[Nonimpacted third molars and the periodontal homeostasis of their adjacent second molars].

Due to the limitations of eruption time and space, third molars (M3s) are often impacted and induce a variety of oral diseases, bringing adverse effects on the health of their adjacent second molars (M2s). For a long time, a large number of studies have focused on the harm of impacted M3s (I-M3s) to the health of their adjacent teeth, while less attention has been paid to nonimpacted M3s (N-M3s) that have already erupted. In recent years, however, a growing number of studies and evidences have shown that the existence of N-M3s is also an important risk factor for various diseases of their adjacent teeth, whose hazard has not been taken seriously by dentists and patients. Based on the latest results of both domestic and international researches as well as our group, this review summarizes and explains the effects of N-M3s on the periodontal homeostasis and periodontal health of adjacent M2s, so as to provide reference for clinical decision-making of N-M3s and the healthy maintenance of their adjacent teeth.