Can dental X-rays cause thyroid cancer? The real potential risk factors are these 5, let’s take a look!

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Nowadays, more and more people are aware of the importance of having good teeth and begin to pay attention to the health of their teeth and oral cavity. During the process of going to the dentist, whether it is for periodontal disease, orthodontics, wisdom tooth extraction, root canal treatment or dental implants, there is one examination that is unavoidable, which is taking dental radiographs.

However, surprisingly, for such a common examination, many people are concerned about whether it will have adverse effects on the body. The author has noticed that there are many rumors circulating in thyroid-related forums that " dental X-rays can cause thyroid cancer ."

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So, are these claims true? Today, let’s take a deeper look at this topic and unravel the mystery between dental X-rays and thyroid cancer.

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What is thyroid cancer?

The thyroid gland is a gland located below the Adam's apple and close to the trachea . It looks like a butterfly and is usually impossible to touch. This gland secretes thyroid hormones, which regulate the body's metabolic process, that is, the speed at which energy is utilized. It can be said that it affects the normal functioning of all cells.

If the cells of the thyroid gland change into malignant (cancer) cells, thyroid cancer will occur. [1]

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Fortunately, compared to other cancers, thyroid cancer is a relatively controllable cancer. The mortality rate has been declining in recent years and is expected to continue to decline. Studies have shown that the mortality rate of thyroid cancer in women is expected to drop from 0.46/100,000 in 2019 to 0.40/100,000 in 2030 (a decrease of 13.0%), and the mortality rate in men is expected to drop from 0.81/100,000 to 0.67/100,000 (a decrease of 17.3%). [1]

However, we should be vigilant about some special types of thyroid cancer, such as columnar cell subtype, Ding subtype, diffuse sclerosis type of papillary thyroid carcinoma, medullary thyroid carcinoma, undifferentiated carcinoma, etc., which all have poor prognosis and are not the "lazy cancer" as everyone says.

What causes thyroid cancer?

Currently, many thyroid cancer patients do not have obvious, known risk factors. It has only been found that people with certain factors may be more likely to develop thyroid cancer than those without these factors. There are five known and common potential risk factors . [2,3]

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1. Gender

The incidence of thyroid cancer in women is about three times that in men. There is currently no clear and accurate mechanism to explain this phenomenon, which may be related to estrogen.

Moreover, the peak incidence rate in women is earlier than that in men, usually between 40 and 50 years old for women and 60 to 70 years old for men.

2 Genetic factors

Genetic factors also play an important role in the occurrence of thyroid cancer. Some are known to have clear gene mutations. For example, about 20% of medullary thyroid cancer is caused by RET gene mutations (defects); some specific pathogenic genes are still unclear. As long as a first-degree relative (parent, sibling or child) has thyroid cancer, it means that the risk of thyroid cancer will increase.

Some hereditary diseases that seem unrelated to the thyroid gland, such as familial adenomatous polyposis (FAP), Cowden syndrome, and Carney syndrome, can also increase the risk of thyroid cancer.

3. Obesity

Obesity is also a risk factor for thyroid cancer. Most cases of obesity are accompanied by disorders of insulin metabolism, which can stimulate malignant transformation of normal cells, tumor progression and metastasis.

A study analyzing data from 204 countries and regions around the world found that a high BMI value is a risk factor for adverse prognosis of thyroid cancer[4], and that people with a high BMI have an increased risk of death after developing thyroid cancer.

4 Iodine in Food

Both insufficient and excessive iodine intake can increase the risk of thyroid cancer.

Follicular thyroid cancer is more common in parts of the world where the diet is low in iodine. On the other hand, a high-iodine diet may increase the risk of papillary thyroid cancer, the most common type of thyroid cancer.

Therefore, when iodine was generally lacking in the country in the early years, iodine was added to table salt. Now that the sources of iodine intake have become diverse and abundant, non-iodized salt has gradually appeared. You can choose iodized salt or non-iodized salt according to your own situation under the guidance of a doctor.

5. Radiation

Radiation therapy to the head or neck during childhood is a risk factor for thyroid cancer, most commonly papillary thyroid cancer. The risk depends on the amount of radiation and the child's age, and the effect is much lower in adults.

In general, risk increases with increasing dose and decreasing age at onset of treatment:

Patients exposed to external radiation before age 4 years, with a cumulative dose of 1 Gy every 6 months, have a fivefold increased risk of thyroid cancer compared to patients aged 15–20 years.[5]

During childhood, exposure to 0.05-0.1Gy of radiation significantly increases the risk of thyroid cancer. When the cumulative dose is higher than 0.05-0.1Gy every 6 months, the risk increases linearly with the increase in dose. When the dose exceeds 30Gy, the risk of cancer begins to decrease, which may be related to the damage of high radiation doses to cells. [5]

Therefore, during childhood, the minimum radiation dose should be used as much as possible. [5] However, there is no need to worry that routine medical examinations will pose a threat, as the radiation dose is much smaller than the dose mentioned in the literature.

So can dental plaques cause thyroid cancer?

The use of X-rays and CT scans to assist in the diagnosis and treatment of dental diseases is a common practice both at home and abroad. Proper use can help patients receive better and more accurate treatment. [6,7]

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Different types of dental radiographs are selected according to different treatment and diagnostic needs, and the maximum radiation dose of a dental radiograph is less than 1 mSv (1 mSv = 1000 μSv, 1 mSv is equivalent to 1 mGv in X-rays). [7] Therefore, it is not believed that dental radiographs increase the risk of thyroid cancer, and there is currently no definite evidence to show that there is a relationship between the two [3].

From reference [7]

It is recommended that people with the above risk factors should lose weight, avoid unnecessary exposure to ionizing radiation, and undergo regular thyroid ultrasound screening [8]. Appropriate treatment should be considered based on the type of thyroid cancer found and the age at diagnosis.

However, there is currently no standard screening program, so this article will not make any related recommendations.

in conclusion

The statement at the beginning of the article that "dental X-rays can cause thyroid cancer" has no scientific basis. Normal medical X-ray examinations will not cause cancer. Reasonable use of the examinations can reduce medical errors and is beneficial to patients.

Author: Mr. Ayuan, an internist

Reviewer: Tan Zhuo, Deputy Director (in charge of work) of the Otolaryngology and Head and Neck Surgery Center of Zhejiang Provincial People's Hospital, Associate Chief Physician

References:

[1]Wu J, Zhao X, Sun J, et al. The epidemic of thyroid cancer in China: Current trends and future prediction. Front Oncol. 2022;12:932729.

[2]Bogović Crnčić T, Ilić Tomaš M, et al. Risk Factors for Thyroid Cancer: What Do We Know So Far?. Acta Clin Croat. 2020;59(Suppl 1):66-72.

[3]American Cancer Society. Thyroid Cancer Risk Factors. cancer.org. 2020.

https://www.cancer.org/cancer/types/thyroid-cancer/causes-risks-prevention/risk-factors.html

[4]Bao WQ, Zi H, Yuan QQ, et al. Global burden of thyroid cancer and its attributable risk factors in 204 countries and territories from 1990 to 2019. Thorac Cancer. 2021;12(18):2494-2503.

[5]Iglesias ML, Schmidt A, Ghuzlan AA, et al. Radiation exposure and thyroid cancer: a review. Arch Endocrinol Metab. 2017;61(2):180-187.

[6]AMERICAN DENTAL ASSOCIATION. DENTAL RADIOGRAPHIC EXAMINATIONS: RECOMMENDATIONS FOR PATIENT SELECTION AND LIMITING RADIATION EXPOSURE. 2012.

https://www.fda.gov/radiation-emitting-products/medical-x-ray-imaging/selection-patients-dental-radiographic-examinations

[7] Chinese Stomatological Association Endodontics Committee. Guidelines for the application of oral radiology in the diagnosis and treatment of endodontics[J]. Chinese Journal of Stomatology, 2021, 56(4): 311-317.

[8] Chinese Society of Peritoneal Oncology, China Anti-Cancer Association. Zhonghua Wei Chang Wai Ke Za Zhi. 2023;26(2):111-120.

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