Advances in Dental Research

Advanceshttp://adr.sagepub.com/ in Dental Research

Endodontic Materials D. Ørstavik ADR 1988 2: 12 DOI: 10.1177/08959374880020010301 The online version of this article can be found at: http://adr.sagepub.com/content/2/1/12

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ENDODONTIC MATERIALS D . 0RSTAVIK NIOM — Scandinavian Institute of Dental Materials, Kirkeveien 71B, N-1344 Haslum, Norway Adv Dent Res 2(l):12-24, August, 1988

ABSTRACT ndodontic sealing materials for permanent obturation of root canals are highly variable both in chemistry of setting and in their additives. Conventional materials are based on zinc oxide-eugenol, rosinchloroform, or synthetic resins. These have been extensively tested for biological and technical properties. Most materials 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 biological performance. 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 major obstacle to critical assessment of old materials or to adequate documentation of new formulae. A recently introduced scoring system for the radiographic assessment of apical periodontitis may aid in the future testing of endodontic materials. Results with this scoring system on extensive clinical material indicate that it is possible to discriminate among endodontic materials with small differences in clinical performance.

E

INTRODUCTION Endodontic materials are used for permanent obturation of root canals after cleansing, shaping, irrigation, and medication. Materials for obturation come either as (1) core and sealer combinations, (2) plasticized gutta percha, or (3) setting or non-setting pastes (Fig. 1). The most frequently used cores are made of gutta percha, an isoprene polymer, with additions of heavy metal oxides, primarily zinc oxide. Alternatively, metal points have been used. The sealers and pastes are of widely different compositions, but most of them fall into one of the four categories shown in Table 1. Both the physical and biological properties of endodontic materials are dependent on their chemical composition. As an illustration of the great diversity in chemistry and composition of these materials, Table 2 lists the ingredients and mechanism of setting of some commonly used products. This diversity stems from the fact that several different properties have been considered important for the clinical performance of the materials. Thus, zinc oxide-eugenol sealers have been developed with emphasis on sealing qualities of this cement base, preventing ingress of saliva and bacteria through the root canal. RosinPresented at the International State-of-the-Art Conference on Restorative Dental Materials, September 8-10, 1986, National Institute of Dental Research

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 the surface of the gutta-percha point, thereby improving the adaptation of the point to the root canal wall. Additions of paraformaldehyde or other antibacterial agents to zinc oxide-eugenol sealers were done by endodontists relying on antisepsis for treatment. In contrast, omission of such toxic substances is sought by researchers who emphasize the biocompatibility aspects of the materials. Synthetic resins have been introduced with minimal shrinkage, or slight expan-

12

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Vol. 2 No. 1

ENDODONTIC MATERIALS TABLE 1

CATEGORIES OF ENDODONTIC SEALERS Type

Examples

Zinc oxide-eugenol

Rickert's, Grossman's, N2, Endomethasone, CRCS Diaket, Sealapex, Nogenol Hydron, AH 26, Traitement SPAD Callahan's sol., Chloropercha, rosin-chloroform

Non-eugenol sealers Polymeric resins Rosin-based sealers

sion, on setting as an advantage. Recently, materials containing calcium hydroxide have been introduced which purportedly aid in the healing of apical periodontitis, extending the philosophy of the resorbable pastes which were to perform pharmaceutical functions in the periapical area. The gutta-percha points rely on their flexibility and adaptability for their success; in sharp contrast, the metal points were used when rigidity was considered important for the placement of a root filling in narrow and curved canals. While endodontic treatment in general is a reliable clinical procedure with a predictably high frequency of success (Table 3), the use of endodontic materials often presents clinical problems. Traditionally, longterm stability and sealing properties of the endodontic filling material have been considered important. The minute dimensions of narrow canals or uninstrumented, accessory canals make the flow characteristic of special interest. Additions of x-ray contrasting compounds are necessary for the assessment of filling quality and for prognostic evaluations. Endodontic treatment aims at curing and/or preventing apical periodontitis. The properties of endodontic materials, therefore, become important also with regard to their influence on these curative or preventive aspects of treatment: Antibacterial properties of endodontic materials are a controversial issue, whereas relative non-toxicity and/or bone-growthstimulating activity is considered desirable by most clinicians and researchers.

13

Endodontic materials are intentionally applied directly on vital, soft tissues of the apical pulp or the periodontal ligament. In a sense, this makes them true implant materials and subject to the particularly complex requirements, both technical and biological, of this group of biomaterials. RESEARCH TRENDS

Their dual requirements for biocompatibility and sealing or obturation ability have made endodontic materials, particularly the sealers, popular objects for different types of research studies. The biocompatibility requirement was recognized very early, and Rickert's endodontic sealer was the very first dental material subjected to the now-traditional mucosal implantation test (Rickert and Dixon, 1931). Similarly, endodontic materials were among the first dental materials tested for biocompatibility with tissue cells cultured in vitro (Keresztesi and Kellner, 1966). A long series of biocompatibility studies has followed, including usage studies in monkey and man (Langeland, 1974; Holland et al, 1977; Spangberg, 1981; Horsted et al, 1982). Biological Properties Biological testing has demonstrated a large variation in the toxicological and tissue-irritating properties of the materials (Brown and Friend, 1968; Spangberg, 1981). Cell culture experiments (Fig. 2) have shown that the conventional, zinc oxide-eugenol-based sealers are toxic both in the set and particularly in the unset state (Spangberg, 1981; 0rstavik et al, 1981). Traditionally, this effect has been related to the content of eugenol (Cotmore et al, 1979), which of course is available when the material is freshly prepared, but which is also leached from the set mass (Wilson et al., 1973). The addition of paraformaldehyde to some materials may increase the cytotoxicity of this type of material (Keresztesi and Kellner, 1966; 0rstavik et al., 1981). Rosin-chloroform-type sealers appear to be less cytotoxic, when set, than most zinc oxide-eugenol brands (Spangberg, 1981; 0rstavik et

TABLE 2

CHEMICAL CONSTITUENTS OF SOME COMMONLY USED ENDODONTIC MATERIALS Setting Mechanism

Name

Manufacturer

Gutta-percha

Mynol

AH26

De Trey

Epoxy polymer

Endomethasone

Septodont

Zinc oxide-eugenol

Kloroperka ProcoSol

N-O Therapeutics Star Dental

Chloroform evaporation Zinc oxide-eugenol

Components Gutta-percha; ZnO; S, Cl, Cd, Ba Ti Fe Cu Epoxy-bis-phenol resin; Bi2O3/ TiO, Ag*; metheneamine ZnO, cortisone, paraformaldehyde, Pb3O4/ thymol iodide, BaSO4; eugenol Gutta-percha, Canada balsam, rosin, ZnO ZnO, BaSO4, Bi-carbonate, Na-borate, rosin

Ag omitted from new formula AH26. Downloaded from adr.sagepub.com by guest on July 22, 2011 For personal use only. No other uses without permission.

14

Adv Dent Res August 1988

0RSTAV1K

TABLE 3 RESULTS OF ENDODONTIC THERAPY No. of Authors

Year

Country

Operator

Roots

Diagnosis*

Guignard and Holz Swartz et al. Morse et al.

1985 1983 1983

Switzerland USA USA

Specialist Students Specialist

194 1770 458

N M

Barbakow et al. Delessert et al. Bergenholtz et al. Kerekes and Tronstad Jokinen et al. Adenubi and Rule Harty et ah Grossman et al. Strindberg

1981 1980 1979 1979

S. Africa Switzerland Sweden Norway

GP Students Students Students

1978 1976 1970 1964 1956

Finland England England

Students Specialists Specialists Students Specialists

USA

Sweden

Percent success

Obs. Period (years)

M

81 90 95

7 1 1

124 250 556 501

N V R M

89 96 75 91

1 1.5 2 4

2459 870 1100 432

M M M M M

53 88 90 90 90

2-7

775\

?

2 1-5 Vi-10

Sealer Material ZnO-eugenol ?

Eucalyptolguttapercha ZnO-eugenol ZnO-eugenol Rosin chloroform Chloropercha Chloropercha ZnO-eugenol ZnO-eugenol ZnO-eugenol Rosin chloroform

* N = necrotic pulps; V = vital pulps; R = revisions; M = all diagnoses. t Originally treated roots.

al., 1981). The most commonly used synthetic resins behave differently: Initially marked cytotoxicity (Olsson and Wennberg, 1985) diminishes when the material is cured, making this type of material one of the least cytotoxic in the set state (0rstavik et al., 1981). The mechanisms for cytotoxicity remain obscure, however. It is fortunate for this group of materials that the different biological tests tend to confirm each other. Thus, the implantation tests applied on endodontic materials (Brown and Friend, 1966; 0rstavik and Mjor, 1988) show cytotoxicity profiles similar to those of the cell culture experiments (Spangberg, 1981; 0rstavik et al., 1981). In short-term tests, rosin-chloroform, zinc oxide-eugenol, chloropercha, and synthetic resin, in that order; produce tissue reactions of increasing intensity. Longer-term implantation experiments (Fig. 3) show an almost dramatic resolution of the tissue response to cured synthetic resins, whereas the chemically less stable zinc oxide-eugenol and chloropercha are accompanied by persisting, though diminishing, inflammation (0rstavik and Mjor, 1988). It would be reasonable to compare the results from cell culture or implantation experiments with so-called usage studies of endodontic materials, i.e., histologic assessment of tissue reactions to root fillings in man or experimental animals. A number of studies have been carried out with endodontic treatment of monkeys, dogs, cats, and rats, some of which also include comparisons of different endodontic materials. One major difficulty with the usage test is the frequently uncontrolled influence of other (technical and biological) factors on the outcome of treatment. For instance, control of infection may be difficult, and the filling 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 materials to act less tissue-irritating in usage tests than might be expected from the cell culture or implantation experiments. Physical Properties On the technological side, interest has focused on the sealing properties of the root canal filling. Several studies, mostly performed in vitro, have investigated the leakage of dyes (Antoniazzi et al., 1968; BeyerOlsen et ah, 1983), radioisotopes (Higginbotham, 1967), bacteria (Kos et al., 1982), or electrolytes (Mattison and von Fraunhofer, 1983) at the dentin/endodontic filling interface. Other parameters — e.g., solubility, flow, working and setting time, radiopacity, and adhesive properties —have also been assessed (McComb and Smith, 1976; 0rstavik, 1983 a, b; BeyerOlsen and 0rstavik, 1981; 0rstavik et al, 1983a). Although the results from different researchers are somewhat variable, a pattern of the different material types with respect to sealing properties is emerging. Zinc oxide-eugenol preparations afford good seals against leakage in most tests; resin-based sealers are intermediate in sealing ability; chloropercha formulations show the most leakage (Table 4). On the other hand, adhesion of the materials to dentin is achieved only with synthetic resin (McComb and Smith, 1976; 0rstavik et al., 1983a), and the solubility in water is definitely lower for this type of material than for other endodontic materials (0rstavik, 1983b). Whereas the flow properties and film thickness are important characteristics for the distribution and spread of the sealer inside the root canal and its ramifica-

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Vol. 2 No. 1

ENDODONTIC MATERIALS

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