126 RESEARCH AND SCIENCE Thomas von Arx1 Scott Lozanoff2 Extraoral anatomy in CBCT - Michael M. Bornstein3,4 a literature review 1 Department of Oral Surgery and Stomatology, School of Dental Medicine, University of Bern, Switzerland Part 2: Zygomatico-orbital region 2 Department of Anatomy, Biochemistry and Physiology, John A. Burns School of Medi- cine, University of Hawaii, Honolulu, USA 3 Oral and Maxillofacial Radiol- ogy, Applied Oral Sciences KEYWORDS and Community Dental Care, Anatomy Faculty of Dentistry, The Uni- CBCT versity of Hong Kong, Prince Zygomatic bone Philip Dental Hospital, Hong Orbital cavity Kong SAR, China 4 Department of Oral Health & Medicine, University Center for Dental Medicine Basel UZB, University of Basel, Basel, Switzerland SUMMARY CORRESPONDENCE Prof. Dr. Thomas von Arx This second article about extraoral anatomy as noid bone along the lateral orbital wall. Each of Klinik für Oralchirurgie und seen in cone beam computed tomography (CBCT) the three surfaces of the zygomatic bone displays Stomatologie images presents a literature review of the zygo- foramina that transmit neurovascular structures. Zahnmedizinische Kliniken matico-orbital region. The latter bounds the The orbital cavity is located immediately above der Universität Bern maxillary sinus superiorly and laterally. Since the maxillary sinus from which it is separated Freiburgstrasse 7 CH-3010 Bern pathologic changes of the maxillary sinus are a only by a thin bony plate simultaneously serving Tel. +41 31 632 25 66 frequent indication for three-dimensional radi- as the orbital floor and the roof of the maxillary Fax +41 31 632 25 03 ography, the contiguous orbital cavity and the sinus. Several openings, such as the superior and E-mail: zygomatic bone may become visible on CBCT inferior orbital fissures, the ethmoidal and cra- [email protected] scans. The zygomatic bone forms the cheek nio-orbital foramina, and the optic and infraor- SWISS DENTAL JOURNAL SSO 130: prominence and has large contact areas with the bital canals, connect the orbit to the anterior and 126–138 (2020) maxilla through the zygomaticomaxillary suture middle cranial fossae as well as to the infratem- Accepted for publication: in the infraorbital region as well as with the sphe- poral and pterygopalatine fossae. 2 July 2019 SWISS DENTAL JOURNAL SSO VOL 130 2 P 2020 126-138_T1-1_vonarx_EDF.indd 126 30.01.20 15:26 RESEARCH AND SCIENCE 127 Introduction This is the second article in a series of papers presenting ana- 1 A tomical features outside the oral cavity as seen in cone beam computed tomography (CBCT) images. CBCT scans with a me- dium or large size of the field of view (FOV) may depict anatom- ical regions outside the area of interest. The maxillary sinus is an important anatomical structure that is often associated with dental pathology (periapical lesions, cysts, retained or supernu- merary teeth, oroantral communication, neoplasia, etc.). Con- sequently, the radiographic assessment of the maxillary sinus in conjunction with the clinical examination of the posterior maxillary teeth is a frequent diagnostic procedure (Yeung et al. 2018). For a detailed analysis of the anatomical features and pathologic changes of the maxillary sinus, CBCT has become 1 B the standard of care (Bornstein et al. 2018). Adjacent structures of the maxillary sinus contributing to its anatomical borders include the zygomatic bone and the orbital cavity. These struc- tures may become, at least partly, visible in CBCT scans of the maxillary sinus (Fig. 1–3). This literature review presents in de- tail the anatomy of the zygomatico-orbital region. Zygomatic bone The zygomatic or malar bone is a protuberant structure of the facial skeleton (viscerocranium) (Fig. 4–6). It forms the osseous component of the cheek (von Arx et al. 2018). The zygomatic bone is the most laterally located bone of the face and, as such, influences facial esthetics (Gong et al. 2014; Dechow & Wang 2016). Furthermore, the zygomatic bone contributes to the infe- rior and lateral portions of the orbital rim. The frontal process of the zygomatic bone extends superiorly along the orbit and ter- minates at the frontozygomatic suture. The temporal process of the zygomatic bone reaches posteriorly to the zygoma, or zygo- matic process of the temporal bone, and provides the anterior portion of the zygomatic arch. The zygoma articulates with the temporal process of the zygomatic bone through the zygomati- cotemporal suture. The zygomatic bone, quadrangular in shape, articulates with 1 C four other bones: maxillary, frontal, temporal, and sphenoid bones. Its anatomic position and contour together with the max- illa are responsible for midfacial harmony (Nascimento et al. 2015). The zygomatic bone has large contact areas with the maxilla (zygomaticomaxillary suture) in the infraorbital region and with the sphenoid bone along the lateral orbital wall. The zygomatico- maxillary buttress is a prominent bony structure located above the first or second maxillary molar. The zygomatic bone as well as the zygomatic arch serve as attachment areas for the masseter muscle (von Arx & Lozanoff 2017). The summit of the zygomatic bone, or zygomatic eminence, corresponds to the maximum of its anterolateral dimension. It is often used as a landmark in to- mographic studies of facial bone symmetry ( Lerhe et al. 2017). The zygomatic bone serves as a connection between the mid- dle and upper facial skeleton. Its muscular functional role is as- sociated with the origin of the masseter as well as of some facial muscles including zygomaticus major and minor (Coutinho et al. 2018). Due to its protruding anatomy, the zygomatic bone is frequently involved in external facial trauma requiring fracture repair. Fractures of the zygomatic bone may result in a disloca- tion of the respective bone fragment, formally always causing an orbital floor fracture and sometimes a defect (Czerwinski et al. Fig. 1 Coronal (A) and axial (B, C) CBCT images at the level of the orbits 2008). Corrective surgery for the treatment of malformations of (54-year-old male). 1 = orbit; 2 = lacrimal fossa; 3 = frontal sinus; 4 = perpendicular plate of eth- the midface also includes the zygomatic bone. Furthermore, the moid bone; 5 = optic canal; 6 = superior orbital fissure; 7 = greater wing of placement of zygomatic implants (Fig. 7 and 8) represents an al- sphenoid bone; 8 = lesser wing/body of sphenoid bone; 9 = sphenoid sinus SWISS DENTAL JOURNAL SSO VOL 130 2 P 2020 126-138_T1-1_vonarx_EDF.indd 127 30.01.20 15:26 128 RESEARCH AND SCIENCE 2 A 2 B 2 C 3 A 3 B Fig. 2 Prominent zygomaticotemporal foramen in a 27-year-old male: CBCT 4 rendering (A), coronal (B) and axial (C) CBCT images. 1 = zygomaticotemporal foramen; 2 = coronoid process of mandible; 3 = zy- gomaticomaxillary suture; 4 = infraorbital canal; 5 = inferior orbital fissure; 6 = nasolacrimal duct Fig. 3 Posterior ethmoidal foramina seen in coronal (A) and axial (B) CBCT images of a 62-year-old female. * = posterior ethmoidal cells; 1 = posterior ethmoidal foramen; 2 = inferior orbital fissure; 3 = frontal bone (contributing to anterior floor of anterior cra- nial fossa); 4 = greater wing of sphenoid bone; 5 = superior orbital fissure; 6 = frontal process of zygomatic bone; 7 = zygomaticosphenoid suture Fig. 4 Anterolateral view of the right zygomatico-orbital region (macerated skull of unknown origin). 1 = zygomatic bone; 2 = zygomaticotemporal suture; 3 = zygomaticomaxillary suture; 4 = zygomaticofrontal suture; 5 = zygomaticofacial foramen; 6 = zy- gomatic process of temporal bone; 7 = orbital part of os maxillae; 8 = frontal process of os maxillae; 9 = lacrimal fossa; 10 = lacrimal bone; 11 = lamina or- bitalis (papyracea) of ethmoid bone; 12 = frontal bone; 13 = anterior ethmoidal foramen; 14 = posterior ethmoidal foramen SWISS DENTAL JOURNAL SSO VOL 130 2 P 2020 126-138_T1-1_vonarx_EDF.indd 128 30.01.20 15:26 RESEARCH AND SCIENCE 129 5 Fig. 5 Posterior view of the right zygomatic bone (macerated skull of un- known origin). 1 = zygomatic bone; 2 = zygomaticotemporal foramen; 3 = zygomaticofrontal suture; 4 = frontal bone; 5 = zygomaticotemporal suture; 6 = zygomatico- maxillary suture; 7 = posterior (infratemporal) surface of os maxillae; 8 = zy- gomatic process of temporal bone; 9 = zygomaticotemporal suture Fig. 6 Rendering of CBCT images of the zygomatico-orbital region of a 28-year-old male: anterolateral view (A) and anterosuperior view (B). 1 = zygomatic bone; 2 = two zygomaticofacial foramina; 3 = zygomaticomax- illary suture; 4 = zygomaticofrontal suture; 5 = infraorbital canal; 6 = inferior orbital fissure; 7 = optic canal; 8 = superior orbital fissure; 9 = infraorbital fo- ramen; 10 = lateral orbital wall (greater wing of sphenoid bone) 6 A 6 B SWISS DENTAL JOURNAL SSO VOL 130 2 P 2020 126-138_T1-1_vonarx_EDF.indd 129 30.01.20 15:26 130 RESEARCH AND SCIENCE 7 A 7 B 8 ternative for the rehabilitation of partially or totally edentulous patients with severe atrophy of the posterior alveolar process (Candel-Marti et al. 2012; Aparicio et al. 2014; Wang et al. 2018). Several authors have evaluated the thickness of the zygomatic bone. Rigolizzo et al. (2005) divided the zygomatic bone in sev- eral sections and performed thickness measurements of 60 dry Brazilian skulls. Mean thicknesses (distances from internal to external surfaces) of the central bone sections ranged from 2.8 to 6.5 mm. Hung et al. (2017) determined the available bone dimensions for zygomatic implant placement in 150 Chinese patients using CBCT. Mean thicknesses of the zygomatic bone measured in different sites ranged from 4.4 to 8.0mm and mean lengths (cranio-caudal distances) ranged from 25.7 to 32.5 mm. In a study of 11 Japanese cadavers, the mean height of the zygo- matic bone ranged from 18.2 to 23.1 mm and its thickness from 1.6 to 7.2 mm, depending on the site of measurement (Takamaru et al. 2016). The zygomatic bone shows morphological variation that is determined by various environmental and ancestral factors such as masticatory stress, climate effects, as well as maxillary sinus features (Oettle et al.