The influence of pH levels on mechanical and biological properties of nonlatex and latex elastics

Abstract

Objective: To evaluate the influence of pH levels on interarch elastics with regard to force decay and cytotoxicity.

Materials and methods: One nonlatex (NLAO) group and one latex (LAO) group were tested (n = 10). Elastics were stretched to 25 mm and were held for 1, 6, 12, and 24 hours in artificial saliva solutions with pH levels of 5.0, 6.0, and 7.5. Force magnitudes were measured at 25 mm of activation. The cytotoxicity assay was performed using cell cultures (L929 mouse fibroblast cell line), which were subjected to the cell viability test with neutral red ("dye-uptake"). Force decay and cytotoxicity were assessed using analysis of variance, the Sidak method, and a Tukey's test.

Results: The interactions between group, pH, and time showed no statistically significant differences (P = .29). When pH per time (P = .032) and group per time (P = .0009) were considered, these interactions showed statistically significant differences (P < .05). The pH did not interfere directly in the degradation results of the tested elastics. The cytotoxicity test showed that group LAO presented lower cell viability when compared with group NLAO over the course of the entire experiment. There was a gradual reduction in cell viability from 1 hour to 24 hours. A significant difference (P < .05) was found between the interactions group pH and the control group of cells, except between group NLAO at the time point of 1 hour at different pH values and at the time points of 6 and 12 hours with pH 5 (P > .05).

Conclusions: No significant correlation between pH, force decay, and cytotoxicity was observed.

Figure 1 and 2

Elastic force decay (mean and standard deviation) of the latex (group LAO) and nonlatex (group NLAO) elastics of American Orthodontics for the different pH levels and times evaluated.

Figure 3 and 4

Cell viability (in percent) of latex (group LAO) and nonlatex (group NLAO) elastics of American Orthodontics for the different pH levels and times evaluated and for the control group: group CC = cell control; group C− = PBS solution; and group C+ = Tween 80.