In clinical practice, we often encounter such a case: the mandibular third molar is obliquely blocked in the proximal middle, and then a cavity is formed in the distal middle of the second molar, which causes pulp lesion or apical lesion of the second molar in severe cases. In this case, should we extract the mandibular third molar first or treat the second molar first? To answer this question is a little more difficult than one might think. 1. What we have to consider is whether the proximal mesial oblique obstruction of the third molar will affect our treatment of the second molar. If it does, it should be extracted first and then treated, but if it does not affect much, it can be postponed. Note that this is a “delayed extraction”, but eventually it will have to be done, unless the patient has an absolute contraindication to extraction. Why must it be extracted? The reason is simple, since the proximal mesial oblique obstruction can cause the adjacent teeth to decay, the local structural relationship that causes this caries ring will still exist after you restore the second molar. As long as this structural relationship persists, the local micro-ecological ring will not change and will still cause adverse consequences. Therefore, you must extract the interrupted teeth to have a long-term stable health foundation. 2. For patients with delayed extraction, sometimes it is not because it does not affect the treatment, but the patient is not yet able to accept the extraction, and then we also have to have a corresponding method. We should not compromise the treatment of teeth that need to be retained because the teeth that should be extracted are not extracted. The wisdom teeth in the proximal mesial oblique position sometimes have a very close contact with the second molar in the cervical or root area, and even the long-term unrepaired second molar caries may give the third molar the opportunity to move into the caries cavity, forming a “mosaic” relationship between the two teeth. In this case, not extracting the wisdom tooth in the proximal mesial oblique position will definitely affect the treatment of the second molar and must be extracted before treatment. When it is not extracted for the time being, we have to do some regrinding of the proximodistal oblique teeth, so that the two teeth can be completely separated and enough gap can be formed to restore the anatomical shape of the second molar distal to the middle.