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Clinical techniques for tissue management

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 the indirect restorations. Dental impression materials are utilized to make reproductions of oral structures and these impressions can be poured with a high-strength stone to duplicate the oral structures.

Countless techniques and materials have been developed over the years to improve the accuracy and predictability of this challenging task. Some exciting and promising 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. The digitized information on the prepared teeth can be readily available for precise, computer-assisted fabrication of master casts and definitive restorations and preserved as a digital file instead of a deteriorating impression material. This new digital technology will continue to transform digital intraoral scanning into a routine procedure in more dental offices in the near future.

Healthy periodontal tissue is a prerequisite for the success and accuracy of the final impression. Inflammation of gingival tissues before impression-taking 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 the periodontal health before impression-taking and while the definitive restoration is being fabricated.

Management of soft tissue during the preparation and impression-taking states 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.

Impression materials will only make accurate reproductions of tooth surfaces that are clean, visible, and dry. Therefore, tooth preparations with subgingival finish lines require the displacement of gingival tissue. Several techniques have been proposed such as;
  • electrosurgery
  • diode laser gingival troughing
  • rotary gingival curettage
To achieve low-trauma gingival displacement, the retraction cord technique is the most reliable and predictable regarding control 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.

Retraction pastes provide an alternative method for the displacement of gingival tissue. One method involves the injection of a paste composed of clay into the sulcus, which mechanically separates the tooth from the surrounding tissue, creating space between the prepared tooth and the sulcus. These materials contain aluminum sulfate or aluminum chlorate, which provide retraction and hemostasis. These retraction paste systems include;
  • Astringent (3M ESPE),
  • Expasyl gingival Retraction Paste (Kerr),
  • Traxodent Hemodent Paste Retraction System (Premier Dental).
  • Magic FoamCord retraction paste (Coltene/Whaledent). This system involves PVS materials that expand in the sulcus from the release of hydrogen during the setting process.
  • GingiTrac Gingival Retraction Material (Centrix). This contains a hemostatic agent. Besides, foam or cotton caps can be used to compress the material into the sulcus.
Reports indicate that effective soft tissue management can be accomplished with less histologic damage using retraction pastes (Expasyl and Magic FoamCord) compared with retraction cords.
Clinical studies have shown that these retraction paste systems may provide less separation of the junctional epithelium in the sulcus and less recession than the retraction cord. However, studies indicate that these materials may not provide the same amount of penetration and displacement of the gingival tissue.

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.

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 an 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


Stay tuned for the upcoming post discussing tissue displacement techniques using retraction cords.
REFERENCE: Esthetic and restorative dentistry, material selection and technique, third edition. Douglas A. Terry, Willi Geller

Anterior Crown Preparation

When we are going to start a tooth preparation, we have to pay attention to two main factors:
  1. Amount of clearance/the space for the restorative material for strength
  2. The geometry of preparation that gives the restoration retention and stability.

The principal objective in the anterior crown preparation is to provide adequate space to reproduce the emergence profile, occlusal anatomy, proximal contours, and contact. Because different biomaterials require variations in thickness for strength, the preparation dimensions for full-coverage restorations can vary. The geometric form of the preparation varies according to the anatomical morphology of the tooth. The anterior teeth have an oval form. L
ow tapering of the walls provides such geometry in a simple way. This geometric shape provides inherent resistance to forces of mastication. Therefore, when sufficient tooth structure is missing like in cases of massive destruction or a badly decayed tooth, the biomechanics of the preparation can be optimized by restoring these contours with a core build-up prior to completion of the preparation.
In order to achieve success, it is essential that the preparation presents some features and meets certain requirements. The general shape of the preparation should follow the anatomical contours of the natural tooth with smooth and rounded transitional line angles.

All-ceramic crowns can be fabricated from one ceramic (eg, pressed or machined by CAD/CAM), or a combination of a ceramic coping and a reinforced veneering ceramic, with improved aesthetic features. These copings may be fabricated with different materials - lithium disilicate, alumina, zirconium dioxide - and for different systems, such as e.max (Ivoclar Vivadent), Procera (Nobel Biocare), lnCeram (VITA), and Lava (3M ESPE). Some of these systems allow for obtaining high strength ceramic infrastructures, even in small thicknesses (0.3 mm) facilitating the obtaining of less invasive preparations, without aesthetic impairment.

Clearly, the degree of translucency/opacity of the coping - a critical aspect in defining the aesthetic potential of each restorative system- varies significantly from one material to another. It should be stressed that the thickness of the coping, as well as its degree of translucency/ opacity, must be defined according to the color of the substrate to ensure perfect masking of its shade.
The darker the underlying tooth structure, the less translucent and/or thicker the coping should be.

 

General guidelines :
  • Incisal reduction of about 1.5 to 2 mm in order to create enough space for the reproduction of the translucency and the opalescence effects which characterize the incisal third.
  • The finish line should be sharp and defined, in addition to providing the coping and ceramic veneering the sufficient thickness.
  • The axial preparation thickness varies between 1.2 mm cervically and 1.5 mm (middle and incisal).
  • Deep chamfer finish line (or a rounded shoulder), flat and smooth with a 90-degree cavo-surface angle with the external surface.
As I'm going to feature the preparation of all-ceramic crowns. Thus, it is necessary that the available space, defined through the reduction with diamond points, is compatible with the restorative system to be used. Because of their shape, when used parallel to the axis of the preparation, these points confer ideal tapering to the preparation walls.



I’d like to talk about a preparation that follows three main stages applied to three main areas.

Three main stages to get the final preparation of the crown:
  1. Cutting
  2. Refinement
  3. Finishing & polishing

Three main areas :
  1. Incisal edge
  2. Free surfaces "labial & lingual"
  3. Proximal surfaces "mesial & distal"

So, let’s get started..

Cutting


First of all, let’s divide the tooth into 3 main areas :
  1. Incisal edge
  2. Free surfaces "labial & lingual"
  3. Proximal surfaces "mesial & distal"

Incisal edge :
At first, we start to define depth cuts in the incisal region with a cylinder-shaped diamond point to its full thickness at an angle approximately parallel to the incisal edge and slightly tilted to the palatal surface. This step is designed to ensure sufficient thickness so that the restoration presents strength, enabling the ceramist to reproduce the optical features of the incisal edge. Depending on the ceramic system, the incisal reduction is about 1.5 to 2 mm.



Free surfaces :
using a spherical point angled at about 45 degrees to the labial and lingual surface, a cervical groove is prepared so that only half of the tip penetrates the tooth structure. The groove follows the gingival contour and still remains far from the gingiva. The final placement of its end is always performed while finishing the preparation.


Using a rounded-end diamond point, 
acting at an angle of 45 degrees to the tooth surface to limit the depth to half the thickness of the active tip to prepare longitudinal grooves on both free surfaces "labial & lingual" following the inclination planes of the buccal surfaces. The aim of this maneuver is to create longitudinal depth cuts to guide and limit the depth of the reduction.



Then, the preparation is performed on half of the surface by joining the longitudinal grooves until the required depth of these grooves is reached. Let's say, we will start with the mesial half, thus it is possible to clearly assess the amount of structure removed by the initial preparation before extending on the distal half of the surface. Using a silicone guide sectioned transversely is of great importance in such evaluation.
👉 The point is deepened throughout half of its thickness following the inclinations of the surfaces. 



However, due to the concave shape of the lingual surface, it is easier to define the depth of reduction by making spot marks with a spherical diamond point deepened until its half diameter, then an ovoid or a flame-shaped diamond point is used to join them to accomplish uniform reduction initially. 




👉 Remember the reduction will be increased throughout the preparation to achieve the desired depth.
Proximal surfaces :
The adjacent teeth are protected from accidental reduction with a metal matrix and a slice is made in the proximal area using a thin tapered point in order to separate the prepared tooth from the adjacent teeth. 


After obtaining a preliminary interproximal separation, the cylindrical point is returned to complete the anatomical reduction of the mesial half of the crown taking into consideration the depth previously defined by the depth cuts to standardize the tissue reduction. The adjacent tooth is protected again with a strip of a metal matrix, and the reduction is implemented on the distal aspect the same way.


Then, the tip is moved from the buccal to the lingual direction, in order to define : 
  • The most suitable termination such as deep chamfer
  • The correct taper - characterized at this time - by the parallelism of the mesial wall to the long axis of the crown
  • Rounded internal angles
  • Enough space for the ceramic.




Cervical termination


The best option is a deep chamfer margin or a rounded shoulder with uniform thickness and rounded internal angles. It is also important that the termination provides sufficient thickness that favors the stratification of ceramics. The edges must be sharp and well defined in all indirect restorations. When these conditions are not met, the impression does not clearly define the preparation margins and therefore there is a risk that the restoration remains poorly adapted or presents subcontouring or overcontouring. 
The deep chamfer is a design in which the gingival floor intersects the axial wall at an obtuse sloping angle. This margin can provide an optimal bulk of ceramic material providing strength and an optimal esthetic result.

👉 The slight chamfer margin is a design that is a conservative modification of the deep chamfer in which the gingival margin is concave with a greater angulation than a knife-edge margin. This type is ideal for ceramic restorations on mandibular anterior incisors.


In addition to ensuring space for the restorative material, one must pay attention to its correct positioning and the cervical end should be assessed as to its relationship with the periodontal tissues. Ideally, the end should be maintained as far as possible from the gingiva (supragingival) since this is the most favorable situation for the periodontium. However, for several reasons - aesthetics, retention, the extent of preexisting lesions - the preparation can be extended to the gingival level ( juxtagingival / equigingival )  or slightly inside the sulcus (intrasulcular / subgingival). These three alternatives satisfy the biological distances and are well tolerated by the periodontium.

👉 Of course, whatever the position of the finish line, the preparation should be as atraumatic as possible ( eg, it is useless to have an equigingival termination if excess cement is left after cementation, which could compromise the periodontal health ).

For non-discolored teeth, the finish line can be kept supragingival, but, it should be placed slightly intrasulcular to hide the transition between the crown and the abutment tooth especially in cases of darker abutments.

👉 Importantly, during all stages of the preparation already performed, the depth of the reduction still should not reach the planned final depth.

Endocrown .. Full documentation of a clinical case

Endocrown


Endocrown is an overlay with an extension into the pulp chamber. In other words, it is a crown that extends to include the pulp chamber in endodontically treated teeth, a crown with its core part as a single unit. It is a large ceramic block that fills the pulp chamber and is adhesively cemented to the dental substrate. thereby achieving macromechanical retention provided by the walls of the pulp chamber and micromechanical retention by means of adhesive bonding. This technique presents satisfactory long-term clinical results in molars due to the large surface area available to bonding.



Indications:

  • Successfully treated tooth
  • Excessive coronal loss
  • Limited inter-occlusal space
  • Cavity depth at least 3mm and cervical margin with 2 mm width
  • Short clinical crowns

Advantages:

  • Simple and easy to perform
  • No preparation for root dentin
  • No post
  • Conservative preparation design
  • Reduce chairside time

Clinical case 

Preoperative situation





Treatment plan:
  1. Excision of the pulp polyp 
  2. Root canal treatment
  3. Endocrown

Removal of the polyp and starting RCT


Clean cavity

Implementation of RCT




Obturated canals


Orifices are sealed with flowable composite to prevent contamination and block the undercuts

Protecting the neighboring tooth during cavity preparation using a metallic matrix band

Finished cavity design 
No internal line angles, flat pulpal floor whenever possible & a supragingival finish line as much as possible

The pulp chamber is divergent towards the occlusal surface, the preparation margins exhibit a butt-joint

Preservation of the sound tooth structure

Optical impression using Omnicam

Bite registration

Virtual design




Material: CeltraDuo, DentsplySirona


The restoration is milled

 virtual Vs physical

Final restoration

Absolute isolation

Seated under gentle pressure

Final result

Preoperative Vs postoperative

Lingual view

Buccal view


Feel free to download my presentation focusing on the most important points regarding this topic:
Endocrown from virtual to real



Stay tuned for more clinical cases ..