9. Which one of the biological objectives of root canal preparation? a. The root canal preparation should develop a continuously tapering cone. b. Making the canal narrower apically and widest coronally. c. Necrotic debris should not be forced peri-apically. d. Avoid transportation of the foramen. e. Keep the apical opening as small as possible.

The correct answer is:<br /><br />a. The root canal preparation should develop a continuously tapering cone.<br /><br />Explanation: One of the biological objectives of root canal preparation is to create a continuously tapering cone within the tooth structure. This helps in facilitating the cleaning and shaping of the root canal, as well as in the subsequent obturation process. A continuously tapering cone ensures that the canal is adequately cleaned and shaped, promoting better irrigation and reducing the risk of incomplete cleaning. Additionally, it helps in achieving a more efficient and complete obturation, which is crucial for the success of the root canal treatment.