Journal of Oral Rehabilitation, 1976, Volume 3, pages 19-24

Biological tests of an experimental glass ionomer (silicopolyacrylate) cement B J 0 R N L. D A H L and'LElT T R O N S T A D Department of Prosthetic Dentistry and Dental Institute of Experimental Research, University of Oslo, Norway, and Department of Endodontics, Faculty of Odontology, University of Lund, Sweden

Summary

The biological compatibility of an experimental glass ionomer (silicopolyacrylate) cement has been assessed in in vitro (cell culture) and in vivo (monkey teeth) tests. For comparison a conventional silicate cement (Super Syntrex®) was included in the in vivo experiments. In vitro, the glass ionomer cement was toxic when freshly prepared. The toxicity decreased, however, with increasing setting time. In experiments with prolonged cell-material contact time with specimens which had set for 24 h, the material appeared to be non-toxic. The in vivo experiments confirmed previous reports concerning unfavourable pulp reactions caused by silicate cement, while the glass ionomer cement caused mainly a mild pulp reaction after 8 days of observation. Unfortunately no longer-term observations were obtained since the material had been washed out of the cavities within 36 days. Introduction

Translucent cements are desirable for restoration of anterior teeth and for use as a luting agent, especially for porcelain jacket crowns. To a certain extent silicate cements possess such a property. However, their incompatibility with the dental pulp (Palazzi, 1924; Manly, 1944; Klotzer & Langeland, 1973) has made them unsuitable for cementing purposes. This also appears to be the case with silicophosphate cements (Dahl, Tronstad & Spangberg, 1975). Thus the reports of research on a new type of translucent cement (Wilson & Kent, 1972) was received with much interest. The new cement has been termed a glass ionomer cement or an aluminosilicate polyacrylate (ASPA) cement. As the name implies the cement is an aluminiumoxide reinforced silicate powder which will set to a hard mass when mixed with an aqueous solution of polyacrylic acid and not as conventional silicate cement with phosphoric acid. The purpose of the present investigation was to evaluate the biological compatibility of the glass ionomer cement. Since the cement was not yet in production, a sample of a batch of ASPA III was generously supplied by The Laboratory of the Government Chemist, Cornwall House, Stamford Street, London SEl 96Q. For comparison a conventional silicate cement (Super Syntrex®, de Trey, Zurich, Switzerland), bought on the open market, was included in the study. Correspondence: Bjorn L. Dahl, University of Oslo, Department of Prosthetic Dentistry, Dental Faculty, Geitmyrsveien 69, Oslo 4, Norway.

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B. L. Dahl and L. Tronstad

Materials and methods

In vitro experiments The cytotoxicity of the glass ionomer cement was established in tissue culture experiments, using the radio-chromium release method. The experimental equipment and procedures have been described in detail previously (Spangberg, 1973; Dahl, Tronstad & Spangberg, 1974). In vivo experiments The experimental material comprised fifty-five teeth from three young monkeys. Deep buccal class V cavities were cut with an inverted cone carbide bur no. 35 in an air turbine with water spray. Seventeen cavities were filled with silicate cement and thirty-eight cavities with glass ionomer cement. Observation periods of 8, 36 and 72 days were used. The detailed distribution of the experimental material is presented in Table I. Table 1. Distribution of experimental material Observation periods Material Silicate cement Glass ionomer cement

No. of teeth

8 days

36 days

72 days

17 38

7 18

3

7

Routine histological procedures were used to produce 4 |Ltm thick serial sections which were stained with haematoxylin and eosin and examined in the light microscope

{D'Met al, 1974). The experimental material was grouped into teeth with slight, moderate, or severe reactions in the pulp according to the criteria suggested by Langeland (1957). These criteria have been summarized in a previous paper (Dahl et al, 1974). Results

In vitro experiments The results are sumtnarized in Table 2. In the experiments with 4 h cell-material contact time the glass ionomer cement caused an increased ^^Cr release when freshly prepared. The cytotoxic effect decreased somewhat with increasing setting time. Table 2. Effect of the materials on HeLa cells. Release of

(%) Cell-material contact time 4h

Material

24 h

No. of experiments

Fresh material Mean±s.e.

Mean±s.e.

4 h setting 24 h setting Mean±s.e.

Mean±s.e.

5 10

6 2±0 2 391±0 4

6- 2±0 2 34- 5±1 0

30 0 ± 0 1 58 0 ± 0 - 5

Controls Glass ionomer cement

6 2±0 2 19-5±1 0

4 h setting 24 h setting Mean±s.e. 30 0 ± 0 ] 36 9 ± 2 0

Biological tests on glass ionomer cement

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Fig. 1. Area of pulp subjacent to cavity filled with ordinary silicate cement. Observation period 8 days. An abscess is present next to the dentine (H & E, x 100). Fig. 2. Area of pulp subjacent to cavity filled with glass ionomer cement. Observation period 8 days. A few scattered inflammatory cells may be seen (H & E, x 250). Fig. 3. Area of pulp subjacent to another cavity filled with glass ionomer cement. Observation period 8 days. Many granulocytes are present in the odontoblast and subodontoblast regions (H & E, x 100). Fig. 4. Area of pulp subjacent to cavity filled with ordinary silicate cement. Observation period 72 days. Signs of inflammation are still seen next to the secondary dentine (H & E, x 100).

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B. L. Dahl and L. Tronstad

With 24 h cell-material contact time the glass ionomer cement caused increased radio-chromium release after 4 h setting. However, when the material had set for 24 h before being tested, the '^^Cr release closely approached the spontaneous release. In vivo experiments The results after 8 days of observation are presented in Table 3. The severity of the Table 3. Pulp reaction after 5? days of observation Material

No. of teeth

Slight reaction

Moderate reaction

Severe reaction

7 18

2 17

4 1

1

Silicate cement Glass ionomer cement

pulp reaction caused by the conventional silicate cement varied. In two teeth the reaction was slight with only a few scattered infiammatory cells in an area ofthe pulp subjacent to the cavities. In four teeth this area of the pulp was moderately infiltrated with granulocytes, and in one tooth an abscess was seen (Fig. 1). In the 8 days experiments with glass ionomer cement the observed pulp reaction was mild with only a few scattered inflammatory cells subjacent to the cavities (Table 3; Fig. 2). In one tooth, however, the odontoblast and subodontoblast regions contained many filled vessels and were moderately infiltrated with granulocytes (Fig. 3). In the experiments with observation periods of 36 or 72 days nine of ten teeth filled with the conventional silicate cement exhibited a chronic inflammation in the pulp (Table 4; Fig. 4). Table 4. Pulp reaction after 36 or 72 days of observation Material Silicate cement Glass ionomer cement

No. of teeth

Repair

Chronic inflammation

10 20

1

9

No observations could be made in the long-term experiments with the glass ionomer cement, as the material had been washed out of the cavities within 36 days. Discussion The most widely used luting agent, zinc phosphate cement, is on a zinc oxide phosphoric acid base and has poor translucent properties. It is moderately toxic, may cause a certain reaction in the dental pulp (Dahl et al, 1975), and may also give rise to post-operative pain. The introduction of zinc polycarboxylate cement (Smith, 1968) seemed to give a biologically (Klotzer et al, 1970; Peters et al, 1972) and physically (Phillips, Swartz & Rhodes, 1970) favourable material, but the translucent properties were no better than for zinc phosphate cement. It seemed logical to ascribe the difference in biological compatibility of these two cements to properties of their liquid phase since their powder phase was about the same. It is conceivable, therefore, that a combination of silicate powders possessing

Biological tests on glass ionomer cement

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high strength and translucency and the biologically favourable polyacrylic acid (Peters et al, 1972) would make up the material of choice both for restorative and cementing purposes. Reports of successful progress in this field of research seemed promising (Wilson & Kent, 1972; Kent & Wilson, 1972), as did a later report on the physical properties of a glass ionomer cement (Kent & Wilson, 1973). The in vitro results of the present investigation indicated that the glass ionomer cement exhibited a certain toxic effect in the freshly prepared state, but that the toxicity decreased with increasing setting time. Thus when the cell-material contact time was 24 h, the ^^Cr release caused by a sample of the cement which had set for 24 h, closely approximated the spontaneous release, indicating that the material was no longer toxic. This observation is clearly in contrast to what has been found with the same technique in experiments with conventional silicate cement which apparently has a lasting toxic effect (Spangberg et al, 1973). Therefore, as far as the toxic properties are concerned the glass ionomer cement is clearly superior to conventional silicate cement, and behaves more like zinc phosphate cement (Dahl et al, 1975). The results ofthe in vivo experiments apparently confirm those of previous reports that conventional silicate cement may cause a lasting pulp reaction (Shroff, 1946; Zander, 1946; Klotzer & Langeland, 1973). The glass ionomer cement, however, was well tolerated by the dental pulp as judged by the results of the 8-days experiments. Unfortunately, no results were obtained from the long-term experiments with the cement. Repeated experiments were performed in twenty teeth in two monkeys, but the material had always been washed out of the cavities within 36 days. Still, there seems to be no doubt that the mixing of silicate powders with polyacrylic acid has resulted in a cement which in respect of biological compatibility is superior to conventional silicate cement. It is to be hoped, therefore, that further research in this field may result in a biologically acceptable and clinically applicable translucent cement. References B.L., TRONSTAD, L. & SPANGBERG, L. (1974) Biological tests of a temporary crown and bridge material. Journal of Oral Rehabilitation, 1, 299. DAHL, B.L., TRONSTAD, L. & SPANGBERG, L. (1975) Biological tests of a silicophosphate cement. Journal of Oral Rehabilitation, 2, 249. Kent, B.E. & Wilson, A.D. (1972) Development of a new translucent dental cement. Journal of Dental Research, 51, 1252. KENT, B.E. & WILSON, A.D. (1973) The properties of a glass ionomer cement. British Dental Journal, 135, 322. KLOTZER, W.T. & LANGELAND, K . (1973) Tierexperimentelle Prufung von Materialien und Methoden der Kronen- und Briickenprothetick. Schweizerische Monatsschrift fiir Zahnheilkunde, 83, 163. KLOTZER, W.T., TRONSTAD, L., DOWDEN, W.E. & LANGELAND, K . (1970) Polycarboxylatzemente im physikalischen und biologischen Test. Deutsche zahnarztliche Zeitschrift, 25, 877. LANGELAND, K . (1957) Tissue changes in the dental pulp. An experimental histologic study. Odontologisk Tidskrift, 65, 239. MANLY, E . B . (1944) Pulp reactions to dental cements. Dental Record, 64, 75. PALAZZI, S. (1924) Einige Konklusionen aus meinen drei-jahrigen Experimenten iiber die Veranderungen der Zahnpulpa nach Eullungen mit Silikatzementen. Zeitschrift fur Stomatologie, 22,238. PETERS, W . J., JACKSON, R . W . , IWANO, K . & SMITH, D . C . (1972) The biological response to zinc polyacrylate cement. Clinical Orthopaedics and Related Research, 82, 228. PHILLIPS, R.W., SWARTZ, M.L. & RHODES, B.E. (1970) An evaluation of a carboxylate adhesive cement. Journal ofthe American Dental Association, 81, 1353. SHROFF, F.R. (1946) Effects of filling materials on the dental pulp. An histological experimental study with special reference to synthetic porcelain. New Zealand Dental Journal, 42, 99. DAHL,

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SMITH, D.C. (1968) A new dental cement. British SPANGBERG, L. (1973) Kinetic and quantitative

Dentat Journal, 125, 381. evaluation of material cytotoxicity in vitro. Oral

Surgery, 35, 389. & LANGELAND, K . (1973) Biologic effects of dental materials. 2. Toxicity of anterior tooth restorative materials on HeLa cells in vitro Oral Surgery, 36,713. WILSON, A.D. & KENT, B.E. (1972) A new translucent cement for dentistry. The glass ionomer cement. British Dental Journal, 132, 133. ZANDER, H.A. (1946) The reaction of dental pulps to silicate cements. Journal of the American Dental Association,'ii, 1233. SPANGBERG, L., RODRIGUES, H., LANGELAND, L.

Manuscript accepted 10 March 1975

Biological tests on an experimental glass ionomer (silicopolyacrylate) cement.

Journal of Oral Rehabilitation, 1976, Volume 3, pages 19-24 Biological tests of an experimental glass ionomer (silicopolyacrylate) cement B J 0 R N L...
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