factors determining post selection
DESCRIPTION
Factors determining post selection: a literature reviewTRANSCRIPT
FACTORS DETERMINING POST SELECTION
A LITERATURE REVIEW
Aquaviva Fernandes, Sharat Shetty, Ivy Continho.
JPD 2003;90:556-62
Dr Talib AminGDC 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
ENDODONTICALLY TREATED TEETH WITH POST AND CORE HAVE GOOD PROGNOSIS
Serve well in function
Act as an abutment in FPD or RPD
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
DEFINITION
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)
Also called DOWEL CORE CROWN
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
METALLIC
NON METALLIC
Carbon fiber
Glass fiber
Woven fiber (polyethene)
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
Retrievability
ESTHETIC FACTORS
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 significant bulk to accommodate most post systems
TOOTH ANATOMY
POST WIDTHFactors 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 structure
CONSERVATIONIST APPROACH
Minimal canal preparation
Maintaining as much as residual dentin as possible
(Pilo & Tamse; JPD 2000)
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
o Increase retention
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
can be used in moderate to severe tooth loss
1.5-2mm of coronal tooth structure to achieve resistance form
PREPARED WITH A FERULE (ARROW)
STRESS Compressive
Tensile
Shear --- most detrimental
Inc. post length
minimum diameter
•Reduces shear strength
•Preserves tooth structure
•More fracture resistance
Holmes 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)
Active post designs provide greater tortional resistance than passive posts
Posts having high 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 carbon post than
zirconia
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
Zinc phosphate & Slow polymerizing dual
polymerizing luting agents are recommended
POST DESIGNo 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
Sufficient retention due to parallel design
Threaded postsinferior 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 danger in using highly rigid posts
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
•Undiagnosed root fracture
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
Composite core materials can bond both to tooth structure and post with bonding agents
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 metal
DISCUSSION
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
11. Reasonable cost
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 2001
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
11. Easy to use & Cost effective
Use a post system that best fits the individual needs of each tooth
CONCLUSION
REFERENCES1.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.
