23.在正常齒列咀嚼食物時,下列牙齒形態特徵,何者可提供有益牙齦的適當刺激?(A)頰舌側外形(facial and lingual contour)(B)牙骨質牙釉質交界(cementoenamel junction)(C)點角(point angle)(D)窩(fossa)