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Orthodontic radiographs can promote cell toxicity

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 Orthodontic radiographs can promote cell toxicity


Orthodontic radiographs appear to promote cell toxicity in the oral mucosa, according to a new study in Dentomaxillofacial Radiology (October 2010, Vol. 39:7, pp. 437-440) -- calling into question once again whether multiple cephalograms are warranted in every orthodontic case.

 

 

To better understand the effects of radiographic radiation on the cellular system, researchers from the Methodist University of São Paulo and the Federal University of São Paolo investigated the frequency of micronucleated cells in the oral mucosa of individuals following orthodontic radiography. They also evaluated the cytotoxic effects -- including pyknosis, karyolysis, and karyorrhexis -- in these patients following exposure.

"Orthodontic radiographs carried out in radiological clinics are essential for diagnosis, planning, and control of orthodontic treatment," researchers from Federal University of São Paolo wrote. For example, they noted, both a lateral cephalometric x-ray and panoramic x-ray should be obtained from all patients prior to treatment to enhance the diagnosis and treatment plan.

"Frontal cephalometric analysis is also a valuable complementary examination in establishing the correct diagnosis and orthodontic planning," they wrote. "At present, lateral and frontal cephalograms are considered mandatory in orthodontic therapy."

That said, the possible risk associated with exposure to x-rays must be weighed against the benefits of clinical interpretation, they noted.

"It is well-known that ionizing radiation damages DNA," the researchers wrote. While a variety of assays have been proposed as potential biomarkers, these methods are typically laborious and time-consuming or require highly trained technicians to accurately read and interpret slides, they noted.

So they chose instead to evaluate chromosome damage (micronucleus) and cellular death in exfoliated buccal mucosa cells from patients exposed to cephalometric and panoramic radiographs. Micronucleated cell indexes are thought to reflect genomic instability, and an elevated frequency of micronuclei indicates an increased risk of cancer, they noted.

Small sample

The study comprised 18 healthy volunteers (six male, 12 female) with a mean age of 14.2 years who were referred to the Methodist University of São Paulo for orthodontic therapy. All participants underwent lateral and frontal cephalometric x-rays and panoramic dental radiography prior to orthodontic treatment. Oral mucosa cells were collected immediately before x-ray exposure and 10 days afterward.

"Damage that leads to the formation of micronuclei takes place in the basal layer of the epithelial tissue where cells undergo mitosis," the researchers wrote. "Rapid turnover of epithelial tissues brings the cells to the surface, where they exfoliate. As a result, the maximal rate of micronuclei formation in exfoliated cells is seen one to three weeks after exposure to the genotoxic agent."

Prior to x-ray exposure, the mean frequency of micronucleated cells was 0.02%, the researchers reported. While there was no significant statistical difference (p > 0.05) in the frequency of micronucleated cells following x-ray exposure, an increase in the frequency of karyorrhexis, pyknosis, and karyolysis was observed.

"Despite the lack of cytogenetic damage, our results demonstrated that panoramic and cephalometric radiographs induced cellular death," they wrote. "These results suggest that radiography is able to induce cytotoxicity but not mutagenic effects in oral mucosa cells; therefore, radiographs should be used only when necessary."

Other side effects?

However, while he agrees with the study's overall conclusions, Jay Friedman, D.D.S., M.P.H., author of The Intelligent Consumer's Complete Guide to Dental Health, noted that the researchers did not address some key related issues, including the assumption that all orthodontic cephalograms that are taken will benefit or enhance diagnosis and treatment. He cited a study in Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology which concluded that three-quarters of orthodontic radiographs were of no value for either diagnosis or treatment planning (February 1991, Vol. 71:2, pp. 238-245).

In addition, Dr. Freidman said, the current study does not consider the effects of cephalographic radiation on the brain.

"If oral cells are damaged, then is it not likely that brain cells also are damaged?" he said. "We can only conclude that cephalography is not only cytotoxic to oral tissues but also cytotoxic to brain tissues. Therefore, they are contraindicated for routine orthodontic treatment."

 

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Orthodontic radiographs can promote cell toxicity

Taking cone-beam CT (CBCT) scans prior to orthodontic diagnosis and treatment planning is warranted for patients with unerupted teeth or severe root resorption, according to a new study in the American Journal of Orthodontics & Dentofacial Orthopedics (May 2013, Vol. 143:5, pp. 665-674).

Researchers from the University of California, Los Angeles (UCLA) wanted to measure the impact of CBCT on orthodontic diagnosis and treatment planning, and determine what patient characteristics might play a role in deciding whether to use CBCT for this application.

"Previous research has shown that lateral cephalograms and panoramic, anterior periapical, and posterior bitewing radiographs provide sufficient information for most orthodontic patients," they wrote. "With the advent of CBCT, it became possible to evaluate the hard and soft tissues of the maxillofacial region in three dimensions and in high spatial detail."

This, in turn, offers the potential to provide orthodontic diagnostics and treatment planning, although it can also increase the cost of treatment and patient exposure to radiation, the researchers noted.

                                                   

Common clinical characteristics

For this study the researchers selected the records of six patients treated in the orthodontic clinic at UCLA. The records included medical and dental histories; stone study models; full-mouth intraoral and extraoral images; cephalometric, panoramic, and full-mouth series images; and the initial CBCT exam.

"The cases were selected to represent a broad range of clinical characteristics commonly encountered in orthodontic practices," the study authors wrote, including class I, II, and III molar relationships; canine impactions; open bites; cross bites; crowding; and airway and temporomandibular joint (TMJ) problems.

The researchers then invited members of the Pacific Coast Society of Orthodontists and directors of the orthodontic programs at UCLA, University of Southern California, and Loma Linda University to participate in the study. A total of 24 dental professionals agreed to participate; they were mostly men (21), trained at 10 orthodontic programs, with an average of 24 years of experience.

Each participant underwent a two-hour interview in which they were asked to review the six preselected orthodontic cases and provide hypothetical diagnoses and treatment plans. During the interview, they were given each patient's medical and dental histories and shown the study models and various images, with the exception of the CBCT. After describing their diagnostic problem list and their diagnostic degree of certainty for each case, they were then asked if a CBCT scan was warranted as well.

"Regardless of whether they requested a CBCT scan, the participants were asked to evaluate the CBCT examination and note any changes, enhancements, or confirmation to their diagnosis, including reasons for these changes," the study authors wrote.

The study participants were also asked to view preconstructed images of the TMJ, impacted teeth, and teeth with root resorption, and encouraged to create other CBCT cross-sections that would aid in their diagnosis and treatment planning.

Not necessary for all patients

 

Here are some of the study's findings:

A total of 64 CBCT scans were ordered. Two participants never ordered a CBCT scan for any of the cases, 16 participants ordered two to four scans, and two participants requested a CBCT scan for all six cases.

An unerupted tooth was the most frequently cited reason for ordering a scan (64% of orders), followed by root resorption (33%).

Of the 72 observations on patients with unerupted teeth, a CBCT scan was ordered 39 times when the characteristic was present and only twice when it was not.

Root resorption was cited as the rationale for ordering a CBCT scan 13 times when the characteristic was present and eight times when it was not.

Orthodontists in practice for a decade or less ordered significantly fewer CBCT exams than the more experienced orthodontists.

"Our participants requested a CBCT scan during diagnosis and treatment planning substantially more often than they reported using CBCT scans for patients in their private practices (45% versus 12%)," the study authors wrote. This might be due to the higher prevalence of patient problems selected for the test cases than in private practice, they acknowledged.

The study participants changed their diagnosis and treatment plans "significantly more frequently" when an unerupted tooth, root resorption, or severe skeletal discrepancy was present, the researchers noted.

"Of the six patient characteristics cited as reasons for a change to the diagnosis or treatment plan, unerupted tooth, root resorption, and severe skeletal discrepancy were the most frequent," they wrote. "For these characteristics, there were significantly more changes to the diagnoses and treatment plans when the case had the characteristic when compared with cases without the characteristic."

Obtaining a CBCT scan to examine for abnormalities of the TMJ, airway, or crowding did not result in significant changes in the diagnosis or treatment plan, they added.

These findings support obtaining a CBCT scan before orthodontic diagnosis and treatment planning when a patient has an unerupted tooth with delayed eruption or a questionable location, severe root resorption as diagnosed with a periapical or panoramic x-ray, or a severe skeletal discrepancy, the study authors noted.

 

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