Atlas of Human Fetal Jaw Development

Atlas of

Human Fetal Jaw Development

Lawrence S. Freilich, DDS, PhD

Collaborating Scientist
National Museum of Natural History
Smithsonian Institution

Retired Faculty and Periodontist
Georgetown University School of Dentistry
Washington, District of Columbia

David R. Hunt, PhD, D-ABFA

Physical Anthropologist
Department of Anthropology
National Museum of Natural History
Smithsonian Institution
Washington, District of Columbia

Contents

Preface

1. Introduction

2. Developmental Origins of the Maxilla and Mandible

3. Photographic Study of the Maxilla and Mandible: Three Ascending Age Specimens

4. Mandibles of Eight Ascending Age Groups

5. Whole Skulls of Eight Ascending Age Groups

6. Whole Skeletons of Three Ascending Age Groups

7. CBCT Scans: Maxilla, Mandible, and Whole Skull

PREFACE

Detailed photographic studies were carried out in order to illustrate the development of the human fetal maxilla and mandible. This photographic record was derived from known-age skeletal specimens in the collections of the Department of Anthropology, National Museum of Natural History, Smithsonian Institution. To demonstrate the developmental progression, specimens at 4, 7, and 10 lunar months of age are presented photographically to show the distinct physiologic and morphologic developmental progression of the maxilla and mandible. In brief, at 4 lunar months, the facial surface of the maxillary body displays a prominent trabecular or spongy bone topography without any cortical production; the mandibular body and ramus surfaces show more cortical bone than the maxilla. Maxillary height is limited because of early alveolar process development, but dental crypt formation is evident. The coronoid process exhibits greater development than the condyle. The 7-lunar-month maxilla and mandible display increased vertical dimension as a result of the higher alveolar processes and anterior dental crypt development. The maxillary facial surface still possesses a prominent spongiosa, while mandibular facial and lingual surfaces exhibit a mixture of spongy and cortical bone. The 10-lunar-month facial surfaces of both maxilla and mandible have more cortical composition with an abundance of small and midsized neurovascular foramina more evident in the maxilla. The alveolar processes and dental crypts of both the maxillae and mandibles are well developed, and some tooth crowns are visible.

To augment the developmental changes in fetal mandibular growth and development, a series of eight mandibles are presented in buccal and lingual orientation to show the growth and developmental stages. Also, a series of eight whole prepared fetal skulls are presented to illustrate developmental change in the skull. To put these growth and developmental changes in perspective, a series of three complete fetal skeletons are presented photographically.

Cone beam computed tomography examinations of full maxillae and mandibles and of a whole prepared skull were produced. Results reveal a relatively low bone density in the specimens at 4 and 7 lunar months. Proportional density increase is evident in the three stages of development that were studied.

Acknowledgments

The authors wish to express their indebtedness to several individuals without whose time, efforts, and invaluable editorial review this work could not have been completed:

• Stephen Mappen for his superior editing and reformatting of the photographic images in this atlas. Without his exceptional dedication and commitment, this atlas would have not been possible.

• Bruno Frohlich in the Department of Anthropology at the National Museum of Natural History, Smithsonian Institution, for his very helpful expertise and assistance with this project.

• Andrew T. Grant, chief photographic editor, for his invaluable expertise.

Capt Gerald T. Grant, Mr Shayne Kondor, and their colleagues at the Naval Postgraduate Dental School at the Walter Reed National Military Medical Center in Bethesda, Maryland, are recognized for their untiring efforts and expertise in the special imaging included in this project. Their cone beam computed tomography scans of fetal jaws and skulls offer new structural information about these osseous tissues not previously available.

CHAPTER 1

Introduction

Project Goals: Documenting Human Fetal Jaw Development by Photographic and Computed Tomographic Illustration

The goal of this project is to present an ordered study of human fetal jaw development, primarily focused on the hard tissues of the maxilla and mandible, in an image-driven format not well presented in the current scientific literature. This is an investigation of the growth and development of the human maxilla and mandible from approximately 4 months in utero until term (circa 10 months) by photographs and descriptive observations of the changes occurring in the bony tissue.

Previous studies

Although there have been numerous studies that have presented the growth and development of the human gnathic region^1–10 (see Sperber et al¹¹ for a recent in-depth volume), the results presented are generally in histologic, radiologic, or drawing formats, and few illustrations are made of dissected and cleared bone. The most relevant comparisons would be in cephalometric radiologic illustrations.^5,8,12,13

In the recent past, a number of studies have employed varying techniques to examine human fetal craniofacial growth and development. Radlanski and colleagues have published several studies using three-dimensional (3D) computed tomography (CT) to obtain craniofacial reconstructions from serial sections of fetal specimens.^14–17 Other recent studies have documented craniofacial growth using fetal bones from frozen whole skulls¹⁸ or dried mandibles.¹⁹ A third popular technique has been the use of 3D ultrasonography to study fetal craniofacial structure.^20–22 Of these studies, McGahan et al²¹ included a new version known as multislice display to visualize both normal facial structure as well as specimens exhibiting both cleft lip and palate.

All of these studies and other comparable works provide valuable data on fetal craniofacial development. However, these publications have examined sequential human fetal jaw development in soft tissue specimens rather than by examining the dry bony tissue. This study focuses on the paired maxillae and mandibles from specimens of a single ancestry and presents the observations of change by means of high-definition photography. Well-preserved maxillary and mandibular jaw elements from human fetal skeletons contained in the collections of the Smithsonian Institution’s National Museum of Natural History (NMNH) Department of Anthropology were used in this study. The Smithsonian Collection constitutes one of the largest documented human fetal skeleton collections in any institution worldwide, containing well over 300 individual fetal skeletons obtained in the early 20th century from the Baltimore, Maryland, and Washington, DC, regions. There are roughly an equal number of specimens representing both Caucasian and African American ancestry and nearly equal numbers of males and females within each ancestral group.

Project phase I

In this study human fetal jaw development is examined and documented in three phases. First, the maxillae and mandibles of each of the examined individuals are photographed in close-up using a Nikon digital camera with a 60-mm macro-Nikkor lens (Nikon). Several aspects of each jaw element were recorded, including lateral, medial, and anterior views. At these early developmental stages, the right and left halves of the maxilla and mandible are not yet fused into single bones. Photographs of the individual halves and, in some instances, the articulated right and left maxillae and mandibles are presented. All photographic studies were conducted within the Anthropology Department of the NMNH with assistance from Dr Bruno Frohlich.