GC-MS Detection of PCA in Root Canals: Antioxidant Irrigant Study

Researchers at the Federal University of Santa Maria (Brazil) set out to test whether certain antioxidant rinses could prevent or reduce the formation of para-chloroaniline (PCA), a harmful chemical byproduct in root canals, depending on whether the rinse was used between or after the main cleaning solutions. The levels of this byproduct were measured in the laboratory using gas chromatography-mass spectrometry (GC-MS), and its presence was also evaluated visually. A paper based on this study was published in the journal Odontology.¹

What is PCA, and What Are The Risks Associated With It?

Rinsing solutions used during root canal treatment are essential for flushing out bacteria and breaking down tissue and debris inside the canal.² However, the first rinsing solution is not always fully cleared out before the next one is introduced, which can cause the two solutions to mix and react in unwanted ways, potentially producing harmful byproducts.^3,4 The main byproduct of this reaction is PCA, which can interfere with the quality of the root canal seal and cause the tooth to become discolored. It also raises safety concerns, as it has been identified as potentially cancer-causing and capable of damaging genetic material.^5-8

Can Antioxidant Rinses Prevent a Harmful Byproduct Formed During Root Canal Treatment?

This study did not require approval from a research ethics committee, as it was conducted using bovine teeth that were to be discarded. The teeth were then split into 16 groups to test different rinsing methods aimed at preventing a harmful byproduct that forms when two common dental cleaning solutions, sodium hypochlorite and chlorhexidine, are used together. Three antioxidant rinses were tested either between the two main solutions, with varying wait times, or as a final rinse after both. The harmful byproduct was measured using a chemical detection method, and its presence was also assessed visually. It was found in all groups, but the antioxidant rinses significantly reduced its levels compared to the untreated control group. Using the antioxidant as a final rinse worked better than using it in between the two solutions, regardless of how long the wait time was. Of the three antioxidants tested, sodium ascorbate as a final rinse was the most effective at reducing the byproduct, followed closely by sodium thiosulfate and proanthocyanidin. The visual assessments matched well with the chemical measurements.¹

“The use of investigated antioxidant solutions as intermediate or final irrigants,” wrote the authors of the paper,¹ “demonstrated promising performance in the prevention and elimination of PCA in root canals.”

The researchers pointed out that, while the antioxidant rinses did reduce levels of the harmful byproduct, they did not eliminate it in any of the tested conditions. Since this was a laboratory-based study with no testing on living cells or tissues, the results should not be directly applied to real dental treatments without further research. This caution is especially important given that the byproduct is known to be harmful to human cells even in very small amounts; brief exposure has been shown to interfere with normal cell function and produce toxic breakdown products. It can also cause damage by triggering harmful chemical reactions inside cells, which has been linked to cell injury and disrupted cell function. In real-world settings, exposure to this compound (even through breathing it in or skin contact) can lead to serious health effects, showing that even low levels can be dangerous in a biological context. While these findings suggest that antioxidant rinses may help reduce the byproduct, the researchers believe that more research is clearly needed. Future studies should include cell and tissue testing and better replicate real clinical conditions, with the goal of developing rinsing methods that are both safe and effective at fully eliminating this byproduct during root canal treatment.¹

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References

1. de Pellegrin, S. F.; Padoin, Y.; Hoffmann, D. M. et al. Effect of Antioxidant Solutions on the Prevention and Elimination of Para-Chloroaniline in Root Canals: An in vitro Study. Odontology 2026. DOI: 10.1007/s10266-026-01411-6
2. Jena, A.; Sahoo, S. K.; Govind, S. Root Canal Irrigants: A Review of Their Interactions, Benefits, and Limitations. Compend Contin Educ Dent. 2015, 36 (4), 256-261; quiz 262, 264.
3. 3.Boutsioukis, C.; Arias-Moliz, M. T. Present Status and Future Directions - Irrigants and Irrigation Methods. Int Endod J. 2022, 55 (Suppl 3), 588-612. DOI: 10.1111/iej.13739
4. 4.Rossi-Fedele, G.; Doğramaci, E. J.; Guastalli, A. R. et al. Antagonistic Interactions Between Sodium Hypochlorite, Chlorhexidine, EDTA, and Citric Acid. J Endod. 2012, 38 (4), 426-431. DOI: 10.1016/j.joen.2012.01.006
5. 5.Basrani, B. R.; Manek, S.; Mathers, D. et al. Determination of 4-chloroaniline and its Derivatives Formed in the Interaction of Sodium Hypochlorite and Chlorhexidine by Using Gas Chromatography. J Endod. 2010, 36 (2), 312-314. DOI: 10.1016/j.joen.2009.10.031
6. Souza, M.; Cecchin, D.; Barbizam, J. V. et al. Evaluation of the Colour Change in Enamel and Dentine Promoted by the Interaction Between 2% Chlorhexidine and Auxiliary Chemical Solutions. Aust Endod J. 2013, 39 (3), 107-111. DOI: 10.1111/j.1747-4477.2011.00311.x
7. Homayouni, H.; Majd, N. M.; Zohrehei, H. et al. The Effect of Root Canal Irrigation with Combination of Sodium Hypo-chlorite and Chlorhexidine Gluconate on the Sealing Ability of Obturation Materials. Open Dent J. 2014, 22, 184–187. DOI: 10.2174/1874210601408010184