The acceptance of a material for use in prosthodontics must be based on the absence of toxic and allergic or irritant effects. The above requirements are connected with the nature of the material as well as with the presence of additives which can be leached into the oral cavity. In the case of denture-base resins, which are usually coloured with cadmium pigments, the migration of cadmium ions has already been studied by many authors. Their studies have focused on the determination of the amount of cadmium leached from a denture base [1], and the evaluation of a series of pigments for alternative use [2], whereas very few data have been published related to the migration mechanism [3-5]. The determination o? the migration mechanism is of great importance because it could dictate methods to retard or eliminate the leaching of cadmium ions. On the other hand, a model mechanism could become a first step for the definition of a generalized model concerning the migration of any additive from poly(methyl methacrylate) constructions in the vicinity of extracting media. In this work, some factors related to the material were studied in order to define their effect on cadmium migration. In addition, some data relating the material structure and cadmium leaching were collected, in order to give a first idea for a possible migration mechanism. The materials used and the procedures followed for the specimen preparation are presented in Table I. The specimens had the form of a full upper denture base and were prepared according to the manufacturer 's recommendations. Two specimens for each case were immersed separately in 500ml synthetic saliva and retained in an oven at 37°C. The composition of synthetic saliva was the following: KSCN, 0.33g; KHCO3, 1.12g; NaC1, 0.33g; CO(NHz) 2, 0.2g; NaeHPO4, 15 g; NaHzPO4, 7.5 g; CaC12, 0.24 g; H20, to 1500 g. The pH of the above solution was measured using a Beckman pHmeter Zeromatic SS-30. The corresponding value was 7 at 25 ° C. The cadmium concentration in the synthetic saliva was followed by atomic absorption spectrometry. The quantitative analysis process provided sampling of 200 ml synthetic saliva. The sample was then concentrated by evaporation to 10 ml, in order to reach the sensitivity limits of the spectrometer used (Perkin-Elmer 2000). After each sampling the solution was topped up to its initial volume. The concentration of the cadmium ions, determined during the analysis of each sample, was expressed as total loss of cadmium in #g per gram of denture base. These data are plotted, in order to give an idea about the cadmium migration as a function of time. This correlation, for specimens with different colouring and curing procedures, is shown in Fig. 1. As the curves of Fig. 1 indicate, there are some differences in the leaching rate and the equilibrium values for the specimens C, A, N and I. The lowest value corresponds to the specimens derived from the acrylic resin with "internal colouring" (i.e. incorporation of the pigment during polymerization of the acrylic resin) and the highest for the cold-cured acrylic without crosslinking agent. The behaviour of specimen I must be emphasized, because the total cadmium content in the specimen is the highest compared with that of the other types of acrylic resins used. The curing procedure (water bath or air oven)
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Dec 1, 1995
Jose V Bonilla + 1
Open Access