Etiology-Based Dental and Craniofacial Diagnostics explores the role of embryology and fetal pathology in the assessment, diagnosis, and subsequent treatment planning of a wide range of disorders in the dentition and craniofacial region. Initial chapters cover various aspects of normal dental and craniofacial development, providing the necessary biological background for understanding abnormal patient cases. Chapters then focus on the etiology behind a wide range of cases observed in everyday practice--including deviations in tooth morphology and number, tooth eruption, root and crown resorption, and craniofacial malformations, disruptions and dysplasia. * Unique new work from a leading authority in orthodontics, craniofacial embryology and fetal pathology * Demonstrates how human prenatal development offers unique insights into postnatal diagnosis and treatment * Clinical significance and implications are highlighted in summaries at the end of each chapter * Ideal for postgraduate students in orthodontics, paediatric dentistry and oral medicine
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Content and Structure of the Book
Chapter 1: Craniofacial Development and the Body Axis: Normal and Pathological Aspects From Early Prenatal to Postnatal Life
Body Axis Pre- and Postnatally
Craniofacial Development Pre- and Postnatally
Craniofacial Morphology and Growth
Highlights and Clinical Relevance
Chapter 2: Craniofacial Development and the Brain: Normal and Pathological Aspects from Early Prenatal to Postnatal Life
Central Nervous System in Relation to Neurocranial Development Pre- and Postnatally
Peripheral Nervous System Pre- and Postnatally
Highlights and Clinical Relevance
Chapter 3: Developmental Fields in the Cranium and Alveolar Process
Definition of Developmental Field
Developmental Fields in the Cranium
How can Craniofacial Fields be Proven?
Developmental Fields in the Alveolar Process
Highlights and Clinical Relevance
Chapter 4: Tooth Development and Tooth Maturation from Early Prenatal to Postnatal Life
Histological Evaluation of Early Tooth Development
Radiographic Evaluation of Normal Dental Maturation
Clinical Evaluation of Dental Maturity
Tooth Formation from the Initial Stages to the Eruption Stages: Relation to Fields, Gender, Age, and Skeletal Maturity
Similarities and Differences in Primary and Permanent Dental Development
Highlights and Clinical Relevance
Chapter 5: Periodontal Membrane and Peri-Root Sheet
The Peri-Root Sheet in the Primary and Permanent Dentition
Highlights and Clinical Relevance
Chapter 6: Normal Tooth Eruption and Alveolar Bone Formation
Tooth Eruption Mechanism and Alveolar Bone Formation
Tooth Eruption and Jaw Growth
Eruption Sequences in the Primary and Permanent Dentition
Highlights and Clinical Relevance
Chapter 7: Etiology-Based Diagnostics: Methods and Classification of Abnormal Development
Why Use Etiology-Based Diagnostics?
Definitions of Key Words
Analyzing the Dentition, Oral Cavity, and Cranium: Practical Guide
Diagrams for Diagnostics
Highlights and Clinical Relevance
Chapter 8: Deviation in Tooth Morphology and Color: Normal and Pathological Variations Including Syndromes
Primary Dentition: Crown, Root, and Pulp
Permanent Dentition: Crown, Root, and Pulp
Abnormal Dental Development: Fields and Bilateralism
How to Analyze the Etiology Behind Deviation in Tooth Morphology: is it Malformation, Disruption Or Dysplasia?
Highlights and Clinical Relevance
Chapter 9: Deviations in Tooth Number: Normal and Pathological Variations Including Syndromes
Agenesis: Possible Etiologies
Agenesis of the Primary and Permanent Dentition: Hypodontia
Supernumerary Teeth: Possible Etiologies
Supernumerary Teeth in the Primary and Permanent Dentition: Hyperdontia
How to Analyze the Etiology Behind Deviation in Tooth Number
Highlights and Clinical Relevance
Chapter 10: Tooth Eruption and Alveolar Bone Formation: Abnormal Patterns Including Syndromes
Pathological Eruption of Primary Teeth
Pathological Eruption of Permanent Teeth
Abnormal Eruption in Syndromes and Dysplasia
Segmental Odontomaxillary/Mandibular Dysplasia
Eruption and Heredity
Eruption Problems in Both Dentitions
Localized Abnormal Alveolar Bone Formation
Why Analyze the Etiology Behind Abnormal Eruption?
Highlights and Clinical Relevance
Chapter 11: Root and Crown Resorption: Normal and Abnormal Pattern Including Syndromes
Tooth Resorption Theory
Resorption in the Primary Dentition
Resorption in the Permanent Dentition
Other Examples of Resorption
How to Analyze the Etiology Behind Abnormal Root Resorption in the Permanent Dentition
Highlights and Clinical Relevance
Chapter 12: Apparently Normal Nonsyndromic Dentitions are Phenotypically Different: The Interrelationship between Deviations in the Dentition and Craniofacial Profile
Heredity and the Dentition
Dentitions with Agenesis of Single Teeth
Dentitions with Multiple Tooth Agenesis
Dentitions with Macrodontic Maxillary Central Incisors
Dentitions with Supernumerary Teeth
Dentitions with Ectopic Canines
Dentitions with Transpositions
Dentitions with Arrested Eruption of Primary Molars
Dentitions Suitable for Tooth Transplantation
Dentitions with Arrested Eruption of Permanent Teeth
Dentitions with Persistence of a Primary Molar in Adulthood
Dentitions with Idiopathic Collum Resorption
Highlights and Clinical Relevance
Chapter 13: Craniofacial Syndromes and Malformations: Prenatal and Postnatal Observations
Holoprosencephaly/solitary median maxillary central incisor (SMMCI) syndrome
Cerebellar Hypoplasia/Cri-Du-Chat Syndrome
Myelomeningoceles/Spina Bifida and Hydrocephalus
Down's Syndrome (Trisomy 21)
Fragile X Syndrome
Cleft Lip and Palate
Comparison between Pre- and Postnatal Findings: Results and Restrictions
Malformations: Nonsyndromic Examples
Highlights and Clinical Relevance
Chapter 14: Craniofacial Disruptions: Prenatal and Postnatal Observations
Highlights and Clinical Relevance
Chapter 15: Craniofacial Dysplasia: Prenatal and Postnatal Observations
Endochondral and Intramembranous Bone Dysplasia in the Cranium
Dysplasia in Nonosseous Tissue
Highlights and Clinical Relevance
Chapter 16: Hard Tissue as a Diagnostic Tool in Medicine
Perspectives for Prenatal Craniofacial Pathology
Perspectives for Perinatal and Pediatric Pathology
Perspectives for Clinical and Basic Research
Perspectives for Anthropology
Chapter 17: Clinical Cases and Unanswered Questions
Conditions in Diagnostics, Treatment Planning, and Outcome
Examples of Diagnostics and Treatment of Eruption Problems
End User License Agreement
Table of Contents
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Library of Congress Cataloging-in-Publication Data
Names: Kjær, Inger, author.
Title: Etiology-based dental and craniofacial diagnostics / Inger Kjær.
Description: Southern Gate, Chichester, West Sussex, UK ; Ames, Iowa : John Wiley & Sons Inc., 2017. | Includes bibliographical references and index.
Identifiers: LCCN 2016018619| ISBN 9781118912126 (cloth) | ISBN 9781118912102 (ePub) | ISBN 9781118912119 (Adobe PDF)
Subjects: | MESH: Tooth Abnormalities–diagnosis | Skull–embryology | Skull—growth & development
Classification: LCC RK308 | NLM WU 101.5 | DDC 617.6/3075–dc23 LC record available at https://lccn.loc.gov/2016018619
A catalogue record for this book is available from the British Library.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.
It is a great pleasure for me to dedicate this book to dentists and other professionals working in the community dental clinics in Denmark. I would like to take the opportunity to express my admiration for this public dental institution which serves nearly all of the children in the country.
A hearty thanks for:
Mutual collaboration and inspiration regarding diagnostics and treatment of patients in the clinic
The helpfulness and confidence that I have received over many years
Interest and support in this project for the benefit of our future patients.
What makes this book different from other textbooks on dental and craniofacial diagnostics?
This book is meant for clinicians, for pre- and postgraduate students, and for researchers in different fields of dental and craniofacial diagnostics. Every deviation in dental and craniofacial disorders, as described in this book, is based on embryological insight. Thus embryology is not restricted to an isolated chapter; insight from embryology and fetal pathology is applied throughout the entire book.
Etiology implies the cause or origin of a disease or disorder. In this book, the embryological origin is the foundation for the etiology-based postnatal diagnostics of disorders in the dentition and craniofacial region.
Every congenital condition has a developmental path from conception to late adulthood. If the etiology is known, there is a series of possibilities for predictions of development and treatment during the entire life span. Normal and pathological fetal development should in all medical disciplines be the biological basis for postnatal diagnostics. This way of thinking – from the very beginning and forward – is not restricted to medicine and odontology.
I would therefore like to end this foreword with a quote by Winston Churchill:
“The further you can look back, the further you can look ahead.”
The scientific and clinical knowledge presented in this book is primarily based on personal research in normal and pathological prenatal cranial development combined with postnatal clinical experience in pediatrics, orthodontics, and diagnostics of rare human developmental conditions.
The purpose of this book is to focus on the etiology behind the clinical questions that are encountered in everyday practice, and which make diagnostics and treatment difficult. These questions include the following.
What is the mechanism behind tooth eruption? Can we explain this phenomenon?
How and when does the periodontal membrane develop?
After a tooth has emerged, it continues to erupt. What happens in the periodontal membrane during this continued eruption?
How is continued eruption associated with growth of the alveolar process?
Why do some areas in the jaws frequently contain abnormalities while others do not?
Can we explain correlations between findings in the maxilla and the mandible?
Why is there such a great difference between primary and permanent teeth regarding the occurrence of agenesis, resorption, and eruption?
What protects a permanent tooth root from resorption?
Are there similarities between the periodontal membrane of a primary tooth and the periodontal membrane of a permanent tooth?
Can signs in the primary dentition predict the later development of the permanent dentition?
How do diseases and/or the intake of medicine influence dental and craniofacial development?
All these central questions have had no clear answer until now. The issue has been that traditional research in the craniofacial region has been restricted by ethical, technical, and biological limits. In this book, experience from prenatal research is introduced and it is demonstrated how several but not all of these questions can be answered. The results presented are primarily based on the author's research referred to in the reference lists at the end of each chapter.
Prenatal human studies only allow studies on spontaneous or medically induced abortions by special indications and permissions before gestational age (GA) 20 weeks. At this early stage, the roots of the primary teeth have not developed and the periodontal tissue is therefore not available for histological research. The cranium, however, is nearly completely formed and can be studied radiographically, histologically, and anthropologically. A main problem with prenatal tissue studies is that the tissue is often fragmented and it can be partially autolyzed.
Postnatal studies of the dentition are conducted clinically and are supplemented by radiological analysis, including three-dimensional (3D) analysis. These analyses concern tooth maturity and morphology. Migration of teeth before eruption can also be studied. Histological studies of normal tooth development can be done on extracted teeth, but in these cases the periodontium is often lacerated and it can be difficult to describe the structure. The entire periodontium surrounding a tooth can only be studied in autopsy materials or by surgical removal of a tooth and the surrounding tissue. Both cases provide a cross-sectional insight into a periodontal membrane which can be normal but which is most likely not normal. In cases of pathological tooth development where the tooth is removed, the specimens can provide information about the histomorphological diagnosis. Postnatally, the cranium can be studied using anthropological, radiographical, and histopathological methods.
The only studies that allow longitudinal observation are radiographical studies after birth. It is possible to conduct animal studies, but results from these studies cannot be transferred uncritically to human conditions.
A book like this has not been written before. It concerns normal hard tissue development in the cranium and the dentition and creates a foundation for clinical diagnostics and for the etiology behind the diagnosis. Furthermore, this knowledge creates a basis for later genetic and molecular-biological research.
The book is structured into three main parts.
The first part includes chapters which cover different aspects of normal dental and craniofacial development. The text is supplemented with fetal pathology cases. These chapters cover the basic biological background for understanding abnormal patient cases. Such cases are demonstrated.
The second part (
) demonstrates the obstacles faced in etiology-based diagnostics of the dentition and cranium. This part also introduces the international classification of abnormal development used in the final part of the book.
The third part covers abnormal development and focuses on the etiology behind everyday cases and unusual cases sporadically observed in the clinic. The text is again highlighted with fetal pathology cases. The final chapter discuss questions on the treatment of severe cases as well as cases in which the etiologies are still unsolved. It is hoped that this text will lead to thoughtful discussions and collaborations between professionals in the clinic and the science laboratory.
In each chapter, the “why” questions will be the focus. This applies to both normal and pathological developmental processes. Some explanations of these “why” questions have been documented. Others are still hypothetical and there are others that have no clear answer. This book has been written to promote the improvement of dental and craniofacial diagnostics and to provide ideas for future research.
As a student of former Professor Arne Björk and as a colleague of former Professor Beni Solow, I would like to acknowledge the valuable and inspiring scientific environment that these distinguished teachers created in the orthodontic department in Copenhagen for science, pioneer research and critical thinking during the years 1951–2000. Professor Björk inspired me to attack scientific problems nontraditionally and he gave me complete freedom through five years to develop my own way of thinking.
This book has become a reality due to collaboration between outstanding experts in widely varied subject fields: pedodontics, orthodontics, pediatrics, fetal pathology, anthropology, and multidisciplinary hospital units for cleft lip and palate treatment and rare human developmental conditions. It is therefore both an obligation and an honor for me to thank the following co-workers for their constant support for my research which has made this book possible.
. Assoc. professor M. E. Matthiessen, DDS, MD is acknowledged for permission to use the laboratory facilities at the Department of Anatomy, University of Copenhagen, during a 5-years period, for fruitful collaboration and introduction to histochemistry.
. A large network of dentists working in the Danish healthcare systems for children and adults as well as dentists abroad have demonstrated cases for me and also inspired my studies by forwarding more than 2900 clinical inquiries.
. National and international specialists in orthodontics supported my studies by asking questions and by demonstrating difficult cases regarding orthodontic diagnostics and unexplainable treatment outcomes.
. Medical doctors in pediatrics are thanked for their collaboration. These are especially doctors in the fields of neuropediatrics and pediatric endocrinology. They appear as co-authors in the references of this book and have provided valuable input for craniofacial disorders.
. Chief pathologist, Birgit Fischer Hansen, MD Dr Med, specialist in fetal pathology, has contributed tremendously to the concept of transferring the fields of embryology and fetal pathology to the clinic to allow improved diagnostics and treatments. Without Birgit Fischer Hansen's professional and encouraging support over many years, this book could not have been written.
Chief pathologist, Jean Keeling, MD, specialist in fetal pathology in the UK, has outstandingly supported the early research and promoted the international conceptualization of craniofacial diagnostics.
Several other pathologists specializing in fetal pathology are acknowledged for their support of my studies. Among these is chief pathologist Ingermarie Reintoft MD who introduced me to unique cases of malformations for which I am very grateful.
Professor in oral pathology, Jesper Reibel, DDS Dr Odont, is acknowledged for guidance in questions of oral pathology.
. Colleagues at the medical museum, Medicinsk Museion, Copenhagen, have introduced me to the Saxthorp collection for which I am very grateful. Special thanks to the director of the museum, Professor PhD Thomas Söderqvist. Jan Jacobsen, DDS, and Pia Bennike, PhD and MSc, are both former anthropologists at the university whom I would like to acknowledge for supporting my studies in dental and craniofacial anthropology.
Hospital teams for rare developmental conditions
. Kirsten Mølsted, DDS PhD, Head of the Cleft Lip and Palate Unit at Rigshospitalet, Copenhagen, is thanked for many fruitful years of collaboration and for scientific inspiration. Kirsten Mølsted has been an excellent colleague. Bjørn Russel, DDS, former Head of the Dental Clinic at Vangedehuse Children's Hospital for Severely Handicapped Children, is thanked for collaboration.
Jette Daugaard-Jensen, DDS and MS, Head of the Center for Rare Diseases at Rigshospitalet, Copenhagen, has through many years been a faithful and inspiring colleague whom I thank for scientific support.
Hans Gjørup, DDS and PhD, Head of the Center for Rare Diseases at Aarhus University Hospital, is thanked for being an excellent co-worker and colleague.
The outstanding collaboration over many years with biomedical laboratory technologist Dorrit Nolting, BA, who has prepared all the histological images in the book, is highly appreciated. Her skills, compassion, and dedication to tissue analysis have been essential for the results presented.
Linguistic support in several scientific papers forming the base for this book has been provided during the years 2002–2012 by Academic Secretary Maria Kvetny, MA. I am grateful for her many professional contributions in this respect.
Ghita Lemminger, Secretary for Postgraduate Education, was an excellent colleague during my time as Director of the Postgraduate Program until 2014.
A special thank you to Sarah Liv Fischer Richmond, medical student, for constant, professional, linguistic support and preparation of the manuscript for this book.
If you ask a dentist or a medical professional “From where does the cranium develops in its initial phase?” they will probably not be able to answer you. Going back to basic embryology, recall your memory of the germ disk. From this very early two-layered disk, the whole body arises. Gradually the mesoderm forms the third layer in the body and the notochord develops. The notochord is an axial row of cells of ectodermal origin which are decisive for the closure of the neural tube, formation of the central nervous system and visceral and skeletal development. The germ disk folds and begins to close centrally at approximately day 18 of gestational age (GA) and openings in the cranial and caudal ends arise (Figure 1.1). These openings are called neuropores.
Figure 1.1 (Upper) Schematic drawing of the early human embryonic formation of the germ disk (left), closure of the germ disk with a caudal neuropore, lower and upper cranial neuropores (center) and the neural tube (right). Yellow marks the central nervous system. The red line indicates the notochord and the green dot the prechordal plate (region of the later pituitary gland/sella turcica). The arrows mark directions of molecular signals from the notochord. (Lower) Schematic illustration of the location of the germ disk in the body, the neural tube and the contour of the early body development in the frontal plane (left) and in the midaxial plane (right).
The ridges (left and right) that surround the cranial neuropore are called the neural crest (Figure 1.2). The neural crest cells are ectodermally derived and represent a “contact ridge” between the outer surface ectoderm and the inner neuroectoderm. The tissues that are derived from the neural crest are called the ectomesenchyme – having ectodermal origin with the ability to differentiate into various cell types, including connective tissue (e.g. cartilage, bone). From different regions on the neural crest, different ectomesenchymal cell groups migrate anteriorly through the fold between the neuroectoderm and the surface ectoderm, bulging out and gradually forming the craniofacial skeleton.
Figure 1.2 A schematic drawing of an embryo gestational age (GA) 4 weeks with an open cranial neuropore. Yellow contours mark the central nervous system and the colored dots mark the neural crest which borders the inner neuroepithelium and the outer surface epithelium. Red dots mark the frontonasal region of the crest. Green dots mark the maxillary and palatine regions and blue dots mark the mandibular region of the crest. Source: Drews (1995) reproduced with permission of Thieme Publishing Group.
More posterior parts of the cranium arise from tissue located laterally to the notochord, called paranotochordal tissue.
Gradually, the neuropores close and the germ disk forms the brainstem. From here the cerebral hemispheres develop from the foramen of Monro. Figure 1.3 depicts the craniofacial skeleton and the central nervous system.
Figure 1.3 A schematic drawing of the skeleton of a human fetus about GA 17 weeks. The spinal cord and the brainstem (not the cerebellum) are marked dark yellow, and the hemispheres of the cerebrum and cerebellum are marked beige. Green arrows indicate paths of neural crest cell migration to the jaws forming the green jaws and facial bones. White indicates the theca bones and the vertebral column. Red lines mark structures with an ectodermal origin which includes the notochord within the vertebral bodies. Peripheral nerves to the jaws are marked in orange.
The notochord forms the body axis at a very early stage (Figure 1.4). The notochord is essential for the folding and closing of the germ disk and for formation of body structures and the vertebral column. The bodies of the individual vertebrae form around the notochord (Figure 1.5). Remnants of notochordal tissue remain in the intervertebral disks after birth but not in the vertebrae. In the cranial portion of the body axis, the notochord ends in the region of the posterior wall of the sella turcica (Figure 1.6). Thus the notochord also organizes the main parts of the occipital bone and parts of the sphenoid bone corpus.
Figure 1.4 Midsagittal section of a part of the body axis of a human embryo GA 24 days demonstrating the early morphology of the notochordal cells (red).
Figure 1.5 A midsagittal section of the developing vertebral column in a human embryo GA 7 weeks. The cartilaginous vertebral bodies are marked purple. The notochord is a lightly marked (nearly white) cell structure centrally and vertically located within the vertebral bodies.
Figure 1.6 Profile radiograph of a child. The red line indicates the former location of the notochord from the vertebral bodies, through the basilar part of the occipital bone to the rostral location in the posterior wall of the sella turcica.
The sequence in which the vertebral bodies ossify is always the same, starting with the lumbosacral region and gradually moving cranially. The arches in the vertebrae protecting the medulla spinalis develop in a sequence which is also constantly the same, but the ossification of the arches starts cranially and moves gradually caudally. The region in which the ossification of the vertebral bodies and vertebral arches meet each other is near to the upper thoracic vertebra (Figure 1.7). In summary, the development of the head and brain is completely integrated with body axis development.
Figure 1.7 (Left) A schematic drawing of the entire body ossification of a human fetus GA 12 weeks. Note that several bones including bones in the head have started ossification. (Right) A radiographic image of the thoracic and cervical parts of the vertebral column in a human fetus GA 12 weeks. Note that the bodies of the cervical vertebrae have not ossified at this early stage. Source: Kjær et al. (1999). Reproduced with permission of John Wiley & Sons.
Malformations in the vertebral bodies occur in relation to the notochord. These malformations could be twin bodies (completely separated body units) or partially cleft vertebral bodies. Also fusion between bodies or the absence of a vertebral body may occur. Different types of abnormal vertebrae are demonstrated in Figure 1.8.
Figure 1.8 Radiographic images of the vertebral bodies in a prenatal, human body axis. (Left) Lateral view GA 16 weeks. The bodies are complete or partially cleft. (Right) Frontal view GA 20 weeks. The lower bodies appear fused.
The mapping of the body axis in fetuses with different genetic abnormalities demonstrates that abnormal development often occurs regionally in so-called developmental fields. Thus fetuses with trisomy 18 predominantly have abnormalities in the thoracic and lumbosacral vertebral fields and not in the cervical field. This is not the case in trisomy 21, trisomy 13 or triploidy. Mapping of the body axis shows that the different genotypes affect the different fields in the vertebral column (Figure 1.9).
Figure 1.9 Schematic view of the body axis in a human fetus (left, lateral view; right, frontal view). The black contours marked from above: nasal bone, maxilla, sphenoid corpus, basilar occipital bone, corpora, arches of the vertebral column. (Right) Indication of malformed (red) and not malformed (green) areas in the body axis of a trisomy 18 fetus. Yellow indicates areas in which malformations sometimes occur. Source: Kjær et al. (1999). Reproduced with permission of John Wiley & Sons.
The bony bodies (corpora) of the cervical spine are formed by ossification of the cartilage encircling the early notochord. Remnants of the notochord may persist in the nucleus pulposus in the intervertebral disks. The arches of the vertebrae encircle the spinal cord. The atlas, which is the upper vertebra of the cervical spine, articulates with the occipital condyles on the external cranial base.
Figure 1.10 demonstrates the normal cervical spine in a child.
Figure 1.10 Radiograph from a child demonstrating the normal structures of the uppermost part of the body axis including the vertebral column, basilar occipital bone, and sella turcica.
Prenatal defects are always present postnatally as well. Mapping of the malformations in the vertebral column is therefore essential for clinical diagnostics of postnatal vertebral development. Figure 1.11 demonstrates examples of malformations of the cervical column observed in children with known and unknown diagnoses.
Figure 1.11 Radiographic images from children with known and unknown diagnoses illustrating different malformations including fusion of vertebrae in the upper part of the body axis. (a) Patient with a mandibular overjet, etiology unknown. (b) Patient with Goldenhaar's syndrome. (c) Patient with extreme maxillary overjet, etiology unknown. (d) No diagnosis. (e) Patient with skeletal deep bite and abnormal resorption of primary teeth, etiology unknown. Note the open sphenobasilar synchondrosis, (arrow) etiology also unknown.
In 1974, Nicole Le Douarin published a study on cell migration in animals from the front-most part of the neural crest field to the cranium and face. Le Douarin found that the face and cranium had different regions with tissues that stem from different parts of the neural crest. The original research involved radioimmune marking which is a method not possible in human studies. Research on the early, embryological, facial development from the neural crest can therefore only be conducted on animals.
The cells from the neural crest are multipotent and can form cartilage, bone, muscles, nerves, and vessels. In 1997, the knowledge gained by Le Douarin was applied to human cranial and facial development. Figure 1.3 is a schematic drawing of how the neural crest might influence the development of various parts of the cranium and face. Immunohistochemical markings of the body axis in rat embryos have demonstrated how gene expression differs in the different fields of the body axis. For example, the Pax9 gene is expressed in the lumbosacral body axis and also in the craniofacial region (see Chapter 13).
Occipitalization is a postnatal condition in which the upper vertebra (atlas) is fused to the occipital condyle (see Chapter 13). This is an abnormality observed postnatally which could be explained by a prenatal fusion or by nonseparation of the cartilage which forms both the atlas and the occipital bone.
Bone tissue develops after the embryo has reached GA 7 weeks (Figure 1.12). The main components of the cranium are the bones in the cranial base, the maxilla, the mandible, the theca cranii, the vomeral bone, the nasal bone, and the temporal bone (Figure 1.13). These and other bones will be described in this section. It is characteristic for bone development that the individual ossification sites always develop in a constant sequence at the same locations and with the same morphology. The prenatal skeleton can therefore be used as a map to reveal where a malformation is located and when it arose.
Figure 1.12 A human fetus GA 8 weeks in a lateral and posterior view. The length of the body and head is 15 mm. Note that the head is very large compared to the length of the body. Eyelids have not formed and the ear openings (arrow) appear low-set. During downward and forward growth of the face, the interrelationship between the ears and the lower face will alter.
Figure 1.13 A profile radiograph of a cranium and cervical spine from a human fetus, GA 20 weeks. The ossification of the vertebrae, cranial base, jaw bones, and lower parts of theca cranii appears distinct, while the most cranial parts of the frontal and occipital bones and the parietal bone appear unossified radiographically. (Inset) A drawing of the most rostral part of the path of the notochord. From below, the notochord (red) crosses through the basilar part of the occipital bone and ends in the posterior sphenoid corpus.
We now focus on the horizontal plane and midaxial plane of the cranial base (Figure 1.14). The bones ossify midaxially in the following sequence: basilar part of the occipital bone, sphenoid bone corpus, ethmoid bone, lower part of the frontal bone. The sequence is always the same. The morphology of the individual bone components differs with age. The developmental outline of the basilar part of the occipital bone at GA 20 weeks is seen in Figure 1.14.
Figure 1.14 Horizontal and midaxial views of a normal prenatal human cranial base. (Upper) The figure demonstrates the internal cranial fossae (left) seen from above (note the large sella turcica; arrow) and a horizontal histological section (right) of the caudal part of the cranial base, larynx, and mandible from a fetus GA 15 weeks. Note the cartilage surrounding the foramen magnum (star), the cartilage of the hyoid bone (black arrow), and the mental lower part of the mandible (red arrow). (Center) A radiograph of the cranial base from a fetus GA 20 weeks. (Inset)A deviscerated basilar part of an occipital bone from a fetus GA 20 weeks. (Lower) Midsagittal section (anterior direction to the left) of a human cranial base GA 15 weeks demonstrating ossification of the basilar part of the occipital bone and the morphology of the sella turcica formed in cartilage (purple, marked by arrow). The sella contains the pituitary gland marked dark blue for the adenopituitary gland (anteriorly) and light blue for the neuropituitary gland (posteriorly).
All parts of the osseous cranial base has been formed from cartilage before birth. Between the bone components there are multiple cartilaginous synchondroses. In a five-month-old fetus, there are synchondroses between the sphenoidal bone and occipital bone (sphenooccipital synchondrosis) and three synchondroses between the different sphenoidal components (presphenoid, intersphenoid, and basisphenoid synchondrosis). There are also two synchondroses between the occipital components (anterior and posterior intraoccipital synchondroses). Synchondroses also exist between the occipital bone and temporal bone (petrooccipital synchondrosis), and between the temporal bone and sphenoid bone (sphenopetrosal synchondrosis). These synchondroses allow growth of the cranial base in the sagittal and transversal planes.
At birth, the synchondroses are significantly diminished. Only the sphenopetrosal and sphenooccipital synchondroses are maintained.
At puberty, there is only one active synchondrosis left – the sphenooccipital synchondrosis. This synchondrosis is a relatively common finding on a profile radiograph (Figure 1.15). It is difficult to analyze the amount of growth in this synchondrosis, which was studied in detail by Melsen in 1974. The growth of the cranial base has also been attempted in an anthropological analysis (Figure 1.16). This study shows that the central part of the cranial base that supports the brainstem only grows until approximately four or five years of age. This was determined by analyzing the distance between the stable innervation foramens in the cranial base (see Chapter 2).
Figure 1.15 A section of a profile radiograph from a child displaying normal sella turcica morphology. Behind the sella to the right is the sphenooccipital synchondrosis marked with an arrow.
Figure 1.16 (Left) External human cranial bases from newborn to adult. The cranium from a newborn has persisting interoccipital synchondroses. (Right) Schematic drawing of an adult human cranial base. The striped part of the cranial base supports the brainstem and only grows until the age of four or five years. This was concluded by measuring the transverse distance between the nerve canal openings. The dotted area marks the area formed from neural crest cells. This area grows until after puberty. Source: Sejrsen et al. (1997). Reproduced with permission of Taylor & Francis Publishing Group.
Different prenatal malformations can be traced in the basilar part of the occipital bone. As an example, different occipital bone malformations related to specific diagnoses are shown in Figure 1.17. There may also be signs of early fusion of bone components in the cranial base (see Chapter 13). These early malformations indicate early phenotypic characteristics for a given disease.
Figure 1.17 Deviant morphology of the pathological, prenatal, human, basilar occipital bone. The malformations illustrated are associated with deviations in signaling from the notochord. (Left) Deviscerated bone from a trisomy 18 fetus. (Center) Radiographic image from an anencephalic fetus. (Right) Radiographic image from a hydrocephalic fetus.
If the cartilaginous tissue is abnormal, as seen in dwarfism (with short extremities), then the cranial base is also short. This results in a large, rounded, protruding frontal bone in order to provide enough space for proper brain development (Figure 1.18). Clefting of the basilar part of the occipital bone can also arise prenatally and persist through adulthood. This is observed in the anthropological case provided in Figure 1.19.
Figure 1.18 An anthropological, human cranium demonstrating a retrognathic maxillary complex which is supposed to be associated with an abnormal development in the cartilaginous tissue in the short cranial base. The maxillary incisors compensated for this skeletal deviation by increasing inclination.
Figure 1.19 External cranial base from an anthropological cranium with an occipital cleft. (Left) Overview. (Right) Magnification of the cleft (arrow). It is presumed that signaling from the notochord has not functioned in the cleft area.
The sella turcica is formed by cartilage which gradually ossifies from the lower aspects and progresses cranially. The posterior wall, the dorsum sellae, may retain remnants from the rostral end of the notochord (see Figure 1.6). The sella turcica is the only part of the medial cranial fossa which appears on a profile radiograph.
The sella turcica develops around the pituitary gland (hypophysis). The anterior part of the sella arises from the neural crest cells while the majority of the floor and the posterior wall arise from the notochordal mesoderm (Figure 1.20).
Figure 1.20 Profile radiograph from a child. The red and green markings represent the internal cranial base as it appears from a lateral view. Red indicates the anterior cranial fossa, green indicates the posterior cranial fossa. Note that the sella turcica, red anteriorly and green posteriorly, in fact belongs to the medial cranial fossa. The red area is formed by neural crest cells. The green area is formed along the notochord by the paraxial mesoderm.
The morphology of the sella turcica formed in cartilage corresponds completely to the morphology of the sella later formed in bone.
The mapping of the sella turcica in malformed fetuses with known and unknown genotypes has demonstrated that some conditions are associated with an abnormality in the anterior wall, some with abnormality in the posterior wall and some with an opening in the floor. Examples are given in Figure 1.21. Irregular cartilaginous walls have also been described.
Figure 1.21 Midaxial, histological sections of the pituitary gland/sella turcica region from three human fetuses. All sellae are malformed. Anterior points to the left. (Upper) From a hydrocephalic fetus with an absent anterior sella wall. (Center) From a trisomy 18 fetus with a deep cleft (arrow) in the bottom of the sella turcica and a malformed posterior sella wall. Ossification appears anteriorly to the cleft. Source: Kjær et al. (1999). Reproduced with permission of John Wiley & Sons. (Lower) From a facially malformed fetus. The sella turcica appears without normal contours – there is just a hole/canal in the region filled with adenopituitary gland tissue. A severely malformed trace of the notochord remains (arrow).
When observing a profile radiograph, it is important to notice the posterior and anterior walls of the sella turcica. Absence or malformation of the posterior wall may be associated with abnormalities in the spine due to the notochordal relationship between the spine and the posterior wall of the sella (Figure 1.22). Meanwhile, abnormalities in the anterior wall are often associated with malformations of the facial bones. In several skeletal malocclusions, the sella often has an overlying bridge between the posterior and anterior walls (Figure 1.23). This is a sign which often appears early in postnatal life and indicates a malocclusion with a grade of severity that cannot be corrected orthodontically but which should rather be treated surgically.
Figure 1.22 Radiograph from a child referred for diagnostic clarification. Notice the malformed cervical vertebral column, malformed sella turcica, short cranial base, frontal bossing, thick occipital squama, maxillary retrognathia, and skeletal open bite. This child had several skeletal malformations, associated with malformation in the cervical vertebral column and cranial base. The etiology is unknown.
Figure 1.23 Sections of the sella turcica region on four profile radiographs from four children with various diagnoses. (Upper left) Patient with maxillary hypoplasia. Notice the broad sphenooccipital synchondrosis (arrow). (Upper right) Patient with reverse overjet. Note a sella bridge on the radiograph “uniting” the anterior and posterior walls. (Lower left) Patient with ectopia of a maxillary canine on one side and transposition of a canine and first premolar on the contralateral side. Note the abnormal slant of the anterior wall. (Lower right) Radiograph from a deaf child demonstrating an abnormal posterior wall.
The sella turcica appears as a border region in the cranial base between the anterior, neural crest-formed cranial base and the posterior, notochord-related cranial base (see Figure 1.20). This is important to bear in mind in cases where deviations are restricted to the anterior or posterior sella wall. As the cranial end of the notochord ends in the posterior sella wall, it is important in clinic to determine whether deviations in the posterior sella wall are related to deviations in the basilar part of the occipital bone and/or in the vertebral bodies which are also formed around the notochord. Examples of sella turcica malformations are demonstrated in Figure 1.23.
The maxilla is attached through the ethmoid bone and the vomeral bone to the cranial base. Ossification of the maxilla appears in week 9 GA starting in the canine region. Again, there is a completely reproducible sequence in the formation of the different bony elements. The orbital foramen is bound by bone tissue encircling the maxillary nerve. The infraorbital canal develops gradually as a result of external bone apposition. The palate is formed by vertically located, soft tissue palatal processes on each side of the tongue (Figure 1.24). These processes shift from a vertical to a horizontal position at the time when the tongue is lowered. This process is explained in further detail in the section on the mandible. The midpalatine suture arises gradually, as does the transverse palatine suture (see Figure 1.24). The transverse palatine suture is a layer of connective tissue between the slanted edges of the horizontal processes of both the palatal bones and the maxillary bones. This suture allows the maxilla to move downward and forward during growth. The palatal sutures are demonstrated in Figure 1.24. In the frontal region, the incisive fissure borders the posterior aspect of the incisors. This fissure is not a suture where growth occurs, nor is it a structure which borders the frontonasal region from the maxillary region (see Chapter 3). The fissure extends from the midpalatine suture to the region behind the canine and has a function during the enlargement of the incisive tooth buds and later during eruption of the incisors. After eruption has occurred, the fissure has no known function.
Figure 1.24 Developmental aspects in the human maxilla. (Upper left) Frontal section of a human fetal head demonstrating the two soft tissue palatal shelves bordering the tongue. The palate has not yet formed. GA 11 weeks. (Upper right) Frontal section of the nasal cavity after palate formation. GA 15 weeks. (Lower) Radiographic appearance of the ossified palate. GA 17 weeks. (Inset) A schematic drawing of the sutures in the palate and a sagittal cut (dotted line) demonstrating specifically the transverse palatine suture and the direction of growth in this suture (arrow). Source: Kjær et al. (1999). Reproduced with permission of John Wiley & Sons.
The maxilla is composed of two, bilateral, osseous, hemimaxillary components which meet the axial plane where they form the midpalatine suture. This midpalatine suture is named differently in different regions: anteriorly –interincisal suture; centrally –intermaxillary suture; posteriorly –interpalatine suture. The midpalatine suture forms the base for transverse growth of the palate.
The height of the maxilla depends on the growth of the sutures between the maxilla and the neighboring bones (nasal bone, frontal bone, zygomatic bone, and palatine bone). In the palatine process of the maxilla, there is resorption of the surface facing the nasal cavity and apposition on the palatine surface. All sutures that are responsible for growth in height have an orientation which is mostly oblique and which ensures that the maxilla moves downward and forward. Lastly, the growth of the maxilla must also support the development of the alveolar process for erupting teeth. The growth in the transpalatine suture with an oblique orientation ensures that the maxilla during growth is transported forward and downward. During this sutural growth, there is a gradual apposition of the maxillary tuber (Figure 1.25). The palatine nerve is located in a groove in the horizontal part of the palatine bone. The palatine foramen is therefore located on the opposite side of the first molar in early childhood, but due to the gradual forward movement of the maxilla, as a result of growth in the transpalatine suture, it appears at the level of the second molar during puberty (see Figure 1.25). One can therefore appreciate that space for the third molar depends on the growth in the transverse palatine suture and on bone apposition in the tuber region.
Figure 1.25 Different aspects of the human maxilla under development. (Upper) An anthropological maxilla in the occlusal view from a child approximately five years of age. Note that the horizontal process of the palatine bone is absent on the left side. Also notice the incisive fissure and the vague marking of the borderline between the frontonasal area and the maxillary area of the maxilla (arrows). (Center) Schematic drawing of the sutures in the palate. A sagittal cut (dotted line in Fig. 1.24) demonstrates the transverse palatine suture which makes the direction of growth downward and forward possible. The three figures are from three different ages (left, six years; middle, 14 years; right, 20 years). Red marks the horizontal processes of the palatine bone. Green marks the maxillary and palatine alveolar processes including the tuber maxillae. White marks newly formed bone and the small circles within the red area (palatine bone) mark the palatine foraminae. Note that the forward growth of the maxilla occurs predominantly at the maxillary edge of the transverse palatine suture. The stable position of the red squares indicates why the palatine foramen appears opposite to the first molar at six years, and later opposite the second or third molar. (Lower) A right hemimaxilla from a child approximately three years of age (left) and a left hemimaxilla from an adolescent (right) demonstrating the difference in bone size and bone apposition at the alveolar process and resorption in the floor of the nasal cavity and of the orbital cavity. Source: Damgaard (2011). Reproduced with permission of Taylor & Francis Publishing Group.
The infraorbital canal arises gradually during the early growth period by apposition at the anterior maxillary surface. The direction of the canal reflects the transverse and sagittal growth pattern in the maxilla. This direction also is supported by radiographic studies by Bjørk and by Solow of maxillary growth. Solow found that the midpalatine suture has a fan-shaped growth with more growth in the posterior than the anterior region. The incisive fissure is not a growth zone but a fissure which merely adapts to the gain in size of the incisors, and thus this fissure functions only until the permanent incisors have attained their full crown size (see Figure 1.25).
The most commonly observed malformations in the maxilla are clefts. Some of these are very severe and may extend all the way to the sella turcica region where the entire floor may be absent. Other midaxial malformations may involve a malformed palate, having a round shape as opposed to the normal horseshoe formation. This “round” palate is associated with abnormalities in the nasal cavity and the anterior cranial fossa and the absence of the anterior part of the midpalatine suture.
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