d. Modified step uun e. Passive step back 13. Which one of the following is apical to coronal technique of root canal preparation? a. Step down b. Step back c. Crown down d. Modified double flared e. Balance forced

The apical to coronal technique of root canal preparation involves removing dentin from the apex of the tooth to the coronal portion. The correct answer to the question is:<br /><br />c. Crown down<br /><br />This technique involves starting the preparation at the apex and gradually removing dentin towards the coronal portion of the tooth. It is often used in cases where there is a need to preserve the integrity of the apex or in situations where the coronal portion of the tooth is compromised.