Cone Beam Computed Tomography and Impacted Maxillary Canines : Dose, Optimisation, and Justification

Retinerte hjørnetenner i overkjeven som er sperret av andre tenner for å vokse ut, er den vanligste grunnen til bruk av Cone Beam Computed Tomography (CBCT) hos barn og unge. Hvis diagnostisering av de retinerte hjørnetenner mangler eller kommer sent, kan rotresorpsjon forekomme på de permanente nabo tennene. Resorpsjonene kan senere føre til behov for kjeveortopedisk behandling, kirurgiske ekstraksjoner og i noen tilfeller implantat eller andre proteseløsninger. Retinerte hjørnetenner oppdages vanligvis hos barn ved klinisk undersøkelse i kombinasjon med intraorale og panorama røntgenbilder. Når mer informasjon er nødvendig for diagnostikk og planlegging, er CBCT-undersøkelse berettiget. På grunn av råd om strålevern er det enighet om at CBCT ikke bør brukes ved førstehånds undersøkelse, men det er fortsatt ingen konsensus om hvorvidt CBCT påvirker terapiplanlegging blant klinikere. Den ideelle radiografiske modaliteten og eksponering varierer, avhengig av den klinisk situasjonen. Når ioniserende stråling benyttes for å undersøke pasienter, må man være oppmerksom på balansen mellom fordelene for pasienten og klinikeren og risikoen ved stråling. Denne doktorgradsavhandlingen hadde som mål å vurdere belastningen ved strålingsdose for barn der retinerte hjørnetenner ble undersøkt. Avhandlingen ser også på metoder for å begrense doseeksponering ved å bruke protokoller for å optimaliserte en lav dose og begrense CBCT-undersøkelsene. Første artikkel i avhandlingen hadde som mål å se effektiv dose ved å sammenligne todimensjonale (2D) undersøkelser (panorama og periapikale røntgenbilder) og tredimensjonale (3D) CBCT. Dosen fra 2D-undersøkelse og CBC fra to enheter (Promax3D og NewTom 5G) ble sammenlignet etter måling av doser på et antropomorft barnefantom. Dosen fra CBCT-undersøkelsen var fra 15 til 140 ganger høyere enn for de konvensjonelle 2D-undersøkelsene, avhengig av CBCT-enhet og type 2D-undersøkelse. Andre artikkel evaluerte bildekvalitet og synlighet av anatomiske strukturer på lavdose CBCT-skanning og effekten av et støyreduksjonsfilter for vurdering av overkjevens front. Flere CBCT-protokoller (Promax3D), blant annet fire lavdoseprotokoller, ble testet på skallefantomer for å sammenligne bildekvalitet og synlighet av anatomiske strukturer som er relevante for vurdering av retinerte hjørnetenner. Tre av lavdoseprotokollene gav akseptabel diagnostisk bildekvalitet, selv om dosen ble redusert med 61 % – 77 %. I tredje artikkel ble det undersøkt hvordan CBCT påvirker behandlingsplanen til pasienter med retinerte hjørnetenner, samt mulige kliniske og 2D-bilde markører for planlagt CBCT-bruk. For å avgjøre om CBCT var berettiget for planlegging av behandling, evaluerte og planlagt en tverrfaglig gruppe 89 kasus med retinerte hjørnetenner. Mer enn halvparten av CBCT-undersøkelsene ble vurdert som uberettiget. Planlagt behandling ble endret i 9,8 % av tilfellene. Variable målt før CBCT som predikerte behovet for ytterligere CBCT, var horisontalt plasserte hjørnetenner, strategi for ekstraksjon på permanente tenner, og bukkalt posisjonerte hjørnetenner. Denne avhandlingen viser at, CBCT medfør høyere effektiv dose for pasienter sammenlignet med konvensjonell 2D røntgenbilder. Dosene pasienter får ved undersøkelse av retinerte hjørnetenner kan minimeres ved å 1) optimalisere protokoller for lavdose CBCT og 2) begrense bruk av CBCT til tilfeller der ytterligere 3D-informasjon er viktig for videre terapeutisk behandling.Impacted maxillary canines are the most common reason for Cone Beam Computed Tomography (CBCT) examinations of the anterior maxilla in children and adolescents today. If impacted canines are missed or diagnosed late, root resorptions may occur on permanent adjacent incisors. In turn, these resorptions may lead to the need for further orthodontic treatment, surgical extractions, and even implants or other prosthetic solutions. Impacted canines are usually discovered in children via clinical examinations in combination with intraoral periapical radiographs and panoramic images. When more diagnostic information is needed, the next step is a CBCT examination. While regulating authorities in radiation protection agree that CBCT should not be used first-hand, there is still no consensus over whether CBCT alters therapy planning amongst clinicians. The ideal radiographic modality and exposure parameters vary, depending on each individual clinical task. When using ionizing radiation to examine patients, attention must be paid to the balance between the benefit to the patient and clinician contra the radiation risk. This thesis aimed to assess the radiation dose burden to children examined for impacted canines and explore methods of limiting dose exposure by applying optimised low-dose protocols and by limiting CBCT examinations through a justification process performed at the therapeutic thinking level. The first paper aimed to measure the effective dose using two-dimensional (2D) examinations (panoramic and periapical radiographs) and three-dimensional (3D) CBCT devices. 2D examination doses and CBCT doses from two devices (Promax3D and NewTom 5G) were compared after measuring organ doses on an anthropomorphic child phantom. The dose from CBCT examinations ranged from 15 to 140 times higher than conventional 2D examinations, depending on the CBCT unit and the type of 2D examination. The second paper evaluated overall image quality and visibility of anatomic structures on low-dose CBCT scans and the effect of a noise reduction filter for assessment of the anterior maxilla. Multiple CBCT protocols (Promax3D), including four low-dose protocols, were tested on dry skull phantoms to compare overall image quality and visibility of anatomic structures pertinent to impacted canine assessment. Of the low-dose protocols, three provided acceptable diagnostic image quality while reducing the dose by 61% – 77%. The third paper investigated how CBCT affects the treatment plan of patients with impacted canines, as well as identified possible clinical and 2D imaging markers for the justified CBCT examination at the therapeutic thinking level. To decide whether CBCT was justified for therapy planning, an interdisciplinary therapy-planning group evaluated impacted canine cases and decided treatment alternatives, first without and later in addition to diagnostic information from CBCT examinations. More than half of the CBCT examinations were considered unjustified, and the therapy plan changed in 9.8% of the cases. Variables measured prior to CBCT that predict the need for further CBCT examinations were horizontally positioned canines (OR= 10.9, p = 0.013 when compared to vertically positioned canines), when extraction strategy was involved (OR = 6.7, p = 0.006), and buccally positioned canines when compared to palatal (OR = 5.3, p = 0.047), central (OR = 25.0, p = 0.001), and distal or uncertain positions (OR =7.7, p = 0.005). Even when optimised, CBCT examinations come at the cost of a higher radiation dose than conventional 2D images. Based on the papers comprising this thesis, patient dose burdens can be minimized when assessing impacted maxillary canines in radiosensitive paediatric patient populations by 1) optimising low-dose CBCT protocols and 2) limiting CBCT exposures to cases where additional 3D information is important for therapeutic thinking and planning.Doktorgradsavhandlin

Comparative study of orthopantomograph & cone beam computed tomography as pre-operative diagnostic tools for lower third molar surgery

Introduction Lower third molar surgery is a common and relatively uncomplicated procedure. Commonly indicated where there is infection, bony pathology, soft tissue pathology or damage to the adjacent tooth. Difficult surgical challenges and unpredictable surgical outcomes can be caused by wide variations in the position and anatomy of the mandibular third molar roots, and relationship of these roots to the mandibular canal containing the Inferior Alveolar Nerve (IAN) may at times present the surgeon with inadvertent crush injury, stretch injury or even severing of the inferior alveolar nerve. Appropriate imaging and treatment planning results in predictable surgical outcome. The relative relationship and proximidity of the mandibular third molar roots to the inferior alveolar canal can be predicted by several radiographic signs displayed on an orthopantomograph (OPG), including darkening of the roots, deflection of the roots, narrowing of the roots, dark and bifid roots, interruption of white line(s), diversion of the inferior alveolar canal and narrowing of the inferior alveolar canal. An OPG is however limited by depth of view, superimposed structures and distorted structures with positioning errors. Cone-Beam Computed Tomography (CBCT) is a radiographic imaging method which may provide the ability to predict more accurately the relationship of the root(s) to the inferior alveolar canal, and therefore a more predictable and favourable outcome. CBCT has been in use at Sydney’s Westmead Centre for Oral Health (WCOH) since 2006. The purpose of this study is to evaluate whether OPG alone or utilisation of OPG and CBCT together provides the more predictable outcome following surgery where there has been a close relationship of the roots to the inferior alveolar canal. Methods A retrospective study was performed of lower third molar cases that were managed at Westmead Centre for Oral Health, Westmead NSW, between November 2005 to August 2006 prior to CBCT (Group one) and November 2010 to August 2011 following CBCT (Group two). The study involved examination of de-identified pre-operative, operative and post-operative written records, as well as the OPG and relevant CBCT records. Relevant data was tabulated along with any associated complications in an excel spreadsheet. The variables within the data and the two groups were crosstabulated and analysed with a statistic software (SPSS). Results Total of 590 surgical cases were included in the study, with 265 in group one and 325 in group two. Post-operative complications totalled 9, where group one had 6 and group two had 3. Numbers with no post-operative complications totalled 581, with 259 for group one and 322 for group two. Discussion A two by two risk calculation demonstrated reduction of IAN complication by 50% with CBCT, with a risk ratio of 2.45 and risk difference of 0.0134. The numbers needed to be treated were calculated from there as 75. With CBCT, the superimposed structures can be eliminated and distortions minimised, via the mode of image scanning and digital software manipulation of the DICOM data set, so providing more depth of view and allowing a more accurate measurement of relative position between the roots of lower third molar teeth and inferior alveolar nerve. Coronal, sagittal, axial and panoramic views obtained from CBCT allow three-dimensional evaluation of the relationship between the roots of lower third molar teeth and inferior alveolar nerve. This may influence surgical techniques to provide more accurate and safer surgery or influence an alternative treatment plan such as coronectomy or leaving the impacted tooth in-situ. Safer outcome would not only benefit the patient and the surgeon, but may reduce costs to the institution, the community and the profession in terms of medico-legal liability and indemnity. One disadvantage of CBCT include the higher radiation dosage that the patient is exposed to when compared to OPG, but relatively lower radiation dosage than helical beam CT. Another disadvantage of CBCT is the high initial cost, as well as maintenance and replacement cost of each unit, whilst that of OPG remains relatively low. The cost effectiveness of CBCT needs to be considered, whereby an institution such as WCOH receives high numbers of external and internal referrals, which may justify these associated costs when weighted against the benefits to the patient and the surgeon by the 50% reduction in complications. Conclusion It can be concluded from the results that seventy five lower third molar surgeries are needed to be performed utilising CBCT as pre-operative diagnostic tools in order to reduce the incidence of inferior alveolar nerve complication by one. This study has been a retrospective study. A randomised prospective study would be the next step to verify the accuracy and demonstrate the benefits of CBCT

Evidence-Based Indications of Cone Beam Computed Tomography in Children with maxillary impacted canines - A literary review

Prosjektoppgåve/masteroppgåveOD3PROSJMAOD-ODON

Development of a Deep Learning Algorithm for Periapical Disease Detection in Dental Radiographs

Periapical radiolucencies, which can be detected on panoramic radiographs, are one of the most common radiographic findings in dentistry and have a differential diagnosis including infections, granuloma, cysts and tumors. In this study, we seek to investigate the ability with which 24 oral and maxillofacial (OMF) surgeons assess the presence of periapical lucencies on panoramic radiographs, and we compare these findings to the performance of a predictive deep learning algorithm that we have developed using a curated data set of 2902 de-identified panoramic radiographs. The mean diagnostic positive predictive value (PPV) of OMF surgeons based on their assessment of panoramic radiographic images was 0.69(± 0.13), indicating that dentists on average falsely diagnose 31% of cases as radiolucencies. However, the mean diagnostic true positive rate (TPR) was 0.51(± 0.14), indicating that on average 49% of all radiolucencies were missed. We demonstrate that the deep learning algorithm achieves a better performance than 14 of 24 OMF surgeons within the cohort, exhibiting an average precision of 0.60(± 0.04), and an F1 score of 0.58(± 0.04) corresponding to a PPV of 0.67(± 0.05) and TPR of 0.51(± 0.05). The algorithm, trained on limited data and evaluated on clinically validated ground truth, has potential to assist OMF surgeons in detecting periapical lucencies on panoramic radiographs

Evaluation of cone beam computed tomography with respect to effective radiation dose and diagnostic properties

Cone beam computed tomography (CBCT) is an x-ray modality providing three-dimensional x-ray images. CBCT devices have high resolution compared to traditional medical CT, making them suitable for examination of fine details. However, CBCT devices are worse at showing contrast differences, making them less suitable for examinations of soft tissue such as the brain and many other internal organs. An x-ray modality suitable for imaging of small details and hard tissue fits dental and maxillofacial radiology well. After the introduction of dentomaxillofacial CBCT in 1998, CBCT examinations have spread to become a common and important diagnostic tool in odontology. Today, CBCT examinations complement or replace examinations previously performed by other methods. When choosing an x-ray imaging modality and examination parameters, concern must be taken for the diagnostic value and the radiation dose. The examination should be chosen to provide as low radiation dose as possible while not sacrificing the diagnostic value. In order to provide guidelines on the use of CBCT, scientific knowledge on CBCT and alternative examinations are needed. What is the radiation dose for different examinations and how does the examination affect diagnosis and treatment? This thesis aims to provide additional information in this field, to provide reference data when considering the choice of examination and the establishment of guidelines. In the first paper, examinations of the temporomandibular joint, using CBCT and traditional medical multi-detector CT (MDCT), were compared to determine if CBCT examinations would result in lower radiation dose. The examinations were optimized to find the lowest suitable dose levels, and at these optimized dose levels no significant difference was found between CBCT and MDCT. The second paper investigated the radiation dose from multiple different x-ray examinations of possible resorption impacted maxillary canines in children. CBCT examinations were compared to two-dimensional examinations using intraoral radiographs, and in some cases panoramic radiographs. CBCT examinations ranged from 15 to 140 times higher radiation dose, depending on x-ray device. The third paper investigated the possibility of reducing the image size, and therefore the x-ray dose, in panoramic radiographs. A full-size panoramic radiograph was required in 20% of adult patient cases. The introduction of two different image sizes for adult patients would reduce the collective radiation dose from panoramic examinations by about 40% in our university clinic. The fourth paper investigated radiation doses from different examinations and settings using the Newtom 5G CBCT device. This CBCT model use automatic exposure control and does not allow manual adjustment of exposure parameters. The resulting effective doses should be applicable to examinations of adult patients using this CBCT model

Development of a Web-based Instructional Module for Interpretation of Craniofacial Cone Beam CT Pathology

The introduction of Cone Beam Computed Tomography (CBCT) in dental practice constitutes a paradigm shift in the way clinicians look at and interpret diagnostic information. With the rapid pace of CBCT development, and with new manufacturers and models appearing in the market each year, it is clear that this technology is assuming an increasingly important role in dental diagnosis. Because of this it will be important to provide a solid foundation on which dental students, general practitioners and specialists alike can build diagnostic skills utilizing this imaging modality. CBCT provides volumetric scans of the patient head that can be visualized in a variety of ways both in 2D and 3D. The newly developed MARCILAN website offers a highly interactive, multimedia rich, web-based, didactic module for interpretation and correlation of 3D anatomical structures as seen on CBCT. However, the current offering does not include a module to aid clinicians in the diagnosis of pathological conditions. The purpose of this study is to develop a web-based instructional module to interpret pathology as presented on cone beam CT images

Diagnostic accuracy of maxillary periapical pathology perforating the sinus floor: a comparison of pantomograph and CBCT images

>Magister Scientiae - MScPeriapical lesions are fairly common pathology associated with the apex of a non-vital tooth. Some chronic lesions develop without an acute phase with no recollection of previous symptoms. It is known that maxillary odontogenic infections can breach the sinus floor with succeeding complications. Pantomography, a widespread conventional radiographic technique, provides a generalized view of the maxillofacial region. Advanced modalities like CBCT may facilitate in navigating complex anatomy, which would otherwise be obscured

The prevalence and pattern of mid facial fractures at Tygerberg oral health centre

>Magister Scientiae - MScBackground: Changing trends have been observed in the prevalence, etiology, imaging practice and pattern of presentation of mid facial fractures in different geographical regions. Conventional (plain) radiographs remain the most common initial investigative tool for general appraisal of suspected fractures, while advanced imaging is currently the most common final investigation. This study explored the clinico-radiologic patterns of mid facial fractures with main focus on demographic characteristics, etiology, fracture patterns and imaging practice. Aim: To determine the Prevalence, Clinical and Radiologic patterns of mid-facial fractures at Tygerberg Oral Health Centre, Faculty of Dentistry, University of the Western Cape Methodology: A retrospective cross sectional quantitative descriptive study of mid facial fractures was conducted at The University of the Western Cape’s Faculty of Dentistry based at the Tygerberg Oral Health Centre (TOHC). The study population comprised 239 patients who presented with mid facial fractures over 2 years, from January 2015 to December 2016. The data captured included demographic details, etiology, fracture site(s) and radiological investigations performed. Results: A vast male predominance was observed (M: F=5.3:1). The age range was 7-76 years (mean 31.94; SD 13.13). The most affected age category was 21 to 30 years (39.7%) while the least affected groups were children aged 0 to 10 years and patients above 70 years old. A total of 285 individual fractures were identified among the 239 patients (mean of 1.2 fractures per patient). The most common pattern of fracture was zygomatic complex (24.9%) while Le Fort fractures were the least common (5.3%). 20.1% of patients had concomitant fractures of other bones of the face and skull. There was no association between gender and site of fracture (p = 0.812). Panoramic radiography was the most common initial investigation. A panoramic radiograph in combination with various conventional extraoral views were sufficient for diagnosis in 18.8% of the patients. However, majority (53.6%) had all the three types of imaging performed (panoramic radiograph, conventional extra oral views and advanced imaging). The most common etiological factor was assault (73.6%). There was no association between gender and aetiology of fracture (p = 0.537