Fra

trea

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Érico Braga Fran

aPrivate practice, Bauru, SP, Brazil. DbProfessor, Department of ProsthodcProfessor, Department of ProsthododProfessor, Department of ProsthodeProfessor and Research Coordinato

The Journal of Prosthetic

cture resistance of endodontically

ted teeth restored with glass fiber

ts of different lengths

co, DDs, MSc,a Accacio Lins do Valle, DDS, PhD,b

Ana Lúcia Pompéia Fraga de Almeida, DDS, MSc, PhD,c

José Henrique Rubo, DDS, MSc, PhD,d andJefferson Ricardo Pereira, DDS, MSc, PhDe

Bauru Dental School, University of São Paulo (USP), São Paulo,Brazil; Dental School, University of Southern Santa Catarina(UNISUL), Santa Catarina, Brazil

Statement of problem. Endodontically treated teeth are known to have reduced structural strength. Glass fiber posts mayinfluence fracture resistance and should be evaluated.

Purpose. The purpose of this study was to evaluate the influence of glass fiber post length on the fracture resistance ofendodontically treated teeth.

Material and methods. Forty intact human maxillary canines were selected and divided into 4 groups, the control groupconsisting of teeth restored with a custom gold cast post and core, with a length of two-thirds of the root. Other groupsreceived prefabricated glass fiber posts in different lengths: group 1/3, removal of one-third of the sealing material (5 mm);group 1/2, removal of one-half of the sealing material (7.5 mm); and group 2/3, removal of two-thirds of the sealing material(10 mm). All the posts were cemented with resin cement, and the specimens with glass fiber posts received a composite resincore. All the specimens were restored with a metal crown and submitted to a compressive load until failure occurred. Theresults were evaluated by 1-way ANOVA, and the all pairwise multiple comparison procedures (Tukey honestly significantlydifference test) (a¼.05).

Results. The ANOVA showed significant differences among the groups (P<.002). The Tukey test showed that the controlgroup presented significantly higher resistance to static load than the other groups (control group, 634.94 N; group 1/3,200.01 N; group 1/2, 212.17 N; and group 2/3, 236.08 N). Although teeth restored with a cast post and core supported ahigher compressive load, all of them fractured in a catastrophic manner. For teeth restored with glass fiber posts, the failureoccurred at the junction between the composite resin core and the root.

Conclusion. The length of glass fiber posts did not influence fracture load, but cast post and cores that extended two-thirds ofthe root length had significantly greater fracture resistance than glass fiber posts. (J Prosthet Dent 2014;111:30-34)

Clinical Implications

The technique of using glass fiber posts and composite resin cores maybe appropriate because no root fractures were detected even whenone-third of the root length was used. Therefore, this method appears toprotect tooth structure against fracture.

epartment of Prosthodontics, Bauru Dental School, University of São Paulo (USP).ontics, Bauru Dental School, University of São Paulo (USP).ntics, Bauru Dental School, University of São Paulo (USP).ontics, Bauru Dental School, University of São Paulo (USP).r, Department of Prosthodontics, Dental School, University of Southern Santa Catarina (UNISUL)

Dentistry Franco et

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January 2014 31

Many dentists assume that endo-dontically treated teeth are fragile andmore susceptible to fractures than vitalteeth. However, failures tend to occurwhen remaining coronal walls are lostand the roots weakened.1-3 Issues suchas the failure load and mode of frac-ture have been extensively studied.4-6

The more frequent types of failure areloss of post retention,7 root fracture,3

and loss of crown retention.7 Somestudies have reported that increasingthe post length resulted in a significantincrease in retention, fracture resistance,and a decreased shear stress concen-tration.8-13 However, when the postis placed beyond two-thirds of theroot depth, the level of stress in theapical region increases.14 The risk ofperforation and the weakening of theroot caused by decreasing the dentinvolume in root preparation must beevaluated because of the compromisedprognosis of the restored tooth.15 Thepresence of a ferrule is considered themost important feature for the fractureresistance of endodontically treatedteeth.1,15-17

For many years, the restorativemethod of choice for endodonticallytreated teeth has been the cast postand core, with a high rate of success.15

However, new techniques and materialssuch as prefabricated posts and com-posite resin core materials have emergedas alternatives.7,18-21 More recently, anincrease in the use of prefabricated postsystems has been observed.22 The use ofnonmetallic materials with physicalproperties similar to dentin is nowpreferred in restorative dentistry.15 Glassfiber posts have been reported as havinga favorable indication, with their excel-lent biomechanical properties, esthetics,and clinical performance.22-27 However,other studies have shown that glass fiberposts had inferior results to other pre-fabricated posts.26-30

Given the relationship between intra-radicular length and the success of res-torations, the purpose of this study wasto evaluate the influence of the length ofglass fiber posts in the fracture resistanceof endodontically treated teeth. The nullhypotheses were that no significant

Franco et al

difference would be found in the effect ofpost length on fracture resistance andthat no significant difference would befound among the types of post.

MATERIAL AND METHODS

This studywas approved by the ethicscommittee of Bauru Dental School,University of São Paulo. Forty extractedhuman maxillary canines were selectedwith similar anatomy and with rootlengths between 16 and 18 mm. Theteeth were cleaned and stored in anti-fungal isotonic 0.9% sodium chloridethat contained 0.1% solution thymolcrystals during the experiment. Thecrowns were sectioned at the cemen-toenamel junction with a diamond diskunder continuous coolant to stan-dardize the remaining root length at15 mm. After this procedure, the rootswere prepared to a no. 40 file (DentsplyMaillefer), and obturation was donewith endodontic cement (Sealapex;Sybron Endo).

The roots were fixed with acrylicresin in cylindrical tubes (20 mm � 20mm) parallel to the long axis of thecylinder (Duralay; Reliance Dental MfgCo) (3 mm between the cementoena-mel junction and the acrylic resin wasleft without acrylic resin to representin vivo distances). The specimens werethen randomly divided, by drawinglots, into 4 groups (n¼10). All thespecimens were identified according tothe group to which they belonged(Fig. 1).

The length of root canal preparationvaried according to the post length: thecontrol group and group 2/3 had 10mmof endodontic filling material removed;group1/3had5mmof endodonticfillingmaterial removed, and group1/2 had7.5mm of endodontic filling materialremoved. During and after the end-odontic preparations, irrigation wasperformedwith solutions of 2.5% sodiumhypochlorite and 17% EDTA and salinesolution to remove remnants of guttapercha and dentin.

Cast posts and cores were obtainedfrom acrylic resin patterns of the rootcanals (Duralay; Reliance Dental). The

core height (6.5 mm) and dimensionswere standardized by using a core-forming matrix (TDV Dental). The pat-terns were cast in Type IV gold alloy(Stabilor G; Degussa Dental AG). Aftercasting, they were adjusted and adapt-ed to their respective post spaces.

The glass fiber posts used wereFibrekor no. 2 (diameter, 1.25 mm)(Jeneric/Pentron). The posts were inser-ted into the prepared post spaces toevaluate whether they achieved thedesired length and crown extension of 4mm. Marks were made, and the finallength of the posts was achieved bycutting off the excess with a diamonddisk under water cooling. Beforecementation, the posts were cleanedwith 70% ethanol and water, air-dried,and silanized (Clearfil SE Bond Primerand Porcelain Bond Activator; KurarayCo Ltd).

The remaining root dentin of speci-mens from groups 1/3, 1/2, and 2/3were etched with 37.5% phosphoricacid for 30 seconds, washed for 10seconds, and partially dried with air jetsand absorbing paper points, which leftthe dentin moist. The adhesive system(Excite; Ivoclar Vivadent) was appliedto both the root surface and glass fiberpost and was photopolymerized for 20seconds with a polymerization unit(Ultraled 110 W; Dabi Atlante) used ata 450 MW/cm2 light intensity; then acomposite resin core (Z100; 3M ESPE)was made.

All the posts were cemented withPanavia 21 (Kuraray) by following themanufacturer’s recommendations. Thetooth was prepared with 1.5 mm offacial reduction with a chamfer finishline and 0.5 mm of chamfered lingualreduction to receive a complete metalcrown. The waxing of the crowns to theshape of a canine tooth was performeddirectly on the teeth. On the lingualsurface of the waxed crowns, an areawas demarcated for loading from theuniversal testing machine (Kratus ModelK-2000; Dinamômetros Kratos Ltda) toapply the load. The wax patterns weresprued, invested (Cristobalite; WhipMixCorp), and cast in a nickel-chromiumalloy (Durabond; Comercial Odonto

1 A, Control group, cast post and core with 10 mm of intracanal length.B, Group 1/3, prefabricated glass fiber post with 5 mm of intracanal length.C, Group 1/2, prefabricated glass fiber post with 7.5 mm of intracanal length.D, Group 2/3, prefabricated glass fiber post with 10 mm of intracanal length.

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Import Ltd). The crowns were cementedwith the same material as for the posts.

The roots were tested with a uni-versal testing machine (Kratus K2000MP, Dinamômetros Kratos), with a 500N load cell at a crosshead speed of 0.5mm/min. The specimens received thecompressive load 3.0 mm below theincisal edge of the crowns,22 at a 135-degree angle to the long axis of the

The Journal of Prosthetic Dentis

root (45 degrees relative to the hori-zontal plane), which simulated theocclusal contact of the antagonist toothin an angle class I relationship (Fig. 2).The value of the force (N) to causefailure in each specimen was recordedfor statistical analysis. Statistical testsperformed were a 1-way ANOVA andthe all pairwise multiple comparisonprocedure (Tukey test) (a¼.05).

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RESULTS

Statistically significant differencesamong the groups were found (ANOVA)(P<.002). The Tukey honestly signifi-cantly difference (HSD) test confirmedthat the mean shear strength for thecontrol group was significantly higherthan for the other groups.When the shearstrength among the groups restored withglass fiber posts was compared, no sig-nificant differences were found amongthem (P>.05) (Table I).

DISCUSSION

The first null hypothesis, that nosignificant difference would be found inthe effect of post length on fractureresistance was not rejected, but thesecond null hypothesis that no signifi-cant difference would be found amongthe types of posts was rejected. Themain function of an intraradicular postis to offer retention and support to thefuture restoration.23 The increase in theintraradicular length of the glass fiberposts did not significantly influence theresistance to shear load of endodonti-cally treated teeth.

There are several formulas to deter-mine the intraradicular length of metalprefabricated posts or custom castposts and cores.7,18 In this study, in asimilar manner to the study performedby Isidor et al,5 3 intraradicular lengthsof glass fiber posts were used. At least4.5 mm of apical gutta percha wasretained in the canal to assure apicalsealing of the root canal.12,18

Catastrophic root fractures occurredwhen cast post and cores were tested.This has been observed in otherstudies.3,11,19 In contrast, retrievablecore fractures occurred in the groupsrestored with glass fiber posts. Allrestored teeth with glass fiber postsfailed because of cementation failurebetween the core and the remaining rootdentin. This type of failure is consideredreparable and has been reported in otherstudies.2,3,15,20,25 The average load offailure in this study was higher than theaverage load of failure found in otherstudies for cast posts and cores6 and

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2 Specimen placed on universal testing machine.

Table I. Means (SDs) of failure loadfor each group and Tukey honestlysignificantly difference test

Group Mean (SD)

Control 634.94 �53.2a

1/3 200.01 �28.07b

1/2 212.17 �17.12b

2/3 236.08 �19.68b

SD, standard deviation.Groups with same superscripted letters are notsignificantly different at P<.05.

January 2014 33

fiber posts.13,25 The probable cause ofthese differences is the variation in themethodology used.6,13,25

The teeth in this study presented noremaining coronal dentin and no ferrule.This represented the more challengingcondition for the use of posts becausethe presence of at least 2.0 mm ofremaining coronal dentin increases theresistance to fractures of teeth restoredwith prefabricated posts.3,5 In teeth withcast posts and cores, and in those withglass fiber posts, a complete metalcrown was used to simulate a typicalrestorative clinical condition; thismethodology has been adopted inanother study.14 However, it is impor-tant to highlight that in vitro studiespresent several limitations. The mostimportant is the difficulty in simulatingthe mechanical condition present in theoral environment. First, the tooth is notrigidly fixed in the bone because theperiodontal ligament allows micro-movement of the root and modifies the

Franco et al

distribution of forces, thereby acting as abuffer. A second important factor is themodification of the distribution offunctional loads, which can influencethe final results.With a cemented crown,the stresses of functional loads concen-trate at the cervical portion of thetooth.9,10,15 This stress concentrationapplied to glass fiber posts with a lowermodulus of elasticity than Type IV goldalloy explains the failures observed ingroups 1/3, 1/2, and 2/3 of the presentstudy. With the dislocation of the crownand of the core, an increase of the stresson the post occurs, which causes thecementation failure. A third importantfactor was that this study was performedin vitro by using static loading, whichcould not completely replicate clinicalconditions. Formoremeaningful results,further studies should incorporate ther-mocycling and mechanical fatigue untilfailure.

In the control group, because thecast post and core had a much highermodulus of elasticity and rigidity,15 thecrown walls provided higher retentionand stability to the crown restoration.However, this core transmitted morestress from the crown to the post andcore, and, therefore, to the remainingroot dentin, and the failure occurredwhen the load exceeded the limit ofresistance to the root fracture.7

Although many suggestions havebeen made regarding the intraradicularlength of posts, few studies have beenperformed to specifically evaluate thisvariable with metallic and glass fiber

posts.5,20 Even though few studies havebeen performed with glass fiber posts,the disadvantages of post length are thesame in metal and nonmetal posts. Thepost length, although important to themechanical behavior of metal posts, isnot as important in glass fiber posts. Inthis study, all the experimental speci-mens were made of glass fiber withdifferent lengths and failed at similarloads. These loads are below those ex-pected during function when consid-ering the masticatory forces reported byNeill et al.20 Catastrophic root fracture isa rare occurrence, and the major clinicalcomplication of fiber reinforced com-posite posts is adhesive failure (clinicallyexpressed as post-crown debonding).26

Pereira et al27 reported that the self-adhesive resin cements and the glassionomer cements presented higherpush-out bond strength values than thedual-polymerizing resin cements.

CONCLUSIONS

The intraradicular length of glassfiber posts was not a relevant factor inthe failure load of endodonticallytreated teeth. Irreparable root fracturesoccurred in the group with cast postsand cores, whereas repairable failuresoccurred in the groups with glass fiberposts.

REFERENCES

1. Bonfante G, Kaizer OB, Pegoraro LF, doValle AL. Fracture strength of the teeth withflared root canals restored with glass fiberpost. Int Dent J 2007;57:153-60.

2. Zogheib LV, Pereira JR, Valle AL,Oliveira JA, Pegoraro LF. Fracture resistanceof weakened roots restored with compositeresin and glass fiber post. Braz Dent J2008;19:329-33.

3. Pereira JR, Valle AL, Shiratori FK, Ghizoni JS,Melo MP. Influence of intraradicular postand crown ferrule on the fracture strength ofendodontically-treated teeth. Braz Dent J2009;20:297-302.

4. Fokkinga WA, Kreulen CM, Vallitiu PK,Creugers NH. A structured analysis of in vitrofailure loads and failure modes of fiber,metal and ceramic-post-and-core systems.Int J Prosthodont 2004;17:476-82.

5. Isidor F, Brodum K, Ravnholt G. The influ-ence of post length and crown ferrule lengthon the resistance to cyclic loading of bovineteeth with prefabricated titanium posts. Int JProsthodont 1999;12:78-82.

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6. Heydecke G, Butz F, Hussein A, Strub JR.Fracture strength after dynamic loading ofendodontically treated teeth restored withdifferent post-and-core systems. J ProsthetDent 2002;87:438-45.

7. Standlee JP, Caputo AA, Collard EW,Pollack MH. Analysis of stress distribution byendodontic posts. Oral Surg Oral Med OralPathol 1972;32:952-60.

8. Pereira JR, Valle AL, Shiratori FK,Ghizoni JS. Effect of post length onendodontically treated teeth: analyses oftensile strength. Braz J Oral Sci2011;10:277-81.

9. Valle AL, Pereira JR, Shiratori FK,Pegoraro LF, Bonfante G. Comparison of thefracture resistance of endodontically-treatedteeth restored with prefabricated post andcomposite resin core with different postlengths. J Appl Oral Sci 2007;15:29-32.

10. Pereira JR, Valle AL, Juvencio TM,Fernandes TM, Ghizoni JS, Só MVR. Effect ofpost length on endodontically-treated teeth:fracture resistance. Br J Oral Sci 2010;9:176-80.

11. Pereira JR, Neto EMR, Pamato S, Valle AL,Paula VG, Vidotti HA. Fracture resistance ofendodontically treated teeth restored withdifferent intraradicular posts with differentlengths. Br J Oral Sci 2013;12:1-4.

12. Leary JM, Aquilino SA, Svare CW. An evalu-ation of post length within the elastic limitsof dentin. J Prosthet Dent 1987;57:277-81.

13. Nergiz I, Schmage P, Özcan M, Platzer U.Effect of length and diameter of taperedposts on the retention. J Oral Rehabil2002;29:28-34.

14. Cecchin D, Farina AP, Guerreiro CAM,Carlini-Junior BC. Fracture resistance of rootsprosthetically restored with intraradicularposts of different lengths. J Oral Rehabil2010;37:116-22.

The Journal of Prosthetic Dentis

15. Fernandes AS, Dessai GS. Factors affectingthe fracture resistance of post-core recon-structed teeth: a review. Int J Prosthodont2001;14:355-63.

16. Oliveira JA, Pereira JR, Valle AL, Zogheib LV.Fracture resistance of endodontically treatedteeth with different heights of crown ferrulerestored with prefabricated carbon fiber postand composite resin core by intermittentloading. Oral Surg Oral Med Oral PatholOral Radiol Endod 2008;106:e52-7.

17. Pereira JR, de Ornelas F, Conti PC, do Valle AL.Effect of a crown ferrule on the resistance ofendodontically treated teeth restored with pre-fabricated posts. J Prosthet Dent 2006;95:50-4.

18. Hudis SI, Goldstein GR. Restoration ofendodontically treated teeth: a review of theliterature. J Prosthet Dent 1986;55:33-8.

19. Santos-Filho PCF, Verissimo C, Queiroz CL,Saltarelo RC, Soares CJ, Barreto BCF. Theeffect of type post, crown, and ferrule pres-ence on stress distribution of maxillary cen-tral incisors with weakened roots: FiniteElement Analysis. J Res Dent 2013;2:154-64.

20. Neill DJ, Kydd WL, Wilson NJ. Functionalloading of the dentition during mastication.J Prosthet Dent 1989;62:218-28.

21. Pereira JR, Oliveira JA, Valle AL, Zogheib LV,Martins PF, Bastos LGC. Effect of carbon andglass fiber posts on the flexural strength andmodulus of elasticity of a composite resin.Gen Dent 2011;59:e144-8.

22. Akkayan B, Gülmez T. Resistance to fractureof endodontically treated teeth restored withdifferent post system. J Prosthet Dent2002;87:431-7.

23. Robbins JW. Restoration of endodonticallytreated tooth. Dent Clin North Am 2002;46:367-84.

24. Pitel ML, Hicks NL. Evolving technology inendodontic posts. Compendium Cont Educ2003;24:13-28.

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25. Mangold JT, Kern M. Influence of glass-fiber posts on the fracture resistance andfailure pattern of endodontically treatedpremolars with varying substance loss:an in vitro study. J Prosthet Dent 2011;105:387-93.

26. Monticelli F, Grandini S, Goracci C,Ferrari M. Clinical behavior of translucent-fiber posts: a 2-year prospective study. Int JProsthodont 2003;16:593-6.

27. Pereira JR, Valle AL, Ghizoni JS, Só MV,Ramos MB, Lorenzoni FC. Evaluation ofpush-out bond strength of four lutingagents and SEM observation of thedentine/fibreglass bond interface. Int EndodJ 2013;46:982-92.

28. Chang JW, Soo I, Cheung GS. Evaluation offiber post-supported restorations undersimulated occlusal loading. J Prosthet Dent2012;108:158-64.

29. Basaran EG, Ayna E, Halifeo�glu M. Micro-leakage of endodontically treated teethrestored with 3 different adhesive systemsand 4 different fiber-reinforced posts.J Prosthet Dent 2012;107:239-51.

30. Valdivia AD, Raposo LH, Simamoto-Júnior PC, Novais VR, Soares CJ. The effectof fiber post presence and restorativetechnique on the biomechanical behaviorof endodontically treated maxillary incisors:an in vitro study. J Prosthet Dent 2012;108:147-57.

Corresponding author:Dr Jefferson Ricardo PereiraRua Recife 200, Apto 601Bairro Recife Tubarão, SC 88701-420BRAZILE-mail: jeffripe@rocketmail.com

Copyright ª 2014 by the Editorial Council forThe Journal of Prosthetic Dentistry.

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