Vinay PavanKumar K

2nd year MDS

AECS Maaruti College of Dental Science and Research Centre

Procedure

Historical

perspective &

Rationale

Post fabrication

Core fabricationSelection of post

Interim Types of post

Ikram OH etal compared the volume of hard tooth tissue lost

after caries removal, access cavity preparation, root canal

preparation, fibre post space and cast post preparation in

carious premolar teeth.

The percentage of preoperative hard tooth tissue volume lost

after caries removal was 8.3 +/- 5.83, after access cavity

preparation the loss of volume reached 12.7 +/- 6.7%

(increase of 4.4%). After root canal preparation, fibre post

space and cast post preparation the hard tissue volume lost

reached, 13.7 +/- 6.7 (increase of 1%), 15.1 +/- 6.3 (increase

of 1.4%) and 19.2 +/- 7.4 (increase of 4.1%) respectively

Each procedure performed after caries removal significantly

increased the amount of hard tissue volume lost with the

exception of the root canal preparation

Ikram OH etal Micro-computed tomography of tooth tissue volume changes following

endodontic procedures and post space preparationInt Endod J. 2009 Dec;42(12):1071-6

The survival relationship between the root

canal treated posterior teeth with and without

crown placement

Coronal coverage with full cast crown reduced

the risk of tooth fracture

Endodontically treated teeth with crowns had a

survival rate six times greater than that of teeth

without crowns

1700s Fauchard inserted wooden dowels in

canals of teeth to aid in crown retention

The wood would expand in the moist

environment to enhance retention of the dowel

In 1869, Black favored the use of metal posts

in which a porcelain-faced crown was secured

by a screw passing into a gold-lined root canal.

In mid-1800s, Clark developed a device which

was extremely practical for its time because it

included a tube that allowed drainage from the

apical area or the canal

In 1878, Richmond crown was introduced it

incorporated a threaded tube in the canal with a

screw retained crown

In 1958, Hampson EL etal and Demas NC et al;

modified to eliminate the threaded tube and was

redesigned as a 1-piece dowel and crown

Endodontically treated teeth are weakened

due to decreased or altered tooth structure

attributed to:

caries and/or previous restorations

fracture or trauma

endodontic access and instrumentation

decreased moisture

The weakness is directly correlated to the

quantity of lost dentine.

Microbial induced degradation or modification of collagen can cause deterioration of strength and toughness of dentin.

Products used for root canal irrigation and disinfection interact with mineral and organic contents and significantly reduce dentin modulus of elasticity & micro-hardness

Disinfectants like eugenol and formocresolincrease the tensile strength of dentin via protein coagulation chelation with hydroxyapatite

Randow and Glantz reported that teeth have a

protective feedback mechanism that is lost in

nonvital and root canal treated teeth,which also may

contribute to tooth fracture

Sedgley and Messer tested the biomechanical

properties of dentin of endodontically treated teeth

and vital teeth of contralateral side and concluded

that endodontically treated teeth are not more brittle

Sorensen, J.A. and J.T. Martinoff reported that

endodontically treated posterior teeth with intra-

coronal restorations show a high risk of unrestorable

cusp fracture. The use of crowns can significantly

improve the success for posterior teeth.

Based on the material

Metallic

Non-metallic

Based on method of fabrication

Pre-fabricated

Custom-fabricated

Based on configuration

Tapered

Parallel

Based on surface texture

Smooth sided

Threaded

Serrated

Wagnild et al (2002) summarized the ideal physical properties of a post that include:

Maximum protection of the root.

Adequate retention within the root.

Biocompatible / noncorrosive

Maximum retention of the core and crown.

Maximum protection of the crown margin cement seal.

Pleasing esthetics

Radiopaque

Amount of coronal tooth structure

Tooth anatomy

Position of the tooth in the arch

Root length

Root width

Canal configuration

Functional requirements of the tooth

Torquing force

Stresses

Development of hydrostatic pressure

Post design

Post material

Material compatibility

Bonding capability

Core retention

Retrievability

Esthetics

Crown material

Of paramount importance to the longevity of

the restored endodontically treated tooth is the

presence of adequate height (1.5-2 mm) of

sound tooth structure, or ferrule, between the

core and the crown margin

A tapered post without

a ferrule predisposes

the tooth to root

fracture, due to occlusal

forces being directed

internally down the

canal.

The post to

dislodgement,

due to occlusal

forces directed

down the canal

causing fatigue

failure of

cement.

Rosen in 1961 suggested that the “hugging action”

Eissman and Radke (1987) used the term ferrule effect to

describe this 360-degree ring of cast metal and

recommended extension of the definitive cast restoration at

least 2 mm apical to junction of the core and remaining tooth

structure.

The ferrule provides bracing or casing action to protect the

integrity of the root.

Wagnild et al (2002) emphasized that the crown and core

must meet five requirements for a crown preparation to be

successful:

(1) a minimum of 2 mm dentin axial wall height

(2) parallel axial walls

(3) the metal (core) must totally encircle the tooth

(4) it must be on solid tooth structure and

(5) it must not invade the attachment apparatus.

Gegauff AG (1999) reported although the crown-lengthening allows a ferrule, it also leads to a much less favorable crown-to-root ratio and therefore increased leverage on the root during function

adequate circumferential tooth structure for the vital tooth can best be gained by

surgical crown lengthening

forced orthodontic eruption or

sub-gingival preparation and prolonged temporization to allow reestablishment of the

biological width

Root anatomy such as root curvature, mesio-distal width,

and labio-lingual dimension dictates post selection

ANTERIOR TEETH

If no crown is required, a post is generally unnecessary.

If a crown is necessary, a post is generally required.

POSTERIOR TEETH (crowns generally required)

Molar with an adequate pulp chamber don’t require a post.

Molar with inadequate pulp chamber may require a post.

Maxillary bicuspids generally require a post.

Mandibular bicuspids require independent consideration.

Goerig et al (1983) found that lateral excursive forces can shear the remaining cusp or cause vertical root fracture

Greater emphasis on the adhesively retained core is given to posterior teeth because of their close approximation to the transverse hinge axis, muscle of mastication and the morphological characteristics of the tooth

All endodontically treated maxillary premolars and most mandibular second premolars should receive cuspal coverage to protect the remaining cusps during occlusion.

The greater the post length, the better the retention and stress distribution

The length and shape of the remaining root determines the length of the post

The use of reinforced composite luting agents may compensate for the reduced post length

For molars with short roots the placement of more than one post will provide additional retention for the core foundation restoration

Stern and Hirshfeld (1973) suggest

the post width should not be

greater than one third of the root

width at its narrowest dimension.

(Propotionist)

Preservationist (Halle EB et al; 1984) proposed that the

post should be surrounded by a minimum of 1mm of sound

dentin.

Pilo and Tamse (2000) advocated minimal canal

preparation and maintaining as much residual dentin as

possible (conservationist approach).

Torsional forces on the post-core-crown unit

may lead to loosening and displacement of the

post from the canal

resistance to torsional forces is integral to the

survival of the post-core-crown unit

Active post designs provide greater torsional

resistance than a passive post

Post and core restored endodontically treated

teeth are subjected to various types of

stresses: compression, tensile and shear

an increase in the post length with the diameter

kept to a minimum will help to reduce shear

stresses and preserve tooth structure.

Peters MT et al; 1983, and Fernandes AS et al; 2001 reported an increase in stress within the root canal during cementation because of the development of hydrostatic pressure

The fitting stresses can be reduced by careful placement of the post and by using a proper post design with a cement vent to permit escape of the luting agent

The more viscous the cement, the greater the development of the hydrostatic pressure

The surface characteristics of the post also change

the retentive values

threaded > serrated surface >smooth surface

if the available post space is short 5 to 6 mm, a

more retentive active post is indicated.

If post space is 8 to 9 mm and the canal is not

funnel shaped, a tapered post may be a better

choice,

The material used for the post should have

physical properties similar to that of dentin, can be

bonded to the tooth structure, and biocompatible in

the oral environment

Posts with a high modulus of elasticity do not flex

with the tooth under loading and are empirically

believed to cause root fractures

the modulus of elasticity for stainless steel and

Zirconia is roughly 20 times greater than dentin

72% of longitudinal and oblique root fractures to prolonged electrolytic reaction between dissimilar post and core metals

Corrosion of the post may be initiated because of the access of the electrolyte to the post surface, through microleakage around the coronal restoration, and through the accessory canals

Noble metals > titanium alloys > non metallic

The bonding of a post to the tooth structure

should improve the prognosis by increasing

post retention and by reinforcing the tooth

structure

resin luting agents showed good adhesion to

carbon fiber posts and glass fiber posts.

The adhesion to Zirconia posts was found to be

unsatisfactory

The primary reason for using a post is to retain

the core and the post head design is an

important factor

It should provide adequate retention and

resistance to displacement of the core material.

Bonding techniques are crucial to reinforce the

retention of the core to the post head

Ideally the post system should be easy for the clinician to retrieve the post without substantial loss of tooth structure

Post removal can be preformed by conventional rotary instruments and solvents

Other Post retrival intruments include the MasseranKit, Post Removal System, Endodontic extractors, and ultrasonic unit Roto-Pro bur

a combination of tube extractors with cyanoacrylate will aid in post removal by breaking up the cement

Freedman (2001) and Vichi (2000) have emphasized the need to have the color of the foundation restoration as close to that of natural dentin

This concern has led to the development of posts made from reinforced resins or ceramics in an effort to eliminate the color deficiency

The availability of different cement shades permits minor esthetic corrections under all ceramic crowns

good apical seal

no sensitivity to pressure

no exudate

no fistula

no apical sensitivity

no active inflammation

Optimal Post Preparation

Use of non-end-cutting rotary instruments

Minimal canal enlargement

Diameter one-third root width or less

Length at least equivalent to crown height

(short and extra long posts increase root fracture)

Minimum 4-5 mm gutta percha remaining

Post modification to fit canal

Passive post design and placement

Adequate ferrule (1.5-2 mm) between core and

crown margins

Direct technique with autopolymerizing resin

Direct procedure using thermoplastic resin

Indirect procedure

o replaces missing coronal tooth structure

o combined with remaining coronal tissue, forms

shape of tooth preparation

o shaped in resin or wax

o cast directly onto the prefabricated post

o Can be made from plastic materials

o place rubber dam, remove GP till 4mm remains

o matrix band or copper band is placed

o condense amalgam into the root canal with

endodontic plugger

Direct procedure for single rooted teeth

o prefabricated metal or custom

acrylic resin post

o resin added by bead technique

to post

o overbuild slightly and allow

polymerization

o carbide finishing and diamond

burs for shaping

Direct procedure for multi-rooted teeth

o fit prefabricated posts into the canal

o roughen the post to be incorporated

in core and lubricate the others

o build the core with autopolymerizing

resin

o remove the lubricated posts

o cast the core with the roughened

post

o post loosening – mean incidence 5%

o root fracture – 3%

o caries – 2%

o periodontal disease – 2%

Goodacre C.J et al, Clinical complications in fixed prosthodontics, J

Prosthet Denr 2003; 90: 31-41.

Restoration of the endodontically

treated teeth using exisiting coronal restoration

Rosenstiel S.F, Land M.F, Fujimoto J, Contemporary fixed prosthodontics, 3rd edition, 2001, Mosby, St. Louis, pp 272-312.

Shillingburg H.T, Hobo S, Whitsett L.D, Jacobi R, Brackett S.E, Fundamentals of fixed prosthdontics, 3rd

edition, 1997, Quintessence, Canada, pp 194-209.

Ingle J.I, Endodontics, 4th edition, pp 913-950.

Morgano S.M, Brackett S.E, Foundation restorations in fixed prosthodontics: Current knowledge and future needs, J Prosthet Dent 1999; 82: 643-57.

Cheung W, A review of the management of endodonticallytreated teeth: Post, core and the final restoration, J Am Dent Assoc 2005; 136: 611-619.

Ikram OH etal Micro-computed tomography of tooth tissue volume changes following endodontic procedures and post space preparation Int Endod J.2009 Dec;42(12):1071-6

Goldberg I.S et al, Restoration of endodontically treated teeth :Review and Treatment recommendations, International Journal od Dentistry 2009; 1-9.

Fernandes A.S, Factors determining post selection: A literature review, J ProsthetDent 2003; 90:556-6.

Fages M, The Endocrown: A different type of all ceramic reconstruction for molars, J Can Dent Assoc 2013;79:d140