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I. Introduction
Craniofacial anomalies are heterogeneous developmental malformations that affect the growth of the bones of the face and skull. These abnormalities are reported to affect a wide population, with a prevalence rate of 2% worldwide.
Craniofacial abnormalities can occur in the lower or middle segments of the facial massif.
Abnormalities of the lower floor generally involve deviations of the branchial arch and, therefore, manifest as malformations of the mandible, external auditory canals and certain segments of the middle ear. These anomalies appear only occasionally in isolation, most of them being found within systemic syndromes; these abnormalities do not generally involve respiratory conditions.
Abnormalities of the middle floor of the face can extend from the upper lip to the forehead, reflecting the complex embryology of this region. Most of these defects appear in isolation, but some patients with facial clefts, especially in the case of syndromes involving median clefts and holoprosencephaly, also have other abnormalities, which is important to note, because the therapeutic management of these patients will require detailed imaging examinations and high accuracy of face and brain; abnormalities of the middle floor of the face tend to involve the nose and its airways.
The goals of diagnosis and treatment planning for patients with craniofacial anomalies (CFA) are no different than those of any patient, which are: (1) to achieve an ideal, stable occlusion, (2) to achieve an esthetic appearance when smiling and at rest, and (3) ideal facial proportions. What differs, however, between craniofacial and non-craniofacial patients is the initial severity of the discrepancy in CFA patients from these ideals and the extent of changes required to achieve relatively normal anatomical and functional relationships.
Orthodontists and surgeons who treat patients with CFA are extremely receptive to technological advances that help them improve the quality of care they can provide to their patients. It is not surprising that these technologies later find their place in everyday practice for the benefit of all patients with this complex pathological entity. Three-dimensional (3D) imaging is one such technology, of which techniques cone beam computed tomography (CBCT) is widely used.
CBCT provides 3D images that greatly improve diagnosis, treatment planning, and assessment of treatment progress and outcomes for all CF patients(1). Moreover, CBCT imaging joins the rapidly expanding arsenal of digital photography, radiography, and dental imaging that are replacing photographs traditional film-based examinations, cephalometric examinations, panoramic and intraoral radiographs and plaster casts.
Clearly, digital records have many advantages, among which we mention: (1) they can be viewed immediately to verify the correctness and accuracy of the acquisition, (2) they provide the necessary detailed information, and (3) they can be replayed immediately if necessary (they can be backed up for storage, and images can be printed immediately or sent electronically for communication with patients, parents, and other physicians).
In this article, we will present the current basic uses of three-dimensional imaging techniques, radiographic and non-radiographic, in the diagnosis and treatment of patients with common and rare craniofacial anomalies, with an emphasis on how these technologies improve diagnosis, treatment planning, and assessing outcomes for people with these disorders.
II. 3D imaging techniques for patients
with craniofacial anomalies
II.1. Conventional computed tomography (CT)
This technique is particularly useful in lip and/or palate cleft (CLP) for the visualization of bony and dental anatomy, and it is often used before plasty of dentofacial deformities; it is usually performed in patients with complicated or syndromic cleft palate as seen in the Pierre Robin sequence; multiplanar reconstructions of helical CT images, with the use of specific bone and soft tissue algorithms, can help visualize anatomical malformations, and three-dimensional reconstructions can facilitate surgical planning.
The size, shape and symmetry of the mandible can be well determined. Mandibular ramus length can be measured using reformatted oblique sagittal sections (mandibular ramus length of at least 17 mm is required to allow osteotomy and implant placement)(2). The identification of the inferior alveolar nerve foramen is important to avoid nerve damage during osteotomy in orthognathic surgery or of implant insertion(2). The existence and degree of airway obstruction can also be appreciated on the conventional CT examination (Figure 1).
II.2. Multislice computed tomography (MSCT)
Multislice computed tomography (MSCT) acquisitions provide excellent detail of skeletal morphology and pathology, suture patency, and temporomandibular joint (TMJ) anatomy and pathology. While computed tomography (CT) is particularly useful for imaging hard tissues, MSCT also captures soft tissues. This is valuable for patients with CFA who may have soft tissue abnormalities such as soft palate clefts or velopharyngeal insufficiency.
II.3. Cone beam computed tomography (CBCT)
Cone beam computed tomography is a recent radiological technique that became more widely available for imaging the craniofacial region after 2005. Previously, multislice computed tomography, which involves a much higher radiation dose than CBCT, has been the most widely used technique for 3D imaging of hard tissues(3,4).
Both techniques use X-rays to produce the images; however, while a CT scan uses a fan-shaped beam that scans the patient acquiring multiple sections, the CBCT scan produces a diverging cone-shaped beam and the desired field of view is captured in a single rotation. Regarding radiation dose, the SEDENTEXCT Consortium stated that “CBCT in patients with cleft lip and palate has been shown to be the most appropriate technique”; they also stated that “CBCT is preferable to CT scanning for use in dentistry”(5).
As a general concept, CBCT is mainly used for the planning and evaluation of orthognathic surgery procedures and for the evaluation of the anatomy of the bony structures of the nose and paranasal sinuses(6-10). Also, this imaging technique is used to evaluate acceptor and donor sites (e.g., mandibular symphysis) before and after alveolar cleft bone grafting. In this way, the amount of bone required can be carefully planned and the results can be easily evaluated(11,12).
CBCT has become an extremely useful tool in the diagnosis and treatment planning of patients with CFA. There are several advantages of the CBCT technique over other imaging methods:
the effective radiation dose from CBCT depends on the field of view (FOV) and can be up to 20% of traditional MSCT;
another important advantage of CBCT examination in CFA patients is given by the increased accuracy of anatomical details and measurements, which are essential for planning orthodontic and surgical treatment;
3D digital images can be used to accurately map the amplitude and directions of dental and skeletal movements needed to optimize treatment outcome;
in addition, CBCT is invaluable for evaluating the position of the unerupted tooth and identifying root resorption caused by unerupted teeth, pathological elements frequently found in patients with CFA(1).
CBCT can also be used to obtain a 3D image of the maxillary structures in order to print an obturator to close oronasal fistulas (Figure 2).
As an increasing number of advanced orthodontic programs and orthodontists use CBCT and other forms of 3D imaging for diagnosis and treatment planning, the demand for easy-to-use software packages for managing and analyzing Digital Imaging and Communications in Medicine (DICOM) images is increasing; in response to this demand, clinicians now have a wide selection of software that eases the transition from conventional two-dimensional (2D) radiography to 3D imaging.
For both CBCT and MSCT, available software allows multiplanar reconstruction to visualize the craniofacial skeleton and soft tissues in all three planes of space (Figure 3).
In addition, the 3D models generated by CT scans allow clinicians to fully appreciate the extent of the patient’s craniofacial abnormality, and can optimize treatment planning and sequencing among members of the multidisciplinary therapeutic management team for patients with craniofacial abnormalities.
With all the benefits demonstrated to date, the influence of this new 3D facial imaging modality on treatment planning and evaluation of therapeutic outcomes needs to be further studied.
II.4. Magnetic resonance imaging (MRI)
MRI provides precise imaging of intracranial soft tissue structures without radiation. In the craniofacial region, the MRI examination is widely used in the diagnosis of brain and spine pathology. For example, MRI has been used to study brain morphology in patients with Van der Woude syndrome and cleft lip and palate(13).
MRI is also the imaging modality of choice for diagnosing TMJ abnormalities, particularly articular disc displacements(14). Interesting, recently, the use of MRI is expanding more and more in prenatal diagnosis(15).
Various measurements of velopharyngeal structures (including hard palate length, soft palate length, velopharyngeal depth, palatal width and height; Figure 4) can be made on MRI sections. According to Ruda et al.(16), the choice of treatment method for velopharyngeal insufficiency depends on numerous factors that can be evaluated by MRI; of these, of great importance are the symmetry and degree of separation between the veil and the pharynx, and the configuration of the velopharyngeal muscles.
A recent study by Ali et al.(17) demonstrated that resting velopharyngeal MRI measurements in cleft palate patients correlated with their speech performance; velar thickness had a moderate significant positive linear correlation with the degree of velar motion and global speech intelligibility(17).
Measurements provided by MRI images help surgeons choose the most appropriate approach to optimize velar coverage in separating the nasopharynx and oropharynx during phonation.
A limitation of MRI imaging is that it cannot be used in patients with fixed orthodontic appliances, because the metal in the appliances interferes with the strong magnetic field required to generate the images; however, improvements in MRI technology are reducing this limitation(18).
II.5. 3D photography
Three-dimensional photography records the soft tissue surfaces of craniofacial structures without irradiation. Although useful, its accuracy, inferior to other imaging techniques, may not meet the diagnostic requirements of craniofacial anomalies(19).
However, it can be added as a technique to evaluate the results of certain surgical interventions, such as cleft lip plasty (Figure 5); it has also been used to evaluate the variations and phenotypes of certain syndromes, such as trisomy 21. Three-dimensional virtual models and nasal malformations of DL/P patients after secondary reconstruction intervention have been studied using 3D stereophotogrammetry(20). In addition, 3D color maps have been used to provide an objective assessment of outcomes during the treatment of craniofacial anomalies.
3D motion analysis systems developed over time for gait analysis are now being adapted for facial motion capture, as represented by the 3dMD dynamic face imaging system(21). This technology has recently been used to study facial movements in children with cleft and non-cleft malformations(22).
II.6. 3D dental models
Impressions or dental models can be scanned with laser equipment, or intraoral scans can be performed to recreate 3D digitized dental models. 3D images have the advantage of allowing viewing by rotating on a 2D screen, which also facilitates accurate measurements. Physical models can be produced from the digital data by a computer-aided design/manufacturing (CAD/CAM) system (Figure 6), and can also be merged with the data obtained from the CBCT examination.
Three-dimensional imaging provides virtual models that can be manipulated to evaluate the effectiveness of various therapeutic methods. In complex cases, such as CL/P, this feature is especially valuable when the examination of the models is correlated with CBCT images that highlight the positioning of teeth likely to erupt in the cleft site. The orthodontist and surgeon can also use the merged images to determine the ideal graft volume needed for permanent teeth or possible osseointegrated implants.
II.7. 3D surgical simulation models
Dento-maxillary anomalies are characterized by primary or acquired growth and development disorders of the dental system or maxillary bone bases, which causes major imbalances in the dento-alveolar and occlusal arches(23). Orthognathic surgery comes to correct these anomalies by performing surgical interventions on the upper, lower or bimaxillary jaw.
Traditionally, in planning the treatment of these anomalies, specialists in the field use patients’ photographs, two-dimensional radiological images, and articulator-mounted cast study models transferred via the facebow. But these methods, two-dimensional imaging such as orthopantomography and teleradiography, present a series of shortcomings, especially due to the acquisition technique and the superimposition of anatomical structures on the same radiographic film. This error intensifies in patients with obvious asymmetries and complicates estimations of the real size and shape of the anomalies; consequently, there is the potential risk of a greater degree of discrepancy between surgical planning and interventional outcome.
In the last decade, the technological revolution of digital radioimaging has facilitated the diagnosis of complex maxillofacial anomalies; the 3D images obtained on the basis of CBCT or multispiral CT allowed the virtual planning of the surgical intervention with real transposition by means of static virtual assisted surgery or computer assisted surgical navigation – computer assisted surgery (CAS) or image guided surgery (IGS). 3D surgical simulation models overcome many of the limitations associated with the traditional surgical model, particularly the simultaneous access to information about the patient’s skeletal anatomy during the planning process(24).
The success of orthognathic surgical interventions largely depends on the surgical technique and the exact transposition of the preoperative surgical plan(25). For this purpose, various information programs (software) have been designed, among the most well-known being ProPlan CMF (Figure 7A; Materialise, Leuven, Belgium) and Dolphin 3D (Figure 7B; Dolphin Imaging and Management Solutions, Patterson Dental, Chatsworth, USA), which were adapted to the needs of orthognathic surgery.
While the imaging techniques used to generate three-dimensional models vary, 3D surgical simulation programs typically use a combination of CT imaging, soft tissue surface scanning, and digitized dental casts. Simulation software is used to plan individual procedures and evaluate results.
The collection of information for virtual surgical planning begins with the acquisition of three-dimensional images using a cone beam or multispiral computed tomography. Both the conical fascicle and the multispiral computed tomograph offer a clearly superior visualization of the anatomy of the oro-maxillo-facial region compared to two-dimensional images, which facilitates the establishment of the diagnosis, the elaboration of the treatment plan and the evaluation of the result of the gnathosurgical treatment. CBCT allows obtaining three-dimensional images, with increased detail of anatomical structures, at a scale of 1:1.
The next stage is represented by the conversion of DICOM data into a 3D image, using the segmentation procedure, which is actually a mathematical algorithm; the three-dimensional reconstruction is obtained based on the estimated density range in Hounsfield units for multispiral CT and grayscale for CBCT (Figure 8A). Superimposition of computer tomograph data with the virtual models of the scanned dental arches (Figure 8B) is performed using the semiautomatic registration procedure.
Virtual surgical planning allows the simulation of different surgical intervention techniques. The processing of three-dimensional images through planning software allows the virtual simulation of osteotomies, the repositioning of bone fragments in the desired position, the control of intercuspidation, the interference between osteotomized fragments and the visualization of postoperative results in real time.
Virtual surgical planning technology is also a tool for evaluating the postoperative results obtained (Figure 9). Because this technology allows for more predictable planning of surgical treatment, it is well suited for use in craniofacial anomalies(26). In fact, recent studies have indicated that such fusion techniques can predict actual postoperative outcomes more accurately than single treatment planning approaches(24).
These studies indicate that the mean linear differences between simulation and surgical results in patients with complex craniofacial deformities were only 0.85 mm, with an angular discrepancy of only 1.7°(26). Given previous data suggesting that differences of up to 2 mm and 4° are clinically insignificant, it is clear that the analysis and manipulation of the 3D images by the software contribute to the highly predictable results in these cases(27).
During digital planning, the surgeon is able to visualize the dental arches, facial skeleton and soft tissues in a single three-dimensional virtual image. This allows the evaluation of the symmetry or asymmetry of the bone structures, the visualization of the position of the teeth in correlation with the neighboring anatomical formations, the study of the occlusal relations, of the temporomandibular joint, as well as the evaluation of the upper airways. Also, the digitization of the treatment plan gives us the opportunity to store and encrypt data that can later be transmitted and kept online, which can be accessed and viewed whenever necessary for curative and didactic purposes.
III. Conclusions
Early diagnosis and proper management of craniofacial anomalies are essential and involve a multidisciplinary team with specialists from different fields who are highly responsive to technological advances that help them improve the quality of care they can provide to their patients.
The therapeutic management of patients with craniofacial anomalies is a complex and multidisciplinary task that requires periodic imaging investigations, closely correlated with the patient’s age.
Imaging protocols should be based on specific diagnostic criteria designed to support optimal treatment planning and case management. These protocols should use the number of radiographic examinations absolutely necessary, and all images should use exposure settings that produce diagnostically acceptable images at the lowest possible radiation dose to the patient.
Autor corespondent: Diana-Monica Preda E-mail: diana_monica_preda@yahoo.com
CONFLICT OF INTEREST: none declared.
FINANCIAL SUPPORT: none declared.
This work is permanently accessible online free of charge and published under the CC-BY.
