A gingival retraction cord is a small, temporary string placed around a prepared tooth to gently push the surrounding gum tissue away from the tooth margin. This procedure, known as gingival retraction, creates a clear, dry space necessary for various dental procedures. The cord mechanically displaces the gum tissue, ensuring the working area is fully exposed. This guide details the preparation, technique, and management of the retraction cord packing process.
Understanding the Need for Retraction
The clinical goal of gingival retraction is to achieve unimpeded access and visibility of the tooth preparation margin. This margin is the detailed edge where a custom restoration, such as a crown, veneer, or bridge, meets the natural tooth structure. If the margin is obscured by gum tissue or blood, the impression will be inaccurate because the material cannot flow precisely past the edge. An inaccurate impression results in a restoration with a poor fit. A faulty marginal fit creates gaps that allow bacteria to enter, potentially leading to recurrent decay and failure of the restoration.
Selecting the Right Materials and Agents
The effectiveness of the packing technique depends heavily on material selection. Retraction cords are typically made from cotton or polyester fibers and come in various forms, including twisted, braided, and knitted. Knitted cords are often preferred because their looped design allows for better absorption of chemical agents and provides slight outward expansion once placed.
Cords are used with hemostatic agents to control bleeding and reduce gingival fluid flow. Common agents include aluminum chloride (15–25%) and ferric sulfate (15–20%). These agents coagulate proteins to achieve hemostasis and cause temporary tissue shrinkage. Aluminum chloride is preferred for routine use as it is less likely to cause permanent tissue or tooth discoloration compared to ferric sulfate. The cord is inserted using a specialized instrument called a cord packer, which has a thin, often serrated tip designed to fit into the narrow gingival sulcus without causing tissue trauma.
Step-by-Step Cord Packing Technique
The first step involves selecting the appropriate cord diameter based on the depth of the gingival sulcus. A piece of cord is cut to encircle the prepared tooth, typically with slightly overlapping ends. If the cord is not pre-impregnated, it is soaked in the hemostatic solution and blotted to remove excess liquid.
The cord is stabilized by placing one end into the interproximal area, which helps anchor it. Using the cord packer, the cord is gently tucked into the sulcus, working circumferentially around the tooth. The technique involves a rolling motion, applying light pressure toward the tooth. This pressure ensures the cord is firmly seated at the base of the sulcus.
A common variation is the double-cord technique, which uses two cords of different diameters. A smaller cord is placed first to the base of the sulcus to control bleeding and provide initial vertical displacement. A second, thicker cord is then packed on top, providing lateral displacement to widen the sulcus for impression material. The cord is left in place for five to ten minutes to allow the actions to take full effect before the impression is taken.
Managing Complications During Placement
Complications can arise during the packing process, with excessive bleeding being a primary concern. If bleeding persists after the initial application of the medicated cord, the cord should be removed, the area rinsed, and additional hemostatic agent reapplied before repacking a new segment. For persistent hemorrhage, switching to a stronger agent like ferric sulfate may be necessary, though this requires meticulous rinsing afterward to prevent tissue irritation.
Another common issue is the cord springing out of the sulcus, which indicates the cord diameter is too small or the packing pressure was insufficient. In this situation, a thicker cord should be selected for repacking to ensure a more stable fit. To prevent tissue trauma, apply gentle, controlled force with the packer. Always wet the cord before removal, especially the inner cord of a double-cord technique, to avoid tearing the delicate epithelial attachment.