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J Dent Educ. 70(10): 1061-1065 2006
© 2006 American Dental Education Association
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Critical Issues in Dental Education

Radiographs Associated with One Episode of Orthodontic Therapy

Philippe Hujoel, D.D.S., Ph.D.; Lars Hollender, D.D.S., Ph.D.; Anne-Marie Bollen, D.D.S., Ph.D.; John D. Young, B.A.; Molly McGee, B.A.; Alex Grosso, B.S., M.S., M.A.

Key words: ionizing radiation, cancer, orthodontic therapy, practice patterns

Submitted for publication 04/20/06; accepted 07/31/06


   Abstract
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 Abstract
Materials and Methods
 Results
 Discussion
 References
 
Obtaining lifetime diagnostic radiation histories in head and neck cancer studies is often challenging due to the almost universal lack of centralized registries on X-ray utilization in medicine and dentistry. Both the common nature of orthodontics and the young age at which orthodontics typically occurs make it important to quantify what diagnostic radiographs are typically taken during orthodontic therapy. The aim of this study was to assess the number and type of radiographic films associated with one episode of orthodontic therapy in an educational setting. Charts stored in an orthodontic clinic at one academic setting were randomly sampled, and the type and number of radiographic examinations were tallied for the 325 individuals who were in orthodontic therapy for at least one year. Being under orthodontic therapy for one or more years was associated with a median number of seven extra-oral radiographs and twenty-four intra-oral radiographic films. The extra-oral radiographs included three panoramic radiographs and three cephalometric radiographs. Less than 10 percent of the variability was explained by factors such as age, gender, calendar year, surgical orthodontic therapy, and duration of therapy. Head and neck cancer etiology studies should take into account the ionizing radiation during episodes of orthodontic care. The substantial variability in radiographic practices in orthodontics could be reduced by research into clinical utility and by establishing guidelines.

Numerous studies have evaluated the role of medical/dental diagnostic radiation in head and neck cancers.1–9 For these studies, reconstructing a lifetime history of diagnostic radiation is often challenging, and some studies on head and neck cancers have largely ignored dental sources of diagnostic radiation.1,4 For organs such as the thyroid, the brain, and the parotids, the deletion of dental diagnostic radiation in cancer etiology studies can be misleading for two reasons. First, several studies have implicated dental radiation in head and neck cancers,3,5–8,10,11 making refutation or confirmation of these findings important. Second, children and adolescents have a higher lifetime risk for cancer development than do adults, and the most prevalent form of radiography in this age category may be dental, not medical, in origin.

Orthodontic therapy is one source of diagnostic radiation where statistics on utilization are needed. It has been estimated that 5.75 million individuals (19 percent adults; 81 percent children and adolescents) in the United States and Canada underwent orthodontic therapy in 2004.12 Typically, over 50 percent of subjects with a history of orthodontic therapy report that pre-adult orthodontic therapy occurred between the ages of twelve and fifteen.13 In the United States there are no practice guidelines available for the type and number of radiographs suggested for an episode of orthodontic therapy.14 The European Union has guidelines with respect to indications for taking orthodontic radiographs,15 but to our knowledge no surveys of compliance with these guidelines are available. While there have been two surveys regarding which radiographic records orthodontists request for hypothetical patients,16,17 we know of no surveys determining the actual number of radiographic records present in the patient’s charts. The aim of this study was to determine both the types and number of radiographic records present in orthodontic treatment records in a university setting and to evaluate whether this number depends on a patient’s age, gender, or decade during which orthodontiuc therapy was initiated.


   Materials and Methods
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 Abstract
 Materials and Methods
Results
 Discussion
 References
 
The Department of Orthodontics at the School of Dentistry of the University of Washington maintains approximately 3,500 records of individuals who were referred for orthodontic treatment and who are no longer seen on a regular basis; the charts are classified alphabetically. A systematic sample of available charts was taken between July and November 2005. Data were abstracted by a dental student (J.D.) and an investigator (P.H.). Data from the selected charts were abstracted using a standardized approach. Approval for conducting the research was obtained from the Human Subjects Division at the University of Washington. For this report, we deleted empty charts, patients with no orthodontic care, or patients who were seen for a limited short-term procedure (<1 year of treatment).

The following types of films were identified in the charts: periapicals, bitewings, maxillary and mandibular occlusals, panoramic radiographs, lateral and frontal cephalometric radiographs, submental cephalometric radiographs, and tomographic records of the TMJ or other areas. A full-mouth survey is a series of periapicals and bitewings that represent all teeth. The number of full-mouth surveys was not abstracted from the charts but was estimated based on the dates the radiographs were taken and on the number of periapical radiographs and bitewing radiographs present in the chart.

Descriptive statistics (mean, median, standard deviation, 5th and 95th percentile) were calculated for the various types of radiographs. The total number of radiographs and the number of extra-oral radiographic films were related to age, gender, and duration of orthodontic therapy using general linear models (Proc GLM in SAS).


   Results
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 Abstract
 Materials and Methods
 Results
Discussion
 References
 
The selection process identified 418 patients, 325 or 78 percent of whom had orthodontic therapy for at least one year’s duration (194/325 or 60 percent female). Of these patients, twenty-seven were classified as having received surgical therapy (8 percent), 211 as having received nonsurgical therapy (65 percent), fifty-nine as having had two-phase therapy (18 percent), and twenty-eight (9 percent) as having discontinued orthodontic therapy without further description regarding the nature of the orthodontic therapy received.

Patients who had at least one year of orthodontic therapy had on average 33.7 radiographic films present in the chart (standard deviation 12.4) (Table 1Go). When expressed as a median, the typical number of radiographic films per patient was thirty-three with a range spanning from one to ninety radiographs per patient. The 5th and the 95th percentiles were 18 and 57. The mean number of intra-oral films was 26.4 (standard deviation 11.3). The number of intra-oral films ranged from zero to eighty-two with a median of twenty-four. The mean number of extra-oral films was 7.3 (standard deviation 3.7). The number of extra-oral films ranged from zero to twenty-nine with a median of seven.


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  		Table 1. Typical diagnostic radiation exposures associated with orthodontic therapy
 
The mean number of 7.2 extra-oral films per patient consisted predominantly of panoramic radiographs (mean 3.7; standard deviation 1.7) and lateral cephalometric radiographs (mean 3.1; standard deviation 1.8) (Table 1Go). The number of panoramic radiographs per patient varied between zero and thirteen. The number of lateral cephalographic radiographs per patient varied between zero and twelve. The mean number of frontal cephalographic records was 0.3 (standard deviation 0.8), and the number per patient varied between zero and eleven. The mean number of intra-oral radiographic films was 26.4 and consisted predominantly of periapicals (mean 19.7; standard deviation 8.6) and bitewings (mean 6.7; standard deviation 4.8). The number of periapicals ranged from zero to seventy-two, and the number of bitewings ranged from two to sixteen. Both the mean and the median number of full-mouth radiographs was one (standard deviation 0.5), ranging between zero and four.

Surgical orthodontic patients had on average 3.5 more extra-oral radiographs taken than nonsurgical orthodontic patients (p-value <0.0001) (Table 2Go). When orthodontic therapy was of a duration longer than three years, there were significantly more extra-oral X-ray films taken (p-value <0.0001) and to a lesser extent more radiographic films in total (p-value <0.02). Pre-adult orthodontic patients had approximately the same number of extra-oral films taken (7.4 versus 6.9 X-rays, respectively), but adults had significantly more X-rays (37.8 versus 32.8). Gender did not have a substantial impact on the number of X-ray films taken. There was a marginally significant drop (p<0.02) in the total number of radiographs between those individuals starting therapy before 1980 and those starting therapy between 1980 and 1990. Apart from this change, no substantial changes in the number of radiographic records occurred between 1965 and 2002.


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  		Table 2. Factors influencing the number of total radiation exposures and the number of extra-oral films
 

   Discussion
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 Abstract
 Materials and Methods
 Results
 Discussion
References
 
The findings of this study suggest that orthodontic therapy is typically associated with three panoramic radiographs, three cephalometric radiographs, and one full-mouth series of intra-oral films. There was substantial variability around these typical numbers, and less than 10 percent of this variability could be explained in terms of the duration of the therapy, gender, age, surgery, and the calendar year when orthodontic therapy took place. The large unexplained variability may, in part, be due to the lack of guidelines for radiography during orthodontic therapy.17 The findings of this study suggest that an assessment of the ionizing radiation associated with orthodontic therapy should form part of etiologic studies on head and neck cancers and that guidelines on what radiographs, if any, are needed could reduce the large variability in the number of radiographs taken per patient.

To our knowledge, this is the first survey of the type and number of radiographs present in charts of orthodontic patients. Two surveys have been conducted asking orthodontists what radiographs they would request for a hypothetical patient.16,17 One survey of U.S. and Canadian educational institutions reported in 1990 indicated that orthodontic therapy in a hypothethical patient should be associated with a median of four panoramic and four cephalometric radiographs, a number higher than reported in this survey.16 Another survey of U.S. orthodontists, which was limited to an investigation of what radiographs should be taken at the initiation of therapy in a Class II hypothetical patient, indicated that the majority of the surveyed orthodontists request a panoramic and cephalometric radiograph.17

Our study was limited in scope in the sense that, from a geographical perspective, a convenience sample in an academic setting was used to estimate typical practice patterns. It has been reported that educators take more radiographs than private practitioners,16,17 and as a result our reported estimates may be an overestimate of what typically occurs in private practice settings. This difference between the private practice orthodontists and educators was reported to depend on the type of radiograph.16 For the panoramic radiographs, there was no reported difference between the total number of radiographs ordered by private practitioners and by teaching institutions. However, teaching institutions tend to order more intra-oral and other types of extra-oral radiographs.

A more reliable estimate could be obtained by taking a national representative sample of orthodontic patients and reconstructing their lifetime orthodontic radiation exposures by means of self-report of dates of seeking orthodontic care, regardless of whether they actually received care, and obtaining all radiographic records. Such an approach could, in the absence of recall bias, fully capture the radiation exposures associated with all episodes of seeking and receiving orthodontic care. By using a convenience sample, our study did not result in a representative sample, did not capture multiple episodes of care, and did not capture the potential diagnostic radiation associated with "shopping" for an orthodontic provider.18 In addition, the number of radiographic films associated with one episode of orthodontic care was probably underestimated due to misplaced and lost films.

The limitations of the current study have to be evaluated in light of the generalized poor knowledge regarding the utilization of diagnostic radiation exposures. For some countries, the World Health Organization (WHO) has to rely on the estimates of one hospital regarding the number of diagnostic radiation exposures in a country.19 A study published in the Lancet largely ignored dental diagnostic radiation, which possibly is the most common form of head and neck radiation in children and adolescents.1 In light of such gaps in reliable information on diagnostic radiation utilization, small-scale surveys or chart audits provide information that at the very least brings to attention that multiple diagnostic radiation exposures may be associated with an episode of orthodontic care.

The absence of guidelines regarding the use of diagnostic radiation in orthodontic therapy may be partly responsible for the large variability in the number of radiographs observed. The current guidelines by the FDA for radiographic examinations suggest that, for monitoring growth and development for children and adolescents, "clinical judgment be used in determining the need for, and type of radiographic images necessary for, evaluation and/or monitoring of dentofacial growth and development."14 No guidelines for diagnostic radiation during orthodontic therapy are provided. In contrast, the European guidelines on radiation protection in dental radiography are evidence-based and provide specific guidelines for when to take radiographs such as cephalometric.15 Nonetheless, the extent to which these guidelines (or their absence) are followed is unknown since no national monitoring processes appear present. It has been reported in one European country that 22 percent of the orthodontic extra-oral radiographs are not evaluated,20 indicating that at least some radiation exposure to patients is without direct clinical benefit.

In summary, our study suggested that the typical orthodontic patient in one university setting had three cephalometric radiographs, three panoramic radiographs, and one full-mouth set of intra-oral radiographs. Regardless of the direction of the bias associated with these estimates, the presented information appears more useful than simply ignoring dental diagnostic radiation during childhood or adolescence in the conduct of head and neck cancer studies. Further research into the clinical utility of orthodontic radiographs and guidelines could help reduce the substantial variability present in the number of radiographs taken for an episode of orthodontic care.


   Footnotes
 
Dr. Hujoel is Professor, Department of Dental Public Health Sciences, School of Dentistry, University of Washington; Dr. Hollender is Director of Oral Radiology, Radiology Clinic, and Oral Medicine, School of Dentistry, University of Washington; Dr. Bollen is Professor, Department of Orthodontics, School of Dentistry, University of Washington; Mr. Young is a dental student at the School of Dentistry, University of Washington; and Ms. McGee and Mr. Grosso are Health Physicists in the Department of Environmental Health and Safety, University of Washington. Direct correspondence and requests for reprints to Dr. Philippe Hujoel, Department of Dental Public Health Sciences, University of Washington, School of Dentistry, Box 357475, Seattle, WA 98195; 206-543-2034 phone; 206-685-4258 fax; hujoel{at}u.washington.edu.

This project was supported by NIH/NIDCR T32DE07132.


   REFERENCES
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 Materials and Methods
 Results
 Discussion
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