Prevention of Bismuth Oxide-containing Tricalcium Silicate Discoloration of Dentin

Objectives: Previous studies have shown that Bismuth oxide-containing tricalcium silicates can cause tooth discoloration, mediated by the chemical reaction between bismuth oxide and sodium hypochlorite. The objective of this study was to determine if sodium thiosulfate can be utilized following hypochlorite irrigation to neutralize the hypochlorite, thereby preventing tooth discoloration.
Methods: Fifty extracted anterior teeth were sterilized, accessed and then divided into one of the following five irrigation groups: 1) 10 mL of 4.12% Hypochlorite irrigation followed by 10 mL of 0.5% thiosulfate then MTA (Proroot, Dentsply/Sirona) 2) 10 mL of 4.12% Hypochlorite irrigation followed by 10 mL of 5.0% thiosulfate then white MTA 3) 10 mL of 4.12% Hypochlorite irrigation followed by 10 mL saline then MTA (Positive Control) 4) Only 10 mL saline then MTA (Negative Control-1) 5) 10 mL of 4.12% Hypochlorite irrigation followed by 10 mL saline then Bioceramic putty (Endosequence, Brasseler) (Negative Control-2). Pre-operative and post-treatment color measurements were taken using a Vita Easyshade Advance 4.0 spectrophotometer in a booth with controlled lighting. Color measurements were taken at 4, 8, 12 and 24-week intervals. The color values of Delta E, L, a and b were evaluated with 2-way analysis of variance and then further analyzed with the post hoc Dunnett's multiple comparisons test to determine amount of tooth discoloration.
Results: Results showed that significant discoloration occurred in all groups over time. The change in color was reduced by 5% thiosulfate in the earlier time points, reaching significance at 8 weeks (P<0.05). However, later time points showed not difference in color among the groups.
Conclusions: Five percent sodium thiosulfate concentration did display less discoloaration compared to the other groups in the earlier time points. All groups displayed more red and yellow hue. All color changes were more than the color acceptability threshold of 2.7.