University of Manchester



(Periodontology 2000)The use of cone beam computed tomography (CBCT) in implant dentistry: current concepts, indications and limitations for clinical practice and researchMichael M. Bornstein1,2, Keith Horner3, Reinhilde Jacobs21Department of Oral Surgery and Stomatology, Section of Dental Radiology and Stomatology, School of Dental Medicine, University of Bern, Bern, Switzerland2OMFS IMPATH Research Group, Department of Imaging and Pathology, Faculty of Medicine, University of Leuven and Department of Oral and Maxillofacial Surgery, University Hospitals Leuven, Leuven, Belgium 3University Dental Hospital of Manchester, School of Dentistry, Oral and Maxillofacial Imaging, Higher Cambridge Street, Manchester M15 6FH, United KingdomCorrespondence to:Prof. Dr. Michael M. BornsteinDepartment of Oral Surgery and StomatologySection of Dental Radiology and StomatologyFreiburgstrasse 7, CH-3010 Bern, SwitzerlandPhone: +41 31 632 25 45/66, Fax: +41 31 632 09 14e-mail: michael.bornstein@zmk.unibe.chAbstractDiagnostic radiology is an essential component of treatment planning in the field of implant dentistry. The present narrative review will present current concepts for the use of cone beam computed tomography (CBCT) imaging prior to and following implant placement in daily clinical practice and research. Guidelines for the selection of 3D imaging will be discussed, and also limitations highlighted. Current concepts of radiation dose optimisation including novel imaging modalities using low dose protocols will be presented. For pre-operative cross-sectional imaging, data are still not available that CBCT results in less intraoperative complications such as nerve damage or bleeding incidents, or that implants inserted using pre-operative CBCT data sets for planning purposes will exhibit higher survival or success rates. The use of CBCT following the insertion of dental implants should be restricted to specific post-operative complications such as damage of neuro-vascular structures or post-operative infections in relation to the maxillary sinus. Regarding peri-implantitis, the diagnosis and severity of the disease should be evaluated primarily based on clinical parameters and radiological findings based on periapical radiographs (2D). The use of CBCT scans in clinical research might not yield any evident beneficial effect for the patient included. As many of the CBCT scans performed for research have no direct therapeutical consequence, dose optimisation measures should be implemented by using appropriate exposure parameters and reducing the field of view (FOV) to the actual region of interest. IntroductionSince its initial description in 1998 by Mozzo and co-workers (99), three-dimensional (3D) radiographic imaging using cone beam computed tomography (CBCT) has become an established diagnostic technique in dental medicine for various indications in the fields of orthodontics (80, 87, 116), endodontics including apical surgery (109, 129, 153), periodontology (154), oral and maxillofacial surgery (3), and implant dentistry (17). CBCT imaging appears to offer the potential of an improved diagnostic value for a wide range of clinical applications, and usually at lower doses than with multislice computed tomography (CT). However, apart from applications in implant dentistry, CT has few uses in dentistry, and CBCT results in increased radiation doses compared with conventional (two-dimensional / 2D) dental radiographic techniques. Although CBCT imaging still continues to gain popularity, its use currently is primarily recommended in cases in which clinical examination supplemented with conventional 2D intra- and extra-oral radiography cannot supply satisfactory diagnostic information. Thus, CBCT scanning has to be considered basically as an adjunctive diagnostic radiographic modality (40, 41).In 2009, the European Academy of Dental and Maxillofacial Radiology (EADMFR) published basic principles on the use of CBCT imaging (Table 1; 69). The set of 20 principles was formulated to act as core standards for EADMFR, and to be adopted and to be of value in national standard-setting procedures within Europe. The first eight statements relate principally to justification of CBCT examinations, while the first four of these implicitly condemn routine 3D examinations. Statements nine to fifteen deal broadly with optimisation and dose limitation. The final statements (sixteen to twenty) discuss training and competence issues as in some countries of the European Union, CBCT equipment can be purchased, installed and used by a dentist with no specific requirement for additional training. The EADMFR maintains the view that, with adequate training, it is reasonable to expect dentists to perform evaluation of images in the familiar area of teeth and their supporting structures, while advocating a specialist evaluation for other anatomical areas. This vision is also maintained in the 2012 European evidence-based guidelines on the use of CBCT for dental and maxillofacial radiology (44).The present review will present current concepts for the use of CBCT imaging prior to and following implant placement in daily practice and research. Guidelines for the selection of 3D imaging will be discussed, and also limitations highlighted. Current concepts of radiation dose optimisation including novel imaging modalities using low dose protocols will be presented. Finally, new imaging technologies under investigation will be reviewed, and evaluated for their potential as future options for imaging in oral implantology.Aspects of radiation exposure when using CBCT in implant dentistry Patient risk from radiation is a continuing concern, due to the high frequency of dental radiographic examinations in developed countries (145). In the context of dental CBCT, where higher radiation doses are usually seen than for conventional (2D) radiography, it is important to consider the risks that are associated with exposure to X-radiation. These risks are stochastic in nature; specifically cancer induction. “Stochastic” means that there is a statistical probability (risk) of an adverse event occurring as a result of the X-ray exposure. The risk is proportional to the dose, but it is generally accepted that there is no “safe” dose of radiation. The risk is age-related, with children having higher risks than adults for the same radiation dose, a fact that has particular dental relevance. It is reassuring therefore, that in implant dentistry, the age of patients tends to be concentrated in older adults (14, 44) and the risk is lower. Nonetheless, in the absence of a ?safe“ dose of X-rays, attention to radiation protection of patients cannot be neglected. Pauwels et al. (111) reported that the lifetime attributable cancer risk for CBCT, expressed as the probability to develop a radiation-induced cancer, varied between 2.7 per million (age > 60) and 9.8 per million (for patients ranging between 8 to 11 years) with an average of 6.0 per million. On average, the risk for female patients was 40% higher. Overall, the estimated radiation risk was primarily influenced by the age at exposure and the gender, pointing out the continuing need for radiation protection, particularly in younger age groups.Principles of radiation protectionTo reduce levels of radiation-associated risk, it is essential to adhere to radiation protection principles. These are: justification, optimisation and limitation of doses (73). Only the first two of these apply to patients because there can be no dose limits in this context. For staff working with radiation and the wider public (excluding patients), dose limitation is the paramount principle of radiation protection, although optimisation of patient dose will sometimes translate into lower doses to the clinical staff performing the procedure.Under normal circumstances, the risk from dental radiography is very low. Nonetheless, it is essential that every radiographic examination should show a net benefit to the patient. The use of radiation is accepted when it is expected to do more good than harm, weighing the total potential diagnostic benefits it produces against the individual detriment that the exposure might cause (justification). The criteria for X-ray imaging should be reviewed from time to time as more information becomes available about the risks and effectiveness of the existing procedure, and as new procedures emerge. The process of justification requires adequate knowledge of the patient’s history and the results of the clinical examination. When acting as a referrer, the dentist should therefore ensure that adequate clinical information about the patient is provided to the person taking responsibility for the radiographic examination (63, 69).Optimisation of dose in radiological procedures is often defined by the ALARA principle. ALARA is the acronym for "As Low As Reasonably Achievable", referring to the radiation dose (45). Implementing ALARA into practice involves consideration of many factors, including initial equipment selection, maintenance, individualised selection of X-ray exposures and an ongoing quality assurance programme, all aimed at consistent production of adequate diagnostic information at the least exposure to ionising radiation, taking into account economic and social factors. Regular quality control tests are involved, including regular equipment testing, patient dose audit and image quality assessment. Radiation doses with CBCT equipmentRadiation dosimetry can be confusing to the novice, as there are several different concepts and multiple units used. The dose metric commonly reported in literature is effective dose (E), defined by the International Commission on Radiological Protection (ICRP) as the weighted sum of absorbed doses from different radiosensitive organs (73). It is measured in sievert (Sv) or, more usually, as millisieverts (mSv) or even microsieverts (?Sv). The reason for this complicated concept is that different organs and tissues have different radiation sensitivities; thus a specific x-ray exposure to one part of the body, e.g. the abdomen, would give a very different dose and risk if applied to another, e.g. the face.Because almost all the organs and tissues for which dose measurements are needed to calculate E are internal, it cannot be measured in patients directly, so it is usually measured using an anthropomorphic phantom, representing an average human (141). E provides an estimation of the stochastic risk for an average sized adult reference patient. In practice however, patient dose will vary between individuals, with patient size and mass as main influencing factors (25, 92). Although it is possible to purchase different sizes of dosimetry phantoms representing females and children to provide more appropriate measurements of E, multiple calculations of E for different scenarios is very time-consuming. Dedicated Monte Carlo computer simulations offer a valuable alternative which can model a wide variety of imaging systems, exposure variables and examination of different gender and ages (134, 158, 159).A large number of dental CBCT devices are currently available on the market (104), and considerable variability in radiation doses has been reported for these (17, 110). In a recent systematic review by Bornstein and co-workers (17), CBCT devices were grouped according to their FOV, resulting in three categories: CBCT devices with small, medium, and large FOVs. When analyzing the reported E ranges for all three groups, there were wide range of doses ranging from 11-252 ?Sv for small, from 28-652 ?Sv for medium, and from 52-1'073 ?Sv for large FOVs. The authors therefore concluded that a single average E value is not a concept that should be used for the CBCT technique as a whole, when comparing it to alternative radiographic methods. As most devices exhibited E in the 50-200 ?Sv range, it can be stated that CBCT imaging results in higher patient doses than standard 2D radiographic methods used in dental practice but remain well below those reported for common multi-detector CT protocols. It is important to recognise that doses in children may be different to those in adults, due to relative sizes and different radiosensitive organ positions in the body (140). For example the proportionally greater thyroid dose in children was highlighted in a recent meta-analysis (91).?Image quality and radiation doseWhen trying to practise ALARA, it is essential to recognise the close relationship between image quality and radiation dose. It would be easy to reduce radiation doses to extremely low levels, but this might make images diagnostically useless. In reality, we require diagnostically adequate images rather than the highest quality. Consequently, the ALARA principle has been recently modified to emphasise the need to give equal weighting to image quality and dose in optimisation. This has resulted in the new concept of ALADA / "As Low As Diagnostically Acceptable“ (75). For CBCT equipment, a key influence on radiation dose and image quality is the selection of exposure factors, e.g. X-ray tube current exposure time product and operating potential (55). Some CBCT equipment offers high resolution programs; these achieve their image quality by increasing the exposures. In contrast, some equipment offer low exposure options through reducing exposure factors. A few manufacturers have incorporated automatic exposure controls (AECs) into their CBCT machines. AECs have the advantage of selecting exposures specific to each patient. The disadvantages are that the choice of image quality is taken away from the clinician and could easily be set at the wrong level for specific diagnostic tasks. Several studies have considered the impact of lowering exposure factors in the context of implant dentistry (4, 38, 135, 147, 155). All show substantial scope for reducing exposure factors, and hence patient dose, without significant loss of image quality. The impact of dose reduction techniques on the quality of 3D virtual models fabricated using CBCT data should, however, be considered when performing optimisation efforts (38). Low dose protocols have been recommended to assist practitioners in optimisation, such as that proposed by Harris et al. (63). A low dose protocol for pediatric CBCT has been developed which represents as much as a 50% reduction compared with manufacturer's recommendations for that specific piece of equipment (65). However, in practice, dentists are likely to depend on manufacturers‘ instructions on appropriate exposure settings, so it is encouraging that new low-dose protocols have also been developed by manufacturers. An example is the Ultra Low Dose protocol proposed by Planmeca (Helsinki, Finland) which allows operators to adjust imaging parameters individually, in particular the mA values. These can be adjusted for patient groups by selecting the mA value of the scan according to patient size (small / medium / large). This results in E values for CBCT scans in the range of panoramic views. Although there is still a need to determine for which clinical indications the image quality provided by these low-dose protocols is sufficient, these radiation doses (in the range of those given by panoramic radiography) could allow CBCT scans to be used as primary imaging modalities in specific circumstances (18). Although a dose advantage is frequently cited for CBCT compared with mulitslice CT, low-dose protocols are possible for the latter. Depending on the model and setting used, radiation levels for multislice CTs may even be lower than for CBCT scans (67, 156). This progress in dose optimisation for 2D and 3D technologies in dentomaxillofacial radiology demonstrates clearly that radiation dose exposure and risks are a dynamic field, and need to be constantly monitored and updated by the clinician for the respective radiographic device used in daily practice. Only by doing so, the practitioner can really comply to ALADA principles and implement radiation protection into daily routine.Recommendations for CBCT imaging for dental implant treatment planning (pre-operative imaging)In a recent survey from Norwegian dental clinics on the use of CBCT (68), the most common indications for this imaging modality were implant treatment planning (34% of all clinics) and localization of impacted teeth (43% of the clinics). As implant treatment planning is one of the most common indications for radiographic 3D imaging, accepted recommendations and guidelines for the use of CBCT for this purpose are clearly needed. Clinical guidelines are able to provide a framework for the use of a new technology or technique, and are designed to assist the clinician and patient in making appropriate decisions for certain specific clinical circumstances. There are three fundamental approaches to guideline development. The first is to rely on the opinion of an expert panel. The second is to employ a consensus method, and the third is to use an “evidence based” guideline development methodology. Evidence-based methods are considered as being optimal to limit the influence of individual opinion and bias by using defined and objective methods based upon a systematic review of the literature (58, 92). In a recent review, Horner and colleagues (70) identified 26 publications containing guidelines on the clinical use of CBCT in dental and maxillofacial radiology. The articles selected by the authors that were specifically addressing the use of CBCT in dental implant treatment planning were somewhat conflicting in their recommendations: three publications recommended CBCT imaging for planning prior to all dental implant placements (39, 105, 143), other guidelines consider a selective approach as appropriate (10, 63), while a further group of publications gave equivocal statements (2, 34, 61).Diagnostic imaging is an essential component of treatment planning in oral rehabilitation by means of osseointegrated dental implants. Some authors have demonstrated that clinical examination and panoramic radiography alone may provide sufficient imaging for posterior mandibular implant placement (71, 137), especially when there is a 2 mm margin of safety above the inferior alveolar canal (150). The European Association for Osseointegration (EAO) Guidelines for the use of diagnostic imaging in implant dentistry were published in 2002 (62). Since the publication of the EAO Guidelines in 2002, CBCT has become available offering cross sectional imaging and 3D reconstructions at potentially lower radiation doses when compared to medical multislice CT. Experts in both clinical practice and radiology were invited for a closed workshop held at the Medical University of Warsaw, Poland in May 2011, to review and update the initial EAO guidelines (63). Regarding the issue of what radiological information does a surgeon require when planning for implant placement, the authors stated that a clinician requires information on bone volume, structure and density, topography and the relationship to important anatomical structures, such as nerves, vessels, roots, nasal floor, and sinus cavities and any clinically relevant pathology. This information is initially obtained with a clinical examination and appropriate conventional (2D) radiographs. The decision to proceed to cross-sectional 3D imaging should be based on clearly identified needs and the clinical and surgical requirements of the clinicians involved. The EAO made the following specific recommendations for the use of pre-operative cross-sectional imaging (including CBCT): when clinical examination and conventional radiography have failed to adequately demonstrate relevant anatomical boundaries or the location of important anatomical structures (1); when imaging was deemed appropriate in cases where extensive bone augmentation is anticipated (2); for all sinus floor elevation (SFE) procedures (3) and guided implant surgery (computer-assisted planning and placement of dental implants) cases (4); when further information regarding intra-oral autogenous bone donor sites is needed (5); when planning the use of special surgical techniques such as zygomatic implants or osteogenic distraction (6).In a recent systematic review by the International Team for Implantology (ITI) from the consensus conference in Bern in 2013 (17), the authors have identified numerous articles describing the importance of various anatomic structures identified on cross-sectional imaging including the inferior alveolar (mandibular) canal, anterior loop and mandibular incisive canal, mental foramen, lingual canal, submandibular gland fossa / lingual undercut, maxillary incisive / nasopalatine canal and maxillary sinus and their relation to implant placement. Although the placement of dental implants is an important cause of iatrogenic inferior alveolar nerve injuries (51, 118, 133, 138), especially when focusing on permanent neurosensory disturbances (88), it has to be stated that it will be difficult to prove a clear benefit of CBCT over conventional 2D imaging such as panoramic radiography with respect to damage prophylaxis of the IAN or other vital neurovascular structures in prospective studies. This is simply related to the fact that the sample sizes needed for such controlled prospective clinical trials will be difficult to achieve (120), and furthermore, many institutional review boards and ethical committees will not approve studies comparing complex surgical interventions performed in a randomized fashion using 2D alone versus a group of patients that benefits from 2D in combination with 3D imaging (CBCT; 59). Besides neurosensory disturbances, neurovascular complications due to implant surgery can also result in severe post-operative hemorrhage. Significant hemorrhages are mostly described after anterior mandibular implant placement, and SFE procedures prior to or with implant placement (for review see 74).A scientifically proven beneficial effect of CBCT imaging over 2D radiographs alone to decrease complications caused by anatomical constraints is still missing. Yet, there is evidence that planning dental implants based on panoramic views versus CBCT scans exhibits siginificant deviations from normal anatomy (139). In a recent study, the efficacy of observers’ prediction for the need of bone grafting and presence of perioperative complications was evaluated on the basis of CBCT and panoramic radiographic planning as compared to the surgical outcome (60). Patients were included if both panoramic images and CBCT scans had been taken with a maximum interval of four months and if the presurgical planning phase was followed by implant placement. Four observers carried out implant planning using panoramic image datasets, and at least one month later, using CBCT scans. The findings of the study indicated that CBCT-based pre-operative implant planning enabled treatment planning with a higher degree of prediction and agreement as compared to the surgical standard. In panoramic-based surgery, the prediction of implant length was poor. There have been similar studies in recent years that at least partially confirm these findings, but also emphasize that importance of subjective factors such as observer opinion or experience (8, 35, 36, 47, 81, 115, 126).A recent systematic review by Vogiatzi and co-workers (151) stated that one of the main reasons for CBCT imaging in dental medicine was the assessment of the residual ridge and maxillary sinus prior to SFE or dental implant placement. Cross-sectional imaging (CBCT) has been recommended for pre-operative evaluation of the avaliable bone in the posterior maxilla and assessing health or pathology of the maxillary sinus by several professional organizations (10, 17, 63). Vogiatzi and co-workers (151) have stated that the most common anatomic variation in the maxillary sinus is the thickness of the Schneiderian membrane, which seems to be significantly thicker in the mid-sagittal aspect and in males. Furthermore, septa within the maxillary sinus are common findings and are most frequently located in the middle region of the sinus. Their prevalence seems to be independent of age and gender. In a recent study using CBCT images to evaluate the presence and type of septa, the authors found that 66.5% of the included patients had septa, and 56.5% of the sinuses, respectively (19). In the majority of these cases, septa were observed in the first or second molar region of the floor of the maxillary sinus. Furthermore, the most common orientation of the septa was coronal (61.8%), followed by axial (7.6%), and sagittal (3.6%), but more than one fourth of the septa could not be classified as coronal, sagittal or axial, and were grouped as "other" septa. The authors also underlined that their study did not provide evidence that the frequency of maxillary sinus septa was associated with age, gender or status of the dentition of the patients. The presence of septa has been related to an increased risk for perforation of the Schneiderian membrane during SFE. In the study by Zijderveld and co-workers (160) on 100 patients scheduled for SFE, the authors reported 11 membrane perforations, 5 of them directly related to the presence of septa. In a recent investigation by von Arx et al. (152), the authors found a percentage of perforations in patients with septa of 42.9% versus 23.8% in patients without septa. There are several other factors than sinus septa that can influence the risk of a Schneiderian membrane perforation during SFE such as the presence of a narrow sinus, previous sinus surgery and absence of alveolar bone (106). Thus, detailed knowledge of the anatomic structures of the maxillary sinus seems to be beneficial prior to SFE to avoid surgical complications, which ideally is gained radiographically by the use of CBCT scans. According to the literature, a mucosal thickening of > 2 mm is classified as pathological according to the criteria defined by Cacigi and co-workers (25). If the width of mucosal thickening is < 3 mm, the detection rate on panoramic radiographs versus CBCT scans has been reported to be significantly decreased (127). To assess a potential treatment need of pathological findings in the maxillary sinus based on CBCT imaging, a classification for the morphology of the Schneiderian membrane was proposed using sagittal and coronal CBCT scans according to criteria adapted and modified from Soikkonen & Ainamo (128) in several studies (Figure 1; 16, 76, 114, 123):Healthy Schneiderian membrane: no thickeningFlat: shallow thickening without well-defined outlinesSemi-aspherical: thickening with well-defined outlines rising in an angle of > 30° from the floor of the walls of the sinusMucocele-like: complete opacification of the sinusMixed: flat and semi-aspherical thickeningsRegarding the high incidence of antral mucosal thickening found in the studies using a mucosal thickening of > 2 mm as a threshold value to distinguish physiological from pathologic findings (16, 76, 114, 123), the clinical significance of this value has to be questioned. In clinical situations when there is evidence of sinus pathology, or when the clinician believes that sinus drainage is impaired and may jeopardize the outcome of the prospective implant procedure to be undertaken, it seems advisable to consult an ear, nose, and throat (ENT) specialist (66). This is especially true for maxillary sinuses with partial or complete mucocele-like opacification of the antrum. This is also supported by a case series analyzing failures of SFE procedures reported that out of 13 patients included, pre-operative chronic maxillary sinusitis had been present in 4 patients (5). The authors therefore stated that elimination of sinusitis and other potential pathological conditions is necessary before SFE. If findings such as mixed flat and semi-aspherical thickening of the antral mucosa are visible, and the bony walls of the sinus are resorbed, leading to a discontinuity of the cortical outline, and if the roots of the maxillary teeth are resorbed, rapidly growing diseases or malignancies have to be suspected (9, 15).A still controversial issue regarding assessment and diagnosis of the maxillary sinus using CBCT imaging prior to SFE or dental implant placement is the adequate FOV. Vogiatzi and co-workers (151) have reported that there was insufficient data to comment on the effect of the FOV (small / medium versus large; one versus both maxillary sinuses visualized) of the CBCT scans on the detection and prevalence of maxillary sinus pathology. Therefore, they were not able to recommend an ideal FOV scan, nor to state that both maxillary sinuses should always be visualized when performing 3D imaging (Figures 2, 3, 4). Harris et al. (63) have stated that a pre-operative screening of the maxillary sinuses using large FOVs is not recommended for dental implant treatment planning. But in some clinical situations, when there is evidence of sinus pathology that may jeopardise the outcome of the planned surgical procedure, there may be a justification to extend the FOV to include the whole of the sinus including the ostio-meatal complex (63, 76, 123, 151). This is further emphasized by the high radiation doses applied to the eye lens using cross-sectional imaging (CBCT or multislice CT) or in the area of the paranasal sinuses, and the need to adhere to ALADA principles by always trying to implement dose reduction procedures. It needs to be pointed out here that there is increasing attention and evidence in the literature towards negative effects (i.e. cataract) to the eye lens even at low doses by radiographic imaging (112, 125). Thus, to decrease eye lens doses through FOV reduction should be kept in mind, and clinical recommendation such as visualization of the entire maxillary sinus or even bilateral maxillary sinuses using CBCT scans with medium to large FOVs for pre-operative treatment planning of dental implants is not supported by the literature, and thus not justified.In a recent study, indications and frequency for 3D imaging for implant treatment planning in a pool of patients referred to a specialty clinic over a three-year period was evaluated (19). The data exhibited that 40% of the patients included were radiographically assessed by using 2D technology alone. This demonstrated that even in a specialty clinic patients are not routinely exposed to CBCT imaging prior to implant placement. The authors reported that a typical patient receiving additional CBCT scanning for dental implant treatment planning would be over 55 years old with an extended or distal edentulous gap in the maxilla with the need for bone augmentation (simultaneous or staged). A further interesting finding of the study regarding the frequency of 3D imaging was that there was a significant increase in CBCTs over the study period from 2008 (52.4% of all patients) to 2010 (65.9%). This is certainly also an effect of the growing popularity of this radiographic methodology and its acceptance by clinicians. Therefore, it seems realistic to predict that the percentage of 3D imaging – primarily CBCT scans – will still increse over the next few years. Nevertheless, if patients are limited to straightforward implant cases, with no clinically identified local problems such as a limited horizontal ridge width, cross-sectional imaging made no difference to the implants selected based on panoramic views alone (48). The authors stated that the clinical examination provides sufficient information for selecting implant diameter and the panoramic radiograph provides sufficient information for implant length selection in standard cases.Recommendations for CBCT imaging during and / or following dental implant placementDespite careful planning, surgical complications can arise following implant placement including infection, intraoral haemorrhage, wound dehiscence, post-operative pain, lack of primary implant stability, inadvertent penetration into the maxillary sinus or nasal fossa, neurosensory disturbances, injuries to adjacent teeth, tissue emphysema, and aspiration, or ingestion of surgical instruments (56). The evaluation of complications includes careful clinical examinations and selected radiographic imaging. The EAO has published clear statements on radiographic imaging during and following dental implant surgery (63). The authors emphasized that during implant surgery conventional 2D radiographic techniques would be adequate in most cases to confirm the position of an implant in relation to anatomical landmarks. Regarding follow-up examinations, the authors stated that in the absence of symptoms, there would be no indication for cross-sectional imaging. However, 3D imaging might be helpful for the diagnosis and management of specific post-operative complications such as nerve damage or post-operative infections in relation to sinus cavities close to the inserted dental implants.Even when taken careful measures including appropriate clinical and radiographic assessments prior to surgery, nerve injuries may occur. The literature seems to indicate that three quarter of the neural injuries after implant placement result in permanent injury (88, 118, 119). In general, damage to sensory nerves can result in anaesthesia, dysaesthesia, pain or a combination of these. In case of acute nerve injury, timely nerve and implant decompression are essential with supportive analgetic or anti-convulsant therapy. Indeed, early removal of implants associated with mandibular nerve injury (less than 36 hours post-injury) may assist in minimising or even resolving neuropathy (82). The correct diagnosis of post-surgical complications based on presenting clinical symptoms (anaesthesia, dysaesthesia, pain or a combination) using 3D imaging is recommended to asses the extent of damage to neural structures (42). In this case series of inferior alveolar nerve injuries, the authors could evaluate the trauma by CBCT imaging and distinguished implant impingement, penetration, and even complete obliteration of the canal (Figure 5). Similary, neuropathic pain following implant placement in the interforaminal region of the mandible (86, 121) and the nasopalatine canal in the anterior maxilla (Figure 6; 146) have been described. When suspecting such a complication, CBCT scans can visualize the correct location of the implant. Thus, perforation of the incisive canal and nerve during implant insertion should be considered as a complication of implant surgery in the mandibular anterior area (86, 101).Accidental displacement of endosseous implants into the maxillary sinus and potential migration throughout the upper paranasal sinuses and adjacent structures is an unusual complication in implant patients. Peri-operative displacement of implants into the sinus is the obvious consequence of incorrect surgical planning, such as placement of implants in sites with inadequate bone height and volume, surgical inexperience with the anatomic landmarks of the maxillary sinus, or poor surgical performance like overpreparation of the recipient site, application of heavy force during implant insertion, or perforation of the sinus membrane during the drilling sequence (28, 50). Implant migration into the maxillary sinus may also be the more remote consequence of loss of osseointegration due to peri-implantitis or, in the case of loaded implants, inaccurate distribution of occlusal forces. In a review of published literature about accidental displacement and migration of dental implants into the upper jaw, the authors identified a total of 24 articles, the majority related to accidental displacement and migration of dental implants to maxillary sinus, but there were also case reports with migration into other craniofacial structures such as the ethmoid sinuses, sphenoid sinuses, orbit, and cranial fossae (53). Invasion of the maxillary sinus or related structures with dental implants might not be detected during implant placement. However, these complications might cause problems in the long run, and might not be adequately diagnosed using 2D imaging such as panoramic or periapical radiographs alone (157). The diagnosis of peri-implantitis is based on clinical parameters and radiological findings (122). The radiographic diagnosis of peri-implant lesions is based on periapical radiographs (2D) due to their wide accessibility in dental practice. However, this methodology has shown a significant variance in inter- and intraobserver reproducibility of the acquired measurements (57) and an underestimation of bone loss (27). Thus, CBCT scans have been proposed for diagnosis of peri-implant bone defects with the added benefit of visualizing the buccal and lingual aspects of the dental implant, and have shown an acceptable correlation with histological measurements (52). In an in vitro study comparing periapical radiographs, panoramic views, CBCT and CT scanning, CBCT showed the best image quality, and was able to visualize peri-implant bone defects in all three planes, true to scale, and without distortion (96). In a similarly designed more recent in vitro study, the best performance in detecting peri-implant bone defects and correctly confirming their absence was found for periapical radiographs, while CT scans demonstrated the lowest performance in detecting peri-implant bone defects (85). Therefore, the authors concluded that periapicals should still be recommended as favourable method evaluating bone loss around dental implants, and that 3D imaging using CBCT should rather be performed as adjunctive imaging for specific indications, where clincial and 2D radiographs have not provided sufficient information. The superiority to detect peri-implant bone defects of intraoral radiographs compared to 3D imaging using CBCT was also reported in a study assessing implants placed in fresh bovine ribs in osteotomy sites with varying peri-implant spaces (37). One important issue that limits CBCT imaging for the diagnosis of peri-implant bone defects is its association with beam hardening artefacts around metal (Figure 7; 124). It has been shown that artefacts in CBCT were always present in the proximity of implants made from titanium irrespective of the implant position in the jaw (12). Additionally, patient movement during scanning - especially when occurring several times and for an extended time period - results in motion artefacts, and may even result in a need for re-exposure of the patient (131, 132). Therefore, it is questionable whether CBCT imaging represents an adequate technique for the assessment of structures in direct or close proximity of dental implants. It should be further emphasised that CBCT machines performe differently, and only a couple of CBCT devices on the market are delivering images that are almost free of visible artefacts in the peri-implant vicinity. Yet, the resulting image quality will still depend on the local situation and the number and relative density of the available metals in the FOV and/or the entire orofacial area.CBCT imaging for clinical research purposesResearch involving human subjects is critical for advancing clinical medicine, and this is also true in the field of radiology in general. To advance our clinical understanding and practice in an appropriate manner, we must always be mindful of the requirements of ethics when conducting research with humans. Although a wide variety of ethical issues are expected to emerge in the conduct of radiology research, one ethical challenge that may be particularly likely to occur in this context is distinguishing pure research endeavors without evident and immediate benefit for the patients included from innovative treatment concepts or standard practice (21). Standard clinical practice involves interventions that are intended solely for the benefit of patients and that have a reasonable expectation of success. Innovative therapy (also termed “off-label use”) can be defined as an activity that lacks a formal evidence base. Regarding the use of CBCT imaging in the context of implant dentistry, there is often no clear benefit for the patient using 3D imaging - especially post-operatively. Therefore, justification of each additional CBCT scan is ethically important, both with regard to the interval and the total number of exposures. From a pure scientifc perspective, longterm data is always of greater value than shorterm outcomes. One should consider that there is no grey level calibration, as making the comparative appreciation of density values of CBCT scans over time unreliable (113). Furthermore, bone remodelling with its de- and remineralisation processes may take up to 6 months and more before regaining the original mineralisation level, which renders CBCT taking with shortterm intervals to assess the effect and durability of bone grafting procedures somewhat doubtful. If possible, CBCT scans should be therefore rather taken with longer intervals than planning multiple exposures during the initial postsurgical follow-up period. In a recent review, Benic and colleagues (13) stated that in ethically approved clinical research, 3D imaging (CT or CBCT) can be used to pre- and post-operatively to evaluate bone and soft tissues as well as the implant position with reference to the anatomical structures. CBCT imaging is increasingly being used for 3D assessment of bone following ridge preservation (1, 7, 95), sinus floor elevation (54, 94, 107, 144), and implant placement with simultaneous bone augmentation (23, 24, 32, 78, 84) or staged procedures following block grafts (98, 99, 130). Besides visualization of bony structures, CBCT is also used to assess the contour and dimension of the peri-implant mucosa (11, 79). This is accomplished by applying radio-opaque contrast materials such as thin foils on the surface of the mucosa, or by displacing the lips and the cheeks from the alveolar process by means of lip retractors or cotton rolls (13, 29, 30).However, it is important to differentiate the use of cross-sectional imaging which are intended to gather further basic knowledge from those that actually benefit the patient. Research using CBCT scanning should not automatically be seen as valid selection criteria for its clinical application. Before any imaging technique is put into clinical use for a specific purpose, one should ideally have evidence of patient benefit and cost effectiveness (49). Although evidence of a change in treatment plan and / or management through the use of an imaging technique is sometimes used as evidence for its acceptibility, it is weak evidence. This is due to the fact that a change in the treatment plan of a patient may lead to the same, or even poorer clinical outcomes, and may not always improve results. Interesting data has been gathered from orthodontic research, where a study on cadaver heads investigated the accuracy and reliability of buccal alveolar bone height and thickness measurements derived from CBCT images (142). The authors found that buccal bone height and buccal bone thickness was quantitatively assessed with high precision and accuracy, but the buccal bone height had greater reliability and agreement with direct measurements than did buccal bone thickness measurements. These findings were corroborated also by another group, which stated that a thin buccal alveolar bone covering is not depicted reliably by CBCT scans, and there is a risk of overestimating fenestrations and dehiscence type defects on teeth (108). Regarding the assessment of bone dimensions around implants, a study using dry mandibles evaluated the minimum labial bone thickness surrounding dental implants detected using CBCT images (103). The authors reported that only when the buccal bone on the dental implant was 0.6?mm or greater, it might be visually detectable. Thus, when the buccal bone thickness measured less, the bone plate was either underestimated or not detectable. Nevertheless, these measurements also seem to depend on the CBCT device used for the study (117). Bone density has been suggested to be an important factor influencing the success of dental implants. Areas of reduced bone density have exhibited higher failure rates and reduced primary stability values (97). A factor complicating the use of CBCT for clinical bone density assessment and follow-up of bone density changes is the lack of standardized grey value distribution. Hounsfield units (HU) have been designed for medical CT, but do not apply for CBCT (89, 90). Compared to HU units for medical CT, the reliability of CBCT-based jaw bone density assessment has been found unreliable over time and with significant variations influenced by CBCT devices, imaging parameters and positioning (102). This lack of HU standardization is a major problem for most CBCT devices, yet considering the fact that nowadays a healthy vascularized bone structure may be more beneficial for implant placement than a sclerotic poorly vascularized bone, the HU limits for implant treatment may be easily overcome. What one might need instead is a structural bone analysis, like available in dedicated μCT software. Such structural analysis has already been validated to be used for CBCT imaging (72, 148), and thus might even have clinical potential for presurgical assessment of bone quality. Recommendations for communication in a digital environmentDICOM (Digital Imaging and Communication in Medicine) was originally developed by the National Electrical Manufacturers Association (NEMA) and the American College of Radiology to create a worldwide norm for digital image acquisition, storage, and display in medicine, and also to have a standardized method for the transmission of medical images and their associated information. "Digitization" is increasingly widespread in dental medicine in terms of radiographic image acquisition (2D and 3D), optical surface scanning (intra- and extraoral), CAD/CAM systems, and the electronic charting of patient records. Unfortunately, the DICOM standard is not really fully implemented in dental medicine today, with primarily hospital and dental school settings complying with the standard (22). Picture archiving and communication systems (PACS) software act to integrate image acquisition, storage, retrieval, and viewing based on the DICOM standard. In dentistry the use of PACS is primarily limited to academic centers and dental clinics in hospital facilities where there is need for transmission of data between departments (31). Newer standard dental digital imaging devices including intraoral digital radiographic systems, panoramic views, and CBCT scanners in large part are DICOM compliant. Nevertheless, standards for DICOM compliance for some devices including CBCT and CAD/CAM systems and their interoperability with respect to PACS have not yet been fully established. This problem has already been pointed out by an expert panel of the International Team for Implantology (ITI) during the consensus conference in Bern in 2013 (18). These experts stated that to improve image data transfer, clinicians should request radiographic devices and third-party dental implant software applications that offer fully compliant DICOM data export. For most CBCT systems there is a diagnostic data loss upon transfer to DICOM/PACS and/or third party software. In addition, most third party software have some additional filtering (e.g. smoothing) at the import phase, which may result in additional information loss. It is therefore recommended to do presurgical diagnostics in the dedicated CBCT-software of the imaging device, prior to export for presurgical planning purposes. Furthermore, when performing presurgical planning, CBCT images should be made with the recommended protocol, which is not necessarily the highest resolution protocol, as the latter evidently creates more noise. Vandenberghe and co-workers (147) demonstrated that for 3D segmentation and anatomical model making, a voxel size of 200 ?m (0.2 mm) is probably sufficiently low.Other challenges in the digital data flow include the fact that there is a growing availability of non-DICOM 3D imaging data formats required to be used for an integrated virtual patient dataset (64, 77). Examples include STL and OBJ formats, respectively, used for digital intraoral impressions and printing as well as for facial scanning. Transferring those datasets to PACS is actually not possible, as such that the power of the integrated virtual patient information is lost at this level. Another point of attention is the lack of standardised grey level calibration or hounsfield scoring, making the comparative follow-up of bone healing, grafting and implant placement rather difficult and quite unreliable (113). Conclusions and outlook on novel developments in dento-maxillofacial imagingIt can be concluded that CBCT imaging is not only an established radiographic modality in treatment planning for dental implants, but its use is also becoming increasingly popular and widespread among clinicians around the globe. This is partially due to a new understanding of anatomic landmarks and structures at risk during implant placement such as neuro-vascular canals and bundles. Nevertheless, that CBCT imaging results in less intraoperative complications such as nerve damage or bleeding incidents, or that implants inserted using pre-operative CBCT data sets for planning purposes will exhibit higher survival or success rates has not been demonstrated yet in the literature. It even seems at least doubtful that this will be possible to demonstrate using a prospective and controlled trial setting for ethetical reasons. Maybe more soft factures such as the time of surgery, the onfidence of the surgeon, or even patient morbidity need to be evaluated in future clinical studies to demonstrate these potential benefits of 3D imaging over 2D imaging modalities alone prior to dental implant placement. Another reason for the growing use of CBCT scanning is the increasing popularity of computer-guided surgery that relies on digital planning based on high-quality CBCT images (136), but may also include the superimposition of intraoral scans and extraoral face scans to create a 3D virtual dental patient (77). The virtual patient concept is actually demonstrating again the need for an uniform data standard in digital imaging in dental medicine, as creating a craniofacial virtual reality model needs image fusion of DICOM, STL, and OBJ files.The use of CBCT imaging following insertion of dental implants should be restricted to specific post-operative complications such as damage to neuro-vascular structures or post-operative infections in relation to the maxillary sinus. To confirm the position of an implant in relation to anatomical landmarks after insertion, and also for evaluation of peri-implant bone conditions during follow-up visits, conventional (2D) radiographic techniques such as periapicals or panoramic views are sufficient. Regarding peri-implantitis, the diagnosis and severity of the disease should be evaluated primarily based on clinical parameters and radiological findings based on periapical radiographs (2D). To date, the literature suggest that 3D imaging using CBCT should should be rather performed as adjunctive imaging with a clear benefit for the patient in terms of diagnosis or treatment strategy chosen. Other than for daily practice, the use of CBCT scans in clinicial research might not yield any evident beneficial effect for the patient included. CBCT imaging is used in research to pre- and post-operatively evaluate bone and soft tissues as well as the implant position with reference to the anatomical structures. The effect on peri-implant hard and soft tissues of surgical techniques such as ridge preservation, SFE, implant placement with simultaneous bone augmentation or following staged procedures using block grafts is evaluated in a short- and long-term perspective with quite variable frequencies between the actual CBCT scans. As many of the CBCT scans performed for research have no direct therapeutical consequence, dose optimisation measures should be implemented by using appropriate exposure parameters and reducing the field of view (FOV) to the actual region of interest. To minimize dose exposure risks and effects from cumulated effective doses over time, CBCT scans should rather be taken with longer intervals than multiple exposures following surgery and the initial follow-up period, if possible.In radiation protetction, ALARA is the acronym for "As Low As Reasonably Achievable" and is a fundamental principle for diagnostic radiology in medicine and dentistry. This concept has been recently adapted to the ALADA ("As Low As Diagnostically Acceptable“) principle for selection and justification of the ideal imaging modality. Although, when cross-sectional imaging is indicated, CBCT has been recommended to be preferable over CT (18), imaging modalities visualizing cranio-facial hard and soft tissues without radiation exposure would be desirable. Currently, there are two modalities that show some clinical potential for this desire: magnetic resonance imaging (MRI) and ultrasound (6). MRI as a non-ionizing diagnostic tool in the dento-maxillofacial region has been limited mostly due compromised visualization of hard tissues and feasibility concerns such as availibility of the equipment and high costs (83). In a recent study on an ex vivo human jaw and in vivo, a novel protocol for MRI imaging was applied using an intraoral coil that creates an increased signal within a defined FOV to obtain high-resolution images within an acquisition time applicable for clinical routine 3D radiography (46). The authors reported that compared with CBCT and histological sections, MRI images exhibited dimensional accuracy, and the course of the mandibular canal was accurately displayed. Regarding ultrasound in dento-maxillofacial radiology and diagnosis, recent publications have reported its capability of imaging representative features for implant treatment planning in a porcine model such as implants placed in edentulous ridges, implants with simulated dehiscences, or mental foramina (33). Further research for the application of ultrasound is directed towards the sensitivity and changes of the ultrasonic response during the healing period of dental implants that could potentially predict the amount and level of osseointegration, and also be helpful in diagnosing peri-implant bone changes (149). Regarding only these two recent developments in the field of dento-maxillofacial radiology, it can be stated that this field is very dynamic and constantly changing. 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J Oral Maxillofac Surg 2008;66:1426-1438.TablesTable 1: Basic principles on the use of CBCT imaging as proposed by the European Academy of Dental and Maxillofacial Radiology (EADMFR; Horner et al. 2009)1CBCT examinations must not be carried out without a medical history and clinical examination 2CBCT examinations must be justified for each patient to demonstrate that the benefits outweigh the risks3CBCT examinations should potentially add new information to aid the patient’s management4CBCT should not be repeated ‘‘routinely’’ on a patient without a new risk/benefit assessment 5When accepting referrals from other dentists for CBCT examinations, the referring dentist must supply sufficient clinical information to allow for justification 6CBCT should only be used when the question for which imaging is required cannot be answered adequately by lower dose conventional radiography7CBCT images must undergo a thorough clinical evaluation of the entire image data set (reporting)8When soft tissue evaluation is required, the appropriate imaging should be conventional medical CT or MR, rather than CBCT9CBCT equipment should offer a choice of volume sizes and examinations must use the smallest that is compatible with the clinical situation10Where CBCT equipment offers a choice of resolution, the resolution compatible with adequate diagnosis and the lowest achievable dose should be used11A quality assurance programme must be established and implemented for each CBCT facility, including equipment, techniques and quality control procedures12Aids to accurate positioning (light beam markers) must always be used13All new installations of CBCT equipment should undergo a examination and detailed acceptance tests before use to ensure that radiation protection for staff, members of the public and patient are optimal14CBCT equipment should undergo regular routine tests to ensure that radiation protection has not significantly deteriorated15For staff protection from CBCT equipment, the guidelines detailed in Section 6 of the European Commission document Radiation Protection 136. European guidelines on radiation protection in dental radiology should be followed16All those involved with CBCT must have received adequate theoretical and practical training for the purpose of radiological practices and competence in radiation protection17Continuing education and training after qualification are required, particularly when new CBCT equipment or techniques are adopted18Dentists responsible for CBCT facilities who have not previously received ‘‘adequate theoretical and practical training’’ should undergo a period of additional theoretical and practical training that has been validated by an academic institution (university or equivalent). Where national specialist qualifications in DMFR exist, the design and delivery of CBCT training programmes should involve a DMF Radiologist19For dentoalveolar CBCT images of the teeth, their supporting structures, the mandible and the maxilla up to the floor of the nose (e.g. 8 cm x 8 cm or smaller fields of view), clinical evaluation (‘‘radiological report’’) should be made by a specially trained DMF Radiologist or, where this is impracticable, an adequately trained general dental practitioner20For non-dentoalveolar small fields of view (e.g. temporal bone) and all craniofacial CBCT images (fields of view extending beyond the teeth, their supporting structures, the mandible, including the TMJ, and the maxilla up to the floor of the nose), clinical evaluation (‘‘radiological report’’) should be made by a specially trained DMF Radiologist or a Medical RadiologistFiguresFigure 1: Schematic illustrations of the classification for the morphology of the Schneiderian membrane as analyzed using sagittal and coronal CBCT scans according to criteria adapted from Soikkonen & Ainamo (1995). A / B) Healthy Schneiderian membrane: no thickening (A: sagittal view; B: coronal view). C / D) Flat: shallow thickening without well-defined outlines (C: sagittal view; D: coronal view). E / F) Semi-aspherical: thickening with well-defined outlines rising in an angle of > 30° from the floor of the walls of the sinus (E: sagittal view; F: coronal view). G / H) Mucocele-like: complete opacification of the sinus (G: sagittal view; H: coronal view). I / J) Mixed: flat and semi-aspherical thickenings (I: sagittal view; J: coronal view).A B C D E F G H I J Figure 2: Visualization of the entire right maxillary sinus using a CBCT with a small FOV (6x6 cm) for implant treatment planning in a 54-year old female patient. The sinus exhibits good pneumatization and open ostium without enlargement of the Schneiderian membrane. A) Sagittal view of the CBCT scan; B) Coronal view; C) Axial view. A B C Figure 3: Visualization of the basal aspects of the right maxillary sinus using a CBCT with a small FOV (4x4 cm) for implant treatment planning in a 61-year old male patient. The sinus exhibits good pneumatization without visualization of the open ostium. The Schneiderian membrane exhibits a flat and shallow thickening of the mucosa. A) Sagittal view of the CBCT scan; B) Coronal view; C) Axial view.A B C Figure 4: Visualization of the basal aspects of the right maxillary sinus using a CBCT with a small FOV (4x4 cm) for implant treatment planning in a 62-year old male patient. The sinus exhibits radiographic signs of a sinusitis with honeycomb like surface loculations without visualization of the ostium. This finding makes it advisable to consult an ENT prior to sinus floor elevation (SFE). A) Sagittal view of the CBCT scan; B) Coronal view; C) Axial view. A B C Figure 5: CBCT scan (small FOV: 6x5 cm) of the right mandible of a 73-year old male patient after referral by his treating dentist following insertion of two dental implants in regions 45 and 47. The patient reported complete anaethesia of the lower right lip. A) Sagittal view showing proximity of the dental implant in region 45 to the mental foramen located distally to the tooth 44; B) Coronal view of implant penetration in region 45 into the mandibular canal and region of the mental foramen; C) Coronal view of the implant in region 47 exhibiting its relation to the mandibular canal; D) Axial view visualizing penetration of the implant in region 45 into the mental foramen.A B C D Figure 6: CBCT scan (small FOV: 4x4 cm) of the anterior maxilla of a 66-year old female patient after referral by her treating dentist one year following insertion of a dental implants in region 21. The patient reported persisting neuropathic pain in the anterior mandible towards the nose. A) Sagittal view showing penetration of the dental implant in region 21 into the nasopalatine canal; B) Coronal view of the restored implant in region 21. There is also a slight osteolysis visible at the apical region of tooth 11; C) Axial view of the implant in region 21 exhibiting penetration into the nasopalatine canal.A B C Figure 7: CBCT scan (medium FOV: 8x5 cm) of the mandible of a 79-year old female patient referred for analysis of peri-implant bone defects around implants in the symphysis and left first premolar area. A dental implant in the right canine region had been lost a couple of weeks ago. The beam hardening artefacts around the metal make it difficult to assess the structures in direct or close vicinity of the dental implants A) Axial view showing the two implants (symphysis and left first premolar region), and a bone defect resulting from implant loss in the right canine area; B) Sagittal view showing the two implants in the symphysis and left first premolar region; C) Sagittal view showing the implant in the symphysis with almost no visible bone on the buccal and lingual aspects; D) Coronal view showing the implants in the left first premolar region with evident bone loss on the buccal and lingual aspects. A B C D ................
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