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• introduction• classification of dowels• evolution• effect of Endodontics on the tooth surface• retention triad• resistance triad• carbon fiber posts• considerations in the post design• post length• structural limitation• curvature• ferrule• type of posts and core•

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• In the present era of Aesthetic and Adhesive dentistry, Aesthetic and functional restoration of a pulpless tooth is a demanding challenge

• The post endodontic treatment of teeth, present the dental practitioner with the dilemma of selecting from a large array of materials, technique and designs.

INTRODUCTION

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What is a post?

A relatively rigid material

inserted into the root of an

endodontically treated tooth.

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Post & core:Post & core:

– They can be fabricated from metal or non metallic substances.

– It is used in case of insufficient sound tooth structure remaining above the periodontal attachment to secure a coronal restoration.

– The dowel with in the residual root extends apically to anchor the core material that support the crown.

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• A post is a rod which is securely fixed into the root canal of the tooth root.

• A core is restorative material -which is built up over the root to form the foundation for a crown.

• A core may be build on tooth structure alone, with or without a post or pins.

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• “ The fore most purpose of the dowel is to provide retention for the core and coronal restoration”.

• The dowel functions primarily to aid in the retention of the restoration & to protect the tooth by dissipating or disbursing forces, along the length of the root.

• The dowel itself does not strengthen a tooth.

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FunctionsFunctions

• Replacement

• Retention

• Reinforcement

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EvolutionEvolution• 1728- Pierre Fauchard - “Tenons”

• Mid 1800’s- wood replaced metal

• 1849- Dr.F.H.Clark - “spring loaded dowel”

• G.V. Black- porcelain fused to metal crown ,screwed

into canal filled with gold foil.

• 1888 - “Richmond Crown”, single piece post-retained

crown with a porcelain facing

• 1930’s, the custom cast post and core

• 1960’s- Prefabricated post and core

• 1990’s- Duret et al- Fibre based post

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Classification of dowels:Classification of dowels:

• Based on method of fabrication• Preformed dowels • Custom made dowels• Based on the material of manufacture• Metallic dowels• Non metallic dowels• Based on the esthetics• Esthetic dowels• Non esthetic dowels

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• Weins classification• Tapered smooth sided post• Parallel, serrated & Vented posts• Parallel threaded posts• Parallel threaded split shank posts

• Ingles classification • Tapered, smooth, cemented posts• Parallel sided cemented posts• Tapered self threading• Parallel, threaded inserted into prepared channels

• Custom cast post• Direct technique• Indirect technique

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Ideal properties of the dowel:Ideal properties of the dowel:

• Maximum protection of the root • Adequate retention within the root• Maximum retention of the core & crown• Maximum protection of the crown margin cement

seal• Pleasing esthetics, when indicated• High radiographic visibility• Biocompatibility• Retrievability

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• Indication:• Amount of remaining coronal tooth structure is very less• Abutments in bridge• over dentures

• Contra Indication:• Short roots• In adequate bone support• Traumatic occlusion• Edge to edge bite• Abnormal root curvature• dilacerations

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Effect of endodontics on the Effect of endodontics on the tooth tooth

• The tooth structure that remains after endodontic treatment has been undermined & weakened by all of the previous episodes of caries, fracture, tooth preparation & restoration.

• Endodontic manipulation further removes important intra coronal & intra radicular dentin- result in increased fracture susceptibility & decreased translucency in non vital teeth.

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Changes in the endodonticaly treated toothChanges in the endodonticaly treated tooth

• Loss of tooth structure

• Altered physical characteristics

• Altered esthetic characteristic of the residual tooth

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Loss of tooth structureLoss of tooth structure

• The decreased strength seen in endodonticaly treated teeth is primarily because of the loss of coronal tooth structure. It is not a direct result of endodontic treatment. Endodontic procedures have shown to reduce the stiffness by only 5%, where as MOD preparation reduces the stiffness by 60%.

• The endodontic access in to the pulp chamber destroys the structural integrity provided by the coronal dentin of the pulpal roof & allows greater flexing of the tooth under function.

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Altered physical characteristicsAltered physical characteristics

• tooth structure remaining after endodontic therapy also exhibits irreversibly altered physical properties . changes in collagen cross linking & dehydration of the dentin result in a 14% reduction in strength & toughness of endodontically treated molars.

• Maxillary teeth are stronger than mandibular teeth & mandibular incisors are the weakest.

• The combined loss of structural integrity, loss of moisture, & loss of dentin toughness compromise endodontically treated teeth & requires special care in the restoration of pulp less teeth.

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Altered esthetic characteristicsAltered esthetic characteristics

• Medicaments used in dental treatment & remnants of root canal filling material can affect the appearance of endodontically treated teeth.

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the retention triad (factors effecting the the retention triad (factors effecting the retention)retention)

• Retention is defined as the force that resists a tensile or pulling force.

• The difficulty in restoring an endodontically treated tooth is ,when minimal coronal tooth structure remains, the dentist must consider both retention of the post core and resistance of the post- core crown combination

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• Retention of a post can be gained in 3 ways.

• First method is through adequate post length in the canal

• In the anterior tooth, adequate length is commonly considered to be in the range of 7 to 8mm and 4mm of GP that should be left undisturbed at the apex.

• The design of the post may be either tapered or parallel. The tapered post requires less removal of tooth structure during preparation of the post space but exhibits poorer retention than does the parallel post.

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• However, when the parallel post is employed, more tooth structure must be removed, especially at the apical end of the post space.

• Both of these post designs are acceptable, and the decision should be based on the canal & root configurations ,available post space, and the amount of retention required

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Post style Post style

• the second factor affecting retention is post style

• When the decision is made that the canal length is inadequate to retain a passive post, an active post should be selected. This can occur with short clinical roots or because of obstructions in the canal space.

• An active post can also serve effectively when the canal space has been over- enlarged.

• The active post can actively engage the dentin in its terminal 2 to 3 mm to gain retention

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cements cements

• The third part of the retention triad is the luting agent used to cement the post.

• The idea of bonding a post into the canal with resin cement to increase retention is theoretically appealing.

• But no available cement can overcome the problems created by a poorly engineered post

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Resistance triadResistance triad

• The second and the most important consideration in the design of the post restoration is the resistence of the – tooth- post – crown combination.

• If the resistance of the requirements are not met, the probability of failure is high regardless of the retentiveness of the post

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• 3 parameters of resistence must be considered• Crown bevel• Vertical remaining coronal tooth structure• anti rotation features• These features work in combination, if one of the

features is minimal, or non- existent, one or both of the remaining features must be increased.

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• Bevel margin:• The bevel is, that part of the crown

margin that extends past the post & core margin into the natural tooth structure.

• To be effective, it must be encircle the tooth (360) & ideally extend at least 1.5mm onto tooth structure below the post & core margin. It is not always possible to develop a bevel in every crown preparation & in case of minimal tooth structure.

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• if there is no place to construct the bevel –a simple crown lengthening procedure will generally expose enough tooth structure to allow for bevel placement after healing

• if for esthetic reason, or crown length is very short– orthodontic extrution can be done

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• The second feature of the resistance triad is Vertical remaining tooth structure.

• Traditionally, it was taught that the face of a root should be flattened prior to construction of post & core.

• However, it has been shown that leaving as much natural vertical remaining tooth structure as possible will significantly increase the resistance of the final restoration.

• Unfortunately, because of caries, trauma, or iatrogenic removal, vertical remaining tooth structures is not always available.

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Antirotation:Antirotation:• Every post & core must have

an anti rotation feature incorporated in the preparation.

• An elongated or oblong canal orifice can provide the anti rotation for the post and core.

• However, as the canal becomes more round – anti rotational device is must.

• Auxiliary pins & Keyways – prepared in the face of the root, before construction of the post – are the most common anti rotation devices.

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• If there is no place to construct the bevel – a simple crown lengthening procedure will generally expose enough tooth structure to allow for bevel placement after healing.

• It for esthetic reason, or crown length is very short orthodontic extrution can be done.

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Build up materialsBuild up materials

• 5 widely used core materials

• Glass ionomer

• Resin composite

• Resin modified GIC

• Amalgam

• Cast metal

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How much GP should be retained to preserve the How much GP should be retained to preserve the

apical seal ?apical seal ?..

• 4mm GP retained – only 1 of 89 specimen showed leakage

• 2mm GP retained -whereas 32 of 88 specimens (36% leaked)

• two studies found no leakage at 4mm.

• whereas another study found that 1 of 8 specimen leaked at 4mm.

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• portell et al found that most specimens, with only 3mm of apical GP, has some leakage.

• When the leakage associated with 3,5,7mm of GP was compared, Mattison et al- found significant leakage differences between each of the dimensions.

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• They proposed that at least 5mm of GP are required for an adequate apical seal.

• Nixon et al compared the sealing capabilities of 3,4,5,6,7mm of apical GP using dye penetration. The greatest leakage occurred when only 3mm were retained.

• They also noticed that significant decrease in leakage occurred when 6mm of GP remained

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• Kuist et al examined radio graphs from 852 RCT, posts were present in 424 of the teeth roots with posts in which the remaining root filling material was shorter than 3mm, showed a significant, higher frequency of periapical radiolucencies.

• So, greater leakage only when 2-3mm of GP is present. 4 to 5mm should be retained apically to ensure an adequate seal

• therefore, 5mm of GP should be retained apically.

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Considerations in post design:Considerations in post design:Dowel design & dowel retentionDowel design & dowel retention

• .Studies have found retention to be increased in dowels-- with parallel sides, serrated surfaces & longer lengths.

• Parallel sided dowels are more retentive than tapered dowel, & they distribute functional loads to the root more passively than tapered dowel.

• Serrated surfaces of metal dowels increase retention over smooth metal surfaces by, providing mechanical undercuts for cement.

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• However carbon fiber & fiber reinforced, composite resin dowels are smooth to preserve the integrity of the fiber bundles. B’coz there dowels are commonly cemented with resin cements, retention is achieved with chemical bonding, no mechanical undercuts.

• Dowel retention is also proportional to dowel length. In traditional dowels, increasing the length of metal dowels increases the retention.

• Carbon fiber, carbon core & fiberglass – reinforced composite dowels with bonded retention may not need to as long as traditional dowels.

• 1.1 ratio between the dowel length & the replacement crown is sufficient.

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Post length:Post length:

• Range of recommendations are • Post length should equal the inciso cervical or

occluso cervial dimension of the crown.• The post should be longer than the crown• The post should be one, one third the crown length• The post should be half the root length• The post should be 2/3 the root length• The post should be 4/5 the root length • The post should be terminated half way between the

crestal bone & root apex• The post should be as long as possible without

disturbing the apical seal.

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Post diameterPost diameter

• Post diameter is not exceed 1/3 the root diameter.• It has been determined that when a root canal is

prepared for a post and the diameter is increased beyond 1/3 of the root diameter, the tooth becomes weaker

• Each millimeter of increase (beyond 1/3 the root diameter) caused a six fold increase in the potential for root fracture.

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Study for post diameterStudy for post diameter

• Study 1: Study of 700 teeth recommended that post diameter should range from 0.7mm for mandibulare incisors to a maximum of 1.7 mm for maxillary central incisors.

• Since 5mm of gutta perch be retained apically to ensure a good seal (as measured radiographically). Post should be extended to that length in all teeth except molars.

• In molar – posts should be placed in the primary roots (ie palatal root of maxillary & distal root of madibular molars) & should not be extended more than 7mm apical to the origin of the root canal in the base of the pulp chamber.

• Extension beyond this length can lead to root perforation or only very thin areas of remaining tooth structure.

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Anatomic/ structural limitationsAnatomic/ structural limitations

• The practitioner who complete the endodontic treatment is ideally suited to identify characteristics of the pulp chamber, the anatomy of the root canals, and completed endodontic filling that should be reviewed before placing a post and core.

• These characteristics include the presence and extent of dentinal craze lines, identification of teeth for which further root preparation will result in less than 1mm of remaining dentin or a post diameter grater than one third the root diameter area, information regarding areas in which the remaining tooth structure in thin, and the post at which significant root curvature begins.

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Craze linesCraze lines

• Craze lines in dentin, are areas of weakness. Where further crack propagation may result in root fracture and tooth loss.

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Root curvatureRoot curvature

• When root curvature in present, post length must be limited to preserve remaining dentin, there by helping to prevent root fracture or perforation

• Root curvature occurs most frequently in the apical 5 mm of the root. i.e if 5mm of gutta percha retained apically, curved portions of the root are usually avoided.

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ferruleferrule

• Ferrule is an encircling band of cast metal around the coronal surface of tooth

• It is a metal ring or cap used to strengthen the end of a stick or tube

• They increases the tooth resistence to fracture• Furrules r more effective when the crown encompasses

relatively parallel prepared tooth structure than when it engages beveled/sloping tooth surfacess

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Type of post & coreType of post & core

• Post – or dowels can be generally classified as cement/ bonded posts or threaded posts.

• Cemented posts depend on their close proximity to prepared dentin walls & the cementing medium. Examples are– custom cast posts & cores & variety of prefabricated designs.

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• The prefabricated designs include parallel sided metal posts, or different types of threaded posts.

• A. tapered,smooth• B.parallel serated• C.tapered,self threading• D.parallel,threaded• E.parallel,serated,tapered end

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• Other recent post are- carbon fiber post, ceramic posts fiber reinforced polymers & zirconium post, zirconium coated carbon fiber posts.

• Research indicates that carbon fiber posts possess adequate rigidity, are not prone to produce tooth fracture.

• They can be removed from the tooth• Ceramic posts have very high flexural strengths and are

very hard• Compared with metal posts, these fiber reinforced posts

reduced the incidence of vertical root fracture.

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EVOLUTION OF AESTHETIC POSTS

CARBON FIBRE

CARBON+QUARTZ

QUARTZ / GLASS

LIGHT TRANSMITTING

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Fiber based post system --Fiber based post system --carbon fiber postscarbon fiber posts

• This is a non- metallic material, based on carbon- fiber reinforcement principle.

• The chemically bondable carbon fiber posts are made up of parallel carbon or silica fibers surrounded by a matrix of polymer resin, usually an epoxy resin

• The fibers are unidirectional & approximately 8 micros in diameter uniformly embedded in epoxy matrix & are aligned along the long axis of the post.

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• The carbon fiber acts as the filler of the system.• Carbon- fiber posts are black in color -so do not

lend themselfs to aesthetic restorations with – all ceramic units.

• Silica- fiber posts which are translucent & more tooth colored. There posts are also called -Glass fiber and quartz- fiber posts.

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• The resin fiber post is more similar in its characteristics to natural dentinal structure than any previously used post.

• It has excellent transverse strength and acts as a shock absorber, dissipating much of the stress place on the finished restoration, transmitting only a small fraction of these forces to the dentinal wall.

• It is delivered to the patient in a single appointment & is a chair side procedure.

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• Fibers are composed of woven polyethylene, glass, or carbon. In addition of these fibers, improves the mechanical properties of strength, fracture toughness, stiffness, and fatigue resistance.

• Carbon posts were grey in appearances. Replacing carbon with quartz result in tooth colored post

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• Disadvantages:

• Water sorption

• Hydrolytic instability.

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Do we really need a post ?Do we really need a post ?

• Previously it was considered necessary to insert a post to ‘reinforce’ a badly broken down tooth.

• This is no longer widely believed, in fact a post may actually weaken the tooth

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Avoid a post if possible !Avoid a post if possible !

• If the tooth can be rebuilt without pins or posts, using modern bonding techniques, that is preferable

• A post is only considered where there is little or no tooth structure left.

• A POST IS THE LAST RESORT

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•

• Thank u

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technical procedurestechnical procedures

• Coronal tooth preparation:• Post & core fabrication can often best be done,

after the coronal tooth preparation has been completed. The amount of tooth structure that needs to be removed is related to the type of crown to be used & that inturn, determines the extent of core fabrication.

• i.e if some of the remaining tooth structure is very thin after the coronal preparations, it is better to remove that part of dentin & replace it as part of the core.

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• Pulp chamber preparation:• The pulp chamber should be cleaned of any

filling material prior to post space preparation. • If a prefabricated post in to be used,

Undercuts & irregularities in the pulp chamber will help retain the core material.

• If a custom post is indicated, the undercuts in the chamber should be blocked out with filling material or eliminated by removing tooth structure.

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• Root canal preparation:• The best time to prepare the post space is at the time

the root canal treatment in completed.• If the post space needs to be prepared later, the gutta-

percha can be removed using either a warm endodontic plugger, or endodontic file or slow – speed rotary instrument such as gates- glidden drill or a peeso drill.

• The root canal filling material should be removed incrementally until the desired post space dept is achieved.

• For measuring preparation depth use periodontal probe.

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• Prefabricated cemented or bonded post/ Restorative Material core:• The root canal filling material is removed using a warm endodontic plugger

or a small – diameter rotary instrument until the desired post depth is achieved.

• The canal is enlarged is size using the rotary instrument that corresponds to the final dimension of the selected post.

• The post should fit passively into the post space without substantial movement.

• At least the apical half of the post should fit closely to the preparation.• The coronal half of the post may not fit as well because of the root canal

flaring. However, this leack of adaptation can be corrected when the core material is placed around the cemented post.

• If the root canal, cannot be prepared to conform to the round shape of the posts have adequate approximation to the root canal walls, then a custom cast post may be preferable

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• .• Care must be taken not to remove more dentin at the apical extent

of the post space than, is necessary.• Radiographic confirmation is important to ensure proper seating &

length of the post.• The incisal/occlusal end of the post is shortened. So that it does not

interfere with the opposing occlusion, but it must provide support & retention for the restorative core material (2-3mm)

• When metal posts are used, they can be bent coronally, if necessary, to align them within the core material. Post bending in done outside the mouth with orthodontic pliers.

• The post is elecmented into the root canal using resing bonding procedures.

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• If there is little or no remaining coronal tooth structure to provide resistance to core rotation, an auxillayr threaded pin should be placed into the remaining tooth structure.

• Restorative material is then condensed around the post or bonded to the post & remaining tooth structure.

• A slight excess of material is placed, and this is removed during crown preparation.

• The definitive tooth preparation is then completed, and an impression is made for the crown.

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• Direct Procedure:• Select a plastic post that fits within the confines of the post

preparation with out binding leave the post sufficiently long that it can be easily grasped.

• Lightly lubricate the canal.• Place notches on the side of a plastic post pattern if the pst in

smooth & seat it to the depth of the prepared canal.• Use the bead- brush technique to apply resin to the prepared canal

& the body of the plastic post. Seat the post into the full depth of the canal.

• Do not allow the resin to completely harden within the canal. Remove and reseat the post & attached resin several times while the resing in still in its rubbery stage so that the pattern does not inadvertently become locked into the canal.

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• Remove the & polymerized pattern and inspect the resin for integrity and lack of voids.

• Add additional coronal resin toform the desired dimensious of the core remove & reseat the pattern as previously described to prevent it from becoming locked into the coronal tooth structure.

• The core is then removed, invested, and cast.• The posts core are trial placed, adjusted, and then

cemented. The definitive tooth preparation can then be completed.

• A pattern can also be developed using wax rather than resin

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• Indirect procedure:• Nonaequoe us clastomeric impression material make accurate impressions

of the prepared root canal, but some method of supporting the impression material prevents distoration/ displacement of the set material during removal from the mouth & pouring of the cast.

• A metal wire, safety rins plastic posts, orthodontic wire have been used for this purpose.

• When a safety pin or orthodontic wire is selected as the means of supporting the impression material, the coronal portion of the wire should be bent over to form a handle to help retain it in the impression material.

• Fill the prepared canal with impression material using a slowly rotating lentulo spiral instrument accompanied by an up and down motion.

• Seat the wire is plastic post through the impression material to the full depth of the canal.

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ss

• Remove the impression, evaluate it and pour a cast

• Make an interocclusal record & obtain an opposing cast & appropriately sized plastic post to be used in forming a wax pattern.

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

• Place notches on the side of plastic post that seats to the full depth of the canal preparation.

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