JR Et Al-2008-International Endodontic Journal

 

doi:10.1111/j.1365-2591.2008.01424.x

Fracture resistance of structurally compromised root filled bovine teeth restored with accessory glass fibre posts

H. Martelli Jr, E. P. Pellizzer, B. T. Rosa, M. B. Lopes & A. Gonini Jr University North of Parana´, Londrina, Parana´, Brazil

Abstract Martelli H Jr, Pellizzer EP, Rosa BT, Lopes MB, Gonini A Jr.   Fracture resistance of structurally compromised root filled bovine teeth restored with accessory glass fibre posts.   Interna-  tional Endodontic Journal ,  41 ,

  were were pe perf rfor orme med d to ex exam amin inee di diff ffer eren ence cess in fracture fract ure resistance resistance;; fracture fracture mode modess were analysed by Fischer’s exact test. Results   The mean mean fra fractu cture re res resist istanc ancee val values ues (kg (kgf) f) were 61.8 (MP), 63.1 (GP), 55.5 (AGP), 56 (GP-R) and (53.1) AGP-R. No statistically significant difference was found between groups. The Fisher’s exact test indicated significant differences (P  < 0.05) in the fracture mode amongst groups MP, GP and AGP, indicating 100%, 50% and 10% of catastrophic fractures, respectivelly. anova

685–692, 2008.

Aim  To evaluate the mechanical behaviour of structur turall ally y compro compromis mised ed root root fill filled ed bov bovine ine roots roots aft after er restoration with accessory glass fibre posts. Methodology   Fif Fifty ty roo roots ts of bov bovine ine tee teeth th rec receiv eived ed

conventional post preparations with a cervical diameter of 3.5 mm. The roots were assigned to five groups (n  = 10): group MP – cast metal post, group GP – glass fibre fibre post post and and gr grou oup p AG AGP P – gl glas asss fibre fibre post post pl plus us accessory glass fibre posts. In groups GP-R and AGP-R (similar to groups GP and AGP), 2 mm of coronal tooth structure struc ture were left intact. All group groupss were subject subjected ed to an elas elasti ticc li limi mitt assa assay y an and d te test sted ed in an univ univer ersa sall machine mach ine for fracture fracture resis resistance tance.. Repe Repeated ated measures measures

Introduction The restoration of root filled teeth is a challenge. Loss of tooth structure although carious lesions, fractures and and as a re resu sult lt of ro root ot ca cana nall trea treatm tmen entt lead leadss to weakening weak ening of the remaining tooth tissue tissuess (Gutm (Gutmann ann 1992). 199 2). Whe When n the cor corona onall res restor torati ation on is associ associate ated d with an intraradicular post, the likelihood of restoratio tion n fai failur luree increa increases ses,, wit with h roo roott fractu fracture re one of the most unfavourable outcomes (Qualtrough & Mannocci 2003).

Corresponde nce: Alcide Correspondence: Alcidess Gonini Ju´ nior, Rua Pernambuco, Pernambuc o, 390 Sala 903, Londrina, Parana ´´,, CEP 86020-913, Brazil (Tel.: +5 +55 5 43 33 3324 24 70 7016 16;; fa fax: x: +5 +55 5 43 33 3329 29 11 1197 97;; ee-ma mail il:: [email protected]).

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Conclusions   The use of accessory glass fibre posts affected the fracture mode favorably: 90% of fractures in group AGP were in the coronal third. Keywords:  cast metal post, fracture resistance, glass fibre post, pre-fabricated post, root fracture. Received 5 October 2007; accepted 6 March 2008

To prevent fractures, factors such as the amount of  remaining tooth structure, the mechanical resistance of  the post and bondi bonding ng bet betwee ween n the cana canall wal walls ls and restoration restoratio n must be consi considered dered (Sornkul (Sornkul & Stan Stannard nard 1992). 199 2). Alth Althoug ough h a cas castt met metal al post and core is the tradit tradition ional al app approa roach ch bec becaus ausee of its pro proven ven cli clinic nical al effectiveness (Solomon & Osman 2003), its mechanical prop proper erti ties es may may in incr crea ease se th thee ri risk sk of root root fr frac actu ture re (Hornbrook & Hastings 1995). As an alternative to metal, pre-fabricated posts made of glass fibres in a matrix of epoxy resin were developed (Duret   et al.   1990) 1990).. They They have have hi high gh mech mechan anic ical al resistance and their modulus of elasticity is similar to that of dentine (Fokkinga  et al.  2004). Such properties would wou ld all allow ow the them m to for form m a hom homoge ogeneo neous us com comple plex x with the root and provide absorption of loads comparabl rablee with with a soun sound d to toot oth h (Dur (Duret et   et al.   1990). 1990). In

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addition, because of their translucency, glass fibre posts contribute to the aesthetic qualities of tooth-coloured restorations (Ferrari  et al.  2001). Nonetheless, in cases of excessively wide root canal prepar preparati ations ons,, the extra extra spa space ce for the cement cement would would impair the resistance to fracture of the roots (Kimmel 2000, Marchi  et al.  2003). The purpose purpose of thi thiss study study was to invest investiga igate te the

The 15-mm roots were randomly assigned to three groups (n  = 10). In group MP, the roots were restored with cast metal posts (Goldent LA Copper–Aluminum Alloy; AJE Comercio Imp. Exp. Ltda., Sao Paulo, SP, Brazil) cemented with zinc phosphate (SS White, Rio de  Janeiro, RJ, Brazil) (Fig. 2). In group GP, a serrated glass fibre post (Reforpost; Angelus Science and Technology, Londrina, PR, Brazil)

fracture resistance of root filled teeth, considering an innovativ inno vativee techniqu techniquee (acc (accessory essory glass fibre posts) for wide root canals as well as the influence of the amount of remain remaining ing sou sound nd too tooth th str struct ucture ure in the corona coronall third. Resistance values were obtained by a tangential compre com pressi ssion on tes test. t. The mechan mechanica icall beh behavi aviour our of the treated roots was evaluated through analysis of their fracture modes.

was cemented with a composite resin (Rely X ARC; 3M ESPE, St Paul, MN, USA) and a conventional two-step adhesive system (Adper Single Bond 2; 3M ESPE). Filtek Z 250 restorative composite resin (3M ESPE) was used for the core build-u build-up. p. In group AGP, together with the main post, three accessory glass fibre posts of different diameters (Reforpin; orp in; Ang Angelu eluss Sci Scienc encee and Techno Technolog logy) y) wer weree also also cemented (Figs 3–5). The 17-mm roo roots ts wer weree random randomly ly assign assigned ed to two other groups (n  = 10). Roots of groups GP-R and AGPR (Fig. 6) were restored in the same manner as GP and AGP; however, 2 mm of their remaining tooth structure was left intact (Table 1). All samples were fixed in poly polyvinyl vinyl chloride chloride rings with polystyrene resin at a level of 3 mm below the

Materials Mater ials and methods methods One hundred and fifty bovine incisors were extracted and stored stored in a 0.5 0.5% % T-c T-chlo hloram ramine ine soluti solution on unt until il cleaning. After that, the coronal portion of each tooth was sectioned 17 mm coronal to the root apex using a diamond double-face disk (KGSorensen, Sao Paulo, SP, Brazil) cooled with water. Fifty of the teeth were then sel selec ected ted statis statistic ticall ally y on the basis basis of the their ir roo roott canal canal diameter. The buccolingual and mesiodistal diameters for each tooth were obtained using a digital caliper (Z & Y Co., Qindao, Shandong, China) and the average was calculated for each root. Descriptive statistics was used to analyse the samples, based on the collection of the av aver erag ages es.. Acco Accord rdin ing g to th thee resu result ltss (roo (roott av aver erag agee dia diame meter ter of 6.90 6.90 mm with with coe coeffic fficien ientt of variat variation ion 2.15%), the roots were similar in size. Following the selection process, the roots were stored in a 0.9% saline solution. Thirty Thi rty tee teeth th were were adj adjust usted ed to a length length of 15 m mm, m, whilst whi lst 20 rem remain ained ed 17 m mm m lon long. g. Roo Roott canals canals were were prepared with number 4138 diamond bur (KG Sorensen) in a high-speed water-cooled handpiece and a size 5 Largo drill (Dent (Dentsply sply Mail Maillefe lefer, r, Ball Ballaigue aigues, s, Switz Switzererlan land). d). Dep Depths ths of prepar preparati ations ons wer weree 10 mm for the 15 mm roots and 12 mm for the 17 mm roots. To simulate weakened roots, a diameter of 3.5 mm was est establ ablish ished ed at the ent entran rance ce of all can canals als during during prepar preparati ation, on, whilst whilst conver convergen gentt walls walls wer weree cre create ated d towards the apical third, reproducing the external root morphology, with the same remaining wall thickness. After preparation, the apical and middle thirds of the root canal were filled with heated Gutta-percha resulting in an apical root filling of 5 mm (Fig. 1).

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Figure 1   R Radi adiogr ograph aphic ic ima image ge of roo roott after after int intrar raradi adicul cular ar preparation and apical seal.

 

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Figure 2   Sample with cemented cast metal core.

  Resistance of fibre posts

Figure Figur e 4  Radiographic image of posts position after cementation (group AGP).

Figure 3   Main glass fibre post and three accessory posts before

built-up (group AGP).

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Figure 5   Samples of groups AGP.

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Figure 6   Samples of groups AGP-R.

cervical margin of preparations simulating the biological width. The fracture resistance resistance test was performe performed d with a )1 compressive load at 0.5 mm min . The samples were pl plac aced ed at th thee base base of a univ univer ersa sall te test stin ing g ma mach chin inee (Kratos K 500 SMP, Cotia, SP, Brazil) at an angle of  135   in relation to the horizontal plane. The compressive load was applied 2 mm below the incisal edge on the palatal surface of the built-up core. All data were statistically analysed with one-way analysis of variance (anova) at significance level of 5%.

Table 1  Experimental groups and restorative techniques Gr Grou oup p

Re Rest stor orat ativ ive e te tech chni niqu que e

MP

Ca Cast st me meta tall post post an and d co core re ceme cement nted ed with with zi zinc nc phosphate On e mai ain n g las lass s fib brr e po s stt c em emen entted wit ith h composite resin/core with composite resin Four Four glas glass s fibre fibre post posts s (o (one ne ma main in plus plus th thre ree e accessory) cemented with composite resin/core with composite resin Sa Same me as GP GP,, but but root roots s with with 2 mm of  remaining coronal structure Sa Same me as AGP, AGP, but but root roots s with with 2 mm of  remaining coronal structure

GP AGP AGP

GP GP-R -R AGPAGP-R R

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Figure 7  Fracture in coronal third (group AGP).

After After tes testin ting, g, all sam sample pless wer weree rem remove oved d fro from m the rings with a diamond disk, the fracture modes (Figs 7 and 8) wer weree cla classi ssified fied as rep repair airabl ablee or cat catast astrop rophic hic (Heydecke   et al.   2001) 2001) (Fi (Fig. g. 9) 9),, and wer weree com compar pared ed statistically using the Fischer’s exact test.

Results Table 2 shows the values of fracture resistance. There were no stati statistica stically lly significan significantt diff differenc erences es amon amongst gst groups (P  = 0.65). The rela relations tionship hip betwe between en fracture fracture resis resistance tance and fracture modes (Table 3) reveals only root fractures in grou group p MP MP.. In ei eigh ghtt samp sample les, s, they they occu occurre rred d in the the cervical third of the root, whilst two occurred in the middle third of the root. In group AGP, no fractures occurred in the middle third of the root, nine occurred in the coronal portion and one in the cervical third). Groups GP-R and AGP-R did not present fractures in the the mi midd ddle le thir third d of the the ro root ot but but 50 50% % and and 60 60%, %, respective respe ctively, ly, of fractures fractures from these groups occu occurred rred in the ce cervi rvical cal third. third. Fra Fractu cture re mod modee ana analys lysis is by the Fisher’s Fishe r’s exac exactt test reve revealed aled a statis statistica tically lly significant significant difference (P  < 0.05) amongst groups MP, GP and AGP (Table 4).

 

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be required, not only to retain the future restoration (Libman & Nicholls 1995, Morgano 1996, Mannocci et al.   1999, Heydecke  et al.  2001, Zhi-Yue & Yu-Xing 2003 2003), ), bu butt al also so to re rein info forc rcee the the re rema main inin ing g to toot oth h structure (Lui 1987, 1994, Saupe  et al.  1996, Kimmel 2000, Solomon & Osman 2003). It has been reported that th at th thee re rein info forc rcem emen entt of a wi wide de root root ca cana nall with with compos com posite ite res resin, in, pri prior or to the cementat cementation ion of a cas castt

Figure Figur e 8  Fracture in cervical third (group AGP-R).

Discussion Thinning Thinni ng of roo roott canal canal wal walls ls is an inevit inevitabl ablee conseconsequence que nce of roo roott can canal al treatm treatment ent.. Furthe Furthermo rmore, re, the interrupti inter ruption on of root deve developme lopment, nt, exte extensive nsive cario carious us lesion lesionss and tra trauma uma may res result ult in exc excess essive ively ly wide wide canals and weakened roots. In such cases, a core may

metal post, could increase by 50% the fracture resista tanc ncee of a ro root ot (S (Sau aupe pe   et al.   1996) 1996).. How Howeve ever, r, a combination of filling material and intraradicular post, capable capab le of full fully y resto restoring ring the resis resistance tance of weakened weakened roots, is yet to be described (Marchi  et al.  2003). According to previous studies (Newman  et al.  2003, Fokkinga   et al.   2004), 2004), cast meta metall and stainless steel posts provide high failure loads when compared with gla glass ss fibr fibree pos posts. ts. In the prese present nt exp experi erimen mentt and in agreement with other studies (Barkhordar  et al.  1989, Akkayan & Gu¨ lmez 2002, Zhi-Yue & Yu-Xing 2003), there was no statistically significant difference amongst grou groups ps (T (Tab able less 2 and and 3) and and al alll of them them wo woul uld d theoretic theor etically ally withstan withstand d func functiona tionall loads of 23 to 29 kgf in the anterior region of dentate patients (Ahlberg et al.  2003). Regarding the fracture mode, an unfavourable dissipation of stresses (Toparli 2003) on teeth of group MP could explain the 100% of failures below the biological width in this group (Table 3). When group MP is compared with GP, the risk of a catastroph catas trophic ic fract fracture ure is redu reduced ced for the latter. When glass fibre posts were used instead of cast metal, this resultt can be expected resul expected (Newman   et al.   2003). 2003). Glass fibre posts have a modulus of elasticity similar to that of 

Figure 9  Locations and frequencies of fracture in five test groups. Fractures in coronal third were deemed repairable; fractures in

cervical and medium third were deemed catastrophic.

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Table 2  Resistance to fracture (kgf) Group N

MP

GP

AGP

GP-R

AGP-R

1 2 3 4 5

40.25 87.25 69.00 24.50 51.00

87.50 40.13 92.38 74.38 70.13

65.88 55.25 61.25 62.50 89.38

37.50 82.38 71.75 55.63 43.88

58.25 52.25 66.88 54.00 51.38

6 7 8 9 10 Mean Sd CV

59.50 65.63 98.13 56.25 66.63 61.81 21.25 34.40

76.50 35.25 51.38 63.75 39.80 63.12 20.53 32.52

70.88 38.75 30.75 38.50 41.50 55.46 18.11 32.65

71.38 42.25 45.38 46.75 63.75 56.07 15.34 27.35

68.00 38.75 49.50 52.50 39.50 53.10 9.70 18.26

SD, standard deviation; CV, coefficient of variation (%).

dentine, which would reduce the concentration and the intensity of functional loads on the root (Maccari  et al. 2003). 200 3). Thi Thiss ben benefic eficial ial mec mechan hanica icall con condit dition ion is enhanced when comparing GP with AGP, where most of  the space between root canal wall and the main fibre glass post is filled with accessory fibre glass posts in pla place ce of res resin in ce cemen mentt (Asmus (Asmussen sen   et al.   1999). 1999). In additi add ition, on, a thinne thinnerr lay layer er of res resin in ce cemen mentt presen presents ts a reduced redu ced degre degreee of polymeriza polymerization tion shrin shrinkage kage (Alste (Alsterr et al.  1997). The fracture modes of group AGP (90% in the coronal third – Table 3) are in accordance with other studies (Akkayan & Gu¨lmez 2002, Maccari  et al.  2003, Newman  et al.  2003). The mechanical behaviour of glass fibre posts proba probably bly incre increases ases the like likelihoo lihood d of repai repairable rable fractures, which are considered favourable because, in a clinic clinical al situat situation ion,, the they y would would hav havee sim simpli plified fied the rep reprep repara aratio tion n of the too tooth th (Manno (Mannocci cci   et al.   1999), whilst whil st vertical vertical or catas catastroph trophic ic fract fractures ures would result

in sur surgic gical al cro crown wn len length gtheni ening ng or too tooth th ext extrac ractio tion n (Peroz et al.  2005). Ev Even en co cons nsid ider erin ing g th that at the the prop propos osed ed po post st spac spacee preparati prep aration on is a pre-d pre-disposi isposing ng fact factor or for vertical fractures, tures, it is of a sec second ondary ary imp import ortanc ancee (La (Lassi ssila la   et al. 2004) 200 4) if a min minima imally lly suffici sufficient ent dentin dentinee thi thickn ckness ess of  1 mm around the entire circunference after post space pre prepar parati ation on can be pro provid vided ed (Tj (Tjan an & Whan Whan 198 1985, 5, Gluskin   et al.   1995 1995). ). Base Based d on the the root root aver averag agee diameter (6.9 mm) and the cervical diameter preparatio tion n (3. (3.5 5 mm), mm), and con consid sideri ering ng that that ext extern ernal al root root morphology was reproduced during root preparation, it could cou ld be conclu concluded ded that, in the pre presen sentt wor work, k, the remaining dentinal walls were not less than 1 mm in thickness. Regard Reg arding ing the issue issue of remain remaining ing cor corona onall too tooth th structure, the literature is controversial. Some studies report that a height of 2 mm (Saupe   et al.   1996) or 3 mm mm (Me (Melo lo   et al.   2005) 2005) doe doess not provid providee gre greate aterr resistance resis tance to fract fracture ure of the test spec specimen imens, s, which was also observed in this study (Table 2). However, it has als also o bee been n rep report orted ed tha thatt as the intact intact cor corona onall hei height ght in incr crea ease ses, s, th ther eree is a prop propor orti tion onal al in incr crea ease se in the the resistance to fracture (Isidor  et al.  1999). In this study, per perhap hapss the remain remaining ing str struct ucture ure in hei height ght was not sufficiently thick to provide a greater resistance because of the extensive internal preparation. Another possible limitation of the present study may be the absence of a prosthetic restoration, which would certainly cert ainly gene generate rate a diff different erent biomechani biomechanical cal effect. effect. Based Base d on the literature literature (Barkhordar (Barkhordar  et al.   1989, Erkut et al. 2004), the presence of a crown ferrule around the preparation provides greater resistance to fracture. On the other hand, it has been demonstrated that metal ceramic crowns on teeth with 2 mm of intact coronal structure did not increase the fracture resistance of root filled teeth (Zhi-Yue & Yu-Xing 2003).

Table 3   Resistance to fracture (kgf) for each fracture site (coronal, cervical or middle third of root) Fracture site Coronal third of root

690

Group

Mean

MP GP AGP GP-R AGP-R Total

– 46.06 54.31 45.53 49.55 49.95

 

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Cervical third of root n 

 

0 5 9 5 4 23

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Mean 59.33 78.96 65.88 63.09 56.65 62.57

 

Middle third of root  

n 

8 3 1 5 6 23

Mean 71.75 82.00 – – – 76.88

 

 

Total n 

2 2 0 0 0 4

 

Mean 61.81 63.12 55.46 56.07 53.10 57.91

 

n 

10 10 10 10 10 50

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Table 4  Comparison amongst groups (Fischer’s exact test) Groups

Value of  P   

MP   ·  GP  ·   AGP GP   ·   GP-R AGP  ·   AGP-R

0.0002 0.3317 0.1409

 

Significant Yes No No

Conclusions Within Wit hin the lim limita itatio tions ns of thi thiss stu study, dy, the fol follow lowing ing conclusions can be drawn: differencess in fracture strength were 1.   No significant difference detected dete cted amongst the five test group groups. s. Remaining ning sound tooth structu structure re in the coronal 2.   Remai third did not influence fracture resistance. composite osite cores associ associated ated 3.   Glass fibre posts with comp with accessory posts led to a more favourable fracture mode in struct structurall urally y compromise compromised d root filled bovi bovine ne teeth. Acknowledgements This study was based on an MSc thesis submitted to the University North of Parana and supported in part by Angelus Science and Technology (Londrina, PR, Brazil) and 3M ESP ESPE E (St (St.. Paul, Paul, MN, USA and Sum Sumare are,, SP, Brazil).

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International Endodontic Journal,  41 ,

685–692, 2008

 

ª  2008  International Endodontic Journal