Assessment of the Formation, Toxicity and Prevention of Para-chloroaniline in Endodontic Therapy

• Main Author: Sarmast, Nima D
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Dentistry
• ISBN: 1088386547; 9781088386545

OBJECTIVE: 1) to identify the chemical nature of the precipitate that is formed by the consecutive irrigation with Sodium hypochlorite (NaOCl) and Chlorhexidine gluconate (CHX) ; 2) to investigate the toxicity of the precipitate using a eukaryotic small animal model (C. elegans larvae), and 3) to investigate the ability of STS to prevent the precipitate from forming in an ex vivo tooth model with stereomicroscopy.MATERIALS AND METHODS: Identification of the chemical nature of the precipitate by means of qualitative analysis with Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed.NaOCl 6% and CHX 2% were mixed in equal volumes to form the precipitate (BP). Specific concentrations of BP were tested in vivo in C. elegans larvae (L4) and evaluated for viability at set time intervals up to 30h post exposure. M9W buffer served as negative control. The number of dead larvae were recorded under light microscope at 100X magnification. Kaplan-Meier statistical survival analysis was performed.28 single rooted teeth were endodontically accessed, shaped ex vivo and thereafter randomly assigned to 3 groups with different irrigation protocols, i.e. Control group (G1), Sodium thiosulfate (STS) group (G2), No sodium thiosulfate group (G3). Each tooth was thereafter split longitudinally and qualitative analyzed for the presence of precipitate under a stereomicroscope with up to 63X magnification.RESULTS: The chemical nature of the “orange” part of the residue when analyzed with Time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirmed that the specimen is the result of complete reaction between NaOCl and CHX and contains high intensity of the C6H5NCl+ ion. The analysis confirms that the precipitate is composed of 4-Chloroaniline (C6H6NCl). BP75 and BP150 were significantly more toxic and lethal to worms than the no treatment (notx), vehicle only, supernatant and 0.006% CHX treatment groups (p<0.0001). Interestingly, the 0.002% NaOCl had the most drastic effect on lethality of L4 larvae. In the extracted and endodontically prepared teeth, a dark/brown precipitate (BP) was clearly present in all teeth irrigated with 6% NaOCl followed by 2% CHX. However, BP was not observed inside the canals when 10% STS solution was used as an intermediate irrigant as observed under stereomicroscope at 63X magnification.CONCLUSIONS: The precipitate that is formed by irrigating with NaOCl and CHX is mainly composed of 4-chloroaniline (para-chloroaniline). There are dose dependent toxic effects of the BP in C. elegans larvae. STS could serve as a potential inhibitor of BP and as an intermediate irrigant where both NaOCl and CHX are used.