Why are long posts with a circular cross-section not recommended for posterior teeth?

Long posts with a circular cross-section are not recommended for posterior teeth primarily because of the unique root anatomy associated with these teeth. The roots of posterior teeth, such as molars, are typically broader and have more complex shapes compared to anterior teeth. This anatomical variation means that a post designed with a circular cross-section may not adequately fit the contours and space within the root canal of a posterior tooth.

When a post does not conform well to the root anatomy, it can lead to insufficient retention and stability of the post within the canal, potentially compromising the tooth's structural integrity and making it more susceptible to fractures. Additionally, utilizing a post that does not match the root form can result in uneven distribution of forces during biting or chewing, which is critical for maintaining the functionality of posterior teeth. Thus, acknowledging and adapting to the root anatomy is essential for optimal performance and longevity of prosthetic restorations in posterior teeth.