Before taking an impression of a crown preparation, which item is used to make the margins of the tooth clearly visible?

Using retraction cord before taking an impression of a crown preparation is crucial for ensuring that the margins of the tooth are clearly visible for several reasons. The primary purpose of the retraction cord is to temporarily displace the gingival tissue away from the tooth. This retraction helps create a clearer and more defined margin, allowing for a more accurate impression that captures the detailed contours of the tooth preparation.

When the gingival tissue is retracted, it minimizes the chances of capturing unwanted soft tissue in the impression, which could compromise the fit and quality of the final crown. Additionally, the cord can also assist in controlling bleeding or fluid in the area, further enhancing visibility.

In contrast, other items such as the crown form, matrix band, and wooden wedge serve different purposes and do not specifically provide the same level of clarity for the tooth margins during impression-taking. The crown form is primarily used to shape the crown, while the matrix band aids in the formation of the tooth structure and a wooden wedge helps in providing stability or contour during restorative processes. None directly facilitate the visibility of margins as effectively as retraction cord.