1: Diagnosis and treatment planning in the three-dimensional era
Tommaso Castroflorio, Sean K. Carlson, Francesco Garino
Introduction
Orthodontics and dentofacial orthopedics is a specialty area of dentistry concerned with the supervision, guidance, and correction of the growing or mature dentofacial structures, including those conditions that require movement of teeth or correction of malrelationships and malformations of their related structures and the adjustment of relationships between and among teeth and facial bones by the application of forces and/or the stimulation and redirection of functional forces within the craniofacial complex.1
To accurately diagnose a malocclusion, orthodontics has adopted the problem-based approach originally developed in medicine. Every factor that potentially contributes to the etiology and that may contribute to the abnormality or influence treatment should be evaluated. Information is gathered through a medical and dental history, clinical examination, and records that include models, photographs, and radiographic imaging. A problem list is generated from the analysis of the database that contains a network of interrelated factors. The diagnosis is established after a continuous feedback between the problem recognition and the database (Fig. 1.1). Ultimately, the diagnosis should provide some insight into the etiology of the malocclusion.2
Orthodontics diagnosis and treatment planning are deeply changing in the last decades, moving from two-dimensional (2D) hard tissue analysis and plaster cast review toward soft tissue harmony and proportions analyses with the support of three-dimensional (3D) technology. A detailed clinical examination remains the key of a good diagnosis, where many aspects of the treatment plan reveal themselves as a function of the systematic evaluation of the functional and aesthetic presentation of the patient.3
The introduction of a whole range of digital data acquisition devices (cone-beam computed tomography [CBCT], intraoral and desktop scanner [IOS and DS], and face scanner [FS]), planning software (computer-assisted design and computer-assisted manufacturing [CAD/CAM] software), new aesthetic materials, and powerful fabrication machines (milling machines, 3D printers) is changing the orthodontic profession (Fig. 1.2).
As a result, clinical practice is shifting to virtual-based workflows.4 Today it is common to perform virtual treatment planning and to translate the plans into treatment execution with digitally driven appliance manufacture and placement using various CAD/CAM techniques from printed models, indirect bonding trays, and custom-made brackets to robotically bend wires or aligners. Furthermore, it is becoming possible to remotely monitor treatment and to control it.5
The introduction of aligners in the orthodontics field led the digital evolution in orthodontics. The two nouns evolution and revolution both refer to a change; however, there is a distinctive difference between the change implied by these two words. Evolution refers to a slow and gradual change, whereas revolution refers to a sudden, dramatic, and complete change. What has been claimed as the “digital revolution” in orthodontics should be claimed as the “digital evolution” in orthodontics. Orthodontics and biomechanics have always had the same definitions, and we as clinicians should remember that technology is an instrument, not the goal. This differentiates orthodontists from marketing people.
The diagnosis and problem list is the framework that dictates the treatment objectives for the patient. Once formulated, the treatment plan is designed to address those objectives.2 In aligner orthodontics, CAD software displays treatment animations, helping the clinician to visualize the appearance of teeth and face that is desired as treatment outcome; however, those animations should be deconstructed by the orthodontist frame by frame or stage by stage, to define how to address the treatment goal from mechanics to sequence. Only an accurate control of every single stage of the virtual treatment plan can produce reliable results. As usual, it is the orthodontist rather than the technique itself that is responsible for the treatment outcome.
Contemporary records should facilitate functional and aesthetic 3D evaluation of the patient.
Intraoral scans and digital models
IOSs are quickly replacing traditional impressions and plaster models. These scanners generally contain a source of risk for inaccuracy because multiple single 3D images are assembled to complete a model. Recent studies, however, have shown that the trueness and precision of IOSs of commercially available scanning systems are excellent for orthodontic applications.6 Digital models are as reliable as traditional plaster models, with high accuracy, reliability, and reproducibility (Fig. 1.3).
Furthermore, the models can also be used in various orthodontic software platforms to allow the orthodontist to perform virtual treatment plans and explore various treatment plans within minutes as opposed to expensive and time-consuming diagnostic setups and waxups. Performing digital setups not only allows the clinician to explore a number of treatment options in a simple manner but also facilitates better communication with other dental professionals, especially in cases that require combined orthodontic and restorative treatments. The virtual treatment planning also allows for better communication with patients and allows them to visualize the treatment outcome and understand the treatment process.5
Further advantages of virtual models of the dental arches are related to study model analysis, which is an essential step in orthodontic diagnostics and treatment planning. Compared to measurements on physical casts using a measuring loop and/or caliper, digital measurements on virtual models usually result in the same therapeutic decisions as evaluations performed the traditional way.7 Furthermore, with their advantages in terms of cost, time, and space required, digital models could be considered the new gold standard in current practice.6
Digital impressions have proven to reduce remakes and returns, as well as increase overall efficiency. The patient also benefits by being provided a far more positive experience. Current development of novel scanner technologies (e.g., based on multipoint chromatic confocal imaging and dual wavelength digital holography) will further improve the accuracy and clinical practicability of IOS.7
Recently near infrared (NIR) technology has been integrated in IOS. The NIR is the region of the electromagnetic spectrum between 0.7 and 2 μm (Fig. 1.4). The interaction of specific light wavelengths with the hard tissue of the tooth provides additional data of its structure. Enamel is transparent to NIR due to the reduced scattering coefficient of light, allowing it to pass through its entire thickness and present as a dark area, whereas the dentin appears bright due to the scattering effect of light caused by the orientation of the dentinal tubules. Any interferences/pathologic lesions/areas of demineralization appear as bright areas in a NIR image due to the increased scattering within the region. Therefore IOS provides information regarding possible decays without any x-ray exposure.8
Through the use of digital impression making, it has been determined that laboratory products also become more consistent and require less chair time at insertion.9
3D imaging
Cone-beam computed tomography
3D imaging has evolved greatly in the last two decades and has found applications in orthodontics as well as in oral and maxillofacial surgery. In 3D medical imaging, a set of anatomic data is collected using diagnostic imaging equipment, processed by a computer and then displayed on a 2D monitor to give the illusion of depth. Depth perception causes the image to appear in 3D.10 Over the last 15 years, CBCT imaging has emerged as an important supplemental radiographic technique for orthodontic diagnosis and treatment planning, especially in situations that require an understanding of the complex anatomic relationships and surrounding structures of the maxillofacial skeleton. From the introduction of the cephalostat, Broadbent stressed the need for a perfect matching of the lateral and posteroanterior x-rays to obtain a perfect 3D reproduction of the skull.11 CBCT imaging provides unique features and advantages to enhance orthodontic practice over conventional extraoral radiographic imaging.12 Lateral cephalometrics provides information on the sagittal and vertical aspects of the malocclusion with little contribution about unilateral or transversal discrepancies. The latter seem to be related to urbanization and industrialization becoming more frequent in the last decades.13–15 Therefore, the need for a diagnostic tool providing information on the 3D aspects of the dentoskeletal malocclusion is increasing. While the clinical applications span from evaluation of anatomy to pathology of most structures in the maxillofacial area, the key advantage of CBCT is its high-resolution images at a relatively lower radiation dose.16
Exposing patients to x-rays implies the existence of a clinical justification and that all the principles and procedures required to minimize patient exposure are considered. The ALARA concept should always be kept in mind: ALARA is an acronym used in radiation safety for as low as reasonably achievable. This concept is supported by professional organizations as well as by government institutions.17,18 Recognizing that diagnostic imaging is the single greatest source of exposure to ionizing radiation for the US population that is controllable, the National Commission on Radiation Protection and Measurements has introduced a modification of the ALARA concept.19 ALADA represents as low as diagnostically acceptable. Implementation of this concept will require evidence-based judgments of the level of image quality required for specific diagnostic tasks as well as exposures and doses associated with this level of quality. Little research is currently available in this area.
For 2D imaging modalities used in orthodontics, the radiation dose for panoramic imaging varies between 4 and 10 µSv, while a cephalometric exam range is between 3 and 5 µSv. A full mouth series ranges from 12 to 58 µSv based on the type of collimation used.16 While 2D and 3D radiation doses are often compared for reference, they cannot truly be compared because the acquisition physics and the associated risks are completely different and cannot be equated. The actual risk for low-dose radiographic procedures such as maxillofacial radiography, including CBCT, is difficult to assess and is based on conservative assumptions as there are no data to establish the occurrence of cancer following exposure at these levels. However, it is generally accepted that any increase in dose, no matter how small, results in an incremental increase in risk.20 Therefore there is no safe limit or safety zone for radiation exposure in orthodontic diagnostic imaging.12 A recent meta-analysis about the effective dose of dental CBCT stated that the mean adult effective doses grouped by field of view (FOV) size were 212 µSv (large), 177 µSv (medium), and 84 µSv (small). Mean child doses were 175 µSv (combined large and medium) and 103 µSv (small). Large differences were seen between different CBCT units.19
The American Dental Association Council on Scientific Affairs (CSA) proposed a set of principles for consideration in the selection of CBCT imaging for individual patient care. According to the guidelines, clinicians should perform radiographic imaging, including CBCT, only after professional justification that the potential clinical benefits will outweigh the risks associated with exposure to ionizing radiation. However, CBCT may supplement or replace conventional dental x-rays when the conventional images will not adequately capture the needed information.17
Recently, a number of manufacturers have introduced CBCT units capable of providing medium or even full FOV CBCT acquisition using low-dose protocols. By adjustments to rotation arc, mA, kVp, or the number of basis images or a combination thereof, CBCT imaging can be performed at effective doses comparable with conventional panoramic examinations (range, 14–24 µSv).21 This is accompanied by significant reductions in image quality; however, viewer software can be helpful in improving the clinical experience with low-quality images. Even at this level, child doses have been reported to be, on average, 36% greater than adult doses.21 The use of low-dose protocols may be adequate for low-level diagnostic tasks such as root angulations.
Benefits of CBCT for orthodontic assessment
The benefits of CBCT for orthodontic assessment include accuracy of image geometry. CBCT offers the distinct advantage of 1:1 geometry, which allows accurate measurements of objects and dimensions. The accuracy and reliability of measurements from CBCT images have been demonstrated, allowing precise assessment of unerupted tooth sizes, bony dimensions in all three planes of space, and even soft tissue anthropometric measurements—things that are all important in orthodontic diagnosis and treatment planning.22–24
The accurate localization of ectopic, impacted, and supernumerary teeth is vital to the development of a patient-specific treatment plan with the best chance of success. CBCT has been demonstrated to be superior for localization and space estimation of unerupted maxillary canines compared with conventional imaging methods.25,26 One study indicated that the increased precision in the localization of the canines and the improved estimation of the space conditions in the arch obtained with CBCT resulted in a difference in diagnosis and treatment planning toward a more clinically orientated approach.25 CBCT imaging was proven to be significantly better than the panoramic radiograph in determining root resorption associated with canine impaction.27,28 One study supported improved root resorption detection rates of 63% with the use of CBCT when compared with 2D imaging.28 When used for diagnosis, CBCT has been shown to alter and improve the treatment recommendations for orthodontic patients with impacted or supernumerary teeth.29,30
Based on the findings of a recent review30 and in accordance with the DIMITRA (Dentomaxillofacial Paediatric Imaging: An Investigation Towards Low Dose Radiation Induced Risks) project,31 CBCT can be considered also in children for diagnosis and treatment planning of impacted teeth and root resorption (Fig. 1.5).
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