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BEHANDLING-God og treffsikker diagnostikk, behandling og rehabilitering

When and how to apply ultra-low dose Cone Beam Computed Tomography on children with impacted canines

Awarded: NOK 0.30 mill.

Impaction of the permanent maxillary canine is a condition, in which the tooth is embedded in the jawbone, and its eruption is prevented. Apart from wisdom teeth, canines are the teeth that are most often impacted, with an incidence of 2-3% in Scandinavian children and adolescents. If the canines are not palpable at the age of 10-11, X-rays should be taken to ensure the position of the teeth in the maxilla. Most impacted teeth can be localized with conventional two-dimensional radiographs, but the assessment is sometimes tricky since maxillary canines often overlap the incisors root, making it difficult to assess possible resorption in the bucco-palatal direction. When the conventional radiographs cannot provide adequate diagnostic information, one should then supplement a localized Cone Beam Computed Tomography (CBCT) examination. CBCT is a 3-dimensional X-ray technique that has quickly become popular for localizing the eruption disturbance and evaluation of possible root resorption of adjacent teeth. While ease of 3D image acquisition and reconstruction is impressive, adequate attention must be paid to the radiation risk, which may irreversibly damage cellular DNA and cause cancer. A study showed that the effective dose of a CBCT examination in the maxillary front area was up to 132 times higher than the conventional intraoral radiographs (Kadesjö et al. 2017). Assessment of the risks associated with the use of ionizing radiation for diagnostic imaging is a significant public health issue; it is especially important for children since the estimated risk for cancer formation is at least three times higher than that for adults (SedentexCT 2012). Recent reports have increased concerns over the potential association between radiation exposure and cancer (Claus et al. 2012 and Pearce et al. 2012). Therefore, efforts have been made to develop low dose CBCT by applying more sensitive image receptors and by sophisticated image processing algorithms. Unfortunately, using a lower dose comes at the expense of image quality, which simultaneously is reduced. If the image quality becomes too poor, there is no longer a clinical benefit of a CBCT examination for the patient in question. Before low dose protocols can be recommended for clinical use, image quality in relation to the specific diagnostic task needs to be verified as diagnostically acceptable. The primary objective of this study is to determine and compare image quality differences of a newly introduced CBCT with ultra-low dose protocols when examining the anterior maxilla. The secondary objective is to recommend an examination protocol for clinical use on patient with impacted maxillary canines. We took CBCT images on eight dry skulls with two standard protocols (one with normal resolution and one with high resolution) and four low-dose protocols (ProMax 3D, Planmeca Oy, Finland). Five radiologists evaluated the overall image quality and precision of eight important anatomical structures in the upper jaw front. The assessment of subjective image quality shows that the observers experienced differences in image quality between the six protocols. Of the four low-dose protocols, Ultra-Low Dose with High Resolution (ULHD) was the only one that did not differ from the standard protocol on the detection of anatomical structures. In other words, dentists could see as much diagnostic information on a CBCT image exposed with ULHD as the standard exposure protocol. The radiation is only 37% of the standard protocol. Therefore, we recommend testing this exposure protocol under a clinical situation on patients. References: Claus EB, Calvocoressi L, Bondy ML, Schildkraut JM, Wiemels JL, Wrensch M. Dental X-rays and risk of meningioma. Cancer; 2012. http://dx.doi.org/10.1002/cncr.26625. Accessed June 7, 2012. Kadesjö N, Lynds R, Nilsson M and Shi X-Q. Radiation dose from x-ray examinations of impacted canines: cone beam CT vs 2D imaging. Dentomaxillofac Radiol. 2018;47:20170305. doi: 10.1259/dmfr.20170305. Pearce MS, Salotti JA, Little MP, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet. 2012;380:499-505 Radiation Protection: Conebeam CT for dental and maxillofacial radiology. Evidence based guidelines. A report by the SEDENTEXTCT project 2012

This preproject on image quality of ultra low dose CBCT indicated that the image quality of a ultra-low-dose protocol with high defination (ULHD) was diagnostically acceptable for evaluation of impacted canine. The in vitro findings need to be confirmed and transferred into clinical use. Therefore, we recommend the ULHD for clinical trail since it provides comparable diagnostic information at a radiation dose of 37% of the standard protocol. The outcome of this project has significant implications in minimizing the late stochastic radiation-induced cancer risk for children with impacted canines.

Maxillary canine impaction is a common problem in children with an incidence of 1-5.2%. The impacted tooth may hinder orthodontic movement, cause root resorption on adjacent teeth and compromise both esthetic and functional outcome. An accurate diagnosis based on proper clinical and radiographic evaluation is critical for the success of treatment. Until the introduction of cone beam computed tomography (CBCT), two dimensional radiographs with multiple projections have been used as routine radiographic examination for diagnosis on impacted teeth. The potential for extracting additional diagnostic information from CBCT images and the ease of obtaining volumetric scans, make CBCT both useful and popular in dentistry. On the other hand enough attention has to be paid on the radiation risk, which may irreversibly damage cellular DNA and cause cancer later in life. A recent publication shows that the radiation risk is up to 132 times higher when applying CBCT on child phantom compared with that of two intraoral radiographs. Therefore the aims of present proposal are first to investigate whether the newly introduced ultra-low dose CBCT, up to 77% dose reduction, provide diagnostically acceptable image quality for assessment of impacted canine through a prospective study. Secondly, to compare the diagnostic efficiency of CBCT examinations on children with impacted canines, with a special interest to investigate whether additional diagnostic information, extracted from the CBCT images, would affect the therapy planning of the patients. The outcome of this project has significant implication in many aspects including minimizing radiation risk for children with impacted canines; correct targeting the group of patients in which the CBCT examination is beneficial for their therapeutic planning and eventually enhancing the cost-effectiveness of CBCT examination for the society.

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BEHANDLING-God og treffsikker diagnostikk, behandling og rehabilitering