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Post & Core: An Essential and Time Proven Procedure

Core-Flo_DC_Lite_Syringes

Paul L Child Jr., DMD, CDT

Introduction

Why are posts still relevant, especially when implants are so readily available? Knowing when to place a post and core build-up versus extraction, possibly socket preservation with a bone graft, and subsequent implant placement and restoration can be a challenging task, and often an ethical dilemma. With the advent of implants and their known longevity, has the profession been too quick to deem a tooth hopeless or non-restorable?

A tooth has a known restorative life cycle: 1) sealant; 2) filling; 3) most likely another one or two fillings; 4) an inlay/onlay (which often gets skipped); 5) crown; 6) possibly root canal therapy (RCT); 7)  post/core/new crown; 8) possibly retreatment of the RCT and/or endodontic surgery; 9) and finally extraction and replacement with a prosthesis (removeable or fixed prostheses including implant supported crown). However, due to patient finances, desires, misguided assumptions, and lack of knowledge about this lifecycle, many stages are omitted or simply not explained to the patient. It is our responsibility to fully explain and offer all options to patients, including prolonging the tooth with a post and core build-up.

The primary purpose of a post is to retain the coronal restoration in an endodontically treated tooth that has suffered extensive loss of crown structure. There is no current evidence that suggests a post actually reinforces the root. In fact, the wrong choice of post can lead to tooth and root fracture (see Figure 1 and 2). Rigid posts with a high elastic moduli (>100 GPa), such as titanium, stainless steel, cast posts, and zirconia, are more likely to result in root fracture. However, there is clinical evidence as described in randomized controlled clinical trials that supports the use of fiber reinforced composite posts.

1_Right_Maxillary

Figure 1
Screw or thread-type posts often result in root fractures.

4_Left_Maxillary

Figure 2
Poor endodontics combined with poorly placed posts that led to recurrent decay and root fracture.

Root fractures are rare with fiber reinforced posts due to their ability to allow relatively uniform stress distribution to the tooth and surrounding tissues, thus providing a protective effect against root fracture. These elastic properties are similar to dentin. However, the most frequent mode of failure of fiber reinforced composite posts is debonding. Generally, achieving adhesion to intraradicular dentin, particularly at the apical level, remains a challenge. Therefore, meticulous care must be taken in choosing the correct post and following a proven technique. 

D.T. Light-Post Illusion X-RO

BISCO’s D.T. Light-Post® Illusion X-RO® is a double-tapered, radiopaque yet translucent fiber post system that has consistently won rave reviews from users and independent evaluation organizations. Its unique features include: translucency that enhances esthetics and light transmission; high radiopacity for ease of visibility on radiographs; a double-tapered design that closely conforms to the shape of the prepared canal to minimize dentin removal; unidirectional, pretensed, quartz fibers bound in a resin matrix giving it greater flexural strength than metal posts; maximized strength, with no notches or serrations to compromise strength; a patented color-on-command technology that allows the post to disappear at body temperature, but reappear with application of cold water (for retreatment or removal); and fiber optic design allows light to transmit through the post so it can be cemented with light activated materials.

There are three key conditions for long-term success of posts and core build-ups:

   1.  Preservation of tooth structure
   2.  Presence of a ferrule effect (at least 1-2mm)        
   3.  Adhesion

An adhesive that is dual-cure compatible or uses a separate co-initiator (dual/self-cure activator) is the recommended type of adhesive for the best results. Most self-etch adhesives are incompatible with self-cure and dual-cure cements, whereas, total-etch adhesives create a more uniform hybrid layer. Recently, the introduction of Universal adhesives used in their total-etch mode creates a desirable option with their dual-cure compatibility or being a true dual-cure adhesive. Most Universal adhesives are not truly dual-cure or dual-cure compatible (unless they have a separate dual/self-cure activator). However, BISCO offers a solution with  its All-Bond Universal-based Universal Primer – a true dual-cured adhesive that is dual-cure compatible, ideal for posts and core build-ups.

Universal Primer

Universal Primer has a very low film thickness (<5um), ensuring that the post will seat in the canal. It does not require light-curing when used with a dual- or self-cure restorative material. Shear bond strengths to dentin (39 Mpa) and various substrates (eg. lithium disilicate 35 MPa, Zirconia 29 MPa, Composite 40 MPa) are exceptionally high when compared to others due to its unique formula and incorporation of the MDP monomer. Clinically, I have fallen in love with Universal Primer for all my post and core build-ups, as well as all my crown cementations.

A core build-up is a restoration placed in a compromised tooth to replace the coronal portion to support a crown or bridge abutment. Desirable features of a core build-up material include: esthetically pleasing, good mechanical properties to withstand the forces of mastication, high adhesion to dental structures, easy handling, and low solubility and water sorption. BISCO’s Core-Flo DC and Core-Flo DC Lite meet and exceed all these characteristics and demands. 

Core-Flo DC & Core-Flo DC Lite

Core-Flo DC comes in two versions – stackable and self-leveling (Core Flo DC Lite). Both have nearly identical physical and chemical properties but allow the clinician to choose which viscosity they prefer. In my practice, I favor the Core-Flo DC Lite, as it flows slightly to ensure void-free margins and is ideal for simultaneous post cementation. For smaller build-ups or for anterior teeth, I use Core-Flo DC (stackable version). Both come in Natural and Opaque White shades. 

The combination of D.T. Light-Post Illusion X-RO, Universal Primer, and Core-Flo DC (Lite) make an excellent choice for all post and core build-ups prior to a crown. They are simple to use and deliver unique features not found in other products. All the materials are compatible with other manufacturers materials as well, but I have found that combining these three BISCO products provide the optimal results I expect.

Clinically Proven Technique for Post and Core Build-up

  1. Take a pre-operative periapical radiograph to determine the ideal length of the post to be placed. (see FAQ’s).
  2. Isolate the tooth to be treated with a rubber dam. Research still indicates that this is the best technique to use.
  3. Remove all provisional material used to seal the root canal access including any remaining caries.
  4. Evaluate the remaining tooth structure and determine the number of posts required and the canal to be used. (Most of the time, one is sufficient, see FAQ’s)
  5. Use a heated endodontic plugger instrument or electronic heat source to remove as much of the gutta purcha to the appropriate length. Leave at least 5-7mm of gutta purcha in the apical end of the canal.
  6. Use only the drills (D.T. Drills) that are specifically designed for the post you are using to carefully shape the canal to the pre-specificed length. Use the smallest size of post as possible to preserve tooth structure.
  7. Take a radiograph of the post tried in the canal. The post should be seated snuggly against the remaining gutta purcha, yet have a slightly passive fit in the canal.
  8. Etch the canal with phosphoric acid for 30 seconds. Rinse thoroughly and use paper points to ensure all remaining irrigant and phosphoric acid is removed.
  9. Disinfect the canal with 2% chlorhexidine (Cavity Cleanser) for 1 minute. Use paper point to remove excess irrigant.
  10. Use a dual-cure adhesive (Universal Primer) with an endodontic microbrush in the canal and scrub the adhesive for 10-15 seconds. Air dry the adhesive and use paper points to soak up any excess adhesive in the apical portion of the canal to ensure the post fits completely.
  11. After cleaning the post, place a small amount of a dual-cured, resin-based cement (Duo-Link Univeral) or the core build-up material (CoreFlo DC Lite) on the post. Use the supplied endodontic tip to express the cement from the apical portion of the canal to the coronal portion, keeping the tip in the material, to avoid air bubbles or voids in the cement.
  12. Carefully place the post to length with moderate pressure. Light-cure the cement and post. If the post is designed to allow high amounts of light to transmit thru the post (i.e. D.T. Light-Post Illusion X-RO), then the light will assist in curing the dual-cured cement.
  13. If not already completed, etch and apply adhesive to the rest of the tooth. Continue to apply core build-up material in one layer and allow to self-cure or light-cure. Prepare the tooth for the restoration of choice.

Frequently Asked Questions

What interferes with post bonding?   
Sodium hypochlorite, EDTA, hydrogen peroxide, RC Prep, calcium hydroxide, eugenol, sealers – all can negatively affect the adhesion of luting agents. However, 2% CHX does not affect bonding. Careful debridement of the post space walls should be performed prior to cementation.

How long should I wait after RCT to cement a fiber reinforced post?
At least one-week. Residues of unset sealer may interfere with cement polymerization.

How should I treat the post before cementation?
Silane application may increase surface wettability, but there is no conclusive evidence to support this treatment. Adhesives will not improve the bond strength, but may increase the surface area covered by cement.

How should I treat endodontically treated teeth with 2 or 3 surface cavities?
Cuspal coverages, via onlays or crowns is considered appropriate versus a conservative approach with resin composite restorations.

What length should I place the post?
A length smaller than the crown height is correlated with higher failure rates. Empirically, the post should be 2/3 of the root length leaving at least 4-5 mm of gutta purcha. However, removal of gutta purcha beyond 5-7 mm has been shown to significantly increase susceptibility to leakage. Furthermore, removal of gutta-percha to a level of 6 mm has been shown to lead to an unpredictable and significantly inferior seal compared with an intact root canal filling.

What size of post should I use?
The smaller the post that maintains an intimate yet passive fit will result in favorable outcomes. However, larger posts generate more stress in the root.

How many posts should I use in a multi-rooted tooth?
If the tooth being treated is a premolar or incisor, one post is sufficient. If the tooth is a molar and is severely compromised or lacks adequate tooth structure, two posts may be considered (See Figure 3). However, one post is generally appropriate for most clinical situations.

Figure_4

Figure 3
Two posts were chosen for this severely broken down molar missing
the majority of the coronal tooth structure.
Dentistry courtesy of Dr. Michael Morgan

December 2015 BisDent Globe, Volume XXI, Issue II

 

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