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Post-Core CrownPost-Core CrownHeading to a further clinicalHeading to a further clinical

longevity of teethlongevity of teeth

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Post-Core CrownPost-Core Crown

HistoricalHistoricalBackgroundBackground

Various methods of restoring pulpless teeth havebeen

reported for more than 200 years.

In 1747, PierreFaucharddescribed the process

by which roots of maxillary anterior teeth wereused for the restoration of single teeth and thereplacement of multiple teeth

Posts were fabricated of gold or silver and held in

the root canal space with a heat-softened calledmastic.

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Porcelain pivot crowns were described in the early

1800s by a well-known dentist of Paris, Dubois deChemant

One of the best representations of a pivoted toothappears in Dental Physiology and Surgery, writtenby Sir John Tomes in 1849 5 Tomess post lengthand diameter conform closely to todays principles

in fabricating posts.


HistoricalHistorical

BackgroundBackground

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POST AND CORE PLACEMENTTECHNIQUES

1. Post length

2. Post diameter

3. Anatomic/structural limitations

4. Type of post and core that will be used(prefabricated

post and restorative material core or anatomically

customized cast post and core)

5. Root selection in multirooted teeth6. Type of definitive restoration being placed and its

effect on core form and tooth reduction depths

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Clinical failure rate of posts &Clinical failure rate of posts &

corescores

Mean values 8years =Mean values 8years =

9% clinical failure9% clinical failure

Loss of retention & toothLoss of retention & tooth

fracture are the mostfracture are the mostcommon causes of post &common causes of post &

core failurescore failures

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Clinical Failure Rate of Posts andCores

Mean values 6 yr 9 (196 of 2,220

9 (72 of 788)169 moTorbjrner,1995

14 (8 of 56)40 yWallerstedt,1984

8 (39 of 516)110 yMentink, 1993

11 (17 of 154)3 yHatzikyriakos,1992

7 (9 of 138)10 y or moreWeine, 19919 (9 of 96)5 y 9Bergman, 1989

9 (36 of 420)125 ySorenson, 1984

12 (6 of 52)5 yTurner, 1982

% Clinical FailureStudyLength

Lead Author

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Clinical Failure Rate of Posts and

Cores

Tapered posts are the least retentive ,threaded posts the most retentive & Parallel isintermediate

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Post form & root fracture

Threaded posts produce undesirable levels ofstresses

Henery

Tapered threaded posts increase the root fractureby 20 times as parallel threaded posts

Deutch

Split threaded posts do not reduce stress associated

with threaded pins

Thoresteinsson

posts designed for cementation produced less stress

than threaded posts.

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Clinical Failure of Posts andCoresPost form & root fracture

When parallel-sided cemented posts have beencompared with tapered cemented posts, stresstesting results have generally favored parallel-

sided posts.

parallel-sided posts distribute stress more evenly tothe root

Henery

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Post Form and ToothFracture

Clinical Data

(% of Post and Cores Studied That Failed via ToothFracture)

Threaded Posts 7% Mean

Parallel-Sided Posts 1% MeanTapered Posts 3% Mean

5 Studies (Sorensons,Ross,Wallestedt,Linde & Morfis)

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Post form & root fracture A parallel post ensures the greatest retention of the post

within the canal, and is perhaps utilized with only theslightest loss of tooth structure to the internal wall of thecanal.

A smooth-surfaced post, although less retentive thaneither serrated or threaded post surfaces, transmits theleast amount of force to the root structure.

While both smooth and serrated posts are passive, in thatthey simply lie within the post space after being

cemented, threaded posts actively engage the internalwalls of the root canal as they are screwed in, and, whilebeing the most retentive by far, produce such a force onthe brittle root structure that they are contraindicated inmost situations.

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Post Selection

The best design for a post to decrease the risk of failure is thenarrowest & longest smooth, parallel post that one can fit

into the post space.

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The use of a post and core does not

strengthen the tooth prior to restorationwith a crown; rather, it may contributeto the weakening of the tooth structure,

as the forces placed upon the futureprosthetic crown and core are nowtransmitted along virtually the entirelength of the brittle, endodontically

treated tooth.
http://upload.wikimedia.org/wikipedia/en/9/9e/Screwpost.jpg

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Do posts Improve Long-Term Clinical PrognosisDo posts Improve Long-Term Clinical Prognosis

Both laboratory & clinicalBoth laboratory & clinical

data failed to providedata failed to provide

definitive support for thedefinitive support for theconcept that post strengthenconcept that post strengthen

endodontically treated toothendodontically treated tooth

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Clinical failure rate of posts & coresClinical failure rate of posts & cores

Mean values 8years = 9% clinical failureMean values 8years = 9% clinical failure

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Types of post & core failuresTypes of post & core failures

(of 100 failures Turner found )(of 100 failures Turner found )

LooseningLoosening (59 )(59 )

Apical AbscessApical Abscess (42 )(42 ) Dental CariesDental Caries (19 )(19 )

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WhenWhen 4mm4mmgutta-perchagutta-percha leftleft 11 ofof8989 specimenspecimenshowed leakageshowed leakage

WhenWhen 2mm2mmgutta-perchagutta-percha leftleft 3232 ofof8989 specimenspecimenshowed leakageshowed leakage(MJattison)(MJattison)

Post apical endPost apical end

2 studies found when2 studies found when

4mm4mm

gutta-percha leftgutta-percha left

nono

leakageleakage

(Portell)(Portell)

When less thanWhen less than 3mm3mm gutta-percha leftgutta-percha left significantly highersignificantly higherfrequency of periapical radiolucenciesfrequency of periapical radiolucencies

(Kvist)(Kvist)

WhenWhen 4mm4mm gutta-percha leftgutta-percha left nonoleakageleakage

(Raiden)(Raiden)

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4-5 mm4-5 mmgutta-perchagutta-percha should be leftshould be left

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Basically, it is important to leave at least 5 mm ofgutta percha at the apex of the root canal, because

it is within the apical 5 mm of the root canal that95% of lateral accessory canals split off from themain canal and anastomose with the exteriorsurface of the root. Should these lateral canals notbe blocked with the gutta percha and the cementused to place the gutta percha, the chances ofmicroleakage and percolation of microbes isdrastically increased, thereby increasing thelikelihood of an endodontic failure.


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the largest ideal diameter for a post is thediameter of the root at the most apical

portion of the post space.

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Tapered posts are the least retentive andthreaded

posts the most retentive in laboratory studies.Most of

the clinical data support the laboratory findings.

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Post Form and ToothFracture

laboratory tests generally indicate that all types of

threaded posts produce the greatest potentialfor root fracture

When comparing tapered and parallel cementedposts, the results generally favor the parallel

cemented posts.

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WHAT IS THE PROPER LENGTH FOR A POST?

A wide range of recommendations have been made

regarding post length, which includes the following:

(1) the post length should equal the incisocervical or

occlusocervical dimension of the

2) The post should be longer than the crown

(3) the post should be one and one-third the crown length

(4) the post should be half the root length

(5) the post should be two-thirds the root length

(6) the post should be four-fifths the root length(7) the post should be terminated halfway between the crestal

bone

and root apex

(8) the post should be as long as possible without disturbing the

apical

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Johnson and Sakumura determined that posts thatwere three quarters or more of the root length wereup to 30%

more retentive than posts half of the root length orequal to the crown length.86

Leary et al. indicated that posts with a length at leastthree-quarters of the root offered the greatest

rigidity and least root bending.

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WHAT IS THE PROPER LENGTH FOR A

POST?

Abou-Rass . proposed a post lengthguideline for

maxillary and mandibular molarsbased on the incidence

oflateral root perforationsoccurring when post

preparations were made in 150extracted teeth.90 They

determined that molar posts should

not be extended

more than 7 mm apical to the rootcanal orifice.

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When teeth have diminished bone support, stresses increasedramatically and are concentrated in the dentin near thepost apex.

A recent study established a relationship between post lengthand alveolar bone level.

To minimize stress in the dentin and in the post, the postshould extend more than 4 mm apical to the bone.

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Reasonable clinical guidelines for length include thefollowing:

(1) Make the post approximately three-quartersthe length of the root when treating long-rooted teeth;

(2) when average root length is encountered, then post

length is dictated by retaining 5 mm of apical gutta-percha

and extending the post to the gutta-percha

(3) whenever possible, posts should extend at least 4 mmapical to the bone crest to decrease dentin stress.

(4) molar posts should not be extended more than 7 mminto the root canal apical to the base of the pulp chamber

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WHAT IS THE PROPER POSTDIAMETER

post diameter is to not exceed one-third theroot Diameter

(Based on measuring the root dimensions of 1,500teeth

Each millimeter of increase (beyond one-third theroot diameter) causes a sixfold increase in thepotential for root fracture.)

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WHAT IS THE PROPER POSTDIAMETER

Instruments used to prepare posts should berelated in

size to root dimensions to avoid excessivepost diameters

that lead to root perforation

Safe instrument diameters to use are 0.6 to0.7 mm for small teeth

such as mandibular incisors and 1 to 1.2 mmfor large diameter

roots such as the maxillary central incisor.

Molar posts longer than 7 mm have anincreased chance

of perforations and therefore should beavoided even

when using instruments of an appropriatediameter.

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Mechanical Aspect of PCRMechanical Aspect of PCR

1. Stressing capability of posts.2. Retention of posts.3. Posts & Restorative materials.

Anatomical Aspect of PCR FoundationAnatomical Aspect of PCR Foundation

1. Anatomy of the root .2. Radiographs.

3. Inclinations.4. Anatomical anomalies

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Mechanico-Anatomical Aspect of PostsMechanico-Anatomical Aspect of Posts1. Maxillary Centrals favorable for posts (Anitrotational required).2. Maxillary Laterals tapered post only indicated.3. Maxillary Cuspid Ideal for posts tapered post & sided parallel

(Anitrotational required).4. Maxillary first Premolars is not advisable to mechanically widenthe canal ( use smallest post ) U-shaped parallel can be used.

5. Maxillary first Premolars is favorable for posts sided parallel ismost indicated & tapered post are least indicated.

6. Maxillary 1st & 2nd Molar, palatal root is favorable for posts sided

parallel is most indicated , it is unadvisable for the buccal roots7. Maxillary 3rd Molar has unpredictable root study carefully before.

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Mechanico-Anatomical Aspect of postsMechanico-Anatomical Aspect of posts1. Mandibular Centrals only the smallest tapered post (Anitrotational

required)2. Mandibular Laterals the same as centrals with better accommodation.

3. Mandibular Cuspid one of the most suitable for posts prime indicationfor tapered post. (Anitrotational required).4. Mandibular first Premolars much more suitable for posts, sided

parallel is most indicated5. Mandibular 2nd Premolars is more stronger favorable for posts

(Anitrotational is not required)

6. Mandibular 1st

& 2nd

Molar, the distal root is favorable for posts, becareful of sided parallel or not because of perforation tendency.

7. Mandibular 3rd Molar has unpredictable root study carefully before.

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POST AND CORE

PLACEMENT TECHNIQUES

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Thanx for

listening

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