Gingival displacement in implant dentistry: A critical review of existing methodsDr. Krishna Prasad D.1, Dr. Chethan Hegde,2 Dr. Gaurav Agrawal,3

Dr. Manoj Shetty.4

Introduction:

The increased need and changing trends towards implant – related treatments results from the combined effect of a number of factors. Implant dentistry is unique because of its ability to restore the patient to normal contour, function, comfort, esthetics, speech and health regardless of atrophy, disease or injury of the stomatognathic system.1 The increased use of implants as a treatment modality for partially edentulous subjects has led to two restorative techniques:

1. Screw retained implant restorations in which fastening screw provides a solid joint between the restoration and the implant.

2. Cement retained implant restorations in which the restoration is cemented on machined or customized abutments.

Cement retained restorations are the restoration of choice 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.1 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 impressions copings which exactly resembles the manufactured final abutment can be adapted accurately and directly to the fixture head on the abutment shoulder.2

1.Professor and Head of the Department of Prosthodontics Including Crown and Bridge and Implantology, A.B Shetty Memorial Institute of Dental Sciences, Mangalore. 2. Professor, Department of Prosthodontics including crown and bridge and implantology, A.B Shetty Memorial Institute of Dental Sciences, Mangalore. 3. Post graduate student, Department of Prosthodontics including crown and bridge and implantology, A.B Shetty Memorial Institute of Dental Sciences, Mangalore. 4. Professor, Department of

Prosthodontics including crown and bridge and implantology, A.B Shetty Memorial Institute of Dental Sciences, Mangalore.

The quest for predictable long term results has raised questions about the gingival retraction techniques and their outcomes in implant treatment, since the architecture of the gingival crevice surrounding natural teeth is different biologically from that around implants. In case of peridental tissues keratinized epithelium is present at the base of the sulcus and the junctional epithelium is adherent, less permeable and has high regenerative capacity along with gingival fibres inserting perpendicularly in the cementum with the biologic width of at least 2.04 mm in comparison with the peri-implant tissue, where 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(Fig 1).2 Hence it is imperative to know if conventional retraction techniques could be applied safely to peri-implant soft tissue. This article compares and reviews the advantages and disadvantages of different gingival retraction techniques on peri-implant and peridental tissues.

Fig -1

The junctional epithelium associated with natural teeth has the cell turnover rate measuring twice that of oral gingival epithelium3 and is more robust than junctional epithelium that surrounds implants. When exposed to trauma, such as during gingival retraction procedures, the junctional epithelium around implants is at greater risk of experiencing penetration damage than is the more robust sulcus of natural teeth, especially for patients with more vulnerable implant situations.2 The influence of natural soft tissue biotype is also very important, such as 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.4

Forces involved with retraction of peridental and peri-implant tissues.

Deformation of gingival tissues during retraction and impression procedures involves four forces: retraction, relapse, displacement and collapse.5

➞ Retraction Fig -2 ➞ Relapsing➞ Displacement➞ Collapsing

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.6 The fibre-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. The peri-implant fibre structure, however, does not provide the same level of support and is not able to prevent the collapse of retracted tissues to the same extent, and hence the attempts to successfully make impressions becomes all the more difficult. This is particularly true in situations in which the depth of sulcus is greater than average, such as when an implant has been placed deeply.2

Gingival Displacement Techniques:

A 0.2-mm sulcular width is necessary for there to be sufficient thickness of the material at the margins of impressions so they can withstand tearing or distortion on removal of the impression.7 Techniques that clinicians have refined to work well for teeth may not address the challenges faced by clinicians in implant dentistry. The following sections review the available retraction techniques for natural teeth8 and their potential application for implant restorations.

A.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.2

A minimum bulk of 0.2-millimeter 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 four minutes before making the impression. Rapid reclosure of the sulcus requires that clinicians make the impression immediately after removing the retraction material.9 A survey by Hansen et al10 showed 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.11

A histological study confirms trauma to sulcular epithelium and connective tissue attachment on placement of retraction cords.12 Inflammation of the sulcus can get exacerbated due to contamination of sulcul wounds by residual filaments/fibres of the cord.13 Application of inappropriate amount of force while placing retraction cords can also contribute towards gingival inflammation and shrinkage of marginal tissues.14 Plain cords, not moistened with suitable medicaments, are not a good choice for retraction, as the sulcular haemorrhage cannot be controlled just by the pressure applied by the cord on gingival tissues.15 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.16

The use of plain cords around implants is not advisable as peri-implant tissue is more fragile and there are high chances of damaging the junctional epithelium, which posses lesser regenerative capacity as compared to natural teeth.

Advantage: Inexpensive

Disadvantages: Rapid collapse of sulcus after removal Trauma to epithelial attachment No haemostasis Time-consuming Risk of sulcus contamination Painful

B. 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.

1. Epinephrine :

Although epinephrine provides effective vasoconstriction and hemostasis,17 33% of its application is accompanied by significant local and systemic side effects. “Epinephrine syndrome”, which is characterised by tachycardia, hyperventilation, raised blood pressure, anxiety and postoperative depression, can occur in patients who are susceptible to epinephrine.18

Advantages:

Vasoconstrictive Hemostatic

Disadvantages:

Systemic effects -“epinephrine syndrome” Risk of inflammation of gingival cuff Rebound hyperemia Risk of tissue necrosis

Owing to its established potential to cause damage to soft tissues around natural teeth, the use of epinephrine as a chemical agent for chemicomechanical retraction around implants cannot be justified and hence requires clinician’s absolute vigilance in its application.

2. Aluminium sulphate and aluminium potassium sulphate:

Both the agents are hemostatic and retractive, and results in minimal postoperative inflammation at therapeutic concentrations,17 although severe inflammation and tissue necrosis results from concentrated aluminum potassium sulphate solutions.19 These act by precipitating tissue proteins with tissue contraction, inhibiting transcapillary movement of plasma proteins and arresting capillary bleeding.20

Advantages: Haemostasis Least inflammation of all agents used with cords Little sulcus collapse after cord removal

Disadvantages:

Offensive taste Risk of necrosis if in high concentration

The literature stated above suggests that the cautious use of aluminium sulphate in suitable concentrations can effectively and safely displace marginal gingiva around implants.

3. Ferric sulphate:

Owing to its iron content, ferric sulphate stains the gingival tissue yellow-brown to black color for few days after its use.6 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.21

Advantages: Haemostasis

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

4. Aluminium chloride:

Aluminium chloride is an agent that acts by precipitation of tissue proteins22 but causes less vasoconstriction than epinephrine.23 It is least irritating of all the medicaments used for impregnating retraction cords24 but it possess a vital shortcoming of inhibiting the polyvinyl siloxane and polyether impression materials.21

Advantages: No systemic effects Least irritating of all chemicals Haemostasis 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

The aluminium chloride is an appropriate choice as a chemical agent for impregnating retraction cords that has to be placed around implants due to its least irritating effect on soft tissues. This agent proved more effective in keeping the sulcus open after clinicians remove the cord (10-20 percent of original opening eight minutes after the cord is removed) than are epinephrine-

medicated cords (50 percent closure of sulcus observed over a similar time).After 12 minutes, only sulci packed with aluminium chloride remained open at 80 percent of the original space created.25

However, the elimination of residues of aluminium 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.

5. Inert matrix-Polyvinyl siloxane:

This material acts by generating hydrogen that causes expansion of material against the sulcus walls during setting.2

Advantages: No risk of inflammation or irritation Non traumatizing Ease of placement Painless No adverse effects

Disadvantages: Limited capacity for haemostasis (no active chemistry) Less effective with subgingival margins

This method, although non traumatic, can cause significant problem in capturing precise details during impression, in cases where implant abutment junction is placed few millimetres subgingivally.

6. 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 aluminium chloride resulted in less pain and discomfort, was quicker to administer.2,26

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 aluminium chloride enhances the haemostatic action. Application of an air and water spray will remove the paste from the sulcus.27

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

Apart from situations in which implants are placed deeply into the gingival, this approach of gingival displacement is of considerable value in retracting peri- implant marginal gingiva.

C.Surgical retraction:1. 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.28

Neodymium:yttrium-aluminum-garnet( Nd-YAG )lasers – Its use is contraindicated near implant surface as they tend to absorb energy and heat up. This heat can be transmitted to bone and may result in bone loss.

Erbium:yttrium-aluminum-garnet (Er:YAG) lasers-These are reflected by metal implant surfaces and minimally penetrate the soft tissues, so they are fairly safe to use.

CO2 laser –The prime chromphore for CO2 laser is water, hence it reflects off metal surfaces., CO2 lasers absorb little energy near metal implant surfaces, with only small temperature increases (< 3ºC) and minimal collateral damage. Also these lasers do not alter the structure of the implant surface.28

Advantages: Excellent haemostasis–carbon dioxide CO2 laser safe for implants as reflected by metal Reduced tissue shrinkage Relatively painless Sterilizes sulcus

Disadvantages:

Nd-YAG laser contraindicated with implants Er:YAG laser reflected by metal but not as good at haemostasis as CO2

laser CO2 laser provides no tactile feedback, leading to risk of damage to

junctional epithelium

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.2

2. Electrosurgery:Advantages:

Efficient precise haemostasis

Disadvantages:

Contraindicated with implant (risk of arcing) Gingival sulcus too small for two electrodes, impractical in implant

dentistry.2

3. 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 teeth.29

Advantages:

Fast Ability to reduce excessive tissue Ability to recontour gingival outline

Disadvantages:

Causes considerable haemorrhage High risk of the bur damaging the implant surface Risk of tissue retraction exposing implant threads High risk of traumatizing the epithelia attachment2

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.30

Thus this approach is contraindicated with implants.

Discussion:

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 patient’s sulcus depths are shallow, their mucosal health is impeccable and a robust, thick periodontal biotype is present.2

The addition of chemical adjuncts to retraction cords further complicates the situation. While using chemicomechanical means of gingival retraction, absorption of chemicals, like epinephrine, at the sulcus interface is dependent on patient’s gingival health.18 Healthy gingiva acts, to some extent, as a barrier to absorption of epinephrine.23

This may be a reason why the theoretical overdose levels are not observed clinically. 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.8 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.31

Surgical retraction procedures are rapid but at the same time destructive and involve excision of tissue. The results of studies have supported using electrosurgery, lasers and rotary curettage around natural teeth, however, evidence does not support the use of such destructive procedures in the implant situation.32 The grounds for this reasoning are that the peri-implant mucosa does not have the same capacity for regeneration as peridental mucosa. Lasers with appropriate wavelengths may be applicable in some of the implant situations during retraction and when making impressions.2

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 percent aluminium 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 aluminium chloride in the injectable matrix offers the best outcome of the chemical choices to date. 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).2

Conclusion Although injectable matrix technique sounds promising for implant situations, further development is needed. As compared to 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.

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