Background & Aims: The thyroid gland is involved in the body's endocrine system and the synthesis of thyroid hormones (mainly triiodothyronine (T3) and thyroxine (T4)). These hormones play a vital role in regulating the basal metabolic rate and facilitating multiple metabolic processes in different organ systems. Stimulation of thyroid hormones refers to the fact that conditions such as hyperthyroidism often appear as a disorder of metabolic activity in various body systems, and its purpose is to meet the increased needs caused by excessive secretion of this hormone. The prevalence of thyroid disease in the world has a different situation and is influenced by environmental factors, especially iodine consumption. Iodine deficiency or excess in the body can cause a range of thyroid damage (from goiter and swelling of the thyroid gland to more serious conditions such as hyperthyroidism and hypothyroidism). Hyperthyroidism or thyrotoxicosis is characterized by an increase in the level of T3 or T4 in the bloodstream, and the occurrence of Grave's disease in these conditions often causes hyperthyroidism. On the other hand, hypothyroidism stems from insufficient hormone production, which causes symptoms such as fatigue, weight gain, and cold intolerance. This situation shows a decrease in the speed of the body's metabolism. In addition to the role of the thyroid gland, the oral microbiome (including billions of microorganisms such as bacteria, fungi, and viruses) plays an important role in local and systemic health. This complex microbial colony is responsible for the regulation of nutrient absorption, substance metabolism, and regulation of immune responses. Among a wide range of microorganisms, Streptococcus mutans and Streptococcus sobrinus stand out due to their serious participation in tooth decay through their acidogenic ability and biomembrane formation. The relationship between oral health and thyroid diseases, such as infectious thyroiditis, emphasizes the relationship between oral and systemic health. Infectious thyroiditis can be caused by bacterial infections of the oropharynx. This situation shows how oral microbial imbalance can have systemic consequences. Also, the accumulation of some bacteria in the oral cavity, such as Streptococcus mutans and Streptococcus sobrinus bacteria, is effective not only in local tooth decay but also in the aggravation or potential impact of systemic conditions. Saliva contains organic and inorganic ions and has essential functions in the oral cavity, such as maintaining the moisture of the oral mucosa, neutralizing acids or bases, and protecting against demineralization. The ability of these bacteria to metabolize sugars into organic acids demineralize tooth enamel cause tooth decay, and contribute to inflammatory processes that affect the body in a wide way. Streptococcus mutans is a remarkable case for the synthesis of extracellular glucan polymers with the help of sucrose due to its role in the formation of biomembranes on tooth surfaces. This process can facilitate the adhesion of bacteria to dental surfaces and its persistence in the oral cavity the transmission of Streptococcus mutans from mother to infant, which is mainly through saliva, shows the importance of oral hygiene. The resilience of these bacteria is characterized by their ability to grow in acidic environments, and this feature allows them to be stronger than other microbial species and dominate the biological membrane. Diagnosis of Streptococcus mutans usually depends on selective media, growth on Mitis salivarius agar, colony morphology, and biochemical characteristics. Also, the SB-20M medium is a selective medium for direct morphological identification and detection of Streptococcus mutans and Streptococcus sobrinus and has the necessary efficiency. The pathogenesis of Streptococcus mutans involves complex mechanisms for sensing environmental conditions and regulating gene expression to adapt to fluctuations in pH, nutrient availability, and host immune responses. This adaptive capacity emphasizes the role of bacteria in oral health and its potential implications for systemic health conditions such as thyroid disorders. Similarly, although less studied, Streptococcus sobrinus shares many of the virulent features of Streptococcus mutans that exacerbate dental caries.Thyroid hormones play an important role in maintaining oral and dental health, and their imbalance can cause various oral injuries. This study aims to evaluate the relationship between the serum levels of thyroid hormone (FT3, FT4 and TSH) and the number of live pathogens in oral saliva (Streptococcus mutans and Streptococcus sobrinus) in patients with thyroid disorders (hypothyroidism and hyperthyroidism) compared to the control group.
Methods: A "case-experimental" study was conducted on 58 patients with thyroid disorders (29 with hypothyroidism and 29 with hyperthyroidism) and 29 healthy people as a control group. The subjects were between 30 and 60 years old, and saliva samples were collected for microbial count and serum samples were also collected to determine the concentration of FT3, FT4, and TSH.
Results: The results of the comparison between the hyperthyroid and control groups show that there is a significant difference at the P>0.01 level in terms of the studied thyroid hormones, and for the comparison between the hypothyroid and control groups, it was also determined that there is a significant difference at the P>0.01 level regarding the TSH hormones. While there was no significant difference at the level of P>0.05 with other comparisons. For the comparison between the hyperthyroid and hypothyroid groups, the results show that there is a significant difference at the P<0.01 level according to the studied thyroid hormones. These results are consistent with the observations of previous researchers. This situation showed that there is a significant difference in fT4 and TSH levels between the control group and hypothyroid patients. Various research studies have been able to express the relationship between salivary function and numerous systemic diseases. There is a strong connection between salivary function and joint diseases (such as thyroid dysfunction, which is one of the most common endocrine disorders). The results of this study show that there is a significant difference at the P<0.01 level between hyperthyroid patients and the control groups regarding SFR and also among the patient groups, while there was no significant difference at the P>0.05 level between the hypothyroid patients and the control groups. . This indicator is too sensitive due to hyperthyroidism. This study showed a decrease in SFR in the study group compared to the control group. Decreased salivary flow is associated with decreased buffering capacity and causes disturbances in the clearance of oral sugar and increases the risk of severe dental caries in people with thyroid dysfunction. According to the results obtained by Al-Naif and El-Soud (2013), there is a decrease in SFR among patients with hyperthyroidism. This study showed that patients with hyperthyroidism had lower salivary flow rate (SFR) compared to the control group, and patients with hypothyroidism also had higher SFR levels compared to the control group (P<0.05). The number of viable salivary Streptococcus mutans and Streptococcus sobrinus had a significant difference in patients with hypothyroidism and hyperthyroidism compared to the control group.
Conclusion: This study concluded that although thyroid disorders greatly alter hormone levels, they have no effect on salivary levels of Streptococcus mutans and Streptococcus sobrinus, and this means that there is a complex relationship between thyroid health and the oral microbiome that needs to be further evaluated.