Root End Filling Materials_ a Review

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Endodontics &Dental Traumatology

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Root end filling materials: a review

Review article

Torabinejad M, Pitt Ford TR. Root etid filling tnaterials: a review.Endod Dent Traumatol 1996; 12: 161-178. © Mtmksgaard, 1996

Abstract-When non-surgical attempts pixnv tiusticccssiul or arecouti aindicated, sttrgical endodontic therapy is needed to savetbe tootb. Tbe procedute usually consists of ex]Dosure of tbe in-volved area, root end lesection, root end piepaiation and inser-tion of a root end fiUing material. Nunietotts materials havebeet! suggested as root end filling materials. This article is a re-view of tbe literattne on tbe suitability of variotis root end fillingliiatet ials based ou tbeir leakage assessment, marginaladaptatioii, cytotoxicity, and usage test iii expetiniental animalsand Innnans.

M. Torabinejad\ T. R. Pitt Ford^

'Department ot Endodontics, Loma LindaUniversity, Calitornia. USA, 'Departmet otRestorative Dentistry, United Medicai and DentalSchools, University ot London, England

Key words: root end tilling; retrograde tiiling;endodontic materials

Mahmoud Torabinejad, Department ot Endodontics,Loma Linda University, Loma Linda, Calitornia,USA.

Accepted January 8,1996

Studies have shown that pulpal and periiadicularpatbosis develop only when tbese tissties are ex-posed to bacteiial contamination. To determinetbe impoitance of bacteria, Kakebasbi et al. (1) aswell as Paterson (2) exposed tbe dental ptilps ofccinventional and germ-free rats to tbeir own oralflora, wbicb resulted in tbe development of pulpaland ]:)eritadictilar lesions in conventional tats, butfailed to create lesions in germ-free rats.

Moller et al. (3) severed tbe pulps of teeth intnonkeys and eitber sealed aseptically the ampti-tated pulps immediately, or left them open to becontaminated with indigenotis oral flora for 1week and then sealed. Clinical, radiograpbic, andbistological examinations of tbe teeth tbat weresealed aseptically showed an absence of any patbo-logical changes in their peritadicttlar tissues. Incontrast, teetb witb infected root canals had in-flammatory reactions in their tissues.

Fabticitis et al. (4) inoculated root canals ofmonkeys with 11 bacterial species sejDarately, or incombinations, and sealed tbe access cavities for aperiod of 6 tiiontbs. Tbeir bacteriological and bis-tological examinations showed tbat mixed infec-tions have a gieqter capacity to cause apical le-sions than do monoinfections. Fttrtberniore, the)'reported that the Bacteroides strain did not sur-vive in tbe root canals when inoculated as ptue

cultures. Enterococei sur\ived as ptue ctiltures,and facultative streptococci induced small pet-iiadicular lesions.

As a consequence of patbological changes intbe dental pulp, the root canal system acquires tbecapacit)' to harbour several species of bacteria,tbeir toxins and tbeir by-products. Egress of theseirritants from the root canal system into tbe peri-apical tissue restilts in tbe formation of periradicu-lar lesions which are mediated by nt)nspecific aswell as immtme responses (5).

Complete cleaning and shaping of root canalsand sealing tbem in tbree dimensions sbould re-sttlt in resoltition of periradicttlar lesions in all pa-tients wbo have undergone non-surgical root ca-nal therapy. Tbe degree of sticcess follo\dng rootcanal therapy has been reported as bigb as 98.7%(6) and as low as 45% (7). Ingle & Glick (8) re-ported a success rate of 95% of all treated endo-dontic cases, wliich compares favotirabh- withotber reports of success. In an examination offailed cases from the Washington study Itigie et al.(9) reported tbat over two thirds of tbese failureswete related to incomplete cleaning atid obttira-tiou of root canals. Harty et al. (10) bave also re-ported tbat the majority of non-stirgical endodon-tic procedtues wbicb fail do so because of inade-qtiate apical seal.

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Itl addition to the factors cited in tbe abovestudies, a number of recent investigations bavesbown tbat the exposttre of the coronal pat ts offilled root catnals to oral flora tesitlts in total con-tamitiation of the filled t oot canals in a few days(11-1.5). This occttrs as a restilt of either the pres-ence of voids between tbe deutinal walls and tbefilling materials used to ot:)tuiate tbe root canal.system and/or "wasbitig otit" of tbe toot canalsealers.

Tbe preferted treatment of failing etidodonticcases is non-stngical retreatnient. According toBergenboltz et al. (16) tbis treatment usually te-sults itl successful outcomes. Howevet, becaitse oftbe complexity of root canal systems, inadequateitistitmientatiou and presetice t)f pbysical barriers(anatomical, post atid core restoration, separatedinstrimients, etc.), ideal goals tiiay be difficult toacbieve witb a non-surgical approach. Surgical en-dodontic therapy then becomes tbe fiist altetna-tive. Endodontic stngery lias a lotig bistoty. Tbeprocedure involves expositig tbe involved apex, re-secting the root-end, pi eparing a class I cavity, andmost often inserting a root-end filling material.

Because most endodontic failures occur as a te-stilt of leakage of irritants from pathologically in-volved root canals the root-end ftlling tnaterialsbould ptovide an apical seal to an otbei wise un-obtttrated root catial or improve tbe seal of exist-ing root canal filling materials and be biocompati-ble witb periradictilar tissties. To seal the root-end,the operator should remove the apical 2—3 mm ofthe root-end, prepare a root-end cavity, atid placea root-end filling matetial. A bevelled resectedroot is crttcial to good visibility (17). However, Gil-heany et al. (18) demonstrated that as tbe angle oftbe bevel increases, the apical leakage also in-creases due to tbe permeability of tbe dentinal tu-bules. After a toot resection, as perpetidictilar totbe lotig axes of tbe root as possible, a class I cavitypreparation wbicb incltides tbe apical foramen ofthe root should be prepared witb a bur or an idtia-sonic instrument. Despite tbe advantages of tiltta-sonic tips sbown by Wuchenich et al. (19), Abediet al. (20) bave demonstrated tbat tbey cteatemore iiiicrofractures tban bins during toot-etidcavity preparations. Recently, O'Conner et al. (21)compaiecf tbe sealing ability of SuperEBA andanialgatn with varnish when placed into cavityprepatations made witb ulttasonic tip or fissurebur. Their resttlts showed uo sigtnficant diffetencebetween tbe two root-end resections and prepata-tion teclniiques. Howevet; tbey sbowed Sttpei EBAleaked significantly less tban amalgam witb var-nish.

Once tbe loot-cnid pre]3atation lias been com-

pleted, a suitable root-end filling material must becbosen. According tc:) Cartner & Dorn (22), anideal tnaterial to seal tbe root-end cavities sbouldprevent leakage of microorgatiisms and tbeir by-ptoducts into tbe petitadictilar tissues. It sbouldalso be non-toxic, non-carcinogenic, atid biocom-patible witb tbe bost ti.ssttes. In addition, it sbouldiDe iusoluble in tissue flttids atid dimetisiotially sta-ble. The presence of moistute should uot affect itssealing ability. For practical putposes it sbouldalso be easy to ttse and be radiopaque to be recog-tiized on tbe radiogiapbs.

Numerous materials bave been suggested astoot-end lilling materials: gutta-petclia, amalgam,polycaiboxylate cements, zinc pbospliate cements,zinc oxide eugeiiol paste, IRM cement, EBA ce-ment, Cavit, glass ionomers, composite tesiiis, atidotber matetials sucb as gold foil and leaf, silver]Doints, cyanoactylates, polyFlEMA and bydton, Di-aket root canal sealet, fitanium screws, and Tefion(23).

Tbe suitability of root-end filling materials liasbeen tested by their leakage assessment, matginaladaptation, cytotoxicity, and tisage test in experi-metital atiimals and man.

I. Leai<age assessment

The qtiality of apical seal obtained by toot-end fill-ing materials bas been assessed by the degrees ofdye, ladioisotope or bactetial penettation, electro-cbemical tiieans, and fluid filtration technique(24-67).

A. Particle ieai<age

Tbe results of tbese stuches sbow tbat various alloysleak differently and conventional alloy leaks signif-icantly less than otber t)'pes (27). Amalgam byitself does not prevent penettation of various trac-ets and its .seal improves by addition of vatnisb (31,3,5, .51, 55, 62). In contrast to tbese findings. Kinget al. (58) and Olsoti et al. (59) found no sigtiifi-cant diffeience in leakage of amalgam witb andwithottt applicatioti of a cavity vat nish. Szetetneta-Brower et al. (34) showed good apical seal with ajii-coectomy alotie while Kajalati et al. (30) detiion-strated inferior seal witb apicoectomy aUjnecotnpared witb beat or cold btttnisbed giitta-percba. However, Bramwell & Hicks (37) reportedno significatit difference between tbe amount ofleakage of root-end resected teetb wben cotn|3aiedwith those of hot atid cold btnnisbed gittta-]:)etcbaor root-end cavities filled with amalgatn. Becker &Voti Fraittihofer (48) showed that the seal of thet-moplasticized gutta-percha withottt a root catial

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sealei' was worse thati that with a sealer atid atnal-gam with varnish. Woo et al. (57) also showed thattltermo])lasticized gutta-percha with sealer had sig-nificautl)' less leakage than amalgatn wben used asa toot-eticl filling material. Olson et al. (59) alsofotmd tbat injectable bigb-tetiiperatitte gtuta-percba witbout sealer demoustrated sigtiific antlymore leakage tban tins matetial with a sealer, aglass iotiotner cetiic^nt and amalgam with atid with-oitt vatnisli. K iplan et al. (30) tejjorted itnprosx'dsealability of gutta-percha after cold btnnisliiug oftbis material, and Minnicb et al. (52) notedbeneficial effects of cold btttnisbing for poorlyobtutated canals. Otber invesfigatots (34, 39, 41,51), bave repot ted no improvetiient in sealing abil-ity of gtttta-petcba fbllowitig cold burnisbiug. Anutnbet of investigatots bave teported tbat heatbttt nishing of gittta-petcba does not inipro\e tbesealitig abilit)' of tbis substance as a root-end fillingmaterial (30, 34, 39, 44, 46). Bramwell & Hicks(37) tejjorted no significant difference betweendye leakage of beat or cold burnislied gutta-petcliain monkeys. In contrast, Abdal & Retief (28)sbowed that heat sealed gtttta-petcba ptovided abetter seal tban most comtnonly used root-end fill-ing tnatetials sttcb as atnalgam, IRM and Sttjjet-EBA. MacPberson et al. (47) as well as Wii et al.(56) and Woo et al. (57) teported obtainitig abetter seal witb tliernioplasticized gutta-percbatban amalgatn witb and witbout \'arnish. In con-trast Escobar et al. (3()) atid Olsoti et al. (59)reported equal sealing ability for tbertno-plasticized gutta-petclia atid atnalgam witb atidwithout varnisb.

Because amalgam and gtttta-petcba fail to pro-vide ideal apical seal, otber substances sticli asZOE based cements, glass ionomets, compositesand otber substances bave been suggested as root-end filling materials. Some investigators (28, 43,45, 49, 54, 60, 61), sbowed tbat glass ionomer ce-ments ptovide better seal tban atnalgatn. In con-trast. King et al. (58) showed tbe seal pto\ided byKetac-silver was itiferioi- to tliose obtained by Su-perEBA, and amalgam witb and \vitbout varnisb.In additioti, MacNeal & Beatty (40) deniotistratedtbat tbe seal of two glass ionomers (Ketac and FtijiII) was adversely affected wben the root-end cavi-ties were contaminated with moisture at the timeof placetnent of these materials. Abdal &: Retief(28), McDonald & Ditmsba (39), Thirawat & Ed-munds (54) and Danin et al. (63) reported thatcomposite resins provided better seal than tbat ob-tained with amalgam. Szeremeta/Brower et al.(34), and Bondia et al. (50) tepotted that Stiper-EBA iîovided a better seal compared witb amal-gam as a root-end filling tnatet ial. Howevet; otber

itivestigatots (44, 51, 54, 58, 66) ba\e sbown tbatSu]3et EBA provided eqttal seal to atnalgam in coti-jitnctiou witb a cavity xarnisb. Abdal & Retief (28),Sniee et al. (42), and Boiidta et al. (50) sbowedtbat IRM provided a better seal tbati amalgam orSnperEBA. Bondta et al. (50) slitnved tbat Supet-EBA's seal was equal to that oflRM.

Conipat iug- the data obtaitied frotn vat ious leak-age studies sliows considerable variations in tbe re-sults of these in\'estigations and even witbin tbesame group of studies using similar experimentaltnetliods. The data genet ated in most of thesestudies were collected after longitudinal or ciosssectioning, or clearing ofthe roots, and measuringthe linear ttacer penetratioti. These studies pto-\lded setni-qnatititati\e data atid lia\'e a high levelof variation. In addition to the fact that dye or iso-tope penettatioti studies do not pro\'ide the vol-ume of tt acet s which penetrate through the inter-face between lt)otb structtires and root-end fillingmaterials, otber vatiables, sucb as molecular sizeof ttacer, immetsion petiod, pH of ttacer sohitioiiand etitiapped air, bave not been standardized.

Ketsten & Mooter (68) compared tbe ability offour obttttation metliods to pie\ent leakage ofbacteria-sized particles or large protein tnolectiles,and found leakage of tbe commonly used dye,metliyleue blue, was coniparalile witb tbat of asmall bacterial metabolic product of similar tnolec-tilar size. Tbeir findings sbowed tbat microleakageof tbe small molecules could not be prevented,wliile leakage of bacteria-sized pardcles and largesi/e jjtoteiti niolectiles could be prevented witbsotiie of tbe obttnation teclniiques. Higa et al.(67) evaluated the influetice of storage finie (0versus 24 bout s) ou the atnount of dye leakage ofamalgam, SuperEBA, or IRM. Their resultsshowed SuperEBA and IRM leaked significantlyless than amalgam and storage time bad no signifi-cant infiuence on tbe amount of dye leakage. Al-tbougb pH of tracer sohuicMi may affect the leak-age pattet n of root-end filling materials, it is inter-esting to note that most studies did not give thepH of tbeir solntions.

Tbe gap betAveen root-end cavity walls and root-end filling materials may contain air and/or fluid.C.ofdiiian et al. (69), Spangbeig et al. (70) as wellas Oliver & Abbott (71) sbowed that the tise of a\acitutii increased tbe amount of dye penettation.However, recetit studies by Petets & Harrison (72)as well as Masters et al. (73) questioned tbe benefi-cial effects of this procedtire in leakage sttidies.

Tbe majority of leakage studies bave been per-fbtniecl ill r'/7?mvitb little or no similarities to con-ditions in x>iv(). One ol tbeir major limitations isthe atnoittu of flttid rxcbange between the apical

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toot canal walls and tbe root-end filling material.Tbe amount of tissue fitiid presetit iu tbe apical re-gioti is tnttcli less in xrivo cotnpared witb in xriirotests. In addition, most in vitro studies bave beenperfotined in dry conditions wliich do tiot detet-mine the advetse effects of humidity oti diese ma-tetials. Tbe sealing ability of some of tbe toot-endfillitig materials, sncb as glass ionotiier ceinetits,can be adversely affected by tbe pt esence of mois-ture as sbowti by MacNeil & Beatty (40). Dye pene-ttation tecbnique is tbe most freqtteutly tisedtnetbcid to evaluate tbe sealitig ability ol variottsroot-end fillitig tnaterials. Autoradiogtapliy is asubjective Cjuantitative tecbtiiqite of tneasttring tbeapical leakage. Factot"s sticb as type of isotope, dis-tance between tadiadon source and etnnlsion, andthe length of exposute of the fihn can affect theresults obtained by tbis tecbnique. Matloff (74)showed that niethylene bltie dye penetiated fur-ther up tbe canal tban ''(ia, ' 'Olabelled utea, or'^Î-labelled albumin, and questioned tlie validityof tbe results obtaitied in tadioisotope studies.

Delivanis & (]baptiian (75) cotnpated tbe relia-bility of tbe electrocbemical method, atitoradiog-raphy and dye penett ation for leakage assessment.They concluded that the correlation betweenthese tiiethods was correct at the two extremeetids of the scot e ratiges. Tbey stated tbat dyes at esimplei; cbeaper, safet; atid easier to handle tbanradio-isotc:)pes. Tbe leakage assessmetit does notrecjtiire a special set-tip cotnpated with tbatneeded for tbe electrocbemical metbod. It is alsopossible to obtain false leakage otber tban irotntbe apex witb tbe electrocbemical method.

Tbe majotity of in vitro apicoectotiiies bavebeen performed pet pendicular to tbe long axis ofthe teeth, in conttast to a 45 degree lingtio-buccalbevels ofteti used in cotiditions in viiio. Bevellingof the root surface at an angle results in exposureof dentinal tubules. Tbese ttibtiles may provide ad-ditional patbways for leakage. Cillieany et al. (18),usitig a fluid filtration tecbnique, determined tbeapical leakage of extracted teetb resected at 0, 30,and 45 degress to tbe lotig axis of tbe root andfilled the root-end cavity with various incrementsof a glass ionomer cemetit. Their results indicatethat apical leakage significantly increases as tbeamoLtut of tbe bevel increases. In addition, tbeysbowed tbat increasing the thickness of root-endfilling materials significantly decreased tbe apicalleakage.

Tbe tbickness of toot-end filling tnaterials is an-otlier uncontrolled variable in leakage sttidies andhas varied from 1 to 5 mm (28, 31, 35, 76-78). Fi-nally, most apical leakage studies bave detet-minedthe sealing ability of various tnaterials by placing

the apical ends iti the ttacets. Pracfically, the pur-pose of placing a root-end filhng material is to pre-vent penettatioti of itritatits fVom the root canalsystem into periradictilar tissues. In reality, coto-nal seal of toot-etid filling tnatetials is jirobablymote importatit tban tbat of tbe apical seal.

King et al. (58), Ctooks et al. (64), Gilbeany etal. (18), and MacDonald et al. (66) used tbe fluidfilttation tecbniqtte develojjed by Derkson et al.(79) to determine tbe leakage ]3atterns of vat ionsroot-etid fillitig tnatet ials. Tbe tnain advantages ofthis tecbnique are: 1) the sam]:)les are not de-stroyed 2) the leakage can be detet tnined at diffet-ent time intetvals and 3) tbe collected data isquantitative. However, applicatioti of solution ttn-der pressttre does not simttlate clitiical cotiflitiotis.

B. Bacterial leakage

Despite tbeir ijopitlarity atid ease of tise, tbet esttlts atid clinical sigtiificatice of leakage sttidiesbave been questioned (14, 80-84).

Mortensen et al. (80) and Ktakow et al. (81)sbowed fliat microotganistii jDenetration tnight bemore approjjiiate tliati dye or isotojDe penetrationfor stttdying leakage in vitio. Goldtnan et al. (82)bave pointed out tbat bactetia gi\e better itidica-tioti tbati dye iti testing for leakage of bydrophilicmaterials atid that dyes cati gi\e a false positiveleading if tbeir tnolectiles were stnall etioitgb. Tor-abitiejad et al. (14) used two species of bactet ia,Stnphylococcus cpidcrmidis and Proteus viitgaris, tc:)evaluate the coronal leakage of root canal-filledteeth. Eighty-eight percent of tbe root canals werecompletely recotitaminated in 30 davs followingexposures to Stapliylococrus epidermidis and 85% in66 days following expcjsure to Proteus vulgaris.Magitta et al. (15) evaktated tbe coronal leakagein obturated root canals using fresb liutnan saliva.Tbey found that salivaty leakage was slc:)wer thandye penettation. They also reported that salivarypenetration at 90 days was significanfly greaterthan that seen after 2, 7, 14, and 28 days. Kliayat etal. (83) detertnined the time needed for bacteriain saliva to contaminate tbe entire length of obtu-rated root canals and found all root canals wererecontaminated in less than 30 days. Wti et al. (84)used tbe movement of a bacterium (PsetidomonasAeruginosa) in a capillary glass ttibe connected totbe apex of root filled extracted litiman teetb asan indicator of leakage and found most obttti atedroot canals do not allow the ]3assage of tbis bacte-rittm.

Because of inherent inadequacies in dye and ra-dioisoto]3e leakage stttdies, and a lack of correla-tion between bacterial leakage and those of dye

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and isotope molecules, bacterial leakage studiesbave been tecomtnended to test the stiitability ofpotential root-end filling materials (85—87).

Kos et al. (85) e\ahiated the ability of poly-HEMA as a toot-end ftllitig material and fonndtbat tbis material prevetited leakage oi Proteus rnil-garis, at! actively mc:)tile gram negative rod andStrt'ptoeoceus stdivurius, a gram positive coccns nor-mally foittid itl tbe liuman oral niictoflora. In con-ttast, ccjld-btittiisbed gtitta-petcba, beat-sealedgutta-percba, and zinc-free amalgam sbowed abigb incidence of leakage ranging from 80% to100% of tbe specimens tested. Euomanen ScTtiompo (86) compared tbe tightness of fitaniumscrews versus amalgam as roc3t-etid filling tnatet i-als, using Sermtia inarceseeiis in an in vitro model.They found that die bacteria penetrated aroundtbe apical fitanitim screws in 2-7 days, and atotindtbe t ettograde amalgam fillings on tbe first day ofthe expetitnent. Stainitig of tbe teetb witb Itidiaink sbowed tbat penetration of bactetia bad oc-cut red at the tooth/filling mat gin.

Wotig et al. (87) compared tbe apical seals ob-tained by placing either amalgam as a t oot-etid fill-ing material ov lasing the root apices witb tbeNchYACi Easet\ After instrtimentation and obttna-tion, otie group received amalgam as tocn-end fill-ing material and eigbt other groups wete lasedwitb tbe Nd:YAG Easer at wattages tatiging fVom0.75 W to 3.0 W for 20 s. Streptocoerus snIixKiriu.s wasplaced in the cc:)iotial tesetvoitof each toot atid itsapical 10 mm was placed in brain-beart inftisionbtotb and pbetiol red indicator. Their restiltssbowed no significant difference between bacte-tial leakage in the laser-treated gtoups and tbesamples tettofilled witb amalgam.

(4:)mpared witb clinical conditiotis, tnoclels usedin bactetial leakage stttdies to determine sealingability of variotis toot-end fillitig materials baveseveral shortcomings. Tbey are static and tbeirbacterial contents are dissimilar to those found inhuman saliva. In addition, these sttidies did notdetermine the ability of toot-end filling materialsto ptevent leakage of bacterial metabolites andtbeir by-ptochtcts. In vitro txnd in rv'r'( > animal mc d-els simulating clinical conditions are needed toobtain quantitative data and detetmitie tbe rela-tionship between leakage of bacteria and their by-products and pet iradicular iiiflainmatic:)n.

l i . Marginal adaptation

Tbe scanning election microscope (SEM) basbeeti used in dental tesearcb to sttidy normal anditifiamed gitigival tissues. (88), plaque structure(89), caties fortnation (90), tbe effects of etching

on niarginal adaptatic:)ti of vatious restorativematerials (91) and tbe interface between tootbstructure and testorative tnaterials sucb as gold,composite atid atnalgatn (92).

Itl scantiitig electton mictoscopy. specimens areconsidered as a collection of point sources of tadi-atic:)ti, eacb of wbich ttansinits information con-certiing" composition and sttiu tine. The SEM usesa 2-3 nm spot of electrons tbat scans tbe surfaceof tbe specimen to getietate secotidaty electic:)tisfiotn the specimen which are tbeti detected by asensot; Tbe sensor uses tbis emitted ladiatioti tc:)build up a picture of tbe complete object. In ef-fect, oiitpnt signals fiom tbe SEM are reflectedfiom at! ojDaqne stit face. Geomettically, tbe reflec-tioti of electrotis fiom the SEM specitneti surfaceobeys tbe same laws as tbe reflecticin of light froman irregular surface. The result is tbat SEM imagesate fbrtned in topogtapbic conttast - tbe imageintensities ate related to vatiations in surface to-pograpliy. Tbe images appear like tbose viewedtiiactoscopically ot; iti otber wotds, tlnee ditnen-sional. In general, electron mictograpbs representan overlav' in wbicb details fiotn tiiatiy levels of tbespecimen appear, in focus, witbin a sitigie plane(93).

In endcidotitics, a tiumber of investigatots baveutilized SEM to investigate tbe marginal adapta-tioti c:)f tocn-etid filhng materials (28, 94—99).

By using SEM and teplication tecbnique, Cun-ningbam (94) comparecl tbe apical appeatance ofeigbt teetb obturated witb silver cones and sealet;gutta-percba and sealer with and without rocî-endresection, and atnalgatn as toot-end filling mate-rial. Considerable disinpdon of tbe apical seal wasseen in tbe roots apicected after gutta-petclia ob-tutatic:)n. Tbe stnc:)otbest sut face and best seal ap-peared to bave been acbieved b) toot fillitig vsitli asilver poitit befbte apical resection. Rettc:)gradeamalgatn fillings appeared satisfactory, btit giitta-petcba points used befbre and specially after tbereduction of tbe apex appeared to bave titidei-gone considetable clisttiption.

Moodnik et al. (95), fbnnd defects of 6-150 |umaround amalgam tettofillings using tbe SEM.These deficiencies atound amalgam retrofillitigsquestic:)ned tbe validity of ibis widely acceptedtecbnique. However, tbe authors did not elaborateon tbe clinical significant of tbeir findings. Tanzilliet al. (100), cotnpated tbe tiiargitial adaptatioti,using tbe SEM, of retrogtade amalgam, beat-sealed gtitta-petcba, cold-burnished gutta-petcha,and apicoectomy only. Tbey concluded cold4)ut-nisbed gutta-percha was "90% better tban ativ oftbe otber tecbniqnes investigated." Retrogradeamalgatn, heat-sealed gutta-percba, and tbe apic-

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oectomy control showed mean marginal defectsfrom 22 \xm to 10 |J,m, while cold-btunished gutta-percha exhibited a mean defect of only 1.8 jim.

Alxlal & Retief (28) used SEM to compare themarginal adaptation obtained by jDost-resectionfilling with heat-sealed gutta-percha and when re-inforced with 16 retrofilling materials (one sampleper material). Most materials tested had gaps.However, no gajos were found in Cavit, Sybraloy(high-copper), polycaiboxylate cement, gkiss ion-omer cement, heat-sealed gutta-percha, and Adap-tic.

In an SEM study, Stahholz el al. (9(3), comparedthe marginal adaptation of root-end filling withRestodent, zinc phosphate cement, Cavit-W, Dtue-lon, and amalgam. Restodent sealed significantlybetter than the other fotir materials and demon-strated the best adaptation lo cavit)' walls, whileamalgam was significantly inieiior to the fourother mateiials in both marginal adaptation andseal. In addilion, they showed zinc phosphate didnot differ signillcanlly from Cavit or Durelon.

Yoshinuua el al. (97), in a coronal and apicalmicroleakage study using a pressurized fluid filtra-tion technique and SEM examination of teethwith retrograde amalgam fillings, showed leakagedecreased markedly in the 90 minute to six hourinterval after filling. Small changes in leakagewere noted belween 1 clay and 8 weeks. Leakagefrom the coronal direction was not significantlymore than that noted from the apical direclion.Gaps as wide as 20 |im were noticed between amal-gam and the toolh structure in some selectedspecimens. They found no correlation betweenmicroleakage and the width of the gap appearingon the sttrface.

Inoiie et al. (98) compared the microleakage ofamalgam, amalgam with a cavity \'arnisli, a silvet-containing glass ionomer (Miiacle Mix) and IRMusing a lltiid filtration t:echniqiie and SEM obser-vations. Cilass ionomer cement and IRM showedsiguificantly less microleakage compared with theamalgam group without varnish. The use of cavityvaitiish reclticfd the apical leakage of amalgamsignificantly. Examitiation of scanning clectrotiphotomicrograplis of some selectied spccinu-tissliowed tlie presence of gaps ranging 5-10 fJni be-tween the root-end materials and tlieir surround-ing denlinal walls.

Toial)inejad et al. (99) in a clyc leakage andSEM examination of four retrogtade amalgamroot-end fillings from lbttr radiogiaphically suc-cessful lcc[h showed presence of nietliylcne hlitedye pencti alien through the interlace of amalgamand rool-end cavities and varying size gaps l)e-tween the cavity walls and amalgam. These invesli-

gatots qttcstioned the cortelation lietween d)'eleakage, SEM studies and clinical succe.ss.

Specimen piepaialion (or examination with theSEM involves several steps, each capable of induc-ing artificial changes in the specimen. These stepsinclude: fixation, dehydration, drying, hea\')' metalsputter-coating, and high-prcsstirc vacutuiiingwhich can result in the fortnalion of artifacts.

To prevent or icdttce the amcnuit of ai tilacts,different methods have been proposed to ]jr()dticcteplicas ol the original samples. Invesligatots havedescribed replication techniques to study ihetoolh structure-filling material interfaces, and diemiciovasciilaUue of ihe pulp (101-103).

Moodnik et al. (95), and Torabinejad et al. (99)in their case reports revealed the presence of largedefects at the amalgani-loodi interface, 'fhesestudies wiih dieh' small sample sizes as well as thestudy by Tanzclli et al. (100) did not utilize anyreplication technique lo minimize the introduc-tion of artifacts. Al:)dal & Relief (28) employed anegative/positive replication techtiiqtie to e\alti-ale only a single sain]3le of each ofthe Hi root-endfilling materials. However, in this study, ihe teetliwere sectioned longitudinally with a diamond saw,which may have alfecled ihe findings. Stahholz etal. (9(T) used a negative replica technique and sec-tioned their samples which might ha\e affecledthe results of this invesligalion. Yoshinuua et al.(97) and Inoue et al. (98) also reported presenceol gaps between root-end ca\'ity walls and amal-gam in some selected cases in iheir leakage andSEM investigations.

Despite its shortcomings (introduction of arti-facls during sample preparalien, showing only 1stnface which may not represfnt adaptation of 2surfaces in ?> dimensions and a lack of tort elationlêtween maighial adaptation and sealahility).SEM examination of mat ginal adaptation of vari-ous root-end filling materials to iheir surround-ing strtictitres cati ]3nn'ide itifoiiiiation whichcould he used as an iiiflit ator of the scaling abil-ity of these materials.

ilL Biocompatibility

The materials tiscd in endodontics are Ireqtientfyplaced in intimate contact wiih ihc liard and soiltissues of the pcriodontittm. This is partictilarl)'true for the substances ttscd as root-end lillingmaterials. Therefore, it is essential that a potentialroot-end filling material be non-toxic and hiocom-patihlc with its sttrrottncfing host tissues. CAU-tently, there are three recomniended tests loevaluate biocompatiljility of dental materiafs. Aninitial test which provides general loxicity profile

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of potetitial materials, secotidary tests, wliicb e\al-uate local toxicity, and usage tests iti wliicli thepotential sitbstances are used in tbe teetli ofexperitiiental animals accorclitig to clitiical prc:)to-cols.

A. Cytotoxicity tests

Cytotoxicity is one of tbe most connnonly tised invitro tests to tneasure biocompatibility. It is a sim-ple, rapid, and inexpensive screening test, aticlgives a valuable iticlication as to which materialsshould be discarded or subjected to further test-ing. Many methods have beeti used to determinetbe cytotoxicity of variotis dental tnaterials. Tbesemethods itivolve either observitig the inbibition ofcell growth or recorclitig cellular injuty ancl/ordeatb. Tbe tliree most commonly used cytotoxicitytests include agar overlay tecbtiique, millipore fil-ter tiietbod and radiochromium release test.

1. Agar overlay technique

In this test the cells are first cultivated to a conflu-ent monolayer in 24 bours. After removal of theculture mediutii, tbe cells are covered witb Fagle'sMinimum Essetitial Medium (MEM) supple-mented witb 1% calf sertun and 1% agar andstained witb 0.01% Neutral Reel solution. Tbe testmaterial is tlien placed oti tbe agar sitrlace andincubated for 24 hours. Tbe cell monolayers arethen examined utider an inverted microscope andthe plates are vistiallv atialyzed for celltilar lysis.Tlie dead cells lose their Neutral Red staining atidwill provide a clear zone subjacent to the testmaterial. The toxicity of the niaterial can then heregistered according to a lysis index from 0 to 5(104).

2. Millipore filter method

Wennherg et al. (10.5) introchtced the "Milliporefilter method" iti which Millipore filter disks areplaced in tissue cultiue disks and covered with cellsuspensions cotitaitiing hutiiati epithelial cells,HeLa cells or mouse fibroblasts (L929). Alterestablishmetit of a cell monolayer on the filtersand removal of culture mecliitni, the filters arecovered with Fagle's MEM and 1.5% agar. Thenutrient agar is allowed to stiliclily and then theagar filter is placed in the Petri dish ttpside down.The test material is placed oti the filters atulallowed to infiuence the cells foi 2-24 hours. Thestainitig ititen.sity of monolayer cells for sticcitiatedehyclrogenase activity is used as the indicator o.fcell vitality around the test materials. The relative

degree ol toxicity ofthe material can be registeredfrom 0 to 3 indicadng the extent of the zone withredticed or inhibited enzyme acti\'ity (fO.'i).

3. Radiochromium release test

According to Spangberg (106) the radiochro-mium release test is the third commonly usedmethod to asses cytotoxicit} of \aiioits dentalmaterials. In this tnethod, the test tnaterial is firstjDlaced in the bottom of the wells of tissue cnltiueplates. It is then covered and itiocnlated withgrown, harvested atid prelabelled cells withNa'^'CrO, for 1-24 hours depetiding on the exper-imental design. After appropriate incubatiotiperiod, a standardized amount (1.0 niL) of thecitltttre niecliitni is withdrawn from each well andthe amount of ''C'-r released into the medium ismeasiuecl iu a ganinia particle countei. A compar-ison between the amount of the original incorpo-rated radio-clironiiinn in the cells wth thatreleased from cells after incubation with the testmaterial as well as the positive and negative con-trols is used as ati iuclicator of toxicity of a dentalmaterial (106).

The cytotoxicity of potential root-etid lillitig ma-terials have beeti determined by several investiga-tors using various techniques (107-117).

Spangberg et al. (107), used radiochrotnium-la-belled HeLa cells to test the biological effects ofsome potential root-end filling materials and re-ported that freshly prepared 11^4 proditced totalcell lysis, while after setting for 1-4 weeks the tox-icity decreased slightly. Iti addifion, they showedrelati\ely low cytotoxicity of polycarboxylates ascompared with ZOE atid IRM.

Dahl &• Tronstad (108) deteiininecl the cytotox-icity of a glass ionomer (ASPA III) cetnent and acotiventioual silicate cement using the racHo-chro-tiiiuni tnethod. Based on their findings, it ap-peared that the silicate cement was less toxic thanthe glass ionomer cement and the toxicity of thelatter decreased with setting time.

Antrim (109) used radioacti\e Cr released fromKB carcinotiia cells as a measnre of cell lysis in re-sponse to Groosinan's sealer, N2 (permanent),Rickert's sealer, and Ca\ it. He reported that all thematerials tested possessed lastitig tisstie toxicity;Cirossman's sealer was the most toxic material, fol-lowed h\' N2, Rickert's, and Cdvh. Cavit showed alow initial toxicity (24 hoius), bitt this increasedwith titiie and remained highly toxic theteafter.The response to C.a\it was somewhat erratic andwas attrihttted to the deterioration of the tnaterial.

Tronstad & \A'ennberg (110) compared the tox-icity ol" dental amalgam.s, silicate cement, methyl

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metliactylate resin, composite resitis, zitic phos-phate cement, polycarboxylate cement, ZOE pasteand caiciutn hydroxide GR-isotonic paste onmouse libtoblasts by means of Millipore tecb-nique. Tbe convetitional amalgams and a bigbcopper atnalgatn (Dispersalloy) sbowed sitiiilar re-sponses. Tbe ccjiivetitional atnalgam atid bigb cop-per amalgam were initially sotiiewliat toxic witb adecrease in toxicity after 24 bouts. Hc:)wevet; tbeold style bigb copper alloys (30% copper) weremore toxic. Zinc phosphate atid silicate cemetitsas well as methyl methacrylate resin were highlytoxic when fieslily mixed. The wet and dry varie-ties o[ ZOE paste were moderately tcjxic and cal-cium hydroxide paste proved to have a sttong andlasfing toxic effect.

Wennbetg & Hasselgreti (111) evaluated tbe cy-totoxicity of a number of temporary filling materi-als including Cavit, IRM, atid ZOE cement by tbeMillii:)ore filter tnetbod and sbowed tbat all tbe ce-ments had some degree of cytotoxicity tlnottghthe experimetital petiod; ZOE atid IRM showed acotititiuitig decrease iti their cytotoxicity withtime.

Meiyon et al. (112) compared the cytc:)toxicityof two glass ionomer cements (ASPA and Chetn-Bond) on fibroblasts and tnacropbages. BcDtli tna-terials wete fbund to be itiitially cytotoxic to fi-broblasts; tbis was evidetit by tbe itibibition of stic-cinic debydtc:)genase stainitig iti cells grown onMillipore ftltets. These sttbstatices were also cyto-toxic to macro|3bages assessed by a teduction iticell ntimbets and by enzyme staining kinetics atidquantitative enzyme atialysis. Tbe cytotc:)xicity ofbotb tnatetials decreased considetably after 24bours.

Milleding et al. (113), cotnpared tbe telative cy-totoxic effect of corroded and non-cot roded amal-gams of different types using a cell culture andMillipore filter metliod. C/ortosioti was producedby storing the anialgatn in distilled water or attili-cial saliva with a pFI of 4, 5, or 7 for up to 28 weeks.Tbe set, non-corrc:)ded amalgam did not show anycytotoxic effects, whereas corroded amalgam sut-faces showed various degress of cytotoxicity.

Al-Nazhan et al. (114), compared the cytotoxic-ity of a composite resin (Restodent) with tbose ofCavit and Dispersallc:)y using the radiocbromiumlabelling tecbtiique. Tbeir results showed tbat Re-stcjdent was mc:)re toxic tban atnalgam; Cavit badno toxic effect. They concluded that amalgam wassdll tbe material of choice due to its lc:)w cytotoxic-ity, and that composite was tbe most toxic tnaterialtested and should not be used.

Safavi et a l (115), attetnpted to gtow fibtoblastsoti root-ends filled witb amalgam c:)r compcjsite

tesiti. Study of tbe cell attacbment to tbe sttbsttateuticler SF M sbowed cell attacbtneut to tbe cotn-posite surface was tematkably less tbati tbat toamalgatn.

Pissiotis et al. (116), conipated tbe cvtotoxicityof silver glass iotiomer (SGI) cetnent atid atnal-gam ttsing '''Cr telease test and foutid tbat SCilpltis varnisb was less cytotoxic tban amalgam. Tbeycotichided that SGI sbould be cotisidered as an al-ternative rocjt-end filling material.

Brtice et al. (117) measured the cytotoxicity ofsevetal dentitie botiding systems, SttpetEBA atidamalgam using tbe agar overlay test at 24 bouts, 7,15, and 30 days. Except for amalgam aticl Ten tit eVisar Seal, the test of the materials wete itiitiallycytotoxic. SupetEBA, Cattlk-filled tesin, andGliima sealer &• Glitma bond were itiitially toxicand tbey lost tbeir toxicity 7 days after incubatiotiwith the monkey kidney cells (Vl^RO). (Xtotoxic-ity of atnalgam inct eased as it aged. Based on theirresults tbey concluded that sotne detititie bondingagents are cytotoxic; bovvevet, they lose tbeir cyto-toxicity as tbey age.

Based on tbe results of tbese sttidies it appearstbat ZOE-based tnaterials iti tbe fi esbly tnixed andunset state ate vet"y cytotoxic atid tliev' lose theircytotoxic effect as tbey age (107, 109, 111-117).Confiictitig teports bave been made regarding cy-totoxicity of Cavit, glass iotiomer cements andcomposites. Despite tbe ease cjf conttol of experi-tnetital factots iti cytotoxicity tests tbere ate sev-etal disadvantages with perfbttnitig these yiroce-cltires. Tbe resttlts of tbese tests at e relative, can-not be cc:)mpared with one atiotber, atid are cle-pendent on cell types atid degree of dilTusibility oftest matetials. Iu addifion, these invesfigationscannot study the complex interaction between ma-tetial and bost tissue and tbe measurements ob-tained by tbetnselves bave little relevance to clitii-cal citctunstances (106).

B. Implantation tests

Because of limitation of cytotoxicity tests, in vix'ostibcutaneous and itittaosseous itnplatitafion tecli-nicjues in small laboratc:)ry anitnals bave beeti tec-otnmended (107, 118-121). Subcutaneous and in-traossecius implantation tecbniqnes are consid-eted stiitable secotidaiy tests to evaluate the bio-compatibility o{' variotis dental materials. Earlyimplantation sttidies involved placemetit of pelletso[ dental materials in vatious soft tissues audbones. The iinjilantatioti metbod was refinedwhen Friend and Browne (118) used Tefion ttibesas a vehicle to place small staudat clized surfaces offresh or set dental materials in contact witb desig-

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nated tissties. Accotclitig to Spangbeig (106) tbesetests can provide valuable information witbotitexcessive cost and unnecessary animal sacrifice.

Potential root-end filling materials bave beenimplanted stibctitaneotisly and intraossecnislv insmall labotatory anitnals (122-133).

Wolfsoti & Seltzer (122) used an injection tecb-nique atid implanted sevetal brands of gittta-petcba, natural gutta-percba, latex, ati expetinien-tal formtiladon containing gtitta percha (20%) andcalcitmi bydroxide (80%), and Kloioperka N-'O intbe subcutaneous tissue of tats. Histological exami-nation of specimens sbowed an initial acute re-sponse followed by fibrotis tissue encapsulation.Kloioperka N-"O caused severe tissue destructionand infiaminatoty cellular infiltrate cotitainingPMN leukocytes, mactophages, lymphocytes,plasma cells and giants cells. The gutta-percba for-mulation with calcium hydroxide elicited a fbt eign-body giant cell response.

Flanders et al. (123) itnplanted zinc-fiee atnal-gam atid Cavit stibctitaneonsly and next to thebone itl rats and evaluated tbem liistologicallv' af-ter 10, 30, 90 and 180 days. Cavit produced moreof a foreign body reaction than amalgam in bothtissues. Cavit ptodnced osteocvtic deatb in tbe ad-jacent botie and a tbicker fibrotis capsule next toconnective tissue. The iuflaimnatory response tobotb tnatet ials decreased witb titne.

In a bone implantation study, Zartner, et al.(124) placed ficsbly mixed amalgam and zincpolycarboxylate (ZPC) cement into tbe tibias oftabbits atid evaltiated tbem bistologically at 2weeks, 2 and 4 montlis. ('ompatison of tbe boneadjacent to ZPC cement atid amalgam sbowedidentical fissue respotises. Tbete was evidence ofviable osteocytes, liealtby vascular and connectivetissue, aud a lack of iuflammafion.

Martiti et al. (125), evalnaied tbe tal cotinectivetissue response to zinc containing amalgam, zinc-fiee amalgam, and zinc catbonate crystals atidevaluated tbem bistologically at 2, 14 and 30 days.Tbere was tic:) significant difference in inflatimia-tory respotises to zinc contaitiing or zinc-freeamalgams at atiy time ititetval. Iti conttast. zinccatbotvate showed a severe ibreigti body giant celland maciophage response. No zinc carbonate wasfoi med in any of tbe zJnc containing s])ecitnens.However, tbe specimens were nc:)t placed in cou-lact witb another metal to allow for the electrolysisrequired for zinc catbonate lormatioti.

Liggett et al. (12f)) placed fVesbly mixed ziticaud liou-zinc amalgam in ibe tibias of rats and ex-atnined them via light mictoscojiy, SEM, and tiii-cro]>robe analysis. Over a period of 12 weeks tbeyfound botli types of atnalgatn to be well tolet ated

bv' tbe rat c:)sseous tissue. Hovvevet\ tbe inicroprobeanalysis showed evidence of tin and sulpbiir in tbebone adjacent to tbe implants witb bc:)tb amalgamtypes. Tbey attributed this to the formation of cor-rosion prodticts aud breakdown of the alloy.

Ztnener & Domingtiez (127) compared tbe bio-compatibility of zinc ]Dliospbate cetnent witb aglass ionomer cement b\ itnplantaticMi in clog tib-ias. Initially, tbe glass ioiK:)iner cement caused lessinfiammatorv response than the zinc phosphate.Hovvevet, at tbe end of 90 days tbe tissue responseto both tested materials appeared to be similar,with resoliitioti of inflammation and progtessivetievv bone formation. Based on tbeir findings, tbeautbors tecommended tbat glass ionomer sbouldbe considered as a re]Dlaceinent for tbe zinc pbos-pliate cetnent as a luting material.

Blackmail et al. (128) placed freshly mixed pel-lets of glass iouomer-silver cement lightly cc:)atedwitb a cavity vartiisb and IRM into tbe connectivetissties and bones of rats and exatnitied them his-tologically after 14, 30 and 80 days. Despite pt es-ence of mild inflammation UJD to 80 days, each ma-terial ap]Deaied to be well tolerated. Bone apposi-tion occntred acijacent to glass ionomet-silver,while fibrosis was observed next to IRM.

Eeonardo et al. (129) studied histologically thesubcutaneous connective fissiie responses of ratsto tbe placement of tbree different formulationsof gutta-percba: Obtura, Ultrafil, and gutta-percbapc:)iuts tecotntnended for use witb tbe McSpaddencompactor svstem. Obtiira giitta-percba showed asevere inflammatory response fiom the 7tli to tbe120tb dav similar to that seen witb gtitta-percbarecommended for tbe McSpaddeu technique.The Ultrafil gtitia percha caused a severe responseinitially wbicb became modetate and mild in sub-sequent observation periods. At 21-, 60-, and 120-day intervals, tbe Ulttafil giuta-petcba was assc:>ci-ated witb mature grannlatioti tissue with neitberc:)edema nor vaseular cc^ngestiou, iu contiast to theresponses observed with the other twc:) formula-tions.

Mcaiee & Ellender (130) compared tbe bio-compatibility of SnperEBA and Ketac-silver glassionomei; ati atnalgatn, a ZOE cetnent atid silvet-free /VH26 by sufxutauecnis implaiUatiou of ibesetnaterials iti rats. Initially, ZOE, amalgam, and Su-perEBA were associated witb moderate inflamma-tion. By 100 days, tbe latter tnatetials and Ketac-sil-ver glass ionomer were encapsulated witb fif^rouscotmective tissue. Howevei; .'VH26 was associatedwitb necrosis and persistent inflatnmatic:)n andgtatiiilatioti tissue formation.

To test tbe disinfection effect of parafbrmalde-byde on gutta-petclia, Ckniry et al. (131), com-

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pated tbe bistological tespotise of a 7-clay expo-sure of parafbrmaldeliyde treated gutta-percbawitb untteated gtttta-petcba (Obtiita) implatitedin lat cotinective tisstte. Tbe untreated gtitta-perclia sbowed moderate to sevete inllatiimationfor 4—7 days, wbicb decreased progressively. At 56days tmtreated gutta-percba was associated witbmild to no infiammatioti witb fibrous capsule for-mation. Tbe parafbt tnaldebyde treated gtitta-percba sbowed significantly less inflatnination inthe early stages (4-7 days) of implantation. Thetissue responses to botb treated and untteatedgutta-percha were very similar at the end of tbe ex-periment (56 days). Tbe samples were associatedwith capsule Ibtmatioti and presetice of tnacro-phages and giant cells.

Bliambliani & Bolanos (132) implanted Teflon,IRM, and Ptisma VEC Dycal in tbe tnandible ofguinea pigs for 4 and 12 weeks. Tbeir bistologicalfindings indicated apposition of botie adjacetit tothe Prisma Vl.C Dycal: none io mild itifiatiimationand a thin fibtous connective capsule near IRM,and a tbick capsule acijacent to well condensed Te-fion |iowder tnatetial. Eoosely condensed Teflotimateiial caused cbronic itinamtnatioti ancl activepbagocytosis.

To evaluate the ossec:)tis teaction to IRM,Opotow Alumina EBA, atid atnalgatn, Olsen et al.(133) implanted these siibstauces iu tat tibias andexamitiecl tbem liistc:)lc)gically fiom 7-100 clays.Complete healing occiitred arotmcl Teflon cupscontaining IRM or amalgam wbile EBA specimenshad mote innammation at 56 days. At 100 days,healing also progressed to completion adjacent toEBA cement grotip with only ati itifreqtietit pte,s-ence of leukocytes. Based on their i esults, tbe au-thors stated that botb IRM atid EBA cement weteacceptable biological altetnatives to amalgam.

The results of implantatioti studies show thatmost potential toot-end filling materials initiallycause itifiammatioii and tbey become more bio-compatible as Ibey age (122, 1 30, 131,133). Tbis ispartly as a tesitlt of sttrgical ttatttna atid also re-lease of leacliable substances fiom tbese tnatetials.In additic:)n these studies sbow that iniplatitedgutta-|K-tcba is usually encapsulated witb fibrousconnective tissue (122, 129) and (bete are no hi,s-tolf)gi<al differences between tbe tissue re,spc:)iisesto zinc-conlaining and zinc-fiee amalgams (125,126). Fill tbermore, IRM, EBA, and glass ionomercemetits are well tolerated by cotmective tissue aswell as bone (127, 128, 130, 1,32, 133).

Becatise of possible diffetetices in tissue re-sponses ill different animal species and locations,vatious tnethods of evaltiation atid shot f observa-tion periods, the tesults of various implantation

sttidies catitiot be cotn|3ated. hi subcittatieous im-plantation, tnechanical displacement of implantedtnatet ial has been recognized atid is tioted as a dis-advantage of tbis techtiique (134). Tbis deficiencycati cattse ati itiability to acbieve jiroper matetial-tissite contact.

Despite advatitages, ati artificial botiy cavity andits content (Teflon cup & test tnaterial) used in in-traosseous implatitation are diffetent from a toollisuspeuded iu tbe periodotital ligament. As statedby Olsson et al. (135), botb itnplantation tecb-niques can provide important infotniation tegard-ing tbe cellular t espotise to deutal materials. How-evet\ tbe autbors state tbat it is difficult to maketbe asstimpfion tbese tests ate cotiipatable to us-age tests. Tbe results of tbese tnetliods like thoseobtaitied iti in vitro tests should not be used as ab-solute values and can be only itsed as indicatots olbiocompatability of test matetials.

IV. Usage tests

As discussed earlier (Section III-B), implantafionmetliods have several shortcomings compared tonsage tests. Despite dieir costs atid lack of com-plete standatclization of clinical variables, tbeusage tests cati ]jtovide infc:)rmation related to bio-logical projDerties as well as bandling cbaracteris-tics of test materials under clinical cit cumstances.Tbe usage tests ate performed iu expetitnentalanimals and clinical trials iti man.

A. Periradicular tissue responses to root-end fillingmaterials

To examine tbe petiradicular tissue tesponses topotential root-end filling tnaterials, tbe root canalsof experimental animals ate usually cleaued,shaped, obturated, and after loot-eud tesectionatid ptepatation of root-etid cavities, tbey arefilled with test materials. The animals at e then sac-rificed aud their petiradicular tissues ate exam-ined bistologically to determine the biocompatib-ility of test tnatetials at diffetetit time intervals. Anumber of bistological evaltiations of periradicu-lar tissue reponses of monkeys, dogs ancl ferret tosome of the commonly tised and potential toot-eud filling matetials bave been reported (77, 78,

Marcotte et al. (136) compared tbe periradicu-lar tisstie responses of the pettnanent anteriorteetb of two tbesus monkeys to gutta-percba (fol-lowing apicoectomy) and zinc-free amalgam. Alterperforming root canal fillings ancl apicoectoiniesoti 12 antetior teeth, tbey filled six toot-end cavi-ties witb amalgam. Tbeir bistological evalitatioii of

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two specinietis jier time ititetval at 3-15 weekssbowed bealing of siitgical defects regardless ofwbicb of tbe two ioc3t-end filling materials badbeen used. Starting at 5 weeks, collagenotis fibrouscc:)nnective tisstie coveied gutta-percba and amal-gam. Maturation of ibis tisstie atid formation ofbone wete observed at subsecjuetit time intervals.New cemetitntn covered tesected toot-etids start-itig at tbe 7 week interval.

Kimura (77) evaluated the petit adicular fi,s,sttereactioti of four dog teeth t etrolilled witb zinc- orzinc-ftee alloys. Histological exaniinatioti of fourspecitneiis at various time intervals (1-22 inontbs)sbowed presence of some inllamination in the 1-and 7-inotUb sjiecimeiis ancl severe itiflammationadjacent to botb materials after 12 ancl 22 moiitbs.In tbe second patt of bis study, Kitnuta (78) deter-mined tbe concentration of eletiients by c:)pticalemission spectrograpbic analysis in eigbt speci-mens at eacb time interval (1-22 montlis) andfbuucl no zinc precipitate iu jieriaiDical bone adja-cent to toc:)t-etids ftlled witb zitic-cotitaiiiing orzinc-free alloys.

Callis & Santini (137) cotnpated tbe periapicaltissue t espouse of 10 let rets lo gutta-percba andglass iotiotner cement wben used as root-end fill-ing matetials fbr 7 and 28 days. Botb materialscaused otily a mild infiammatory tesjiotise after 7days. At 28 da) s tbe glass ionomei- samjiles sbowedmore bone formation and no inflammation. Thegutta-percha specimens bad good liealiug wiibtnild infiainmation. Tbe sealer (Tnbiseal) usedwith the gutta-percba migbt bave contribtited totbe presence of inflammation. Iti conttast to thepresence of a layer of fibrous connective tissueseparating gtttta-percha from bone, botie formedin direct contact witb tbe glass ionomer cement(Ketacfil) used.

Mangkornkatn &• Harrison (138) evaluatedamalgam and thettnoplasticized gtttta-petcha asrc:)Ot-eiid filling materials in six monkeys at tbreetitne intervals (4-16 weeks). Tbeir bistologicalfindings indicated slower bone bealing associatedwith tbermo-plasticized gutta-percba than amal-gam at 4 and 8 weeks and no significant difiet eticein tbe o,sseoiis healing at 16 weeks. Both matetialsap|:>eaiecl to be well tolerated and biocompatibleto the periapical tissties.

Zetteicjvist et al. (139) compared tlie periradic-ular fi,ssue responses to glass ionomer and atnal-gam in eigbt monkeys afler 2 weeks, I, 3, aud 6motitbs. At 2 weeks, itiliamtnatoty cells wete ol>setved close to tbe loot-encf filling materials. Onemonth after siitgety, (be granttlation tisstie hadstarted to be replaced by new bone. Alter 3 and 6tiiontbs, cotnplete healing was noted adjacetK to

botb rooi-etid ftlling materials. Based on tbeir te-snlts, tbe aiitbors recommended glass ionomer ce-ment to be considered as an alternative to amal-gam fOr patients suffering from alletgic or toxic1 eactious to mercury present in amalgam.

Pitt Eotd &: Roberts (140) examined the per-iradicular tissue t espouse of eigbt centt al incisorsin fbtir Cyiic:)inolgus monkeys to a tadiopaqtieglass ionomer cement with and v\itlioiit root canalfilling materials. Contaminated canals witb apicalglass ionomer as a root-etid filling mateiial butwitbont a root canal filling bad severe infiainma-tion and abscess fbrniation adjacent to root-etidfilling matetial. However, teeth with glass ionomerroot-eud fillings ancl gutta-percha root canal fill-ings were associated witb either no infiainmationor a mild response. Bacteria were fonnd in tbe in-terface of glass ionomer and dentine in everytootb witbotit a root canal filling and bad ex-tended apical to tbe root-end filling matet ial.

Rud et al. (141) examined tbe periradicttlar tis-sue tesponse of two green Veivet inonkevs to acotnposite resin (Retroplast) as a root-end fillingmatetial. After filling toot canals of two maxillaryinciscM s and canines and placing Retroplast at theirtesected root-ends, tbe tissues were examined his-tologicallv' 1 year following surgerv\ In some" casc\sepithelium and inflammatory cells were seen inperiapical tissues. In c:)iher eases, there was an ab-sence of inflammatorv cells adjacent to tbe fillingmaterial, but close contact between the Retroplastancl fibroblasts with collagen iibies. In one case, ce-mentum and Shaipey's fibres were Ibuud in con-tact widi tbe filling material.

Pitt Ford et al. (142), examined tbe effxxl ofIRM and amalgam as root-eud fillitig materialsptior to replantation in 42 roc:)ts c:)f mandibularmolars of monkeys. Following extraction and con-tamination of canals witb tbe mc:)nkey"s oral floraand placement of IRM or atnalgatn as root-end fill-ing materials, tbe teelli were teplanted and the ti.s-sttes examined after 8 weeks. Tbe tissue tespousetcT IRM was less sevete tban tbat to amalgam. Sixtypercent of roots filled with IRM were associatedwitb inflatnination. In contrast, 92%. of roots filledwith amalgam bad petiapical itillatntnation. Noroot with IRM as tbe root-end filling material badinnanimation iti (be bone tnattow space. In con-ttast, iuflanimation was present in the alveolarbone mat tow space witb every root-end filled withamalgam. Using a similar surgical tecbnique. PillFold el al. (14,3) itivestigated the periradicular tis-sue response lo root-end fillings of SujieiEBA ineight toots of tnotikevs and tepotted a tnild in-llammalory response.

ExcejM for one sttidy Pitt Fotd et al. (14,3), the

171


sample size in usage tests in experimental animalsfc:)r eacb time intet val seems very small (2—4 sam-ples). Tbe observadon periods in most of tbesestudies ate relafively sbort and may or may notrepresent clitiical citcmnstances. Except for fourstudies (77, 78, 140, 142), wbicb contaminated dieroot canals of teetb put posely, tbe rest of thesesttidies filled tbe canals witb root-end filling mate-rials under ideal citctimstances. Mcjst of tbesestudies used subjective ctiteria for tbeir bistologicassessment. Becatise of limited sample numbetsno statistical tests wete used to analyze tbeir find-ings.

B. Clinical usage

Sealing ability, marginal adaptatioti, in vitro cyto-toxicity tests, itnplantation atid usage tests inexperimental animals are screening means toeliminate materials with unacceptable degrees ofleakage ancl bigb levels of toxicity. Tbese tests areprerequisite exercises and are not stibstitutes fbrclinical studies.

C llinical comparison of potential roc3t-end fillingmaterials under similar c:)petative and postopera-tive ccjnclitions is the ultimate and tbe most relia-ble metbod for evaltiation of tbeir clinical useful-ness and tbeir long-term efficiency. Clitiical inves-tigations ate perlbtmecl iti retrospective or pro-spective manners. A mitnber of clinical stttdiesbave been reported on vat ious toot-end filling ma-terials (144-162).

Harty et al. (144) iti a tettospective study exam-ined tbe success rate of apicoectomy in 1,016 casesat 6 and 12 months and yearly thereafter at leastfor 2 years and reported no significant diffetencebetween using amalgam as a root-end filling mate-rial and nonsurgical root canal therapy usinggutta-pet clia or silver points in cotijunction with aZOE sealei. They reported teeth with preoperativeradiolucencies had mote failures than tbose with-oul them.

Rtid et al. (145) exatnined tbe coutse of bealingof 1000 teetb tteated by surgical endodontics andreported tbat most completely healed or tmsuc-cessfully bealed cases had nc:) significant cbatiges(were stable) irrespective of the observatioti pe-riod. Bee ause significant cfianges were noted in in-cotiipletely healed cases within the first few yearsfollowing periapical .svirgery, they recommended afinal 4-year fbllow-tip observation period in casessbowing uncertain bealing. Rud et al. (146) per-fbttned a nitikivariate analysis ofthe satiie siiigicalcases wbicb had been followed fiom 1 to 15 yearsafter opetation. Their results showed tbat caseswitb gutta-percha toot fillings had significantly less

infiainmation than tbose rettofilled; retreatedcases bad more petiapical itiflammafion dianteetb without previous root canal filling; tnediutnsized bone cavities bad more periapical infianmia-tion; maxillary lateral incisors wete iiior fieqtientlyassociated witb scar fbrmafion tban maxillary ca-nines ancl premolars; perforation of lingual corti-cal bone was associated with a later occurrence ofscar tisstie; scar tisstte was fbtind more often afteropetation on cysts; atid tbe age group from 20-40years often sbowed scar tissue at final follow-uptimes.

Ill a radiogtapbic atid clitiical examination of93 apicoectomized roots over a period ol 1-6years, Altoneti & Mattila (147) found over 80%witb complete bealing, 6% uncertain bealing, and13% ccjtnplete failure. No differeuce iti bealingwas tioted betweeti cases with cysts comparecl withtbose witb granulomas. Tbeir findings also indi-cated tbat placement of a toot-end filling materialitnproved tbe success rate of existing ottbogtaclefilling materials. In addition, tbey found tbat diepresence of multiple periapical lesions advetselyaffected tbe prognosis of teetb requiriug surgicaleudodonfic tlietapy and removal of one balf oftbe toot led to mot e complete healing (89%) tbanlemoval of apical '/•) cif the roots.

Finne et al. (148) condticted a 3-year postopera-five clinical evaluafion of padents wbo bad Cavit(102 cases) and amalgam (116 cases) as root-endfilling matet ials, atid coticluded that atnalgam wassigtiificantly better tban Cavit. They made thestatement that i eti eatment of incomplete root ca-nal fillings is not necessary when amalgam is usedas a rettofilling because of its su]:)erior seal.Twenty-five teetb toot-end filled witb Cavit demon-strated a considerable amount of clissolutioti oftbis material.

Tay et al. (149) examined tbe relatiotisbip be-tween the size of periradiculai" lesiotis ancl tbe suc-ce,ss or failure of apicoectomy iu 86 cases. Theirfindings indicated tbat large lesions (>12 mm indiameter) bealed as completely as tbe small ones,and removal of cysts increased tbe cbances forcomplete healijg.

Flirsch et al. (150) examined the infiiieuce ofclinical factors iti the healing of 572 cases follcm'-ing periapical surgery up to 3 years. Factors foundto be impcM tant for ptogtiosis included: exletit ofbone destrtiction, cjtiality of root canal filling, ageof patienl, and ptesetice of tnarginal buccal boue.Cases with smaller lesions, better root canal filling,atid ititact buccal cc:)t tical plates in older patientsbealed better tban tbeir counterparts.

hi a clinial examination, Goel et al. (151) re-planted 40 maudibular molars ancl tised ZOE-

172


based cements, amalgam, Dutelou, or gold foil asroot-end filling materials. Tbeir clinical assess-ment (biting force) up to 6 montlis showed gc:)ldfoil to be the best matet ial, followed by amalgam,Durelon, and ZOE-based cements. They attril>uted the low success rate in teeth with ZOE/basedcements as root-end filling mateiial to the ]Dre,s-ence of eugenol in tbese compounds.

Mikkonen et al. (152) studied clinically and ra-diograpliically the success of apicoectomy in 174teeth root filled with chlotc:)percha ancl gutta-percha with and without atnalgatn. Their tesultssbowed locaticDU of teetb in tbe jaws, sex, age, andottbograde or rettogiade methods bad no signifi-cant influence on success rate. Eack of periradicti-lar lesions, root lesorption, and presence of good-quality root canal fillings in teeth requiring per-iradicnlar stitgerv significantlv increased (be suc-cess rate.

Reit aud I Iirscli (153) pet formed tetrograderoot canal tteatnient using Hedsttotii liles and so-dium bypocblorite to clean tbe canals and cbloto-form-sofieued gntta-percba technique to obturate35 teetb wbose t oot canals contained posts. Tbeirclinical and tadiograpbic examination performed"evety oUier year" sbowed evidence of 71% siic-cessftil bealing of these cases.

In a clinical retiospective study, Dorti &: Cartner(154) exatnined tbe success rate of 488 casc\swbose root-end cavities bad been filled vvitli Sn-perEBA, IRM, and zinc-fiee high-copper amalgamfor a minimum of 6 mouths to 10 yeras. Their clin-ical and radiographic examinafions showed tbatbotb StijieiEBA and IRM bad significantly bigbersuccess tates (ban amalgam. Tbe success rateswere 75% for amalgatn, 91 % for IRM, and 95% forSu]DeiEBA.

Grung et al. (155) assessed radiograpbic beal-ing of 477 teetb treated by endodontic siitgety fora period of 1-8 yeats and reported no cotrelalionbetween placement of rc3c:)t-end filling mate-rialsatid bealing. Tbey found tbat 28% of tbe casestteated willi rettogtade fillings failed, comparedwitb 4% in cases with ordiogiade root canal fill-ings. In tbeir cases, apical curettage was per-formed if tbe root canal cotild be completely pi e-lâred and adequately obturated; otbervvise apic-oectomy was performed. This might have cattsed(be difference in tbe tesiilt. Furtbermore, tbeyfotmd tbat there was a marked cottelation be-tween tbe ]:)resence of a larger periapical rarefac-tion or perforation of lingual and buccal cot ticalplates and tbe occurrence of incomplete bealingin fhe maxillary lateral incisors.

Eustmann et al. (156) examined tbe relation ofvarious operadve factors to the tt eatment results of

apical sill get y iu 103 premolar or molar teetb.Tbev reported a significantlv higher success t ate ititoots obtut ated <2 tnni of tbe apex tban iti rootsobtiit ated to or beyond tbe apex. In addition tliev'Ibund roots witli posts bad significantly more fail-ures tban tbose witbotit posts. They attribnted thefailures in these toc:)ts to the presence of fiacturebefore periapical surgery, or to (bat oi'd tetrofillingtnaterial contacting the post and formalion of cot-rosin products. Using tbe data fiom tbe abovestiidv, Friedman et al. (157) investigated the long-term prognosis of stirgical cases in premolars andmolars for a period of 6 montlis to 8 years. Tbeirclinical and radiograpbic findings sbowed tbat only44.1% of tbe roots were siicces,sful, aud tbe restwere eitber imsticcessfiil (33.1%) or doubtful(22.8%)). Furtbennore, tbeir tesiills sbow that well-obtutated cauals bave siguificautly bigber successrates tban poorly obturated canals.

Rapp et al. (158) studied die effects c:)f variousfactors on 428 surgicallv treated eudodoutic casesatid fouud tbat pafients over 60 years of age badtbe liigliest percentage of complete bealing. Tbeirexplanafion was tbat canals in (bese patients aresmaller and are easier to seal dm iug siirgei). Pres-ence or absence of retrofilling bad no significanteffect on bealing. In addition, tbey reported nosignificant diffetence between bealing wben dif-fetent toot-end filling materials were used. Tbeyalso reported tbat significantly better bealing wasseen in teetb tbat wete petmanenlly restored fol-lowing snrgerv.

Waikakul & Punwulikoru (159) compared beal-ing in 66 teetb of ]ia(ients wbo bad eitber gold leafor amalgam as root-end filling materials. A follow/ii]3 of 6 (o 24 months showed no significant differ-ence between tbe two groups. The authots recom-mended gold foil as an alternative to amalgam be-cause of the following cbaracterisfics: its ease ofstetilizafion, fewer or no residual particles, no set-ting time, cohesiveness, and its antibacterial effect.

Ftatik et al. (160) evaltiated the long-term (10-yeais) success of 104 teetb witb amalgam as a root-eud filling material. Tbey listed a case as a failureif there was a root-end radiolucency, even when aprevious tadiograph indicated that bealing badoccurred. Tbese investigators reported tbat only57% of cases retroftlled with amalgam were suc-cessful after a 10-year observation period and tberest failed in (he same time period.

In a clinical and radiograpbic examination of103 teeth whose toot-end cavitic\s bad been filledwith amalgam of EBA, Pantschev et al. (161)fbund 52% and 57% succe.ss rates fbr atnalgamand EBA samples respectiveh 3 vears after surgery.Tbe percentage of teeth classified as uncertain was

173


23% for EBA and 19%; fbr amalgam. No signifi-cant differences wete noted between tbe successtates of tbe two treatment grotips.

Jesslen et al. (162) evaluated healing of toot-end filled teeth with amalgam or glass ionc^mer ce-ment clinically and raclicDgtaiDhically and reportedsuccess rates of 90%) at 1 year aud 85% at 5 years inbotb gioitps. Tbe autbors concluded tbat pres-etice of moisture dtiring periapical siitgety did tiotaffect healing adversely ancl tecommended theglass ionomer as an alternative to amalgam as atoc:)t-eiid filling material.

Examinafion of clinical stttdies using variotisloot-end filling materials shows tbat tbete aremany variables in tbese inve,stigations. Tbe mainvaiiables include: the number of cases, follow-upobservation periods, matetials tested, diflerentprocedures and tecbniqnes used dtiring tionstitgi-cal and surgical endodontic treatments, and lackof standardization of evaluation criteria for quali-tative results obtained in these studies. Because ofthe presence of tbese variables in tbese studies,tbey are diffictilt to compare with one anotbei. Ex-cept for studies by Finn et al. (148) and Grutig etal. (155), tbe rest are retrospective studies.

Standardization oi: clinical parameters sucb ascleaning and sbaping of tbe root canal system, ob-turation of the toot canals, root-end preparations,taking radiographs, and post operative time inter-vals are easier to acbieve in |:)tospective studiescompared with tbe retrospective ones. In addition,the information obtainecl in retrospective studiesis testticted to available information. More well-controlled niulti-ceutre prospective stuches witbstandardized clinical procedures along with largesam]3le sizes and appropriate statistical analysis areneeded to investigate ancl compare tbe effec-tivenss of various rcjcH-eiid filling materials.

Based on the teview of the litetatiiie i( a|3]ieatsto date that exising tocjt-end filling materials donot po,sse,ss "ideal" characterisfics. Recently an ex-perimental mateiial. Mineral Trioxide Aggregate(MTA), has been investigated in a series of tests: //(•vitro dye leakage witbout and with blood contami-nation, in vitro bacterial leakage, SEM examina-tion of re]Dlicas for marginal adaptation, settingtime, compressive strengUi, solubility, antibacterialproperties, cytotoxicity, im]:)lantation in bone, andan usage (est in toot-ends in dogs. Existing materi-als were used for comparison (I(i3-173).

Tbe sealing ability of MTA was siipetior to tbatof amalgam or Su]ierEBA in botb dye and bacte-tial leakage tnethods, and was tiot adversely af-fected by bloc:)d cc:)ntamination (163-165). Tbemarginal adaptation of MTA was better than thatof amalgam, IRM or SuperEBA (166). Tbe setting

time of MTA was fotttid to be <3 liouts, wbicb ismuch longer (ban amalgam or IRM. Ckimpressivestrength and solubility of MTA were similar to IRMand SnperEBA respecfively (167).

Tbe antibacterial effects of MTA and (bree ex-isting materials were investigated on facultativeand stricdy anaerobic bacteria; none were foundto be cotnpletely anfibactetial (168). Tbe cyUXox-icity of MTA was itivestigated b\' two metliods, agaroverlay and tadiocbrotniutn release. Tbe MTA wastanked less cytotoxic dian IRM or SiipetEBA, butmore cytotoxic tban amalgam in tbe agar overlaymetbocl. It was found to be less cytotoxic tbanatnalgam, IRM or SupetEBA vvbeu tbe radiocbto-mium release method was used (1(>9). Wbeti tbeAmes test was used (o determine tbe mutagenifictyof toot-end filling materials, MTA and commonlyused root-eud filling matetial proved to be noti-tnntagenic (170). Witb implantafion of materialsitl guitiea pig mandibles, tbere was no observabledifference between MTA and SnperEBA (171).

When root-end fillings of MTA or amalgamwere placed in tbe premolar teetb of dogs and ex-amined bislologically at vatious postopetative pe-tiods up (o 18 weeks, tbete was less itiflammationaround tbe root-eucls filled witb MTA, aud tbetewas evideuce of bealiug of tbe sttrrouiiditig tis-sues. In addition, witb the longet-lerin teedi filledwith MTA, new cementnm was found ou (be sur-face of tbe matetial; tbis was not (be case withamalgam (172). Similar peritadicular tisstie te-sjDonses were noted when MTA was used as root-etid ftlling material in the maxillary incisots ofmonkeys (173). These studies supported die fiir-tlier development of MTA for use as a root-etid ftll-iug material in man.

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Root End Filling Materials_ a Review