post endodontic restorations

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Post Endodontic Restorations

Introduction :

Introduction The success of endodontic therapy is attributable, not only to the quality of the endodontics, but to the quality and stability of the post-endodontic restoration (Scianamblo, 1974; Torabinejad et al, 1990; Trope et al, 1995). Ray and Trope (1995) found that endodontic success was more dependent on the quality of the post endodontic restoration than the endodontics itself.

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loss of tooth structure altered esthetic characteristics Altered physical properties due to loss of collagen bound water Effects of Endodontics

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Endodontically treated dog teeth were found to have 9% less moisture than vital teeth. Also, with aging, greater amounts of peritubular dentin are formed, which decreases the amount of organic materials that may contain moisture. It has been shown that endodontic procedures reduce tooth stiffness by 5%, attributed primarily to the access opening.

Possible causes of brittleness:

Possible causes of brittleness Access preparation Extensive caries Absence of pulp and moisture Effect of root canal preparation Resorption

Principles of restoration of root treated teeth:

Principles of restoration of root treated teeth Provide good coronal seal Protection of tooth structure Favorable stress distribution Adequate retention Satisfy functional and esthetic needs Reinforcement

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FACTORS RELATING TO CHOICE OF POST ENDODONTIC RESTORATION Amount of remaining tooth structure Anatomic position of the tooth Functional load on the tooth Esthetic requirements for the tooth

POST AND CORE:

POST AND CORE Introduction History Treatment planning for post and core Classification of posts Factors affecting selection of post Principles of tooth preparation for post and core The ferrule effect Core and core materials Techniques of fabrication Recent advances conclusion

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Why post and core? Retain the core buildup material & Replace the missing portion and to protect the remaining tooth structure Basically consists of Post Core and Final restoration

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POST AND CORE POST(DOWEL): The dowel is a post or other relatively rigid restorative material placed in the root of a non vital tooth” CORE: The core consists of restorative material placed in the coronal area of a tooth It replaces the carious, fractured or otherwise missing coronal structure and retains the final restoration/crown. CLASSIFICATION OF POST(DOWEL): Categorized by number of different ways Broadly categorized into: Custom cast posts and Preformed post systems

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Preformed dowel system can be further categorized based on their geometric shape Tapered posts Parallel posts further classified by their surface configuration as Smooth posts Serrated posts Threaded posts Based on mode of retention of the post to the canal portion Active posts Passive posts v-lock post c-post snow post flexi-post cosmopost aestheti post

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Based on material Non metallic posts C-post Aestheti Plus post Cera post Metallic posts Dentatus post Root post Para post

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Ideal properties of a post .Maximum protection .Adequate retention with in the root .Maximum retention of the core and crown .Maximum protection of the crown margin/cement seal .Pleasing esthetics when indicated .High radiographic visibility .Retrievability .Biocompatibility

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Factors which effect the post selection post length post shape post diameter Surface configuration post material/composition Luting agent

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POST LENGTH Equal to the cervico incisal or cervico occlusal length of crown Longer than the crown Two third the root length Half way between crestal bone and root apex 4.00mm safety zone is required for apical seal

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POST SHAPE Parallel sided parallel sided posts - removal of more tooth structure less chance of root fracture Parallel design improves post retention and force distribution . More retentive than tapered forms Tapered form Produce wedging effect - significant lateral forces vertical root fracture Requires less removal of tooth structure Limited to use in tapered root systems

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POST DIAMETER Increase in diameter - no significant increase in retention -Kurer,Harison Length is most important factor in post retention and diameter is only a secondary factor - Krupp et al Increase in post diameter causes higher stress in the tooth — Mattison

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SURFACE CONFIGURATION Smooth surface - least retentive Serrated surface - more retentive Threaded surface - most retentive intended to engage canal walls significant stress in the tooth

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Threaded Post (Dentatus):

Threaded Post (Dentatus)

Parallel sided serrated post :

Parallel sided serrated post

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Advantages Close approximation High Strength Better fit Disadvantages Less retentive Time and technique Casting inaccuracies Corrosion Unaesthetic The cast post

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Post space preparation

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LUTING AGENTS Resin cements Higher retention Lower microleakage protection by strengthening of root Bonded resin cements - strengthening effects in roots for some period of time Technique sensitive Contamination

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PRINCIPLES OF TOOTH PREPARATION Many of the principles relating to the tooth preparation apply equally to the endodotically treated teeth Additional concepts to avoid failure Conservation of tooth structure Retention form Resistance form

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Conservation of tooth structure ROOT CANAL Remove only minimal tooth structure from the canal Over enlargement lead to weakening or perforation chances of splitting while cementation or functioning Canal be enlarged to enable the post to fit snugly for strength & retention

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Crown The amount of remaining tooth structure is the single most important predictor of clinical success Caries, previous restoration and endodontic cavity preparation considerable loss of tooth structure Further reduction to accommodate the crown and to remove undercuts little coronal dentin As much coronal tooth structure should be conserved to reduce the stress concentration at the gingival margin Extension of the axial wall of the crown apical to the missing tooth structure provides as a ferrule - hold the remaining tooth structure preventing root fracture during function

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RETENTION FORM Retention of the post is mainly affected by – The preparation geometry Post length Post diameter Surface texture The luting agent

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PREPARATION GEOMETRY Anterior teeth Some canals have nearly circular cross section - prepared to give parallel walls or a minimum taper allowing the use of preformed post of respective configuration Retention is proportional to the surface area

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Posterior teeth Relatively long post with circular cross section should be avoided Relatively short posts in divergent canals better retention Widest canals are selected for post placement in posterior teeth

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RESISTANCE FORM An excessive internal preparation of root weakens the root and possibility of failure in restoration Post design should distribute stresses as evenly as possible FACTORS AFFECTING RESISTANCE 1. Crown bevel- Part of the crown extends past post & core margin - extends on natural tooth structure

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2. Vertical remaining tooth structure- 3. Anti rotational features- Oblong canal space provides resistance to rotational forces When coronal dentin is lost, anti rotation element can be placed in the bulkiest aspect of teeth

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Crown& crown preparation Minimum of 2mm dentin axial wall height Parallel axial walls Metal should encircle the tooth Margins on solid tooth structure Not invade attachment apparatus

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THE FERRULE EFFECT FERRULE is a metal ring or cap put around the end of a tool, cane to provide added strength OR Is a vertical band of tooth structure at the gingival aspect of a crown preparation Primarily -- resistance form and enhances longevity Circumferential contra bevel reinforces the coronal aspect Positive occlusal seat - acts as a anti rotational device In teeth with little or no clinical crown remaining large contra bevel on root surface with finish of crown preparation acts as ferrule

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Types of ferrule & Core ferrule and Crown ferrule 2mm of dentin ferrule of crown more effectively enhances # resistance of custom cast post and core. -----JPD2003 Even presence of 1mm of ferrule provides twice the amount of resistance to fracture

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CORE AND CORE MATERIALS The core is anchored to the tooth by a direct connection of the core into canal or through a post The remaining tooth structure can be altered to enhance retention of the core or to provide resistance to core rotation under function The irregular nature -residual coronal tooth structure, morphology of the pulp chamber & canal orifices additional alterations

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Desirable properties of core material include Dimensional stability Ease of manipulation Natural tooth color Rapid and hard setting > immediate crown preparation High compressive and tensile strength High modulus of elasticity and fracture toughness Low plastic deformation Bio compatibility

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CAST CORE A cast core forming a one piece post and core traditional and proven method of restoring a tooth Advantages Core does not depend on mechanical means Can be retrieved for endodontic retreatment Non corrosive when cast with noble metal Disadvantages The number of appointments required are more Laboratory expenses and time required for fabrication Technique sensitive in the laboratory phase

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COMPOSITE RESIN CORE Advantages Ease of manipulation Less time consuming and A additional retention and anti rotation features easily achieved Disadvantages Polymerization shrinkage & contraction- marginal discrepancy & micro cracks Difference in co-efficient of thermal expansion Technique sensitivity Retention of core with zirconium posts

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GLASS IONOMER/ METAL MODOFIED GIC CORE In teeth with significant amount of dentin remaining and additional retention is available Main advantage is the anticariogenic potential High solubility and moisture sensitivity Limited for building up of small area Low retention to preformed dowels Low strength and fracture toughness Technique sensitivity

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RMGIC CORE: Improved properties conventional GIC Bond strength close to that of bonded composite restoration Minimal microleakage Disadvantage Dimensional instability in the presence of moisture > expansion

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CORONAL RADICULAR CORE Used as an alternative - traditional cast post and core This consists of core that replaces the coronal tooth structure extends 2-4mm into coronal portion of root canal Utilizes conventional restorative materials- amalgam , composite resins or modified GIC Provides adequate strength and retention as a core In combination with bonding - gingival discoloration, provides protection against coronal leakage

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TECHNIQUES FOR POST AND CORE FABRICATION Tooth preparation for post and core can be accomplished in 3 steps- 1.removal of root canal filling material 2.enlargement of the canal 3.preparation of the coronal tooth structure post and core fabrication is best done after the coronal preparation of the tooth structure

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REMOVAL OF ENDODONTIC FILLING MATERIAL The amount of gutta percha removal is dictated by the desired post length, type, bone height and the root morphology The Peeso reamers & Gates Glidden drill Available in sizes 0.7-1.7mm & 0.6-1.5mm dia in graduated sizes from 1-6 canal preparation - keyway or a groove with bur no. 170 in the bulkiest portion of Canal to a depth of diameter of the bur and length of bur

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PROCEDURE Measure as large size Peeso reamer as will fit the obturated space against a radiograph leaving apical 5mm of filling with reference to a stable land mark Once gutta percha is removed check the accuracy Enlarge the canal to a desired size - preserve a minimum of 1mm around the post at mid root and beyond and should not be one third the diameter of the root at the CEJ

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PREPARATION OF THE CORONAL TOOTH STRUCTURE Prepare the remaining tooth structure adequately for the extra coronal restoration All internal and external under cuts are removed Any unsupported tooth structure if present should be removed The remaining portion is prepared perpendicular to the post which will create a positive stop while cementing the post

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PREFABRICATED POSTS Enlarge the canal one to two sizes with a drill or reamer smaller than the drill prescribed by the manufacturer A wide range of prefabricated posts shapes and sizes parallel sided prefabricated are recommended for conservatively prepared root canals with roots of circular cross section.

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CUSTOM CAST POST AND CORE FABRICATION TECHNIQUE Direct or indirect technique A direct technique using inlay wax, for single teeth restoration Indirect technique – multiple teeth or tooth with multiple canals The post/pin should extend the full length of prepared canal

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The finish line prepared should be on tooth and not on the core Remove the pattern and proceed with the laboratory steps

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Indirect technique impression is made with a elastomeric impression material with adequate reinforcement to prevent distortion the impression material can either be placed in the canal with a lentulo spiral or can be injected into the post Space impression is removed , evaluated and working cast prepared post pattern prepared and other procedures carried out

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PROVISIONAL RESTRORATIONS IN POST AND CORE FABRICATION A provisional restoration plays an important role in the successful restoration of a tooth FUNCTIONS Esthetics Protection of the tooth from further damage Prevents migration of adjacent teeth provides occlusal function

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crown formers and posts can be used in various combinations- Polycarbonate crowns relined with acrylic Plastic posts relined with acrylic resin Silicone post reinforced with a paper clip or orthodontic wire Braided SS wire with acrylic resin crown SS crowns with reinforcement Reamers or files reinforced with acrylic

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RECENT ADVANCES Prefabricated posts- increasingly popular Ease of placement and Crown preparation FIBER POSTS CARBON FIBER COMPOSITE POSTS- More flexible than metal posts and have same modulus of elasticity of dentin approximately Even distribution of forces when bonded with resins Biocompatible and non cytotoxic Less root fracture Have the highest strength among the fiber posts

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CUSTOM MADE VS PRE FABRICATED POST The canal is prepared to fit the prefabricated post, but custom made post is made to fit the tooth Custom made cast post better adaptation to canal configuration Do not require auxiliary means of retention routinely Gives the best results when change in the path of insertion or crown angulation is required

AMALGAPINS :

AMALGAPINS circular chambers cut vertically into dentin to provide resistance and retention form for the restoration are called amalgam inserts. Preparations for the inserts were made with a No 35 inverted cone bur and were approximately 1.4 mm in diameter and depth Amalgam inserts provided resistance to displacement similar to that provided by self threading pins Shavell described a variation of the amalgam insert, which he termed the amalgapin The amalgapin channel described by shavell was prepared with a No 1157 or 1156 bur and had a depth of 3.0 mm

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The margin of the channel entrance was bevelled to decrease stress concentration in the amalgam It has been demonstrated that a depth of 1.5 to 2.0 mm is adequate for amalgapins and that an amalgapin with a diameter of 0.8 mm provides resistance similar to that of an amalgapin with a diameter of 1.0 mm

CHAMBER RETENTION:

CHAMBER RETENTION For developing foundations in multirooted endodontically treated teeth, an alternative technique has been recommended only when: dimension to the pulp chamber is adequate to provide retention and bulk of amalgam dentin thickness in the region of the pulp chamber is adequate to provide rigidity and strength to the tooth

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Kane et al showed that extension into the root canal space 2 to 4 mm is recommended when the pulp chamber is 2mm or less. When the pulp chamber height is 4 to 6 mm, no advantage is gained from extension into the root canal space. After matrix application, amalgam is thoroughly condensed into the pulp canals, the pulp chamber and the coronal portion of the tooth

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Natural undercuts and divergent canals provide necessary retention form Resistance form is improved by gingival extension of the crown preparation approximately 2mm beyond the foundation onto sound tooth structure. This extension should have a total taper of opposing walls of less than 10 degrees If the pulp chamber height is less than 2 mm, use of prefabricated post, cast post and core, pins slots should be considered After placement of the foundation, the tooth may be prepared for the crown or onlay, and the indirect restoration may be completed.

SHOULD CROWNS BE PLACED ON ENDODONTICALLY TREATED TEETH?:

SHOULD CROWNS BE PLACED ON ENDODONTICALLY TREATED TEETH? It was determined that coronal coverage crowns did not significantly improve the success of endodontically treated anterior teeth. This finding supports the use of a conservative restoration such as an etched resin in the access opening of otherwise intact or minimally restored anterior teeth

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Crowns are indicated only on endodontically treated anterior teeth when they are structurally weakened by the presence of large and/or multiple coronal restorations or they require significant form/color changes that cannot be effected by bleaching, resin bonding, or porcelain laminate veneers.

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Therefore, restorations that encompass the cusps should be used on posterior teeth that have interdigitation with opposing teeth and thereby receive occlusal forces that push the cusps apart.

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Restorations that encompass the cusps of endodontically treated posterior teeth have been found to increase the clinical longevity of these teeth. Therefore, crowns should be placed on endodontically treated posterior teeth that have occlusal interdigitation with opposing teeth of the nature that places expansive forces on the cusps. Since crowns do not enhance the clinical success of anterior endodontically treated teeth, their use on relatively sound teeth should be limited to situations in which esthetic and functional requirements cannot be adequately achieved by other, more conservative restorations.

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CONCLUSION Prefabricated posts - popular + ease of placement and + allow restoring the tooth for immediate crown preparation It is possible to achieve high level of clinical success with most of the current available materials Further understanding and modification currently available material with their physical and mechanical properties will improve their performance.

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