Factors Determining Post Selection
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Factors Determining Post Selection



Factors determining post selection: a literature review

Factors determining post selection: a literature review



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Factors Determining Post Selection Factors Determining Post Selection Presentation Transcript

  • FACTORS DETERMINING POST SELECTION A LITERATURE REVIEW Aquaviva Fernandes, Sharat Shetty, Ivy Continho. JPD 2003;90:556-62 Dr Talib Amin GDC Srinagar
  • Greater tooth loss in endodontically treated teeth is due to  Caries/Pathological disease  Endodontic treatment  Previous restoration Loss of tooth structure compromises retention of subsequent restoration and increases chances of fracture during functional loading
  • Longevity of endodontically involved teeth has been greatly enhanced with the use of intra radicular devices varying from conventional custom cast post to one visit techniques using pre fabricated post systems
  • Sufficient tooth structure GROSS DESTRUCTION Simple restoration POST & CORE RESTORATION FACTORS INFLUENCING CHOICE OF TREATMENT  Type of tooth (anterior or posterior)  Amount of remaining tooth structure
  • POST-AND-CORE: A one-piece foundation restoration for an endodontically treated tooth that comprises a post within the root canal and a core replacing missing coronal structure to form the tooth preparation. (GPT 8)
  • POST & CORE Provides retention & support for cast restoration Post retains core Core replaces missing tooth structure
  • TYPES OF POSTS Method of fabrication  Prefabricated  Custom made Material used  Metallic  Non metallic
  • Tapered smooth posts Tapered serrated posts Tapered threaded posts Parallel sided smooth posts Parallel sided serrated posts Parallel sided threaded posts Combination PREFABRICATED POSTS
  • CUSTOM MADE  Direct pattern in patients mouth  Indirect pattern in operatory
  • Pt- Au- Pd Ni- Cr Co- Cr Stainless steel Au- Pt Ni- Cr Ti Parallel sided Tapered METALLI C
  • NON METALLIC Carbon fiber Glass fiber Woven fiber (polyethen Zirconia fiber Ceramic fiber
  • This article is basically a review of literature in which various factors that influence the selection of post and core assembly are mentioned.
  • BIOLOGICAL FACTORS  Root length  Tooth anatomy  Root width  Canal configuration  Amount of coronal tooth structure
  • MECHANICAL FACTORS  Torquing forces  Stresses  Hydrostatic pressure  Post design  Post material  Material compatibility  Bonding capability  Core retention
  • ROOT LENGTH  Determines length of post  Greater the post length, better the retention and stress distribution (Holmes et al JPD1996;75:140-7)  3-5 mm of GP in the apical region to maintain apical seal (Mattison et al JPD 1984; 51: 785-9)
  • Parallel sided threaded post or Reinforced composite luting agents can compensate for reduced post length (Nissan et al JPD 2001 ;86 : 304 - 8) For short rooted molars more than one post will provide additional retention for core.
  •  Variations in terms of root curvature, MD & LL widths  Root anatomy dictates post selection  Improper post space preparation and use of large diameter post may cause apical or lateral perforation  Radiographic assessment is important to evaluate root  length, width and canal structure  Roots of maxillary centrals and laterals, mandibular premolars have TOOTH ANATOMY
  • POST WIDTH Factors to be considered:  Preservation of tooth structure  Reduction of perforation  Resistance to fracture Approaches regarding selection of post diameter o Conservationist o Preservationist o Proportionist(Lloyd & Palik JPD 93) (Tilk et al J Endod JPD 82) (Pilo, Tamse JPD 2000)
  • PROPORTIONIST APPROACH  Post width should not be more than 1/3rd root width at its narrowest dimension (Stern & Hirshfeld JPD 73)  Advocated to preserve tooth
  • CONSERVATIONIST APPROACH  Minimal canal preparation  Maintaining as much as residual dentin as possible
  • PRESERVATIONIST APPROACH Post surrounded by minimum of 1 mm of sound dentin ( Halle,Nicholls, Hassel. J Endod 1984 )
  •  Increase in post width has no significant effect on retention (Standlee et al JPD 1978)  Large diameter posts provide least resistance to fracture (Trabest, et al J Endod 1978)
  • CANAL CONFIGURATION & POST ADAPTABILITY Canal configuration determines whether to use custom designed or prefabricated post Post should o Fit closely o Aptly conform to canal shape & size o Less dentin removal o Enhance fracture resistance
  • Funnel shaped canal  Parallel-sided posts & fill remaining space with cement  Tapered post  Large prefabricated parallel sided post Canals requiring extensive preparation  Cast post and core is more retentive than pre fabricated (Cohen et al JPD 1996) Wide canal root  Reinforcement with composite (Scurpe et al QI 1996)
  • Well adapted tapered posts  Increased resistance to fracture (Sorensen et al JPD 1990) ( Jan, Whang JPD 1985)  More extensive tooth loss on fracture  Custom cast posts success rate of 90% after 5 yrs in fracture (Morgano, Milot JPD 1993)
  • CORONAL STRUCTURE  1.5-2mm of coronal tooth structure to achieve resistance form Non-metal posts (carbon fiber)  Can be used only when ample Coronal dentin remains and crown is well supported  Inferior stength Cast Post & Core
  • 1.5-2mm of coronal tooth structure to achieve resistance PREPARED WITH A FERULE (ARROW)
  • STRESS  Compressive  Tensile  Shear --- most detrimental Inc. post length minimum diameter •Reduces shear strength •Preserves tooth structure •MoreHolmes et al JPD 1996
  • TORTIONAL FORCE May cause loosening and displacement of post from canal failure of post & core system Anti rotational features  provide resistance  integral for survival of post & core system (Burgess et al JPD 1992)
  • modulus of elasticity are stiffer and transmit forces directly to the tooth interface with shock absorption (No Damping Effect) E Zirconia> E Carbon Post Fracture is less with
  • HYDROSTATIC PRESSURE Cementation enhances retention, stress distribution, seals irregularities & increases pressure within the canal  Depends on viscosity of cement  Prevents complete seating of post  Can cause fracture of root PREVENTION  “Cement vent” design in post for excess  Tapered posts are self venting
  • POST DESIGN o According to shape: 1. Parallel 2. Tapered 3. Combination o According to surface characteristics: 1. Active posts Engage mechanically into dentin with threads 2. Passive posts Depend on cement and close adaptation in canal for retention
  • Active posts  More failures Tapered posts  Preservation of tooth structure  Wedging effect  Stress concentration at coronal portion of root  Lower retentive strength Parallel sided post  Increase retention  Uniform stress distribution along post length
  • Combination (parallel tapered) Stress conc. Is found at apex of canal due to un necessary removal of tooth structure at the apical end and sharp angles of post This type of post is parallel throughout the length except for the most apical portion Preservation of dentin at apex
  • Threaded posts inferior to custom casts exert a greater stress Parallel sided, serrated and vented posts exert least amount of stress
  • Retention of posts Threaded > serrated > smooth
  • To prevent placement stresses by threaded posts  Pre tapping post channels  Limiting the no. of threads  Counter rotating the post by ½ turn after full engagement  Incorporating split shank mechanism (Cohen, Musikant, Deutsh JPD 1994)
  • POST MATERIAL Physical properties of material should be similar to dentin  Bond to tooth structure  Biocompatible  Shock absorber  METAL POSTS  NON METAL POSTS o Metal and other rigid posts resist greater forces without distortion ;potential
  • Carbon fiber posts  exhibit mechanical properties similar to those of tooth  absorb and dissipate stress  inferior strength than metal posts
  • Zirconium posts  High modules of elasticity  No shock absorption  More root fractures than carbon fiber posts
  • MATERIAL COMPATIBILITY  Ideally made from same alloy  Dissimilar core and post material create galvanic current and corrosion & accumulation of corrosion products can increase volume and cause root fracture (Peterson J Can Dent Ass 1971) Causes of corrosion of post • Access of an electrolyte to post surface through Cementum & dentin •Micro leakage around coronal restorations •Accessory canals which have opened during post preparation
  • Titanium alloy posts are most corrosion resistant Alloys containing brass have low corrosion resistance Noble metal alloys are corrosion resistant but expensive
  • BONDING ABILITY Single unit tooth-post-core-crown system  Difficult due to difference in physical properties of materials and tooth structure  Traditional cements produce only frictional resistance (Zinc phosphate)  Newer adhesive resins bond post to tooth stucture
  • Bonding of post to tooth  Improve prognosis of post core by improving retention  Reinforce tooth structure (Distribution of stress by bonding material) •Nature of material is responsible for bonding of post to tooth structure adhesion •Carbon fiber & glass fiber post adhere better with resin luting cements than Zirconia posts
  • CORE RETENTION  core replaces missing tooth structure  main function of post is to retain core  design of head of post should provide adequate retention & resistance Design of core • crenellated • flat • spherical
  • As the no. of interfaces increases the potential for failure also increases  Prefabricated posts with direct cores are less reliable than one piece cast post and core
  • RETRIEVABILITY  Ideally post system should be easy to retrieve without any substantial loss of tooth structure if RCT fails or post fractures  cast metal posts are difficult to retrieve , involves removal of tooth structure around the post  Carbon fiber posts are easy & rapid to remove  Zirconia posts are more difficult to remove Use of conventional rotary instruments & solvents for removal  more preservation of residual dentin  minimizes chances of perforation
  • Certain post systems facilitate easy removal by providing a milled head, a wrench & retrieval drills Other commercially available systems are Messeran kit Post removal system Endodontic extractors Ultrasonic devices
  • ESTHETICS  Post and core material should be esthetic compatibility with crown and surrounding tissue  custom cast posts provide grey tint  composite core material with prefabricated metal posts aid in masking color of post
  • Masking depends on thickness of core Ceramic crown with opaque substructure can be used when complete masking is difficult Metal ceramic crown allows use of any post and core All ceramic are translucent and allow metal to show through Opaque porcelain fused to core eliminates the grayish effect of cast
  • Post & core contributes in providing predictable restorative options for endodontically treated teeth.
  • After reviewing the literature, it appears that an ideal post system should have the following features:
  • 1.Physical properties similar to dentin 2.Maximum retention with little dentin removal 3.Even distribution of functional stresses along root surfaces 4.Esthetic compatibility 5.Minimum stress during displacement and cementation
  • 6. Resistance to displacement 7. Good core retention 8. Easy retrievability 9. Material compatible with core 10. Ease of use, safety & reliability
  • Use of reinforced composite resin cement significantly increases retention of parallel sided posts & tapered posts when compared to zinc phosphate cement Parallel sided posts had greater increased retention than tapered posts Nissan ,dmitry, assif JPD
  • o Titanium system posts least fracture resistance most catastrophic failures o Quartz fiber posts higher fracture resistance o Glass fiber & zirconia posts fracture loads did not vary Akkayan, Gulmez JPD,2002
  • This review identified factors that influence the selection of the post & core system and offers the following clinical recommendations:
  • 1. Maximum conservation of tooth structure 2. Custom-cast post and core for moderate to severe tooth loss and non circular root canals 3. Parallel sided, passive serrated, self- venting prefabricated posts for small circular canals 4. Posts with anti-rotational features in circular canals 5. Adequate apical seal 6. More than one post for multi-rooted short teeth
  • 7. When apical thickness of dentin is minimum parallel tapered posts should be used 8. Retentive qualities of post head may facilitate firm retention of core material 9. Ensure material compatibility, bonding ability, adequate rigidity, esthetic compatibility 10. Easy retrievability
  • Use a post system that best fits the individual needs of each tooth CONCLUSION
  • REFERENCE S1. Contemporary fixed prosthisdontics. Rosensteil, Land, Fujimoto. 2. Shillinburg HT, Hobo S, Whitsett L, Brackett S. Fundamentals of fixed prosthdontics. 3rd ed. Chicago: Quintessence; 1997. 3. Nissan J, Dmitry Y, Assif D. The use of reinforced composite resin cement as compensation for reduced post length. J Prosthet Dent 2001;86:304-8. 4. Akkayan B, Gulmez T. Resistance to fracture of endodontically treated teeth restored with different post systems. J Prosthet Dent 2002;87:431-7.
  • 5. Cohen BI, Pagnillo MK, Condos S, Deutsch AS. Four different core materials measured for fracture strength in combination with five different designs of endodontic posts. J Prosthet Dent 1996;76:487-95. 6. Stockton L. Factors affecting retention of post system: a literature review. J Prosthet Dent 1999;81:380- 7.Cohen B1, Pagnillo MK, Newman I, Musikant BL, Deutsch AS. Retention of a core material supported by three post head designs. J Prosthet Dent 2000;83:624-8.