Endodontically treated posterior teeth are more susceptible to fracture than untreated posterior teeth. The best explanation for this is:

The destruction of the coronal architecture refers to the removal of the tooth structure during endodontic treatment, such as drilling and shaping the root canal. This removal weakens the tooth and makes it more susceptible to fracture. Option A, moisture loss, may play a role in weakening tooth structure, but it is not the primary reason for increased fracture susceptibility. Option B, loss of root vitality, may also contribute to weakened tooth structure but is not the main cause for increased fracture risk. Option C, plastic deformation of dentin, refers to changes in the physical properties of the tooth structure and may occur in both treated and untreated teeth, but it is not directly related to the destruction of the coronal architecture. Therefore, option D, destruction of the coronal architecture, is the best explanation for why endodontically treated posterior teeth are more susceptible to fracture than untreated teeth. It is important to note that while this is the most likely reason, there may be other factors that contribute to increased fracture risk in endodontically treated teeth.