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Table of Contents
REVIEW ARTICLE
Year : 2011  |  Volume : 1  |  Issue : 2  |  Page : 80-86

Gingival displacement in prosthodontics: A critical review of existing methods


Department of Prosthodontics Including Crown and Bridge and Implantology, A.B Shetty Memorial Institute of Dental Sciences, Mangalore, India

Date of Web Publication17-Sep-2011

Correspondence Address:
Krishna D Prasad
Department of Prosthodontics Including Crown and Bridge and Implantology, A.B Shetty Memorial Institute of Dental Sciences, Mangalore
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2229-5194.85023

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   Abstract 

Tremendous progress has been made in procedures for making fixed prosthodontic impressions over the past few decades. A common objective for impressions and interim crowns or fixed dental prostheses is to register the prepared abutments and finish lines accurately. For all impression procedures, the gingival tissue must be displaced to allow the subgingival finish lines to be registered. Retraction is the temporary displacement of the gingival tissue away from the prepared teeth. This article discusses the current methods that are applied for displacement of gingival tissues so that adequate amount of unprepared tooth structure can be recorded with least distortion of impression material as well as minimal damage to attachment apparatus of the tooth. In addition to this, gingival displacement techniques around implants and for computer aided design/computer added manufacturing (CAD/CAM) based restorations have been discussed. PubMed and Google Scholar were used to search any studies involving gingival retraction techniques. The keywords used were gingival retraction, gingival displacement, gingival retraction in implants and retraction cord. Gingival retraction holds an indispensable place during soft tissue management before an impression is made. Swift increase in research work in the recent past leaves no option for a clinician, but to be updated and to possess optimum knowledge to rationalize the use of materials and techniques that are employed for gingival displacement in proximity to both teeth as well as implants.

Keywords: Chemicomechanical retraction, gingival displacement, gingival displacement in implants, matrix impression system


How to cite this article:
Prasad KD, Hegde C, Agrawal G, Shetty M. Gingival displacement in prosthodontics: A critical review of existing methods. J Interdiscip Dentistry 2011;1:80-6

How to cite this URL:
Prasad KD, Hegde C, Agrawal G, Shetty M. Gingival displacement in prosthodontics: A critical review of existing methods. J Interdiscip Dentistry [serial online] 2011 [cited 2019 Jul 16];1:80-6. Available from: http://www.jidonline.com/text.asp?2011/1/2/80/85023


   Introduction Top


Tremendous progress has been made in procedures for making fixed prosthodontic impressions, over the past few decades. Extensive research and development has led to establishment of a preferred method or at least sorting them to a select number. Fixed prosthodontic impressions persist to involve a wide range of procedures and even wider choice among the materials and little indication of consent on the most preferred method. [1]

A common objective for impressions and interim crowns or fixed dental prostheses is to register the prepared abutments and finish lines accurately. For all impression procedures, the gingival tissue must be displaced to allow the subgingival finish lines to be registered. An effective management of the sulcular environment is needed for successful subgingival impression. It involves two key aspects: the force that comes to bear on the gingival tissues and contaminants that may be present or generated in the sulcus. [2] Gingival retraction, hemostasis and sulcular cleansing are frequently combined and closely related procedures but they have specifically separate objectives. Retraction is the temporary displacement of the gingival tissue away from the prepared teeth. [1] This article discusses the current methods that are applied for displacement of gingival tissues so that adequate amount of unprepared tooth structure can be recorded with least distortion of impression material as well as minimal damage to attachment apparatus of the tooth.


   Method for Data Collection Top


PubMed and Google Scholar were used to search original research articles, case reports and other reviews involving gingival retraction techniques from 1961 to 2009 from peer reviewed journals. The keywords used were gingival retraction, gingival displacement, gingival retraction in implants and retraction cord.


   Forces Involved with Retraction of Peridental Tissues Top


Deformation of gingival tissues during retraction and impression procedures involves four forces: retraction, relapse, displacement and collapse [Figure 1]. [2] The aim of gingival retraction is to atraumatically allow access for the impression material beyond the abutment margin and to create space in order to provide sufficient thickness of impression material in gingival sulcus region so that it can better withstand the tearing forces encountered during removal of impressions. [3] The fiber-rich, highly organized periodontal complex surrounding natural teeth provides support for gingival tissues when they are retracted, mitigating the collapse of the tissues when the retraction agents are removed before making the impression. [1]
Figure 1: Forces involved with retraction of peridental tissues (red arrow - collapsing force, dark blue arrow - retraction force, light blue arrow - displacement force and brown arrow - relapsing force)

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   Gingival Displacement Techniques Top


A 0.2-mm sulcular width is obligatory for enough thickness of the material to be there at the margins of impressions so that they can endure tearing or distortion on removal of the impression. [4] The following sections review the available retraction techniques for natural teeth. [5]

Mechanical retraction (retraction cord)

Considerable attention needs to be paid to the correct use of cord packing instruments. Packing instruments having serrated circular heads are commonly used with braided cords as fine serrations on the head of the instrument sinks into the braided cord and keep it from slipping off and traumatizing the epithelial attachment. Smooth, nonserrated circular heads can be used to place and compress twisted cord with a sliding motion. [6]

A minimum bulk of 0.2-mm thickness in the sulcus area has to be maintained to make an undistorted impression with polyvinyl siloxane impression materials, which can be achieved by retracting the gingiva for at least 4 minutes before making the impression. Rapid reclosure of the sulcus requires that clinicians make the impression immediately after removing the retraction material. [7] A survey by Hansen et al. [8] has shown that 98% of prosthodontists use cords out of which 48% use a dual cord technique and 44% use single cord technique. The dual cord technique possesses the advantage of declining the tendency of gingival cuff to recoil and partially displace the impression material as it sets. [9] A histologic study confirms trauma to sulcular epithelium and connective tissue attachment on placement of retraction cords. [10] Inflammation of the sulcus can get exacerbated due to contamination of sulcul wounds by residual filaments/fibers of the cord. [11] Application of inappropriate amount of force while placing retraction cords can also contribute toward gingival inflammation and shrinkage of marginal tissues. [12] Plain cords, not moistened with suitable medicaments, are not a good choice for retraction, as the sulcular hemorrhage cannot be controlled just by the pressure applied by the cord on gingival tissues. [13] More than 50% of the situations are associated with bleeding on removal of plain retraction cord, although wetting the cord before removal may play a crucial role in controlling bleeding from gingival sulcus. [14]

Advantage

  • Inexpensive


Disadvantages

  • Rapid collapse of sulcus after removal
  • Trauma to epithelial attachment
  • No hemostasis
  • Time- consuming
  • Risk of sulcus contamination
  • Painful


Chemicomechanical retraction

Research has been carried out on a wide variety of chemicals for use with retraction cords. The chemical agents that are commonly used are discussed below.

Epinephrine

Although epinephrine provides effective vasoconstriction and hemostasis, [15] 33% of its application is accompanied by significant local and systemic side effects. "Epinephrine syndrome", which is characterized by tachycardia, hyperventilation, raised blood pressure, anxiety and postoperative depression can occur in patients who are susceptible to epinephrine. [16]

Advantages

  • Vasoconstrictive
  • Hemostatic


Disadvantages

  • Systemic effects: epinephrine syndrome
  • Risk of inflammation of gingival cuff
  • Rebound hyperemia
  • Risk of tissue necrosis


Aluminum sulfate and aluminum potassium sulfate

Both the agents are hemostatic and retractive, and result in minimal postoperative inflammation at therapeutic concentrations, [16] although severe inflammation and tissue necrosis result from concentrated aluminum potassium sulfate solutions. [17] These act by precipitating tissue proteins with tissue contraction, inhibiting transcapillary movement of plasma proteins and arresting capillary bleeding. [18]

Advantages

  • Hemostasis
  • Least inflammation of all agents used with cords
  • Little sulcus collapse after cord removal


Disadvantages

  • Offensive taste
  • Risk of necrosis if in high concentration


Ferric sulfate

Owing to its iron content, ferric sulfate stains the gingival tissue yellow-brown to black color for a few days after its use. [3] The use of this agent for gingival displacement in implants is further questionable due to its ability to disturb the setting reaction of polyether and polyvinyl siloxane impression materials. [19] Conrad et al. [20] have described a case report in which they concluded that the combined use of ferric sulphate gingival retraction fluid and transluscent porcelain restoration is hypothesized to have resulted in black internalized discoloration of the dentine and patients' dissatisfaction. An in vitro study demonstrated that dentinal exposure to highly acidic ferric sulfate, for 30 seconds, can result in superficial smear layer removal. [21] Removal of smear layer by hemostatic agents has been shown to negatively affect the bonding mechanism of self-etching adhesive which may further explain possible marginal microleakage and discoloration. [22]

Advantages

  • Hemostasis


Disadvantages

  • Tissue discoloration
  • Acidic taste
  • Risk of sulcus contamination
  • Inhibits set of polyvinyl siloxane and polyether impressions


Aluminum chloride

Aluminum chloride is an agent that acts by precipitation of tissue proteins [23] but causes less vasoconstriction than epinephrine. [24] It is least irritating of all the medicaments used for impregnating retraction cords [25] but it possesses a vital shortcoming of inhibiting the polyvinyl siloxane and polyether impression materials. [19]

Advantages

  • No systemic effects
  • Least irritating of all chemicals
  • Hemostasis
  • Little sulcus collapse after cord removal


Disadvantages

  • Less vasoconstriction than epinephrine
  • Risk of sulcus contamination
  • Modifies surface detail reproduction
  • Inhibits set of polyvinyl siloxane and polyether impressions


This agent proved more effective in keeping the sulcus open after clinicians removed the cord (10-20% of original opening 8 minutes after the cord is removed) than are epinephrine-medicated cords (50% closure of sulcus observed over a similar duration). After 12 minutes, only sulci packed with aluminum chloride remained open at 80% of the original space created. [26]

However, the elimination of residues of aluminum chloride, after removing retraction cord and before proceeding with the impression procedure, becomes all the more important owing to its ability to interfere with complete setting of polyether and polyvinyl siloxane impression materials. [19]

Inert matrix-polyvinyl siloxane

This material acts by generating hydrogen that causes expansion of material against the sulcus walls during setting. [6]

Advantages

  • No risk of inflammation or irritation
  • Nontraumatizing
  • Ease of placement
  • Painless
  • No adverse effects


Disadvantages

  • Limited capacity for hemostasis (no active chemistry)
  • Less effective with subgingival margins


Chemicals in an injectable matrix

Injection of 15%aluminum chloride in Kaolin matrix, into the gingival sulcus, provides noteworthy mechanical retraction for the clinician to make adequate impressions. In contrast to any chemicomechanical method, the injectable aluminum chloride resulted in less pain and discomfort, and was quicker to administer. [6],[27]

The strength of the epithelial attachment is 1 N/mm. A very low pressure (0.01 N/mm) enables opening of the sulcus and a recovery that is quasi immediate; and a pressure of 0.1 N/mm enables a sulcus opening of 1.5 mm and a delayed recovery up to 2 minutes per 0.5 mm opening. The paste is injected into the sulcus, exerting a stable, non-damaging pressure of 0.1 N/mm. When the paste is left in place for 1 minute, this pressure is sufficient to obtain a sulcus opening of 0.5 mm for 2 minutes. This injectable matrix contains white clay to ensure the consistency of the paste and its mechanical action, while aluminum chloride enhances the hemostatic action. Application of air and water spray will remove the paste from the sulcus. [28]

Advantages

  • Reduced risk of inflammation (injectable form)
  • Nontraumatizing to junctional epithelium
  • Hydrophilic
  • Ease of placement
  • Painless
  • No adverse effects


Disadvantages

  • Inhibits set of polyvinyl siloxane and polyether impressions
  • More expensive
  • Less effective with very subgingival margins



   Matrix Impression System Top


0In 1983, Livaditis [1] introduced a new system that requires a series of three impression procedures, using three viscosities of impression materials. A matrix of occlusal registration elastomeric material (semi-rigid) is made over tooth preparations before gingival retraction is done. The matrix is trimmed to prescribed dimensions and after the retraction cord is removed, a definitive impression is made in the matrix of the preparations with a high viscosity elastomeric impression material. After the matrix impression is seated, a stock tray filled with a medium viscosity elastomeric impression material is seated over the matrix and the remaining teeth to create an impression of the entire arch.

This system effectively controls all the four forces that impact on the gingival during the critical phase of making the impression when attempting to register subgingival margins. The design of matrix gently forces the high viscosity impression material into the sulcus, which does not allow it to collapse as the medium viscosity material in the stock tray is seated for the pick-up impression. The sulcus is also cleaned of unwanted debris. Tearing is virtually eliminated because of improved configuration of sulcular flange and by elimination of voids or contaminants in the sulcus. Matrix impression system (MIS) maintains retraction by trapping a highly viscous material in the sulcus when the matrix is fully seated. The matrix procedure may be considered to be a compilation of the syringe/tray/and tube/coping categories. This system possesses only one noticeable drawback which is increased chairside time. [2]

Surgical retraction

Lasers

Properties of laser mainly depend on their wavelength and waveform characteristics. Diode lasers are commonly used for gingival retraction around natural teeth, as they result in less bleeding and gingival recession.

  • Neodymium: yttrium-aluminum-garnet (Nd-YAG)lasers
  • Erbium: yttrium-aluminum-garnet (Er:YAG) lasers
  • CO 2 laser [29]


Advantages

  • Excellent hemostasis: carbon dioxide laser
  • Reduced tissue shrinkage
  • Relatively painless
  • Sterilizes sulcus


Disadvantages

  • Er:YAG laser is not as good at hemostasis as CO 2 laser
  • CO 2 laser provides no tactile feedback, leading to risk of damage to junctional epithelium. [29]


Electrosurgery

To enlarge the gingival sulcus, a small J-shaped electrode is used and is oriented parallel to the long axis of the tooth so that only tissues from inner wall of the sulcus are removed. Retaining focus on minimizing the production of lateral heat is significant. [30]

Advantages

  • Efficient
  • Precise hemostasis while incising the tissues


Disadvantages

  • Contraindicated in patients with pacemakers
  • Cannot be used concomitantly with nitrous oxide-oxygen sedation as nitrous oxide is a flammable agent
  • Cannot control hemorrhage once it starts
  • Adequate band of healthy attached tissue is necessary. [31]


Rotary curettage

Even though slight deepening of the sulcus may result, rotary curettage does not have much effect on gingival margin heights if adequate keratinized gingiva is present around the teeth. [32]

Advantages

  • Fast
  • Ability to reduce excessive tissue
  • Ability to recontour gingival outline


Disadvantages

  • Causes considerable hemorrhage
  • High risk of traumatizing the epithelia attachment


The absence of keratinized gingiva at the base of the sulcus may result in gross recession and deepening of the sulcus due to exaggerated response of tissues. [33]


   Gingival Displacement in Digital Impressions Top


A major restraint of direct optical impressions is their limitation to line of sight. A clean sulcus is a requirement of paramount importance while making digital computer aided design/computer added manufacturing (CAD/CAM) impressions. Retraction cord fibers that remain in the sulcus may affect the accuracy of gingival retraction and may result in artifact generated errors. Fifteen percent aluminum chloride in an injectable matrix reduces these artifacts by leaving a clean sulcus on removal. Indirect capture of digitized information is considered more accurate by clinicians. [34] On the other hand, the method of data collection is influenced by thickness of impression material in the sulcus area. This can result in significant errors in cases of thin impression margins with radius less than the contacting probe tip. [35]


   Gingival Displacement in Implants Top


The increased need and changing trends toward implant-related treatments result from the combined effect of a number of factors. Cement retained restorations are the restoration of choice, as compared to screw retained restorations, due to several advantages that they posses over screw retained restorations. Few situations in implant restorative phase requires fabrication of customized abutments with its margin placed subgingivally specially in esthetic regions and where minimal inter-arch space exists which necessitates reduced height of the abutment. [36] With this type of cement retained prostheses, pickup impression technique cannot be used owing to unique contour of the abutments, unlike for screw retained implant restorations where impression copings which exactly resemble the manufactured final abutment can be adapted accurately and directly to the fixture head on the abutment shoulder. [6]

The peri-implant fiber structure does not provide the same level of support as peridental structure and is not able to prevent the collapse of retracted tissues to the same extent, and hence attempts to successfully make impressions become all the more difficult. In the case of peri-implant tissue, the junctional epithelium is poorly adherent, more permeable and has low regenerative capacity, with the gingival fibres parallel to implant collar with the biologic width of 2.5 ± 0.5 mm [Figure 2]. [6] Collagen fiber orientation was similar, regardless of the implant material, demonstrating a predominantly parallel or parallel-oblique pattern. [37] The influence of natural soft tissue biotype is also very important, i.e., thin periodontal biotypes with fragility that requires delicate management to avoid recession owing to tissue damage whereas thick, fibrotic biotypes have a tendency to form pockets rather than recede. [38] In addition, initial gingival tissue thickness at crest may be considered as a significant influence on marginal bone stability around implants. [39]
Figure 2: (a) Biologic width around implants; (b) biologic width around natural teeth

Click here to view


Owing to the inherent potential of mechanical retraction techniques of damaging the gingival epithelial structures, the use of this approach may be contraindicated around implants, except in situations in which the patient's sulcus depths are shallow, their mucosal health is impeccable and a robust, thick periodontal biotype is present. [6] Serrated packing instruments, if not handled appropriately, may increase the probability of damaging the implant collar and may create microscopic scratches on the surface. Increase in surface free energy and surface roughness will further facilitate biofilm formation on dental implant and abutment surfaces. [40] The atraumatic application of an injectable matrix certainly faces a few limitations. The force of retraction offered is limited due to the elevated viscosity of the injectable matrix, and, while this protects the implant sulcus from the trauma of overpacking, it may not offer sufficient retraction for situations that are unique to implant dentistry in which the relapsing and collapsing forces are important. Deeply placed implants often are associated with an increased sulcus depth compared with that found around natural teeth (greater biologic width in dental implants). Rotary curettage has a high risk of the bur damaging the implant surface as well as the risk of tissue retraction exposing implant threads. Electrosurgery is contraindicated with implant as there is a risk of arcing. In addition, gingival sulcus too small for two electrodes is impractical in implant dentistry. [6] Unlike other lasers, prime chromphore for CO 2 laser is water. Hence, it reflects off metal surfaces. CO 2 lasers absorb little energy near metal implant surfaces, with only small temperature increases (<3°C) and minimal collateral damage. Also, these lasers do not alter the structure of the implant surface. Lasers expose the implant margins by creating a trough by excision rather than by displacing soft tissue. Therefore, large defect would result if they are used around deeply placed implants. Their use in anterior applications, where esthetics play a critical role, is also questionable. [41] Although injectable matrix technique sounds promising for implant situations, further development is needed. [6] As compared to the research linked to implant fixture designs, there is relatively little research to guide clinicians the appropriate use of various gingival retraction techniques around implant abutments. As implants become mainstream treatments for tooth loss, this topic certainly deserves further research.


   Discussion Top


While using chemicomechanical means of gingival retraction, absorption of chemicals, like epinephrine, at the sulcus interface is dependent on patient's gingival health. [16] Healthy gingiva acts, to some extent, as a barrier to the absorption of epinephrine. This may be a reason why the theoretical overdose levels are not observed clinically. [24] Absorption varies with the degree of vascular bed exposure, the length of cord used, the concentration of cord impregnation and the length of application time. [10] Clinicians should avoid applying high concentrations of epinephrine to large areas of lacerated or abraded gingival tissues as its absorption increases substantially due to large vascular bed exposure. [5]

Surgical retraction procedures are rapid but at the same time destructive and involve excision of tissue. On the other hand, few authors advocate the use of electrosurgery, rotary curettage and lasers around natural teeth. [30],[31],[32],[33]

Clinicians can make a good use of an injectable matrix for gingival retraction as it offers the opportunity to perform an atraumatic procedure. The materials such as 15% aluminum chloride in a Kaolin matrix can be introduced into the sulcus surrounding natural teeth with no risk of laceration. With no damage to the junctional epithelium at the base of the sulcus or to the sulcus walls, the risk of inflammation caused by chemicals delivered in the matrix is reduced significantly. In addition to this, it is as effective as epinephrine soaked cord in reducing the flow of sulcular exudate. Inflammation results from the use of chemical agents, but the aluminum chloride in the injectable matrix offers the best outcome of the chemical choices to date. [42]


   Conclusion Top


Gingival retraction holds an indispensable place during soft tissue management before an impression is made. Several problems that can arise from poor marginal fit of fixed dental prostheses can be prevented if the margins of prepared tooth are recorded after adequate exposure by any of the above mentioned gingival retraction methods. The choice of technique and material depends on operator's judgement of the clinical situation apart from availability and cost of the materials. Swift increase in research work in the recent past leaves no option for a clinician, but to be updated and to possess optimum knowledge to rationalize the use of materials and techniques that are employed for gingival displacement in proximity to both teeth as well as implants.

 
   References Top

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    Figures

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