Introduction

Minor asymmetry is a desirable variation of the craniofacial structures because these little inconsistencies are perceived as esthetically pleasing (Peck et al. 1991). Laterality in the normal asymmetry of the face is consistently found in humans and it is likely to be a hereditary rather than an acquired trait (Haraguchi et al. 2008).

A considerable number of patients suffer from noticeable asymmetry expressed in the face, jaws, and occlusion. However, there is no consensus concerning its degree, side prevalence, or localization. In a survey at a university dentofacial clinic, 34% of the patients were found to have clinically apparent facial asymmetry. When present, asymmetry affected the upper face in only 5%, the midface (primarily the nose) in 36%, the chin in 74%, and with the occlusal plane tilted in 41% (Severt and Proffit 1997).

Dentofacial and occlusal asymmetries can be found in children, adolescents, and adults and their categorization is limitless.

Classification based on etiology and time of appearance includes (a) congenital malformations with associated growth disorders, (b) primary growth disorders, and (c) acquired diseases or trauma with associated growth disorders (Pirttiniemi et al. 2009).

If syndromes and rare diseases with asymmetry in the craniofacial and dental regions are excluded, there is still a plethora of groups of patients characterized by mild, moderate, and severe manifestations of asymmetries affecting hard and soft tissues of the face and the dentoalveolar regions. They include cases with hemifacial microsomia (craniofacial microsomia), hemimandibular elongation, hemimandibular hyperplasia, condylar fractures, ankylosis of the temporomandibular joint, functional mandibular displacement, rheumatoid arthritis, muscle pathology, benign tumors, cleft lip and/or palate, craniosynostosis, temporomandibular disorders, etc. (Figure 5.1).

In an attempt for a systematic classification of facial asymmetry the skeletal structures of this kind of patients were analyzed and classified according to their structural characteristics using three‐dimensional computed tomography (Baek et al. 2012). The two main groups consisted of patients with asymmetry caused by a shift or lateralization of the mandibular body (44%) or significant difference between the left and right ramus height with menton deviation to the short side (39%).

When an investigation was undertaken for evaluating how severity of asymmetries affecting the mandible and chin point influence perceived attractiveness, asymmetry of 10 mm is perceived as being significant, but at 5 mm and below, it is largely unnoticed. The greater than 10 mm the degree of asymmetry, the more noticeable and the greater the desire was for correction. Clinician and patient ratings were similar and more critical than ratings of laypeople (Naini et al. 2012).

In general, the approach to diagnosis and treatment planning is the same for patients with asymmetries as for those with other malocclusions or dentofacial deformities (Proffit and Turvey 1990). However, it is important to realize that the word “asymmetry” comprises innumerable morphological variations as teeth, dental arches, skeletal components, and soft tissues may in theory be displaced and rotated in three planes of space leaving six degrees of freedom to every component. In the Chapter “Rotational diagnosis and treatment of dental asymmetries” of this book, a comprehensive presentation of the three‐dimensional assessment is described. In this section, the examination of special features in patients with dentofacial and occlusal asymmetries will be addressed and only in relation to head posture, stomatognathic function, face evaluation, and malocclusion.

Head Posture

Before getting into the facial, oral, and occlusal clinical examination, it is important to verify whether the head posture is influenced by factors outside the stomatognathic region that either can be taken care of before focusing on the dentoalveolar asymmetry or have to be accepted and compensated for.

An example of a deviation that should be taken care of as early as possible is torticollis that is shortening of the sternocleidomastoids muscle leading to a torsion of the neck and affecting physiologic head posture. This is a dystonic condition defined by an abnormal asymmetrical head or neck position, which may be due to a variety of causes. The head becomes persistently turned to one side, often associated with painful muscle spasms. Being untreated this pathological condition will lead to marked craniofacial and dental asymmetries (especially in Class III malocclusions) (Pirttiniemi et al. 1989; Kawamoto et al. 2009; Yuan et al. 2012).

The younger the patients are when the affected sternocleidomastoid is cut the easier it is to correct the asymmetry, but even in older patients dentoalveolar corrections can be obtained without the need of orthognathic surgery (Do 2006; Sargent et al. 2019) (Figure 5.2). On the other hand, there are cases of torticollis in which the effect on facial appearance and occlusion are very moderate (Figure 5.3).

A more severe condition that influences the head posture is the Sprengel’s deformity (also known as high scapula or congenital high scapula). It is a rare congenital skeletal abnormality where a person has one shoulder blade that sits higher on the back than the other. The deformity is due to a failure in early fetal development where the shoulder fails to descend properly from the neck to its final position. This deviation is characterized by a small and undescended scapula often associated with scapular winging and scapular hypoplasia. The diagnosis is made clinically with a high‐riding, medially rotated, triangular‐shaped scapula, with associated limitations in shoulder abduction and flexion leading to an asymmetric position of the head and the dentition (Harvey et al. 2012) (Figure 5.4).

Another example of a condition outside the stomatognathic region that may influence the head posture and cause asymmetrical dentoalveolar development is scoliosis. This is a sideways curvature of the spine that most often is diagnosed in adolescents. While scoliosis can occur in people with conditions such as cerebral palsy and muscular dystrophy, the etiology of most cases of scoliosis in children remains unknown. In this pathological condition, a lateral curvature of the spinal column can influence the position of the shoulders and the head posture (Zhou et al. 2013; Furlanetto et al. 2016) (Figure 5.5).

Functional Assessment

Once the factors having an influence of the head posture are taken into consideration the clinical examination can be performed and the asymmetry should be classified as functional or morphological.

The first step when identifying an asymmetry is to verify whether an abnormal function, namely a forced bite, is contributing to the asymmetry (Figure 5.6