关键词: 乳牙固连, 乳牙下沉, 金属预成冠

Abstract: Tooth ankylosis is a rare clinical disease，in which cementum and surrounding alveolar bone become fused directly，and most cases had lower occlusal plane than the adjacent teeth. So far，the etiology is still uncertain and the criteria of diagnosis is controversial；besides，treatment plan is formulated by dentists based on their personal experience. If there′s no early diagnosis or intervention，it often leads to tipping of the adjacent tooth，supra-eruption of the antagonists，impaction of the successor premolars and other severe complications. At present，there are no standardized clinical treatment guidelines. The paper summarizes the research progress in the causes and treatments of tooth ankylosis.

Key words: tooth ankylosis, infraocclusion, preformed metal crown