Post: Direct vs indirect

Indirect: anteriors up to the premolars. Esp in canal shapes that are abnormal e.g oval shapes where the direct post system won't fit snugly. Indirect posts in multirooted teeth require either split posts or telescopic post

Direct: generally posteriors. Less broken down teeth often have undercuts as more of the walls are present. therefore the internal anatomy must be prepped to remove undercuts to allow insertion and removal. Once the external anatomy is prepared for a crown, the remaining wall will be quite thin and may  fall off. In this case, a direct post will be more conservative and if done in composite resin then the remaining thin walls will bond to the core material and is less likely to chip off as compared to amalgam where there is no bonding.