Atraumatic Tissue Management for a Perfect Impression
Techniques and guidelines
Gildo Coelho Santos Jr, DDS, MSc, PhD | Leendert Boksman DDS, BSc, FADI, FICD | Maria Jacinta Moraes Coelho Santos, DDS, MSc, PhD
The atraumatic management of gingival tissues when making an impression is one of the most challenging aspects of crown-and-bridge. Tissue management includes the necessary movement of the gingival tissues away from the preparation margins so that they can be accurately impressed, as well as the management of vascular hemostasis when the gingival tissues are susceptible to bleeding.1,2 Whether the impression is made with a conventional impression material or by a digital impression technique, the rationale for and methodology of tissue management is a critical aspect of impression making; all tooth preparation margins must be totally captured in the impression to assure an excellent marginal fit of a laboratory-fabricated restoration.1,3
The aim of the present article is to discuss materials, techniques, and guidelines to promote atraumatic tissue management leading to a perfect impression. It includes a rational step-by-step description of the “double cord” gingival displacement method associated with a one-step/double-mix impression technique.
Tissue Management Materials
The gingival crevice is normally only about 2 mm in depth and must be treated with caution. Any technique used to expose the tooth margins and control bleeding and moisture must be conservative and atraumatic in order to avoid detachment of the tissue from the tooth or causing either mechanical or chemical injury to the tissue, which might result in permanent tissue recession.
To obtain a low-trauma, non-permanent gingival displacement, great importance must be given to the choice of products used and the technique employed. Frequently, the materials used for gingival retraction can be used alone or in combination with other materials and techniques.
Among the different techniques proposed in the literature, the retraction cord procedure seems to be less traumatic than electrosurgery4 or rotative gingival curettage,5 and it lowers the risk of gingival recession caused by the impression.
Gingival retraction cords can be knitted, woven, braided, or twisted in a variety of configurations to accommodate various thicknesses and diameters. Knitted cords, when placed in the gingival sulcus, expand post insertion, thus producing the physical effect of enlarging the sulcus by mechanical displacement, creating access for impressions. Examples of knitted cords are UltraPack® CleanCut (Ultradent Products, Inc., www.ultradent.com) and Re-Cord (Clinician’s Choice, www.clinicianschoice.com).
There is a variety of currently available chemical solutions and gels that have been recommended for use with gingival retraction cords because of their ability to act as an astringent or hemostatic agent.1,2 In most cases, these drugs are both an astringent—causing a transient ischemic contraction, thereby shrinking the gingival tissue—and a hemostatic, which creates blood vessel coagulation. When these reagents are placed on a retraction cord, the result is both a chemical and mechanical retraction of the gingival tissues and hemostasis, constricting blood flow through coagulation.
A 20% to 25% aluminum-chloride solution (Hemodent®, Premier Dental www.premusa.com), a 25% aluminum-chloride gel (ViscoStat Clear, Ultradent), a 25% aluminum-sulfate gel (Tissue Goo, Clinician’s Choice), and a 15.5% to 20% ferric-sulfate gel (ViscoStat, Ultradent) are among the most popularly used chemical reagents. They cause minimal tissue damage when used within the gingival sulcus for durations of less than 10 minutes.1,2,6 Epinephrine-impregnated retraction cords are not recommended because they can induce local necrosis and systemic effects.7 In fact, it has been previously shown that no discernible clinical benefit in gingival retraction could be recognized between an epinephrine-containing cord and other cords.8
The insertion of two different retraction cords of different diameters, which are adapted to the variable morphology of the sulcus, is suggested. The first thinner cord, the compression cord (#000), is applied deep in the sulcus around each preparation with light pressure and without overlapping (Figure 1). The aim of this cord is to “seal” the sulcus and to avoid contamination of the margins by blood or crevicular fluid, and it is maintained in place during application of the impression material. This cord should be pre-moistened with water and squeezed to artificially reduce its volume to facilitate insertion and avoid tissue damage. If the cord is inserted dry, it will attach to the intrasulcular epithelium, and, if pulled back while packing, may cause bleeding.
The second wide-diameter cord, the deflection cord (most frequently #00), is then soaked in an astringent/hemostatic solution such as Hemodent (aluminum-chloride solution), Astringedent (aluminum-chloride gel), or Tissue Goo (aluminum-sulfate gel) and inserted in the entrance of the sulcus to achieve tissue displacement (Figure 2 and Figure 3). Again, these solutions act as a lubricant during cord placement. Both the first and second cords will expand after placement, causing a mechanical displacement of the soft tissue. Ideally, the cord should remain in place for about 5 minutes to achieve the optimum tissue displacement. The astringent or hemostatic agent will complement the retraction because transient ischemia shrinks the gingival tissue (Figure 4). Again, the hemostatic agent needs about 5 minutes to promote the chemical retraction of the soft tissue, which helps the dentist to achieve a perfect impression (Figure 5).
The selection of the second cord size is based on the depth of the sulcus and soft-tissue type. In general, when there is minimal sulcus depth, the clinician is limited in many cases to placing only a single cord. A thin and delicate gingiva needs to be treated with small retraction cords in order to avoid permanent retraction. A thick gingiva needs a larger-size cord in order to achieve best displacement. In general, the second cord needs to be visible after packing (Figure 4). If it “disappears” inside the sulcus, a larger size should be considered. The bottom line is that the second cord must be small enough to allow an atraumatic placement and large enough to promote a perfect impression with clear margins (Figure 5).