One of the main uses of hemostatic agents in combination with retraction cords is to control humidity and bleeding from the gingival sulcus during impression, so that a usually hydrophobic material may faithfully reproduce the details of tooth preparation3. Therefore, this type of solution should be compatible with the material that will be used in reproducing oral structures. However, aluminum sulfate and ferric sulfate used as hemostatic solutions, due to the presence of the sulfur radical in their molecular structure, raised the suspicion that they might inhibit polymerization of polyvinyl, such as in the case of sulfur incorporated during the process of vulcanization of latex gloves. Therefore, by analogy, sulfur found in the sulfate radicals was thought to interact with the catalytic sites of addition silicone materials and to block setting.
Although these suspicions were serious and involved sulfur solutions, few authors studied it directly. One of the few studies to focus on this subject evaluated several solutions, including ferric and aluminum sulfates, and found that they did not have any inhibitory potential on silicone materials3. There were suggestions that clinical reports to the contrary might be better explained by contamination with latex found in gloves rather than by the medicaments used for gingival retraction. The results of our study are in agreement with those findings because silicone materials were nonreactive to the hemostatic solutions tested here.
The reason why sulfur solutions did not react in the polymerization of polyvinylsiloxane materials may be explained by the molecular position of sulfur atoms. The molecular analyses of these solutions show that the sulfur in their composition is in a state different from the one found in the latex gloves, whose inhibition potential has already been confirmed in the literature1,4,7,8. Sulfur in the sulfate solutions, contrarily to that found in latex gloves, has greater electrical stability, saturated by oxygen atoms, less reactive, and, therefore, incapable of reacting with metal catalysts8. For this reason, the mere presence of sulfur does not give the material any inhibitory properties. To find out whether a substance has any inhibition potential, direct inhibition tests18 or molecular analysis of the compound should be performed to provide indications about the degree of reaction of the element of interest.
After the confirmation of the inhibitory effects of the direct contact between polyvinylsiloxane and products containing latex, studies about indirect contamination became important in the literature referring to addition elastomers. The principles of "indirect contamination" or "crossed contamination" reside in the fact that all contact between two surfaces or materials is followed by exchanges of substances between them, even if only at a molecular level. To confirm this principle, the dental literature has already demonstrated that sulfurous materials may be exchanged between latex gloves and the structures exposed to the gloves, such as teeth, soft tissues, gingival retraction cords and dental office instruments5,9,12-14. According to other authors, the sulfur transferred, in some cases, would produce the same inhibitory effects triggered by the latex gloves.
The inhibitory potential of indirect latex contamination should not be downplayed. In a previous study, the chemical analysis of the surface of vinyl gloves and gingival retraction cords, both contaminated by latex gloves, showed that sulfur particles and sulfur chloride compounds were found in all the samples analyzed. For the authors of that study, those particles should be able to interfere in polyvinylsiloxane polymerization14. Another study evaluated the inhibition of addition silicone polymerization by direct and indirect contact with latex gloves and found that 96% of the gloves tested inhibited silicone polymerization by direct contact and 40% by direct and indirect contact, which is a contraindication for their use when handling these materials.
Despite the several findings reported in the literature, the results of the present study did not show inhibition of polymerization in any of the polyvinylsiloxane samples that were exposed to contact with retraction cords previously handled with latex gloves. On the contrary, the elastomeric material reproduced the cord texture accurately in all samples (N=120), and there was no sign of inhibition or retarded setting detected by visual analysis of the impressions or pieces of fabric. It may be inferred that the cord surfaces had sulfur particles that would contaminate the silicone catalyst14; however, the low concentration of this element seems to have been insufficient to trigger any inhibition that may be perceived by the methods used in this study.
The presence of reactive sulfur on the surface of the cords14 suggests that some type of change in polymerization may have occurred in practice, but was subclinical,