A Study On The Temporal And Sequential Characteristics Of Permanent Teeth Eruption

The eruption of permanent teeth has certain characteristics, mainly temporal and sequential. Before the 1960s, some large scale clinical investigations had been conducted to observe the characteristics of permanent teeth eruption among Chinese adolescents. The data obtained in the 1960s showed that the eruption of permanent teeth was earlier as compared with the data of the 1950s. Changes in permanent teeth eruption sequences were also observed. However, there have been few studies in this area after the 1960s. Therefore, in this study, we examined the permanent teeth eruption time and sequence of 6,755 adolescents living in Xian. The purpose of this study was to find out the rules of permanent teeth eruption.We first analyzed the temporal characteristics of permanent teeth eruption. We found that the homonymous teeth on both sides of the occlusal arch erupted almost simultaneously. And with the exception of premolars, the mandibular permanent teeth erupted significantly earlier than their maxillary counterparts. Permanent teeth erupted earlier in females than in males. Compared with Prof. Yuanchuang Jiang's data collected in the 1960s, our data showed an averaged 10 months earlier permanent teeth eruption.We then analyzed the sequential characteristics of permanent teeth eruption. We found that the sequence of permanent eruption was D1, C1, C6, D6, B6, A6, A1 and B1. We also found that mandibular incisors erupted earlier that maxillary and mandibular first molars in most people investigated, which was different from previously reported data. The eruption sequences of mandibular and maxillary second premolars ,mandibular incisors and mandibular first molars were different from those reported by Jiang.The relationship between permanent teeth eruption and development was also statistically analyzed. It was found that the eruption time was correlated with height and body weight. The permanent teeth eruption was earlier in those with higher height and body weight, suggesting that permanent teeth eruption was an indicator of development.Finally, we observed the relationship between permanent tooth eruption and malocclusion. The most frequent malocclusion was found to be Angel's I, followed by Angle's III. The least frequent malocclusion was Angle's IV. Temporal and sequential disturbances in tooth eruption could lead to different malocclusion. The incidences of malocclusion were 19.2% in deciduous teeth period, 54.4% in leeway period and 6.8% in permanent teeth period respectively.In conclusion, with the economic development and the living standard increase, the eruption of permanent teeth was earlier nowadays as compared with that of the 1960s. The eruption sequence was also different with the data reported previously. Permanent teeth eruption could be an indicator of development. We also demonstrated that the incidence of malocclusion increased with the increase of the numbers of erupted permanent teeth. Therefore, a deep understanding of the temporal and sequential characteristics of permanent teeth eruption will help dentists in the prevention and treatment of dental diseases.