COLLEGE OF DENTAL SCIENCES

DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS

Seminar On

Presented by : -

Dr. Niju Aelias

CONTENTS

Introduction

History

Indication

Definition

Classification

Retentive Features of Post

Types of Post

Core and Core Material

Technique

Post selection

Root selection

Post embedment depth

Gutta Percha removal

Channel preparation

Post installation

Crown preparation

Preparation of Orifice

Preparation of Ferrule

Fabrication of custom cast post

Direct

Indirect

Temporization

Cementation

Recent Advances

Carbon fibre post

Esthetic post and core

References

Conclusion

INTRODUCTION :

All the teeth that have undergone root canal therapy will require some

form of restoration to enable them to function again. Because endodontic

treatment removes the vital contents of the canal, which subsequently leads to

reduction in elasticity, dessication and increases brittleness of remaining tooth

structure. The objective is to return them to full occlusal and cosmetic

function.

It is the manipulation of the pulp chamber that leads to the greatest

weakness of a treated tooth. The roof of the pulp chamber has the

configuration of an arch, which extremely resist to pressure and stress. When

the roof of the pulp chamber is removed for endodontic access, the inherent

resistance of the treated tooth is greatly reduced. This weakening leads to the

need for strong interior as well as exterior support that is achieved by post core

system. Often due to mechanical reasons, the prepared tooth is reinforced by

post core systems.

HISTORY :

During 18th century Pieree Fauchard used a wooden post to retain

crowns.

G.V. Black (1869) used a porcelain crown held by a screw inserted into

a canal filled with gold foil.

1880 Richmond Crown – Threaded tube in the canal with a screw

placed through the crown.

1999 Fibre reinforced composite and strengthened ceramics.

INDICATIONS :

1. A root canal treated tooth, if any proximal surface is involved.

2. Loss of 2 incisal angles together with more than half of the proximal

surfaces of the tooth.

3. Loss of more than 50% of the tooth structure.

1

4. Loss of more than one axial angle to a depth more than the anticipated

axial reduction for the reinforcing restoration.

5. A shorted tooth due to nature of destruction or the removal of

undermined undesirable tooth structure.

6. When a root canal treated tooth is to be used as a bridge abutment.

7. Discoloured tooth, malaligned tooth, overdenture.

DEFINITIONS :

Dowel (Post) :

The dowel is a metal post or other rigid restorative material placed in

the radicular portion of a non vital tooth.

Core :

Refers to properly shaped and well restored substructure, which

replaces missing coronal structure and retains the final restoration.

Ferrule (Rosenstiel):

Is defined as a metal band that encircles the external dimension of the

residual tooth.

Ferrule (Weine) :

A ferrule is a metal ring or cap placed around the end of a cane or tool,

giving it added strength. The ferrule around the circumference of the tooth

strengthens it by increasing resistance to wedging forces.

Dowel functions primarily to aid retention of the restoration and

secondarily to distribute force along the length of the root, thus dowel has a

retentive role but doesnot strengthen a tooth, instead the tooth is weakened if

dentin is sacrificed to facilitate large dowel placement.

Role of the Dowel / Post :

1. Occlusal forces are transferred through the core to the post and

ultimately along the length of the root. The post must be designed in

2

such a way that it serves its retention function without endangering the

root or coronal integrity.

2. The dowel must remain in the root for successful restoration but must

not damage the root in attempts to achieve the maximum retention.

3. Dowels must be retained by cementation to the dentin walls of the root,

active engagement of the dowel spaces by screw threads is

contraindicated.

CLASSIFICATION :

Endodontic posts can be classified into 2 broad categories ;

Custom cast post

Prefabricated post

o Active retention post

o Passive retention post

Custom Cast Post :

1. Fabricated at the chair or laboratory from a negative reproduction of the

prepared canal.

2. Wax or cold cure resins are used to make these patterns.

Type I : Medium Wax (Direct technique)

Type II : Soft wax (Indirect technique)

3. Uses a casting procedure to make a one piece metal dowel and core.

4. Technique can be direct in patients mouth or indirect with impression

stones and dies.

Prefabricated Post :

This is classified as follows ;

1. Tapered smooth sided post systems :

They are cemented into a channel prepared with endodontic files or

reamers of matching sizes.

Eg. Kerr Endo Post (Prefabricated gold alloy dowel)

3

2. Parallel sided serrated or vented post system :

Cemented into a matched channel prepared by twist drill of matching

size.

Eg. Whaledent para post.

3. Tapered self threading post system :

Screwed into a channel prepared with matched reamers.

Eg. Dentatus screw post.

4. Parallel sided :

Threaded post systems : Engages dentin by self threading or with the use

of matched taps.

Eg. Radix Anchor – Self thread

Kurer Anchor – First tapped then threaded into dentin.

5. Parallel sided : Threaded split shank post :

Engages the dentinal wall in a channel prepared with matched reamers.

Eg. Flexi post

6. Parallel sided, tapered apical end :

Cemented into matched channels.

Eg. Degussa, Unitech BCH

RETENTIVE FEATURES OF POST / FACTORS AFFECTING

RETENTION OF POSTS :

These are ;

1. Dowel length

2. Taper

3. Diameter

4. Surface configuration

5. Cement type

6. Embedment depth

7. Number of posts

4

1. Dowel Length :

Dowel or post retention is proportional to length of post. Increased

length Increased retention.

The standard parameter for selecting post / dowel length in a tooth with

normal PDL support is

A. 2/3rd length of canal.

B. An amount equal to coronal length of tooth.

C. Half the length of root supported by bone.

Final length of dowel in periodontally healthy tooth is limited by 2

major variables.

o The root morphology

o The need for sufficient apical seal in root canal system.

Root morphology is dictated by ;

Root taper

Root curvature and

Cross sectional root form

Root should have more than 1 mm of tooth structure remaining

circumferentially around the apical end of the dowel to avoid perforation and

fracture (This concept dictates shorter dowel in a tapered root so that apical end

of the dowel doesnot impinge on converging root walls).

Root Morphology :

In root morphology furcations and developmental depressions should be

considered.

Maxillary Molars :

94% deep concavities on the furcal surface of mesiobuccal roots.

31% of distobuccal roots

17% of palatal roots.

Mandibular Molars :

5

Root concavities on furcal surface of

o Mesial roots 100%

o Distal roots 99%

Apical Seal :

3-5 mm of filling material is adequate to maintain apical seal.

Most preferred roots for Dowel.

Maxillary molars – Palatal roots

Maxillary premolars – Palatal roots

Mandibular molars – Distal roots

Clinical Guidelines for Length Include the Following :

1. Make the post approximately three quarters the 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 part to the gutta

percha.

3. Whenever possible, post should extend atleast 4 mm apical to the bone

crest to decrease dentin stress.

4. Molar post should not be extended more than 7 mm into the root canal

apical to the base of the pulp chamber.

2. Dowel Shape :

Tapered Post Parallel Sided Post1. Less Retentive More retentive than tapered post2. Creates a wedging effect with

greatest stress created at coronal shoulder.

Creates less stress, smooth parallel post creates stress at the apex of preparation.

3. Uneven distribution of stresses along the length.

Resist tensile, shear, and torquing forces better then tapered and distribute stresses more evenly along their length during function and provides greatest protection against dentin fracture.

6

Tapered Post Parallel Sided Post4. Because of taper these post are

self venting and can be easily cemented, taper doesnot act as a position. Only area where stress occurs during cementation is irregularities in post channel.

Hydrostatic pressure develops during cementation if no venting because post act as a piston.

5. The wedging effect of tapered post is related to the flare of the post channel. Greater the flare more will be the wedging effect.

6. Tapered dowel that is more closely adapted to the internal shape of root canal is more likely to result in extensive root fracture.

Than parallel sided post.

Parallel side posts are more retentive than parallel posts with tapered

ends. This dual design post creates higher wedging stresses than

parallel sided post.

3. Post Diameter :

Post must be of sufficient diameter to resist functional forces. Retention

is not increased by increasing the diameter beyond a critical point. Prevention

of dentin fracture in radicular area takes a upper hand over large diameter of

post.

Suggested width of post preparations (Weine) :

Tooth (Maxillary) Enlarge to SizeCentral incisor 80-100Lateral Incisor 70-80Canine 80-100Bicanaled bicuspid 80Single canal bicuspid 80-100Molar (palatal canal) 80-110

7

Tooth (Mandibular) Enlarge to SizeIncisors 70 – 80Canines 80 – 100Single canal premolars 80 – 100Molar (Distal Root) 80 – 110

Post diameter should not increase 1/3 of the root diameter.

4. Surface Configurations / Surface Texture:

Surface texture of post has a dramatic effect on post retention and stress

distribution.

Retention decreases as we progress from Threaded serrated

smooth surface post.

This serrated surface provides mechanical undercut for cement More

retention. These serration can be horizontal with a single vertical vent.

Cutting a venting channel along the length of serrated or cast post with a

carborundum disc or a fine long tapered diamond reduces the hydraulic

forces produced during cementation by allowing air and cement to

escape coronally.

The surface of the cast post can be sandblasted to improve retention.

Parallel sided serrated post are cemented in the canal passively. They

are retentive and produce less stress in the root dentine than threaded

system.

Parallel sided post are recommended for conservatively prepared root

canals in teeth with roots of circular cross section.

Excessively flared canals (eg. Those found in young persons or on

individual after retreatment of endodontic failure) or oval in cross

section then a custom cast post are used.

Threaded post produce greater stresses within the root dentin.

Pretapping the screw thread and avoiding over tightening reduces these

forces.

8

Parallel threaded post can be useful in situations where there is limited

root length available.

Tapered threaded post should be avoided since they produce wedging

forces within the root canal that can result in fracture.

5. Cementation :

The type of cement used also has little effect on retention, cement type

does affect retention of tapered smooth sided post.

6. Rotational Resistance :

Post preparation in teeth such as maxillary anterior and mandibular

premolars would make the post space circular in cross section, which would

rotate during function. This would not occur in areas where sufficient coronal

tooth structure remains, because rotation is usually prevented by a vertical

coronal wall.

In areas where coronal dentin has been completely lost, a small groove

placed in the canal serve as an anti rotational element.

The groove is normally located where the root is bulkiest usually on the

lingual aspect

Alternatively rotation can be prevented by an auxiliary pin in the root

face.

7. Preparation Geometry :

Some canals particularly maxillary central incisors have a nearly circular

cross section. These can be prepared with a twist drill or reamer to prepare a

cavity with parallel walls allowing the use of a prefabricated post of

corresponding size and configuration.

Canals with elliptical cross section must be prepared with a restricted

amount of taper (6 to 8o) to ensure adequate retention while eliminating

undesirable undercuts. In this canal parallel sided post will not be effective

unless the canal is considerably enlarged which would significantly weaken the

9

root. In this situation a custom made post will best fit into the shape of the

canal.

TYPES OF POSTS :

Posts or dowels can be generally classified as ;

- Passive retention post

- Active retention post

Passive Retention Post : Retention depends upon their close proximity to the

dentinal walls, but mostly by adherence of the cementing medium.

Eg. Cast posts, Smooth tapered posts, Serrated parallel posts.

Active Retention Post : Retention depends primarily on engaging the dentin

directly. Consist of threads that either screw into the dentin, such as a wood

screw or threads that fit into threaded channels ‘tapped’ into dentin much like a

bolt.

Eg. Flexi post, Kurer Anchor.

PASSIVE RETENTION POST : Tapered Smooth Sided Posts : Eg. All custom cast post, Kerr Endopost, Mooser Post (Mallifier).

Widely used, as tapered form is easy to use in tapered canal, which is

the natural shape of an endodontic canal.

Parallel Sided Posts : Posts with parallel sides when cemented into prepared parallel channels,

provide much greater retention with less stress than tapered post.

Eg. Whaledent para posts

Boston post

Parkell parallel post

The para post, parallel and serrated is the most widely used.

Para Post System :

10

Introduced by Whaledent

Has 3 designs

o Original para post

o Para post plus and

o Unity system

All these are passive, parallel, vented, posts made of either stainless

steel or titanium.

Cement retention is gained by

o Horizontal serrations on the para post

o Spiral flutes and grooves on para post plus and

o Raised diamond pattern on the unity post

Any cementing medium can be used

Has greater retention than the smooth tapered design

Can be used effectively in areas where higher applied forces are

expected.

Vent allows for easy escape of cementing medium and reduces stresses

that may be induced in the dentin by other cemented parallel posts.

No wedging effect.

Transfer of occlusal forces occurs through the cement layer This

buffer the forces Uniform distribution of stresses.

Parallel, serrated vented post produces stresses that are distributed more

evenly along its length and is betable to protect the dentin.

Boston Post System : In physical design, the Boston post is similar to parapost but no vertical

venting.

It has 99.65% titanium with horizontal, non engaging serrations.

In 1993 Boston post was redesigned with deeper grooves and an etched

and roughened surface to allow greater retention.

Smear layer removal is recommended.

11

Studies have shown that the use of unfilled BISGMA resin was the best

cementing medium than zinc phosphate or polycarboxylate cements or a

filled resin.

Parkell Parallel Post System : This is a stainless steel passive, vented, serrated post with an

antirotational lock that fits into a seat prepared in the root surface.

Supplied with plastic core former that come with the posts. These allow

the dentist to build up an immediate composite resin crown core.

Cementing the post and core with 4 META adhesive, bonding both to

the tooth surface, might allow for the lack of a ferrule.

The parallel post also comes in a plastic burnout pattern for a cast

version. This model would encourage root preparation to receive a

ferrule in the core casting.

Parallel Sided Posts with Tapered Apical End : Parallel post in tapered roots risk perforation and weakening of dentin

wall, parallel post with tapered ends has been developed.

These posts are designed for greater retention of parallel post plus good

adaptation to tapered apical portion of canal.

Available in 2 variations.

Degussa : Completely smooth sided

The straight and tapered apical portions are equal in length

Unitek BCH System : Less serrations along the parallel sides and a smooth apical taper of

about 2 mm.

BCH post has a large coronal portion to provide retention for core build

up materials.

Disadvantages :

12

- Parallel post with tapered ends has a lower retention potential than

regular parallel posts of comparable length and diameter.

- Produces wedging forces in area of apical taper, more prone for root

fracture than parallel sided post.

ACTIVE RETENTION POST : These are of two types ;

1. Those with self threading screws – Engages the dentinal walls of a

prepared post channel, cuts their own counter threads.

Eg. Dentatus post

Radix Anchor post

Flexi post

2. Those that bolt into preformed threads – These are tapped in dentin. Eg.

Kurer Anchor post.

Posts with Self Threading Screws :

Self Threading Tapered Post Tapered Dentatus :

One of the earliest of the self threading tapered posts.

More retentive than passive / cemented posts

It gains its retention by spreading the dentin as it self threads May

cause root splitting.

Act as a tapered wedge and cause stress concentration, which become

worse on occlusal loading.

Usually used in molars, dimension – 2.6 mm long and 1.6 mm across, so

not preferred in anterior teeth.

Used on teeth with a minimum of coronal tooth structures and multiply

divergent canals.

Tapered Flexi Post :

13

Flexi post is a prefabricated, split shank, parallel sided, threaded post

that absorbs the stresses of insertion (by gradually closing during

placement) while providing maximum retention.

As apical ½ collapses it becomes a tapered post.

It gains its retention by its threads cutting into dentin by 0.1 mm – 2

mm.

Further retention can be gained by cementing the post with a titanium

reinforced composite.

Channel is prepared by drill slightly larger than the diameter of the shaft

of the post.

The blades (thread) extend beyond the shaft by 0.2 mm and engage into

the dentin.

It is first screwed into the prepared canal with a tiny Wrench then

removed counter clockwise and reinserted with cement into the same

dentin threaded grooves.

Flexi post comes in 5 sizes, from 00 to 3.

Self Threading Parallel Post : 2 designs are available

V – Lock

Radix Anchor system

Both have low frequency sharp threads and both are vented to reduce hydraulic

cementation stress. They differ in the length of the threads down the shaft.

Parallel V Lock Drill and Post System : This is a parallel sided micro threaded post.

Micro threads extend 0.5 mm from the shaft and continue its full length.

V-Lock drills are supplied with precise drills that prepare a parallel

walled canal just slightly larger than the post shaft. They can be

cemented with any cement or adhesive.

V-Lock post was more stressful than flexi post when threaded and

cemented.

14

Parallel Radix Anchor System : Radix anchor posts gain their primary retention by self cutting counter

threads in the dentin.

Differ from V lock post by number of its threads, which are sharp, low

frequency helical blades that extend only partly down the shaft.

It is vertically vented.

It is designed to fit snugly in a channel prepared for it in the root.

It can be cemented with any cement.

Because of limited number of threads, the radix anchor has less retention

than other actively retained posts.

Parallel Threaded Post with Pretapped Channels : Kurer Anchor Post

These are the only dowels in the market that fit into pretapped counter

threads in the dentin.

Most retentive post available.

Parallel in design with no vertical vent.

They have rounded high frequency thread that fit into counter threads

‘tapped’ into the dentin with a manual thread cutter.

They come in a number of configurations.

o Standard anchor

o Crown saver

o Fin lock anchor

o Press – Stud Denture retainer.

Kurer root facer prepares a flat seat in the root face (counter sink) into

which the coronal portion is to fit perfectly.

Parallel sided threaded posts, cemented into tapped channels are

superior in retention than all other post design.

Kurer anchor post is more retentive than the Radix anchor because of

higher frequency of threads.

15

Because of increased retention it is preferred in areas of high load such

as partial denture abutments, overdenture abutments, long span bridges

etc.

Also very useful when only short embedment depths are possible

because of root length and shape.

Kurer post produce severe apical stress, if the apex of the post fully

engages the bevel produced by the twist drill at the channel apex. In that

it is similar to the Radix anchor.

This can be prevented by trimming the post length short of the apical

bevel in the canal.

When cemented it should be fully seated with the end of the threaded

shank just short of the tapered post of the channel.

The coronal seat in the root facer preparation should be just touching, no

screwed down so tightly as it produces strains (Counter Rotation of Post

One ½ turn).

Disadvantage :

Kurer crown anchor system include, removal of a considerable amount

of dentin that cause root perforation and high risk of splitting the root by

rotation of the screw causing a wedge type action.

CORES :

The core consists of a restorative material placed in the coronal area of a

tooth, which replaces carious, fractured or missing coronal structure and retains

the final crown.

The core can be anchored to tooth structure by extending into coronal

aspect of the canal or through the endodontic dowel. Attachment between

tooth, Dowel and Core is mechanical or chemical. Remaining tooth structure

can also be altered to add retention of the core or to prevent rotation of core

during function. These modifications are pins, channels, grooves placed away

from dowel.

16

Desirable Physical Characteristics of Core are ;

1. High compressive strength.

2. Dimensional stability

3. Ease of manipulation

4. Short setting time for cement

5. An ability to bond both to tooth and dowel

Types of Core :

1. Cast metal cores

2. Amalgam cores

3. Composite resin core

4. Glass Ionomer core

5. Glass Ionomer resin core

Cast Metal Cores : Core is an integral extension of dowel.

Core doesn’t depend on mechanical means of retention to dowel.

It can provide antirotational features.

Indications are

o Small anterior teeth

o Premolars

o Teeth with major coronal destruction

Disadvantages are

o Increased cost

o More appointments required

o More lab work required

o Chances of fracture at dowel and core interface are high.

Amalgam Cores : Fast setting high copper alloy has to be used.

Higher retention when used with preformed dowels in posterior teeth.

17

Retention is enhanced by using dentin bonding agents, auxiliary pins,

irregular preparations.

Transmit minimal stress to tooth structure.

Advantages :

1) High compressive strength.

2) High tensile strength.

3) Stable under functional stress

Disadvantages :

Potential for corrosion Discoloration of gingiva or dentin.

Composite Resin Core : Advantage :

Easy to manipulate and sets rapidly.

Anti rotational effect and additional retention can be achieved by pins,

dentin bonding agent.

Disadvantage :

Polymerization shrinkage and contraction away from tooth structure.

If non fluoride releasing – no anticariogenic property.

Microleakage more than amalgam, GIC, GIC – Resin.

Dimensionally unstable in wet conditions.

Lower modulus of elasticity, higher coefficient of thermal expansion.

Glass Ionomer Core : High viscosity GIC or GIC silver core material can be used.

Advantages :

1. Anticariogenic – fluoride release.

2. Forms ionic bond

3. Microleakage is less

Disadvantages :

18

1. Soluble and sensitive to moisture.

2. Low fracture toughness – low strength and brittle cannot be use d in

anterior teeth or replace unsupported cusp.

Indications :

For posterior teeth

- A bulk of core material is possible if sound dentin remains.

- If addition retention is available with pins and dentin preparation.

Glass Ionomer Resin Core (RMGIC) : Moderate strength, greater than conventional GIC.

Solubility is between composite and GIC

Exhibits properties of both the materials

Release fluoride

Insoluble, minimal leakage

Titanium Core Composite Material (Extensive Dental System) :

Fluoride releasing.

Reinforced by titanium and lanthanide. Increased strength without

potential by products that results from oxidation of silver filled glass

ionomers.

High compressive and tensile strength.

CAST VERSUS PRE-FABRICATED POST AND CORE: Prefabricated Post Core : Advantages :

1. Simple to use

2. Less time consuming

3. Can be completed in one appointment

4. Easy to temporize

5. Cost effective

6. Strong

19

Disadvantages :

1. Root is designed to accept the post rather than post designed to fit the

root.

2. Application is limited when considerable tooth structure is removed.

3. Possibility of chemical reaction when post and core are of dissimilar

materials.

4. Attachment for removal prosthesis cannot be applied to post and core

unless a separate casting is fabricated to place over it.

Cast Post Core : Advantages :

1. Custom fit to root configuration.

2. Adaptable to large, irregularly shaped canals and orifices.

3. Can be used with wrought post and prefabricated plastic pattern.

Disadvantages :

1. Expensive

2. Require multiple appointments

3. Less retentive

4. Temporization between appointment is difficult.

5. Chances of corrosion because of casting procedure or use of dissimilar

metals.

6. Risk of casting inaccuracy

Amount of tooth Structure Removal :

Custom cast post core – Minimal amount of dentin removal. Canal

enlarged with reamers and files during endodontic treatment for shaping the

canal. Final post core preparation done with peeso reamers.

Para post – Conservative tooth preparation (Less removal of tooth structure

when compared to Kurer anchor).

20

Kurer Anchor – More amount of tooth structure removal because of

counter sink leads to perforation and root splitting (when compared to all

other post).

DOWEL AND CORE SELECTION :

This depends on 3 important factors.

1. Amount of tooth structure remaining.

2. Functional stresses anticipated

3. Morphology of root

TECHNIQUES :

Post Selection : Depends on

Root morphology.

Remaining coronal tooth structure

Occlusal forces

Post core selection should be done after crown preparation.

Root Morphology :

Most roots gradually taper from the cemento enamel junction to the apex

of the tooth. The use of parallel post in these teeth may come dangerously

close to perforating the lateral surface of the root.

Consideration should be given to use a tapered or a parallel post of

shorter length. Both these alternatives have their drawbacks.

The use of a tapered post could introduce wedging during load transfer,

whereas a shortened parallel post reduces the protective function of the post by

spreading occlusal stresses over a shorter root length.

When the outline of the canal is oval or ribbon shaped, it is difficult to

prepare a circular post channel to receive a parallel post. In these situations, a

custom post formed to the shape of the canal conserves tooth structure and

involves less preparation in the apical region of the root. This custom post will

21

also have the coronal core attached, allowing antirotational component to be

incorporated into the post preparation.

If it is possible to prepare cylindrical channels equal to or longer than

the clinical crown of the tooth, a parallel cemented post in combination with a

coronal core will best fulfill restorative requirements. The coronal core can be

formed with amalgam or composite or as part of a post casting.

Remaining Coronal Tooth Structure :

The retentive and protective function of a post depends upon the amount

of tooth structure remaining after caries and previous restoration have been

removed.

The use of a post should be considered.

1. For anterior teeth when one or both proximal walls are missing.

2. For posterior teeth when two or more adjacent proximal walls are

missing.

Type of Post :

1. Preformed post and core combination used when no dentinal walls

remains on crown and shorter root - Kurer Anchor system.

2. Preformed metal post, combined with a composite or amalgam core

when one or more dentinal walls remain.

Endo post

Para post system

BCH post system

Boston post

Flexi post

3. Cast core additions to a preformed metal post when no dentinal walls

remains, such as casting a core addition to a Metal Para Post.

4. Threaded post – limited root length is available.

Occlusal Forces :

22

Occlusal forces on individual teeth are influenced by tooth type and

position, the presence or absence of adjacent teeth, the function the tooth must

serve (for eg, the single unit or partial or bridge abutment) and the patients

occlusal habits.

Each of these variables, either singly or in combination, determines the

selection of a post system that satisfies the retentive and protective criteria the

individual clinical situation demands.

Root Selection : Post should be placed in area where there is greatest amount of lost

tooth structure. Mesial roots of mandibular molars and buccal roots of

maxillary molars are often curved and narrow and cause perforations when

these roots are chosen for post placement.

Distal roots of mandibular molars and palatal roots of maxillary molars

are best suited for post placement.

Post Embedment Depth : More length, more will be the retention and more even stress

distribution along the root surface.

Guidelines for Post Embedment Depth : Gutta-Percha Removal :

Coronal portion of gutta percha is removed to provide a post space. To

maintain the integrity of apical seal gutta percha removal is delayed until the

root cement is set 48 hours or wait a week.

Recent studies have shown that post space can be prepared immediately

after condensation if hot instrument is used to remove gutta percha.

More recent studies reported no difference in apical leakage between the

use of heated pluggers, chloroform with files or Peero drills, or between heated

pluggers and Gates-Glidden drills. Among the solvents, chloroform was found

to be more effective than xylene.

23

After removing the gutta percha it is necessary to go back and

recondense the face of the remaining gutta percha filling.

There is additional advantage in immediately preparing the post space.

The clinician who has just filled the canal has clearly in mind the length and

shape of the preparation. Moreover, additional vertical condensation of the

remaining gutta percha will result in a well condensed apical seal.

If the endodontic status of the treated tooth is uncertain, immediate gutta

percha removal and post space preparation is best delayed.

Methods of Removal :

Root Canal Plugger : The rapid placement and removal of a well heated root

canal plugger removes gutta percha as it softens and adheres to the plugger.

This process is repeated until the desired depth is achieved.

At least 3.0 mm but preferably 5.0 mm of apical gutta percha should

remain. This should be verified by radiograph after a final recompaction using

vertical condensation.

Peeso Reamers : Have also been used to remove gutta percha. The reamers

non cutting tip facilitates centering the reamer in the gutta percha.

Problems encountered during preparation of post space include;

1. Canal over enlargement.

2. Perforations – Deviation of the reamer, caused by the remaining gutta

percha can lead to perforation.

3. Dislodgement of the master point from the apical area, if post space is

prepared with a reamer or rotary instrument immediately following the

obturation.

Channel Preparation :

24

Can be prepared by endodontic reamers, files peeso reamers and

specified drills with prefabrication post kits.

The prefabricated post system use endodontic reamers or files, peeso

reamers or specified drills with prefabricated post kits to establish proper

channel width for each post size. Measurement of the post space length from

the occlusal or incisal landmarks from the radiograph is transferred to the

appropriate file, reamer or drill for the post system selected. The walls of the

canal are then reamed to the proper width.

As previously started, post diameter has much less influence on retentive

capability than the embedment depth in the canal. Therefore, canals should not

be overly enlarged at the expense of surrounding dentin, especially in the apical

portion where the root diameter is severely reduced.

It is recommended that preparation widths should be kept as narrow as

possible, never exceeding one third the root diameter. At least 1.0 mm of root

structure must remain along side the post.

The space provided by removing the gutta percha serves to centre the

reamer or drill and greatly reduces the risk of perforation. Peeso reamer

because of their non cutting tips are less likely to cause deviation from the

canal center. Therefore, in post system where a drill is used to shape the final

post space, progressively larger peeso reamers may be used initially to make

the canal close to parallel. Then, the twist drill or thread cutter used to form the

final channel will have much less cutting to do and more precise channel will

result. Deviation of drill and possible perforation are most unlikely.

Post Installation : Cemented post should not bind when inserted nor should they be so

loose that retention is questionable if the post binds, it should be removed and

the channel redefined with the appropriate drill.

25

Complete seating can usually be ascertained without taking a

radiograph. This is accomplished by comparing the measurement of the last

used files or reamer with the measurement of the post seated within the canal.

The coronal extension of the post should be adjusted to well below the

occlusal plane but with sufficient length to retain the core material. The

coronal portion of the post may also be bent to position it more strategically for

core retention. This is done out of the mouth and prior to cementation. When

the fit and length of the post have been verified, it is cemented with permanent

cement or resin.

Crown Preparation : All margins of the final restoration should always be on sound tooth

structure, and apical to margin of any internal core build up. This allows for

control over margin design, minimizes leakage at the final margin and

facilitates continuation of the internal core.

With endodontically treated teeth, extension of the final crown below

the internal core provides a more even stress distribution of functional forces

and serves to minimize the risk of coronal radicular fractures.

The crown should extend, where possible 1.5 to 2 mm on tooth structure

beyond the tooth core junction to ensure a protective ferrule effect (Crown

ferrule). This surrounding band of metal helps to prevent vertical fractures in

the root or horizontal fractures of the crown.

Ferrule can also be used in dowel core casting (core ferrule). However

care should be taken to avoid damage to the epithelial attachment.

Preparation of Orifice : For cast post in some teeth such as maxillary anterior and mandibular

premolars, post preparation around the orifice leads to symmetrical shape. So

26

to avoid purely round preparation orifice is modified by placing slots or

cloverleaf with tapered diamond stone or carbide bur.

Antirotational groove :

Use a No.170 carbide bur to make a key way or groove in the orifice of

the canal.

Grooves should be plexed in the area of tooth where there is greatest

bulk.

The keyway should be kept to the depth of the diameter of the bur

(approximately 0.5 mm) and up to the canal to the length of the cutting

blades of the bur (approximately .4 mm).

On a premolars second canal serves the same anti rotational features.

Regardless to the type of post used all internal designs should be

smooth, free of debris, caries and old restoration.

In teeth with large pulp chamber occlusal inlay preparation is made to

increase retention.

If core is build directly around prefabricated post orifice it is notched

along the post towards the apex. This act as undercut and aids in retention plus

the space for core material.

Preparation of Ferrule : Ferrule :

It is defined as a metal ring or cap placed around the end of a cane or

tool, which gives it, added strength. Ferrule increases the resistance to wedging

forces.

Ferrule is an encircling band of restoration that is metal or ceramic

which encircles the external aspect of the residual tooth.

There are two types of Ferrule :

a. Crown ferrule

b. Core ferrule

Crown Ferrule:

27

When less than 3 mm of circumferential sound tooth structure remains –

desirable core is full cast coping. This produces an apron of metal

around tooth. This distributes the forces equally, produces a ferrule as a

part of core coping and thus gives maximum protection.

Core Ferrule:

Imparting a 45 bevel to the occlusal or incisal portion of the preparation

guards the preparation against fracture from lateral forces of

mastication, since the core portion of casting will incorporate and hold

in the top portion of the preparation.

This contrabevel will provide a collar around the occlusal circumference

of the preparation, which aids in holding the tooth together and prevents

fracture. This serves as a safeguard on a precision fitting dowel, which

can exert lateral forces during cementation.

The crown and Crown preparation together must meet 5 requirements :

1. A minimum of 1-2 mm of dentin axial wall height is required.

2. Axial walls must be parallel

3. The metal must totally encircles the tooth.

4. The metal must be on solid tooth structure.

5. The metal must not invade the attachment apparatus.

Advantages of Ferrule :

1. Reduces the incidence of fracture by reinforcing the tooth and

dissipating the forces.

2. Resist lateral forces from tapered dowels and leverages from the crown

in function.

3. Increases resistance and retention of restoration.

Effectiveness of ferrules in preventing tooth fracture:

Differences of opinion exit regarding the effectiveness of ferrules in

preventing tooth fracture. Ferrules have been tested when they are part of the

core and also when the ferrule is created by the overlying crown-engaging

tooth structure. Most of the data indicate that a ferrule created by the crown –

28

encompassing tooth structure is more effective than a ferrule that is part of the

post and core. Ferrule effectiveness is enhanced by grasping larger amounts of

tooth structure. The amount of tooth structure engaged by the overlying crown

appears to be more important than the length of the post in increasing a tooth’s

resistance to fracture. Ferrules are more effective when the crown encompasses

relatively parallel prepared tooth structure than when it engages beveled /

sloping tooth surfaces.

Best 2 mm or more of tooth structure is covered as ferrule

Ferrule length more important than post length in increasing the fracture

resistance.

CUSTOM CAST POST AND CORE :

Can be fabricated by

- Direct Technique

- Indirect technique

Direct Technique :

In this technique a cast able dowel and core pattern is fabricated directly

on the prepared tooth in the patients mouth.

The pattern can be made of inlay wax or self cure acrylic resin

reinforced with a plastic rod, a bur, metal pin or a paper clip, nails, tooth

pick.

Also wax and acrylic resin can be combined. The use of resin allows

the pattern to be formed into a well adapted, solid dowel that can be

manipulated easily in the mouth without becoming distorted or loose in

the canal.

This technique can be used for single rooted teeth or multirooted teeth.

For Single Rooted Teeth :

This is done in the following steps :

1. Preparation of a tooth for a cast restoration (for anterior teeth metal

ceramic crown).

29

This determines the amount of sound dentin remaining (All undermined

thin, weakened tooth structure is removed).

2. Preparation of a Ferrule (360o Collar). Buccal and lingual surfaces are

slopped.

3. Preparation of Post space

o Placement of anti rotational groove

o Elliptical canal –no antirotational groove.

4. Post preparation :

Following materials are available which can be used as post.

1. Endo Post :

o High fusing precision metal alloy.

o Available in sizes between 70-140 corresponding to standardized

endodontic instruments.

o Can be cast with gold or other precious metals.

2. Endowel :

o Endowel is a plastic pin.

o Available in standard sizes 80-140

o When fitted a post preparation and incorporated in a wax or resin

pattern, it will burn out of the investment and yield a casting of one

metal.

3. Para Post :

Unlike endodontic instruments, it has no taper and requires the use of

rotary instruments for canal preparation. Not available in standardized size.

Dowel is checked for fit at the base of the prepared canal.

The canal is lubricated (eugenol/petroleum jelly).

If smooth plastic dowel is used it is roughened or slightly notched to

facilitate retention of acrylic resin.

30

Acrylic resin is applied to the dowel and prepared canal. After the resin

reaches the doughy stage the dowel is inserted in the canal.

Do not allow the resin to completely harden within the canal. The

dowel is pumped in and out in the canal to prevent interlocking of dowel

in the canal.

Remove the polymerized pattern and inspect the resin for integrity and

lack of voids. Repeat the post and test for adaptation and passivity.

Acrylic resin is added with brush to reconstruct the coronal aspect. A

slight excess of core resin is added so that the hardened core can be

prepared with a high speed diamond and water spray to the desired form.

The core is then removed, invested and cast.

The pattern can also be developed using inlay wax (Type I), which can

be carved with a carver.

After removing the pattern, dowel orifice is protected with cotton

pledget and provisional crown is cemented (no cement in canal).

For multirooted teeth :

Parallel Walls :

Palatal for maxillary and distal canal for mandibular is selected for

primary post.

Secondary post is placed which is 3-4 mm in length shorter than primary

post.

Technique is same as above mentioned.

Non-Parallel Walls :

If a severely damaged tooth is to be subjected to the stresses of acting as

an abutment for a fixed bridge or removable partial denture, more resistance

and retention are required. Because of the root divergence found in most

molars, using a dowel core with two or three parallel dowels extended into

multiple roots can be quite hazardous. Therefore, a multiple-piece dowel-core

with separate dowels should be employed. The dowel-core for a mandibular

molar is usually divided into mesial and distal segments. The maxillary molar

31

dowel-core is composed of facial and lingual components, with the dowels in

the two facial canals paralleling each other. When the mesiofacial and

distofacial canals are too divergent to permit parallel dowels, a separate third

dowel is required.

For a two-piece dowel core to achieve maximum strength and retention

from the dowels in divergent canals, the pieces must be rigidly bound together

after insertion. A number of ingenious methods have been proposed for

accomplishing this. The core can be made in two halves held together by

interlocking lugs which can be formed from a commercially available non-rigid

connector pattern or by cutting a key way or dovetail in one half of the core

pattern. Horizontal bolts have also been described for this purpose.

These interlocking methods can be fabricated by the direct technique, or

by the indirect technique.

Indirect Technique :

A custom dowel core can also be fabricated by making a wax or resin

pattern on a cast of the prepared tooth.

An impression of the prepared canal (elastomeric impression material)

can be made by injecting impression material into the canal.

In order to prevent distortion / displacement of impression material,

during removal from the mouth and pouring of the cast, the impression

is reinforced with some type of rigid dowel. These include paper clips,

orthodontic wire, plastic post and root canal instruments.

Only use plastic posts when they are totally passive and do not bind on

any tooth structure.

When a safety pin or orthodontic wire is selected the coronal portion of

wire should be bent over to form a handled to help retain it in the

impression material.

Notch the wire and coat it with adhesive.

32

Fill the prepared canal with impression material using a slowly rotating

lentulo spiral instrument accompanied by up and down motion to reduce

voids and uniform coating.

Alternatively, an anesthetic needle can be placed to the full depth of the

canal. Syringe additional impression material around the post as well as

the prepared tooth and seat the impression tray.

Remove the impression, evaluate it and pour a cast.

Lightly lubricate the canal of the working cast with die lubricant.

Place notches on the side of a plastic post (tooth pick can also be used)

that seats to the full depth of the canal preparation.

Apply a very thin layer of sticky wax to the plastic post and then add

soft inlay wax (Type II) in small increments, fully seating the plastic

post after each increment of wax is added (Also beading wax can be

used because it is soft and can be easily removed from irregularities and

undercuts in canals).

After the post pattern has been fabricated, the wax core is added and

shaped and then the pattern is removed from the cast, inverted and cast

in metal.

The cat post and core are then cemented in the tooth and the definite

tooth preparation completed.

PROVISIONAL RESTORATIONS (TEMPORIZATION) :

A temporary restoration plays an important role in the successful

restoration of a tooth.

Functions :

1. It protects the tooth from further damage.

2. It prevents migration or drifting of opposing or adjacent teeth.

3. Provides occlusal function

4. Esthetic role

Poly carbonate crowns are well suited for the routine single crown.

33

A custom made plastic shell will probably provide the best result in

shortest time.

Polycarbonate Crown :

In most cases the polycarbonate crowns will not adapt the existing tooth

structure. Excess length is removed from gingival margin of crown while

incisal area is left intact.

A paper clip of appropriate diameter is selected and is placed to the full

depth of the post space. Wire is cut above 2-4 mm of coronal tooth

structure.

Place a bend near the end of the wire. When embedded in the temporary

crown, this bend will prevent the post from pulling out and rotating.

The root surface is highly lubricated with petroleum jelly to prevent any

acrylic resin from sticking to the tooth during polymerization.

A thin mix of temporary acrylic resin is placed around the canal orifice,

avoid pushing resin deep into canal space, because this can make crown

difficult to remove.

Insert the paper clip post into the canal.

Fill the polycarbonate crown with the same acrylic resin.

Seat the crown and confirm it to proper position with the adjacent teeth.

Excess acrylic is removed with a sharp explorer, the temporary crown is

finished and polished.

Temporary cement is placed only in the coronal position of restoration.

Avoid getting cement in canal space.

Seat the pin temporary crown and hold it in place with firm finger pressure

until the cement is set.

CEMENTATION :

Dowels can be cemented with ;

Zinc phosphate

Glass Ionomer

Glass Ionomer Resin

34

Resin Cements

Non Adhesive Cements :

Zinc Phosphate Cement :

Provides retention by interlocking of small mechanical undercuts in the

tooth structure and restorative material.

Inability to bond chemically is a disadvantage.

It retains the restoration, but doesnot increases resistance to fracture, does

not inhibit marginal leakage.

No anticariogenic properties.

Adhesive Cements :

Bond to dentin within the root, residual tooth and dowel.

Glass Ionomer Cement :

Fluoride releasing Anticariogenic.

Moisture sensitive, slow setting, soluble.

GIC – Resin

Moderate retention, high strength

Low or no solubility

High fluoride release

Easy to use

Resin Cements :

Maximum retention, but retreatment difficult

Less microleakage

Cementation Procedure :

Mixed cement is delivered into post space by either lentulo spiral or

endo instruments. Dowel or dowel and core are coated with thin layer of

cement. The post and core is inserted gently to reduce hydrostatic pressure

with little finger pressure.

35

The excess cement is removed, allow some time for cement to set. Then

impression of coronal restoration (crown) is made.

Coronal Radicular Restoration : Alternative to traditional post and core technique for posterior teeth.

When posterior teeth are largely intact, a coronal radicular restoration may

be used.

This restoration consists of a core that extends 2 to 4 mm into the coronal

portion of the canals.

The core is retained by a combination of the divergence of the canals in a

multirooted teeth, natural undercuts in the pulp chamber, adhesion with

dentin bonding agents, retentive channels or preparation in dentin.

Materials used : Amalgam, Bonded Amalgam, Composite, GIC.

Restoration has equal strength to Pin Amalgam.

Technique :

Gutta percha is removed from 2-4 mm of the canals.

Undercuts and irregularities found in the canal wall increase retention of

the restoration.

Restorative materials should be bonded to the available tooth structure to

increase retention, decrease microleakage and increase fracture resistance

of tooth.

The tooth is now ready for final coronal restoration.

Recent advances :

Carbon Fibre Post Carbon fiber posts are made of unidirectional carbon fibers embedded in

an epoxy matrix. Carbon content is 64%.

The system was developed to reduce the occurrence of root fracture due

to wedging of metal posts.

Esthetic versions of this post have a quartz exterior that makes the post

tooth coloured.

36

Design : Smooth sided cylindrical with tapered apical portion.

Diameter : 1- 1.2 mm

Length : 22 mm

Advantages :

Better mechanical properties when compared to metal posts.

Increased strength

Increased stiffness

Increased lightness and

Resistance to corrosion, Chemical bonding with resins.

Chemical bonding with resins - Modulus of elasticity similar to

dentin, high fatigue and tensile strength.

Disadvantages :

Carbon fibre post is grey in appearance.

Replacing carbon with quartz fibre results in a tooth coloured

restoration.

Esthetic Post And Core : Disadvantages of Non Esthetic / Metal Posts :

Metal post and core decreases the translucency of coronal restoration

and the post may shine through in the cervical region.

Non biocompatible

Tendency to corrode

Unequal stress distribution because difference in elasticity between

dentin (18.6 MPa) and metal (200MPa)

Advantages of Esthetic Post and Core :

Maximum esthetic benefit.

As its elasticity is similar to dentin structure, it acts as a shock absorber

and thereby equal distribution of stress.

37

Resistance to corrosion

Biocompatible

Indication :

When patient desires increased esthetic benefit.

CLASSIFICATION

Ceramic Post and Core Fibre Reinforced Post and Core

- Glass ceramic post and core- Glass infiltrated aluminum oxide

ceramic. - Pre fabricated zirconia

endodontic posts

- Aesthetic post (carbon and quart fibers)

- Aesthetic plus post (quartz fibers)- Fiber Kor post (glass fibers in

resin)- Para post fibre white technique- Snow post (silica zirconium glass

fibers in epoxy resin)- Light post- Luscent anchor- Glassix - Mirafit white- Style post- Double taper post system (quartz

fibers and epoxy)

Ceramic Post :

Glass ceramic post and core.

Glass infiltrated aluminous porcelain post and core

Zirconia post : (Tetragonal zirconic poly crystals)

When heated undergoes structural changes enlargement of crystal lattice

Increases toughness.

Design is parallel sided post.

Flexural strength (1400 MPa) and fracture toughness (6-11 MPa) increase

Biocompatible

38

Technique :

Prior to cementation the apical tip of the post is rounded or reduced with the

help of diamond bur to reduce the mechanical stress during and after

cementation. Post is then sand blasted with 50 m aluminium oxide and

cleaned with chloroform.

Dentin bonding agent is applied and post is cemented with chemical cure

composites.

Core semi translucent hybrid composite.

Cosmo Post :

Cylindrical shape with a conical tip.

Disadvantages of Ceramic Post :

Very stiff and strong with no plastic behaviour.

Fiber Reinforced Composite Post :

The addition of fibers to a polymer matrix can result in a significant

improvement in the mechanical properties of strength, fracture toughness,

stiffness and fatigue resistance.

Fibers may be composed of :

Carbon or glass

Silica Woven polyethylene

Ribbon fibre.

Two categories of fiber reinforced posts are available.

Chair side fabricated and prefabricated

Chair side fabricated posts are custom design that uses polyethylene

non-pre-impregnated woven fibers or glass fibers to reinforce the root

and hold a composite core.

Prefabricated post are constructed of two kinds of fiber

o Carbon fibers embedded in an epoxy matrix and

o S type glass fibers embedded in a filled resin matrix

39

Prefabricated Fiber Reinforced Post : Types :

a. Aesthetic Post :

Central core of carbon fibers bundle

Surrounded by quartz fibers

Arranged longitudinally.

b. Aesthetic Plus Post

Entirely of quartz fibres.

c. Light post

Translucent quartz fiber designed to permit light curing material to be

used for luting.

d. Snow Post :

60% longitudinally arranged Si-Zr glass fibers in epoxy resin matrix

(Surface treated with silane to increase bonding with resin cements).

e. Para Post fiber white :

Longitudinally arranged glass fibers.

f. Glassix :

Braided fibre arrangement

For increase resistance to bending and torsion.

g. Mirafit White :

Glass fibre version of mirafit carbon.

h. Luscent Anchor :

Translucent longitudinal glass fibres in resin matrix.

i. Fiber Kor :

Longitudinal glass fibres in filled composite resins.

j. Style Post :

Parallel sided, tapered end quartz fibre post system.

k. Double Taper Post System :

Made up of quartz fibre and epoxy.

40

Quartz fiber/epoxy post is available in translucent (DT light post) for

L.C. composite and off white for (DT White Post) chemical cured

composite.

Consist of 3 post system :

ISO 90, 100, 120

Apical 5 mm 2o for all 3 sizes.

Middle section shows increase chambers from post 1 to 3.

Advantages :

Minimal tooth structure removal during canal shaping.

Greater post to canal adaptation in the apical and coronal half of the

canal.

Good retention.

Lower modulus of elasticity – Less incidence of root fracture.

Clinical Technique :

Luminex Light Transmitting System :

In case of widely flared canals simply placing a post inside the canal

will leave a thick layer of cement. Therefore intraradicular rehabilitation is

required. Canal is reamed to the desired depth with a size matched reamer.

Procedure :

First etching, rinsing, drying, then bonding agent applied and light

cured. Then composite resin is placed inside the canal and light post placed

inside this resin. Light curing of both post and resin is done for 60 seconds.

Then with hemostat light post is removed canal orifice is shortened /

narrowed / rehabilitated.

41

Self cure resin is injected into the canal and luscent anchor is placed into

this self cure resin. Some self cure resin (luxacore) sets within 4 minutes. The

self cure resin is shaped into the desired core shape.

Advantages :

Light passes through post so adequate curing is done all through the

canal.

Advantages of Fiber Resin System :

The modulus of elasticity of post similar to tooth tissues. So better

shock absorber.

Disadvantages :

Fibre post can undergo degradation in the form of repeated mechanical

loading and also in condition of moisture. Therefore decrease in modulus of

elasticity and decrease in flexural strength with increased risk in debonding.

Advantages of Ceramic Post:

Stiffer material.

Disadvantages :

Brittle material

Difficult to remove a fractured ceramic post.

CONCLUSION :

Reinforcing and restoration of badly broken root canal treated teeth can

be done with post core system. Due to the availability of prefabricated posts of

various designs and surface configuration, the fabrication time and costs has

been reduced.

For a successful post core system, the clinician should keep in mind

regarding proper obturation, post space, post length, post diameter, ferrule

design and should preserve the root dentin as much as possible.

42