endodontic material

ENDODONTIC MATERIALS

D. 0RSTAVIKNIOM — Scandinavian Institute of Dental Materials, Kirkeveien 71B, N-1344 Haslum, Norway

Adv Dent Res 2(l):12-24, August, 1988

ABSTRACT

Endodontic sealing materials for permanent obturation of root canals are highly variable both in chem-istry of setting and in their additives. Conventional materials are based on zinc oxide-eugenol, rosin-

chloroform, or synthetic resins. These have been extensively tested for biological and technical properties. Mostmaterials are slightly or moderately cytotoxic, and some — notably paraformaldehyde-containing materials —have been associated with clinical complications such as paresthesia of the mental and/or inferior alveolar nerve.Recently, Ca(OH)2-containing materials have been introduced with claims of improved clinical and biologicalperformance. However, there is little documentation of the alleged benefits of new materials.

The virtual absence of comparative clinical studies on endodontic filling materials appears to be the majorobstacle to critical assessment of old materials or to adequate documentation of new formulae. A recentlyintroduced scoring system for the radiographic assessment of apical periodontitis may aid in the future testingof endodontic materials. Results with this scoring system on extensive clinical material indicate that it is possibleto discriminate among endodontic materials with small differences in clinical performance.

INTRODUCTION

Endodontic materials are used for permanent ob-turation of root canals after cleansing, shaping, irri-gation, and medication. Materials for obturation comeeither as (1) core and sealer combinations, (2) plasti-cized gutta percha, or (3) setting or non-setting pastes(Fig. 1). The most frequently used cores are made ofgutta percha, an isoprene polymer, with additions ofheavy metal oxides, primarily zinc oxide. Alterna-tively, metal points have been used. The sealers andpastes are of widely different compositions, but mostof them fall into one of the four categories shown inTable 1.

Both the physical and biological properties of en-dodontic materials are dependent on their chemicalcomposition. As an illustration of the great diversityin chemistry and composition of these materials, Ta-ble 2 lists the ingredients and mechanism of settingof some commonly used products. This diversity stemsfrom the fact that several different properties havebeen considered important for the clinical perform-ance of the materials. Thus, zinc oxide-eugenol seal-ers have been developed with emphasis on sealingqualities of this cement base, preventing ingress ofsaliva and bacteria through the root canal. Rosin-Presented at the International State-of-the-Art Conference on Re-storative Dental Materials, September 8-10, 1986, National Insti-tute of Dental Research

12

A B C

Fig. 1—Principles of root fillings. A, solid core (c) and sealer (s);B, softened gutta-percha (in this situation softened by compaction);C, paste-type material applied with spiral filler.

chloroform formulations were developed to soften thesurface of the gutta-percha point, thereby improvingthe adaptation of the point to the root canal wall.Additions of paraformaldehyde or other antibacterialagents to zinc oxide-eugenol sealers were done byendodontists relying on antisepsis for treatment. Incontrast, omission of such toxic substances is soughtby researchers who emphasize the biocompatibilityaspects of the materials. Synthetic resins have beenintroduced with minimal shrinkage, or slight expan-

Vol. 2 No. 1 ENDODONTIC MATERIALS 13

Type

TABLE 1CATEGORIES OF ENDODONTIC SEALERS

Examples

Zinc oxide-eugenol

Non-eugenol sealers

Polymeric resins

Rosin-based sealers

Rickert's, Grossman's, N2, En-domethasone, CRCS

Diaket, Sealapex, Nogenol

Hydron, AH 26, TraitementSPAD

Callahan's sol., Chloropercha,rosin-chloroform

sion, on setting as an advantage. Recently, materialscontaining calcium hydroxide have been introducedwhich purportedly aid in the healing of apical peri-odontitis, extending the philosophy of the resorbablepastes which were to perform pharmaceutical func-tions in the periapical area.

The gutta-percha points rely on their flexibility andadaptability for their success; in sharp contrast, themetal points were used when rigidity was consideredimportant for the placement of a root filling in narrowand curved canals.

While endodontic treatment in general is a reliableclinical procedure with a predictably high frequencyof success (Table 3), the use of endodontic materialsoften presents clinical problems. Traditionally, long-term stability and sealing properties of the endodon-tic filling material have been considered important.The minute dimensions of narrow canals or unin-strumented, accessory canals make the flow charac-teristic of special interest. Additions of x-ray contrastingcompounds are necessary for the assessment of fillingquality and for prognostic evaluations.

Endodontic treatment aims at curing and/or pre-venting apical periodontitis. The properties of en-dodontic materials, therefore, become important alsowith regard to their influence on these curative orpreventive aspects of treatment: Antibacterial prop-erties of endodontic materials are a controversial is-sue, whereas relative non-toxicity and/or bone-growth-stimulating activity is considered desirable by mostclinicians and researchers.

Endodontic materials are intentionally applied di-rectly on vital, soft tissues of the apical pulp or theperiodontal ligament. In a sense, this makes themtrue implant materials and subject to the particularlycomplex requirements, both technical and biological,of this group of biomaterials.

RESEARCH TRENDS

Their dual requirements for biocompatibility andsealing or obturation ability have made endodonticmaterials, particularly the sealers, popular objects fordifferent types of research studies. The biocompati-bility requirement was recognized very early, andRickert's endodontic sealer was the very first dentalmaterial subjected to the now-traditional mucosal im-plantation test (Rickert and Dixon, 1931). Similarly,endodontic materials were among the first dental ma-terials tested for biocompatibility with tissue cells cul-tured in vitro (Keresztesi and Kellner, 1966). A longseries of biocompatibility studies has followed, in-cluding usage studies in monkey and man (Lange-land, 1974; Holland et al, 1977; Spangberg, 1981;Horsted et al, 1982).

Biological PropertiesBiological testing has demonstrated a large varia-

tion in the toxicological and tissue-irritating proper-ties of the materials (Brown and Friend, 1968;Spangberg, 1981). Cell culture experiments (Fig. 2)have shown that the conventional, zinc oxide-eu-genol-based sealers are toxic both in the set and par-ticularly in the unset state (Spangberg, 1981; 0rstaviket al, 1981). Traditionally, this effect has been relatedto the content of eugenol (Cotmore et al, 1979), whichof course is available when the material is freshlyprepared, but which is also leached from the set mass(Wilson et al., 1973). The addition of paraformalde-hyde to some materials may increase the cytotoxicityof this type of material (Keresztesi and Kellner, 1966;0rstavik et al., 1981). Rosin-chloroform-type sealersappear to be less cytotoxic, when set, than most zincoxide-eugenol brands (Spangberg, 1981; 0rstavik et

Name

Gutta-percha

CHEMICAL CONSTITUENTS

Manufacturer

Mynol

TABLE 2OF SOME COMMONLY

Setting Mechanism

USED ENDODONTIC MATERIALS

Components

Gutta-percha; ZnO; S, Cl, Cd, Ba Ti Fe Cu

AH26

Endomethasone

KloroperkaProcoSol

De Trey

Septodont

N-O TherapeuticsStar Dental

Epoxy polymer

Zinc oxide-eugenol

Chloroform evaporationZinc oxide-eugenol

Epoxy-bis-phenol resin; Bi2O3/ TiO, Ag*;metheneamine

ZnO, cortisone, paraformaldehyde, Pb3O4/

thymol iodide, BaSO4; eugenolGutta-percha, Canada balsam, rosin, ZnOZnO, BaSO4, Bi-carbonate, Na-borate, rosin

Ag omitted from new formula AH26.

14 0RSTAV1K Adv Dent Res August 1988

TABLE 3RESULTS OF ENDODONTIC THERAPY

Authors

Guignard and HolzSwartz et al.Morse et al.

Barbakow et al.Delessert et al.Bergenholtz et al.Kerekes and

TronstadJokinen et al.Adenubi and RuleHarty et ahGrossman et al.Strindberg

Year

198519831983

1981198019791979

19781976197019641956

* N = necrotic pulps; V =t Originally treated roots.

Country

SwitzerlandUSAUSA

S. AfricaSwitzerlandSwedenNorway

FinlandEnglandEnglandUSASweden

vital pulps; R

Operator

SpecialistStudentsSpecialist

GPStudentsStudentsStudents

StudentsSpecialistsSpecialistsStudentsSpecialists

= revisions;

No. ofRoots

1941770458

124250556501

2459870

1100432775\

M = all

Diagnosis*

NMM

NVRM

MMMMM

diagnoses.

Percentsuccess

819095

89967591

5388909090

Obs. Period(years)

711

11.524

2-7?

21-5Vi-10

Sealer Material

ZnO-eugenol?

Eucalyptol-guttapercha

ZnO-eugenolZnO-eugenolRosin chloroformChloropercha

ChloroperchaZnO-eugenolZnO-eugenolZnO-eugenolRosin chloroform

al., 1981). The most commonly used synthetic resinsbehave differently: Initially marked cytotoxicity (Ols-son and Wennberg, 1985) diminishes when the ma-terial is cured, making this type of material one ofthe least cytotoxic in the set state (0rstavik et al.,1981). The mechanisms for cytotoxicity remain ob-scure, however.

It is fortunate for this group of materials that thedifferent biological tests tend to confirm each other.Thus, the implantation tests applied on endodonticmaterials (Brown and Friend, 1966; 0rstavik and Mjor,1988) show cytotoxicity profiles similar to those of thecell culture experiments (Spangberg, 1981; 0rstaviket al., 1981). In short-term tests, rosin-chloroform, zincoxide-eugenol, chloropercha, and synthetic resin, inthat order; produce tissue reactions of increasing in-tensity. Longer-term implantation experiments (Fig.3) show an almost dramatic resolution of the tissueresponse to cured synthetic resins, whereas thechemically less stable zinc oxide-eugenol and chlo-ropercha are accompanied by persisting, though di-minishing, inflammation (0rstavik and Mjor, 1988).

It would be reasonable to compare the results fromcell culture or implantation experiments with so-calledusage studies of endodontic materials, i.e., histologicassessment of tissue reactions to root fillings in manor experimental animals. A number of studies havebeen carried out with endodontic treatment of mon-keys, dogs, cats, and rats, some of which also includecomparisons of different endodontic materials. Onemajor difficulty with the usage test is the frequentlyuncontrolled influence of other (technical and biolog-ical) factors on the outcome of treatment. For in-stance, control of infection may be difficult, and thefilling material is often separated from the vital, re-

acting tissue by a mass of dentin fillings. In general,there seems to be a tendency for endodontic materialsto act less tissue-irritating in usage tests than mightbe expected from the cell culture or implantation ex-periments.

Physical PropertiesOn the technological side, interest has focused on

the sealing properties of the root canal filling. Severalstudies, mostly performed in vitro, have investigatedthe leakage of dyes (Antoniazzi et al., 1968; Beyer-Olsen et ah, 1983), radioisotopes (Higginbotham, 1967),bacteria (Kos et al., 1982), or electrolytes (Mattisonand von Fraunhofer, 1983) at the dentin/endodonticfilling interface. Other parameters — e.g., solubility,flow, working and setting time, radiopacity, and ad-hesive properties —have also been assessed (Mc-Comb and Smith, 1976; 0rstavik, 1983 a, b; Beyer-Olsen and 0rstavik, 1981; 0rstavik et al, 1983a).

Although the results from different researchers aresomewhat variable, a pattern of the different materialtypes with respect to sealing properties is emerging.Zinc oxide-eugenol preparations afford good sealsagainst leakage in most tests; resin-based sealers areintermediate in sealing ability; chloropercha formu-lations show the most leakage (Table 4). On the otherhand, adhesion of the materials to dentin is achievedonly with synthetic resin (McComb and Smith, 1976;0rstavik et al., 1983a), and the solubility in water isdefinitely lower for this type of material than for otherendodontic materials (0rstavik, 1983b).

Whereas the flow properties and film thickness areimportant characteristics for the distribution and spreadof the sealer inside the root canal and its ramifica-


75 -

50 -

25 -

ENDOMETHASONE

\

V\r

AH 26 ]l*•— 11'fORFENAN |

75 -

J<LOROPERKA NO

HYDRON

FRESH 7 DAYS

1 DAY

Fig. 2 —Cytotoxicity of endodontic materials as measured by the51chromium-relea?e method. Values for positive ( + ) and negative( - ) controls are indicated by the horizontal lines. From 0rstaviketal, 1981.

0

iCO

LUCO

OQ .COLU

cc

wCOCO

o

CO

o

IMPLANTATION PERIOD, daysFig. 3 —Tissue responses to endodontic sealers implanted subcu-taneously in rats. AH: AH 26. EM: Endomethasone. KP: Kloro-perka N-0. PS: ProcoSol. Tissue responses to materials containedin polyethylene tubes were assessed histologically on a no/slight-to-severe scale. Each point represents a numerically weighted av-erage response based on from four to seven specimens. From 0r-stavik et al., 1981; 0rstavik and Mjor, 1988.

tions, relatively little attention seems to have beenpaid to these properties in the development of thematerials. A minimum of flow is necessary for thesealer to adapt to the irregularities of the canal; how-ever, materials that are too free-flowing may easilybe displaced periapically. Used in conjunction withthe standardized method of root canal filling, sealerswith large grains —i.e., high film thickness — may in-terfere with proper seating of the master point (0r-stavik, 1982). There is great variation among commonlyused materials with regard to both film thickness andflow (Figs. 4,5).

Clinical Tests of Endodontic MaterialsIn striking contrast to the numerous technological

and biological studies is a virtually complete lack ofcomparative, clinical-radiographic studies on endo-dontic materials. This is remarkable, particularly inview of the many clinical-radiographic follow-upstudies that have been published (Strindberg, 1956;Grossman et al., 1964; Harty et al, 1970; Adenubi andRule, 1976; Jokinen et al., 1978; Kerekes and Tronstad,

1979; Bergenholtz et al, 1979; Delessert et al, 1980;Barbakow et al, 1980 a, b; Morse et al, 1983; Swartzet al, 1983; Guignard and Holz, 1985). This lack ofclinical correlates to laboratory assessments of en-dodontic materials is probably the major impedimentto a scientific development of new and improved ma-terials.

In consequence, most changes in the selection andapplication of endodontic materials over the past dec-ades have been fads based on ingenuity in advertis-ing rather than progress based on scientifically foundeddevelopments. Thus, no new material can presentdocumented improved biocompatibility, improvedhealing properties, improved sealing properties, orimproved clinical performance. Technological im-provements in devices for application of gutta-per-cha—e.g., the various compactors (Kerekes and Rowe,1982) and guns for mould injection (Marlin et al,1981) —may offer advantages in the form of time-sav-ing and ease of manipulation. However, there are nodata to indicate that the use of these devices improves

16 0RSTAVIK Adv Dent Res August 1988

TABLE 4RESULTS OF LEAKAGE TESTS

Author Year Technique Material Leakage*

Higginbotham

Antoniazzi et al.

Mattison and vonFraunhofer

Beyer-Olsen et al.

* Due to great variations

1967

1968

1983

1983

among authors

Radioisotope

Dye

Electrochemical

Dye

in experimental design and

Kloroperka + + +Diaket +Procosol +

Kloroperka + + 4-Kerr (Rickert) + +AH26 + +

Diaket + + +Procosol +

Kloroperka + + + +AH26 + + +Endomethasone + +Procosol +/ —

units of measurement, the results have been arbitrarilyassigned values for leakage increasing with increasing number of +.

EstSsoneEndomethasoneEucaryl PoudreTraitement SPADForfenan

Eucaryl Pate FlTubli-SealCresopateDiaketDiaket A

HydronKloroperkkaPulpdentHermeticAH 26

Kerr PCSKloroperka N-0MerpasoneKri 1 PastePropylor

N2 UniversalRoth 811N2 NormalForm.G. IvanoffESiocalex 6-9

20 40 60 160

FILM THICKNESS, pmFig. 4 —Film thickness of endodontic sealers. See also 0rstavik,1982.

the success rate or increases the number of teeth thatmay be conserved by endodontic treatment. More-over, the current, ardent marketing of sealers con-taining calcium hydroxide appears to have very few,if any, comparative studies to back up the claims ofbiocompatibility and healing properties.

It would seem evident from the above that researchand development of endodontic materials are hin-dered by the lack of acceptable procedures for thetesting of their clinical performance. Therefore, newmaterials are marketed which may or may not comply

50-

40-

30-

20-

PROCOSOL

AH 26 ^ • E N D O M E T H A S O N E

PULPDENT RCS

50

40

30

20

-10

2:1 4:1 8:1 8:1 KMPOWOER-TO-UQUO RATIO, g/mi

Fig. 5 —Flow of endodontic sealers as a function of powder-to-liquid ratio. From 0rstavik, 1983a.

with some of the currently recognized laboratory re-quirements, but which rely on unsubstantiated claimsof superior clinical performance as a competing edgein comparison with traditional products.

The lack of clinical correlates also reflects on the"accepted" properties tested in the laboratory: Re-quirements for sealing properties, physical stabilityand biocompatibility, for example, may be well-


founded on thorough considerations of what are de-sirable properties. However, it should be kept in mindthat they are based on just that: considerations, andnot on clinically proven relevance. Therefore, withthe coming of clinical testing of endodontic materials,the so-called "ideal" physical and biological proper-ties of these materials may have to be revised. More-over, with an increased knowledge of clinicalperformance, new in vitro designs may be appliedwhich more accurately assess particular clinical com-plications. Thus, the guinea pig maximization test hasbeen applied and the test results related to the clinicaloccurrence of an allergic reaction to endodontic ma-terials (Hensten-Pettersen et aL, 1985), and a neuro-toxicity model has been adapted for the testing ofendodontic sealers (Brodin et aL, 1982; Brodin and0rstavik, 1982) implicated in paresthetic reactions ofthe inferior alveolar nerve to endodontic treatment(0rstavik et aL, 1983 b; Rowe, 1983).

Finally, the clinical assessment of the materials musttake into account the level, i.e., the frequency andseverity, of the problems. Fig. 6 is an illustration ofsome examples of clinical complications with endo-dontic materials occurring at various levels. It shouldbe remembered that the more severe complicationsmay occur with extremely low frequency. Therefore,in a clinical trial the number of subjects required forthe assessment of these complications may be pro-hibitively large, and we may also have to rely onenlightened inferences in the future.

Another factor which may have influenced the de-velopment of endodontic materials is the compara-tively small market from the point of view ofmanufacturers. Endodontic materials are a low-costarea with little chance of research and developmentrevenue in the form of high-priced new products,and new endodontic materials have usually been spin-offs from other areas of research. Moreover, the en-dodontic establishment may have been overzealousin its skepticism of new products. This traditionalismalso tends to become cemented by the divergent tech-niques and materials taught in different dental schoolsand in the post-graduate programs.

SEVERITY

CURRENT DEVELOPMENTS

Treatment Local com- Systemic Risk offailure plications effects fatality

FREQUENCYFig. 6 —Failures and complications after use of endodontic mate-rials: Incidence versus severity.

GeneralPulp biology and endodontics as areas of scientific

research have prospered in recent years. Pulpal andperiodontal reactions to trauma (Hammarstrom et aL,1986) and to infections (Fabricius et aL, 1982a) areunder study, with application of clinical researchstrategies as well as the tools of the basic sciences:pulpal physiology and the immunology and bacteri-ology of infections of the pulp and periapex.

In endodontic practice, the improvements in thestandardized technique have been disseminated tomany practicing dentists and specialists, who feel thattheir performance has thereby improved. Reciproca-ting angle pieces and, more recently, the introductionof sonic and ultrasonic devices for instrumentationmay ease and improve canal preparation (Klaymanand Brilliant, 1975; Stamos et aL, 1985).

Bacterial StudiesThe current activity in endodontic microbiology may

be of greater significance for endodontic materials.Improved methods of bacteriologic sampling from rootcanals and periapical tissues (Tronstad et aL, 1987)have led to better characterization of the infectingbacteria, which turn out to be a lower number ofgenera than previously believed (Table 5). A strategyof selective antibacterial treatment may therefore beenvisaged, and controlled-release delivery systems forantibiotics or other antibacterial components, also in-volving filling materials, are conceivable. Moreover,with improved possibilities for bacteriological diag-nosis, selection among materials with different activ-

TABLE 5MICRO-ORGANISMS MOST COMMONLY

ASSOCIATED WITH PULPOPERIAPICAL INFECTIONS

Genus Characterization

Bacteroides

EubacteriumBifidobacterium

Fusobacterium

PeptostreptococciPeptococci

WolinellaSelenomonas

StreptococciEnterococci

Lactobacillus

G - , anaerobic, pleomorphic rods

G +, anaerobic rodsG —, anaerobic rods

G + , anaerobic cocci

G —, anaerobic, mobile rods

G -f, facultative cocciG + , facultative rods

Based on Sundquist, 1976; Moller et aL, 1981; Fabriciuset aL, 1982b; Bystrom et aL, 1985; Haapasalo et aL, 1985;Haapasaioef a/., 1986.


ity toward different bacterial species (Cox et al., 1978;0rstavik, 1981) becomes feasible. Work is in progresson the controlled delivery of drugs into root canals;however, at this point in time, activity is mainly fo-cused on temporary dressing medicaments (Barnettet al, 1986).

Tissue Reactions to Endodontic MaterialsIn contrast, the philosophy on endodontic filling

materials has considered release of material compo-nents to be undesirable, indeed associated with in-flammatory reactions to the materials. Whereas thisconcept could change if bacteriostatic or bactericidalagents with no or few tissue-irritating properties couldbe controllably and selectively leached from the ma-terial, current research is concerned with the identi-fication and localization of material components inthe tissues. Moreover, the analysis of vascular andcellular reactions to the endodontic material is still ofprimary interest in endodontic research.

This interest is based on the supposition that toxiccomponents of the material may initiate or perpetuateperiapical inflammation (Fig. 7), which in turn maynecessitate the removal of the tooth. While it has longbeen recognized that unset endodontic sealers are ir-ritating to tissue (Keresztesi and Kellner, 1966;Langeland, 1974), only recently have the mechanismsfor this irritation been subjected to a more detailedstudy.

One of the advances in microscopic diagnosis is theapplication of element analysis to tissue sections andcell culture preparations. At our laboratory, we haveapplied this technique to implantation studies withendodontic sealers and to clinical biopsies from casesof endodontic failures with the material as suggested

etiology. Fig. 8 is a brief outline of the methodology,and shows the use of the scanning electron micro-scope on paraffin-embedded tissue sections. Fig. 9illustrates the results obtained for a clinical specimenanalyzed microscopically, by back-scattered scanningelectron microscopy (BSEI) and by energy-dispersivemicro-analysis of particles identified by BSEI. Whilethe analysis is less efficient for elements of atomicweights below 20, precise, qualitative or semi-quan-titative, measurements may be made of microscopicand submicroscopic (<1 jxm) particles released fromthe endodontic materials. The information obtainedis easily related to inflammatory reactions observedin neighboring sections by light microscopy (0rstavikand Mjor, 1988). Moreover, insight into the mecha-nism of tissue damage may be obtained through cor-relation with more basic studies on cytotoxicity ofendodontic material components. Thus, the recentdocumentation of the toxic properties of zinc (Helge-land, 1977; Meryon and Jakeman, 1985), combinedwith the demonstration of zinc in particles associatedwith inflammatory reactions to endodontic sealers(Table 6), may indicate that the zinc oxide so com-monly used in endodontic materials may exert a neg-ative influence on the tissues.

Recent research into the cell and tissue reactions toendodontic materials and their components also shedsnew light on the influence of these materials on cel-lular functions. Particularly, studies on macrophagefunction (Biggs et al., 1985; Syrjanen et al., 1985) inthe presence of material components may indicatethat inflammatory cells attack and dispose of differentendodontic materials with different mechanisms andefficacy. Improved knowledge of the host's ability todeal with elements and particulate matter from en-

Fig. 7 —Adverse tissue reactions to en-dodontic filling material displaced peri-apically. M: Material particles. I:Inflammatory reaction. Zinc oxide-eu-genol cement with paraformaldehydeaddition (N2). Original magnification40 x.


ELECTRONBEAM OF SEM

EDXA

BSEI

SEI

SPECIMEN

Fig. 8 —Element analysis of tissue sections in the scanning electronmicroscope (SEM). SEI: Secondary electron image (regular SEM).BSEI: Back-scattered electron image displaying components withelements of high atomic weights. EDXA: Energy-dispersive spec-trum of elements detected.

dodontic materials may aid in the selection amongexisting products and in the manufacture of newproducts.

Case Reports of Adverse Reactionsto Endodontic Materials

The literature is replete with case reports of atypicalreactions to and mishaps during endodontic treat-ment. As a whole, endodontic materials are fortu-nately relatively innocuous, and adverse reactions arefew and therefore not easily compiled and analyzedwith respect to incidence and severity. Case reportstherefore remain an important source of information

on the clinical qualities of endodontic materials. Re-cently, damage to the inferior alveolar nerve subse-quent to endodontic treatment of posterior teeth ofthe lower jaw has been the subject of several reportsand literature surveys (0rstavik et al., 1983b; Rowe,1983). In laboratory testing, a modified neurotoxicityassay to endodontic filling materials has demon-strated that the part played by the material may beimportant in this clinical state. The pattern of neu-rotoxicity in vitro correlates well with the associationof the material with clinical paresthesia (Fig. 10), andthis model may be advantageous in the testing ofnewly-developed products (Brodin et al., 1982; Brodinand 0rstavik, 1982; Schippers et al, 1986).

Allergic reactions to endodontic materials may oc-cur, and reports of clinical cases have surfaced in theliterature (Horsted and S0holm, 1976; Barkin et al.,1984). Also for this clinical condition there are ac-cepted laboratory methodologies which may be usedto screen materials for allergenic properties (Hensten-Pettersen et al., 1985). Particularly with regard to thesensitizing properties of many synthetic polymer sys-tems and antibacterial agents, it would seem properto suggest that new materials should be subjected toa sensitization test. The fairly high sensitizing poten-tial of commonly used sealers (Table 7) may actuallypoint to the desirability of improving some of themost commonly used materials in just this respect.

Clinical StudiesBeing engaged in standardization work on both

technological and biological aspects of endodonticmaterials, NIOM launched a research program withthese materials which also included a clinical study.As indicated previously, few if any comparative clin-

w .*.

— Bi

4 8 12

X-RAY ENERGY, KeV

Fig. 9 —Tissue reaction to subcutaneous implant of AH 26. A: Section stained with hematoxylin and eosin displays intense inflammation.B: BSEI image for orientation in the scanning electron microscope showing tissue-associated bright patticles of high atomic weights (arrows).C: Identification of bismuth in EDXA spectrum from area encircled in B. Original magnification of micrographs 40 x .

20 0RSTAVIK Adv Dent Res August 1988

TABLE 6ELEMENTS IDENTIFIED IN TISSUE SECTIONS FROMIMPLANTS WITH ENDODONTIC SEALERS IN THE

RAT

Sealer

AH26EndomethasoneProcoSolKloroperka N 0

ParticleSize

25 fim25 \xm25 |xm50p,m

Elements

Ti, S, AgZn, Ba, S, PbZn, Bi, PZn, Ca, P

Data from 0rstavik and Mjor, 1988.

UJ

h§1-IHUJ i.Q ©

IJQ.

<

100--

8 0 -

60 -

4 0 -

20 -

• AOPROCOSOL

/ AH26 ^

| fc DIAKET

i I ys^KLOROPERKA N-0

VrX-\ ENDOMETHASONE, N2

-30 -20 -10 10TIME, minutes

20 30

Fig. 10-Neurotoxicity of endodontic sealers. The conductivity ofrat phrenic nerve was followed during (negative time scale) andafter (positive time scale) exposure of the nerve to the sealers.ProcoSol, Kloroperka, Endomethasone, and N2 caused an imme-diate stop in nerve action potential, whereas AH 26 and Diaketonly slowly reduced the amplitude of the action potential. Whenthe root filling material was removed and the nerve was washedin the buffer solution, ProcoSol-exposed nerves regained most oftheir action potential amplitude, whereas nerves treated with En-domethasone or N2 showed permanent blockage of nerve con-ductance. The Kloroperka, Diaket, or AH 26-treated nerves regainedsome conductance. Based on data from Brodin et al., 1982.

TABLE 7INCIDENCE OF SENSITIZATION BY AND SEVERITY

OF RESPONSE TO ENDODONTIC SEALERS

Sealer Incidence Severity

AH26EndomethasoneKloroperkaProcoSol

12/189/20

10/206/20

Data from Hensten-Pettersen et al, 1985.

ical studies on endodontic materials had been per-formed. Probably the main obstacle to this type ofresearch has been the lack of accepted and sensitiveclinical criteria for the results of treatment. The sub-jectivity and non-reproducibility of radiographic as-sessment of endodontic failure or success have beendemonstrated repeatedly (Goldman et al, 1972; Reitand Hollender, 1983), and the tendency has been to

denounce x-ray analyses of root-filled teeth as an ad-equate basis for scientific research. To overcome thisdifficulty, we investigated the possibility of makingthe radiographic diagnosis more objective and repro-ducible by applying a scoring system. As a basis forthe clinical studies on endodontic materials, there-fore, a periapical index termed the PAI was devel-oped (Fig. 11) (0rstavik et al, 1986). Similar in conceptto the successful indices now so familiar in periodon-tal, caries, and plaque research, this index is basedon a delineation of steps on a progressive diseasescale. The steps on PAI are represented by referenceradiographs of teeth with various degrees of apicalperiodontitis verified histologically in a necropsy studyof 299 root-filled teeth, including successes as well asfailures by conventional criteria (Brynolf, 1967). Thisindex allows for a possible blind score of experimen-tal teeth in coded radiographs and permits unbiasedassessment of the radiographic appearance. Exten-sive analyses of parameters for reproducibility andaccuracy indicate that the PAI may be used with clin-ical and statistical confidence in clinical experiments,allowing for comparisons between subgroups of teethwith systematic or randomized differences (0rstaviket al, 1986; 0rstavik, 1988).

The PAI scoring system has been applied in a con-trolled study on the clinical performance of three en-dodontic sealers used in combination with astandardized gutta-percha/sealer technique (Orstaviket al, 1987). The choice of sealer was randomized bythe throwing of a die when the tooth was ready forfilling. A total of 810 roots were filled with either AH26, a synthetic polymer, ProcoSol, a zinc oxide-eu-genol cement, or Kloroperka N 0 , a rosin-guttaper-cha-zinc oxide-balsam-chloroform mixture, inconjunction with a master cone of gutta-percha. Atthe three- and four-year follow-up, 451 and 289 roots,respectively, were available for clinical and radio-graphic re-examination. Computer analysis permit-ted stratification of the material to correct for theinfluence of clinical and radiographic characteristicsof known influence on the prognosis, other than thesealers used.

Tables 8 and 9 and Fig. 12 show some salient re-sults from this study. The results document that thePAI scoring system is suitable for follow-up exami-nations and for experimental, prospective clinicalstudies in endodontics. Apparently, the PAI scoresare highly discriminatory and may be subjected topowerful statistical tests; the possibility for unbiasedrecording of the periapical situation makes the results"true" in a numerical or statistical sense; and the his-tological verification (Brynolf, 1967) of the referenceradiographs lends credence to the supposition thatthe results are also "true" in a biological sense.

The use of the PAI made possible a discriminationof the results obtained with different sealers. Al-though the conventional failure rate was low and didnol permit discrimination between the sealers, thedistribution of scores in the "doubtful" categories 2


Fig. 11—The periapical index. The radiograph of a given root apex area is compared with the radiographs of the scale, and the root isassigned a PAI score corresponding to the PAI score of the reference radiograph which it resembles the most. See also 0rstavik et al.,1986.

TABLE 8IMPROVEMENT IN PERIAPICAL STATUS

SUBSEQUENT TO ENDODONTIC TREATMENT

TimePAI

N Score — RiditSignificant

Change

Pre-operative1 year2 years3 years4 years

810546493451289

0.310.230.160.140.12

tt

* PAI score ridit values connected with vertical lines arenot significantly different (p > 0.05).

t Denotes that the corresponding PAI score ridit valuesare significantly different from all other ridits.

Data from 0rstavik et al., 1987.

and 3 of the PAI clearly documented that KloroperkaN0 performed less well than did AH 26 and ProcoSol.This rating persisted through all stratifications of the

total material, which resulted in a sufficient numberof teeth in each subgroup for adequate statistical (RI-DIT) analysis.

The PAI scoring system, with its possibilities forunbiased scoring and intra- and interobserver har-monization, applied in clinical studies where the en-dodontic material is the only randomized variable,forms a sound basis for clinical testing and compar-isons of endodontic materials. Combined with a ju-dicious selection of physical and biological tests, suchclinical testing may ultimately determine the suita-bility or advantages claimed for new products.

NEW MATERIALS

Regulatory ActionThere is a framework, however frail, which should

be reinforced for the development and approval ofnew materials. Within the US, ADA SpecificationsNo. 56, Endodontic Filling Materials, and No. 41,Recommended Standard Practices for Biological Eval-

TABLE 9PAI SCORE ANALYSIS OF PERIAPICAL STATUS FOR ROOTS FILLED WITH 3 DIFFERENT SEALERS

Time

Pre-operative1 year2 years3 years4 years

AH26 Kloroperka ProcoSol Statistical Significance

0.290.200.150.120.10

0.330.250.190.190.16

0.310.220.160.120.10

N.S.KP > AH, PS(p < 0.05)KP > AH, PS(p < 0.05)KP > AH, PS(p < 0.01)KP > AH, PS(p < 0.05)

Data from 0rstavik et al., 1987.The figures in the Table are mean ridit values of the PAI score data. The lower the mean ridit, the better the periapical

radiographic status of that group.


.100 T

oEwoDCUJ

<

.050 -

PREOPERATIVE STATUSPAI score 1Vital pulpSupported function> 1/2 marg. bone

• AH26

O KLOROPERKA

D PROCO-SOL

0 1 2 3 4TIME, years

Fig. 12 —Periapical radiographic status of roots filled with AH 26,Kloroperka N-0, or ProcoSol. Higher ridit values indicate moresigns of apical periodontitis in the corresponding radiographs. Theteeth included were selected on the basis of optimum pre-operativestatus. See also 0rstavik et al, 1987.

uation of Dental Materials, contain a selection of testseasily performed and controlled for evaluation of newendodontic materials. The International Organizationfor Standardization has published, or is in the processof publishing, similar test methods for these materials(Table 10).

In this context, it is interesting to note that the mostrecent entries on the endodontic materials market have

not documented compliance with any of the existingstandards or specifications. Indeed, for some of themit is apparent that they do not comply with importantparts of some specifications. This must be considereda most unfortunate situation: The painstaking workof the endodontists/material scientists leading up tocomplete specifications and standards is put aside,and new materials are marketed with claims of, butwithout documentation of, superior new qualities butwhich are not even tested for mandatory, minimumproperties.

Acceptance of and adherence to the already exist-ing requirements spelled out in specifications andstandards are therefore the first steps in an improveddocumentation of new endodontic materials.

Research AvenuesRegulations based on today's or yesterday's knowl-

edge must not act as obstacles to research and de-velopment of new types of products. New ways tosolve the obturation/biocompatibility/healing prob-lems associated with endodontic materials shouldconstantly be sought. There is currently some re-search activity which may turn up new concepts, ifnot principles, for root canal filling.

(1) Physical separation of the biocompatibility functionand the obturating function (Fig. 13).— The beneficialclinical effects of temporary dressings with calciumhydroxide have prompted attempts to preserve theseeffects in the permanent root fillings. Clinicians areknown intentionally to leave the most apical part ofthe c mal filled with Ca(OH)2 when placing the per-manent filling. The sealers containing Ca(OH)2 havebeen marketed with the same philosophy. Packing ofthe apical part with "biocompatible" powders of den-tin chips (Petersson et al, 1982), hydroxyapatite (Cal-lis and Santini, 1985), or collagen-calcium phosphate(Nevins et al., 1980) has also been attempted. Theo-retically, this approach is an interesting one, in thatthe traditional biological/technical compromise maybe discarded, and the optimum requirements for bothbiocompatibility and obturating function may besought and satisfied.

(2) Mechanical "plugging" of dentin canal walls. —Laser

TABLE 10REGULATORY DOCUMENTS PERTAINING TO THE TESTING OF ENDODONTIC MATERIALS

Agency Document

ISO — International Organization for Standardization

ANSI/ADA—American Dental Association

BSI- British Standards Institution

ISO/TR 7405 —Biological evaluation of dental materialsISO/DIS 6876 —Dental root canal sealing materialsISO/DIS 6877-Dental root canal obturating pointsANSI/ADA Specification No. 41. Recommended Standard Practices

for Biological Evaluations of Dental MaterialsANSI/ADA Specification No. 56. Endodontic Filling MaterialsBS 5828:1980 Methods of Biological Assessment of Dental Materials

Vol. 1 No. 1 ENDODONT1C MATERIALS 23

Fig. 13 —Separation of biocompatibility and sealing functions inendodontic materials. A: "Biological" plug, e.g., dentin chips orcalcium hydroxide. B: "Mechanical" plug, e.g., conventional orimproved sealing materials.

technology seeks new applications, one of which isthe surface glazing of root canal walls. The conceptwould be to seal off the dentinal tubules, apical fo-ramen, and accessory canal openings with sinteredmasses of dentin or enamel powder (Zakariasen etal., 1986). Another approach to the problem of dentintubule plugging is impregnation of tubules with syn-thetic resin. Research activity in this area may be tem-pered by the lessons of history: Riebler's paste andmore recently Traitement SPAD were developed onthis principle with a water-compatible bakelite-typeresin. The many adverse tissue reactions to these ma-terials call for caution when attempts are made toadapt this principle once more to endodontic treat-ment. Finally, the development of dentin bondingagents may improve adaptation of the material to theroot canal walls (Zidan and ElDeeb, 1985).

C O N C L U S I O N S

Endodontic treatment is reported to succeed in from80 to 95% of the cases treated. Failures are mostlyassociated with the occurrence or persistence of in-

fection, to a lesser extent with adverse tissue reac-tions to the root-filling materials. Whereas root-fillingmaterials and techniques display widely differentsealing qualities, their clinical performance is not sim-ilarly divergent. Although improved sealing proper-ties may be desirable, great improvements in successrates are unlikely. Moreover, although the materialsvary greatly in biocompatibility, there are few data toindicate that superior biocompatibility is essential forendodontic treatment success. Endodontic problemcases are usually successfully treated when the anti-infective measures have been effective. Significantimprovement in endodontic therapy may be expectedwhen control of infection can be achieved regularlyand predictably. To the extent that new materials,material combinations, or techniques can contributeto this end, real improvements in endodontic mate-rials may be feasible.

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