Bone thickness and bisphosphonate use
Researchers publishing in the May 2015 issue of Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology found that measuring the thickness of the mandibular inferior cortical bone using panoramic radiography may be a promising method for detecting bisphosphonate-induced dimensional bone changes.
Although bisphosphonates (BP) have improved the quality of life for patients with osteoporosis and cancer, a well-recognized side effect of therapy is bisphosphonate-related osteonecrosis of the jaws (BRONJ). Among the most common risk factors for BRONJ in patients taking bisphosphonates is invasive tooth procedures, including extractions. Risk varies from 2 percent to 3 percent for intravenous medications and 0.02 percent to 0.4 percent for oral therapy. Authors surmised that identifying early radiographic signs of BP-related changes in bone may assist in predicting the development of BRONJ and guide treatment planning.
Considering previous findings showing that cortical bone volume, area and height were significantly higher in study subjects with BRONJ, scientists aimed to compare mandibular inferior cortical bone thickness of patients taking bisphosphonates with those that were not. Their secondary aim was to correlate bone thickness with type, dose and duration of therapy in patients with and without BRONJ taking bisphosphonates.
They enrolled patients with panoramic radiographs from two medical centers in Washington. The subjects came from three groups: patients taking the bisphosphonates who did not have BRONJ (27), patients taking bisphosphonates who did have BRONJ (10) and patients who were not taking bisphosphonates (47). Scientists compared mandibular inferior cortical bone thickness as measured by the panoramic radiographs for all three groups. Among patients with and without BRONJ and who were taking bisphosphonates, thickness was also compared with respect to the dose and duration of bisphosphonate treatment. Scientists obtained bisphosphonate use history, including type, dose and duration of treatment from subjects’ questionnaires and medical records.
Results showed significant differences in bone thickness between the three groups. The mean thickness was higher for both groups taking bisphosphonates — with and without BRONJ — than for those who weren’t taking the medication. Moreover, there were significant differences in the mean thickness between patients with BRONJ and patients taking bisphosphonates without BRONJ.
“The present study indicates that dimensional changes may be detected even in patients taking BPs who do not have BRONJ,” authors reported. “The significant differences between patients with BRONJ and patients taking BPs who do not present BRONJ suggest that MICBT [mandibular inferior cortical bone thickness] can be a tool in the detection of BP [bisphosphonate]-induced dimensional changes in cortical bone.”
Correlations between cortical bone thickness and the dose and duration of BP therapy were also verified among study findings. “These data corroborate the statement that the risk for developing BRONJ is higher in patients taking higher doses of BPs and those taking BPs over longer periods,” authors said.
Although previous research used cone beam computed tomography in a study finding dimensional changes in mandibular inferior cortical bone thickness associated with bisphosphonate use, panoramic radiographic images are easily available, use lower radiation doses and cost less, according to the authors. They called for future prospective studies to verify if this measurement can predict the risk of developing BRONJ, particularly those which measure individual changes “which may be a more reliable tool for detecting BP-associated changes in the mandibular cortical bone than comparisons of groups."
Read the original article.
Consulting Editor: Laurie C. Carter, DDS, PhD
Past president, American Academy of Oral and Maxillofacial Radiology
Better panoramic radiography results for edentulous patients
A new bite block designed for taking panoramic radiographs of edentulous patients is likely to work better than conventional devices, according to a report in the June 2015 issue of Imaging Science in Dentistry.
Bite blocks and chin-support devices are widely available for positioning patients for panoramic radiography who are missing front teeth. Between these two options, chin supports offer greater vertical dimension of the edentulous area and are generally preferred.
Previous research includes studies showing that reproducibility of panoramic radiographs taken of edentulous patients using a conventional chin-support device was worse than that of dentulous patients and also that 89 percent of radiographs of edentulous patients had at least one error. The literature describes a variety of inaccuracies, including: chin too high; chin too low; chin too far forward; tongue not raised; head tilted; head turned; or head too far back.
It’s a problem for diagnosis and treatment planning because clinicians frequently use panoramic radiographs to screen for cysts, foreign bodies, neoplasms, bone resorption, osteopenia of the jaws and when installing implants. Securing suitable positioning and then assessing it using anatomical structures shown on panoramic radiographs is more difficult in edentulous patients.
By modifying the bite portion, scientists designed a new bite block that brought reproducibility to a similar level as that of a bite block for dentulous patients. The new block compensates for the missing anterior teeth and resorbed anterior alveolar bone tissue of patients missing front teeth. Results were achieved by comparing panoramic radiographs of anterior edentulous patients taken using the new bite block with the radiographs previously taken using conventional chin support device.
Researchers observed better stability in intermaxillary vertical space, antero-posterior position and bilateral symmetry than radiographs taken with the conventional chin-support device. The radiographer reported that patients showed less movement and more stable positioning during the procedure.
Authors encouraged ongoing evaluation of the new bite block, including assessment of image quality and reproducibility.
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Factors affecting CBCT re-exposure occurrence
As worldwide use of cone beam computed tomography (CBCT) increases, so do concerns about unacceptable examinations. The presence of image artefacts, such as black and white stripes or double contours, may hamper diagnosis and lead to re-exposure, doubling radiation dose to the patient.
Although the literature shows that head movement may result in motion artifacts that compromise CBCT image quality, scientists from Aarhaus University in Denmark found no studies focusing on understanding the factors leading to patient movement. To explore the topic, they conducted a study and published their findings in the May 2015 issue of Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology. Their objectives were to assess operator, examination and patient-related factors with impact on patient movement and re-exposure.
To explore, three dentists watched video recordings of 248 CBCT examinations performed on 190 patients (122 females and 68 males) to determine if the patient moved or did not move. Operator factors that might have an impact on patient movement and re-exposure that were recorded included the patient’s head position, chin position, presence of cotton rolls to stabilize jaws and CBCT unit arm touching the patient’s hair during exam. Examination-related factors included small or large field of view (FOV) and the diagnostic task at hand when re-exposures occurred. Patient-related factors included age, gender and whether the patient’s eyes were open or closed during most of the examination.
Results showed that of 16 re-exposures (6.4 percent), 14 were due to FOV adjustments, one was due to a computer error and one was due to severe artefacts. Only the use of a large FOV was significant. In fact, for those cases in which a large FOV was used, the risk for re-exposure was almost six times higher than when a small FOV was used.
Authors noted that almost 90 percent of re-exposures were related to FOV adjustments, meaning that the area of interest was not being imaged. The majority of these were in cases in which two regions of interest were intended in the same examination but were located too close to the edges of the selected FOV.
“Of course, the intention had been to avoid excess radiation to the patient by selecting a large FOV instead of two smaller FOVs,” authors noted in discussion. “However, recent studies show that the dose from two small-FOV CBCT examinations may be lower than the dose of one CBCT examination using a large FOV, depending on the selected settings.”
Other results showed the prevalence of movement was 21 percent, with cotton roll stabilizing the patient’s jaws, CBCT unit touching hair and the patient’s age 15 years or greater related to movement. Patient movement resulted in re-exposure in one case. “Even minor patient movements, which might be difficult to perceive (and therefore do not label an examination as unacceptable), contribute to a discrepancy between the image dimensions and reality,” authors said.
The researchers considered guidelines (European Association of DentoMaxilloFacial Radiology SEDENTEXCT Project), ratifying the ALARA principle (As Low As Reasonably Achievable) and stating that no more than 5 percent of examinations should be classified as unacceptable and lead to re-exposure of the patient.
“Well-defined training protocols on how to position and instruct the patient for CBCT examination must be further developed,” authors said.
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Diagnosing head and neck lesions
The ability to distinguish between hemangiomas and vascular formations is critical to treatment decisions. A 2014 classification system for such diagnosis proposed by the International Society for the Study of Vascular Anomalies garnered support of scientists publishing in the June 2015 issue of Imaging Science in Dentistry.
They examined the new system and the difficulties of diagnosing with older classification systems via five cases of vascular anomaly of the head and neck. Although classification methods for vascular anomalies have evolved through the years, only involuting lesions were previously classified as hemangiomas. Asserting that non-involuting lesions can be either hemangiomas or vascular malformations depending on signs, symptoms, clinical examinations and imaging characteristics, scientists said the new system solves the problem of diagnosing lesions with characteristics of hemangiomas that don’t involute.
“It is important to distinguish between a hemangioma and vascular malformation as treatment differs markedly for these lesions, and life threatening complications could occur during treatment procedures,” authors said. “Hemangiomas, being the result of abnormal cellular proliferation, often respond to treatment with corticosteroids and irradiation (although the latter is not recommended), while vascular malformations have stable cellularity and thus may require embolization and surgical resection.”
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AAOMR to hold 66th Annual Session Sept. 30-Oct. 3
Registration is now open for the 66th Annual Session of the American Academy of Oral and Maxillofacial Radiology, Sept. 30 to Oct. 3, 2015, at the Hyatt Regency Indianapolis. This year’s program will include a wide variety of continuing education opportunities, including an interactive interpretation session, imaging of the sinonasal complex and in-depth courses on cone beam computed tomography (CBCT). The CBCT training courses are designed for general dentists and dental specialists. The meeting will also feature a variety of social and networking events and an exhibition hall that opens at 7 a.m. each day and offers attendees continental breakfast.
To register, make hotel reservations, book transportation from the airport to the hotel and explore Indianapolis attractions, visit the AAOMR website. If you need help with your registration, please call at 217-529-6503 and ask for Stacey Melotte, Member Services.
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What is Specialty Scan?
This is one in a series of quarterly newsletters updating dentists on selected specialties in dentistry. Information presented is aggregated and summarized from previously published materials, each item attributed to its publication of origin. This issue of JADA Specialty Scan focuses on oral and maxillofacial radiology, the third in the series on this topic for 2015. Other Specialty Scan issues are devoted to endodontics, oral pathology, orthodontics, pediatric dentistry, periodontics and prosthodontics. The ADA has engaged the specialty organizations in these areas as well as its own Science Institute and Division of Legal Affairs to assist with these newsletters. We welcome feedback on this and all Specialty Scan issues.
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