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Soft tissues displacement... PDF file download

The clinical success of the indirect restoration requires a precise working model and thus depends on the accuracy of the final impression. An accurate impression is one of the primary determinants for a precisely fitting indirect restoration. Taking a precise impression is one of the most challenging steps in restorative dentistry, yet it is the foundation and the key to the longevity of indirect restorations. 

The need to retract the gingiva for taking impressions is universally acknowledged. The complexity of the procedure arises from a need to provide adequate horizontal space for the impression materials. Some authors have determined that the horizontal space must be between 0.2 and 0.4 mm. Gingival retraction during any stage of restoration, no matter the technique, may cause a lesion to form on the periodontal tissue. Periodontal tissue with normal healing capacity will repair itself.











Impregnating chemicals

The use of any retraction system requires healthy periodontal tissue that has not been damaged or injured during tooth preparation. The selection of a retraction technique depends on the operator's experience, the periodontal biotype, and, in the authors' view, the principle of choosing the least invasive technique that will produce the most effective results. Based on these criteria, mechanical or mechanicochemical methods can be used, but surgery, whether with a rotating instrument or electric scalpel, should not be considered because of the clinical difficulties and the uncertainty of outcome.


Mechanicochemical techniques combine mechanical and chemical interventions. The term often refers to the use of retraction cords impregnated with solutions that have hemostatic or vasoconstriction effects, such as epinephrine, aluminum chloride, aluminum sulfate, and ferrous sulfate and their various combinations. The cords are used to keep the chemicals in contact with the tissue and confine them to the application site. Thus, enlargement of the gingival sulcus and fluid control can be readliy accomplished.

Impregnating chemicals

For mechanicochemical techniques, retraction cords are impregnated with chemical solutions that augment the effect of retraction and hemostasis. However, animal studies using dogs have shown that chemical solutions cause a certain amount of inflammation of the connective tissue. Among the most frequently used solutions are epinephrine; various astringents, such as aluminum chloride, aluminum sulfate, and ferrous sulfate; and combinations of these compounds. 


Epinephrine is frequently used because it offers excellent vasoconstriction, provides considerable tissue retraction, and results in minimal postoperative tissue loss. One study, however, found no significant difference compared with aluminum sulfate. Epinephrine should never be used in patients whose gingiva has been damaged during preparation or for patients with hyperthyroid conditions, cardiovascular pathologies, or hypersensitivity. The latter conditions may lead to cardiovascular reactions, such as an increase in blood pressure, tachycardia, accelerated respiration, or headache.


Aluminum chloride is a commonly used astringent that causes no adverse systemic effects and only a few undesired localized effects. It is usually found marketed as a 14% solution. The hemostasis and retraction that are provided by aluminum chloride are inferior to those of epinephrine; moreover, if used at high concentrations, this chemical can cause significant postoperative paramarginal tissue loss. However, it can be used on damaged tissues with only moderate tissue loss after healing. 

The impregnating solutions can inhibit the polymerization of impression material when they come in contact; a similar phenomenon has been found when latex gloves are used with polyvinyl siloxanes.

 

Aluminum chloride is compatible with polyvinyl siloxanes, but it inhibits the reaction of the polyether chains, and if they remain in contact, the impression material loses its contours and detail and will appear melted. Many clinicians continue to use aluminum chloride as a hemostatic agent, making it necessary to carefully clean the surface of the cord with cotton pellets and water spray to reduce or eliminate the polymerization interference.


Aluminum sulfates offer a good gingival retraction and efficient working time. Some authors believe this chemical is toxic to tissues and, because of the sulfur, can interfere with the polymerization of polyvinyl siloxanes if the cord is not rinsed thoroughly before impression. On the other hand, aluminum sulfate shows excellent compatibility with polyethers in general, and it is recommended for use with these impression materials.


Ferrous sulfate is commonly used as an astringent because of its excellent hemostasis and negligible tissue loss. However, this chemical provides minimal retraction and stains the gingival tissues. The precipitate that forms on the cord is difficult to eliminate before taking impressions, and since ferrous sulfate is incompatible with polyethers, clinicians must use hydrocolloid impression material. In the authors' view, the use of this chemical and its associated impression technique are obsolete.


Various combinations of astringents can also be used for retraction. The combination of aluminum sulfate and aluminum chloride seems to provide better results than either of the two used in combination with epinephrine.


You can review Retraction cords... Why? When? How?


Retraction cords.. Why? When? How?

To achieve low-trauma gingival displacement, the retraction cord technique is the most reliable and predictable regarding controlling gingival recession caused by impression.

One study indicates that a minimal crevicular width of 0.20 mm is required for consistent accuracy and defect-free impressions, and the minimum time in the sulcus to achieve this dimension is 4 minutes.

There are several guidelines for predicting the post restorative gingival margin levels and the periodontal health after preparation, gingival retraction, and impression-taking. These guidelines should be considered during the diagnostic phase and before the restorative appointment because they can provide the patient with a stable and healthy periodontium after preparation, impression-taking, and placement of the restoration.

Measurements on the facial and interproximal regions of the unprepared tooth can provide predictable categorization. These osseous crest positions can be divided into three categories: normal, low, and high.

  • For a normal crest position, these two measurements for anterior teeth should be approximately 3 mm on the facial and 4 mm on the interproximal when adjacent teeth are present, and this relationship occurs in approximately 85% of patients.

  • When the depth of the osseous crest to the gingival margin is greater than these measurements, it is considered to be a low crest position, which occurs in approximately 13% of patients.

  • If the depths are less than these measurements, it is considered to be a high crest position, which occurs in 2% of patients.

In a normal osseous crest position, the gingival complex will return to a normal crest relationship after tissue manipulation and impression-taking. However, in a high crest relationship, traumatic manipulation and placement of subgingival preparation margins will position the definitive restoration too close to the osseous crest, creating a violation in biologic width. The low crest position with a thin biotype is considered the most unstable clinical situation and can result in the most variation in the final gingival position. For optimal restorative results, the low and high osseous crest positions should be identified in the diagnostic phase and corrected through osseous and/or orthodontic treatment before restorative treatment. In clinical situations where adjunctive therapy is not planned, careful and gentle manipulation during the impression-taking process is critical. During gingival displacement, therefore, the size and number of retraction cords should be modified according to the osseous crest position and tissue biotype. It is suggested to use a single-cord technique on high and low crest positions and a double-cord technique on normal crest positions.

Retraction cords

In prosthodontics, retraction cords are the most common method used to displace tissue for impression taking, and many different types of cords and chemical solutions are available. Most cords are made of various textile blends of wool, silk, cotton, and synthetic fibers, which are twisted, braided, or knitted together. Cords also can be distinguished as either soft or compact. Soft cords are easy to position and have a high capacity for absorbing gingival fluids or chemical solutions, but they can break easily during positioning and removal and disintegrate when in contact with retraction fluids. Compact cords provide better horizontal displacement, exhibit minimal degeneration from retraction fluids, and are less prone to breaking, but they are difficult to position and absorb minimal gingival or retraction fluids.

Twisted cords are the oldest type of cord used in dentistry; these are composed of two or three threads twisted together. Twisted cords are easy to insert, and larger cords can be separated into two smaller ones. However, the threads come apart easily during positioning and can get tangled in the rotating bur during preparation.

The braided cords are woven so tightly that it is impossible to separate the threads. These cords are very stable, remain intact during positioning, do not get tangled or torn by rotating diamond burs, and come in two varieties: solid core and hollow core. Cords with a solid core exhibit greater volume and more horizontal retraction, but they are stiffer and more difficult to insert. Cords with hollow cores have greater flexibility and are easier to position, but they are less voluminous and exhibit less horizontal displacement.

The knitted cords are knitted together without a central thread. They are easily compressed, do not break, hold the chemical solutions 2.5 times longer than other kinds of cords, and do not get tangled in rotating diamond burs during preparation. However, they are easily cut during preparation and, because they are more easily compressed, offer a less gingival retraction.


Retraction procedures
"Mechanical techniques"

Although the cord-positioning procedure is the same regardless of cord type, retraction cords can be used in single-cord, selective double-cord, or double-cord approaches.

The single-cord technique generally requires a cord of the smallest diameter (no. 000 or 00). For cord insertion, the clinician uses a manual instrument with a thickness to suit the cord type (twisted, braided, or knitted). In the authors' view, cord placement can be accomplished using a composite spatula or other tool and does not require the purchase of expensive, specially designed instruments. Using an instrument compatible with the cord type, the clinician begins by gently inserting the cord in the interproximal zone. The greater quantity of gingival tissue found in the interproximal zone makes it more favorable than the buccal area for starting cord placement. The cord is inserted using a single spatula or two spatulas at the same time (the bimanual technique). The clinician must not push too hard, as this could result in placing the cord too deep. After the first part of the cord is positioned, the clinician must work along the buccal zone. toward the initial point of insertion. If the clinician begins working away from the initial point of insertion, the portion of the cord already in place tends to shift. After inserting the cord along the buccal zone, the ends should be inserted in the palatal area, where overlaps are better tolerated.


Some authors recommend that when using the single-cord technique, the cord be removed immediately before taking the impression. This technique, however, should be avoided, because once the cord is removed, the sulcus tends to close immediately, preventing the penetration of the impression material. Cord removal also can result in bleeding. The clinician must keep the cord in place throughout the operative stages, from repositioning and completing the finish line to taking the impression. The cord must retract the gingiva enough to expose a portion of the unprepared tooth lying beyond the finish line, without interference from the soft tissue. If the gingiva is not retracted sufficiently, the impression material will not properly record the finish line preparation and intact tooth.

The selective double-cord technique involves inserting small pieces of a cord of equal or greater diameter (no. 0, 1, or 2) in the interproximal area directly over the first cord, to further displace the papillae. This method of selective horizontal displacement facilitates impression taking without involving the delicate buccal tissues. Only the pieces of the cord will be removed immediately before taking the impression leaving the smaller cord inside the sulcus.

The double-cord technique requires the insertion of the second cord of equal or greater diameter (no. 0, 1, or 2) directly over the first cord to obtain the horizontal retraction for the entire circumference of the prepared tooth. The second cord is removed just before the impression is taken, while the first cord is left in place. In the first 20 seconds after cord removal, the horizontal displacement of the soft tissue is reduced by 35%, and in the subsequent 20 seconds, another 18% of the displacement space is lost. The speed at which the impression material is inserted after the second retraction cord is removed is therefore critical.


Selecting a retraction technique depends on various clinical factors and the type of cord used. For instance, the clinician would be well advised to use the double-cord technique for a patient with thick periodontal tissue and/or slight inflammation. The drawback of using a second cord is the inevitable compression and apical repositioning of the first cord, which makes cord positioning difficult to control and healing from the gingival displacement unpredictable.

However, in the authors' experience, a second retraction cord must never be used during tooth preparation and positioning of the finish line because of the serious risk of a gingival recession. Thus, choosing a technique depends on which instruments are used for the finish line positioning and which impression materials are used.

During tooth preparation, the clinician must never lose the points of reference, especially of the gingival margin, when using rotating instruments for primary tooth reduction, the clinician must avoid accidentally touching or damaging the gingiva in order to keep the tissue intact and free of bleeding.

Above all, the retraction cords must be placed, no matter how temporarily, only after the guide groove and finish line position have been defined.

If the clinician repositions the finish line with oscillating instruments to minimize gingival damage, and if a continuous jet of water and air is used to prevent overheating, the ideal horizontal displacement can be obtained mechanically. Impression material can subsequently be injected into the sulcus without requiring a second retraction cord. If, after repositioning and completing the finish line with rounded chisels, the first retraction cord (which was positioned 0.2 or 0.3 mm apical to the finish line) is not visible, the clinician may need additional horizontal displacement.
Localized displacement can be accomplished manually by retracting the gingival tissue with the spatula used to position the cords immediately prior to inserting the impression material.


Sometimes it's not only one technique but maybe a combination of more than one technique to manage the tissue regarding recording a precise impression. I'm going a clinical case that I had to take the final impression the same visit because of a time issue related to the patient and there was no way to delay the impression for better tissue management. This is my way to manage such cases:
  1. Implementation of initial preparation and it is preferred to put the finish line away from the gingival margin at this time.
  2. Application of astringent, 3M ESPE for 2-4 minutes to control bleeding.
    Application of astringent for 2-4 minutes
  3. Insertion of the smaller-sized retraction cord for initial tissue displacement.

  4. Bleeding control and gingival troughing using electrosurgery/diode laser.
  5. Application of astringent, 3M ESPE again for 2-4 minutes to control bleeding.
  6. Finishing and adjusting the final position of the cervical margin and any residues of the retraction paste will be eliminated and the margin will be clean and visible.
  7. Application of the larger-sized retraction cord for at least 10 minutes.

  8. Removal of the larger and superficial cord with simultaneous injection of the light body impression material, while the smaller cord will be maintained inside the sulcus, and the air is applied to force the impression to record the sulcus details beyond the margin and prevent bubbles on such critical area. * It doesn't matter if I'm using a single-step or a two-step impression technique. but this step has to be done as quickly as possible.

  9. Immediately after pouring the impression.



    Palatal view


In the upcoming posts, we are going to discuss Impregnating chemicals & the other Gingival displacement techniques including photos and explained in detail.
REFERENCES are going to be collected and mentioned... Stay tuned...

Violation of the biological width

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The clinical success of the indirect restoration requires a precise working model and thus depends on the accuracy of the final impression. An accurate impression is one of the primary determinants for a precisely fitting indirect restoration. Taking a precise impression is one of the most challenging steps in restorative dentistry, yet it is the foundation and the key to the longevity of indirect restorations. 

The need to retract the gingiva for taking impressions is universally acknowledged. The complexity of the procedure arises from a need to provide adequate horizontal space for the impression materials. Some authors have determined that the horizontal space must be between 0.2 and 0.4 mm. Gingival retraction during any stage of restoration, no matter the technique, may cause a lesion to form on the periodontal tissue. Periodontal tissue with normal healing capacity will repair itself. 

Healthy periodontal tissue is a prerequisite for the success and accuracy of the final impression. Inflammation of gingival tissues before taking the impression can complicate the procedure.  Bleeding and moisture from the crevicular fluid can displace impression material, resulting in voids and rounded, indistinct finish lines that can cause an inaccurate cast and an improperly fitting definitive restoration. Furthermore, if a subgingival margin is placed in the presence of inflammation, there is a potential risk of gingival recession and exposure of the restorative finish line. Therefore, the soft tissue must be properly managed.

The preoperative considerations during initial therapy are to control and eliminate all sources of irritation and inflammation. This can be accomplished by control of plaque-related etiologies and/or correction of restorative contributing factors. Unfortunately, this may require delaying the impression procedure after tooth preparation to allow for the improvement in the soft tissue condition. 

The provisional restoration is an essential component of this initial therapy and can improve the quality of the impression. It preserves the position, form, and color of the gingiva and maintains periodontal health before impression-taking and while the definitive restoration is being fabricated.

Countless techniques and materials have been developed over the years to improve the accuracy and predictability of this challenging task. Some exciting developments have recently emerged alongside the growing application and widespread use of CAD/CAM technology. Improved intraoral optical scanners may be able to simplify or someday even eliminate the mechanical aspect of taking an impression with impression material and tray. This new digital technology will continue to transform digital intraoral scanning into a routine procedure in more dental offices in the near future.

Management of soft tissue during the preparation and impression-taking stages requires an understanding of the gingival tissue architecture. The most important determining factor in predicting how the tissue will respond to preparation and impression techniques begins with the relationship of the free gingival margin to the osseous crest. Preoperative recordings of facial and interproximal bone height and determination and preservation of the biologic width can provide predictable post restorative gingival margin levels and periodontal health.

A very important trend in dentistry nowadays is represented by the increased attention paid to the connection between periodontal and prosthetic treatments. This connection is the weak point and the place where patients most often notice that “ the tooth is a fake ”. 


Violation of the biological width

With regard to the interaction of restorations to the periodontium, the most important region is that portion between the tooth, the crestal bone, and the cervical margin of the restoration. In this region, the biological components responsible for the maintenance of periodontal homeostasis are inserted. The connective insertion and the junctional epithelium together compose the biological width, defined as the height of the gingival tissue to the tooth inserted coronally to the bone crest. The dimensions of each of the components of the biological width were determined from findings of histological studies, with the following average values:  junctional epithelium (0.97 mm) and connective insertion (1.07 mm) with the sum of 2.04 mm. The gingival sulcus is 0.69 mm by the way. These values are determined biologically, ranging between individuals, between teeth, and between different surfaces of the same tooth.


The adherence of these structures to the dental tissue - through dentogingival fibers to the connective tissue attachment and through hemidesmosomes to the junctional epithelium - results in an organic sealing around the tooth neck. This allows for the host to maintain periodontal health against continuous bacterial invasion. The gingival sulcus, on the other hand, does not present any adherence to the tooth surface and therefore may be broken during restorative procedures, without prejudice to the periodontal homeostasis.

Since its average length is only 0.69 mm, it has been suggested that - if necessary - the preparations may be extended up to 0.5 mm within the sulcus. Therefore,  the margin is restricted to the intrasulcular area without compromising its biological seal. However, when the biological width is invaded and consequently the dentogingival attachment is compromised whether by pathological (e.g. carious lesion), traumatic (e.g. fractures), or iatrogenic processes (e.g. inappropriate placement of the preparation margins), there is a disruption of the organic seal allowing bacteria and their byproducts to reach the underlying connective tissue which can result in inflammation. Since the biological width is violated, the body itself is responsible for promoting resorption of the bone crest to allow apical migration of its components.





Violation of that space by restorations impinging on the biological width has been associated with gingival inflammation, discomfort, gingival recession, alveolar bone loss, pocket formation, and the like. There is a great body of evidence that the destruction of the periodontal attachment device is preceded by inflammatory changes in the region of the margin. Regarding the appearance of the gingival tissue, one should observe not only its shade - this varies greatly between individuals - but the chromatic pattern in an attempt to detect localized changes. The correction of the biological distances whether by a surgical or a non-surgical approach and the elimination of the inflammation are essential conditions for the implementation of a restorative treatment that will not interfere with the local homeostasis of the periodontium. To have a harmonious and successful long-term restoration, it is advocated to keep 3 mm of sound supracrestal tooth structure between bone and prosthetic margins, which allows for the reformation of the biological width plus sulcus depth. This can be achieved surgically (crown lengthening) or orthodontically (forced eruption) or by a combination of both.

To be continued...

Stay tuned for the upcoming topics discussing Soft tissues management




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