Dental x-rays and the risk of thyroid cancer: A case-control study

Figures & data

Table I. Distribution of 313 thyroid cancer patients in Kuwait by age at diagnosis, gender, nationality, and histology.

	No. (%)
Age at diagnosis (years)
5–14	6 (1.9)
15–24	51 (16.3)
25–34	88 (28.1)
35–14	93 (29.7)
45–54	53 (16.9)
55–64	19 (6.1)
65–70	3 (1.0)
Gender
Female	238 (76.0)
Male	75 (24.0)
Nationality
Kuwaiti	172 (55.0)
Non-Kuwaiti (expatriates)	141 (45.0)
Arabs*	71 (50.4)
Southeast Asian	37 (26.2)
Bedouin Arabs^†	28 (19.9)
Other	5 (3.5)
Histology
Papillary	186 (59.4)
Papillary/follicular variant	75 (24.0)
Follicular	27 (8.6)
Medullary	3 (1.0)
Other	4 (1.3)
Unknown	18 (5.8)

*Arabs from Middle East and North Africa.

^†“Stateless” Arabs resident in Kuwait.

Table II. Association between exposure to dental x-rays and risk of thyroid cancer.

	Case/Control	Cases %	Controls %	OR	95% CI	P-value
Dental x-ray
No	208/255	66.7	81.7	1.0	–
Yes	104/57	33.3	18.3	2.1	1.4–3.1	0.001
Number of dental x-rays						<0.0001*
1–4	75/43	72.2	75.4	2.2	1.4–3.5	0.001
5–9	16/4	15.4	7.0	4.6	1.4–14.7	0.01
10+	11/3	10.6	5.3	5.4	1.1–26.7	0.037

Conditional logistic regression analysis adjusted for upper-body (head, neck, and chest) x-rays.

One case-control pair was excluded from the analysis because the case had received radiotherapy. Information on no. of x-rays was missing for two cases and seven controls.

Baseline for ORs was taken as those subjects who had not reported any dental x-ray exposure.

*P for trend.

Table III. Association between exposure to dental x-rays and risk of thyroid cancer by age at diagnosis, gender, nationality, level of education, parity, and histology.

	Cases %*	Controls %*	OR	95% CI	P-value
Age at diagnosis/pseudo-diagnosis (years)
≤35	32.6	15.8	2.1	1.1–3.8	<0.05
35 +	33.9	20.6	1.9	1.0–3.4	0.05
Gender
Females	33.2	19.0	2.0	1.2–3.3	<0.01
Males	33.3	16.0	2.4	1.0–5.6	0.05
Nationality
Kuwaiti	32.2	19.9	2.0	1.1–3.6	<0.05
Non-Kuwaiti	34.8	16.3	2.1	1.2–3.9	<0.05
Education (years)
No formal education	27.4	8.2	4.6	1.3–16.3	<0.05
1–12+	36.6	22.0	1.7	1.0–3.1	<0.05
Number of live births^†
1–4	38.8	24.4	1.8	0.9–3.6	NS
5 +	33.6	12.8	2.7	1.3–5.9	<0.05
Histology
Papillary**	34.5	18.0	2.3	1.4–4.0	0.002
Follicular	30.8	19.2	0.9	0.2–4.7	NS

Conditional logistic regression analysis adjusted for upper-body (head, neck, and chest) x-rays.

One case-control pair was excluded from the analysis because the case had received radiotherapy.

Baseline for ORs was taken as those subjects in the respective subgroup who had not reported any dental x-ray exposure.

NS = Not significant.

*Percentage exposed to dental x-rays.

^†Includes only ever-married women; ORs based on unconditional logistic regression analysis, adjusted for age, nationality, district of residence, and upper-body x-rays.

**Includes cases classified as mixed papillary/follicular variant.