Natural variation of the zygomaticomaxillary complex symmetry in normal individuals☆
Introduction
The most frequently encountered midfacial fractures are zygomaticomaxillary complex (ZMC) fractures (Gupta et al., 2009, van Hout et al., 2013, Arangio et al., 2014). In ZMC fracture cases, the restoration of facial symmetry is the main treatment goal after functional recovery (Ellis, 2013, Ellis and Perez, 2014) because symmetry plays an important role in the visual perception of faces (Grammer and Thornhill, 1994, Perrett et al., 1998, Rhodes, 2006). Furthermore, a symmetrical face is correlated with perceived healthiness and attractiveness (Rhodes et al., 1998, Jones et al., 2001, Fink et al., 2006).
Computer-assisted surgery (CAS) plays a significant role in several fields of oral and maxillofacial surgery (Cevidanes et al., 2007, Cevidanes et al., 2009, Nada et al., 2011, Moubayed et al., 2012, Swennen, 2014, Schepers et al., 2015, Dubois et al., 2015). CAS has gained clinical importance for facilitating the accuracy of achieving symmetrical surgical reconstruction of the orbit and midface (Metzger et al., 2007, Schramm et al., 2009, Gander et al., 2015, Dubois et al., 2015, Wagner et al., 2015), especially in unilateral, hard-tissue, maxillofacial trauma management. The main steps in CAS protocols concerned with unilateral defects consist of the creation of a three-dimensional (3D), virtual, hard-tissue model, followed by segmentation, mirroring, and finally superimposing of the non-traumatized segmented region of interest onto the defect. The basis for this technique is the assumption that faces are symmetrical. However, the craniofacial bone is generally regarded as being slightly asymmetrical (Rossi et al., 2003). Several papers have been published in which a method is proposed for measuring the amount of asymmetry of the ZMC, emphasizing the interest, relevance, and importance of the ZMC (Nechala et al., 1998, Furst et al., 2001, Czerwinski et al., 2005, Pham et al., 2007, Metzger et al., 2007, Moubayed et al., 2012).
The main aim of this study was to test the hypothesis that the ZMC can be considered to be fairly symmetrical, which would justify the use of a CAS protocol in unilateral ZMC defects. For this purpose, the range of gender-specific, hard-tissue ZMC symmetry was measured through the use of a validated 3D semi-automatic method. Secondly, the ZMCs of males 40 years and younger were evaluated, because this is the demographic most frequently encountered with ZMC fractures (Ellis and Kittidumkerng, 1996, van den Bergh et al., 2012, Ellis and Perez, 2014). Finally, based on the normal variation in ZMC symmetry, a benchmark was proposed that can contribute to the diagnostic and clinical decision-making process, in addition to the postoperative evaluation of ZMC fracture cases.
Section snippets
Materials and methods
This study was approved by the Medical Ethical Committee of the Academic Medical Centre (AMC) of the University of Amsterdam (Ref. No. W16_216) and was done in accordance with the Declaration of Helsinki guidelines for human research. The study was conducted at the Department of Oral and Maxillofacial Surgery in conjunction with the Department of Radiology of the AMC.
Results
The mean age of the patients from whom the CT scans were obtained was 58 ± 19 years (range 18–94) (Table 2). The mean AD calculated for the total study population was 0.9 ± 0.3 mm (95% CI: 0.3–2.3); the corresponding mean NPD was 1.7 ± 0.5 mm (95% CI: 0.5–3.9) (Table 3, Table 4). A mean AD of 1.0 ± 0.3 mm (95% CI: 0.3–2.3) and a mean NPD of 1.9 ± 0.5 mm (95% CI: 0.5–3.9) were found for the male study population (Table 3, Table 4). For the female study population, the mean AD and NPD were
Discussion
In clinical practice the human skull is considered to be in symmetrical harmony (Schmelzeisen et al., 2004, Nowinski et al., 2011, Wagner et al., 2015). However, a limited amount of asymmetry of the craniomaxillofacial bones is not unusual (Rossi et al., 2003). Over the years many methods for symmetry measurement of the ZMC have been described, such as direct measurements on dry skulls, cephalometric radiographic image analysis, and anthropometrics (Farkas and Cheung, 1981, Furst et al., 2001,
Conclusion
Through the use of a recently validated, 3D, semi-automatic method this study illustrates the anatomical variance in symmetry of the ZMC. The authors submit that the amount of ZMC asymmetry found is insignificant, which in our opinion justifies the use of mirroring techniques. A baseline criterion is proposed for normal anatomical (overall and maximal) symmetry of the ZMC, which can function as a benchmark for evaluating asymmetry in ZMC trauma cases for diagnostic and evaluation purposes.
Conflict of interest
The authors declare that they have no conflict of interest.
Ethical approval (Ref. No. W16_216)
The local ethics committee considered this study not subject to consent, and the study was performed in accordance with the Declaration of Helsinki.
Ethical standards
In compliance with ethical standards.
Informed consent
Not required. CT data were collected from an earlier study.
Funding
No funding was received for this study.
Acknowledgements
The authors thank Serge A. Steenen for his kind assistance in preparing the illustrations used in Figures 1–6.
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This work should be attributed to the Department of Oral and Maxillofacial Surgery, Academic Medical Centre/Academic Centre for Dentistry Amsterdam (ACTA) and University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Head of Department: J. de Lange, MD, DDS, PhD, Professor of Oral and Maxillofacial Surgery.
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Equal contribution.