[The study on third molar changes following second molar extraction (1)].

The purpose of this study was to observe the changes of the third molars following the extraction of second molars by orthopantomograms. The subjects were consisted of 96 cases in upper second molar extraction, 74 cases in lower second molar extraction. The obtained results were as follows: 1. The favourable eruption condition of upper third molar appeared in both groups with pre-extraction angle under 25 and pre-extraction angle above 25. 2. More favourable eruption condition of lower third molar appeared in group with pre-extraction angle under 25 than the other group with pre-extraction angle above 25. 3. The favourable eruption condition of upper third molar appeared in both group extracted in Nolla's Stage 4, 5 and Nolla's Stage 6,7,8. 4. More favourable eruption condition of lower third molar appeared in group extracted in Nolla's Stage 4, 5 than the other group extracted in Nolla's Stage 6,7,8.