"B," which stands for buccal, is the surface of the tooth that faces the cheek.

D2150 Amalgam - two surfaces, primary or permanent No Tooth and surface designations required. Allowance includes polishing. D2160 Amalgam - three surfaces, primary or permanent No Tooth and surface designations required.

D2388 Resin-bonded Composite. This code describes a composite resin placed on a posterior tooth, involving four or more surfaces.

Code D2391 (one-surface posterior resin-based composite) explicitly states that it should be “used to restore a carious lesion into the dentin.” The rationale for the requirement that the lesion extends into dentin can be questioned.