endodontically_treated post&core system impt

8/9/2019 Endodontically_Treated Post&Core System IMPT

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Restoration of

EndodonticallyTreated Teeth

Post andand Core System


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Characteristics of endodontically treated teethCharacteristics of endodontically treated teeth1. Tooth structure loss by:

i. Caries, trauma, erosion, abrasion, attrition.

ii. Previous restorations and recurrent caries under restorations.

iii. Endodontic treatment; due to removal of coronal and intraradicularDentine during access and root canal preparation.

2. Micro cracks in remaining tooth structure produced by endodonticprocedures.

3. Weakened collagen intermolecular cross-links of Dentine lower shearstrength.

4. Dehydration; non-vital teeth have less moisture content than vital teeth.

5. Esthetics; biochemically altered Dentine modifies light refraction through the

tooth and modifies its appearance.

The combined result of these changes are: increased fracturesusceptibility and decreased translucency.


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Treatment planning for nonTreatment planning for non--vital teethvital teeth

1. Pretreatment Evaluation:

i. Quality of the endodontic

treatment

ii. Periodontal conditioniii. Restorative evaluation

i.i. Strategic importanceStrategic importance

ii.ii. Anatomic position of theAnatomic position of the

toothtooth

iii.iii. The amount of remainingThe amount of remaining

coronal tooth structurecoronal tooth structure

iv.iv. The functional load on theThe functional load on thetoothtooth

iv. esthetic evaluation

2. Treatment plan:

i. Post

ii. Core

iii. Definitive restoration


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Treatment planning for nonTreatment planning for non--vital teethvital teeth

1. Pretreatment Evaluation:

i. Quality of the endodontic treatment:

The endodontic treatment should be properly done.

Retreatment should be considered if tooth exhibits any clinical

signs of inflammation, a periapical pathology exists, orinappropriate endodontic filling material was used ( silver

pointes).

ii. Periodontal condition:

This is important for long-term success of teeth.

Weak teeth should be extracted.

A mutilated tooth in which the restorative treatment would violatethe junctional epithelium or the attachment level (e.g. extensive

caries, perforations, external root resorption) should be

considered for crown- lengthening surgery or orthodontic

extrusion.


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iii. Restorative evaluation:

a.a. Strategic importanceStrategic importance::

does the final restoration depends on this tooth ? Are theadjacent teeth reliable? What about an implant ?

b.b. Anatomic position of the tooth:Anatomic position of the tooth:

Anterior teeth:

They receive mainly angular forces reinforcementeffect of posts is doubtful.

If the tooth is intact except for the endodontic accessopening etched resin in the access is sufficient.

A post and core is only indicated when the tooth isweakened by the presence of large or multiple coronalrestorations or they require form or/and color changesthat cannot be affected by bleaching, resin bonding orlaminate veneers.

Mandibular incisors and maxillary lateral incisors usually require a post.

Maxillary central incisors and canines crownpreparation, the remaining tooth structure, isaccomplished before deciding a post should be placed.


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Posterior teeth:

They receive mainly vertical forces.

When there is sufficient tooth structure to retain a core andcrown posts are not needed.

Teeth which dont have occlusal interdigitation or have an

bucco-occlusal form that preclude interdigitation ( e.g.

Mandibular 1st premolars with small poorly developed lingual

cusps) , with sufficient coronal tooth structure, restoration of

the access should be acceptable. Teeth which have interdigitation with opposing teeth full

coverage crowns or onlays should be used as occlusal forces

push the cusps apart.

Maxillary premolars are subjected to angular and vertical

forces if the clinical crown length > its cervical width a post

may be indicated.


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c.c. The amount of remaining coronal tooth structure:The amount of remaining coronal tooth structure:

More than half conservative treatment with coronalrestorations without posts.

minimal post, core, and definitive restoration.

d.d. The functional load on the tooth:The functional load on the tooth:

The post, core, and crown system is indicated, when more

extensive protective and retentive features are required in

the restoration:

1) Bruxism and heavy occlusion.

2) Abutment teeth for long-span fixed bridges.

3) Abutment teeth for free end removable partial denture.


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iv. esthetic evaluation:

Esthetic zone (Anterior teeth, premolars, and

often 1st molar) requires:

1) Careful selection of restorative materials.

2) Careful handling of the tissues.

3) Timely endodontic intervention to prevent

darkening of the root as it looses vitality.


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2. Treatment plan: (post and core)

The purpose of a post is to provide retention for a core; as both

laboratory and clinical data fail to provide definitive support for theconcept that posts strengthen endodontically treated teeth.

If the walls of the root are thin owing to removal of internal root caries

or over-instrumentation during post preparation then a post may

strengthen the tooth.

Reinforcement of a tooth by a post means: moving the point of

fracture from the gingival margin of the crown some distance up theroot towards the root apex.

The following characteristics should be determined prior to beginning

the clinical procedures :

1) Post length

2) Post diameter

3) Type of post and core that will be used (prefabricated post andrestorative material core or anatomically customized cast post and core)

4) Root selection in multi-rooted teeth

5) Core material and definitive restoration.


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1) Post Length:

It is of more importance for retention than diameter. 4 - 5 mm of gutta-percha should be retained apically to ensure a good

seal.

posts should be extended to that length, or equivalent to the crown

length, in all teeth except molars. With molars, posts should not be extended more than 7 mm from the

orifice of 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.

Posts should extend 4 mm apical to the bone crest to decrease stress

in dentine and in the posts.


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2) Post Diameter:

It is important to resist distortion or permanent bending underfunctional forces.

Ideally, after completion of endodontic treatment, the canal shouldntbe further enlarged. Rather, the post should be modified to fit thecanal.

Do not exceed one-third the root diameter.

Optimal post diameter measurements have been determined to be:

1) Mandibular incisors 0.6 0.7 mm

2) Maxillary central incisors, canines, and the palatal root of themaxillary 1st molar 1.0 1.2 mm & may even reach 1.7 mm.

3) The rest of teeth 0.8 mm.

Mesial roots of mandibular molars and the buccal roots of maxillarymolars shouldnt be used for posts.

Mandibular premolars with oval or ribbon shaped canals shouldnt beprepared further for a post the gap is filled with luting cement whichadd elasticity to it.

Roots with remaining dentine thickness less than 1mm are indicatedFor custom made posts.

The amount of remaining intraradicular dentine after endodontictreatment:

Canines, maxillary incisors, and the palatal root of maxillary 1st

molar = > 1mm.

All other teeth = < 1mm.


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N.B

Craze Lines:Craze lines in dentin are areas of weakness where

further crack propagation may result in root fracture

and tooth loss.

The patient should be informed of their presence. Ifpossible, avoid post placement in favor of a

restorative material core.

If a post is required, it should passively fit the canal,

and the definitive restoration should entirely

encompass the cracked area, whenever possible, by

forming a ferrule.


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3) Type of post:

A. Acc. to type of material:

Metallic.

Non-metallic:

1. Carbon fiber posts: composed of unidirectional carbonfibers in an epoxy matrix. Esthetic version containsquartz. It is smooth, rigid, highly radiopaque, and can beremoved.

2. Ceramic posts: composed of zirconium dioxide. It is hardand can withstand high flexural stresses.

3. Fiber-reinforced posts: composed of woven polyethylenefiber ribbon that is coated with a dentine bonding agentand packed into the canal, when it is light cured. It isesthetic, smooth, less stiff, reduce incidence of rootfracture, and less radiopaque.

Excessive retention of zirconia (ceramic) posts may precludeconventional endodontic retreatment if cannot be removedatraumatically.

Carbon fiber and Fiber-reinforced posts may not need to be aslong as traditional posts. A 1:1 ratio between the post and thecrown is sufficient.


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In laboratory tests metallic posts are more fracture resistant than carbon

fiber posts.

Most metal, carbon fiber, and ceramic posts chemically bond to resin

cement.

Stainless steel posts are more retentive to composite cores than carbon

fiber posts.

Carbon fiber and Fiber-reinforced posts have a lower modulus of elasticity

than metal posts and are considered to have elasticity similar to dentine,

this provide more force dissipation, reducing the risk of root fracture.

Stainless steel contains nickel which may cause allergy. Non-metallic

posts are highly biocompatible.

Prefabricated Stainless steel posts may show corrosion. Custom-cast and

non-metallic posts dont show corrosion.


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B. Acc. to retention:

Active: include many designs (e.g. threaded, split threaded).they produce high stresses which increase the potential forvertical fracture. They should be unscrewed one fourth of aturn after installation. Split threaded posts even produceshigher stresses. Active posts are indicated in short canals.

Passive: it is cemented to the root canal using zincphosphate, glass ionomer, or a resin cement. Resin modifiedglass ionomer is not indicated as hygroscopic expansion maycause root fracture. Low expansion formulations of resinmodified glass ionomer can be used.

C. Acc. to fabrication:

Pre-fabricated post:

tapered smooth, se , or threaded.

parallel smooth, se , or threaded

Custom-cast post:

indicated in:

i. Non-rounded root canals.

ii. Extremely divergent sidewalls of root canals.


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Tapered smooth posts are the least retentive. And may cause

wedging effect on the tooth. Tapered threaded posts are more retentive than parallel

threaded.

Parallel posts distribute stresses less evenly and cause apical

stress concentration.

Tapered posts cause post-core junction stress concentration and

equal stress distribution between the cementoenamel junctionand the apex. So , it should be considered for teeth that have thin

apex.

Tapered posts require no further canal preparation after

endodontic treatment as it can be modified to fit into the canal.

So, it can be used in thin fragile roots.

Venting and surface roughness are important features whichshould be added to custom-cast posts.


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4) Root selection in multi-rooted teeth

posts are best placed in (the primary roots) in palatal roots of

maxillary molars distal roots of mandibular molars, they are the.The buccal roots of maxillary molars and the mesial root of

mandibular molars should be avoided if at all possible. If these

roots must be used in addition to the primary roots, then the post

length should be short (3 to 4 mm) and a small-diameter

instrument should be used (no larger than a No. 2 Peeso

instrument, which is 1.0 mm in diameter).

Use cast interlocking post:

It is two pieces, characterized by depressions parallel to the

sidewalls of other canal. The distal post is put first then the other

will interlock with it finally.


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Technical procedure for prefabricated postsTechnical procedure for prefabricated posts


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Pattern construction of custom-cast post

I. Direct method

Material:

A. Wax.

B. Self cure A.R.

C. Plastic ready-made burn out post.

Steps:

1. Lubrication of root canal (die lubricant).

2. If direct wax pattern:

1) Select a metallic sprue former:

- Fits loosely inside R.C.

- Length > than that of core.

- Serrated using diamond stone or disc (to ensure good retention

bet. wax & sprue).2) Softening of blue casting wax and insertion into the R.C.

3) Heating of sprue.

4) Wait till hardening of wax.

5) Add for any deficiencies until its removed with slight resistancesnugly fit.

6) Core can be made of wax, followed by investing and casting.


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3. If direct A.R. pattern:

1) Select a plastic dowel:

- Fits loosely inside R.C- Long.

- Serrated (notched).

2) Mixing of A.R. and insertion into the R.C. before the dough stage.

3) Before complete curing, moisten the dowel with monomer andinsert into R.C.

4) Also before complete curing, move the plastic dowel inward andoutwards to prevent interlocking in any undercuts or roughness.

5) Add any modifications until its removed with slight resistancesnugly fit.

6) Investing and casting.

4. Plastic ready made burnout post:

1) Plastic posts supplied with its special drills (same size & shape).2) Prepare root canal.

3) Build up core with wax or acrylic resin.

4) Investing and casting.


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II. Indirect method:

Steps:1. Impression:

- By light body elastomer applied by a syringe, starting from apex.

- Insert an st.steel wire to: 1- support imp. Material.

2- prevent imp. tearing during

removal.

- Use a (Cu band) or (tray) to complete impression procedures.

- Remove the impression and evaluate it, then pour a stone cast.


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endodontically_treated post&core system impt

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