Development of a toxicity evaluation program for dental materials and products I. Screening for Irritant Responses

Abstract

A broad dental toxicology screening program has been initiated to develop suitable testing methods for new dental materials or products which presently are not considered as drugs. In the report presented here, 42 materials or products have been included in an acute toxicity screening program for the evaluation of irritancy properties. Depending upon the state of the material or product, one or more testing procedures were employed. These included: (1) implantation in rabbit muscle, (2) a tissue culture test, (3) an intradermal test in rabbits, (4) an eye test in rabbits, and (5) a dermal test in rabbits. With the limited number of materials or products, the most suitable method of testing solids was the implantation method and tissue culture. Tissue culture appeared to be the only useful method for powders while tissue culture and an intradermal test the most suitable method for liquids. Other materials and products will be included using these test procedures to note if one or two might eventually be selected as a preferred method of “irritancy” testing when a large number of materials or products are to be screened for a dental or medical application. The final evaluation of safety for a dental material or product must of course be based upon its intended use.

In vitro toxicity tests of zinc phosphate cement

“…The material has also been tested in cell culture systems by Keresztesi & Kellner (1966); Kawahara, Yamagami & Nakamura (1968); Spanberg (1969a, b, c), Powell et al (1970) and Dahl et al (1975). It was found that zinc phosphate cement was cytotoxic when freshly mixed, but that toxicity decreased as the cement set.…”

“…A number of workers (Brannstrom & Nyborg, 1960;Dubner & Stanley, 1962;Dahl, Tronstad & Spangberg, 1975;Plant & Jones, 1976) has evaluated zinc phosphate cement for irritancy by placement in prepared cavities in teeth, and it is generally agreed that initial pulpal irritation occurs but decreases at longer time intervals. The material has also been tested in cell culture systems by Keresztesi & Kellner (1966); Kawahara, Yamagami & Nakamura (1968); Spanberg (1969a, b, c), Powell et al (1970) and Dahl et al (1975). It was found that zinc phosphate cement was cytotoxic when freshly mixed, but that toxicity decreased as the cement set.…”

Biological testing of dental restorative materials in vitro—a review

“…There are two types of method in which this can be achieved, and both methods also use freshly mixed material which can set normally. In the agar overlay method (Guess et al, 1965;Powell et al, 1970) it is the solid medium which separates the test material from the cells in culture, whereas in other methods (Tronstad, Hasselgren & Wennberg, 1977;Tyas, 1977b) separation was achieved by 'Millipore' filters. Although neither of these methods simulates the clinical situation exactly, the conditions more closely approximate it.…”

“…There are three methods in which the material can be placed into the test system in the freshly mixed state and subsequently allowed to set. In the agar overlay method (Guess et al, 1965;Powell et al, 1970) cells are grown as a monolayer on the base of a culture dish and the liquid medium replaced by a semi-solid medium consisting of nutrient agar. Specimens of freshly mixed material can be placed on the surface of the agar and allowed to set.…”

“…Many early workers simply counted the number of cells present in the culture dish after incubation with the test material for known periods of time, but such a method gave no indication of whether the cells were dead or alive. The use of vital staining techniques, in which dyes such as trypan blue are taken up only by dead cells, allows differentiation between living and damaged cells (Powell et al, 1970;Dahl & 0rstavik, 1976). Alternatively, some dyes, such as neutral red, are taken up only by normally functioning cells (Paul, 1973).…”