A new glass ionomer root canal sealer

A new glass ionomer root canal sealer

0099-2399/91/1712-0598/$03.00/(3 JOURNAL OF ENDODONTICS Copyright 9 1991 by The American Association of Endodontists Printed in U.S.A. VOL. 17, NO. ...

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0099-2399/91/1712-0598/$03.00/(3 JOURNAL OF ENDODONTICS Copyright 9 1991 by The American Association of Endodontists

Printed in U.S.A.

VOL. 17, NO. 12, DECEMBER1991

A New Glass Ionomer Root Canal Sealer Herbert Ray, DMD, and Samuel Seltzer, DDS

Various physical characteristics of a new glass ionomer root canal sealer were tested. These included setting time, ease of delivery to the root canal, adaptability and adhesion to the dentinal wall of the root canal, and radiopacity. Scanning electron micrographs and electron microprobe analyses were made. The characteristics were compared with those of Grossman's sealer. The results indicated that, with respect to the properties tested, the glass ionomer sealer was superior to Grossman's sealer.

seal when compared with other sealers (9, 13). Thus, it seemed logical that glass ionomer cements might serve as root canal sealers used in conjunction with master gutta-percha cones. A new glass ionomer root canal cement has been developed by the ESPE Co. (ESPE GMBH & Co., KG, Seefeld/Oberbay, FRG). Pilot studies were conducted in our laboratory to test several of its properties including working tirne, ease of insertion, flow/adaptability, and radiopacity. Twenty extracted human anterior teeth were used. Access openings into the root canals were made. The root canals were then instrumented by either a modified step-back technique, or by ultrasonics using the Cavi-Endo (Caulk-Dentsply). The material was inserted either solely as a paste filler or as a sealer in a single gutta-percha cone technique. The material was activated and triturated for 7 s at an H 1 setting on the Varimix III (Caulk-Dentsply) amalgamator. The material was then placed on a clean glass slab and spun into the root canals with a Lentulo spiral instrument. The results of our pilot study follow. Working time: The material underwent a quick-snap set, leaving a 60-s working time, which was inadequate. Refrigeration of the material increased the working time, adding an additional 30 s. Freezing the glass slab and placing the capsules in the refrigerator extended the working time to 7 min and 30 s. Ease of Insertion: The material was difficult to transport into the root canal. When used as a sealer in conjunction with a gutta-percha cone, the cement was difficult to pick up. When inserted into the root canal by a Lentulo instrument, there was a clinical impression that the canal had been obturated completely. Adaptation: As a result of air entrapment, many voids were detected radiographically throughout the mass. Radiopacity: The material exhibited excellent radiopacity, showing good contrast to the appearance of the dentin. In summary, the initial material was found to be too difficult to manipulate. There was insufficient working time for placement into the root canal with a Lentulo instrument. By cooling both the capsule and the glass slab, the working time was extended. However, a large amount of material was wasted. Thus, because of the difficult delivery system, the material in that form was judged to be impractical for clinical use. Recommendations were made to the manufacturer concerning the need for increased setting time, easier handling,

Glass ionomer cements were developed in the mid-1960's. Further changes in the formulation and their introduction into dentistry by Wilson and Kent occurred in the 1970's (1). The material is a hybrid with both organic and inorganic properties. It is composed of a fine calcium fluoro-aluminosilicate glass powder and aqueous solutions of homo- and copolymers of acrylic acid containing tartaric acid (2). The most significant property of the material was found to be its long-term adhesion to the hydroxylapatite structure of enamel and dentin even when applied under moist conditions (3, 4). Its physical, chemical, and biocompatibility properties appear to be desirable attributes for use in dentistry (5, 6). Tissue toxicity studies have shown that the unset glass ionomer material was cytotoxic to various cell lines (7, 8). However, with the passage of time after setting, cytotoxic reactions were reduced (9). By altering the chemical composition, the physical properties have been changed to allow for a greater range of clinical applications (10-12). Thus, glass ionomers have been formulated for use in virtually every aspect of restorative dentistry. The use of glass ionomer cements in endodontics has been suggested by several investigations (13, 14). Blackman et al. (5) investigated the possible use of a silver containing glass ionomer cement as a root end sealer. They implanted the material into rat soft tissue and bone. Inflammation was produced initially. After 1 month, the inflammation had subsided. The bone surrounding the material healed rapidly and new bone was elaborated directly upon the surface of the material, a finding in agreement with that of Jonck et al. (16). Microleakage at the glass ionomer-tooth interface has been shown to occur in the oral cavity (17). However, in the root canal, several leakage studies have demonstrated that glass ionomer root canal filling materials provided a superior apical

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TABLE 1. Setting time No

Sample

A B C D E F G H

Longer Workable (min)

Complete Setting (min)

3:35 2:03 1:52 0:39 7:23 5:00 1:56 1:38

9:00 9:00 7:42 6:14 13:47 12:30 11:42 7:50

FiG 2. Close adaptation of glass ionomer (sample A) to dentin, (original magnification x500).

MATERIALS AND M E T H O D S

FtG 1. Radiographic appearance of glass ionomer-filled root canals.

and a more effective delivery system. Based on these recommendations, a new formulation was developed. The purposes of the succeeding study reported here were to evaluate eight different new formulations (A to H) differing primarily in thickness and setting time of the glass ionomer endodontic sealer. These formulations were recommended to the manufacturer based upon the findings of the preliminary study described above. The following qualities were investigated: ease of administration, setting time, radiopacity, and adaptation or adhesion to the root canal walls. Adhesion was compared with that exhibited by Grossman's root canal sealer.

Fifty-six human extracted maxillary and mandibular anterior teeth were used. The teeth were stored in 0.5% NaOC1 solution until used. Access openings to the root canals of the teeth were made with a #2 or #4 round bur in a high-speed handpiece. The teeth were then instrumented according to the instrumentation protocol stated in the preliminary study. The teeth were stored in a physiological saline solution until obturation. The teeth were randomly divided into the following two groups: (1) 28 teeth were instrumented by the modified step-back technique. Of this group, 14 teeth were irrigated with a 2.5% solution of NaOC1 alone and the remainder with a 2.5% solution of NaOC1 during instrumentation followed by a 6% solution of citric acid. (2) The root canals of 28 teeth were instrumented with the Cavi-Endo; of these, 14 teeth were irrigated with a 2.5% solution of NaOC1 and the other half with the 2.5 % solution of NaOC1--6% solution of citric acid combination, as used in the first group. Thirty-two of the prepared teeth were then subdivided into eight groups of four teeth each for obturation with various glass ionomer root canal sealer formulations; 16 teeth were filled with Grossman's sealer. The root canals of eight teeth were instrumented and irrigated and served as controls. Prefitted single gutta-percha cones were placed into the root canals in conjunction with the sealers. The glass ionomer sealers were injected into the root canals. The Grossman's sealer was delivered to the root canals via a Lentulo spiral

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Ray and Seltzer

FiG 3. Voids in glass ionomer (sample C) due to air entrapment in apical third of root canal (original magnification x50).

instrument. The ease of manipulation, setting time, and radiopacity of the materials were noted. The teeth were then stored in 100% humidity for 24 h. The teeth were prepared for scanning electron microscopic examination by dehydration in ascending grades of ethanol. They were embedded in EPO-MIX epoxide (Buehler Ltd., Lake Bluff, IL). The samples were then ground with abrasive discs until the sealer/dentin interface became visible. The surfaces were etched with a 10% solution of hydrofluoric acid for 30 s, dried, and coated with gold. Coronal, middle, and apical areas of the samples were examined by scanning electron microscope. Representative sections were photographed at x50, • and • The photomicrographs were examined for the presence of material in the dentinal tubules, penetration of the material into lateral or accessory canals, and the adaptation and adhesion of the material to the walls of the root canal. A rating of 1 to 5 was given, with 1 representing the closet adaptation and/or adhesion and 5 the poorest. In addition, electron microprobe analyses of the materials were made. The formulations exhibiting the most favorable characteristics were then selected as the materials of choice. The identification of the lettered samples which exhibited the most favorable characteristics was then revealed to the manufacturer, who then prepared new batches for further clinical testing. Those clinical findings will be reported in a subsequent article.

Journal of Endodontics

FiG 4. Glass ionomer-dentin interface (sample F) (original magnification x500).

F~G5. Gutta-percha cone cemented into root canal with Grossman's sealer (original magnification x50).

RESULTS Glass Ionomer Sealers

EASE OF MANIPULATION The new materials (Table 1) were injected into the root canals which markedly enhanced placement. The delivery

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and G were rated 1. They presented the closest adaptation (Fig. 4). Generally, the appearance of glass ionomer-dentin interface gave the impression that the two surfaces were chemically bound. FLOW

FIG 6. Higher magnification of Grossman's sealer-cement interface (original magnification x500).

Samples A and B were too watery and were thus judged to be clinically unacceptable. Samples C, E, and F appeared to have low surface tension and appeared to flow well. Samples G and H were too viscous; use of sample H created the clinical impression that during obturation, the gutta-percha was being pushed back out of the root canal. Overall, sample F was chosen as the glass ionomer sealer with the best physical qualities for use as an endodontic material. Grossman's Sealer

The rheological properties and the characteristics of ease of manipulation, setting time, and radiopacity of Grossman's sealer are well known. Generally, Grossman's sealer appeared to be adapted closely to the root canal wall (Fig. 5). However, the adaptation was not as close as that obtained with the glass ionomers and was rated 2. In addition, numerous voids and cracks were found throughout the material (Fig. 6). Influence of Preparation of the Root Canals on Adhesion

FiG 7. Scanning electron microscopic appearance of glass ionomer cement prepared for microprobe analysis (original magnification x 1000).

The preparation of the root canals by the two instrumentation techniques (step-back and ultrasonic), and the irrigants used did not appear to influence the adaptation of the material to the dentinal walls. Furthermore, removal of the smear layer by the combined NaOCl-citric acid treatment did not enhance the bonding of the material when compared with irrigation with NaOC1 alone. Microprobe Analyses

into the root canal was found to be quick, clean, and efficient (nonwasteful). RADIOPACITY The radiopacity was excellent for all materials tested. Contrast to dentin and surrounding bone was highly significant in all of the samples (Fig. 1). ADAPTATION TO THE DENTIN-SEALER INTERFACE Samples A and B were rated 3. They exhibited close dentinal adhesion and a tight sealer-dentin interface (Fig. 2). Samples C and D were rated 3. However, they showed voids in the sealers throughout the apical third of the root canal (Fig. 3). Samples E, F, G, and H exhibited few voids and close adaptation at the sealer-dentin interface. Of these, samples F

All microprobe analyses of the glass ionomer sealers uniformally detected the presence of silicon, tungsten, lanthanum, aluminum, fluorine, and calcium (Figs. 7 and 8). The exact formulations, however, were a trade secret not revealed by the manufacturer. DISCUSSION Ideal root canal sealers should meet nine specifications: nonirritating to pulp and periapical tissues; impervious; bacteriostatic or bactericidal; nonstaining; insolubility to tissue fluids; adhesiveness to dentin and solid core materials; sufficient working time; lack of shrinkage after setting; and solubility in common solvents to facilitate removal (18). At the present time, no root canal sealer is known to possess all of these properties. The newly developed glass ionomer cement appeared to have many of the ideal characteristics. However, currently there are no known solvents for glass ionomer

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Ray and Seltzer

Journal of Endodontics

,t'aiD

13

',3,.+

,3:

C~

~L

2.e

4 ~1 F{,JEF'G r

6 ( t,-'E',

E~

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F~G 8. Microprobe analysis of new root canal glass ionomer cement.

FIG 9. Root canal and lateral canal filled with glass ionomer cement. Cracks due to dehydration of specimen (original magnification x50).

cements. Because the tetrahedral units of the poly (acrylic acid) chain are covalently linked, attempts to solubilize the material permit the replacement of aluminum ions only, reducing the cross-linking but not allowing fragmentation of the units. These events are not similar to the exchange of hydrogen ions found in the disassociation of other related compounds (19). Thus, the need to develop a simple method of removing this material from the root canal, in the event that retreatment becomes necessary, warrants further investigation. At the present time, to facilitate retreating teeth when indicated, a single gutta-percha cone technique in combination with the glass ionomer cement must be used. Removal of the gutta-percha would then permit removal of the glass ionomer sealer by reinstrumentation of the root canal.

In contrast to Grossman's root canal sealer, which physically filled the voids between the gutta-percha and the canal wall, the glass ionomer material appeared to bond chemically to the dentin of the root canal. Such bonding would confer a distinct advantage in endodontic therapy, preventing percolation and bacterial penetration at the sealer-dentin interface. Root canal preparation invariably leaves a smear layer on the dentin. Various irrigation techniques do not uniformly remove the smear layer. Use of combinations of organic and inorganic solvents is thus recommended. However, in this study, irrigation of the root canals with a view toward removal of the smear layer did not enhance adhesion. Our results were in agreement with those of Mitchem and Gronas (20), whc found that the presence of physiological fluid or the presenc~ of the smear layer had no effect on the adhesion of glas, ionomer to the dentinal surface. Several possible areas of misinterpretation of the finding~ are inherent to all scanning electron microscopic studies Usually, only one surface level is viewed. Unlike histologica sections, various depths of the interface between sealer anc dentin are not examined, since this would require makin! additional cuts into the sample. The use of such procedure would be highly arbitrary. The grinding of the samples is alst subject to variation since the dentin thickness varies with eacl specimen. The reaction of glass ionomer cement and tooth structur, is a simple inorganic reaction in which the calcium ion of th tooth is released by the epoxyacrylic acid component of th cement. The released free inorganic ions complex with th tartaric acid of the cement, facilitating the cross-linkage ofth polyacrylate chains. During the dehydration of the sample for scanning electron microscopy, artifacts in the form c cracks were produced (Fig. 9). The creation of these artifacl support the hypothesis that there is a bond between the gla,

Vol. 17, No. 12, December 1991

ionomer and the dentin surface. The cracks that were produced as a result of scanning electron microscopic preparation were found in the bulk of the sealer. However, the sealer adhered to the dentin, showing no separation at the sealerdentin junction. On the other hand, the Grossman samples all showed cracks through the tooth but spreading out at the sealer-tooth interface, indicating lesser adhesion. The physical properties and ease of manipulation of the glass ionomer samples were judged to be equal, or superior, to those of Grossman's sealer. This study was supported by a grant from ESPE GMBH & Co., Seefeld/ Oberbay, West Germany. The authors are grateful to Ms. Diane Mendez for assistance in the preparation of this manuscript. Dr. Ray is an advanced education student in endodontology and Dr. Seltzer is professor emeritus, Department of Endodontology, School of Dentistry, Temple University, Philadelphia, PA. Address requests for reprints to Dr. Samuel Seltzer, Department of Endodontology, Temple University School of Dentistry, 3223 N. Broad Street, Philadelphia, PA 19140.

References 1. Wilson AD, Kent BE. The glass-ionomer cement: a new translucent dental filling material. J Appl Chem Biotech 1971 ;21:313-8. 2. Smith D. Composition and characteristics of glass ionomer cements. J Am Dent Assoc 1990;120:20-2. 3. Powis DR, Folleras T, Merson SA, Wilson AD. Improved adhesion of a glass-ionomer cement to dentine and enamel. J Dent Res 1982;61:1416-22. 4. Aboush YEY, Jenkins CBG. An evaluation of the bonding of glassiooomer restorative to dentine and enamel. Br Dent J 1986;161:179-84.

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5. Walls, AWG. Glass polyalkenoate (glass-ionomer) cements: a review. J Dent 1986;14:231-46. 6. Wilson AD, McLean JW. Glass ionomer cement. Chicago: Quintessence, 1988:13-20. 7. Kawahara H, Imanishi Y, Oshira H. Biological evaluation on glass ionomer cement. J Dent Res 1979;58:1080-6. 8. Dahl BL, Tronstad L. Biological tests of an experimental glass ionomer (silicopolyacrylate) cement. J Oral Rehabi11976;3:19-24. 9. Classis PD, Santini A. Tissue response to retrograde root fillings in ferret canines: a comparison of a glass ionomer cement and gutta-percha with sealer. Oral Surg 1987;64:476-9. 10. Wilson AD, Crisp S, Abel G. Characterizations of glass ionomer cements. Four effects of molecular weight on physical properties. J Dent 1977;5:117-20. 11. Hill GR, Wilson, AD. A rheological study of the role of additives on setting of glass ionomer cements. J Dent Res 1988;67:1446-50. 12. Nicholson JW, Brookman PJ, Lacy OM, Wilson AD. Fourier transform infared spectroscopic study of the role of tartic acid in glass ionomer dental cements. J Dent Res 1988;67:1451-4, 13. PittFord T. The leakage of root fillings using glass ionomer cement and other materials. Br Dent J 1979;146:273-8. 14. Zmener O, Dominguez FV. Tissue response to a glass ionomer used as an endodontic cement. Oral Surg 1983;56:198-205. 15. Blackman R, Gross M, Seltzer S. An evaluation of the biocompatibility of a glass ionomer-silver cement in rat connective tissue. J Endodon 1988;15:76. 16. Jonck LM, Grobbelaar CJ, Strating H. Biological evaluation of glassionomer cement (Ketac-O) as an interface material in total joint replacement. A screening test. Clin Mat 1989;4:201-24. 17. Thornton JB, Retief DH, Bradley EL. Marginal leakage of two glass ionomer cements: Ketac-Fil and Ketac-silver, Am J Dent 1988;1:35-8. 18. Seltzer S. Endodontology: biologic considerations in endodontic procedures. 2rid ed. Philadelphia: Lea & Febiger, 1988:281. 19. Kent BE, Lewis BG, Wilson AD. The properties of a glass ionomer cement. Br Dent J 1973; 135:322-6. 20. Mitchem J, Gronas D. Adhesion to dentin with and without smear layers under varying degrees of wetness. J Dent Res 1989;68:321.

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