12.9
Special Treatment Considerations of Face Asymmetries
Giampietro Farronato
Introduction
Dysgnathic facial patterns characterized by asymmetrical function or morphology have always been a subject of serious debate regarding their orthodontic–surgical management. The reason for this is that asymmetrical dysgnathic patterns lead to different interpretations by clinicians and researchers, and there is no definitive consensus on many aspects of their classification and characteristics. Asymmetries present specific diagnostic, prognostic, and therapeutic challenges that clearly differentiate them from other patterns of facial malformations. Certainly, the etiopathogenetic evaluation of causal etiology also offers cues for various interpretations.
In this section, the most salient diagnostic, etiologic, and therapeutic aspects will be considered thus suggesting the interpretive key in genesis‐causal and logical interpretation of treatment. In addition, the various nosological pictures of dentoalveolar and skeletal components in growing and late‐growing patients in need of functional, orthopedic, orthodontic, and orthodontic–surgical treatment will be presented.
Diagnosis
Diagnosis in orthodontics and dentofacial deformities has been based on clinical and cephalometric examination for more than one century. The lateral cephalometric examination of the skull is totally unsuitable for evaluating asymmetrical patterns allowing at most to evaluate the bisection of the lower and posterior border of the mandible. With the advent of posteroanterior cephalometric radiography thanks to the contributions of Ennio Giannì and later of Robert M. Ricketts, the examination was amplified by examining the coincidence of the midpoints with the axis of facial symmetry and the skewness and dysmetria (different distance) of the analogous lateral points.
After the introduction of cone‐beam computed tomography (CBCT) in orthodontics and thanks to the studies performed at the University of Milan, it became evident that the evaluation of points and segments that lie on the median sagittal plane or are parallel to it are accurately evaluated on two‐dimensional radiographs (lateral and posteroanterior cephalometric radiographs) while segments oblique to the median sagittal plane for lateral cephalograms and to the frontal plane for posteroanterior cephalograms undergo underestimation, the greater the obliquity (Farronato et al. 2010a, 2010b, 2015b; Bombeccari et al. 2015; Firetto et al. 2019).
For example, the size of the mandibular body in normal subjects is underestimated by 13 mm when comparing its assessment by lateral cephalograms and CBCT. This underestimation is not a systematic error that can be corrected with appropriate adjustment but it varies as obliquity is different from subject to subject (narrow and long faces, wide and short faces) as well as in the same subject in two successive evaluations as obliquity with growth increases.
Among other things, this limitation may explain why the changes that occur as a result of treatment and growth are not well understood in the literature yet.
Three‐dimensional evaluation by using CBCT allows today a good understanding of the changes that characterize symmetric or asymmetric morphology and their precise qualitatively and quantitatively assessment.
Since 2007, faculty of the University of Milan have proposed an 18‐point cephalometric analysis from which 36 measurements are calculated and lead to a comprehensive evaluation of the subjects under examination (Figures 12.9.1 and 12.9.2). In addition, clinical evidence of asymmetry well justifies the use of CBCT based on the conservative concepts of ALADAIP, beyond ALARA, and toward a personalized optimization for pediatric patients (Oenning et al. 2021).
To facilitate diagnostic judgment and for educational purposes at our institution, evaluation of dental and skeletal changes takes place in the three planes of space namely sagittal, vertical, and transverse. Furthermore, the path that dysgnathia has taken in its genesis is assessed thus highlighting whether it is linear or rotational in nature.
Following this protocol of evaluation, the following findings, by increasing severity, can be verified:
One‐plane, two‐planes, three‐planes with linear, rotational or linear, and rotational alteration (Figures 12.9.3–12.9.5).
At the one end of the great range of variation, alterations affecting only one plane of space with only linear displacement will represent the most easily diagnosed and treated clinical situation (Maspero et al. 2011; Farronato et al. 2013, 2014a, 2014b, 2015a). At the other end of variation, clinical situations of maximum complexity with involvement of the three planes of space with linear and rotational displacements may present serious diagnostic and management challenges. Clinical appearances of asymmetry often involve two or three planes of space with both linear and rotational displacements.
By describing dysgnathic appearances in this way, the clinician can well understand the path that the deformity has followed in its development and the way to achieve correction. Such a described method allows one to understand how some alterations are able to be corrected using dentofacial orthopedic procedures while others can be managed by performing only orthodontic–surgical treatments.
Figure 12.9.1 Everything that is oblique is underestimated in the lateral view.
Figure 12.9.2 The University of Milan cephalometric analysis on CBTC including 18 points and 36 measurements.
Figure 12.9.3 Dentofacial deformity with the discrepancy on one plane.
Figure 12.9.4 Dentofacial deformity with the discrepancy on two planes.
Figure 12.9.5 Dentofacial deformity with the discrepancy on three planes.
Dealing exclusively on complex asymmetry problems by following such a diagnostic‐descriptive pathway allows an understanding of whether favorable or unfavorable treatment consequences may occur.
An asymmetrical Class II dentoskeletal deformity can be treated orthopedically in the dynamic phase of growth by modulating through the construction bite the different major activation on one side versus the other.
An asymmetrical Class I dentoskeletal deformity offers cues for more considerations as it is to be considered a false Class I which is actually Class III on one side and Class II on the other. The correction mostly is surgical, reductive on one side, and additive on the other.
In an asymmetrical Class III dentoskeletal deformity, if it coexists with an increase in vertical height, the worst of the unfavorable correlations develops. If the mandible is set back to the center then the Class III relationship is aggravated.
In most of the cases of increased vertical height, if the mandible is rotated up it also goes forward thus further aggravating the Class III relationship.
Therefore, asymmetrical Class III dentoskeletal deformities with increased vertical height find solution only with orthodontic–surgical treatments since only through osteotomies can the complex corrective movements in the three planes of space can be achieved.
Categories of Asymmetry
It is of great importance to address the most frequent conditions that might be encountered by the clinician in identifying the predisposing triggering factors and the developmental course of asymmetry.
Trauma
In children, the situations that can cause face asymmetry and whose origin can be clearly identified are those related to trauma of the maxillomandibular structures. These structures most exposed to trauma can be identified within the areas of the nose and the mandible.
The nasal septum constitutes a growth center in early life that contributes to the forward and downward displacement of the maxilla. Even a traumatic event of no particular intensity can cause its fracture and the deviation of its median axis. Following this trauma, the surrounding structures undergo a series of consequent progressive adaptations that can be characterized as following:
- Elevation of the maxilla on the side of the concavity of the septum, lowering on the side of the convexity, unevenness, and obliquity of the occlusal plane.
- If the pathogenic cause occurs early and persists for a long time, it affects mandibular growth, which exhibits canting of the occlusal plane, obliquity of the chin, rami of different lengths, and unevenness of the gonial angle and mandibular plane.
- The severity of the condition is determined by the earliness of the event, the intensity of the damage, and the greater or lesser susceptibility of the subject determined by the intrinsic factor of growth (more severe in skeletal Class III, less severe in skeletal Class II) as well as additional concomitant unfavorable dysfunctional factors (abnormal breathing and swallowing).
- Impaired respiratory function, if it is established early and persists for a long time, can trigger impaired transverse and vertical development of the maxilla that will influence the downward development of the nasal septum. When associated, as is often noted, with unilateral crossbite, it will lead not only to the deviation of dental arches’ midlines but also to an increasingly aggravating and complex asymmetry of the maxillomandibular complex (Figure 12.9.6).
The author’s team has amply demonstrated how therapeutic expansion of the maxilla leads to a reduction in nasal septum deviation, correction of unilateral crossbite, and reposition of the mandible to its normal median position. It also allows the resumption of normal respiratory function and normal mandibular kinesiology (Figure 12.9.7).
Occlusal Interference
The mechanism by which an occlusal interference in the transverse plane expresses itself in maxillomandibular growth process deserves further investigation. It has been shown that occlusal interference that intervenes by deviating the path in jaw closure to the side alters the functions of the temporomandibular joint (TMJ) structures in particular. The condyle represents a site of growth, which well demonstrated, responds to functional stimuli that in the norm are symmetrical on the two sides (Andresen 1932; Cozza et al. 2004, 2006).
Deviant interference in the frontal plane leads to a different condylar kinesiology: on the side of the deviation, the movement will be more vertical and reduced in excursion, on the other side, it will be wider vertically and with greater horizontal excursion. This gap will first be expressed by functional positional deviation, and then progressively by structural adaptation and remodeling leading to less predominantly vertical growth of one condyle and more predominantly horizontal growth of the other. The initial positional alteration will become increasingly structural involving not only the mandible but also the maxilla. If the occlusal interference is transient as a result of tooth displacement, exfoliation, occlusal adjustment, or following appropriate orthodontic correction, the anomaly rapidly regresses with restitution ad integrum.
Figure 12.9.6 (a) A clinical case with impaired transverse and vertical development of the maxilla. (b) Rapid maxillary expansion. (c) As a result of the rapid maxillary expansion, the septum deviation was corrected.
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