Clearing the way: retraction methods
There are various ways to achieve proper gingival retraction, which can generally be categorized as mechanical, chemical, surgical, or a combination thereof.
Mechanical methods involve physical displacement of the gingival tissue by placing materials – such as cords or collars – into the sulcus to push tissue away, stop fluids, and exert pressure to stop bleeding (fig. 1).
Cords are the most commonly used mechanical method, in either the single- or double-cord technique. The single-cord method involves one cord that is discarded before impression taking. The double-cord technique utilizes two cords; a thinner cord is placed below a thicker cord to better displace tissue (fig. 2). The thinner cord is then kept in the sulcus during impression taking.1 Cords are useful for deep subgingival situations for sufficient tissue displacement. However, purely mechanical methods have their limitations.
Depending on the preparation margins, cord or other mechanical methods may not be the best choice. Cord placement can betime-consuming and technique-sensitive and, depending on the clinical situation, requires significant skill to execute correctly. Retraction cords can cause injury to the gingival sulcular epithelium, and improper handling of cords can contribute to issues, including gingival recession and marginal exposure of the restoration.2 Plus, placement is generally not well perceived by patients.
Figure 1. A clinical situation clearly showing retraction of the tissues.
Figure 2. To facilitate the removal of the second cord, a continues cord can be used, as seen here.
Chemical retraction agents include a variety of solutions, gels, and pastes that can generally be categorized as either astringents, hemostatic agents, or vasoconstrictors, which cause a local effect on tissues.
- Astringents react chemically with proteins in the soft tissues, decreasing cell permeability and extracting fluid, which causes tissues to shrink and dry
- Hemostatic agents are designed to restrict bleeding by inducing coagulation
- Vasoconstrictors constrict blood vessels themselves, reducing blood flow
Some of the most commonly used chemical retraction options are ferric sulfate (Fe2(SO4)3), Epinephrine, and Aluminum Chloride (AlCl3).
Ferric Sulfate (Fe2(SO4)3
Ferric sulfate is a concentrated astringent with hemostatic properties that is often used together with retraction cord. While ferric sulfate is very effective and coagulates blood very quickly, it is an acidic solution. This acidity can cause unintentional etching if left on the tooth surface, negatively affect bonding of self-etch adhesives, and lead to tissue irritation and post-op sensitivity.1 And depending on the oral flora, ferric sulfate can cause temporary gingival and dental tissue staining to yellowish brown and black (fig.3).
With all of this in mind, it’s important not to overuse ferric sulfate. Make sure to take care of any excess before application, try to keep the prep and dentin clean during the procedure, and rinse thoroughly with water after use.
Figure 3. Dark stains caused by ferric sulfate visible after removal of temporary restoration.
Epinephrine is a vasoconstrictor that’s most commonly used in concert with retraction cords, either soaked or impregnated. When inserted into the sulcus between the tooth and gingival, the blood vessels constrict – inducing haemostasis.3
However, due to its ability to raise heart rate and blood pressure, as well as interactions with some medications, there is some concern surrounding the use of epinephrine on patients with cardiovascular complications or hypertension.4 As there are no universal recommendations on this topic, it’s best to review the patient’s medical and oral health history before use to avoid any unnecessary risk.
Aluminum Chloride (AlCl3)
One of the most commonly used astringents, aluminum chloride which reacts with blood proteins to create a barrier with coagulated proteins, which stops bleeding by either a physical tissue or vascular occlusion. In dentistry, AlCl3 is impregnated into cords or added to pastes and gels, like 3M™ Astringent Retraction Paste, which are then used independently or in tandem with cords (fig. 4). In addition to providing excellent hemostasis, AlCl3 is the least irritating of the chemical retraction solutions and is less acidic than ferric sulfate – reducing the risk of unintentional etching, discoloration, and irritation.
However, as with every chemical solution, AlCl3 can cause negative effects if left on too long or not thoroughly rinsed. It’s important to know that aluminum chloride can disrupt the setting of some impression materials if not rinsed properly.
Regardless of which chemical solution is used, it’s vital to only keep it in place for the recommended amount of time. Once you reach your dry operatory field, the chemical needs to be remove and thoroughly rinsed, because residue can chemically react with impression material, adhesive or cement. It’s also important to remember that chemical methods are intended to be used in the sulcus; don’t overdo it and place any on the prep. As with many other dental materials, timing and attention to detail are important – but if you place your materials carefully, you can minimize potential interference.
Figure 4. 3M™ Astringent Retraction Paste, featuring AlCl3, used to achieve retraction.
The most invasive of the retraction methods, surgical retraction removes or cauterizes soft tissue to create sufficient space between the finishing line and the gingival tissue. These methods (rotary curettage, electro-, and laser surgery) are only recommended in selected clinical situations like hyperplastic gingival or inflamed tissues because of reported damage in the dental-gingival complex.
It’s very rare to complete the tooth preparation and restoration procedure while in contact with the gingiva without causing some bleeding. Often, you will need a combination of the retraction methods listed above to effectively stop bleeding. For example, cord pressure often cannot stop bleeding on its own, which is why many retraction cords are either soaked in or impregnated with a chemical agent