To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter Toppan Best-set. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. Chapter c00143 Oropharyngeal Growth and Skeletal Malformations 143 Stacey Dagmar Quo; Benjamin T. Pliska; Nelly Huynh Chapter Highlights p0010 • Sleep-disordered breathing (SDB) is marked by manifestations has not been determined. The varying degrees of collapsibility of the length and volume of the airway increase until pharyngeal airway. The hard tissue boundaries the age of 20 years, at which time there is a of the airway dictate the size and therefore the variable period of stability, followed by a slow responsiveness of the muscles that form this decrease in airway size after the fifth decade of part of the upper airway. Thus, the airway is life. The possibility of addressing the early forms shaped not only by the performance of the of this disease with the notions of intervention pharyngeal muscles to stimulation but also by and prevention can change the landscape the surrounding skeletal framework. of care. u0015 • The upper and lower jaws are key components • Correction of specific skeletal anatomic u0025 of the craniofacial skeleton and the deficiencies can improve or eliminate SDB determinants of the anterior wall of the upper symptoms in both children and adults. It is airway. The morphology of the jaws can be possible that the clinician may adapt or modify negatively altered by dysfunction of the upper the growth expression, although the extent of airway during growth and development. In turn, this impact is uncertain. These strategies seek to the altered morphology of the jaws can be alter an abnormal facial growth pattern wherein positively influenced by orthodontic treatment. SDB worsens over time. Future research should focus on determining in which individuals u0020 • The association between altered dentofacial morphology and SDB has been well dentofacial morphology makes a significant documented in children, adults, and patients contribution to the pathogenesis of SDB. This with craniofacial syndromes. Whether this may bring clinicians one step closer to targeting disease of childhood has the same origins as specific treatments that more effectively treat adult obstructive sleep apnea but more subtle the disorder. p0040 This chapter is directed to provide an integrated vision to both century, it was believed that differential deposition and resorp- the scientist and clinician dealing with growth and develop- tion on the surface of bones were largely responsible for ment of the oropharyngeal structures. It is divided into three growth of the craniofacial skeleton. This remodeling theory sections. The first reviews the fundamentals of growth of the then gave way to one heralding the role of the sutures, which craniofacial complex and the development of the upper airway. held that similar to the epiphyses of the long bones, it was the The second section outlines those characteristics based on connective tissue and cartilaginous joints of the craniofacial current definitions of the sleep-disordered breathing (SDB) skeleton that produced expansive proliferative growth forcing syndrome, that is, there is a broad range of anthropomorphic the bones and soft tissues away from each other.1 Exemplify- characteristics and OSA severity that needs to be better delin- ing this theory was the concept that the mandible was much eated. The last section reviews management and treatment like a horseshoe-shaped long bone, with the condylar cartilage strategies based on what is known about craniofacial develop- acting like open-ended epiphyseal plates, pushing the man- ment and anatomy. This chapter is a primer to other chapters dible down and away from the rest of the head. in this section and to the ones in Section 14. Several inconsistencies in the hypothesis that sutures alone p0050 could be the determinants of craniofacial growth surfaced. s0010 CRANIOFACIAL GROWTH AND DEVELOPMENT Sutural growth was more similar to periosteal apposition of bone than previously understood, and sutures acted as p0045 Early theories of craniofacial development were based on the reactive sites of bone growth rather than growth centers. Scott, belief that growth of the face and jaws was essentially immu- in 1953, proposed the nasal septum theory of growth, which table because of intrinsic regulation by inherited genetic traits. held as its main tenet that the anterior and inferior growth Research centered on finding the location or sites where these of the nasal septal cartilage was the determining, driving traits were expressed that drove normal form and function of force of facial growth.2 Whereas Scott’s theory contributed the other surrounding structures. During the early twentieth to the understanding that growth at the sutures and surface 1401 ISBN: 978-0-323-24288-2; PII: B978-0-323-24288-2.00143-4; Author: Kryger & Roth; 00143 Kryger_2882_Chapter 143_main.indd 1401 12/10/2015 8:05:31 PM To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter Toppan Best-set. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 1402 PART II • Section 18 Dentistry and Otolaryngology in Sleep Medicine remodeling were essentially reactive sites of bone growth, it controlled molecular signaling between the oral ectoderm and was still founded in the paradigm that craniofacial develop- the underlying core of cranial neural crest.7 Further develop- ment and morphogenesis were genetically predetermined and ment is contingent on the formation and growth of Meckel unalterable.1 In modern perspective, the nasal septal cartilage cartilage, the first skeletal element of the mandible. The sub- is considered an important growth center; however, the mech- sequent elongation of this rod of cartilage leads to promotion anism behind this growth has been appropriately updated as of outgrowth of the mandible, and the primary ossification of described here. the mandible occurs as intramembranous bone formation 10 p0055 A fundamental shift in the field of craniofacial biology along this cartilaginous core. As the bony mandible further emerged with Moss’ introduction of the functional matrix develops, Meckel cartilage largely disappears, eventually to hypothesis in 1960.3 Whereas all previous theories deemed persist only as small portions of the incus and malleus of the craniofacial growth to be predetermined by genetic traits, the middle ear. In addition to the mandible, the mandibular pro- functional paradigm introduced the idea of plasticity of devel- cesses also form the lower lip and the lower areas of the opment and growth of the craniofacial skeleton.1 According cheeks. to this theory, the role of our genes was to initiate the process The lateral and medial nasal processes originate as ectoder- p0075 by setting the initial context under which development could mal thickenings on the surface of the frontonasal process early occur; beyond that, it was the extrinsic environmental and in the fifth week of embryonic life. Subsequent broadening of functional demands of the various craniofacial components the head and medial growth of the maxillary processes result that determined all future aspects of growth. This theory revo- in medial displacement of the early nasal processes. As the lutionized the field by introducing two important concepts. two medial nasal processes merge at the midline, the philtrum First, it brought the possibility of growth modification as a and columella of the nose are formed. Deeper aspects of the treatment option for malocclusions or facial malformations by medial nasal processes will differentiate to form the nasal changing the direction of facial development to a more desired septum, which is a key growth center of the midface postna- outcome. Second and perhaps more important, the plasticity tally. Fusion of the medial nasal process with the maxillary of development opened a new area of research, focusing on process leads to formation of the majority of the upper lip, the the critical time and specific factors that lead to the maladap- zygomas, and the maxilla bilaterally. The lateral nasal processes tive plasticity of the form and function of the craniofacial go on to form the sides and alae of the nose as the subsequent complex.4 2 weeks sees the formation of the future nostrils and nasal p0060 With the emergence of developmental molecular biology, cavity with the development of the primary and secondary the genetic and external or epigenetic regulation of craniofa- palates.11 Secondary palate formation relies on the coordi- cial growth is now better understood, and the modern syn- nated growth and movement of the primordia of the tongue thesis is that both genomic and epigenetic factors are necessary and both lower and upper jaws. During the sixth week of contributors to craniofacial development.5,6 Several genes and development, paired lateral palatal shelves arise as medial pro- gene products regulate the morphogenesis and intrauterine jections from each maxillary process. Critically, at this time, development of the craniofacial complex. There is an extremely there is rapid anterior growth of the early mandible by pro- complex interaction between these genetic factors and epigen- liferation of Meckel cartilage, which displaces the tongue etic influences. The plasticity of early development depends forward, lowering it relative to the palatal shelves.12 Once the not only on the effects of certain environmental conditions on tongue has descended, during the seventh week, the palatal the underlying genetic code but also on previous environmen- shelves rotate from a vertical to a horizontal position directed tal conditions that may have directly upregulated or down- toward the midline.