Post-Core Applications

In teeth that have undergone endodontic treatment, opening of the root canal entrance often becomes necessary in cases where a substantial part of the tooth structure is lost due to decay or trauma-related fractures. To provide sufficient tooth support and restoration, protect these teeth from new fractures, and enhance the...
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Post-Core Applications
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In teeth that have undergone endodontic treatment, opening of the root canal entrance often becomes necessary in cases where a substantial part of the tooth structure is lost due to decay or trauma-related fractures. To provide sufficient tooth support and restoration, protect these teeth from new fractures, and enhance the retention of a crown-bridge prosthesis, post-core systems are commonly used for both vertical and horizontal reinforcement.

Within the prepared root canal, the canal post supporting the core structure is termed the “post,” while the core part located in the crown section, prepared alongside the post and resembling a cut tooth form, is called the “core.” Both provide intracoronal support to the structure. Crowns adhered to this post-core structure offer extracoronal support.

Indications for Post-Core Restorations:

  1. When the tooth loss is so extensive that it cannot be restored conservatively with fillings.
  2. In cases of crown fractures due to trauma.
  3. In teeth with deep erosions.
  4. In cases where orthodontic correction is not considered and prosthetic treatment is used for axis correction.
  5. In the use of telescope crowns, teeth can be restored with a post-core or solely core structure.

Contraindications for Post-Core Restorations:

  1. Periapical infections.
  2. Root canal calcifications that limit endodontic treatment.
  3. In curved and thin roots.
  4. In cracked and fractured roots.
  5. In teeth with instrument breakage inside.
  6. In the presence of perforated roots during endodontic treatment.
  7. In cases with extensive tooth tissue loss and where the gum line imposes limitations.
  8. Internal resorptions.

Application Areas for Post-Core Restorations:

  • In the restoration of material losses in single teeth.
  • In telescope crowns.
  • As support for conventional and precision-attached partial dentures.
  • As support for overdenture prostheses.

The key aspects of post-core restorations, their indications, contraindications, and application areas in dentistry.

Post Systems

The amount of remaining tooth structure, root morphology, periodontal status, tooth position, and occlusion are influential factors in the selection of post systems. Posts are traditionally classified into two groups: cast and prefabricated. However, non-metal post systems have been developed recently, considering their bondability to root dentin and aesthetic properties.

  1. Metal Posts

  • a) Cast posts
  • b) Prefabricated posts

    Non-metal Posts

  • a) Ceramic posts
  • b) Fiber posts
  • c) 1.a. Cast Posts: While typically made with Type III and IV dental gold alloys, non-precious metal alloys like Co-Cr, Ni-Cr, Ti are also used.
  • d) Cast post-core systems are preferred for teeth with extremely tapered, wide canals, and also for posterior group teeth with severe damage and non-parallel roots.
  • e) 1.b. Prefabricated Posts: These systems extend from the root canal to coronal, supporting the core material. They offer time savings, cost advantages, and ease of application.
  • f) Prefabricated posts are made with precious metal alloys, stainless steel, and titanium alloys. The most popular are parallel-sided, threaded posts.
  1. 2.a. Ceramic Posts:

  • i) Glass ceramics
  • ii) Aluminum oxide-reinforced ceramics
  • iii) Zirconium oxide-based ceramics
  • Introduced by Meyenberg and colleagues in 1993, zirconia posts consist of tetragonal zirconia polycrystals stabilized with 3% yttrium oxide.
  • Benefits include high flexural strength, fracture resistance, chemical stability, biocompatibility, optical properties compatible with teeth, and absence of corrosion problems common in metal posts.
  • The high elastic modulus of these posts allows them to resist forces generated during chewing, but also leads to direct transmission of these forces to the tooth interface without absorption. This can be a disadvantage compared to fiber posts, which have mechanical properties closer to dentin and distribute stress more homogeneously between the post and tooth tissue.
  • Removing the remaining part of these posts in the root is quite challenging if they break and require retreatment. Even if removal is possible, it is a time-consuming process, causing significant dentin loss and carrying a high risk of lateral root perforation.
  • Similar to precious metal alloy posts, their high cost is a disadvantage.

2.b. Fiber Posts (Fiber-reinforced Composite Posts)

  • Introduced in 1992, fiber posts have been widely accepted by dentists and serve as an alternative to metal posts.
  • Today’s fiber posts are primarily composite materials consisting of a high volume of continuous fiber filaments embedded in a bonding resin matrix. The matrix polymers are typically highly polymerized and highly cross-linked epoxy polymers. Various types of posts, including parallel, tapered, smooth, or grooved, can be made from this material.
  • Adhesively cemented fiber-reinforced composite (FRC) posts have shown satisfactory success rates over long-term clinical follow-up periods. The clinical success of FRC posts is attributed to their physical properties, similar to the elastic modulus of natural teeth. Especially in cases where less rigid fiber posts are used, root fractures are less common, and failures typically present as re-restorable post dislodgment.

Carbon Fiber Posts

  • These posts consist of carbon fibers arranged parallel in the same direction within an epoxy matrix, accounting for 64% of the post’s weight. The original version is black, which is not aesthetically pleasing. Carbon fiber posts were among the first non-metal posts to be used in dentistry.

Advantages:

  • More flexible and have an elastic modulus closer to dentin compared to metal posts.
  • When cemented with resin cement, they can distribute forces evenly to the roots, reducing the risk of root fractures.
  • Biocompatible.
  • Resistant to corrosion.
  • Durable.

Disadvantages:

  • Their black color makes them unsuitable for use with all-ceramic restorations due to aesthetic concerns.
  • To mask the dark color of carbon, some manufacturers have produced carbon fiber posts coated with quartz fibers.
  • The upper core structure of carbon fibers is shaped with composite resins.

Glass Fiber Posts

  • Glass fiber-reinforced posts with an elastic modulus close to that of dentin were developed after zirconium ceramic posts and carbon fiber posts. Due to aesthetic issues with carbon fiber, glass fiber posts, which are closer to natural tooth color, either white or translucent, have been introduced. These posts are also referred to as silica fiber or quartz fiber, derivatives of glass.
  • Glass fibers can be made from different types of glass:
  • Electrical glass (E-Glass) is the most commonly used type. Materials produced using E-Glass exhibit high electrical propensity.
  • S-Glass (Silica Glass) is a different type of amorphous glass containing magnesium in its composition, distinct from E-Glass. It is particularly suitable for restorations in constant contact with oral fluids, such as S-Glass fiber-reinforced polymers.
  • Quartz fibers can also be used in the production of glass fiber posts. Quartz is crystallized pure silica and is a tissue-friendly material with a low thermal expansion coefficient. Advanced translucency was first achieved with these posts.

Advantages of Glass Fiber Posts:

  • They are the most aesthetic posts.
  • Their physical properties are similar to those of dentin and composite resin.
  • They bond to the hard tissues of the tooth, composite, and cement.
  • Biocompatible.
  • No risk of corrosion or fracture.
  • Can be easily shortened to the desired length and removed from the canal with a drill.
  • Show stability against the leakage of oral fluids.

Disadvantages:

  • Their strength and elasticity modulus are lower compared to carbon fiber posts.
  • Not stable in moist environments.

Olyethylene Fiber Posts

  • Polyethylene fiber, first suggested for use by Braden and colleagues, is known as a superior material for its color similar to tooth tissues, softness, high fatigue resistance, non-brittleness, and biocompatibility. The most commonly used types are in a woven (Ribbond) form.

Advantages of Polyethylene Fiber Posts:

  • Adapts to the shape of the canal.
  • Supports both radicular and coronal structures.
  • Minimizes the risk of root fracture.
  • Increases the retention of coronal restorations.
  • Eliminates irregularities and undercuts in the root canal.

Disadvantages:

  • Manipulations can be challenging.
  • Limited working times.

 

CAST POST-CORE APPLICATION STAGES

  1. PREPARATION OF THE ROOT CANAL Preparation of the root canal for posts is carried out in three steps:
  • Removal of Root Canal Filling: Before removing the apically sealed root canal filling, the estimated length of the post is determined.
  • Canal Enlargement: The canal filling is removed using endodontic burs, leaving the filling intact 5 mm from the apex, or 3 mm in short teeth.
  • Preparation of Coronal Tooth Structure: The length and depth of post placement in the canal are directly proportional to retention. The length of the post should be at least equal to the crown to be prepared. The root canal is enlarged one or two sizes larger than the post using special burs matching the post shape. Care is taken not to remove excess dentin in the apical part of the post socket. In the coronal structure, unsupported structures are removed while preserving the crown as much as possible.
  • Preventing Root Fractures: At least 2 mm of healthy dentin must be left around the canal space to prevent root fractures. Sharp angles are eliminated, and a finishing line is prepared to create a ferrule effect.
  • Guiding Path for Single-Rooted Teeth: To prevent post rotation in single-rooted teeth, a guiding path (keeway) should be created towards the tooth’s largest mass (usually the labial side). This guiding path should be prepared with a bur, 1 mm in diameter and 4 mm in length.
  • Chamfer Step: A distinct chamfer step with 2 mm depth and a 2° angle should be prepared at the cervical margin. This creates a ‘ferrule effect,’ where the tooth is wrapped and protected by a metal ring-like structure, increasing retention and preventing leverage movements on the tooth and restoration.
  1. IMPRESSION

Indirect Method:

  • Before taking the impression, a piece of toothpick is prepared to serve as a support for the fluid rubber impression material. The toothpick is sized to easily enter and exit the root canal and extend 1-2 mm above the cervical surface.
  • The first impression is taken with a suitable prefabricated tray and a heavy-bodied impression material, then washed, dried, and any undercuts and protrusions within the impression are removed with a hand tool.
  • The root canal is washed and dried with paper points.
  • A fluid impression material is prepared and applied into the canal with a lentulo spiral (while also placing the toothpick inside the canal), and the same material is placed inside the impression tray before application in the mouth. Once the impression material has set, it is removed from the mouth.
  • The root canal is temporarily sealed.
  • A plaster model is obtained in the laboratory.
  • In the plaster model, melted wax is poured into the root canal and a paper point is inserted before the wax hardens to prevent deformation.
  • In the coronal part, a wax pattern in the shape of the cut tooth is created, and then the wax post-core pattern is removed and sent for casting.
  • The model is adapted, the antagonist relationship is checked, and then sent back to the clinic.
  • As a result, the post and core are obtained as a single piece through casting.
  • In multi-rooted teeth, the cast post-core can be cast separately for each root canal. The core part integrates through a key system.
  • A cement escape route (vent) should be created on the cast post.

Direct Method:

  • After preparing the post canal, it is isolated with a canal instrument wrapped in vaseline-soaked cotton.
  • A plastic rod is shaped into a post and notched to provide retention. The plastic post is dipped in acrylic liquid and left until it becomes slightly fibrous and sticky.
  • Cold acrylic is injected into the tooth canal, and then the prepared plastic post is inserted. Ensure that the acrylic also covers the beveled areas of the tooth cut.
  • Once the acrylic hardens, it is removed for inspection. Any missing parts are completed and re-inserted into the canal.
  • The core structure is prepared in the shape of the cut tooth.
  • The casting process is carried out using known methods.

III. CEMENTATION

  • For the cementation of cast post-cores, zinc phosphate, polycarboxylate, glass ionomer, resin-modified glass ionomer, and resin cements can be used.
  • During the cementation of the post, if the cement is only applied to the post, air will get trapped in the depths of the prepared canal. As the post is pushed into place, air will pass through the liquid cement, leading to air bubbles that adversely affect the physical properties of the cement layer.
  • Filling the canal with cement before placing the post will prevent air entrapment and ensure an evenly thick layer of cement.

FIBER POST APPLICATION

  • After clinically and radiographically calculating the root’s diameter and length, the root canal filling is removed using Gates Glidden drills or special drills included in the system, leaving approximately 3 mm at the apex. The root canal is enlarged with increasingly larger diameter drills.
  • The post is cut to the measured canal length and the size needed to support the core part.
  • The tooth’s root canal is etched with 37% phosphoric acid following the manufacturer’s recommendations, then washed and dried.
  • Bonding is applied to the root canal.
  • Dual-cure cement is applied to both the post and inside the canal.
  • The post is placed into the canal, excess is cleaned, and the cement is cured with a light device.
  • For core construction, the composite is layered and shaped according to the manufacturer’s recommendations.
  • The preparation is done, followed by the impression process, and the restoration preparation proceeds.

 

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