Degradation of trans-polyisoprene over time following the analysis of root fillings removed during conventional retreatment

AIM

To evaluate in vivo degradation of root filling materials over time.

METHODOLOGY

Thirty-six root filled teeth with or without periapical lesions were selected. Teeth with poor coronal restoration were not included. The teeth had been root filled 3-30 years previous and were scheduled for conventional retreatment. The association of root canal treatment, age, periapical lesion and root filling degradation was investigated. The filling material was removed from the root canal using files and no solvent. Trans-1,4-polyisoprene was isolated through solubilization of root filling remnants in chloroform followed by filtration and centrifugation. Gel permeation chromatography (GPC) and infrared spectroscopy (FT-IR) were utilized to study the occurrence and degree of degradation. The GPC and FT-IR data were collected for each sample and analysed statistically using the Kruskal-Wallis test.

RESULTS

Degradation of trans-1,4-polyisoprene was a slow process. The process was identified as an oxidation reaction through the production of carboxyl and hydroxyl groups. Compared with the control group, significant molar mass decrease was noted after 15 years (P = 0.0146) in teeth with no periapical lesions. However, in teeth associated with periapical lesions the number of years for significant degradation was reduced to 5 (P = 0.0009).

CONCLUSION

Polyisoprene degrades inside root canals as an oxidative process. The presence of periapical lesions was associated with a more rapid onset of degradation.

Ozonation of Unstretched Natural Rubber: Part I. Effect of Film Thickness

Unstretched films of natural rubber from Hevea brasiliensis were exposed to ozone flow of 5 and 15 mL/min for 4 to 60 min. The effect of reaction time and the film thickness was studied by viscometry and gel permeation chromatography (GPC). For film thicknesses, in the range of 40 to 350 µm, an initial increase in the intrinsic viscosity, [η], was observed within 8 min of reaction, followed by a decrease for longer times. For thin films, only a decrease in the [η] was observed. The viscosity increase, followed by its decrease, suggests the formation of crosslinking and chain cleavage, respectively, both expected by Criegge mechanism. The plot of [η] versus film thickness and the Chromatographic analysis, related either to 8 or to 60 min of reaction, show that the ozone penetration and the ozone reaction progresses into deeper layers than those previously described in the literature (∼0.5 µm), in this case, 170 and 250 µm, respectively. One model was proposed to explain the viscosity, GPC and attenuated total reflection (ATR) results.