Non - Surgical Gingival Retraction- Past and Current Trends

Abstract

Oral cavity is not an easy area to treat. Constraints of cheek, lip and tongue and the presence of saliva pose challenges to visualize, gain access and manipulate instruments and materials in the oral cavity. The position of teeth in relation to gingival tissues which bleeds profusely if improperly managed complicates the problem. Gingival management and displacement is of utmost importance for obtaining accurate impression for fabrication of prosthesis with adequate marginal fit and emergence profile. Methods of gingival retraction can be broadly classified into surgical and non-surgical. Non- surgical methods are preferred and more commonly practiced due to obvious reasons. Dentists need to choose a particular retraction technique and alter their armamentarium accordingly to meet to the demands of specific clinical situation. Hence the purpose of this article is to describe and comparitivelyanalyse various existing non-surgical retraction methods which can be furthercategorised into conventional and contemporary. This article provides a critical overview of non-surgical methods available to achieve adequate retraction under frequently encountered clinical conditions.

Key Words- Gingival retraction, Cordless retraction, Gingival retraction cords

INTRODUCTION

Biggest challenge in crown and bridge prosthesis is the management of gingival tissues while impression making. This is especially important if the finish line is pargingival or subgingival. Adequate recording of subgingivally placed finish lines is critical to the marginal integrity and emergence profile of the prosthesis1.Gingival retraction is the deflection of marginal gingiva away from the tooth, to create enough of vertical and lateral space between the prepared finish line and the gingival tissues to allow atraumatic access and bulk of impression material. This ensures adequate material impressing, to record the junction of prepared and non-prepared tooth structure. Gingival retraction should preferably be with hemostasis when the gingival tissues are susceptible to bleeding2. Gingival retraction without hemostasis and control of moisture and sulcular fluid would lead to incomplete impression making of the critical finish line especially when hydrophobic impression materials are used3. The critical sulcular width to adequately record the finish line with elastomeric impression material is said to be .2mm - .3mm4. Sufficient thickness of impression material is needed in gingival sulcus region so that it can better withstand the tearing forces encountered during removal of impression. At least .5mm of vertical unprepared tooth structure below the finish line should be recorded in the impression if the die is to be properly trimmed. Gingival management is also critical in preparation and restoration of cervical caries and abrasion.

Management of gingival tissues for access, visualization, recording the finish lines, cementation and hemostasis can be accomplished by a variety of methods. Whichever the method, goal is harmony of periodontium and restorative procedures. Gingival retraction should never be at cost of periodontal health. From biologic point of view an ideal retraction method is the one which achieves maximum retraction in minimal clinical time with adequate fluid control and without causing any noxious injury to the surrounding periodontal tissues.Baharav et al in 1997 estimated the ideal contact time for the impregnated cord within the sulcus to achieve adequate retraction of .2mm to be 4 minutes, while longer time gave no further benefit. Ideal retraction method does not exist. The questfor an ideal retraction system has led to the introduction of a myriad of methods . There is no single method indicated for all clinical conditions. Broadly these can be classified into surgical and non-surgical. Surgical methods due to obvious reasons and because they are best used by skilled hands, are not very popular. Surgical methods include electrosurgery, gingitage and Lasers.

Non–surgical methods are the most popular conservative method which can be categorised into contemporary and conventional methods.Out of all the methods available till date chemo-mechanical is the most widely used5. But chemo- mechanical method has its own limitations. To overcome these limitations and the perpetual pursuit for an ideal retraction technique has introduced many contemporary gingival retraction methods. A novice might get perplexed by the existing retraction techniques, their indications and limitations. The purpose of this article is to overview the various methods, their advances and application and helps a novice to choose the right method for a particular clinical picture.

CONVENTIONAL MECHANICAL RETRACTION TECHNIQUES

These were the first to be developed and made available to the clinicians for gingival retraction. It refers physical reflection of the gingival tissues away from the tooth to permit visualization and access to impression material2,6. One of the earliest technique for mechanical displacement is the use of heavy and extra heavy dental rubber dam. It is useful when preparing tooth cervically and during placing, finishing and polishing of cervical restoration. Its usefulness is restricted toa limited number of teeth and when the preparation does not extend too far subgingivally. It is a tedious technique and full arch impressions are not compatible with this method6. Use of rubber dam in conjunction with poly vinyl siloxane(PVS) impression material should be avoided as the sulfide compounds utilized in themanufacturing of latex have shown to inhibit the polymerization of PVS7. Other mechanical means of retraction like wedges and matrices have limited use in prosthodontics.Use of retraction crown or sleeve in the form of temporary crown loaded with thermoplastic stopping material or thick temporary cement has got more of a historical importance. It is no longer practiced because of the susceptibility of gingival recession and also because the final impression is not made on same day as the sleeve is placed on the prepared tooth6.

Modified Impression Techniques- These can be considered as the cordless means of conventional gingival retraction. All the impression techniques namely copper band impression technique, temporary acrylic coping technique, interim FPD technique, intraoral relined custom tray technique7 have a typical feature in common. All these techniques use a rigid carrier of impression material. This carrier typically becomes part of the impression( reinforced sulcular flange). Making of the carrier is cumbersome and arduous process in all the techniques. The rigid carrier is always designed to have a sulcular extension, slightly apical to the preparation finish line. This gives a definite direction for the impression material to flow into and record the sulcus details. Retraction and displacement of gingiva from the finish line is provided by the carrier. This technique has little effect on gingival bleeding and control of gingival fluids. Mechanical displacement of the gingiva followed by forceful extrusion of modelling compound or elastomer over the preparation and into the sulcus results in a clean and complete impression. A reinforced sulcular flange results, consisting of sulcular extension of the rigid carrier and the impression material.

These impression techniques are not popular because of the time taking and tedious process of fabricating the carrier. All the prepared teeth need to have a parallel path of insertion. Undercuts in the preparation and beyond the finish line leads to fracture and distortion of compound impression. This is basically why elastomers were introduced in this method. Copper band placement can itself be traumatic to the gingiva. Copper band impression technique is especially useful when a localized impression defect exists in a multiple preparation elastomeric impression. This negates the need to remake the full arch elastomeric impression8.

Retraction Cords- This has proved to be the most popular method of gingival retraction till date. These are supplied as twisted, braided or knitted cords. Desirable features are9 – dark in colour to maximize tissue contrast, absorbent, availability in various diameters to have easy access in all types of gingival biotypesand sulcus configuration and effects on the gingiva should be spontaneously reversible. Depending on their diameter they are colour coded – Black(000), Yellow(00), Purple(0), Blue(1), Green(2), Red(3)10. Effectiveness of non impregnated gingival retraction cord is limited as the mechanism of gingival retraction is pressure alone without any control over sulcular hemorrhage. Recommended time for which the plain cords are placed in the sulcus for effective retraction is 10 minutes.

Twisted cords can be twisted by hand, thus tightening it to ease its placement in the sulcus. As the cords untwist, the expansion of cords create a physical expansion of the sulcus. Braided cords have got a tight and consistent weave. They can be used with both serrated and smooth packing instruments. Knitted cords have a unique knitted weave giving it a chain – like configuration. This minimises cord unraveling and fraying after cord cutting and during cord placement. The design exerts a gentle outward force as the loops seek to open when wet. It opens the sulcus greater than the original diameter of the cord2. Smooth cord packers should be used with knitted cords as they are less likely to pull the cord strand from the sulcus during placement. It has been shown that knitted cords perfom better than twisted cords11.

Impregnated Retraction cords- Of all the methods chemo- mechanical is the most popular method of gingival retraction12. Non-impregnated cords have minimal effect on hemostasis thus the use of cords in conjunction with medicament is recommended to improve its retraction efficacy. Gingival displacement medicaments are broadly be categorized into vasoconstrictors and astringents11. The combined physical and chemical effect of chemically impregnated cords play a synergistic role and offer greater effectiveness in sulcus displacement. Astringent causes contraction – retraction of the gingiva whereas vasoconstrictors constrict the blood flow in the sulcus. Literature suggests, the time for which medicated cords are placed in the sulcus varies from 3-10minutes.

Vasoconstrictors- They cause shrinkage of gingiva by transient ischemia.

• Epinephrine- .8% is used in the racemic form which contains equal amount of l- and d- forms. Endogenous epinephrine is the l- form. Overall activity of the racemic epinephrine is about half that of endogenous form. There exists a debate regarding the safe use of epinephrine impregnated retraction cords. One should avoid using epinephrine impregnated cord because of the possibility of ‘epinephrine syndrome’ exhibiting signs as tachycardia, hypertension, anxiety,rapid respiration and post- operative depression. Epinephrine from the retraction cord may be absorbed into systemic circulation and eventually effect the cardio vascular system11. .2mg-1mg of racemic epinephrine is contained in per inch of cord depending on the diameter and brand. One inch of cord with .2mg of racemic epinephrine is capable of exposing the patient to the maximum dose of .2mg for a healthy adult and nearly 5 times the recommended allowance of .04mg for a cardiac patient12. Amount of epinephrine absorbed depends on its concentration in the cord, length of the cord used, duration of cord application and the amount of vascular exposure to the cord11. The possible cumulative effect of epinephrine from the cord and other sources e.g. endogenous epinephrine secreted during stressful dental treatment or epinephrine administered in local anaesthesia should be considered12. Epinephrine impregnated retraction cord is contraindicated in cardiovascular disease, hypertensives, patient with epinephrine hypersensitivity, patients on monoamine oxidase or tricyclic antidepressant therapy, rauwolfia compound, ganglionic blockers or cocaine.

• Sympathomimetic amines- These are kinder to the tooth structure and soft tissues as they have more acceptable PH than the conventional medicaments13. They have shown to produce local vasoconstriction with minimal side effects and includes non-prescription nasal and ophthalmic decongestants e.g. .05% tetrahydrozolineHCl. .05% oxymetazoline, .25% phenylephrine HCl14.

Astringents- They act as irritants in moderate concentrations and as caustics in higher concentrations. Mechanism of action is primarily by precipitation of protein and inhibition of transcapillary movement of plasma protein. It coagulates blood and tissue fluids which forms a seal preventing further seepage of blood and GCF.

• Aluminium Sulfate compounds- This includes 5%-25%alumininium sulfate and 100% aluminium potassium sulfate ( Alum). Cords in conjunction with thesemedicaments have proven to be effective retraction agents and biologically acceptable with good tissue response6. Cords impregnated in 100% alum are just slightly less effective than epinephrine impregnated cord15. For 20 minutes, 100% alum impregnated cords can be safely left in sulcus without any adverse effects6. Aluminium sulfate compounds inhibit the setting reaction of addition polymerization impression materials16.

• Aluminium chloride- Used in concentration between 5%-25%, it is the least irritating to the tissues of all the astringents and is shown to retard the setting of polyvinyl siloxane impression materials17. A 10 minute application suffices the purpose of retraction6.

• Ferric Sulfate (FS)- It is generally used in concentration of 13%-20%. Recommended time for packing FS impregnated cords is 1-3 minutes. It is the most effective and most aggressive hemostatic agent. FS also disturbs the setting of PVS impression material. Therefore it is advised to flush off all the traces with water prior to impression making17. Because of its iron content FS discolours the gingival tissues with a yellow brown stain for several days18 and even internally discolours the tooth structure thus compromising the esthetics of anterior all ceramic crowns29.

PH of commonly used astringents is low ranging from 1-313,20. Their use leads to removal of smear layer, and opening of dentinal tubules thus causing hypersensitivity20and promoting bacterial entry. Removal of smear layer by the hemostatics also affects the bonding mechanism of self-etch dentin bonding systems21.After removal of the cord ,retracted gingiva rapidly tries to close up within 30 seconds. Thus, if the tray is not placed for impression making within this proposed time period the retraction might have to be repeated.

Retraction cords can be used with single cord or double cord technique. Single cord is best used in thin gingival biotypes or when the finish line is pargingival. This technique is not indicated in deep sulcus as the tissue collapse over the top of the cord in deep sulcus can restrict the access of impression material. Double cord technique also known as dyknatelis preferred in deep sulcus. First cord remains in place while the impression is made thus preventing the recoil of gingival cuff above the cord and ensuring adequate bulk of sulcus impression material. This prevents the tearing or deforming of sulcular impression22. Added advantage of double cord technique is that the first cord acts as sulcus liner. This prevents the tearing of epithelium and eventual hemorrhage upon removal of the first cord. It ensures a clean, clear and wide sulcus for impression making. Disadvantage of double cord technique is failure to remove the first cord as this may cause injury to the gingiva and the first cord might get picked up by the impression causing it to tear or deform.

CONTEMPORARY MECHANICAL RETRACTION TECHNIQUES

Chemo- mechanical method of gingival retraction though very popular, a unanimous consent for it being the most preferable method does not exist. The following reasons can be attributed to this. Some find the use of retraction cord to be time consuming and tedious process. It could be traumatic to the gingiva if not executed properly. Many a times there is a need to anaesthetize the gingiva. It is not uncommon to encounter uncontrolled hemorrhage during cord placement or cord removal. There have been reports of irreversible damage to sulcularand periodontal tissues caused by retraction cords23,24. Loe and Silness found shreds of cotton fibers within supra-alveolar connective tissue presumably resulting from cord tearing during placement or removal25. Use of retraction cords is not preferred with implants as the junctional epithelium surrounding the implant possess lower regenerative capacity, is less adherent and more permeable than junctional epithelium around natural teeth18. It is also not advised to use cords if optical impression is planned as shreds and artifacts of cord fibers remaining in the sulcus can affect the accuracy of optical imaging used in CAD-CAM technology26. The pursuit to bridge thislacuna led to the introduction of newer techniques and products.

Modified impression technique-Matrix impression system was described by Livaditis in 199827. This technique controls four forces namely relapsing,retraction, displacement and collapsing that impact the gingiva. It is an extended concept of now abandoned copper band technique of impression making. It involves three impression steps using three types of impression materials. 1. After tooth preparation and before gingival retraction matrix of polyether occlusal registration material or any other semi-rigid material is made in segments or one unit. 2. Matrix is trimmed till gingival crest, internally relieved except for incisal and occlusal portions which serve as vertical stops. 3. Matrix is filled with high viscosity material and placed in mouth. 4. Before this material sets a conventional stocktray is filled with medium viscosity material and is seated over the matrix. This joins all the three components of impression and creates full arch impression whether matrix is made in segments or as one unit.

Retraction Cords- To overcome the problem of shredding and fraying of cotton fibre which has the potential to cause irreversible damage to the gingiva23,24,25 products likeComprecord (Coltene- Whaledent) have been introduced. These are air texturised polyester and polyamide cords. These cords are claimed to be highly absorbent with ease of handling owingto the pliable nature of the cord. Braided cords are being preferred because of the tight and consistent weave of these cords. Stay-Put ( Coltene-Whaledent) is an impregnated metal reinforced cord. It is a unique braided cotton cord wrapped around central copper filament. It is claimed to be easily adaptable, can be pre-shaped and is more stable in the sulcus once placed. Gel–cord ( Pascal, DUX-Dental) is not only impregnated and braided but is also coated with a reagent gel to improve its efficacy. GingiBraid+ has a modified weave with a unique cotton yarn to allow the cord to have less memory, more absorbency and better tear or split resistance.

Retraction Strips- The use of synthetic retraction material extracted from a biocompatible polymer (hydroxylate polyvinyl acetate) was proposed by Ferrari in 199628. Electron microscopic evaluation has shown that it is a net-like strip, free of fragments or debris. After insertion in the gingiva it absorbs blood and oral-fluids, expands and exerts pressure on the gingiva causing its retraction. It is easily shaped, shows excellent absorption of oral fluids, is non-abrasive, soft and adaptable to the gingival sulcus and gentle to the periodontium. But, its placement is arduous and time consuming. Length and thickness of strips have to be sectioned by hand and customized to be adapted to the abutment28.

Cordless retraction – These are passive, non-traumatic and non-invasive gingival retraction system that provides with moderate retraction and excellent hemostasis. Some materials incorporate the use of patients own bite pressure or compression cap to force the material deep into the sulcus and enhance the effectiveness of retraction. The compression stops bleeding, opens a wide sulcus and ensures a dry clean area with well defined gingival margin. These techniques can be used alone or in conjunction with other methods as gingival cord, laser tissue sculpting or electrosurgery. They can be categorized further into cordless retraction with or without hemostatic or as cordless mechanical retraction or cordless chemo-mechanical retraction. These techniques are significantly less traumatic to the gingival tissue than conventional retraction cord29. These methods are preferable for optical imaging for CAD-CAM prosthesis and cement retained implant prosthesis. These are attributed as novel expensive methods less effective in deep subgingival margins.

• Cordless mechanical retraction. This incorporates retraction paste without hemostatic agent. Magic Foam Cord ( Coltene&Whaledent) utilizes polydimethylsiloxane base with a tin based catalyst to liberate hydrogen. This increases the volume by four times which leads to sulcus dialation. The resultant force achieved for sulcus dialation is not enough to displace the margins appreciably. This necessitates to ask the patient to bite against resistance on compression caps ( Comprecap) while the material sets. Benefits reported for this material are ease of placement and removal, good visibility and minimal rinsing of the residue as it does not contain any reagent to retard the setting of rubber base impression material.

• Cordless chemo-mechanical retraction. This utilizes retraction paste with a hemostatic agent. Pressure, astringent and time allows to get predictable retraction and hemorrhage control. Expasyl( Kerr Dental) was introduced by Satelac Pierre Roland. Its functioning is dependent on hygroscopic expansion of clay and hemostatic properties of 15% aluminium chloride placed in the sulcus for 2 minutes. Gingitrac (Centrix Dental) is another form of retraction paste which is basically a natural astringent in a PVS gel base. Astringent controls oozing while PVS pushes the gingiva away gently. After syringing the paste, Gingicap is used to exert moderate pressure to direct the paste into sulcus for 3-5 minutes.

Studies to evaluate the effectiveness of Magic Foam Cord and Expasyl have demonstrated their effectiveness in retraction and hemostasis during and after retraction24,30. Expasyl was shown to be slightly more inflammatory than Magic Foam Cord and Ultra-Pak knitted cord. Expasyl also shows a higher rate of postoperative sensitivity. A comparative study showed that Magic Foam Cord gave 97% usable retraction compared to 57% given by Expasyl31.

CONCLUSION

As stated by De Van, constant preservation of what remains is more important than meticulous replacement of what is missing. Respect to the gingiva abutting the tooth and harmony between the restoration and periodontium should be the aim of any prosthodontist. Adequate gingival management in conjunction with an appropriate impression is a must for successful fixed prosthesis. Today a wide array of methods are present to achieve a predictable, safe and efficacious management of gingival tissues . Not much of pertinent literature and scientific evidence is available to establish the superiority of one technique over the other. Selection depends more upon preference of the operator and the given clinical condition.

BIBLIOGRAPHY