Fixed prostho Endo Teeth Restoration

FP notes

POST

Rationale 3Rs

RETENTION

Ability13 of13 a13 post13 to13 resist13 vercal13 dislodging13 forces13

Length 13 increasing13 the13 length13 and13 diameter13 of13 the13 post13 can13 increase13 retenon

Diameter Diameter13 is13 less13 important13 than13 the13 other13 factors13 listed13 Even13 though13 retenon13 can13 be13 increased13 slightly13 by13 enlarging13 the13 post13 diameter13 the13 loss13 of13 tooth13 structure13 weakens13 the13 tooth

Taper 13 Parallel13 posts13 are13 more13 retenve13 than13 tapered13 posts

Lung13 cement

Acve13 vs13 passive13 Acve13 posts13 are13 more13 retenve13 than13 passive13 posts

REISISTANCE

ability13 of13 the13 post13 and13 tooth13 to13 withstand13 lateral13 and13 rotaonal13 forces

bull Influenced13 by13 13

bull remaining13 tooth13 structure13

bull postrsquos13 length13 and13 rigidity13

bull presence13 of13 anrotaon13 features13

bull presence13 of13 a13 ferrule13 13

bull A13 restoraon13 lacking13 resistance13 form13 is13 not13 likely13 to13 be13 a13 long-shy‐term13 success13 regardless13 of13 the13 retenveness13 of13 the13 post

REINFORCEMENT

NO bull Sorensen13 et13 al13 198413 (see13 below)13

bull Trope13 M13 1985In13 vitro13 study13 of13 6413 extracted13 maxillary13 central13 incisors13 placed13 in13 copper13 rings13 filled13 w13 cement13 subjected13 to13 slowly13 increasing13 compressive13 force13 ll13 fracture13 occur13 113 The13 preparaon13 of13 a13 post13 space13 significantly13 weakened13 endodoncally13 treated13 teeth 213 A13 post13 (steel13 parapets13 w13 ZnPO413 cement)13 did13 not13 significantly13 strengthen13 endodoncally13 treated13 teeth 313 When13 a13 post13 space13 was13 prepared13 acid13 etching13 and13 restoraon13 with13 a13 composite13 resin13 strengthened13 the13 teeth13 more13 than13 the13 other13 restorave13 methods13 used

Maybe bull A13 post13 and13 core13 may13 help13 prevent13 coronal13 fractures13 when13 the13 remaining13 coronal13 tooth13 structure13 is13 very13 thin13 ajer13 tooth13 preparaon13

bull When13 loaded13 vercally13 along13 the13 long13 axis13 a13 post13 reduced13 maximal13 denn13 stress13 by13 as13 much13 as13 2013

bull reinforcement13 effect13 of13 posts13 is13 doubwul13 for13 anterior13 teeth13 because13 they13 are13 subjected13 to13 angular13 forces(Goodacre13 and13 Spolnik13 199513 Part13 1)

laurarsquos notes 7

FP notes

13 13

Sorensen13 JA13 Marnoff13 JT13 Intracoronal13 Reinforcement13 and13 coronal13 coverage13 A13 study13 of13 Endodoncally13 Treated13 teeth13 J13 Prosthet13 Dent13 198413 51780-shy‐84

Study design bull13 Retrospecve13

bull Endodoncally13 treated13 teeth13

bull Mul-shy‐pracce13 613 densts13

bull 127313 teeth13 selected13 from13 600013 paent13 records13

bull 113 to13 2513 year13 Follow-shy‐Up13

bull Perio13 and13 Caries13 failure13 excluded13

bull Definion13 of13 Failure13 ndash13 Dislodgement13 13 Fracture13

bull NOT13 Survival13 Analysis13 BUT13 Retrospecve13 Records13

bull Confounding13 Variables13

Conclusions Posts13 intracoronal13 reinforcement13 did13 NOT13 significantly13 increase13 the13 clinical13 success13 rate13 (resistance13 to13 fracture13 or13 dislodgement)13 of13 any13 of13 the13 anatomic13 groups13 of13 endodoncally13 treated13 teeth13 =gt13 posts13 do13 not13 reinforce13 teeth

Coronal13 coverage13 Anterior13 teeth13 (max13 amp13 mand)13 -shy‐13 NO13 improvement13 in13 clinical13 success13 rate

Posterior13 teeth13 (max13 amp13 mand)13 -shy‐13 YES13 rate13 of13 clinical13 success13 was13 significantly13 improved13 with13 coronal13 coverage13 9413 of13 endodoncally13 treated13 molars13 and13 premolars13 that13 subsequently13 received13 coronal13 coverage13 were13 successful13 while13 only13 5613 of13 occlusally13 unprotected13 endodoncally13 treated13 posterior13 teeth13 survived

laurarsquos notes 8

In the planning of the restoration of endodonti-cally treated teeth the practitioner must account forthe strength of the remaining tooth structureweighed carefully against the load to which therestored tooth will be subjected

Considerations for Anterior TeethEndodontically treated anterior teeth do not alwaysneed complete coverage by placement of a completecrown except when plastic restorative materialshave limited prognosis (eg if the tooth has largeproximal composite restorations and unsupportedtooth structure) Many otherwise intact teeth func-tion satisfactorily with a composite resin restoration

Although it is commonly believed it has not beendemonstrated experimentally that endodonticallytreated teeth are weaker or more brittle than vitalteeth Their moisture content however may bereduced7 Laboratory testing8 has actually revealed aresistance to fracture similar between untreated andendodontically treated anterior teeth Neverthelessclinical fracture does occur and attempts have beenmade to strengthen the tooth by removing part of theroot canal filling and replacing it with a metal postIn reality placement of a post requires the removalof additional tooth structure (Box 12-1) which islikely to weaken the tooth

Cementing a post in an endodontically treatedtooth is a fairly common clinical procedure despitethe paucity of data to support its success In fact alaboratory study9 and two stress analyses1011 havedetermined that no significant reinforcementresults This might be explained by the hypothesisthat when the tooth is loaded stresses are greatest atthe facial and lingual surfaces of the root and aninternal post being only minimally stressed doesnot help prevent fracture (Fig 12-5) Results of otherstudies however contradict this assumption812

Cemented posts may further limit or complicateendodontic re-treatment options if these are neces-sary In addition if coronal destruction occurs postremoval may be necessary to provide adequatesupport for a future core

For these reasons a metal post is not recom-mended in anterior teeth that do not require complete coverage restorations This view is sup-ported by a retrospective study13 that did not showany improvement in prognosis for endodonticallytreated anterior teeth restored with a post Inanother study post placement did not influence theposition or angle of radicular fracture14 A conflict-ing report however suggests that endodonticallytreated teeth not crowned after obturation were lostsix times more frequently than teeth that werecrowned after obturation15

Discoloration in the absence of significant toothloss may be more effectively treated by bleaching16

than by the placement of a complete crownalthough not all stained teeth can be bleached suc-cessfully Resorption can be an unfortunate sideeffect of nonvital bleaching17 However when loss ofcoronal tooth structure is extensive or the tooth willbe serving as an FDP or partial removable dentalprosthetic abutment a complete crown becomesmandatory Retention and support then must bederived from within the canal because a limitedamount of coronal dentin remains once the reduc-tion for complete coverage has been completed

Chapter 12 RESTORATION OF THE ENDODONTICALLY TREATED TOOTH 339

Box 12-1 Disadvantages to the Routine Use ofa Cemented Post

Placing the post requires an additional operativeprocedure

Preparing a tooth to accommodate the post entailsremoval of additional tooth structure

It may be difficult to restore the tooth later whena complete crown is needed because thecemented post may have failed to provideadequate retention for the core material

The post can complicate or prevent futureendodontic re-treatment that may be necessary

PostLoad

Post Tension

Neutral axis

Compression

A

B

A

B

Fig 12-5Experimental stress distributions in an endodontically treatedtooth with a cemented post When the tooth is loaded thelingual surface (A) is in tension and the facial surface (B) is incompression The centrally located cemented post lies in theneutral axis (ie not in tension or compression) (Redrawn fromGuzy GE Nicholls JI In vitro comparison of intact endodontically treated teethwith and without endo-post reinforcement J Prosthet Dent 4239 1979)

FP notes

MATERIAL OF POST

1) Cast post core

Indicaon bull When13 a13 tooth13 is13 misaligned13 and13 the13 core13 must13 be13 angled13 in13 relaon13 to13 the13 post13 to13 achieve13 proper13 alignment13 with13 the13 adjacent13 teeth13

bull Small13 teeth13 such13 as13 mandibular13 incisors13 when13 there13 is13 minimal13 coronal13 tooth13 structure13 available13 for13 anrotaon13 features13 or13 bonding

+ve13 bull13 Advantages13 in13 certain13 clinical13 situaons13 13

bull when13 mulple13 teeth13 require13 posts13 more13 efficient13 to13 make13 an13 impression13 and13 fabricate13 them13 in13 the13 laboratory13 rather13 than13 placing13 a13 post13 and13 buildup13 in13 individual13 teeth13 as13 a13 chair-shy‐side13 procedure13

bull generally13 easy13 to13 retrieve13 when13 endodonc13 retreatment13 is13 necessary13

bull Possible13 to13 fabricate13 replacement13 crown13 without13 need13 for13 post13 removal13 13

bull Path13 of13 placement13 different13 from13 that13 selected13 for13 post13 and13 core13 may13 be13 selected13 for13 crown13 (especially13 when13 restored13 tooth13 serves13 as13 abutment13 for13 FDP)13

-shy‐13 ve bull Require13 two13 appointments13 temporizaon13 and13 a13 laboratory13 fee13

bull Less13 conservave13 of13 tooth13 structure13 because13 cannot13 have13 undercuts13

bull Biggest13 disadvantage13 -shy‐13 require13 an13 esthec13 temporary13 restoraon13

bull Temp13 postcrowns13 are13 not13 effecve13 in13 prevenng13 contaminaon13 of13 the13 root-shy‐canal13 system13 13

bull When13 a13 temporary13 post13 and13 crown13 is13 needed13 a13 barrier13 material13 should13 be13 placed13 over13 the13 obturang13 material13 and13 the13 cast13 post13 and13 core13 should13 be13 fabricated13 and13 cemented13 as13 quickly13 as13 possible

2) Ceramic amp zirconia post

+ve bull13 Esthec13 can13 use13 for13 translucent13 all13 ceramic13 restoraons13

-shy‐ve bull Weaker13 than13 metal13 posts13 so13 a13 thicker13 post13 is13 necessary13 which13 may13 require13 removal13 of13 addional13 radicular13 tooth13 structure13

bull Not13 possible13 to13 bond13 a13 composite13 core13 material13 to13 the13 post13 making13 core13 retenon13 a13 problem13 13

bull Retrieval13 of13 zirconium13 and13 ceramic13 posts13 is13 very13 difficult13 if13 endodonc13 retreatment13 is13 necessary13 or13 if13 the13 post13 fractures

3) Fibre Elastic post

Characterisc13

More13 flexible13 than13 metal13 posts13 and13 had13 approximately13 the13 same13 modulus13 of13 elascity13 (sffness)13 as13 denn13 13 Elasc13 posts13 the13 tooth13 cement13 and13 post13 will13 all13 deform13 during13 funcon

+ve13 Reinforcing13 effect

bull Reinforcement13 abilies13 of13 fibre13 reinforced13 composite13 posts13

bull bonded13 posts13 are13 reported13 to13 strengthen13 the13 root13 inially13 the13 strengthening13 effect13 may13 be13 lost13 over13 me13 due13 to13 fluid13 leakage13 through13 the13 apical13 foramina13 and13 lateral13 canals13

bull bonding13 to13 radicular13 denne13 has13 been13 shown13 to13 be13 less13 reliable13 than13 bonding13 to13 coronal13 denne13

MATERIAL OF POST

laurarsquos notes 9

FP notes

+ve13 13 Favourable13 failure13 pa9ern

bull Failure13 will13 appear13 at13 the13 weakest13 point13 which13 would13 be13 the13 adhesive13 joints13 at13 the13 corendashdenne13 and13 postndashcementndash13 denne13 interfaces13 13

bull Hence13 the13 mode13 of13 failure13 will13 be13 loss13 of13 marginal13 seal13 core13 fracture13 post13 fracture13 or13 loss13 of13 retenon13

bull 13 The13 less13 the13 remaining13 coronal13 tooth13 structure13 the13 greater13 will13 be13 the13 stress13 at13 the13 adhesive13 interface13

bull Significantly13 lower13 load13 bearing13 values13

bull BUT13 failure13 of13 this13 type13 of13 post13 seems13 to13 be13 protecve13 of13 the13 remaining13 tooth13 structure13 by13 displaying13 a13 more13 favourable13 failure13 pa9ern13 with13 virtually13 no13 root13 fracture13

bull Fracture13 of13 the13 remaining13 tooth13 structure13 has13 been13 shown13 to13 occur13 more13 occlusally13 with13 fibre13 posts13 making13 these13 failures13 restorable13 vs13 a13 more13 apical13 posioned13 fracture13 occurring13 with13 metal13 post13

bull When13 bonded13 in13 place13 with13 resin13 cement13 it13 was13 thought13 that13 forces13 would13 be13 distributed13 more13 evenly13 in13 the13 root13 resulng13 in13 fewer13 root13 fractures13

bull In13 vitro13 studies13 have13 shown13 elasc13 posts13 to13 have13 a13 lower13 tendency13 to13 cause13 root13 fracture13 than13 posts13 of13 higher13 sffness

Decision making

bull Where13 a13 good13 ferrule13 is13 not13 a9ainable13 bonded13 post13 rather13 than13 a13 metal13 post(Jotkowitz13 amp13 Samet13 2010)

Does it actually matter

bull Reinforcement13 effect13 aer13 cementaon13 of13 a13 complete13 crown13 with13 ferrule13 effect13 makes13 the13 difference13 between13 sff13 and13 elasc13 posts13 less13 obvious13

bull Hu13 YH13 200313 No13 significant13 difference13 in13 fracture13 resistance13 between13 teeth13 restored13 with13 four13 post13 and13 core13 systems13 serrated13 parallel-shy‐sided13 cast13 posts13 and13 cores13 prefabri-shy‐13 cated13 stainless13 steel13 serrated13 and13 parallel-shy‐sided13 posts13 and13 resin-shy‐composite13 cores13 prefabricated13 carbon13 fiber13 posts13 and13 resin-shy‐composite13 cores13 and13 ceramic13 posts13 and13 resin-shy‐composite13 cores13 In13 this13 study13 the13 teeth13 from13 each13 group13 received13 endodonc13 therapy13 and13 a13 full-shy‐13 coverage13 metal13 crown13 which13 was13 cemented13 onto13 each13 tooth13 The13 specimens13 were13 subjected13 to13 a13 compressive13 load13 at13 a13 45113 angle13 to13 its13 axis13 unl13 failure

MATERIAL OF POST MATERIAL OF POST

DESIGN OF POST

Active vs passive

bull Acve13 posts13 -shy‐13 threaded13 and13 are13 intended13 to13 engage13 the13 walls13 of13 the13 canal13

bull Passive13 posts13 -shy‐13 retained13 strictly13 by13 the13 lung13 agent13 13

bull Acve13 posts13 are13 more13 retenve13 than13 passive13 posts13 but13 introduce13 more13 stress13 into13 the13 root13 than13 passive13 posts13

bull 13 They13 can13 be13 used13 safely13 however13 in13 substanal13 roots13 with13 max-shy‐13 imum13 remaining13 denn13 Their13 use13 should13 be13 limited13 to13 short13 roots13 in13 which13 maximum13 retenon13 is13 needed

Parallel vs tapered

Parallel13 bull More13 retenve13 than13 tapered13 posts13 13

bull Induce13 less13 stress13 into13 the13 root13 because13 there13 is13 less13 of13 a13 wedging13 effect13 and13 are13 reported13 to13 be13 less13 likely13 to13 cause13 root13 fractures13 than13 tapered13 posts13 13

bull Higher13 success13 rate13 with13 parallel13 posts13 than13 tapered13 posts13

DESIGN OF POST

laurarsquos notes 10

FP notes

LUTING AGENT OF POST The13 most13 common13 lung13 agents13 are13 zinc13 phosphate13 resin13 glass13 ionomer13 and13 resin-shy‐13 modified13 glass-shy‐ionomer13 cements13 Resin13 cements13 (+)13 increase13 retenon13 tend13 to13 leak13 less13 than13 other13 cements13 and13 provide13 at13 least13 short-shy‐term13 strengthening13 of13 the13 root13 Bonded13 resin13 cements13 have13 been13 recommended13 for13 their13 strengthening13 effect13 in13 roots13 with13 thin13 walls13 Examples13 include13 immature13 teeth13 or13 teeth13 with13 extensive13 caries13 Resin13 may13 be13 bonded13 to13 some13 types13 of13 posts13 so13 theorecally13 the13 dennresinpost13 can13 be13 joined13 via13 resin13 adhesion13 into13 one13 unit13 at13 least13 for13 a13 period13 of13 me13

(-shy‐)13 more13 ldquotechnique13 sensiverdquo13 13 require13 extra13 steps13 such13 as13 preparing13 the13 canal13 walls13 with13 acid13 or13 EDTA13 and13 placing13 a13 denn-shy‐bonding13 agent13 13 Contaminaon13 of13 the13 denn13 or13 post13 can13 be13 a13 problem13 Predictable13 delivery13 of13 etchants13 and13 adhesive13 materials13 deep13 into13 the13 canal13 space13 also13 can13 be13 problemac13 Self-shy‐cure13 or13 dual-shy‐cure13 cements13 should13 be13 used13 because13 of13 limited13 light13 penetraon13 into13 the13 root13 even13 with13 translucent13 posts (Schwartz13 Robbins13 Joe13 2004)

Tapered bull Require13 less13 denn13 removal13 because13 most13 roots13 are13 tapered13

bull Indicated13 in13 teeth13 with13 thin13 roots13 and13 delicate13 morphology

Prefab post core

bull typically13 made13 of13 stainless13 steel13 nickel13 chromium13 alloy13 or13 tanium13 alloy13 13

bull very13 rigid13 and13 with13 the13 excepon13 of13 the13 tanium13 alloys13 very13 strong13

bull Titanium13 posts13 have13 low13 fracture13 strength13 which13 means13 they13 are13 not13 strong13 enough13 to13 be13 used13 in13 thin13 post13 channels13 Removal13 of13 tanium13 posts13 can13 be13 a13 problem13 because13 they13 somemes13 break13

bull tanium13 and13 brass13 posts13 should13 be13 avoided13 because13 they13 offer13 no13 real13 advantages13 over13 the13 stronger13 metal13 posts13

bull Round13 -shy‐13 offer13 liBle13 resistance13 to13 rotaonal13 forces13 13

bull This13 is13 not13 a13 problem13 if13 adequate13 tooth13 structure13 remains13 but13 if13 minimal13 tooth13 structure13 remains13 anrotaon13 features13 must13 be13 incorporated13 into13 the13 post13 preparaon13 with13 slots13 or13 pins13 A13 bonded13 material13 should13 be13 used13 for13 the13 core

Does it matter

bull Difference13 in13 fracture13 rate13 between13 various13 posts13 disappeared13 when13 the13 crowns13 were13 placed13 (Kishen13 2006)13 13

bull Sorensen13 JA13 198413 retrospecve13 clinical13 study13 that13 showed13 that13 the13 presence13 of13 a13 post13 had13 li9le13 effect13 on13 the13 fracture13 rate13 of13 a13 crowned13 tooth13

DESIGN OF POST DESIGN OF POST

laurarsquos notes 11

FP notes

PREPARATION OF CANAL SPACE

Apical seal bull Four13 to13 513 mm13 of13 gu9a13 percha13 should13 he13 retained13 apicallyto13 ensure13 an13 adcquatc13 apical13 seal13

bull When13 only13 313 mm13 or13 less13 is13 present13 there13 is13 a13 greater13 incidence13 of13 leakage13

bull Adequately13 condensed13 gu9a13 percha13 can13 be13 safely13 removed13 immediately13 ajer13 endodonc13 treatment13

bull If13 a13 zinc13 oxide13 eugenol13 provisional13 restoraon13 placed13 over13 the13 obturated13 canal13 is13 exposed13 to13 saliva13 for13 long13 me13 periods13 (13 =13 313 months)13 leakage13 will13 occur13 that13 compromises13 the13 gu9a13 percha13 seal13 and13 such13 teeth13 should13 be13 endodoncally13 retreated13

Goodacre

Diameter Minimal13 enlargement13

bull Post13 and13 core13 diameter13 should13 be13 controlled13 to13 preserve13 root13 structure13 so13 that13 perforaons13 are13 less13 likely13 to13 occur13 and13 the13 tooth13 can13 resist13 root13 fracture13 13 during13 post13 cementaon13 or13 subsequent13 funcon13

bull Post13 diameters13 should13 not13 exceed13 one13 third13 of13 the13 root13 diameter13 at13 any13 locaon13 and13 post13 p13 diameter13 should13 usually13 be13 113 mm13 or13 less13

bull increasing13 post13 diameter13 decreases13 the13 toothrsquos13 resistance13 to13 fracture13

The13 thickness13 of13 the13 remaining13 denn13 is13 the13 prime13 variable13 in13 fracture13 resistance13 of13 the13 root13 Root13 canal13 should13 be13 enlarged13 only13 enough13 to13 enable13 the13 post13 to13 fit13 accurately13 and13 yet13 passively13 while13 ensuring13 strength13 and13 retenon13

PREPARATION OF CANAL SPACE

(Fig 12-8) Excessive enlargement can perforate orweaken the root which then may split during postcementation or subsequent function The thicknessof the remaining dentin is the prime variable in fracture resistance of the root Experimental impacttesting of teeth with cemented posts of differentdiameters7 showed that teeth with a thicker (18 mm) post fractured more easily than those witha thinner (13 mm) one

Photoelastic stress analysis also has shown thatinternal stresses are reduced with thinner posts Theroot can be compared to a ring The strength of a ringis proportional to the difference between the fourthpowers of its internal and external radii This impliesthat the strength of a prepared root comes from its periphery not from its interior and so a post ofreasonable size should not weaken the root signifi-cantly19 Nevertheless it is difficult to enlarge a rootcanal uniformly and to judge with accuracy howmuch tooth structure has been removed and howthick the remaining dentin is Most roots are nar-rower mesiodistally than faciolingually and oftenhave proximal concavities that cannot be seen on astandard periapical radiograph Experimentallymost root fractures originate from these concavitiesbecause the remaining dentin thickness isminimal20 Therefore the root canal should beenlarged only enough to enable the post to fit accu-

rately and yet passively while ensuring strength andretention Along the length of a tapered post spaceenlargement seldom needs to exceed what wouldhave been accomplished with one or two additionalfile sizes beyond the largest size used for endodon-tic treatment Because of the more coronal positionof the post space a much larger file must be used toaccomplish this (Fig 12-9)

Preparation of coronal tissueEndodontically treated teeth often have lost muchcoronal tooth structure as a result of caries as a resultof previously placed restorations or in preparation ofthe endodontic access cavity However if a cast coreis to be used further reduction is needed to accom-modate a complete crown and to remove undercutsfrom the chamber and internal walls This may leavevery little coronal dentin Every effort should bemade to save as much of the coronal tooth structureas possible because this helps reduce stress concen-trations at the gingival margin21 The amount ofremaining tooth structure is probably the mostimportant predictor of clinical success If more than2 mm of coronal tooth structure remains the postdesign probably has a limited role in the fractureresistance of the restored tooth2223 The oncecommon clinical practice of routine coronal reduc-tion to the gingival level before post and core fabri-cation is outmoded and should be avoided (Fig12-10) Extension of the axial wall of the crownapical to the missing tooth structure provides whatis known as a restoration with a ferrule which isdefined as a metal band or ring used to fit the rootor crown of a tooth as opposed to a crown thatmerely encircles core material (Fig 12-11) This is

Chapter 12 RESTORATION OF THE ENDODONTICALLY TREATED TOOTH 341

bull Apical sealbull Minimal enlargementbull Lengthbull Stopbull Antirotationbull Margin extension

64

6

2

3

1

5

Fig 12-8Faciolingual cross-section through a maxillary central incisorprepared for a post and core Six features of successful designare identified 1 adequate apical seal 2 minimum canalenlargement (no undercuts remaining) 3 adequate postlength 4 positive horizontal stop (to minimize wedging) 5 ver-tical wall to prevent rotation (similar to a box) and 6 extensionof the final restoration margin onto sound tooth structure

A B C

Fig 12-9Use of a prefabricated post entails enlarging the canal one ortwo file sizes to obtain a good fit at a predetermined depth A Incorrect the prefabricated post is too narrow B Incorrectthe prefabricated post does not extend to the apical seal C Correct the prefabricated post is fitted by enlarging thecanal slightly

(Fig 12-8) Excessive enlargement can perforate orweaken the root which then may split during postcementation or subsequent function The thicknessof the remaining dentin is the prime variable in fracture resistance of the root Experimental impacttesting of teeth with cemented posts of differentdiameters7 showed that teeth with a thicker (18 mm) post fractured more easily than those witha thinner (13 mm) one

Photoelastic stress analysis also has shown thatinternal stresses are reduced with thinner posts Theroot can be compared to a ring The strength of a ringis proportional to the difference between the fourthpowers of its internal and external radii This impliesthat the strength of a prepared root comes from its periphery not from its interior and so a post ofreasonable size should not weaken the root signifi-cantly19 Nevertheless it is difficult to enlarge a rootcanal uniformly and to judge with accuracy howmuch tooth structure has been removed and howthick the remaining dentin is Most roots are nar-rower mesiodistally than faciolingually and oftenhave proximal concavities that cannot be seen on astandard periapical radiograph Experimentallymost root fractures originate from these concavitiesbecause the remaining dentin thickness isminimal20 Therefore the root canal should beenlarged only enough to enable the post to fit accu-

rately and yet passively while ensuring strength andretention Along the length of a tapered post spaceenlargement seldom needs to exceed what wouldhave been accomplished with one or two additionalfile sizes beyond the largest size used for endodon-tic treatment Because of the more coronal positionof the post space a much larger file must be used toaccomplish this (Fig 12-9)

Preparation of coronal tissueEndodontically treated teeth often have lost muchcoronal tooth structure as a result of caries as a resultof previously placed restorations or in preparation ofthe endodontic access cavity However if a cast coreis to be used further reduction is needed to accom-modate a complete crown and to remove undercutsfrom the chamber and internal walls This may leavevery little coronal dentin Every effort should bemade to save as much of the coronal tooth structureas possible because this helps reduce stress concen-trations at the gingival margin21 The amount ofremaining tooth structure is probably the mostimportant predictor of clinical success If more than2 mm of coronal tooth structure remains the postdesign probably has a limited role in the fractureresistance of the restored tooth2223 The oncecommon clinical practice of routine coronal reduc-tion to the gingival level before post and core fabri-cation is outmoded and should be avoided (Fig12-10) Extension of the axial wall of the crownapical to the missing tooth structure provides whatis known as a restoration with a ferrule which isdefined as a metal band or ring used to fit the rootor crown of a tooth as opposed to a crown thatmerely encircles core material (Fig 12-11) This is

Chapter 12 RESTORATION OF THE ENDODONTICALLY TREATED TOOTH 341

bull Apical sealbull Minimal enlargementbull Lengthbull Stopbull Antirotationbull Margin extension

64

6

2

3

1

5

Fig 12-8Faciolingual cross-section through a maxillary central incisorprepared for a post and core Six features of successful designare identified 1 adequate apical seal 2 minimum canalenlargement (no undercuts remaining) 3 adequate postlength 4 positive horizontal stop (to minimize wedging) 5 ver-tical wall to prevent rotation (similar to a box) and 6 extensionof the final restoration margin onto sound tooth structure

A B C

Fig 12-9Use of a prefabricated post entails enlarging the canal one ortwo file sizes to obtain a good fit at a predetermined depth A Incorrect the prefabricated post is too narrow B Incorrectthe prefabricated post does not extend to the apical seal C Correct the prefabricated post is fitted by enlarging thecanal slightly

laurarsquos notes 12

FP notes

Length bull post13 length13 seems13 more13 important13 than13 diameter13 in13 determining13 cervical13 stresses13 stress13 in13 the13 tooth13 generally13 increases13 as13 the13 post13 diameter13 increases13

bull post13 length13 is13 the13 most13 important13 retenve13 factor13 and13 that13 post13 diameter13 was13 a13 secondary13 factor13

Goodacre13 and13 Spolnik13 199513

bull Guideline13 3413 root13 length13 (Goodacre13 and13 Spolnik13 1995)13 bull Minimum13 post13 length13 that13 ideally13 should13 be13 used13 is13 913 mm13 bull posts13 that13 were13 three13 fourths13 or13 more13 of13 the13 root13 length13 were13 2013 to13 3013 more13 retenve13 than13 posts13 that13 were13 one13 half13 of13 the13 root13 length13 or13 equal13 in13 length13 to13 the13 crown13

bull three13 fourths13 of13 the13 length13 of13 the13 root13 offered13 the13 greatest13 rigidity13 and13 least13 root13 deflecon13 (bending)13

bull But13 this13 dimension13 is13 not13 achievable13 without13 compromising13 the13 apical13 seal13 on13 many13 teeth13 bull Clinically13 each13 tooth13 must13 be13 individually13 evaluated13 for13 root13 length13 and13 amount13 of13 remaining13 guBa13 percha13 before13 establishing13 the13 desired13 post13 length13 13 bull long-shy‐rooted13 teeth13 achieving13 a13 length13 as13 close13 as13 possible13 to13 three13 fourths13 of13 the13 root13 length13 is13 desirable13

bull whereas13 many13 teeth13 will13 have13 posts13 that13 are13 equal13 in13 length13 to13 the13 crown13 because13 of13 limited13 root13 length13 and13 the13 need13 to13 retain13 413 to13 513 mm13 of13 apical13 gu9a13 percha

Vertical stop bull Provides13 a13 posive13 seat13 -shy‐gt13 prevents13 wedging13 effect13 -shy‐gt13 spilt13 root

PREPARATION OF CANAL SPACEPREPARATION OF CANAL SPACE

laurarsquos notes 13

FP notes

CORE

NAYYARrsquoS TECHNIQUE ONE-PIECE AMALGAM POST-CORE bull Used13 when13 there13 is13 sufficient13 coronal13 tooth13 structure13 at13 least13 313 walls13

bull Adequate13 retenon13 and13 resistance13 form13 from13 pulp13 chamber13 13

bull Procedure13

bull Removal13 of13 2-shy‐3mm13 of13 GP13 from13 all13 canals13 13

bull AmalgamCR13 used13 as13 posts13 as13 well13 as13 core13 material13

bull Select13 high13 early13 strength13 amalgam13

bull Condense13 into13 root13 canals13

bull Same13 visit13 crown13 prep13 possible13 13

MODIFIED NAYYARrsquoS TECHNIQUE Prefab13 post13 used13 to13 provide13 addional13 retenon13 13

POST-CORE RESTORED - BIOMECHANICAL CONSIDERATIONS In13 a13 postndashcore-shy‐restored13 tooth13 the13 post13 core13 crown13 and13 the13 remaining13 tooth13 structure13 respond13 to13 bing13 forces13 as13 a13 single13 funconal13 unit13 13 Key13 differences13 between13 intact13 tooth13 and13 tooth13 restored13 using13 postndashcore13 are13 13 (1) Occurrence13 of13 regions13 of13 stress13 concentraon13 and13 13 (2) Increase13 in13 the13 tensile13 stresses13 produced13 within13 the13 remaining13 tooth13 structure13 of13 a13 postndashcore13 restored13 tooth13

The13 intensity13 of13 stress13 concentraon13 and13 tensile13 stresses13 will13 depend13 upon13 13 (1) The13 material13 properes13 of13 the13 crown13 post13 and13 core13 material13 (2) The13 shape13 of13 the13 post13 (3) The13 adhesive13 strength13 at13 the13 crownndashtooth13 corendashtooth13 and13 corendash13 post13 postndashtooth13 interfaces13 (4) The13 magnitude13 and13 direcon13 of13 occlusal13 loads13 (5) The13 amount13 of13 available13 tooth13 structure13 (6) The13 anatomy13 of13 the13 tooth13

When13 bing13 loads13 are13 angled13 away13 from13 the13 long13 axis13 of13 the13 tooth13 stress13 concentraon13 intensity13 and13 tensile13 stresses13 have13 been13 noted13 to13 increase13 significantly13 13 because13 (1) the13 greater13 sffness13 of13 the13 endodonc13 post13 and13 core13 restoraon13 13 (2) The13 angulaon13 of13 the13 post13 with13 respect13 to13 the13 line13 of13 acon13 of13 occlusal13 load13 and13 (3) Increased13 flexure13 of13 the13 remaining13 reduced13 tooth13 structure13

GICRMGIC AR CR

bull (-shy‐)13 lack13 adequate13 strength13 as13 a13 buildup13 material13 and13 should13 not13 be13 used13 in13 teeth13 with13 extensive13 loss13 of13 tooth13 structure13 13

bull When13 there13 is13 minimal13 loss13 of13 tooth13 structure13 and13 a13 post13 is13 not13 needed13 glass-shy‐ionomer13 materials13 work13 well13 for13 block-shy‐out13 such13 as13 ajer13 removal13 of13 an13 MOD13 restoraon

bull (+)13 good13 physical13 and13 mechanical13 properes13

bull (-shy‐)13 crown13 preparaon13 must13 be13 delayed13 to13 permit13 the13 material13 me13 to13 set13

bull (-shy‐)13 esthecs13

bull currently13 the13 most13 widely13 used13 buildup13 material13 13

bull can13 be13 bonded13 to13 many13 of13 the13 current13 posts13 and13 to13 the13 remaining13 tooth13 structure13 to13 increase13 retenon13 13

bull not13 a13 good13 choice13 however13 with13 minimal13 remaining13 coronal13 tooth13 structure13 parcularly13 if13 isolaon13 is13 a13 problem

laurarsquos notes 14

FP notes

What13 happens13 when13 lateral13 forces13 are13 applied13 13

bull Lateral13 forces13 -shy‐gt13 high13 stress13 concentraons13 in13 radicular13 denn13 at13 the13 coronal13 one13 third13 of13 the13 root13

bull Rotaonal13 axis13 of13 the13 tooth13 at13 the13 crest13 of13 alveolar13 bone13 13 13

bull Forces13 are13 greatest13 on13 the13 circumference13 of13 the13 root13 lowest13 within13 the13 root13 canal13 13

bull The13 center13 of13 the13 root13 or13 canal13 is13 a13 neutral13 area13 with13 regard13 to13 force13 concentraon13 13

bull This13 force13 distribuon13 explains13 the13 suscepbility13 of13 teeth13 to13 fracture13 at13 the13 cementoenamel13 juncon13 when13 lateral13 forces13 are13 exerted13 on13 the13 coronal13 poron13 of13 the13 tooth13 The13 contribuon13 of13 the13 post13 inserted13 in13 the13 root13 canal13 or13 area13 of13 zero13 forces13 is13 negligible13 because13 the13 post13 absorbs13 only13 minimal13 forces13 in13 this13 posion13 13

bull 13 A13 post13 does13 not13 noceably13 reduce13 forces13 at13 the13 margins13 of13 a13 crown13 and13 does13 not13 cause13 a13 more13 equal13 distribuon13 or13 dispersion13 of13 forces13 along13 the13 length13 of13 the13 root13 (Assif13 et13 al13 1989)13

POST CORE FAILURES 213 most13 common13 occurrence13 13 1) Loosening13 of13 the13 post13 2) Tooth13 fractures13 Other13 reasons13 for13 failure13 bull Apical13 lesions13 and13 caries13 bull Fracturedloose13 crowns13

Root13 fractures13 13

bull 3-shy‐10of13 post13 and13 core13 failures13 are13 a9ributable13 to13 root13 fractures13 13 13

bull Threaded13 post13 forms13 are13 the13 most13 likely13 to13 cause13 root13 fracture13 and13 split13 and13 threaded13 flexible13 posts13 do13 not13 reduce13 stress13 concentraon13 during13 funcon13 13

laurarsquos notes 15

THE JOURNAL OF PROSTHETIC DENTISTRY ASSIF AND GORFIL

I noAnal stress a0

Fig 1 Stress distribution across root in tooth under load F Force applied on lingual surface of tooth Fulcrum (lower vertical arrow) is on buccal surface and corresponds to crest of alveolar bone T tensile stresses C compressive stresses C and T are maximal at external surface of root and decrease to zero at center of root or canal (only available place for post insertion) Center of root or canal is neutral area with regard to force concentra- tion and in its given position post receives minimal stresses under occlusal load and con- sequently does little to reinforce root under such a load

dontically treated teeth resulted from the loss of substan- tial dentin that included the roof of the pulpal chamber Cracks or fractures of roots occurred after endodontic treatment especially in those teeth ldquostrengthenedrdquo by posts after tooth structure was removed from the cana113-17 Metal posts concentrate unbalanced forces to walls of the root

The main factor endangering the survival of pulpless teeth after restoration is loss of dentin during endodontic treatment while preparing the access cavity with excessive widening and additional loss of dentin from post prepara- tion Therefore it is not necessary to strengthen the tooth but it is essential not to weaken it unnecessarily Conser- vation of dentin is mandatory and restorations that sup- port this concept are preferable

Considerable controversy surrounds the need for using coronal-radicular stabilization There are three basic phi- losophies (1) Some dentists advocate posts in each tooth after root canal treatment because posts supposedly strengthen the tooth against occlusal forces18T lg (2) Others discourage the use of posts claiming that the tooth prepa- ration of the root canal and the insertion of the post results in substantial weakening of the toothlrsquo I23 2o (3) A third group believes there is no appreciable improvement in re- sistance of the tooth to occlusal forces Use of posts should be avoided when they are not required to provide retention for a core3

Studies conducted directly on post systems are ques- tionable because they do not reflect specific clinical condi- tions The core is commonly covered by a complete crown with a 2 mm margin on healthy tooth structure and this 2 mm bracing provides a ferrule effect that protects the root against fractures at gingival margins

Studies have shown that artificial crowns alter the distribution of forces to roots and post systems lose signif- icance when the tooth is covered by a complete cast crown

566

Therefore the post design has limited influence on resis- tance of the tooth to fracturing and it is not as critical as a complete cast crown to brace healthy tooth structure apical to the core margin21-25

The metal crown concentrates forces at its margins dur- ing occlusal loading because of pressure of the crown on the finish line of the tooth preparation when the margin design is a butt joint type and because of sharp angles that con- centrate forces when stressed26 In the metal crown forces are concentrated in an area of sharp margins exerting much pressure on the coronal one third of the root In the transitional area between a rigid and a less rigid material there is concentration of high stress with increased forces especially lateral forces The rigid material or the crown absorbs more forces and transfers them to the less rigid material or the tooth27

A post does not noticeably reduce forces at the margins of a crown and does not cause a more equal distribution or dispersion of forces along the length of the root24 There- fore it is questionable whether a post resolves the special needs of the endodontically treated tooth

Cylindrical posts have sharp angles at their apical ends where forces are concentrated These posts exert compres- sive forces on the root apical to the sharp angles and can create dentinal cracks from the tip of the post to the cir- cumference of the root The preparation of the canal for this post leaves a thin dentinal wall at the apex of the preparation where concentration of forces is greatest and also increases the risk of perforation Tapered posts exhibit lower concentrations of stress in the apical portion prob- ably because of the absence of sharp angles and conserva- tion of tooth structures in this area24 28

Lateral forces result in high stress concentrations in radicular dentin at the coronal one third of the root24 The rotational axis of the tooth is located at the crest of alve- olar bone and the forces are greatest on the circumference

VOLUME 71 NUMBER 6

in the remaining tooth structure Stress concentrations

at the cervical region are mostly because of the

increased flexure of the compromised tooth structure

while stress concentrations at the apical region are

generally due to taper of the root canal and character-

istics of the post The regions of high stress concentra-

tion are also associated with the apical termination of

the post (16) Imperfections such as a notch ledge or

crack created in the dentine during root canal prepara-

tion or sharp threading from a post or a pin will also

give rise to localized stress concentration regions that

can be the locus for a potential fatigue failure (Fig 10)

(47) A smooth root canal shape is therefore recom-

mended to eliminate stress concentration sites

Fracture from a biomechanical perspective is a very

complex process that involves the nucleation and

growth of micro and macro cracks Knowledge of

how cracks are formed and grow within materials is

important to understand how a structure fractures

Even microscopic cracks can grow over time eventually

resulting in the fracture of the structure Therefore

structures with cracks that are not superficially visible

could fail catastrophically For fracture to occur in a

material the following factors must be present

simultaneously (1) stress concentrator this can be a

crack or a geometric notch such as a sharp corner

thread hole etc (2) tensile stress the tensile stress

must be of a magnitude high enough to provide

microscopic plastic deformation at the tip of the stress

concentration The tensile stress need not be an applied

stress on the structure but may be a residual stress

inside the structure It should be understood that

material properties such as yield strength and tensile

strength have virtually no bearing on the vulnerability

of a material to crack extension and fracture The

increase in magnitude of tensile stresses and concentra-

tion of stresses will render the remaining tooth

structure prone to fracture Close congruence has been

reported between the regions of stress concentration

observed in photoelastic models and oblique fracture in

extracted teeth subjected to in vitro fracture resistance

tests (16) Besides the tensile strength of dentine is

much lower than its compressive strength (47) Finite-

element analyses (FEA) was also used to study the stress

distribution pattern in teeth restored using a postndashcore

system The FEA studies have highlighted similar

altered stress distribution patterns in tooth structure

after the placement of post core and crown (48ndash50)

LD-Load CS-Compressive stress TS-Tensile stress NA-Neutral axis along which stress is zeroCZ-Compressive zone AF-Axis of forceLR-Line resulting from the reactant stresses produced by the initial contact of tooth with supporting bone

TSCS

LD

NA

LR

CZ

AF

Fig 8 Schematic illustration of bending stress distribu-tion within tooth (15)

CL-Compressive stress concentration regions for axial loads (0deg)CA-Compressive stress concentration for loads at 60deg lingual tothe long axis of the tooth

TL-Tensile stress concentration for axial loads (0deg)TA-Tensile stress concentration for loads at 60deg lingual to thelong axis of the tooth

SC-Regions of stress concentrations

Crown

Dentine

Post

Core

60deg 0deg

CL

SC

CA

SCSCTL

TA

Fig 9 Schematic diagram illustrating stress concentra-tion regions in postndashcore restored teeth (16)

Fracture predilection in endodontically treated teeth

65

in the remaining tooth structure Stress concentrations

at the cervical region are mostly because of the

increased flexure of the compromised tooth structure

while stress concentrations at the apical region are

generally due to taper of the root canal and character-

istics of the post The regions of high stress concentra-

tion are also associated with the apical termination of

the post (16) Imperfections such as a notch ledge or

crack created in the dentine during root canal prepara-

tion or sharp threading from a post or a pin will also

give rise to localized stress concentration regions that

can be the locus for a potential fatigue failure (Fig 10)

(47) A smooth root canal shape is therefore recom-

mended to eliminate stress concentration sites

Fracture from a biomechanical perspective is a very

complex process that involves the nucleation and

growth of micro and macro cracks Knowledge of

how cracks are formed and grow within materials is

important to understand how a structure fractures

Even microscopic cracks can grow over time eventually

resulting in the fracture of the structure Therefore

structures with cracks that are not superficially visible

could fail catastrophically For fracture to occur in a

material the following factors must be present

simultaneously (1) stress concentrator this can be a

crack or a geometric notch such as a sharp corner

thread hole etc (2) tensile stress the tensile stress

must be of a magnitude high enough to provide

microscopic plastic deformation at the tip of the stress

concentration The tensile stress need not be an applied

stress on the structure but may be a residual stress

inside the structure It should be understood that

material properties such as yield strength and tensile

strength have virtually no bearing on the vulnerability

of a material to crack extension and fracture The

increase in magnitude of tensile stresses and concentra-

tion of stresses will render the remaining tooth

structure prone to fracture Close congruence has been

reported between the regions of stress concentration

observed in photoelastic models and oblique fracture in

extracted teeth subjected to in vitro fracture resistance

tests (16) Besides the tensile strength of dentine is

much lower than its compressive strength (47) Finite-

element analyses (FEA) was also used to study the stress

distribution pattern in teeth restored using a postndashcore

system The FEA studies have highlighted similar

altered stress distribution patterns in tooth structure

after the placement of post core and crown (48ndash50)

LD-Load CS-Compressive stress TS-Tensile stress NA-Neutral axis along which stress is zeroCZ-Compressive zone AF-Axis of forceLR-Line resulting from the reactant stresses produced by the initial contact of tooth with supporting bone

TSCS

LD

NA

LR

CZ

AF

Fig 8 Schematic illustration of bending stress distribu-tion within tooth (15)

CL-Compressive stress concentration regions for axial loads (0deg)CA-Compressive stress concentration for loads at 60deg lingual tothe long axis of the tooth

TL-Tensile stress concentration for axial loads (0deg)TA-Tensile stress concentration for loads at 60deg lingual to thelong axis of the tooth

SC-Regions of stress concentrations

Crown

Dentine

Post

Core

60deg 0deg

CL

SC

CA

SCSCTL

TA

Fig 9 Schematic diagram illustrating stress concentra-tion regions in postndashcore restored teeth (16)

Fracture predilection in endodontically treated teeth

65

FP notes

bull tapered13 threaded13 posts13 were13 the13 worst13 stress13 producers13 increased13 the13 incidence13 of13 root13 fracture13 in13 extracted13 teeth13 by13 2013 mes13 that13 of the13 parallel13 threaded13 post13

bull Cemented13 posts13 produce13 the13 least13 root13 stress13

bull Increasing13 post13 length13 increases13 the13 resistance13 of13 a13 root13 to13 fracture13

bull increasing13 post13 diameter13 decreases13 the13 resistance13 of13 a13 root13 to13 fracture13

13

laurarsquos notes 16

Age factors effects of age changes ondentine

Alteration of normal dentine to form transparent

dentine is a common age-induced process Physiologictransparent (or sclerotic) dentine appears to form

without trauma or caries attack as a natural conse-

quence of aging whereas pathologic transparentdentine is often seen subjacent to caries The dentinal

tubules in transparent dentine are gradually filled up

with a mineral phase over time beginning at the apical

end of the root and often extending into the coronal

dentine The large intratubular mineral crystals depos-

ited within the tubules in transparent dentine are

chemically similar to intertubular mineral It was

suggested that a lsquodissolutionndashreprecipitationrsquo mechan-

ism is responsible for its formation (131) In the past it

was believed that transparency required a vital pulp

(132) This belief has been largely discounted It now

appears that endodontically restored teeth have the

same or a greater rate of transparent dentine formation

as teeth with vital pulp (133) The elastic properties of

(2)bull The interfacial failure

approaching the core may cause core fracture

bull The fracture of the core would depend upon the mechanical properties of the core material

(1)bull Initial signs of interfacial failure at the

crown tooth interface This can lead to loosening of the crown

bull This failure depends on the adhesive strength of the crown-tooth interface

(4)bull The interfacial failure approaching

the post may cause post fracturebull The fracture of the post would

depend upon the mechanical properties of the post material

(3)bull The interfacial failure at the

crown-tooth interface mayprogress as interfacial failure at the core-tooth interface

bull This failure depends on the adhesive strength of the core- tooth interface

(5)bull The interfacial failure at

the core-tooth interface may progress as interfacial failure at the post-tooth interface

bull This failure depends on the adhesive strength of the post-tooth interface

(6)bull The post-core restored tooth behaves as a single

unit to functional forces As the interfacial failures progresses the response of the post-core unit and the remaining tooth structure becomes distinctly different And this will lead to the fracture of tooth

bull The location and nature of tooth fracture will depend upon the mechanical properties and shapeof the post anatomy of the tooth direction of the external force and the amount and nature of remaining tooth structure

Fig 17 Schematic diagram showing the progression of interfacial failures and fractures in postndashcore restored tooth

Kishen

76

FP notes

CROWN

CROWNS VS DIRECT RESTORATIONS

Study AF13 Stavropoulou13 PT13 KoidisA13 systemac13 review13 of13 single13 crowns13 on13 endodoncally13 treated13 teeth13 13 Journal13 of13 denstry13 3513 (2007)13 761ndash76713

Method Systemac13 review13 of13 160913 references13 of13 which13 1013 survived13 13 Single13 crowns13 n13 not13 stated13 lsquofailure13 of13 the13 RCTRsrsquo13 is13 defined13 as13 fracture13 of13 the13 tooth13 fracture13 of13 the13 restoraon13 post13 fracture13 post13 decementaon13 dislodgment13 of13 the13 restoraon13 marginal13 leakage13 of13 the13 restoraon13 and13 tooth13 loss13 The13 outcome13 of13 the13 study13 was13 chosen13 to13 be13 lsquosuccess13 of13 RCTRsrsquo13 and13 none13 of13 the13 above13 failure13 criteria13 should13 exist13 for13 the13 restoraon13 to13 be13 considered13 successful13 Data13 pooled13 and13 cumulave13 Life13 Table13 Survival13 Curves13

213 to13 1013 year13 Follow-shy‐Up

Conclusions

Crown13 vs13 No13 crown

bull RCT13 covered13 with13 crowns13 have13 a13 higher13 long-shy‐term13 survival13 rate13 (8113 ajer13 1013 years)13 than13 RCT13 without13 crown13 coverage13 (6313 13 ajer13 1013 years)13

bull Survival13 rate13 for13 RCT13 without13 crown13 coverage13 is13 quite13 sasfactory13 for13 the13 first13 313 years13 (8413 1048576104857710485781048579104858010485811048582104858310485841048585104858610485871048588104858910485901048591104859210485931048594104859510485961048597104859810485991048600104860110486021048603104860410486051048606104860710486081048609104861010486111048612104861310486141048615104861610486171048618104861910486201048621104862210486231048624104862510486261048627104862810486291048630104863110486321048633104863410486351048636104863710486381048639104864010486411048642104864310486441048645104864610486471048648104864910486501048651104865210486531048654104865510486561048657104865810486591048660104866110486621048663104866410486651048666104866710486681048669104867010486711048672104867310486741048675104867610486771048678104867910486801048681104868210486831048684104868510486861048687104868810486891048690104869110486921048693104869410486951048696104869710486981048699104870010487011048702104870313 9)13 while13 there13 is13 a13 significant13 decrease13 in13 the13 survival13 of13 RCT13 ajer13 this13 period13

AR13 vs13 CR13

bull 3-shy‐year13 survival13 rate13 of13 resin-shy‐13 restored13 teeth13 is13 markedly13 be9er13 than13 that13 of13 amalgam-shy‐13 restored13 teeth13

bull AR13 unacceptable13 for13 restoraon13 of13 endodoncally13 treated13 posterior13 teeth13 whether13 amalgam13 is13 used13 as13 a13 temporary13 or13 permanent13 restorave13 material13

bull Enamel-shy‐bonded13 resin13 is13 an13 alternave13 treatment13 opon13 for13 teeth13 that13 are13 in13 the13 need13 of13 a13 temporary13 restoraon13 and13 have13 limited13 loss13 of13 tooth13 structure13 13

13

laurarsquos notes 17

FP notes

Study Fokkinga13 WA13 Kreulen13 CM13 Bronkhorst13 WM13 Creugers13 NH13 Up13 to13 17-shy‐13 year13 controlled13 clinical13 study13 on13 post-shy‐and-shy‐cores13 and13 covering13 crowns13 13 J13 Dent13 200713 35778-shy‐78613

Method Controlled13 Clinical13 Trial13 13 bullSingle13 crowns bullMul-shy‐pracce13 1813 operators bull25713 paents13 30713 core13 restoraons bullRPD13 abutments13 excluded bull1513 to13 1713 year13 Follow-shy‐Up bullSurvival13 Analysis13 ndash13 Kaplan13 Meier13 dropouts13 censored13 date13 13 bullDefinion13 of13 Survival13 ndash13 Restoraon13 Tooth13 13 bullTreatment13 Allocaon13 13 (ldquoThe13 disadvantage13 of13 the13 general13 pracce13 seng13 appeared13 somemes13 to13 be13 the13 lack13 of13 compliance13 of13 the13 operators13 regarding13 the13 treatment13 assignmentrdquo)

ldquoSubstanal13 denne13 heightrdquo

gt7513 of13 the13 circumferenal13 denn13 wall13 has13 minimal13 1mm13 thickness13 and13 at13 least13 a13 height13 of13 1mmabove13 gingival13 level13 Less13 than13 2513 of13 the13 circumference13 has13 less13 than13 1mm13 above13 the13 gingiva13 But13 a13 ferrule13 of13 1ndash2mm13 could13 be13 achieved

ldquoMinimial13 denne13 heightrdquo

lt7513 of13 the13 circumferenal13 denn13 wall13 has13 at13 least13 113 mm13 above13 gingival13 level13 More13 than13 2513 of13 the13 circumference13 has13 less13 than13 113 mm13 above13 the13 gingiva13 Or13 no13 ferrule13 of13 1ndash2mm13 could13 be13 achieved13

CONCLUSION WHICH13 TYPE13 OF13 CORE13 TO13 USE13 IS13 CPC13 ALWAYS13 NECESSARY

bull The13 results13 of13 this13 study13 showed13 NO13 difference13 in13 survival13 probabilies13 among13 different13 core13 restoraons13 under13 a13 covering13 crown13 of13 endodoncally13 treated13 teeth13 13

bull13 No13 difference13 in13 restoraon-shy‐survival13 was13 found13 between13 these13 two13 types13 of13 post-shy‐and-shy‐cores13 for13 teeth13 with13 lsquolsquominimal13 denn13 heightrsquorsquo13 Thus13 one13 should13 be13 careful13 to13 conclude13 that13 in13 the13 situaon13 of13 a13 tooth13 with13 lsquolsquominimal13 denn13 heightrsquorsquo13 always13 a13 cast13 post-shy‐and-shy‐core13 is13 preferred13

DO13 YOU13 ALWAYS13 NEED13 A13 POST

bull No13 difference13 in13 the13 survival13 probability13 between13 restoraons13 with13 and13 without13 posts13 in13 teeth13 with13 lsquolsquosubstanal13 denn13 heightrsquorsquo13 lej13 =gt13 cannot13 be13 recommended13 to13 rounely13 use13 a13 post13 preceding13 a13 crown13 in13 an13 endodoncally13 treated13 tooth13 13

bull -shy‐gt13 in13 an13 endodoncally13 treated13 tooth13 with13 substanal13 remaining13 denn13 a13 post13 in13 a13 core13 does13 not13 perform13 be9er13 than13 a13 post-shy‐free13 core13

WHY13 IS13 FERRULE13 IMPT

bull The13 preservaon13 of13 substanal13 remaining13 coronal13 tooth13 structure13 seems13 to13 be13 crical13 to13 the13 long-shy‐term13 survival13 of13 endodoncally13 treated13 crowned13 teeth13

bull survival13 probability13 of13 post-shy‐and-shy‐core13 reconstructed13 teeth13 with13 lsquolsquosubstanal13 denn13 heightrsquorsquo13 (Trial13 1)13 was13 significantly13 higher13 than13 that13 of13 teeth13 with13 lsquolsquominimal13 denn13 heightrsquorsquo13 (Trial13 2)13

laurarsquos notes 18

FP notes

FERRULE EFFECT

Definition bull An13 encircling13 band13 of13 metal13 that13 embraces13 the13 coronal13 surface13 of13 the13 tooth13 structure13

bull A13 ferrule13 is13 defined13 as13 a13 vercal13 band13 of13 tooth13 structure13 at13 the13 gingival13 aspect13 of13 a13 crown13 preparaon(Schwartz13 et13 al13 2004)13

bull It13 should13 be13 clear13 that13 the13 term13 ferrule13 is13 ojen13 misinterpreted13 It13 is13 ojen13 used13 as13 an13 expression13 of13 the13 amount13 of13 remaining13 sound13 denne13 above13 the13 finish13 line13 It13 is13 in13 fact13 not13 the13 remaining13 tooth13 structure13 that13 is13 the13 ferrule13 but13 rather13 the13 actual13 bracing13 of13 the13 complete13 crown13 over13 the13 tooth13 structure13 that13 constutes13 the13 ferrule13 effect13 ie13 the13 protecon13 of13 the13 remaining13 tooth13 structure13 against13 fracture13 (A13 Jotkowitz13 amp13 N13 Samet13 2010)13

bull 13 Teeth13 prepared13 with13 adequate13 ferrule13 effecvely13 resist13 funconal13 forces13 and13 enhances13 the13 fracture13 strength13 of13 postndashcore13 restored13 endodoncally13 treated13 teeth13

Advantages Increase13 fracture13 resistance

YES13

bull A13 ferrule13 with13 113 mm13 of13 vercal13 height13 has13 been13 shown13 to13 double13 the13 resistance13 to13 fracture13 versus13 teeth13 restored13 without13 a13 ferrule(JA13 Sorensen13 et13 al13 1990)13

NO13

bull No13 difference13 in13 fracture13 resistance13 with13 or13 without13 a13 2-shy‐mm13 ferrule13 using13 prefabricated13 posts13 and13 resin13 cement(al-shy‐Hazaimeh13 and13 Gu9eridge13 2001)13 13

bull No13 difference13 in13 fracture13 resistance13 of13 teeth13 with13 bonded13 posts13 with13 or13 without13 a13 ferrule(WA13 Saupe13 1996)

Fracture13 pa9ern

bull13 Fracture13 pa9erns13 were13 more13 favorable13 when13 a13 ferrule13 was13 present(al-shy‐Hazaimeh13 and13 Gu9eridge13 2001)13

Considerations

Biological13 width13 bull The13 ferrule13 length13 obtained13 will13 be13 influenced13 by13 the13 lsquobiologic13 widthrsquo13 which13 is13 the13 dimension13 of13 the13 junconal13 epithelial13 and13 connecve13 ssue13 a9achment13 to13 the13 root13 above13 the13 alveolar13 crest13

bull 13 It13 is13 generally13 accepted13 that13 if13 unpredictable13 bone13 loss13 and13 inflammaon13 are13 to13 be13 avoided13 the13 crown13 margin13 should13 be13 at13 least13 2mm13 from13 the13 alveolar13 crest13 13

bull Recommended13 that13 at13 least13 313 mm13 should13 be13 lej13 to13 avoid13 impingement13 on13 the13 coronal13 a9achment13 of13 the13 periodontal13 connecve13 ssue13

bull Therefore13 at13 least13 4513 mm13 of13 supra-shy‐alveolar13 tooth13 structure13 may13 be13 required13 to13 provide13 an13 effecve13 ferrule

Crown13 lengthening13

may13 result13 in13 a13 poorer13 crown13 to13 root13 rao13 (and13 therefore13 to13 increased13 leverage13 on13 the13 root13 during13 funcon)13 13 compromised13 aesthecs13 loss13 of13 the13 inter-shy‐dental13 papilla13 and13 a13 potenal13 compromise13 of13 the13 support13 of13 the13 adjacent13 teeth

Ortho13 extrusion13 crown13 to13 root13 rao13 may13 sll13 be13 compromised13 and13 it13 adds13 significant13 me13 and13 an13 addional13 fee

bull 13 Ferrule13 is13 desirable13 but13 should13 not13 be13 provided13 at13 the13 expense13 of13 the13 remaining13 toothroot13 structure(Stankiewicz13 amp13 Wilson13 )

laurarsquos notes 19

FP notes

Jotkowitz amp Samet 2010 - Rethinking ferrule ndash a new approach to an old dilemma

4 direct factors (Influence ferrule)

2 indirect factors (Affects functionality of ferrule)

A) Ferrule13 height13 B) Ferrule13 width13 13 C) Number13 of13 walls13 amp13 ferrule13 locaon13 D) Type13 of13 tooth13 amp13 extent13 of13 lateral13 load13

E)13 Type13 of13 post13 F)13 Core13 material13

A)13 Ferrule13 height13

bull Maximum13 beneficial13 effects13 from13 a13 ferrule13 with13 1513 to13 213 mm13 of13 vercal13 tooth13 structure13

bull Tan13 P13 L13 Aquilino13 S13 A13 Gracon13 D13 G13 et13 al13 2005The13 mean13 fracture13 strengths13 of13 endodoncally13 treated13 maxillary13 central13 incisors13 restored13 with13 a13 crown13 without13 a13 dowel13 and13 endodoncally13 treated13 maxillary13 central13 incisors13 restored13 with13 a13 cast13 dowel13 and13 core13 and13 crown13 with13 a13 uniform13 2-shy‐mm13 ferrule13 were13 not13 significantly13 different13

bull Greater13 the13 height13 of13 remaining13 tooth13 structure13 above13 the13 margin13 of13 the13 preparaon13 the13 be9er13 fracture13 resistance

B)13 Ferrule13 width

bull Walls13 are13 considered13 lsquotoo13 thinrsquo13 when13 they13 are13 less13 than13 113 mm13 in13 thickness13

bull 13 minimal13 ferrule13 height13 is13 only13 of13 value13 if13 the13 remaining13 denne13 has13 a13 minimal13 thickness13 of13 113 mm13

bull No13 consensus13 regarding13 contra-shy‐bevel13 ferrule13 designs13 or13 the13 incorporaon13 of13 a13 cervical13 collar13 and13 therefore13 these13 designs13 are13 not13 widely13 accepted

C)13 Number13 of13 walls13 and13

ferrule13 locaon13

bull Common13 for13 a13 paral13 ferrule13 to13 remain13 ajer13 crown13 prep13 due13 to13

bull Caries13 free13 -shy‐proximal13

bull Erosionabrasion13 -shy‐13 buccal13 wall13 13

bull Tooth13 prep13 to13 achieve13 max13 esthecs13 -shy‐13 thin13 and13 low13 buccal13 walls13

bull Uniform13 all13 around13 ferrule13 gt13 13 ferrule13 that13 varies13 in13 different13 parts13 of13 the13 tooth13

bull Non-shy‐uniform13 ferrule13 is13 sll13 superior13 to13 no13 ferrule13 at13 all13 bull (Paper13 quoted13 Al-shy‐Wahadni13 et13 al13 in13 200213 to13 jusfy13 but13 in13 actual13 fact13 the13 in13 vitro13 study13 did13 not13 cement13 crowns13 over13

the13 cast13 post13 core13 restored13 teeth13 because13 they13 did13 not13 want13 to13 incorporate13 the13 ferrule13 effect13 Anyhow13 quote)13

bull Tan13 P13 L13 Aquilino13 S13 A13 Gracon13 D13 G13 et13 al13 200513 In13 vitro13 study13 invesgated13 the13 resistance13 to13 stac13 loading13 of13 5013 endodoncally13 treated13 max13 incisor13 teeth13 with13 uniform13 (2mm13 all13 round)13 and13 nonuniform13 (213 mm13 buccal13 and13 lingual13 0513 mm13 proximal)13 ferrule13 configuraon13 (Restored13 with13 cast13 post13 core13 crown) =gt13 A13 tooth13 with13 a13 non-shy‐uniform13 ferrule13 is13 more13 effecve13 at13 resisng13 fracture13 than13 a13 tooth13 with13 no13 ferrule13 but13 not13 as13 effecve13 as13 a13 tooth13 with13 a13 uniform13 2-shy‐mm13 ferrule13

bull Mandibular13 premolar13 buccal13 wall13 more13 crucial Maxillary13 premolar13 buccolingual13 ferrule13 more13 crucial13

laurarsquos notes 20

FP notes

CROWN

bull LOCATION13 of13 sound13 tooth13 structure13 to13 resist13 occlusal13 forces13 that13 is13 more13 important13 than13 having13 360deg13 of13 circumferenal13 axial13 wall13 denne13

bull Ng13 CC13 et13 al13 200613

bull In13 vitro13 study13 on13 maxillary13 incisors13 with13 bonded13 fibre13 posts13 and13 resin13 cores13 -shy‐13 good13 palatal13 ferrule13 only13 is13 as13 effecve13 as13 having13 a13 complete13 lsquoall13 aroundrsquo13 ferrule13 as13 this13 tooth13 structure13 will13 resist13 the13 forces13 applied13 in13 funcon13 to13 the13 palatal13 surface13 of13 the13 maxillary13 incisor13

bull a13 maxillary13 incisor13 that13 is13 only13 missing13 the13 palatal13 wall13 despite13 the13 presence13 of13 three13 other13 favourable13 walls13 shows13 poor13 fracture13 resistance13 and13 is13 at13 greater13 risk13 of13 failing13 than13 some13 condions13 with13 fewer13 walls13 remaining13

bull when13 the13 palatal13 wall13 is13 missing13 the13 non-shy‐axial13 load13 from13 the13 palatal13 side13 in13 a13 maxillary13 anterior13 crown13 challenges13 the13 postcoreroot13 juncon

D)13 Type13 of13 tooth13 amp13 extent13 of13 lateral13 load13

Anterior13 vs13 posterior13 teeth13 13 213 disnguishing13 factors13 relave13 size13 and13 direcon13 of13 loads13 they13 need13 to13 withstand13 bull13 anterior13 teeth13 are13 loaded13 non-shy‐axially13 and13 posterior13 teeth13 in13 normal13 funcon13 have13 the13 majority13 of13 the13 load13 in13 an13 occluso-shy‐gingival13 direcon13 Lateral13 forces13 have13 a13 greater13 potenal13 to13 damage13 the13 tooth-shy‐restoraon13 interface13 when13 compared13 to13 vercal13 loads13

(Refer13 to13 previous13 segment13 on13 ldquoPaent13 factors13 occlusionrdquo)

Crown design

Metal13 collar13 enhance13 resistance13 to13 root13 fracture13

Barkhordar13 RA13 et13 al13 198913 13 In13 vitro13 study13 examined13 the13 effect13 of13 a13 metal13 collar13 with13 approximate13 313 degrees13 of13 taper13 on13 the13 resistance13 of13 2013 endodoncally13 treated13 maxillary13 central13 incisor13 roots13 to13 fracture13 13 Teeth13 in13 the13 group13 with13 213 mm13 cervical13 metal13 collar13 required13 a13 higher13 force13 to13 affect13 failure13 then13 those13 without13

Margin design

Avoid13 buB13 joint13 amp13 sharp13 angles13

bull Metal13 crown13 concentrates13 forces13 at13 its13 margins13 during13 occlusal13 loading13 because13 of13 pressure13 of13 the13 crown13 on13 the13 finish13 line13 of13 the13 tooth13 preparaon13

bull when13 margin13 design13 is13 a13 bu913 joint13 type13 and13 because13 of13 sharp13 angles13 that13 concentrate13 forces13 when13 stressed13 13

bull Forces13 are13 concentrated13 in13 an13 area13 of13 sharp13 margins13 exerng13 much13 pressure13 on13 the13 coronal13 one13 third13 of13 the13 root13 13

bull In13 the13 transional13 area13 between13 a13 rigid13 and13 a13 less13 rigid13 material13 there13 is13 concentraon13 of13 high13 stress13 with13 increased13 forces13 especially13 lateral13 forces13 The13 rigid13 material13 or13 the13 crown13 absorbs13 more13 forces13 and13 transfers13 them13 to13 the13 less13 rigid13 material13 or13 the13 tooth

laurarsquos notes 21