Post & core in dentistry / orthodontic continuing education


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Post & core in dentistry / orthodontic continuing education

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. Difficulties and problems should make us stronger, not bitter
  3. 3.
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  5. 5. • Introduction • History • Definitions • Why to restore endodontically treated teeth • Post & core systems • Principles of tooth preparation Contents
  6. 6. • Procedure Post fabrication & Core fabrication Investing and casting Evaluation & cementation • Removal of existing posts • Conclusion • References
  7. 7. Introduction
  8. 8. • The restoration of the endodontically treated tooth is complicated • Destruction by caries • Previous restorations • Trauma • Endodontic access preparation • The endodontically treated teeth require restoration because of • dehydrated dentin, • decreased structural integrity • impaired neurosensory feedback mechanism INTRODUCTION:
  9. 9. POST CORE
  10. 10. History 1747 Pierre Fauchard Posts fabricated of gold or silver. Heat softened adhesive called “mastic Longevity 15-20 years Bone, ivory, animal teeth, natural tooth crowns Porcelain
  11. 11. History “Pivot crown”. Early pivot crowns – seasoned wood Wood posts -“Morbid humors”. 1747 Pierre Fauchard 1800’s – Porcelain pivot crown Dubois de chemant 1878 Richmond crown 1 piece dowel and crown Post and Core
  12. 12. Definitions • Dowel (Post): The dowel is a metal post or other rigid restorative material placed in the radicular portion of a non vital tooth. A dowel usually made of metal is fitted in to a prepared canal of a natural tooth. When combined with an artificial crown or core, it provides retention and resistance for the restoration. (Glossary of Prosthodontics)
  13. 13. • Core: Refers to properly shaped and well substructure, which replaces missing coronal structure and retains the final restoration. A centre or a base of a structure. The core is designed to resemble or become the crown preparation or crown itself. (Glossary of Prosthodontics)
  14. 14. • Ferrule (Rosenstile): Is defined as a metal band that encircles the external dimension of the residual tooth. • Ferrule (Weine) : A ferrule is a metal ring or cap placed around the end of a cane or tool, giving it added strength. The ferrule around the circumference of the tooth strengthens it by increasing resistance to wedging
  15. 15. As prosthodontist – abutment for FPD , RPD, Over denture As a Restorative dentist -Increase the clinical longevity of these teeth. Schwartz et al 1983 found that the failure rate of endodontically treated teeth was almost double in cases with inadequate restoration. Weine 1996 more endodontically treated teeth are lost due to poor restoration than to subsequent endodontic failure. Why to Restore ?
  16. 16. Gutmann 1992 • Moisture loss • Architectural changes • Biomechanical behaviour • Dentinal toughness • Collagen alteration William Robbins 2002  Dentin diff - vital dentin  Structure integrity lost  Neurosensory feedback mechanism impaired
  17. 17. Pre –Operative assessment
  18. 18. Endodontic & Periodontal evaluation:  Apical seal  Percussion  Palpation  Prescence of sinus tract  Diagnostic probing  Mobility
  19. 19. Restorative evaluation  The amount of remaining tooth structure.  The anatomical position of the tooth.  The functional load on the tooth.  The aesthetic requirements of the tooth.
  20. 20. The amount of remaining tooth structure Anterior teeth Do not need posts and full coverage crowns Anterior teeth are inclined at an angle to the occlusal plane Sound tooth with access opening Lack of Coronal tooth structure
  21. 21. Posterior teeth Carry greater occlusal loads Minimal occlusal access preparations Teeth with existing restorations involving the marginal ridge or those with extensive loss of tooth structure Where ever possible posts should be avoided in posterior teeth as the roots are often narrow and or
  22. 22. Post & Core Systems
  23. 23. Ideal properties of a post  Maximum protection to root  Adequate retention within root  Maximum retention of the core and the crown.  Maximum protection of the crown margin cement seal  Pleasing esthetics when indicated  High radiographic visibility  Retreivability  Biocompatibility
  24. 24. • Classification of posts ( D C N A 2002 ) Metallic Non Metallic Custom cast posts Prefabricated Carbon fiber posts Zirconia posts Woven fiber composite post
  25. 25.  Multiple cores- in the same arch  Small teeth  Angle of cores – to be changed  All – ceramic crown - PGP [platinum-gold- palladium] - Nickel –chromium - Cobalt - chromium - Stainless steel - Non oxidizing noble alloys - Au-pt - Titanium Custom cast posts : • Metallic Posts Indication combinations
  26. 26. Pre- fabricated posts : Tapered posts :  Mimics natural canal shape Least amount of retention Parallel posts : provides greater retention Active posts Indicated : in short canal space Passive
  27. 27. Carbon fibre posts Bundles of stretched aligned carbon fibers embedded in an epoxy matrix Modulus of elasticity similar to dentine Unesthetic Radiolucent Can bond to dentine Purton et al 1996 Millstein et al 1999 Bond strength of composite core material to CFP < Composite core to metal post. • Non-Metallic Posts
  28. 28. Trido et al 1999 Bond strength can be increased by air abrasion of CFP. Drummond et al 1999 : Stockson et al 1999 : Retention of CFP = Metal posts. Found decrease in bond strength after air abrasion. Carbon fibre posts
  29. 29. Tooth coloured posts :  Zirconium coated CFP  Aesthetic post plus ( Bisco )  All zirconium posts (Cosmoposts & ceraposts )  Fibre reinforced posts  Light post ( Bisco )  Luscent anchor ( Dentatus )  Fibrekor posts  Zirconium posts modulus of elasticity > Stainless steel lower fracture resistance than metal posts & inability to bond.  Difficult to retrive
  30. 30. Resintritt et al in 2000 compared # strength Titanium post & composite core & Zirconium post & composite core ↨ Vectris resin post & composite Core ↨ Custom cast gold post & core ↓ IPS Empress & All Zirconium
  31. 31. CORE Steven M. Morgano & Susan E. Brackett 1999 Desirable features of a core material : Adequate compressive strength Sufficient flexural strength Biocompatibility Resistance to leakage of oral fluids at the core/tooth interface. Ease of manipulation. Ability to bond to remaining tooth structure Thermal co-efficient of expansion and contraction Dimensional stability Minimal potential for water absorption & Inhibition of dental caries.
  32. 32. Classification of core materials : Cast core Plastic core materials Metal Ceramic to Zirconia dowels Amalgam Glass ionomer cement Resin modified GIC Dual cure fibre reinforced cores
  33. 33. Pissis 1995 proposed a “Monobloc” technique for fabrication of a post and core and a crown as a single component made out of glass ceramic material IPS empress. Kantor and pines 1977 teeth little coronal structure the cast gold post and core was superior to a stock post and composite resin core. Cast core Ceramic to Zirconia dowels
  34. 34. Hoag ED, Dwyer TG 1982 Amalgam can be used for core build ups Due to its self – sealing proprieties, durability and good working characteristics Nayyar, Walton, Leonard 1980 reported a technique of amalgam core build up Amalgam
  35. 35. Barban 1970 was one of the first to suggest the use of composite resin to fabricate cores. Linde LA 1983 found that composite cores showed significantly greater marginal leakage compared with amalgam cores. MC lean 1985 GIC can be tooth substance remains and where limited loading is anticipated. Resin modified GIC not recommended in high stress situations.
  36. 36. Principles of tooth preparation
  37. 37. • Conservation of tooth structure Preparation of the canal Preparation of coronal tissue • Retention form Anterior teeth Posterior teeth • Resistance form Stress distribution Rotational resistance
  38. 38. • Remove minimal tooth structure form the canal. • Excessive enlargement can perforate or weaken the root ~ Thickness of remaining dentin – Fracture resistance from Preparation of the canal : Helfer AR et al 1972. teeth cemented with thicker posts (1.8 mm) fractured more easily than those with a thinner (1.3 mm) one. Photo elastic studies also have show that internal stresses are reduced with thinner posts. Conservation of tooth structure
  39. 39. Root canal should be enlarged only enough to enable the post to fit accurately yet passively while insuring strength and retention. Felton DA 1991 said that most root fractures originate from these concavities because the remaining dentin thickness is minimal. Most roots have proximal concavities
  40. 40. Preparation of coronal tissue : Milton P and Stein R S 1992 if more than 2 mm of coronal tooth structure remains, the post design probably has a limited role in the fracture resistance of restored tooth. A key element of tooth preparation when using a dowel and core is the incorporation of a
  41. 41. A ferrule is a metal band or ring used to fit the root or crown of a tooth. CERVICAL FERRULE • Increased fracture resistance • Antirotational
  42. 42. With Ferrule Without Ferrule
  43. 43. With Ferrule Without Ferrule
  44. 44. The effectiveness of the ferrule has been evaluated by a variety of methods, including Fracture testing Impact testing Fatigue testing and Photo elastic analysis. 1.5 mm of ferrule height Philip et al 2005 have investigated the resistance to static loading of endodontically treated teeth with uniform and non uniform ferrule configuration 2 mm uniform > 0.5 – 2mm ferrule height non uniform 2 mm uniform & 0.5 – 2mm ferrule height non uniform NO ferrule>
  45. 45. what if tooth has inadequate coronal tooth structure to create a ferrule ? Surgical :Crown lengthening Allows ferrule Less favourable crown root ratio increased leverage on the root during function Gegauff 1999: showed that creating ferrule through crown lengthening resulted in a weaker rather than a stronger restored tooth. Orthodontic extrusion •Consider crown lengthening and or extrusion
  46. 46. Anterior teeth  Preparation geometry  Post length & diameter  Surface texture and  Luting agent. Retention form Post retention is affected by the
  47. 47. Preparation geometry : Elliptical cross section Must be prepared with restricted amount of taper 6-8 Taper increases – retention decreases similar to extra coronal preparation. Canals Circular cross section Prepared with a twist drill or reamer to provide a cavity with parallel walls or minimal taper.
  48. 48. Standlee JP et al 1978 confirmed that parallel sided posts more retentive than tapered posts and that threaded posts are most retentive. Increase the retention Not recommended because of residual stress in dentin. Threaded posts :
  49. 49. Studies have shown that an post length increases, so does retention. However the relationship is not linear. A post that is too short will fail Ideally, as long as possible 5 mm apical seal not les than 3 mm Post length : Post that is too long
  50. 50. Post diameter : Increasing the post diameter in an attempt to increase retention Ideally  No wider 1/3 root 2 mm of tooth structure. Tilk M A et al 1979 :1500 teeth (125 of each tooth) 0.6 mm – Mandibular incisors 1.0mm – Maxillary CI, Max and Man canines, Palatal root of max I molar 0.8 mm Other
  51. 51. Shillingburg et al 1982 in a study of 100 teeth 0.7 mm – Mandibular CI 1.7 mm – Maxillary CI.
  52. 52. 4) Post surface texture : A serrated or roughened post is more retentive than a smooth one.  Controlled grooving of the post and root canal increases the retention of a tapered post. 5) Luting agent : Traditional cements – little effect Adhesive resin luting cements – increased retention Note: irrigation with ethanol or etching with 37% phosphoric acid
  53. 53. Long posts avoided – curved roots and elliptical or ribbon shaped canals. Retention is better provided by two or more relatively short posts in the divergent canals. Cast core can be used (made in sections that have different paths of with drawl). Posterior teeth :
  54. 54. Stress distribution Photo elastic materials. Strain gauges and Finite elements analysis The greatest stress concentrations are found at the shoulder, particularly interproximally, and at the apex. Resistance form The influence of post design on stress distribution has been tested using.
  55. 55. Stresses are reduced as post length increases. Sharp angles should be avoided because they produces high stresses during loading High stress can be generated during insertion, parallel sided posts Parallel sided posts Tapered posts
  56. 56. Threaded posts Rotational resistance : Rotation can be prevented by vertical coronal wall. a small groove placed in the canal root is bulkiest – lingual aspect Backed off a half turn Cement layer
  57. 57. Procedure
  58. 58. 1. Removal of the root canal filling material to the appropriate depth. 2. Enlargement of the canal 3. Preparation of the coronal tooth structures 3 stage operation.
  59. 59. Root canal treatment
  60. 60. Post & core treatment
  61. 61. 1.REMOVAL OF THE ENDODONTIC FILLING MATERIAL1. Chemical Removal 2. Thermal Removal 3. Mechanical Removal Schnell FJ 1978 and Bourgeois R S and Lemon RR (1981) gutta-percha can be removed with a warm condenser immediately after obturation. Dickey DJ et al 1982 Rotary instrument can disturb apical seal if used immediately after obturation.
  62. 62. Steps in removal of gutta-percha & Enlargement of the canal IF gutta-percha is old and has lost its thermoplasticity, use a rotary instrument (Peeso-Reames or Gates Glidden drills) Before enlargement of the canal, the type of post system to be used for fabrication of the post and core must be chosen. Calculate the appropriate length of the post
  63. 63. 2.PREPARATION OF THE CORONAL TOOTH STRUCTURE : Remove all internal and external undercuts Complete the preparation by eliminating sharp angles and establishing smooth finish lines. prepared perpendicular to the post, to create a positive stop & to prevent over seating and splitting of the tooth. If insufficient tooth structure remains for this feature, an antirotation groove should be placed in the canal
  64. 64. 3.POST & CORE FABRICATION : Prefabricated post : Custom-made posts : Direct procedure : patients mouth Indirect procedure : laboratory
  65. 65. Direct method using Pre-fabricated post Post selected Core build up Finishing
  66. 66. Basic Procedure for Custom Post & Core Fabrication
  67. 67. 1 2 3 4 5 6 7 8 9 Direct method
  68. 68. Direct pattern for multi-rooted teeth :
  69. 69. Indirect procedure : Pieces of orthodontic wire Lubricate the canals a lentulo spiral syringe in impression material Apply a thin coat sticky wax to the plastic post after lubricating the stone cast, add soft inlay wax in increments Investing and casting
  70. 70. INVESTING AND CASTING Casting should be slightly undersized Cast post-and-core should fit somewhat loosely in the canal Omitting the usual ring liner or Casting at lower mold temperature Extra-hard partial denture gold (ADA type IV) or nickel chromium alloys EVALUATION : Casting defects should not interfere with seating of the post; otherwise, root fracture will result.
  71. 71. Post-and-cores should be inserted with gentle pressure CEMENTATION : A rotary (lentulo) paste filler or cement tube a parallel-sided post is being used, a groove should be placed along the side of the post
  72. 72. Over denture abutment
  73. 73. Removal of existing posts : Thin-beaked forceps Ultrasonic removal Post puller Special hollow end-cutting tubes (or trephines) Drilled out Masserann kit If the fractured post is of the threaded type a groove cut in the end of it may enable it to be unscrewed
  74. 74. Fractured post Ultrasonically powered chisel Masseran trepan and ultrasonic chisel. Masseran trepan Before After
  75. 75. Conclusion
  76. 76. R E F E R E N C E S 7. Harold Gerstein, "Technique In Clinical Endodontics" 347- 87. 8. Pitt Ford, "Problem-solving in Clinical Practice" 149-164. 9. Gutmann, "Problem-solving in Endodontics" 3rd Edn, 325- 46. 10.Stephen Cohen, "Pathways of the Pulp", 8th Edn, 765-795. 11. Franklin S. Weine, "Endodontic Therapy" 4th Edn, 653- 698. 12. Tylman's "Theory and Practice's of Fixed Prosthodontics", 8th Edn, 407-417. 13. Herbert T. Shillingburg, "Restoration of the Endodontically Treated Tooth" 1982Edn. . 14. Herbert Shillingburg, "Fundamental of Fixed Prosthodontics" 3rd Edn, 194-209. 15. Herbert Shillingburg, "Fundamental of Tooth Preparation" 2nd Edn, 321-358. 16. Rosensteil, "Contemporary Fixed Prosthodontics" 3rd Edn., 272-312. 17. Endod Dent Traumatel1998; 14:
  77. 77.
  78. 78.