Introduction

Several studies evaluating asymmetric malocclusions have been reported in orthodontics (Cheney 1961; Wertz 1975; Alavi et al. 1988; de Araujo et al. 1994; Rose et al. 1994; Burstone 1998; Janson et al. 2001; Azevedo et al. 2006; Janson et al. 2007a; Sanders et al. 2010; Minich et al. 2013). Systematic diagnosis and treatment planning have been proposed to achieve adequate and functional treatment results depending on the individual patient’s characteristics (Wertz 1975; Lewis 1976; Forsberg et al. 1984; Shroff et al. 1997; Burstone 1998; Rebellato 1998; Shroff and Siegel 1998; Janson et al. 2003a, 2003b, 2004, 2007a; Turpin 2005; Cassidy et al. 2014). Class II subdivision malocclusion subjects have been compared with subjects with normal occlusion in order to evaluate intrinsic characteristics of the asymmetric malocclusion (Janson et al. 2001; Azevedo et al. 2006; Sanders et al. 2010).

These comparisons have been performed using clinical evaluation, photographs, dental models, 2D radiographs, and computed tomography (Wertz 1975; Lewis 1976; Ritucci and Burstone 1981; Forsberg et al. 1984; Alavi et al. 1988; Rose et al. 1994; Janson et al. 2001; Vitral et al. 2004). In the last years, the use of cone‐beam computed tomography (CBCT) has become an important auxiliary tool for asymmetry diagnosis (Sanders et al. 2010; Minich et al. 2013; Cachecho et al. 2014; Cassidy et al. 2014; Huang et al. 2017). However, its use is limited to specific malocclusions depending on patient’s requirements and ethical issues (American Academy of Oral and Maxilofacial Radiology 2013).

Although CBCT use has been increased, there are still clinicians that do not have access to this diagnostic tool and others that do not include it in their clinical practice as a routine exam. Therefore, the use of clinical parameters and 3D evaluations based on 2D radiograph methods are considered an adequate option for diagnosis, even with their limitations. In addition, they are easier to ask and be obtained by the patients. In this way, this chapter will focus on different 2D radiographic methods that explain the characteristics of asymmetric malocclusions and establish some clinical implications for their diagnosis and treatment planning.

Radiographic Methods for Diagnosis of Asymmetry

Different radiographic methods have been used to evaluate asymmetry. Among them, panoramic, posteroanterior, and submentovertex radiographs could be mentioned.

Panoramic radiographs could be used to detect mandibular asymmetry, differences in the shape and positions of the right and left condyles, differences in the height and width of the ramus, mandibular midline deviation, etc. (Peltola et al. 1995). However, distortion and magnification limit the accuracy of the obtained information.

The most frequent 2D method to evaluate asymmetry has been the posteroanterior radiograph. It allows frontal evaluation of the subjects. Although this projection could bring information about skeletal and dental asymmetries, it does not show the anteroposterior location of the dental components in relation to the skeletal structures.

To overcome these limitations, the submentovertex is also used to evaluate facial asymmetry (Ritucci and Burstone 1981; Forsberg et al. 1984; Arnold et al. 1994; Rose et al. 1994; Janson et al. 2001). The submentovertex radiograph is an option to evaluate skeletal and dental symmetry of the maxillary and mandibular components. It allows an analysis based on an axial projection.

In the next topics, the analyses of some of these radiographic projections will be described.

Submentovertex Radiographs

The submentovertex projection allows the use of specific skeletal landmarks to determine the sagittal axis and to use specific coordinate systems. For the submentovertex radiograph, the patient should be positioned in the cephalostat and seated on a bench without backrest. The patient’s head should be rotated posteriorly until the Frankfurt plane becomes parallel with the radiographic film cassette. In order to maintain this position, the patient should handle, with the two hands, an auxiliary support located in front of him/her (Janson et al. 2001).

During the exam, the subjects should maintain their teeth in centric occlusion, as they do not present functional mandibular deviation (Forsberg et al. 1984; Lew and Tay 1993; O’Byrn et al. 1995). One could argue that radiographs should be taken in centric relation to detect any functional mandibular deviation that might interfere with the evaluation of mandibular asymmetry in relation to the maxilla and the cranial base (Ritucci and Burstone 1981; Williamson 1981; Forsberg et al. 1984). Nevertheless, centric occlusion is preferred in patients without functional mandibular deviation.

Cephalometric structures, lines, planes, and measurements are obtained according to Ritucci and Burstone (1981), with some modifications (Forsberg et al. 1984; Janson et al. 2001). The tracings of the submentovertex radiograph include foramen magnum, foramen spinosum, metallic ear rods, mandibular condyles, gonial angles, coronoid processes, posterior cranial vault, zygomatic arches, anterior cranial vault, pterygomaxillary fissures, vomer, maxillary and mandibular first molars, and maxillary and mandibular central incisors. The structures and landmarks used in this projection are illustrated in Figure 7.3 (Janson et al. 2001).

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