[Correlation study on acute pericoronitis and the position of the mandibular impacted third molar.].

The clinical study was carried out to determine the correlation factors of acute pericoronitis in mandibular impacted third molars.The results showed that the teeth at greatest risk in relation to acute pericoronitis are vertical unerupted lower third molar (79%),at or below the occlusal plane (66% and 30%),partially covered by soft tissue (>1/2 is 64% and <1/2 is 36% respectively),and existed opposite teeth (66%).The three indexes of vertical impaction had significant difference compared with other impactions(P<0.025).Meanwhile it was also obvious difference(P<0.025) compared with the same indexes within vertical impaction that verified it was easier to suffer acute pericoronitis in such conditions as at or below occlusal plane more than half encapsulated by soft tissue and existed opposite teeth than other conditions.Therefore it may act as an indication of tooth extraction whenever it develops acute inflammation in vertical impaction with three indexes as mentioned above.