A recent article by Claus and colleagues[1] reporting an association between dental radiographs and meningiomas has led to renewed concern about the safety of dental x-rays. We will first consider this reported association between dental radiograph and meningiomas, then explore the risks from dental imaging, and finally discuss appropriate use of dental radiographs.
These researchers identified 2228 eligible patients with intracranial meningioma and recruited 2604 matched controls. Participation was 65% for meningioma patients and 52% for controls. Subjects were asked to report their history of bitewing, full-mouth, or panoramic radiographic examinations. The association of meningioma odds with the odds of dental radiographs was calculated by conditional logistic regression for maximum-likelihood estimation of odds ratio, adjusted for age, sex, race, education, and history of head CT.
The amount of radiation received from dental radiography is so low that it is highly unlikely that it results in a measurable risk. Dose reconstructions using techniques commonly used during the last decades of the last century show that the exposure to the brain from 4 bitewings is approximately 0.07 mGy, and from a panoramic examination about 0.02 mGy. A full-mouth examination (typically consisting of 12 periapical and 4 bitewing exposures) results in a brain dose of approximately 0.24 mGy.
However, even though the brain exposure from a full-mouth examination is higher than from bitewings or a panoramic, the study from Claus and colleagues found associations with the 2 low-dose examinations and meningiomas but not the relatively high-dose full-mouth examination. The resolution of this inconsistency is not clear if radiation is causing the meningiomas.
Further, there are no research reports that support the premise that doses as low as those received by the brain from dental radiography, including from a full-mouth examination, are sufficient to cause meningiomas. We know that brain exposure from dental imaging is much smaller than from head CT examinations. Brain exposure from head CT examinations is typically in the range of 43-75 mGy, far more than from dental radiography.[22] Head CT exposures contribute 4.3% of the collective effective dose from all diagnostic sources, 15 times more than from dental radiography.[23]
Previous efforts to link head CT exposures, skull x-rays, or sinus radiographs to meningiomas have been unsuccessful,[24] although recently an association has been reported between multiple radiation exposure from CT scans in childhood and subsequent risk for leukemia and brain tumors.[25] Finally, decades of study of the Japanese atomic bomb survivors as well other exposed populations has not reliably demonstrated evidence of increased cancer risk below 100 mSv.[26] While we believe that dental radiography has the potential to cause harm, including meningiomas, and we concur that the Claus study suggests an association between dental radiographic exposures and meningiomas, it is far more likely because of the low doses involved in dental imaging that the reported association is the result of meningiomas triggering the need for dental imaging than the other way around.
The researchers reported an association between intracranial meningioma and bitewing radiographs obtained at 10-19 and 20-49 years of age, as well as for all ages combined. Additionally, an association between meningioma and panoramic radiographs at younger than 10 and 10-19 years of age is identified. Finally, an association between meningioma and frequency of panoramic radiographs across all groups, for those with yearly or more frequent radiographs is described. Of note, there was no significant association between intracranial meningioma and full-mouth series. The manuscript concludes that "exposure to some dental x-rays performed in the past, when radiation exposure was greater than in the current era, appears to be associated with an increased risk of intracranial meningioma."
This manuscript, studying the largest cohort of subjects to date, is a significant contribution to existing literature reporting a potential association of intracranial meningioma and dental radiographs.[2-7] However, methodologic details are difficult to evaluate, thus creating ambiguities when performing detailed analysis of the data. For example, although controls were matched for state of residence, local differences do not appear to have been considered. Thus, controls with significantly different dental awareness or access to dental care could have been recruited. No distinction is made between bitewing and selected periapical radiographs. No adjustment for income between patients and controls was performed. The ability of patients and controls to accurately recall history of dental radiographs in a way that would not influence the study findings was not assessed. Finally, the prevalence of dental disease that might affect need for dental radiographs was not evaluated.
Notwithstanding such shortcomings, we believe that a weak association between intracranial meningiomas and dental radiographs may exist.[8] However, current understanding of radiation biology and radiation-induced tumorigenesis (see Radiation Risk From Dental Radiography section below) suggests that an additional 0.02-0.07 mGy to the brain from dental bitewing and panoramic radiography is highly unlikely to contribute measurable risk. Other explanations for such a risk should be considered. An obvious possibility is that patients with intracranial meningiomas have increased odds to receive bitewing or panoramic radiographic examinations.
Meningiomas can cause referred pain and discomfort from various structures of the orofacial complex, including the teeth, temporomandibular joint, and face, prior to their diagnosis.[9-18] Such referred pain could lead the patient to the dentist, who would use bitewing, periapical, or panoramic radiographs in an effort to identify an oral etiology for the patient's symptoms. Using the reported, nonadjusted numbers of patients by Claus and colleagues, we estimate that it would take only 40 such patients (<3% of cases) for bitewing or 24 patients (<2% of cases) for panoramic radiographs to account for most of the reported associations.
Yet another possibility that could account for the reported association is that a third variable relates intracranial meningiomas and dental radiographs. Head trauma, particularly in young age, could be such a variable. Head trauma has been associated with risk for intracranial meningioma.[19-21] Furthermore, if head trauma were associated with trauma to the face, dental radiographs might be required to evaluate the integrity of the orodental structures.
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