The Neurobiology of Orthodontics Margaritis Z. Pimenidis The Neurobiology of Orthodontics Treatment of Malocclusion Through Neuroplasticity Dr. Margaritis Z. Pimenidis Marathonos Street 22 152 33 Halandri, Athens Greece [email protected] ISBN: 978-3-642-00395-0 e-ISBN: 978-3-642-00396-7 DOI: 10.1007/978-3-642-00396-7 Springer Dordrecht Heidelberg London New York Library of Congress Control Number: 2009926011 © Springer-Verlag Berlin Heidelberg 2009 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product liability: The publishers cannot guarantee the accuracy of any information about dosage and application contained in this book. In every individual case the user must check such information by consulting the relevant literature. Cover design: eStudio Calamar S.L. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) I dedicate this volume to my son Alexandros and his wife Sophia for their unfailing love, help, and support. I am grateful to Dr. Anthony A. Gianelly and to the late Dr. Melvin L. Moss of Boston University and Columbia University, respectively, two great teachers who have supported my orthodontic and oral biology education and who kindled my interest in this fi eld. My sincere thanks go to my friends Dr. Eugene Eagles and Dr. Paul J. Batastini, as well as to Dr. Robert L. Vanarsdall who kindly reviewed the drafts. Man and Memory Memory itself was identified as a discrete mental faculty in ancient Greece. It could be cultivated and trained like other human skills to generate knowledge through learning. Aristotle (384–322 BC) summarized these mental activities thus: There is an innate faculty of discrimination in all men whereby we perceive sense objects. In some the sense-perception persists, while in others it does not. Where it does not, there is either no cognition at all outside the act of perception, or no cogni- tion of those objects of which perception does not persist. Where sense-perception does persist, after the act of perception is over, the percipients can still retain the perception in the soul (mind). If this happens repeatedly, a distinction immediately arises between those men which derive a coherent impression from the persistence of sensation and those in which it does not persist. Thus sense-perception (aesthesis) gives rise to memory (mneme), as we hold; and repeated memories of the same thing give rise to experience (empeiria), because the memories, though numerically many, constitute a single experience. Accordingly, those that acquire the faculty of memory are more intelligent and are capable of learning than those which cannot remember. Experience in turn, is the starting point of art and science; art in the world of making and science in the world of facts. Thus, the faculty of art and science are neither innate as determinate and fully developed, nor derived from other developed faculties on a higher plane of knowledge; they arise from sense-perception and cognition [53]. Such in brief outline was the theory of Aristotle of the relationship between perception and cognition; and the theory in its essentials holds good today, as described in Chap. 4. vii Foreword In the world of orthodontics, this book, focusing on the neurobiology of the orofacial structures and the interaction of the orofacial sensory input with the brain, is a unique and substantive departure from the usual “nuts and bolts” of contemporary orthodontics. It may both educate and excite the practitioner. The education is in the form of a synopsis of the most current infor- mation of brain function and research, highlighting the ability of sensory input to modulate and change brain activity. Special emphasis is placed on the orofacial sensory network. The excitement comes from opening new and creative pathways to examine the effects of orofacial sensory input in the development of malocclusions of the teeth and the effects of orthodontic treatment on the brain. This book is recommended reading for all orthodontists. Boston, MA Anthony Gianelly ix Preface According to the traditional orthodontic view the sensory and motor functions of the mouth are considered as phenomena coded in the DNA molecule of the neuron, and this coding acts as a template, a blueprint or a program, containing all the necessary informa- tion for normal oral behavior development, with the corollary that evident oral functional disorders, such as seen in certain malocclusions of the teeth are interpreted as DNA coding errors, as mistakes in some inborn or congenital programs [1, 206]. Contrary to this traditional teaching, however, we now know that sensory experiences can modify the structure and function of the brain or structures within it. In other words, the brain is structured by the senses, through patterned sensory input, along with the many different kinds of chemical molecules produced in the brain, such as neurotransmitters, growth factors, and trophic factors. These chemicals mediate the transmission of informa- tion and the changes in the brain, control the growth and survival of neurons, as well as the formation of appropriate neural circuits for the communication between the neurons and processing of information in the cerebral cortex. The changes in the brain, in turn, underlie sensation–perception, motor behavior, mentation, and memory of new learned experiences. The oral sensory experiences can influence these brain functions, through the disposition of the key chemical molecules, along with the generation of action potentials in the sensory axons innervating the oral sensory receptors, which convey the patterned information from the oral senses to the cerebral cortex for decoding and sensorimotor integration function, an obvious circumstance that is relevant to the development of normal oral motor behavior. Conversely, sensory deprivation of the cerebral cortex may affect learning of oral functions, such as speech and chewing, through the impairment of the brain’s respective mechanisms. The implications of these relatively new discoveries are profound. The life plan of a neuron is not in its genes. It is also experience-driven. Accordingly, the growth and func- tion of the nervous system which forms the substrate of the oral sensorimotor functions is an epigenetic process, responding to environmental experiences. This means that the oral functions, such as speech, chewing, etc, do not progress from some innate functional oral abilities, but are new functions that need to be learned actively by the child through the sensory experiences. In fact Schanberg [73] demonstrated that environmental factors such as tactile stimulation can influence genes related to growth and development of the body, through endocrine factors. This is interesting because the first sensory input in life comes xi xii Preface from the sense of touch and pressure while still in womb. Infants and children are depend- ent on touch stimulation for normal growth and development and for building their brain. During the first year of life everything the baby picks up goes into the mouth and is learned through the mouth’s touching. In these perspectives the neuromuscular disorders associated with malocclusions of the teeth may be regarded as brain dysfunctions affecting the mouth’s functions. Orthodontic changes in the occlusion of teeth and of the maxillofacial skeleton may improve the abnor- mal oral functions through neuroplasticity, which in turn, may be incorporated into the rules that govern the structure and function of the oral sensory and motor maps in the post- central gyrus and precentral gyrus of the cerebral cortex as the brain changes. This implies that orthodontic therapy can alter the sensorimotor behavior of the mouth, which is key to the soft and hard tissue anatomy of the mouth. This view is in contrast to the conventional orthodontic concepts, which attribute to orthodontic therapy changes a minor peripheral influence, confined mainly to dentoalveolar structures. This book may help to set the scene for future explorations in this field, which may help to elucidate the abnormal oral motor behavior in malocclusions of the teeth, delving into the underlying brain mechanisms. Our challenge is to discover how oral experience builds the structure and function of the brain. Athens, Greece Margaritis Z. Pimenidis Contents 1 Experience Changes the Brain .......................................................................... 1 1.1 Introduction .............................................................................................. 1 1.2 Oral Experience Strengthens Neuron Synapses ....................................... 2 1.3 How Experience Strengthens Synapses ................................................... 3