A review and clinical tips on gingival retraction methods

Gingival retraction is defined as a procedure resulting in deflection of the gingival tissues away from the tooth surface. The three most common clinical scenarios where gingival retraction may be required include master impression taking, cementation of indirect restorations and during direct adhesive dentistry.

The need for intrasulcular or subgingival preparation margins may be indicated within a variety of clinical scenarios, including: aesthetic demands; the need to increase retention form; the desire to place margins beyond existing restorations; the presence of cervical abrasion or subgingival caries; and/or to manage root sensitivity using bonding agents.^1,2 The presence of such finish lines may require a higher level of operator skill and knowledge in order to capture a sufficient impression, or risk impacting the final restoration longevity.^3,4,5,6,7 Aside from patient symptoms, a poorly fitting restoration can result in caries, pocket formation, loss of periodontal attachment, and debonding/decementation of the restoration. The purposes of gingival retraction in these situations include displacing the sulcular width to at least 0.2 mm to prevent the impression material tearing or distorting upon removal, capturing unprepared tooth surface apical to the finish line and accurately recording the finish line itself.^8,9

Gingival retraction is additionally of value during the cementation of indirect restorations for both moisture control and to prevent excess cement entering the gingival tissues. In the case of direct adhesive restorations, moisture control is of paramount importance, and such isolation will allow for control of the gingival crevicular fluid.¹⁰ There is, however, a risk of damage to the periodontal tissues caused by trauma resulting in gingival recession and changes in the epithelial attachment.¹¹ Thus, the ideal gingival retraction technique should be effective, safe to use and quickly reversible.¹² Several methods exist, each carrying their own advantages and disadvantages, and can be divided into three categories:

• Mechanical methods;
• Chemo-mechanical methods;
• Surgical methods.

A study performed in 2015 found that 92% of North American dentists used gingival retraction cords, 60% used retraction cords impregnated with a medicament, 20.2% used a soft tissue laser and 32% used electrosurgery as an adjunct.¹³ Of the pre-impregnated retraction cords, 29% were impregnated with adrenaline, 13% with aluminium chloride and 18% with aluminium potassium sulphate indicating a decrease in the use of adrenaline-impregnated retraction cords.¹³

This article reviews the current gingival retraction methods used for the most common clinical procedures.

Periodontal prosthodontic assessment

The periodontium should be assessed when considering provision of a subgingival restoration and therefore, gingival retraction. When the gingivae are healthy, there is less chance of damage when the gingival retraction is removed. Bleeding is highly indicative of inflamed gingivae, which are more likely to be damaged with gingival retraction. Additionally, indirect restorations are not indicated for those with active disease.¹⁴ Screening of periodontal health is typically recorded using the Basic Periodontal Examination (BPE) or Gingival Index.^15,16

The supracrestal tissue attachment (STA) consists of the junctional epithelium and supracrestal connective tissue (Figure 1). If the restorative margins violate the STA, this can result in inflammation and loss of periodontal supporting tissue, although this may also be attributed to biofilm, trauma, toxicity of dental materials or a combination of these factors.¹⁷ Therefore, the gingival sulcus must be measured and if margins must extend subgingivally, these should be within 0.5–1 mm of the gingival margin, particularly if the sulcular probing depth is below 1.5 mm, leaving 3 mm distance between the margin and the alveolar bone.^18,19 Correctly designed restoration margins within the gingival sulcus do not cause gingival inflammation if patients demonstrate satisfactory self-performed plaque control and periodontal maintenance.¹⁷ However, the clinical procedures of gingival retraction can themselves be associated with gingival recession and loss of supporting periodontal tissues.¹⁷

Gingival phenotype encompasses gingival thickness and keratinized tissue width based on genetics and environmental factors.¹⁷ Gingival phenotype is described as either thin or thick, and the characteristics of each are clinically evident as follows:

• Thin gingival phenotypes present with a tissue thickness of <1.5 mm, highly scalloped gingival architecture, thin inter-dental papillae and are often associated with narrow, triangular dentitions;
• Thick gingival phenotypes present with a tissue thickness >2 mm, flat gingival architecture, thick inter-dental papillae and are often associated with wider, square dentitions.²⁰

Gingival thickness may be measured directly with a periodontal probe, or by assessing transparency of the gingival margin, using ultrasonic devices and with cone beam computed tomography (CBCT).^21,22,23,24 The transparency method has been found to be highly reproducible and is recommended as the method of choice as although CBCT is more objective and accurate, the assessment of gingival phenotype alone would not justify its use.^22,25 The transparency method involves gently inserting a periodontal probe into the gingival sulcus, and if the probe is visible through the gingiva, it is classed as a thin gingival phenotype.

A thin gingival phenotype is more prone to recession and less resistant to trauma, therefore intrasulcular or subgingival restorative margins in such cases should be avoided if possible.¹⁷ Care is advised with gingival retraction in thin gingival phenotypes, with the use of thin retraction cord, not retaining the retraction cord for more than 15 minutes, or using gingival retraction paste and not exceeding 1–2 minutes.^26,27

Two-dimensional radiography can be used to assess the interdental bone levels and crestal bone height. The presence of underlying deficient bone suggests unsupported soft tissue and thus, a greater risk of recession with gingival retraction.⁸

Gingival retraction for indirect tooth-borne restorations

Mechanical and chemo-mechanical

Mechanical methods physically retract and displace the gingival tissues. Several methods exist of which the most common is retraction cord. Chemo-mechanical methods encompass the use of a chemical or medicament with retraction cords.^13,19

Retraction cords

Retraction cords may be knitted, braided or twisted in design and come in various sizes. Braided cords have a tight and consistent weave, but knitted cords have interlocking loops that do not unravel or fray when cut. Knitted cords are beneficial over braided cords as the interlocking loops also prevent the cord displacing when the adjacent segment is being pushed into the sulcus.¹⁹ Ultrapak (Ultradent, USA) has a knitted design that opens and dilates the gingival sulcus (Figure 2). Stay-put retraction cord has an ultrathin copper filament in the centre, allowing ease of placement and pre-shaping. If using a knitted cord, it is advisable to use a non-serrated instrument for packing to avoid unravelling,⁸ in contrast to braided cords, which are best placed with serrated instruments. Twisted cord has individual threads that are simply rotated as a whole unit. They fray easily and so are not used routinely.²⁸

Retraction cords are inexpensive and provide varying amounts of retraction, but the disadvantages include pain and discomfort for the patient, collapse of the sulcus on removal, limit in haemostasis without medicaments and time needed for placement.¹² Sometimes, it can be difficult to insert one piece of retraction cord around the whole circumference of a tooth and the cord can lift out of the gingival sulcus on the mid-buccal aspect. If this occurs, cutting the cord in the mid-buccal area and separately inserting each end into the sulcus can be helpful to maintain the cord in its correct position (Figure 3).

Retraction cords can either be impregnated or non-impregnated. The latter may be soaked in chemicals or medicaments prior to placement. Medicaments provide more effective control of gingival haemorrhage.¹² These chemicals include vasoconstrictors, which cause direct contraction of blood vessels (adrenaline and noradrenaline), astringents that contract gingival tissues, or chemicals that result in haemostasis and coagulation.

Adrenaline-based vasoconstrictors are not recommended owing to the risk of tachycardia, increased blood pressure, anxiety, hyperventilation and post-operative depression, particularly in patients who have a cardiovascular history.¹⁹

Astringents have few systemic side-effects and result in both haemostasis and gingival contraction.²⁸ This results in less chance of gingival collapse on removal of the cord and a reduction in crevicular fluid, benefiting visibility, impression taking and moisture control for adhesive restorations.¹⁹

Of those available for clinical use as gingival haemostatic agents, the following are recommended:

• Ferric sulphate (15.5–20%) is the most popular coagulant.⁸ The disadvantages include post-operative sensitivity, interference with impression setting and bonding, and discolouration of the dentine.^29,30 Therefore, it is advised to wash the gingival sulcus after cord removal prior to taking the impression.³¹ Additionally, on removal, haemorrhage may restart because the clot may be pulled out.
• Alum and aluminium potassium sulphate are considered the safest because they do not have any systemic effect, but do not control haemorrhage or crevicular fluid as well as ferric sulphate.³²

There are three clinical techniques for retraction cords:

• Single cord technique This is a useful and straightforward technique to use for single teeth with healthy gingival tissue and margins that are either equigingival, or slightly intrasulcular/subgingival. A single piece of retraction cord is packed into the gingival sulcus and removed after adequate gingival displacement has been achieved for an impression, or left in situ during cementation (Figure 4).
• Dual cord technique Two cords are placed in a situation where the gingival tissues would collapse on removal of a single cord, or the sulcus is too deep to be displaced sufficiently with a single cord technique. The smaller-diameter cord, soaked in medicament, is placed first to mainly produce haemostasis. The second, larger-diameter cord is inserted on top of the smaller cord, to cause tissue displacement, and is removed prior to taking the impression, leaving the first cord in situ (Figure 5). Although the single cord technique may not often provide sufficient retraction, there is a risk of gingival collapse upon removal of the larger cord in the dual cord technique, thus displacing the setting impression material.³³
• Infusion technique Ferric sulphate may be extruded gently into the sulcus using a specific Dento-Infuser (Ultradent, USA) while burnishing the sulcus (Figure 6). The tip can also be pressed against any persistently bleeding areas for 2–4 seconds during this process. A knitted retraction cord is then placed within the gingival sulcus, and removed prior to taking the impression. Finally, the sulcus is thoroughly rinsed following retraction to prevent foreign-body reactions.³⁴

It is important that in any of the techniques, a minimal force is applied because it has been shown that epithelial attachment sustains injuries at 1 N/mm^2, but breaks at 2.5 N/mm², which is akin to the force needed in cord placement.³⁵

It has been found that studies recommend a range of times for cord retraction, from 1 to 30 minutes.¹⁹ Too short a time will result in little retraction and faster collapse, while too long a time will result in damage to the periodontal tissues and drying of the cords. The latter would result in haemorrhage on removal. Therefore, it is recommended to note the time a cord has been placed and consider <15 minutes in thin gingival phenotypes.²⁶Table 1 provides a summary of the take home points on the clinical use of retraction cords.

Cordless retraction

Cordless retraction techniques are either in a paste or gel form. The advantages are easier placement, improved patient comfort, reduced pain and are less invasive to the periodontal tissue.³⁶ They were designed to overcome the disadvantages of retraction cords. Examples include Magic FoamCord (Coltene, Switzerland)(Figure 7), astringent retraction paste and Expasyl (Acteon, France)(Figure 8). Magic FoamCord and Expasyl materials and their techniques have been described, whereas astringent retraction paste has not been investigated as thoroughly within the literature.^19,37

Cordless retraction techniques do come with their own disadvantages in turn. For example, Expasyl has a high concentration of aluminium chloride and this has been associated with tissue necrosis and sensitivity.⁷ It may also inhibit the set of polyether and polyvinyl siloxane impression materials, so must be washed out thoroughly prior to impression taking. In a recent study, Expasyl has also been found to generate the highest pressure compared to all other retraction materials.³⁸ Pressure is dependent on the consistency of cordless retraction materials.

Magic FoamCord may still not be more efficient or have a higher quality of retraction when compared to retraction cord.^12,37 However, a comparison of Stay-put (Roeko, Germany) retraction cord with Magic FoamCord and Expasyl concluded that Magic FoamCord was more effective at gingival retraction of the three tested.³⁹ Another study, conducted in 2019, concluded that Magic FoamCord was effective for clinical use but GingiTrac (Centrix, USA) (Figure 9) did not achieve the minimum gingival retraction needed.⁴⁰

Of the few studies including 3M astringent retraction paste (3M, UK), the most recent study without funding bias or conflicts of interest, showed promising results in that 3M astringent retraction paste provided the greatest gingival displacement as opposed to Stay-put retraction cord and Expasyl.⁴¹ The benefit of the 3M astringent retraction paste is that the tip is thinner than that of Expasyl, such that it can be placed into tighter gingival cuffs more easily, with less risk of gingival trauma. However, more high-quality research is required to determine quality of displacement and long-term effects.

A systematic review found that gingival retraction pastes are more effective in achieving a dry field with less gingival tissue damage; however, displacement was reduced when compared to retraction cords.⁴² It was advised to use impregnated retraction cords in cases with thick gingival phenotype and a deep subgingival finish line, and paste for when minimal retraction is required.⁴²

Another systematic review on the influence of gingival retraction cord versus paste on periodontal health concluded that gingival retraction paste may be more protective to periodontal tissue health.⁴³ This was in contrast to Tabassum et al who found that periodontal indices were not significantly affected with different retraction methods.⁴⁴ However, gingival retraction paste showed slower healing as opposed to retraction cord.^7,45 It is recommended to leave gingival retraction paste for 1–2 minutes with a thin gingival phenotype, and 3–4 minutes with a thick gingival phenotype.²⁷ Additionally, using a lower pressure delivery system to reduce the risk of periodontal damage is beneficial.⁴⁶Table 2 summarizes the key points on the clinical use of cordless retraction methods.

Polytetrafluoro-ethylene (PTFE) tape

Although a cordless technique, PTFE tape differs in that it is neither a paste nor a gel (Figure 10). The benefits of PTFE tape as a gingival retraction method are that it is inert, does not leave a residue, is pliable and cannot be impregnated by moisture.⁴⁷ PTFE tape can therefore be used for gingival retraction and is considered a less traumatic technique compared with retraction cord and paste or gel retraction techniques. The clinician must ensure that the PTFE tape does not interfere with the full seating of the restoration.⁴⁷Table 3 summarizes the key points on the clinical use of PTFE tape.

Surgical

Rotary curettage

A high-speed turbine is used to create a trough around the gingival margins with a diamond bur. This may help to remove excess tissue and contour the gingival outline in healthy gingival tissues, but in periodontally involved tissues, or where there is a lack of keratinized tissue, there is a risk of gingival recession and deepening of the sulcus.⁴⁸ This technique has the largest effect on gingival recession and loss of attachment when compared with retraction cords and electrosurgery.¹ Additionally, there will be more bleeding with this technique and therefore, haemostasis will be of concern. It is not recommended in thin gingival phenotypes.

Lasers

Lasers have a number of uses in dentistry, including haemostasis and tissue removal. Therefore, lasers can be used to create a trough within the gingival sulcus to allow visualization of the subgingival margin. The most common type used is the diode laser, although Nd:YAG and Er:YAG lasers have also been used.⁸ The advantages include less bleeding, reduced pain and less gingival recession.⁴⁹ However, it is difficult to see where the beam is active owing to the coolant, and thus there is a potential of damage to the gingivae because there is no tactile feedback. Lasers are also more expensive to run and can be more time consuming than electrosurgery or using a scalpel.^12,49 Therefore, training and experience is required in the use of lasers.

Electrosurgery

Electrosurgery may also be used for gingival retraction; however, the tip must be controlled carefully to avoid touching bone, cementum or metallic restorations owing to the risk of tissue necrosis from heat generation. Additionally, excessive tissue removal may occur, and this technique may result in gingival recession.⁵⁰ The use of electrosurgery is contraindicated in patients with cardiac pacemakers or defibrillators. With training, electrosurgery can be a valuable tool in removing excessive tissue to allow direct visualization of subgingival margins, although extreme care is needed to ensure damage is not caused.

Gingival retraction in direct adhesive restoration

When performing composite restorations, particularly in the case of composite build-ups or Class V restorations, gingival retraction ensures a smooth cervical finish line of the restoration and prevents flash extending subgingivally. The recommended gingival retraction methods include the use of retraction cord without astringent, or PTFE tape after invagination of the rubber dam into the gingival sulcus (Figure 11).⁵¹

The disadvantages of using retraction cord in direct adhesive dentistry include strands becoming incorporated into the restoration, cord displacement (particularly labially or buccally) and a risk of reduced bond strength if astringent is used.³⁰ The disadvantages of using PTFE tape include easy distortion or displacement by high-volume suction if not secured, and if used in thin sections, the tape can become porous and tear.⁴⁷ During the provision of direct adhesive restorations, it can be expected that the retraction method will be in situ beyond 15 minutes. In the authors' opinion and experience, there have been no untoward effects of such methods if they are placed atraumatically without excessive pressure. Ensuring there is no flash of bond or composite subgingivally is more important for the long-term health of the gingiva.

Surgical gingival retraction methods are not indicated unless used as part of soft tissue crown lengthening, as the defects would otherwise be too large, particularly in the anterior zone. Table 4 summarizes the clinical use of gingival retraction methods in direct adhesive restorations.

Gingival retraction for implant-retained restorations

Gingival retraction may be used in implant-retained restorations at the impression-taking stage and at the cementation stage, where an abutment has already been fitted. In peri-implant tissues, the junctional epithelium has low regenerative capacity, and therefore, tissue collapse is not restricted following gingival retraction. Deogade et al compared a conventional open-tray impression technique with a method known as G-Cuff (Stomatotech, Canada) and found that G-Cuff records the peri-implant tissues similar to that of a conventional method with gingival retraction.⁵² G-Cuff has been suggested to improve the accuracy of impressions by supporting the peri-implant tissues to allow the impression material or intra-oral scanner to record the implant abutment (Figure 12).⁵³ The advantages of using G-Cuff include elimination of the need for impression copings, impression analogues, temporary abutments and custom impression trays. It can be used with any implant system and leads to chair-time reduction, precision in framework fit, provides an additional cement barrier and is atraumatic to the peri-implant tissues.⁵²

Care needs to be taken when using retraction cord due to the risk of excess pressure being exerted onto the peri-implant tissues.⁴⁶ An injectable matrix does not provide efficient retraction, despite the benefit of reduced force, because the supracrestal tissue attachment is greater in dental implants compared to natural teeth.²⁷ If a mechanical method is to be used, a clinician may prefer using PTFE tape because it can provide an atraumatic barrier to prevent apical migration of cement material.⁵⁴

Considering surgical gingival retraction methods for abutment level impressions, rotary curettage and electrosurgery are contraindicated owing to the risk of scratching the implant surface and arcing respectively.⁵³ Although CO₂ lasers absorb little energy near the metallic surface of the implant and do not alter the implant surface properties, large defects can be created around deep implants, particularly in the anterior aesthetic zone.⁵³Table 5 summarizes the clinical tips for gingival retraction for implant-retained restorations.

Conclusion

The objective differences in the primary aim of these retraction techniques, which is gingival displacement, was assessed in a systematic review that found that the amount of gingival retraction gained for mechanical methods ranged from 0.19 mm to 0.23 mm, for chemo-mechanical methods, it was 0.02–0.46 mm, while surgical methods yielded a range of 0.03–0.45 mm.⁴⁴ Mechanical methods meet the requirement for gingival displacement of 0.2 mm needed to ensure impression materials do not tear on removal; however, chemo-mechanical and surgical methods would need to be further assessed to specify which techniques would provide adequate gingival retraction.

Currently, no method of gingival retraction is significantly superior to the other in terms of the gingival retraction achieved and the periodontal clinical parameters affected; however, the choice is down to the treatment being performed and clinician preference and experience.⁴⁴

Gingival retraction is a vital component in increasing the longevity of restorations, both at the margin and for aesthetics. Care must be employed to respect the periodontal tissues in undertaking this procedure and there are a variety of methods available to achieve gingival retraction. The clinician is advised that the diverse options may apply to different clinical scenarios, and in the absence of true superiority, the choice is down to preference and experience. Further high-quality research does need to be conducted, particularly with regard to ease of use, time for retraction, expense, trauma to tissues and gingival recession.