Study Guide on Post and Core of Endodontically Treated Tooth

POST AND CORE OF ENDODONTICALLY TREATED TOOTH

Presented by: Dr. Erla Joy A. Bais-Garcia
Course: SS RESTO 1/CLIN CON 1

Major Changes Following RCT

  1. Altered tissue physical characteristics
  2. Loss of tooth structure
  3. Possible discoloration
    • These changes are results of specific tissue modifications at different levels.

Tissue Modifications Following Endodontic Treatment

A. Tooth composition
B. Dentin microstructure
C. Tooth macrostructure

Specific Tissue Modifications and Possible Clinical Implications Following Loss of Vitality or Endodontic Treatment

Alteration Level

  • Composition
    • Specific Changes
      • Collagen structure
      • Tooth moisture
      • Dentin structure
      • Mineral composition and content
      • Elasticity modulus and behavior
      • Tensile and shear strength
    • Possible Clinical Implication
      • Increased tooth fragility
      • Reduced adhesion to substrate
      • Increased tooth fragility
      • Microhardness
      • Tooth macrostructure
        • Resistance to deformation
        • Increased tooth fragility
        • Resistance to fracture
        • Reduced retention and resistance to fatigue stability of the prosthesis

Aesthetic Changes in Non-vital and Endodontically Treated Teeth

  • Several aesthetic changes may occur in non-vital or endodontically treated teeth, including:
    • Color change or darkening of nonvital teeth as a common clinical observation.

Other Factors Contributing to Discoloration

  1. Inadequate cleaning and shaping can leave necrotic tissue in coronal pulp horns.
  2. Root canal filling materials retained in the coronal aspect of anterior teeth can detract from aesthetic appearance.
  3. Opaque substances adversely affect the color and translucency of most uncrowned teeth.
  4. Biochemically altered dentin modifies tooth color and appearance.

Objectives of Restoration for Endodontically Treated Teeth

  1. Protect the remaining tooth from fracture.
  2. Prevent reinfection of the root canal system.
  3. Replace the missing tooth structure.

Choice of Post Endodontic Restoration

  • Depends upon the amount of the remaining coronal tooth structure.
    • Teeth with minimal loss of tooth structure:
      • Inherently stronger; can be restored with only coronal restorations.
    • Teeth with more than 50% remaining coronal tooth structure:
      • Can be restored with a crown.
    • Teeth with 25% to 50% remaining coronal tooth structure:
      • Can be restored with nonrigid posts.
    • Teeth with less than 25% remaining coronal tooth structure (or less than 3-4 mm of cervical tooth structure):
      • Must be restored with rigid posts.

Restorative Materials

  1. Direct Composite Restorations
  2. Indirect Restorations:
    • Composite or Ceramic Onlays and Overlays.
  3. Full Crowns

Direct Composite Restorations

  • Indicated when only a minimal amount of coronal tooth structure has been lost after endodontic therapy.
    • Resin composites are highly aesthetic, exhibit high mechanical properties, and can reinforce the remaining tooth structure through bonding mechanisms.
    • An incremental filling technique is mandatory.
    • Contraindications:
      • Direct composite resins are contraindicated when more than a third of coronal tissue has been lost.

Indirect Restorations

  • Composite or ceramic onlays and overlays:
    • Overlays incorporate a cusp or cusps by covering the missing tissue.
    • Endocrowns combine the post in the canal, the core, and the crown in one component.
    • Ceramics are a material of choice for long-term aesthetic indirect restorations due to translucency and light transmission that mimic enamel.

Full Crown

  • Indicated when a significant amount of coronal tooth structure has been lost by caries, restorative procedures, and endodontics.
    • The crown can be directly built on the remaining coronal structure prepared accordingly (CORE MATERIAL).
    • Cementation of a post inside the root canal is necessary to retain the core material and the crown.
    • The core is anchored to the tooth by extension into the root canal through the post and serves to replace missing coronal structure.
    • The crown covers the core, restoring the aesthetics and function of the tooth.

The Foundation Restoration (Restorative Components)

  1. Post
  2. Core
  3. Luting or Bonding Agent
    • General Rule: The more tooth structure that remains, the better the long-term prognosis of the restoration.

Ferrule Concept

  • The coronal tooth structure located above the gingival level helps to create a ferrule.
    • Ferrule Definition:
      • Formed by the walls and margins of the crown, encasing at least 2 to 3 mm of sound tooth structure.
      • Acts similar to a metal band around a barrel.
    • Benefits:
      • A longer ferrule increases fracture resistance significantly.
      • Resists lateral forces from posts and leverage from the crown in function.
      • Increases retention and resistance of the restoration.

Five Requirements for a Successful Crown and Crown Preparation

  1. The ferrule (dentin axial wall height) must be at least 2 to 3 mm.
  2. The axial walls must be parallel.
  3. The restoration must completely encircle the tooth.
  4. The margin must be on solid tooth structure.
  5. The crown and crown preparation must not invade the attachment apparatus.

Role of the Post

  • Primary Purpose:
    • Retain a core in a tooth with extensive loss of coronal structure.
  • Need for a post is dictated by the amount of remaining coronal tooth structure.
  • Important Consideration:
    • Posts do not reinforce the tooth but can further weaken it by additional removal of dentin and creating stress that predisposes to root fracture.
  • Recommendation:
    • At least 5 to 7 mm of remaining gutta-percha is recommended (Mosby’s NBDE).

Clinical Features of a Post

  • Maximal protection of the root from fracture.
  • Maximal retention within the root and retrievability.
  • Maximal retention of the core and crown.
  • Maximal protection of the crown margin seal from coronal leakage.
  • Pleasing aesthetics, when indicated.
  • High radiographic visibility.
  • Biocompatibility.

Ideal Post Characteristics

Optimal Combination Should Include:

  1. Resilience: Ability to deflect elastically under force without permanent damage.
  2. Stiffness: A material’s ability to resist deformation when stressed.
  3. Flexibility: Depends on the diameter of the post and the modulus of elasticity of the post’s material.
  4. Strength: Ability of a material to resist fracture.

Post Retention and Resistance

  • Post retention: Refers to the ability of a post to resist vertical forces.
  • Post resistance: Refers to the ability of the tooth/post combination to withstand lateral and rotational forces.

Types of Post

  1. Prefabricated Metallic Posts:
    • Frequently used for the fabrication of a direct foundation restoration.
  2. Fiber Post:
    • Consists of reinforcing fibers embedded in a resin polymerized matrix.

Prefabricated Metallic Posts

Classification Criteria

A. Alloy Composition

  1. Gold alloy
  2. Stainless steel - high flexural strength and modulus.
  3. Titanium Alloy - less rigid but similar flexural strength to stainless steel.

B. Retention Mode

  1. Active Post:
    • Derives primary retention from the root dentin via threads; most are threaded and intended to be screwed into the walls of the root canal.
  2. Passive Post:
    • Placed in close contact with the dentin walls; retention relies mainly on the luting cement used.

C. Shape

  1. Parallel:
    • More retentive than tapered posts but requires removal of more root dentin during preparation.
  2. Tapered:
    • Typically used to minimize dentin removal.

Fiber Posts

  • Consist of reinforcing fibers embedded in a resin-polymerized matrix.

Composition

  1. Monomer:
    • Typically bifunctional methacrylates (e.g., Bis-GMA, UDMA, TEGDMA), epoxies also used.
  2. Fibers:
    • Made of carbon, glass, silica, or quartz; specifics vary among systems.

Guidelines Regarding Post Length

For Metal Posts (non-adhesive cementation):

  1. The post should be as long as two-thirds the length of the canal.
  2. The post length should be at least the coronal length of the core.
  3. The post should be at least half the length of root in bone.

For Fiber Posts (adhesive cementation):

  1. The post should extend to a maximum of one-third to one-half the length of the canal.
  2. The length of the post should be at least the coronal length of the core.

Core Material

  • Replaces carious, fractured, or missing coronal structure and helps retain the final restoration.
  • Core materials include:
    • Composite resin
    • Cast metal or ceramic
    • Amalgam
    • Sometimes glass ionomer materials.
  • The core is anchored to the tooth by extending into the coronal aspect of the canal or through the endodontic post.

Desirable Physical Characteristics of a Core

  1. High compressive and flexural strength.
  2. Dimensional stability.
  3. Ease of manipulation.
  4. Short setting time.
  5. Ability to bond to both tooth and post.

Composite Resin Core

Advantages

  1. Adhesive bonding to tooth structure and many posts.
  2. Ease of manipulation and rapid setting.
  3. Available in translucent or highly opaque formulations.
  4. Protects the strength of all ceramic crowns equally to amalgam cores.

Amalgam Core

  • Traditional core buildup material with a long history of clinical success.
    • Can be used with or without a post.

Disadvantages

  1. Non-adhesive nature.
  2. Potential for corrosion and subsequent discoloration of gingiva or dentin.
  3. Declining worldwide use due to legislative, safety, and environmental issues.

Glass Ionomer Core and Modified GI Core

  • Adhesive materials for small buildups or filling undercuts in prepared teeth.

Rationale

  • Based on their cariostatic effect resulting from fluoride release.

Disadvantages

  • Low strength and fracture toughness lead to brittleness, contraindicating use in thin anterior teeth or unsupported cusps.

Indications

  • Indicated in posterior teeth when:
    1. A significant bulk of core material is possible.
    2. Significant sound dentin remains.
    3. Caries control is indicated.

Luting Cement

  • A variety of cements have been used to cement endodontic posts, including traditional cements, glass ionomer cements, and resin-based luting cements.

Traditional Cement

  1. Zinc phosphate Cement
  2. Polycarboxylate Cement
    • Supplied as a powder and liquid; physical properties influenced by mixing ratio of components.

Glass Ionomer Luting Cement

  • A mixture of glass particles and polyacids; resin monomers may also be added.
    • Mechanically more resistant than zinc phosphate cements and bonds to dentin with values between 3 and 5 MPa.

Major Advantages

  1. Ease of manipulation.
  2. Chemical setting.
  3. Ability to bond to both tooth and post.

Important Note

  • Resin-modified glass ionomer cements are not indicated for post cementation due to hygroscopic expansion potentially causing root fracture.

Self-Adhesive Cements

  • Contain multifunctional phosphoric acid methacrylates that react with hydroxyapatite, promoting simultaneous demineralization and infiltration of dental hard tissue.
  • Self-etching capability reduces the risk of incomplete impregnation of conditioned tissue by resins and minimizes technique sensitivity.