On which surface of the preparation is the cord typically placed?

The cord is typically placed on the circumferential surface of the preparation. This placement is crucial as it allows the dentist to adequately control the margin of the preparation while providing optimal visibility of the finish line. When the cord is positioned circumferentially, it helps in managing the soft tissue, allowing for better impression taking. This technique also aids in creating a clear distinction between the tooth structure and the surrounding gum tissue, which is essential for accurate restorations.

By ensuring that the cord provides the necessary retraction around the entire circumference of the preparation, it facilitates the creation of margins that are not only more visible but also more accessible for capturing precise impressions. This is particularly important in prosthetic dentistry, where the fit and function of dental restorations depend heavily on the quality of the impression taken.