California Registered Dental Assistant (RDA) Written Practice Exam

Which wall of the cavity preparation is perpendicular to the long axis of the tooth?

1. Axial wall

2. Gingival floor

3. Pulpal floor

4. Buccal wall

The correct answer is: Pulpal floor

The pulp chamber is located in the center of a tooth, and the pulp floor is the bottom surface of this chamber. Therefore, the pulpal floor is perpendicular to the long axis of the tooth, as it is at a 90 degree angle to the pulpal walls which surround it. The axial wall (A) is the internal surface of the preparation that runs parallel to the long axis of the tooth, while the gingival floor (B) is the internal surface closest to the gumline. The buccal wall (D) is the external surface on the side of the tooth that faces the cheek. These options are not the correct answer because they are all either parallel or at a different angle to the long axis of the tooth, rather than being directly perpendicular. Therefore, the correct answer is C, the pulpal floor.