Post retained endodontic restorations


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Introduction to Endodontics
Forth Year

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Post retained endodontic restorations

  2. 2. POST RETAINED ENDODONTIC RESTORATIONS  When a non vital anterior or posterior tooth has lost significant tooth structure, a coronal restoration is required. A post /dowel is used to retain this restoration.  The post must be fixed firmly in the root → Strong enough not to snap under load → Be able to achieve optimal stress distribution in the root  The final configuration of the restoration includes four parts. 1. residual tooth structure and periodontal attachment apparatus 2. dowel/post material located within the root 3. core material located in the coronal area of the tooth 4. definite coronal restoration
  3. 3.  The primary purpose of a post is to retain a core in a tooth with extensive loss of coronal tooth structure  Earlier posts were regarded as a method of reinforcing a pulpless tooth  But several studies have suggested that the post weakens the tooth rather than reinforcing it.  The placement of posts also may increase the chances of root fracture and treatment failure ,especially if an oversized post channel is prepared
  4. 4. The excessive post diameter in the maxillary second premolar created a perforation in the mesial root concavity
  5. 5. Considerations for use of a post: 1. Anterior teeth:  If an endodontically treated anterior tooth is to receive a crown, a post often is indicated → the remaining coronal tooth structure is quite thin after it has received root-canal treatment and been prepared for a crown.  The amount of remaining coronal tooth structure and the functional requirements of the tooth determine whether an anterior tooth requires a post
  6. 6.  If tooth has non broken circumferential wall of sound tooth structure of adequate thickness after initial tooth preparation then a dowel and core may not be necessary. Plastic restorative material such as composite or amalgam can be used as a build up.
  7. 7.  If an inadequate amount of tooth structure remains after initial tooth preparation then a cast dowel post and core is indicated
  8. 8. Molars:  Endodontically treated posterior teeth are subject to greater loading than anterior teeth because of their proximity to the transverse horizontal axis
  9. 9.  Molar teeth should receive cuspal coverage, but in most cases, do not require a post, unless the destruction of coronal tooth structure is extensive.  If posts are indicated then they are placed in the widest and straightest canals: → palatal of maxillary molars → distal of mandibular molars
  10. 10. Premolars:  Premolars by virtue of their location may be subjected to both the vertical as well as lateral forces.  The pulp chambers are too small to provide the required retention
  11. 11. In order to achieve clinical success a post should satisfy three criteria: 1. It must be atleast as long as the crown it is going to carry 2. It must have parallel sides or atleast 4º off parallel 3. It must have a precision fit within the root canal
  12. 12. IMPORTANT PRINCIPLES FOR POSTS 1. Retention and Resistance  Post retention refers to the ability of a post to resist vertical dislodging forces.  Retention is influenced by the post’s → Length → Diameter and taper → luting cement → whether a post is active or passive
  13. 13.  Resistance refers to the ability of the post and tooth to withstand lateral and rotational forces.  It is influenced by the → remaining tooth structure → post’s length and rigidity → presence of antirotation features → presence of a ferrule.  A restoration lacking resistance form is not likely to be a long-term success, regardless of the retentiveness of the post
  14. 14. Anti-rotational features
  15. 15. 2. Length of the post: When the length of the post = crown length → failure rate was 2.5% When length of the posts = one quarter the clinical crown→ failure rate was 25%  Several studies of teeth with vertical root fractures showed that two thirds of posts were extremely short, terminating in the cervical third.  Invitro biomechanical studies have shown that better stress distribution occurred with longer posts.
  16. 16.  2/3 length of the root  1/2 distance of the remaining root into the bone  4 mm of apical seal  Equal to length of clinical core
  17. 17. 3. Failure mode:  An important factor related to resistance is failure mode.  Teeth restored with less rigid posts, such as fiber posts, tend to have failures that are more likely to be restorable  Studies have reported that composite cores tended to fail more favorably than amalgam or gold.
  18. 18. Fractured post and crown Fractured root
  19. 19. 4. Preservation of the tooth structure:  Whenever possible, coronal and radicular tooth structure should be conserved.  Preparation of a post space should require minimal removal of additional radicular dentin  Custom made cast post are more conservative than the prefabricated posts especially when the posts are required for mandibular anterior teeth
  20. 20. 5. The ferrule effect:  If the artificial crown extends apical to the margin of the core and encircles sound tooth structure for 360º, the crown serves as a reinforcing ring or ferrule to help protect the root from vertical root fracture.  A ferrule is defined as a vertical band of tooth structure at the gingival aspect of a crown preparation. It adds some retention, but primarily provides resistance form and enhances longevity  Ferrule with 1.5 to 2 mm of vertical height has been shown to double the resistance to fracture versus teeth restored without a ferrule
  21. 21. Ferrule criteria and dimensions
  22. 22. 6. Retrievability:  Although nonsurgical endodontic treatment enjoys a reputation as a highly successful treatment, some studies have reported lower rates of success. For this reason, it is important that  posts be retrieved if only endodontic retreatment becomes necessary
  23. 23.  In most cases, metal posts can be removed effectively and safely.  Ceramic and zirconium posts are considered to be very difficult and sometimes impossible to retrieve.  Retrievability should be considered when treatment planning for a post.
  24. 24. 7. Apical seal:  After the post preparation the only barrier against the re-infection is the remaining gutta percha  The apical barrier of Gutta percha should be atleast 4-6mm
  25. 25. TYPES OF POSTS ACTIVE POSTS Pre tapped posts Self threading Parallel PASSIVE POSTS Tapered Combination
  26. 26.  Active posts derive their primary retention directly from the root dentine by the use of threads.  Passive posts on the other hand gain retention by passively seating in close proximity to the post hole walls, and rely primarily on the luting cement for their retention.
  27. 27.  Active posts are more retentive than passive posts, but introduce more stress into the root than passive posts [They can be used safely, however, in substantial roots with maximum remaining dentin]  Their use should be limited to short roots in which maximum retention is needed  Active posts: • Self threading posts • Pre tapped posts
  28. 28. Self threading posts:  Self-threading posts have a shank (shaft) that is fractionally narrower than the post channel that is cut into the root and has a thread of wider diameter.  As the post is screwed into place the threads cut their own counter-channel into the dentine  Can be of two types: i. parallel ii. tapered
  29. 29.  Parallel posts are more retentive than tapered posts  The preparation of a parallel-sided post channel, and subsequent cementation of a square-ended parallel post may produce increased stress in the narrow and tapering root-end  The preparation of the post space for the parallel post system may involve removal of more dentin
  30. 30. a) Stress concentration at the base of a parallel post preparation. b) Reduced stress concentration with a chamfered tip
  31. 31.  Tapered posts, on the other hand, require less dentin removal because most roots are tapered. They are primarily indicated in teeth with thin roots and delicate morphology  Concerns have often been raised over the generation of wedging stresses by tapered posts, and the tendency to promote root fracture
  32. 32.  Flexi-posts have been developed to overcome the disadvantages of both the parallel posts and the tapered posts.  The Flexi-Posts’ unique split-shank design
  33. 33. Prefabricated post designs. A. Tapered, smooth. B. Parallel, serrated. C. Tapered, self-threading.. D. Parallel, threaded. [Note that the post fits into pretapped threads cut into the dentin] E. Parallel, serrated, tapered end
  34. 34. According to Manufacture and materials Pre-fabricated Metallic Custom made Non Metallic Stainless steel Ni-Cr Fiber posts Gold Titanium Carbon fiber Quartz fiber Silicon fibre Composite posts Ceramic posts Zirconium
  35. 35. Prefabricated Post and Cores:  Prefabricated posts are typically made of stainless steel, nickel chromium alloy, or titanium alloy  They are very rigid, and with the exception of the titanium alloys, very strong.  Passive, tapered posts offer the least retention of the prefabricated posts, but allow minimal removal of radicular dentin because  Their tapered shape resembles the overall canal morphology.
  36. 36.  Many of the prefabricated posts are made of titanium alloys Disadvantages of Titanium posts:  Have a radiodensity similar to gutta-percha and sealer and are sometimes hard to detect on radiographs.  Titanium posts have low fracture strength, which means they are not strong enough to be used in thin post channels.  Removal of titanium posts can be a problem because they sometimes break when force is applied with a post removal instrument
  37. 37. Custom Cast Post and Cores  Cast post and cores were the standard for many years and are still used by some clinicians.  Generally, they do not perform as well as other types of posts  They have fallen from favor because they require two appointments, temporization, and a laboratory  A cast post and core may be indicated when a tooth is misaligned and the core must be angled in relation to the post to achieve proper alignment with the adjacent teeth.  Cast post and cores are generally easy to retrieve when endodontic retreatment is necessary
  38. 38. NON-METALLIC POSTS  Rigid, metal post systems are now known to transfer functional stresses to the tooth and root structure and actually increase the risk for root fracture.  Accumulation of metallic corrosion byproducts also weakens the dentin and the interface between the post and the canal.
  39. 39.  The newer fiber-reinforced post systems preserve tooth structure, are noncorroding, and have a similar elastic modulus compared to dentin making them more compatible that their metal counterparts.
  40. 40.  When two or more components are placed into contact with one another, Components with higher e-modulus (cast post/core) will transfer functional stresses to the lower emodulus components (dentin) and ultimately result in endodontic or restorative failure.  When all components have similar e-moduli there is a uniform stress distribution and lowered interfacial stress and failure.  This phenomenon has been coined “monobloc.”  “Monobloc” requires that all components of a tooth restoration have similar emoduli to dentin to allow the components to move, flex, and stress as one assembly.
  41. 41. AESTHETIC POSTS  Introduction of tooth colored materials :    aesthetic demands functional abilities Most of the aesthetic posts used, generally employ resin based composite materials for the cementation and also the core build up.  The use of light cured composites as luting agents encouraged the development of posts that can transmit light into the depth of the canals.  Most of the composite posts, fibre reinforced composite posts (exception of carbon fibre posts) transmit light [light transmitting posts]
  42. 42. CERAMIC AND ZIRCONIUM POSTS: These posts are translucent or white in colour and hence categorized under aesthetic posts. DISADVANTAGES OF CERAMIC AND ZIRCONIUM POSTS  They tend to be weaker than metal posts, so a thicker post is necessary, which may require removal of additional radicular tooth structure.  Zirconium posts can not be etched, therefore, it is not possible to bond a composite core material to the post, making core retention a problem .  Retrieval of zirconium and ceramic posts is very difficult if endodontic retreatment is necessary or if the post fractures
  43. 43. FIBER POSTS  Carbon fiber posts gained popularity in the 1990s.  A carbon-epoxy composite post was reinforced with long carbon unidirectional, high-performance fibers stretched parallel to the axis of the post.  The fibers represented 64% of the structural volume and the matrix, which bound the fibers together, was an epoxy resin.  Their main proposed advantage was that they were more flexible than metal posts and had approximately the same modulus of elasticity (stiffness) as dentin. When bonded in place with resin cement, it was thought that forces would be distributed more evenly in the root, resulting in fewer root fractures.
  44. 44.  The original carbon fiber posts were dark, which was a potential problem when considering post-restorative esthetics.  Other types of fiber posts also are available, including quartz fiber, glass fiber, and silicon fiber posts
  45. 45. A. carbonfibre post B&C . Two examples of translucent quartz-fibre posts, D. The opaque Fiber White A B C D Post
  46. 46. If certain basic principles are followed in the restoration of endodontically treated teeth, it is possible to achieve high levels of clinical success with most of the current restorative systems. These principles include: 1. Avoid bacterial contamination of the root-canal system 2. Provide cuspal coverage for posterior teeth 3. Preserve radicular and coronal tooth structure 4. Use posts with adequate strength in thin diameters 5. Provide adequate post length for retention 6. Maximize resistance form including an adequate ferrule 7. Use posts that are retrievable.