Posts and Cores: Restoration Strategies

Viability of Posts and Cores

• Removing existing restorations before root treatment helps assess restorability while preserving tooth tissue
• Consider all options if a tooth cannot be restored, which includes implants
• Posts may not be necessary; the pulp chamber is an alternative for core retention
• Posts should be retentive and strong enough to resist distortion or fracture, and be retrievable if they fail
• Avoid posts that create internal stresses by actively engaging dentine
• Coronal coverage is important for protection, especially for posterior teeth

Factors Influencing Restoration Success

• Success relies on the quantity and quality of remaining tooth tissue
• Root canal treated teeth can present complexities that make restoration difficult

Common Challenges

• Tissue loss from previous disease and restorations
• Destructive access cavities

Dentine Preservation

• Preserving dentine and performing high-quality endodontic treatment are valuable in overcoming restorative challenges

Assessing Tooth Restorability

• The decision to restore or extract a tooth (with possible replacement) is complex
• Teeth deemed unfit for restoration may be apparent during examination, but can also become obvious as treatment advances and existing restorations are removed

Chapter Focus

• Considers the issues around restoring teeth
• Provides evidence supporting the use of cores and posts with cores for restoring root-treated teeth
• Practicalities of placing cores and posts and cores are considered in Chapter 19

Preoperative Assessment

• Restorability should be determined before RCT
• Remove existing restorations to accurately assess tooth tissue quality, volume, and distribution for restoration planning
• Root treating through existing restorations is risky; unrestorable teeth may be discovered after RCT or may fail due to undetected issues
• Preoperative removal of restorations allows for detection of hidden caries, removal of weak tissue, exploration of cracks, and assessment of tooth structure for core or extracoronal restoration

Ferrule Considerations

• A circumferential band of sound tissue (1.5-2 mm height, 1 mm width) is sufficient for ferrule to resist occlusal forces
• Partial ferrule offers some fracture resistance
• Post/core survival is associated with remaining coronal dentine height
• Alternatives to crowns should be explored if teeth are decoronated to gingival level
• Alternatives include dental implants

Decision Factors

• Dentist skill
• Experience
• Patient preference can affect implant decisions

Single Root Considerations

• A decoronated but substantial single root(canine/central incisor) without fractures
• Surrounding teeth must offset non-axial occlusal loading
• Conservation strategies, such as crown lengthening and orthodontics, might be considered before implants

Implant Considerations

• Implants can provide an excellent solution, but are not without their own problems and shouldn't be a "fit and forget" solution

Unrestorable Teeth

• Replacement options must be discussed
• For single, isolated teeth, an implant-retained restoration is often ideal
• Referrals should be made when necessary for competence issues
• An interim restoration can allow patient to plan their finances for implant supported restoration

Implant Placement

• Timing of tooth extraction is critical for implant success
• Atraumatic extraction helps avoid alveolar bone loss and the need for bone grafting
• Immediate or early implant placement, allowing short-term soft tissue healing, is possible even with an established endodontic periapical lesion

Pain Management

• Unrestorable teeth with uncontrollable symptoms should be removed
• Differentiate tooth-related pain from other sources like neuropathic pain or temporomandibular disorder

Replacement Options

• Consider status of dentition, patient's wishes, active diseases (caries, periodontitis), risk factors (smoking) and prosthetic space
• Implant restorations may not be clinically possible, justifiable or affordable
• Alternatives include bridgework, partial dentures or simply leaving the space

Coronal Seal

• Root-filled teeth require coronal seals to protect against coronal leakage

Posterior Teeth Restoration

• Posterior teeth often need full occlusal coverage restorations to protect remaining tissue from fracture

Periapical Health and Survival

• Periapical health and survival depends on restoration quality

Restorative Planning

• Restoration should be planned before commencing root canal treatment
• Coronal dentine levels will affect core or post choices
• Posts add structural retention support

Risks of Using Posts

• Risks include, weakening the root and perforation
• Post space preparation must be weighed, weighing the pros and cons
• Patients should be made aware of the risks so they are involved in the choice
• Posts do not strengthen the treated tooth

Core Placement

• The conservative core placement involves direct restorative material bonded to tooth tissue and pulp chamber
• Posterior teeth get anchorage with core extensions into divergent root canal anatomy (Nayyar core)
• Core materials include amalgam, composite resin and some GICs
• GICs require sufficient material and remaining tooth structure, due to their brittle nature.

Composite Core Placement Considerations

• Before this is done, it should be determined if the tooth will benefit from internal or external bleaching
• Where margins are unslightly, restoration margins may be noticeable if finished on discoloured tooth tissue
• Margins when placed subgingivally are only a temporary solution, due to gingival recession
• Bleaching can minimize aesthetic problems, if gingival biotype is thin
• Definitive restorations should be delayed for 2 weeks after bleaching for bond and color to improve

Guidelines for Anterior Teeth

• Endodontically treated anterior teeth rarely need post and core

Modern Dental Practice

• Adhesively retained direct composites and veneers are less destructive

Crowns

• Crowns may be needed when severe vertical cracking extends from the incisal edge
• Post-retained crowns should be considered if anterior teeth have lost more than half their natural structure or have patchwork restorations

Post System

• A post is an indirect restoration device luted into prepared canal to retain an indirect restoration
• A post may have an integral core or have a core added via amalgam/composite

Types of Posts

• Custom-made, cast metal post and core: gold alloy or nickel chrome
• Prefabricated posts
  • Fibre: glass (quartz) fibre and carbon fibre
  • Metal: titanium and stainless steel
  • Ceramic: zirconia

prefabricated posts

• These have a retentive component to retain a bonded composite core, or an amalgam core in posterior teeth

Core and Post Designs

• Core may need tooth tissue to be sacrificed
• Posts are either parallel sided or tapered, but experienced dentists prefer passive posts to reduce stress
• Selection may be determined by stress analysis
• Custom-made post and core is traditional approach with strong clinical history
• Integral diaphargm used to improve stress distribution

Preferred Methods

• Dentists have shown a preference for prefabricated posts, due to convenience and a belief that fibre posts cause less fractures
• There is a belief that fibre posts lower tooth fracture, but this is not well supported by meta-analysis

Benefits of Prefabricated Posts

• Immediate placement to maintain coronal seal

Clinical Debate

• Microleakage may be affected by marginal adpatation, although how crucial this is remains debatable

Post Strength

• Post strength and retention affected by luting cement and reliance on tooth structure

Factors of Post-Retained Restoration

• Reasons for failure
• Cementation
• Post preparation optimize retention, biomechanics and aesthetics, and retrievability

Typical Post Failure

• Decementation/debonding
• Caries
• Post/root fracture
• Endoperiodontal pathology

Crown Failure

• Occurs when the core is insufficiently retentive, but prevented if there is suffient material

Cementation Technique

• Is as important as post selection

Occlusion Managment

• Must be managed to avoid cyclic non-axial loads

Considerations for Luting Cement

• Consider the lute interaction with the post and dentine, and cement posts or resin-bond to clean teeth

Lute Effectiveness

• Post must fit the channel with space to accomodate the lute

Building Failure

• Failure comes with not filling the endodontics or not provinding adequate cast posts
• Posts must have accurate space for lube

Luting Material

• Resin-modified glass ionomer cements most frequently used for posts, with limited concrete guidence
• Dentine bonding system should be coupled with filled-dual curved lute as it's reliable

Metal Posts

• Can be luted with conventional cements and mechanical post-adhesion aided by airborne-particle abrasion with 50um alumina

Post Retention

• Use a chemically active APA to use tribochemical silane treatment

Fibre and Ceramic Posts

• These are bonded with resin lute and have smooth surfaces, unless APA and tribochemical silanation are used

Retention Strategies

• Long posts offer better retention than shorter, but disrupt apical seal, risk root perforation, weaken the structure

Apical Gutta Percha Plug

• Must reach 4-5mm length
• Post preparation should stop short of root curvatures
• Stri perforation causes severe effects to teeth

Metal VS Fibre Posts

• Fibre posts have length which is less critical
• Metal needs extension to half root length
• Parallel side posts retain better than tapered, however tapered ones need close-but-passive fit otherwise the bond breaks

Post canal preperations

• Preparations mimic shape of canal but preserve precious teeth

Metal Post Designs

• Better for retention due to threads which engage the walls with high fracture risks
• Pre-tapping techniques needed to avoid crushing thread into dentine

Risk managment

• Reserve Kure K4TM system for short or curved cases
• These are not preferred generally

Biomechanics of Post Systems

• Strength, rigidity and stress concentration are important
• Post strength/rigidity depends on diameter and root width
• Too-wide posts risk weakening the structure
• Tapering or custom posts can offer a bulk preperation

Material Selection

• Fibre posts help reduce fractures
• The belief if based on earlier research but a recent 4752 post meta-analysis saw no difference

Metal/Carbon Fibe Post Fractures

• 2X more likely than cast
• Metal post modules are 4-6X greaters so matching is not critical
• Stress distribution is better in metal/ceramic as fibres cause high dentine stress

Post Cement Lut Analysis

• Metal causes higher stresses so adequate length is important

Fibre Post Performance

• Fiber may fail clinically due to difficult bond and the need for lut technique
• Serrations and carefully placed glass fibre are important

Single Rooted Dentition

• Requires adequate preperations and risk overextending

Diaphragms

• Can be used to help roots, where little tooth surface remains, with increased strength

Aesthetic posts

• Prefabricated from ceramics

Metal post properties

• Reliably and can be retrieved

Retrievability

• Post removal is often due to post fracture on the coronal 3rd of the root
• Table outlines difficulty and methods by post type
• Drilling is hazardous
• Proprietary systems can work but risk perforation
• Convention cement can allow wrestling bond so it's essential in short and fibre posts
• Chapter 19 for discussion of practicals