Post core crown

Post-Core CrownPost-Core CrownHeading to a further clinical Heading to a further clinical longevity of teethlongevity of teeth

Post-Core CrownPost-Core CrownHistorical Historical BackgroundBackground

Various methods of restoring pulpless teeth have been

reported for more than 200 years. In 1747, Pierre Fauchard described the process by

which roots of maxillary anterior teeth were used for the restoration of single teeth and the replacement of multiple teeth

Posts were fabricated of gold or silver and held in the root canal space with a heat-softened called “mastic.”

• Porcelain pivot crowns were described in the early 1800s by a well-known dentist of Paris, Dubois de

Chemant

• One of the best representations of a pivoted tooth appears in Dental Physiology and Surgery, written by Sir John Tomes in 1849 5 Tomes’s post length and diameter conform closely to today’s principles in fabricating posts.

Post-Core CrownPost-Core CrownHistorical Historical BackgroundBackground

POST AND CORE PLACEMENT TECHNIQUES

1. Post length2. Post diameter3. Anatomic/structural limitations4. Type of post and core that will be used

(prefabricatedpost and restorative material core or anatomicallycustomized cast post and core)5. Root selection in multirooted teeth6. Type of definitive restoration being placed and itseffect on core form and tooth reduction depths

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 & tooth Loss of retention & tooth fracture are the most fracture are the most common causes of post common causes of post & core failures& core failures

Clinical Failure Rate of Posts and Cores

Mean values † 6 yr 9 (196 of 2,220

9 (72 of 788) 1–69 mo Torbjörner, 1995

14 (8 of 56) 4–0 y Wallerstedt, 1984

8 (39 of 516)1–10 y Mentink, 1993

11 (17 of 154) 3 y Hatzikyriakos, 1992

7 (9 of 138) 10 y or more Weine, 1991

9 (9 of 96) 5 y 9 Bergman, 1989

9 (36 of 420) 1–25 ySorenson, 1984

12 (6 of 52)5 y Turner, 1982

% Clinical FailureStudy Length

Lead Author

Clinical Failure Rate of Posts and Cores

Tapered posts are the least retentive , threaded posts the most retentive & Parallel is intermediate

Post form & root fracture

Threaded posts produce undesirable levels of stresses

HeneryTapered threaded posts increase the root fracture

by 20 times as parallel threaded postsDeutch

Split threaded posts do not reduce stress associated with threaded pins

Thoresteinssonposts designed for cementation produced less stressthan threaded posts.

Clinical Failure of Posts and CoresPost form & root fracture

When parallel-sided cemented posts have been compared with tapered cemented posts, stress testing results have generally favored parallel-sided posts.

parallel-sided posts distribute stress more evenly to the root

Henery

Post Form and Tooth Fracture

Clinical Data (% of Post and Cores Studied That Failed via Tooth

Fracture)

Threaded Posts 7% MeanParallel-Sided Posts 1% MeanTapered Posts 3% Mean

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

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

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

• A smooth-surfaced post, although less retentive than either serrated or threaded post surfaces, transmits the least amount of force to the root structure.

• While both smooth and serrated posts are passive, in that they simply lie within the post space after being cemented, threaded posts actively engage the internal walls of the root canal as they are screwed in, and, while being the most retentive by far, produce such a force on the brittle root structure that they are contraindicated in most situations.

Post Selection

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

Post-Core CrownPost-Core Crown

• The use of a post and core does not strengthen the tooth prior to restoration with a crown; rather, it may contribute to the weakening of the tooth structure, as the forces placed upon the future prosthetic crown and core are now transmitted along virtually the entire length of the brittle, endodontically treated tooth.

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

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

Both laboratory & clinical Both laboratory & clinical data failed to provide data failed to provide definitive support for the definitive support for the concept that post strengthen concept that post strengthen endodontically treated toothendodontically treated tooth

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

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

Types of post & core failuresTypes of post & core failures(of 100 failures Turner found )(of 100 failures Turner found )

• Loosening Loosening (59 )(59 )

• Apical Abscess Apical Abscess (42 )(42 )

• Dental Caries Dental Caries (19 )(19 )

• When When 4mm4mm gutta-perchagutta-percha left left 11 of of 8989 specimen specimen showed leakage showed leakage

When When 2mm2mm gutta-percha gutta-percha left left 3232 of of 8989 specimen specimen showed leakageshowed leakage (MJattison)(MJattison)

Post apical endPost apical end

• 2 studies found when 2 studies found when 4mm4mm gutta-percha left gutta-percha left nono leakage leakage

(Portell)(Portell)

• When less than When less than 3mm3mm gutta-percha left gutta-percha left significantly higher significantly higher frequency of periapical radiolucenciesfrequency of periapical radiolucencies

(Kvist)(Kvist)

• When When 4mm4mm gutta-percha left gutta-percha left nono leakage leakage

(Raiden)(Raiden)


• 4-5 mm4-5 mm gutta-perchagutta-percha should be left should be left

Basically, it is important to leave at least 5 mm of gutta percha at the apex of the root canal, because it is within the apical 5 mm of the root canal that 95% of lateral accessory canals split off from the main canal and anastomose with the exterior surface of the root. Should these lateral canals not be blocked with the gutta percha and the cement used to place the gutta percha, the chances of microleakage and percolation of microbes is drastically increased, thereby increasing the likelihood of an endodontic failure.


the largest ideal diameter for a post is the diameter of the root at the most apical portion of the post space.

Tapered posts are the least retentive and threaded

posts the most retentive in laboratory studies. Most of

the clinical data support the laboratory findings.

Post Form and Tooth Fracture

laboratory tests generally indicate that all types of threaded posts produce the greatest potential for root fracture

When comparing tapered and parallel cemented posts, the results generally favor the parallel cemented posts.

WHAT IS THE PROPER LENGTH FOR A POST?

A wide range of recommendations have been maderegarding post length, which includes the following: (1) the post length should equal the incisocervical orocclusocervical 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 boneand root apex(8) the post should be as long as possible without disturbing the

apical


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

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

Leary et al. indicated that posts with a length at least three-quarters of the root offered the greatest rigidity and least root bending.


Abou-Rass . proposed a post length guideline for

maxillary and mandibular molars based on the incidence

of lateral root perforations occurring when post

preparations were made in 150 extracted teeth.90 They

determined that molar posts should not be extended

more than 7 mm apical to the root canal orifice.


When teeth have diminished bone support, stresses increase dramatically and are concentrated in the dentin near the post apex.

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

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


Reasonable clinical guidelines for length include the following:

(1) Make the post approximately three-quartersthe length of the root when treating long-rooted teeth;(2) when average root length is encountered, then postlength is dictated by retaining 5 mm of apical gutta-perchaand extending the post to the gutta-percha(3) whenever possible, posts should extend at least 4 mm

apical to the bone crest to decrease dentin stress. (4) molar posts should not be extended more than 7 mm

into the root canal apical to the base of the pulp chamber

WHAT IS THE PROPER POST DIAMETER

post diameter is to not exceed one-third the root Diameter

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

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

WHAT IS THE PROPER POST DIAMETER

Instruments used to prepare posts should be related in

size to root dimensions to avoid excessive post diameters

that lead to root perforation Safe instrument diameters to use are 0.6 to

0.7 mm for small teethsuch as mandibular incisors and 1 to 1.2 mm

for large diameterroots such as the maxillary central incisor.Molar posts longer than 7 mm have an

increased chanceof perforations and therefore should be

avoided evenwhen using instruments of an appropriate

diameter.

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 Foundation1. Anatomy of the root .2. Radiographs.3. Inclinations.4. Anatomical anomalies

Mechanico-Anatomical Aspect of PostsMechanico-Anatomical Aspect of Posts

1. 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 widen

the canal ( use smallest post ) U-shaped parallel can be used.5. Maxillary first Premolars is favorable for posts sided parallel is

most 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.

Mechanico-Anatomical Aspect of postsMechanico-Anatomical Aspect of posts

1. 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 indication for tapered post. (Anitrotational required).

4. Mandibular first Premolars much more suitable for posts, sided parallel is most indicated

5. 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, be careful of sided parallel or not because of perforation tendency.

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

POST AND CORE PLACEMENT TECHNIQUES

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Technology

Post core crown