*2.1. Patients*

The study was approved by the Local Ethics Committee, permission number: R-I-002/386/2016. Each patient was informed of the purpose and the detailed procedure of the study and consented in writing to join the research project.

The study group consisted of 45 women diagnosed with HT. The disease was confirmed when anti-TG and/or anti-TPO levels in serum was above the normal range and occurred with the presence of parenchymal heterogeneity on thyroid ultrasonography (USG). Our experiment included patients with HT in euthyreosis (free thyroxine (fT4) and thyroid- stimulating hormones (TSH) within normal ranges), 24 treated with Eutyrox (doses from 50 to 150 mg; the last tablet taken 24 h before the hormone level test) and 21 untreated. Patients were reported for follow-up visits to the Department of Endocrinology, Diabetology and Internal Medicine of the Medical University of Bialystok. We decided to create only one group, because the results of particular redox balance assays did not differ between patients in the course of a hormone therapy and those not requiring it.

The reference group consisted of 45 generally healthy women, matched to the study group in terms of age and BMI, selected from those who reported for dental check-ups to the Department of Restorative Dentistry, MUB.

Exclusion and inclusion criteria:

Patients with HT and healthy controls did not suffer from any associated diseases, including other autoimmune diseases (type 1 diabetes, rheumatoid arthritis, scleroderma, psoriasis, lupus, Sjögren's syndrome, etc.) or depression. Participants from both the study and control group were qualified for further examinations only if they did not have periodontitis, gingivitis, or active foci of odontogenic infections. Participants had 18.5 ≤ BMI ≤ 25. The subjects had not taken any drugs that could affect saliva secretion (mainly antidepressants or drugs for hypertension) or its redox status (vitamins, antioxidants) within 3 months prior to saliva collection, nor were they on any reducing diet. Patients and the controls who smoked tobacco or consumed any amount of alcohol or other stimulants were not included in the study. All the subjects in the control group had normal serum TSH, fT4, anti-TG and anti-TPO levels as well as thyroid imaging (homogenous parenchyma without nodules) on USG.
