Australian Dental Journal 2002;47:1. 57

Cast post and core foundation for the badly broken downmolar tooth

EV Bass*

AbstractBackground: This article addresses the difficultclinical problem of restoration of endodonticallytreated posterior teeth, where there is nothing left ofthe clinical crown.Methods: A step by step procedure, includinginstrumentation and materials and a new impressiontechnique, is described in detail, with clinicalphotographs.Results: This technique results in the fabrication of arobust and extremely retentive post and core onwhich to place fixed prosthodontic restorations.Conclusions: The author has placed over 600restorations of this type over a five year period,without any reported failures. With the ‘greying’ ofthe population there are increased demands ondentists to restore structurally compromised teeth,and increasing expectations of the performance ofthese restorations. This technique is offered as asuperior alternative to conventional post and coreconstructions methods.

Key words: Cast post and core, sliding prefabricated post,endodontically treated molars.

(Accepted for publication December 2000.)

described by Weiner3 in 1981. Chand4 developed a postselection guide for the para post system (WhaledentInternational, USA) for a pre-operative assessment ofthe para post drill suitable for post hole preparation.He also addressed the problem of post hole clearingbefore cementation. More recently Sadan et al.5

suggested a similar technique to Chiche’s but forindirect fabrication of two separate castings, first – thepost and then – the core for mandibular molars. Aftercementation of this assembly a crown wasmanufactured from a new impression.

Most clinicians suggested, if possible, preparation ofthe dowel space to within 3-5mm of the apical seal.This is not considered to be a requirement nowadays asa post length equal to the length of the expected crownis thought to be sufficient.6 However, in the author’sopinion, in divergent roots, when two posts are utilizedeven this length is not necessary. Neither is it requiredto achieve a diameter of the post equal to one-third ofthe root width as has been suggested by Johnson et al.7

and Trabert and Cooney.8 Indeed, as the posts aredivergent, much shorter ones should provide adequateretention. Goldman et al.9 found posts cemented intoproperly conditioned post holes, where the smear layerhas been removed, exhibit much higher retention,especially when the luting cement is introduced by aLentulo spiral. The best method for removing the smearlayer in their study was rinsing with 17 per centethylenediamine tetra acetic acid (EDTA) followed by5.2 per cent sodium hypochlorite. The post holes weredried with paper points and air. In the techniquedescribed in this paper a similar concentration of 15 percent EDTA is used for this purpose with slightmodifications in the method of delivery and withoutsodium hypochlorite solution.

The luting cement has been changed as the newreinforced glass ionomer cement is claimed by themanufacturer to adhere chemically to dentine and goldand should provide better retention than zinc phosphate.However, in the first hundred or so post coresconstructed using the technique described, the latterwas used with equal success.

In the technique described in this paper, isolation ofbadly broken down molars was achieved by cotton*Prosthodontist, HCF Dental Centre, Sydney.

C L I N I C A L R E P O R TAustralian Dental Journal 2002;47:(1):57-62

INTRODUCTIONThe restoration of a badly broken down

endodontically treated molar tooth is a challengingtask. This is evident from the vast amount of existingliterature on this subject. A comprehensive literaturereview has been presented by Chiche et al.1 This tracedback to 1911 where one of the first methods wassuggested by Robin. In the same article Chiche et al.1

described his own modality, where a prefabricatedplastic post was inserted into the palatal canal of amaxillary molar and the impression of the remainingtooth, already prepared for a crown, was taken withthe plastic post in it. A crown was then fabricated anda gold post cast from a plastic post was insertedthrough the crown immediately following crowncementation.

Mora and Firtell2 suggested replacing a graphite postin the second canal with a metal post, in a technique

rolls and in some cases with the addition of suctionwith a tongue guard. In the author’s opinion a rubberdam would interfere with frequent checks for occlusalclearance and alignment with adjacent teeth. Possibledamage to the surrounding gingiva by clamps maycreate a problem for finalizing the preparation andimpression taking at the same appointment.

TECHNIQUEThe procedure described is for a lower molar.Existing restorations are removed and the tooth is

roughly prepared for a crown, with a chamfer at thegingival level. All unsupported/thin enamel and dentineare removed using a horizontally approachingdiamond, so that sound residual tooth structure has aminimum wall thickness of 1mm. With an ultrasonicscaler and #6 round long shank bur the pulp chamberis rendered free of luting cement, gutta percha (GP),and temporary restorative material. The orifices of thecanals are prepared with a #4 round long shank bur toa depth of 1-2mm.

A dowel space is prepared in the distal canal using aNo 2 Produits Dentaires (PD) reamer with very lightpressure. GP shavings should be observed coming outalongside the reamer. If there are no GP shavings

present, look into the dowel preparation to ensure thatthe GP root filling is in the middle of the dowel space.This is done with a front surface mirror. If GP is not inthe middle you might be going sideways. If obstructionto the advancement of the reamer is felt, go to a depthof no more than 6-8mm from the canal orifice.

Depending on the size and shape of the canal either aNo 2 or No 3 PD reamer could now be used, withlateral pivoting movements so that the walls of thedowel preparation are shaved to conform to the cross-sectional shape of the root; in this case (distal root) it isoval in shape therefore a bucco-lingual movement isused. At this stage ensure that the dowel space walls arecompletely free of extraneous material, and smooth; itis not possible to achieve this result with a parallel-sided post drill, which is not side-cutting. Now themesio-lingual canal is prepared using OP-PO (Optident,West Yorkshire, England) drills consecutively from No 1(white) to No 3 (pink) to a depth of 4-5mm from theorifice (in curved roots it can be shorter), againobserving GP shavings as in the distal dowelpreparation.

The preparations are now washed and dried.The PD reamer with the shank cut off is placed in the

distal canal dowel preparation (No 2 or No 3

58 Australian Dental Journal 2002;47:1.

Products manufacturersProduct Manufacturer

Impression material. President: light body and putty Coltene/Whaledent, New Jersey, USACrown & Bridge Burs Kit: K + B System Prep 2555 Meisinger, GermanyAbsolute Alcohol (100% Ethanol)EDTA 15% Colgate – OrapharmModified PD Reamers – No 1,2,3,4 – Fig 1 Produits Dentaires – SA Vevey SuisseOP-PO titanium posts (OPT – 3) Optident, West Yorkshire, EnglandOP-PO twist drills (OPD 001, 002 ,003)Modified stainless steel (s/s) temporary posts(OPTE - 3) Fig 2Modified Barbed Broach (ISO 6) Fig 5 Kerr, USAModified finger plugger #40(sides flattened with stone to grip cotton wool) Fig 4Modified Lentulo spiral (ISO 40) United Dental Manufacturers, USA(cut to 20mm length)Fuji Plus Luting Cement GC Corporation, Japan

Fig 1. Modified PD reamers (#2 and #3) are on the right with distancepieces removed, guiding tips cut off and depth indicating grooves

marked at 10mm and 15mm.

Fig 2. A modified s/s OPTE-03 temporary post at the bottom. It hasbeen adjusted in length at its smooth end so that when in the dowel

space it is clear of the opposing dentition.

Australian Dental Journal 2002;47:1. 59

depending on the size of the dowel preparation) so itfits snugly and the inclination of it in relation to theopposing wall of the pulp chamber, i.e., the mesial wall,is visualized. The mesial wall of the pulp chamber isnow prepared with a No 3 or No 4 PD reamer to havethe same path of insertion as the dowel in the distalcanal. This is done using the shortened reamer which ispositioned in the distal dowel space as a guide (Fig 3).A wisp of cotton wool is gently rolled around the fingerplugger (No 40) to make a thin coat; this is done byrotating the finger plugger in a thin wisp of cotton woolheld between the fingers. It is then dipped in 15 per centEDTA and placed into the dowel preparation with apumping action. A bubbling effect may be observed(Fig 4). This is repeated two or three times using a newwisp each time. The procedure is repeated with 100 percent alcohol and then a dry wisp.

At this stage ensure that you have washed yourgloves in soap and water to remove powder. The stain-less steel (OPTE-03) temporary post is modified byshortening it sufficiently so that it is clear of theopposing occlusion when it is placed in the mesio-lingual dowel space. The three grooves of the post

facing the occlusion will engage the impression material(Fig 5). A No 40 barbed broach is prepared for theimpression by cutting off part of the plastic headleaving 2mm; then part of the apical barbed end is cutoff and it is folded to half its length. This should fitloosely into the distal dowel preparation to the fullworking length and be clear of the occlusion. The cut-off plastic handle of this broach is clear of the stainlesssteel post in the mesio-lingual dowel preparation, andclear of the occlusion (Fig 5). The barbed broach is nowremoved, the preparation is dried and a thin retractioncord is placed into the gingival crevice.

With the stainless steel No 3 temporary postremaining in the mesio-lingual preparation, Presidentlight body impression material is injected around thispost and into the distal dowel preparation. It is spuninto the distal dowel preparation with a No 40 Lentulospiral shortened to 20mm, so that the dowelpreparation is filled. Immediately after the barbedbroach is placed into the distal dowel space it is furtherinjected to fill the pulp chamber and periphery of thepreparation. A light coat is also applied on the

Fig 3. Preparation of the mesial wall of the pulp chamber to beparallel with the distal dowel space. A PD reamer has been cut off atthe shank and placed in the distal dowel space as a guild to ensure

parallelism of the preparation.

Fig 5. The shortened OPTE-03 s/s temporary post is in the mesio-lingual dowel space and the #40 modified barbed broach (part of thehandle has been cut off and the shortened barbed broach has beenfolded over) is in the distal dowel space. They are clear of each other

and clear of the opposing occlusion.

Fig 4. Distal dowel preparation is cleaned with EDTA on a cottonwisp wrapped around a #40 modified finger plugger; the bubbling

effect of the EDTA is clearly seen.

Fig 6. Dual arch impression for cast metal post/core. The s/s OPTE-03 post has been reinserted into the impression until all three grooves

are engaged.

opposing occlusion. The index finger and thumb of thegloved right hand are wetted with 70 per cent alcoholor glycerine and a President putty ball (made with aquarter scoop of catalyst and base by the assistant) isheld with these two fingers is placed on the toothpreparation with pressure applied by a thumb of theleft hand to ensure close adaptation around the tooth.The patient is then asked to bite down and keep firmlyshut until impression material sets.

After the impression material has set the patient isasked to open their mouth and the impression is gentlyremoved. Often the stainless steel No 3 post may stayin the mesio-lingual dowel preparation; in this case it isremoved gently and relocated into the impressionmaking sure the three clicks of the relocation groovesare heard and felt when they engage the impression (Fig 6, 7). A cotton pellet is placed into the pulpchamber and the cavity is temporized with the materialof choice, which should be easily removed by ultrasonicscaler to avoid altering the shape of the preparation atthe next appointment.

When the cast gold (Type IV) post/core is receivedfrom the laboratory and checked in the mouth for fit, ashort sprue is notched by a carborundum disk leavingonly thin metal attached to the core. This ‘handle’ willhelp during cementation and could easily be broken off

later. A serrated and sand-blasted titanium OPT-3 postis now checked to ensure it can easily slide through thecore (Fig 8). It is now marked on the model level withthe core and checked in the mouth. If this wassuccessful it is notched with a carborundum disk so itcan easily be broken off during cementation (Fig 9).

The dowel preparations are now cleaned with 15 percent EDTA and 100 per cent alcohol, and dry cottonwool, as previously described. Powder from glovesshould be removed by soap and water before cottonwisps are wound around a No 40 modified fingerplugger. This prevents contamination of dowel spacesby glove powder and also presents an opportunity tocheck gloves for possible microholes and leakage. It isbest to wash gloved hands at the commencement of theappointment.

In the author’s opinion the luting cement of choice isFuji Plus. The working time for this cement is relativelyshort, the cast metal post core and titanium post areheld by their tags with locking tweezers in a comfort-able position for fast insertion into the preparation.After the cement is mixed it is introduced into both thedowel spaces and pulp chamber by a modified No 40Lentulo spiral. Immediately the cast gold post and core

60 Australian Dental Journal 2002;47:1.

Fig 7. The impression in Fig 6 sectioned mesio-distally. The #40folded barbed broach supporting the impression of the distal dowelspace and the OPTE-03 post in the mesio-lingual post hole are

exposed.

Fig 8. A titanium #3 serrated and sand-blasted OPT-3 post, is fittedthrough the cast gold core.

Fig 9. The cast gold post/core is checked for fit in the mouth. Theshortened sprue and the OPT-3 post have been notched with a

carborundum disk level with the occlusal surface of the core.

Fig 10. The case gold post/core with OPT-3 post fitted through thecore have been cemented and are ready for the final impression for a

crown.

Australian Dental Journal 2002;47:1. 61

are seated, followed by the titanium post. As soon asthe titanium post is inserted through the cast gold coreinto the dowel space in the mesio-lingual canal, the tagend is broken off and the remaining post is furtheradvanced into the dowel space by applying pressurewith an amalgam plugger.

While it is in a jelly state the excess cement isremoved with a probe two to three minutes after

cementation. The finishing of the shoulder/chamfer andrefining of the axial walls should be delayed by about10 minutes to allow for full initial set to occur. At thistime the notched sprue on the core is broken off and thesmall protruding part of the titanium post is smoothed(Fig 10). An impression for a crown is now taken usingthe ‘Dual Arch Impressions’10,11 technique and a crown

Fig 11. A porcelain fused to metal crown has been issued.

Fig 12. Upper left 5, 6 and 7 after completion of RCT and removalof weak and unsupported coronal tissue present a restorative

challenge.

Fig 13. The same teeth shown in Fig 12 (25, 26, 27) have beensuccessfully restored with cast gold post/cores. 26 and 27 have slidingOPT-3 posts cemented through the cores. All three teeth are ready for

final impression for crowns.

Fig 14. Root filled 46 and 47 ready for restoration. Nothing of theclinical crowns remains.

Fig 15. Two cast gold post/cores with titanium posts sliding throughthe cores. Note that the posts and the sprues have been notched levelwith the occlusal table of the cores to facilitate breaking them off at

cementation.

Fig 16. 46 and 47 with post/cores cemented ready for crowns to beissued. The gingival margins of the preps have been conditioned withtrichloroacetic acid. This prevents contamination with seepage from

the gingival crevice.

is cemented with the same Fuji Plus luting cement (Fig 11). A similar technique for post/core preparationcould be used for upper molars. The only difference isthe palatal canal is prepared for a cast post and thedisto-buccal for a prefabricated one. Difficult restorationsof upper molars may be salvaged successfully using thismethod (Fig 12, 13). This is also the case for badlybroken down lower molars (Fig 14, 15, 16).

CONCLUSIONIn this article another technique is described for

restoration of mandibular molars after endodontictreatment, where very little is left of the clinical crown.Preparation of two post holes in divergent roots usingspecific slightly modified instruments has beenpresented in this paper. A new impression technique forcast post and core restoration, for single unit and shortspan bridges as well as the preparation of the post holesfor cementation with a modern luting cement are alsodescribed.

ACKNOWLEDGEMENTSThe author would like to thank Mr Ian Burrell for his

excellent technical assistance. Dr S Dracopoulos and DrS Bender for their help in preparing this manuscript.The administration staff of HCF Dental Centre,Sydney, for encouragement and support in this project.There was no commercial, government or any othergrant offered for the work described in this paper.

REFERENCES1. Chiche G, Weaver C, Pinault A. Divergent post and tube and

screw systems for the short crown preparation. Quintessence Int1990;10:813-820.

2. Mora AF, Firtell DN. Cast post and core for nonparallel canals.J Prosthet Dent 1984;52:235-237.

3. Weiner AL. A nonparallel cast post and core technique for teethwith divergent canals. J Prosthet Dent 1981;46:240-242.

4. Chan RW. Restoration of endodontically treated teeth: Part II –Selection and insertion of posts. Aust Prosthodont J 1988;2:67-79.

5. Sadan A, Elliot R, Raigrodski AJ. Treatment planning extensivelybroken-down mandibular molars for post-and-core fabrication.Quintessence Int 1998;29:351-355.

6. State-of-art post and core use from global dental literature. CRANewsletter 1998;22:2.

7. Johnson JK, Schwartz NL, Blackwell RT. Evaluation and restora-tion of endodontically treated posterior teeth. J Am Dent Assoc1976;93:597-605.

8. Trabert RC, Cooney JP. The endodontically treated tooth.Restorative concepts and technique. Dent Clin North Am1984;28:923-951.

9. Goldman M, De Vitre R, Tenca J. Cement distribution and bondstrength in cemented posts. J Dent Res 1984;63:1392-1395.

10. Bass EV, Kafalias MC. Dual-arch impressions. Aust Dent J1992;37:1-5.

11. Bass EV, Kafalias MC. Dual-arch impressions. J Dent AssocSouth Africa 1992;47:428-431.

Address for correspondence/reprints:Dr EV Bass

HCF Dental CentreLevel 3, 403 George Street

Sydney, New South Wales 2000Email: sbender@hcf.com.au

62 Australian Dental Journal 2002;47:1.