Introduction

Cone-beam CT is an emerging imaging technology with a wide range of dentomaxillofacial applications. The use of cone-beam CT for pediatric dentistry remains a sensitive point considering the radiation doses involved [1, 2]. However, for orofacial and jaw bone pathologies and a number of specific indications, 3-D imaging might be justified [3,4,5]. Until now, indication-oriented cone-beam CT optimization protocols have not been developed and reports mention inconsistent and insufficient recommendations for reducing radiation doses in children and adolescents [6, 7].

The European DIMITRA project (dentomaxillofacial paediatric imaging: an investigation toward low-dose radiation induced risks) is focused on optimizing pediatric doses. DIMITRA is part of the wider OPERRA research (Open Project for European Radiation Research Area), which aims to develop patient-specific and indication-oriented recommendations for the justified use of cone-beam CT in pediatric dentistry. It is a multidisciplinary effort to approach the involved risks from different interrelated perspectives: radiobiological characterization (oral stem cells response, saliva profiling), dosimetric quantification (Monte Carlo framework), epidemiological survey, image quality and dose optimization. The DIMITRA consortium therefore proposes to move from ALARA (As Low as Reasonably Achievable) and ALADA (As Low as Diagnostically Acceptable) [5, 8] toward ALADAIP (As Low as Diagnostically Acceptable being Indication-oriented and Patient-specific).

Considering the lack of studies addressing indication-oriented optimization of pediatric 3-D imaging protocols, a primary task of the DIMITRA project was to start gathering information on strategies for dentomaxillofacial pediatric image optimization. The goal of the present report is to provide a DIMITRA position statement, being proposed as recommendations and clinical guidance notes for the main cone-beam CT indications in pediatric dentistry. More recommendations will be proposed in the near future taking into account the scientific-based conclusions of the DIMITRA research.

Justification and optimization of cone-beam CT in pediatric dentistry: current evidence

Conventional 2-D imaging methods are inherently limited by the anatomical superimpositions, the limited field of view (intra-oral radiographs) and inherent image distortion. All those factors may hamper specific diagnostic tasks. This position paper presents a list of justified pediatric indications for cone-beam CT, based on current scientific evidence and obvious clinical needs. The recommendations and guidance notes consider optimization strategies, balancing dose and image quality as such to be age- and indication-specific.

Yet the dose overview approach on each specific topic is based in current literature. Effective dose estimations shown in the images in this paper are presented as a reference starting point, based on a previous study [9]. Those dose measurements were made using anthropomorphic pediatric phantoms, five cone-beam CT units, different settings and thermoluminescent dosimetry. There is a wide effective dose range depending on the cone-beam CT unit, the range of protocol options and the size or position of the field of view (FOV) in relation to the radiosensitive organs [9, 10]. Therefore, in the figures and in the text we tried to fit this dose range from the literature, taking into account the indication, FOV features, and level of resolution as accurately as possible.

Impacted and supplementary teeth

Diagnostic as well as therapeutic management of impacted and supplementary teeth are considered a prime and justified indication for cone-beam CT in pediatric dentistry. Some evidence in the literature supports this point of view because 3-D imaging can significantly impact the treatment approach, increasing the confidence and predictability, and decreasing surgical invasiveness [3].

Diagnostic needs in impaction and supplementary tooth cases include analysis of tooth anatomy, position and orientation and any occurring deviation; dental follicular sac appearance and potential widening; periodontal ligament; lamina dura; and surrounding alveolar bone (Fig. 1) [2, 11,12,13,14,15,16,17,18,19]. Proximity of the crown of the impacted tooth nearby the roots of other teeth needs to be carefully addressed (neighboring root resorption) as well as the relationship with anatomical structures (e.g., maxillary sinus, nasal cavities, neurovascular bundle). In addition, impacted teeth need to be carefully evaluated for abnormalities including replacement resorption and ankyloses.

Fig. 1
figure 1

DIMITRA recommendations for impacted teeth (top section) and dentoalveolar trauma (bottom section). Columns delineate indication-oriented recommendations, age groups, diagnostic needs, image requirements, anatomical field of view and level of resolution. The references column cites some relevant papers published in the last 5 years approaching the usefulness of cone-beam CT on each specific indication. The effective doses were based on Theodorakou et al. [9] for children and adolescents (fields of view: partial, 5 cm × 3.7 cm/4 cm × 4 cm; full jaw, 16 cm × 6 cm/14 cm × 5 cm; both jaws, 16 cm × 13 cm/15 cm × 11 cm/8 cm × 8 cm/14 cm × 10 cm). The top cone-beam CT image illustrates an impacted upper primary molar in a 13-year-old boy, coronal (buccolingual section) view, slice thickness 0.2 mm. The bottom cone-beam CT image shows a horizontal root fracture in an upper central incisor (arrow) in a 9-year-old boy, sagittal view (buccolingual section), slice thickness 0.2 mm. Images were obtained from the data collection of the authors’ institution (unit: Promax 3D Max, Planmeca, Finland). CBCT cone-beam computed tomography, FOV field of view, HR high resolution, LR low resolution, PDL periodontal ligament

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In order to fulfill these diagnostic requirements, it is crucial to depict and clearly differentiate tooth, periodontal ligament space, lamina dura and trabecular bone. Within the tooth structure, it is essential to enable distinguishing enamel and dentin of the impacted tooth itself and adjacent teeth. These image requirements are linked to the ability to identify small tissue changes, as observed in root resorptions or cortical disruptions, as well as slight morphological changes. In this way, when doubts rise by 2-D radiographic analysis, evaluations of impacted teeth require a high level of resolution.

Furthermore, the imaging modality must fully include the impacted tooth as well as the nearby anatomical structures. Nevertheless the volume of scanning has to be limited as much as possible. In practice, partial or full jaw fields of view (50 mm to 80 mm high and restricted in horizontal dimension as much as possible) must be chosen to both reduce the dose (limited exposed surface) and improve the image quality (reduction of the voxel size and scattering radiation) [1, 20, 21]. Yet to avoid truncation artefacts, the impacted teeth should not be eccentric inside the selected field of view and this might then require the use of scout viewing to precisely position the FOV and adapt its size.

Although a few cases might be evaluated in 2-D and 3-D low-resolution exams (e.g., root size and morphology, bone level in the impaction area), in the majority of impacted teeth there is a need to evaluate adjacent teeth and visualize the impacted tooth’s relationship with critical anatomical structures [12, 22]. For this reason, the strategy in dose optimization might be related to patient-specific conditions. Considering that high-resolution level is recommended for most of these cases, protocols can be adjusted depending on age and patient size, taking into account the options of voltage and milliamperage (mAs) selection in some units. It must be emphasized that the age range of the children who present with impacted teeth is wide, varying from 6 years to adolescents, reinforcing the need for a case-specific exposure parameter selection.

Dentoalveolar trauma

Traumatic injuries in children are quite common, affecting mostly the dentoalveolar complex. In this context, dental and bone fractures appear as the most frequent early complications associated with trauma. Conventional radiographs are indicated for most of the cases of slight or moderate injuries because they are sufficient for localizing injury and establishing its severity [23]. However the International Association of Dental Traumatology (IADT) has recommended at least three intraoral radiographs, in different horizontal and vertical angulations, for examining the involved teeth [24]. In some cases a 3-D method can be determinant in treating cases involving trauma and root fracture, especially when it is located in the middle third of the root [2, 25]. Cone-beam CT contributes to more precise evaluation of the root fractures, specifically regarding their location, extension and direction [26] (Fig. 1). In addition, in cases of complicated bone fractures involving the alveolar process, mandible and middle third of the face, with or without displacement, analyzing the anatomical craniofacial complexity in 2-D exams can become challenging [23].

Detection of root fractures on conventional radiographs is strongly dependent on factors like the gap between the root fragments, potential pathological consequences on adjacent tissues (surrounding bone or periodontal ligament enlargement) and the angulation of the X-ray beam. The beam must pass through the fracture for its registration on the receptor [27]. On the other hand, minor dental fractures can be detected on cone-beam CT images provided that the voxel size is twice as small as the fracture line. For that reason, it is mandatory to choose parameters conducive to a high level of resolution. Similar to the recommendations for impacted teeth, the FOV must be reduced as much as possible to the region of interest to improve the image quality while reducing the dose. However it is important to take into account the patient history before choosing the exposed area. For instance, a traumatic impact involving the mandible can be followed by condyle fractures. A recent North American survey reported the mandibular condyles and angles as the most common anatomical sites of mandibular fractures in children [28]. Therefore if there is a suspicion of extended dental injuries associated with temporomandibular joint repercussion after the clinical and radiographic examination, wider FOVs should be considered.

It is important to emphasize that the follow-up of children with frontal trauma history is as relevant as the immediate diagnostics [23, 29]. The so-called late lesions — dentoalveolar complications not detected just after the traumatic event — include both the inflammatory periapical lesions and post-traumatic dental resorption. Studies have shown that cone-beam CT is more useful in the diagnostics of periapical pathology arising from traumatic events, in comparison to intraoral radiographs [30, 31]. Similarly, the diagnostics of small lesions of early resorption can be difficult with conventional radiographs [19, 32]. In this way, cone-beam CT can be decisive in the monitoring steps when there is a radiographic doubt of an initial periapical lesion or an early root resorption [2]. It should be highlighted that traumatic horizontal root fractures are prone to spontaneous healing. In this context, cone-beam CT can have a significant role in monitoring these cases [17, 33, 34].

A traumatic event involving the dentoalveolar area can be followed for a range of pathological conditions and their diagnostic needs. In those pediatric cases where a cone-beam CT exam is essential, a high level of resolution must be chosen to accomplish the image requirements described in the Fig. 1. For monitoring, lower-resolution modes can be used, taking into account a case-specific evaluation.

Orofacial clefts

Orofacial clefts are congenital malformations that can affect the lip, alveolar process and hard and soft palates. Concerning the imaging diagnostic, the children with orofacial clefts represent a specific group of patients because it is expected that they will be submitted to several exposures during their lifetime. For this reason, the concepts of justification and optimization must be strongly accomplished in order to minimize the risk. Despite the well-known need for three-dimensional images in different stages of diagnostics and treatment, scans should be optimized and carefully indicated at the right time (Fig. 2) [35,36,37,38,39,40,41,42,43,44,45], mainly considering the improvement in the surgical planning [39].

Fig. 2
figure 2

DIMITRA recommendations for orofacial clefts. For column description see Fig. 1. The top cone-beam CT image illustrates a palato-alveolar cleft in a 9-year-old boy, axial view, slice thickness 0.15 mm (unit: NewTom VGi; NewTom, Verona, Italy). The middle cone-beam CT image illustrates a palato-alveolar cleft in a 15-year-old girl, axial view, slice thickness 0.15 mm (unit: NewTom VGi). The bottom cone-beam CT image shows a bone-grafted alveolar cleft (arrow) in a 17-year-old boy, axial view, slice thickness 0.4 mm (unit: Promax 3D Max, Planmeca, Finland). CBCT cone-beam computed tomography, FOV field of view, HR high resolution, LR low resolution, PDL periodontal ligament

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As described in Fig. 2, the diagnostic needs for clefts management include the deformity detection as well as the determination of its shape, size and volume. Some other primordial diagnostic features are the monitoring of the development and eruption of adjacent teeth and the analyses of the involvement of the nasal cavity. These data are required to plan surgical procedures (bone graft and orthognathic surgery) and orthodontic approaches. Formerly, conventional two-dimensional radiographs were used to estimate these diagnostic tasks based on linear measurements and subjective evaluation [46, 47]. However the use of three-dimensional imaging might increase the predictability of the procedures, reducing morbidity, surgical time and inherent costs like surgical materials and hospitalization [48].

According to the SedentexCT guidelines, the use of cone-beam CT is justifiable for patients with orofacial clefts because this modality represents a reduction up to 12.3-fold with regard to effective doses in comparison to the medical CT [3, 49]. It has been proved that the modification of technical parameters, like FOV and voxel size, does not affect the cleft assessment, even when precise volumetric measures are required [38]. For this reason, low-dose protocols should be selected for this proposal considering mainly the possibility to restrict the FOV to the maxillary area [40]. Half-scan modes (decreasing the amount of projections) and mAs reductions are also encouraged for cleft evaluation.

Others points of attention concerning this indication involve the management of residual clefts after bone grafting, follow-up of the healing and proper tooth eruption through the bone bridge (mainly maxillary lateral incisor and canine). Hereof, cone-beam CT has shown an optimal performance for 3-D assessment of bone-grafted alveolar cleft; studies have pointed that two-dimensional evaluation can overestimate the outcomes, showing an approximate condition of the bone bridge and teeth adjacent to the cleft [40, 50].

When considering age-specific diagnostics in children with clefts, it should be noted that a number of diagnostic aspects at specific ages require an increased resolution. These include canine eruption pattern and detection of dental anomalies.

Dental anomalies

Human teeth, whether regular or supplementary, can show some changes in shape, number, size, time of formation or structural alterations of the tissues. Although these dental anomalies occur in the general population, these are much more common in patients with orofacial clefts and syndromes [44].

Some reports in the literature emphasize the diagnostic relevance of three-dimensional imaging methods for dental anomalies [51,52,53]. However studies approaching the three-dimensional diagnostic of dental anomalies and its impact in the treatment outcomes are rare [54]. Recommendations can be rather similar to those used for impacted teeth. Cone-beam CT is indicated when two-dimensional intra- and extra-oral exams do not answer the diagnostic questions. Despite the paucity of literature, it has been shown that cone-beam CT can contribute to the diagnostics of specific dental anomalies, like dens invaginatus (dens in dente; Fig. 3) [44, 54,55,56,57,58,59,60,61]. However for a real gain over the conventional radiographs, the image resolution should be adjusted in a high level and the FOV restricted to the area of interest for the same reasons mentioned for the former indications. In cases of syndromic conditions where many dental anomalies can be detected in both jaws of the same child, larger FOVs should be preferred when a 3-D evaluation is indispensable.

Fig. 3
figure 3

DIMITRA recommendations for dental anomalies and bone pathology. For column descriptions see Fig. 1. The top cone-beam CT image illustrates dens-in-dente in an upper lateral incisor in a 10-year-old boy, sagittal view (buccolingual section), slice thickness 0.2 mm. The bottom cone-beam CT image shows a follicular cyst in an upper non-erupted canine in a 9-year-old girl, sagittal view (buccolingual section), slice thickness 0.2 mm. Images were obtained from the data collection of the authors’ institution (unit: Promax 3D Max, Planmeca, Finland). CBCT cone-beam computed tomography, FOV field of view, HR high resolution, LR low resolution, PDL periodontal ligament

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It should be mentioned that a number of dental anomalies detected in cone-beam CT are incidental findings [57, 62] and most of the time do not require any treatment.

Bone pathology

The diagnosis and treatment of some bone lesions that involve the maxillofacial area in the pediatric field — mostly inflammatory periapical lesions and dentigerous cysts — can be managed with clinical examination and conventional radiographs. However, panoramic and intraoral radiographs might under- or overestimate the size of the lesions, and the superimposition of structures hampers the accurate determination of their borders. Furthermore, in some cases, the anatomical complexity of the site or the size of the lesion demand three-dimensional methods like multi-slice CT or cone-beam CT (Fig. 3). It is known that 3-D information can provide valuable information regarding the prognosis, improving the predictability of the surgery and reducing its morbidity. For instance, cone-beam CT has shown diagnostic value for lesions presenting calcified foci like adenomatoid odontogenic tumor and calcifying cystic odontogenic tumor [60].

The decision between multi-slice CT or cone-beam CT depends on the soft-tissue involvement (primary site or secondary involvement) and contrast agent needs. When there is a question of malignancies in the diagnosis hypothesis, multi-detector CT or other specific exams (positron emission tomography [PET], magnetic resonance imaging [MRI]) must be chosen [61]. In general, for pre-surgical evaluation of lesions showing a benign pattern and confined in the jaw bones, cone-beam CT must be considered the method of choice knowing its good contrast resolution for mineralized tissues and lower dose of radiation in comparison to multi-detector CT [61, 63].

Interestingly, since the advent of cone-beam CT, the features of some pediatric lesions have been enlightened. This is the case for the buccal bifurcation cyst. Although the last statements of the World Health Organization classified this inflammatory lesion as paradental cyst, some age-specific and site-specific features, as well as the typical expansion of the buccal cortical usually associated with periosteal reaction, include this entity in a full-fledged group [59, 64, 65]. In addition, because the histological aspect of this lesion is similar to that of other inflammatory odontogenic cysts, cone-beam CT exams can play an important role in the diagnostic and surgical planning, especially concerning the amount of alveolar crest involvement and buccal cortical bone loss [59].

Special care must be taken concerning the selection of the FOV. An appropriate image must show the lesion as a whole as well as its horizontal and vertical limits. In addition, it is mandatory to include surrounding tissues and often both sides for the contralateral comparison. Therefore, in many cases the restriction of the FOV cannot be considered as an optimization strategy and other measures should be taken into account in order to reduce the radiation risk (e.g., decreasing exposure parameters and level of resolution). It has been shown that cone-beam CT exams performed in lower-resolution modes can be suitable for the evaluation and follow-up of bone lesions with noise not jeopardizing diagnostic utility [38, 58, 66].

Cone-beam-CT-based surgical planning of autotransplantation

Cone-beam CT is also used for computer-based surgical simulation, guided surgery and printing of 3-D models. For example, in the pediatric field the treatment of permanent tooth loss or agenesis with autotransplantation has been described as a relevant application of these cone-beam CT-based 3-D approaches [67,68,69,70]. Through the virtual planning, production of a surgical guide and a stereolithographic tooth replica, the method is able to reduce the surgical duration and invasiveness, decreasing the extra-oral time and resulting in a lower failure rate compared to the conventional technique [69, 71]. In addition, a recent study has shown that it is possible to optimize the cone-beam CT protocols for planning and follow-up of tooth autotransplantation cases, with an effective dose reduction in a range of 74.6–157.9 μSv (preoperative) and 24.2–41.5 μSv (postoperative) [70]. Therefore, the authors encourage the choice of low-energy and low-resolution protocols associated with small fields of view, mainly for the post-operative monitoring of the autotransplanted tooth. These findings reinforce and justify the cone-beam CT application for this specific indication in the pediatric field.

Syndromes

The usefulness of multi-slice CT for the management of children with syndromes is recognized in both medical and dentomaxillofacial fields. Although each syndrome presents a specific combination of clinical and radiologic signs, many of them present associated dental disorders (e.g., supplementary teeth, multiple or localized agenesis, dental anomalies, enamel hypoplasia, odontodysplasia, malocclusion), bone lesions (e.g., cysts, keratocystic odontogenic tumors, central giant cell lesions) and alterations of the craniofacial morphology [11, 71,72,73,74]. In this context and taking into account the indications, case-specificity and possibility of optimization of the exposures already mentioned in the former sessions, cone-beam CT should be considered in the diagnosis and follow-up of pediatric syndromic cases, especially those with severe craniofacial abnormalities, lesions or multiple dental anomalies and teeth impaction.

Conclusion

Although the European evidence-based guidelines provide recommendations for the use of cone-beam CT, the current research evidence level concerning the indication in children remains limited. In addition, optimization of exposures in young patients is barely performed. This statement will be reviewed and complemented when the DIMITRA results regarding the multidisciplinary approaches are completed. Likewise, it shall be reviewed in 5 years or earlier if the evidence underlying it is judged to have changed significantly.