎，并需要接受治疗。
2. 2. Periodontitis can lead to tooth loss if left untreated.
   如果不治疗，牙周炎可能会导致牙齿丢失。
3. 3. The dentist advised him to brush his teeth twice a day and floss regularly to prevent periodontitis.
   牙医建议他每天刷牙两次并定期使用牙线来预防牙周炎。