Dental Neuroimaging. Chia-shu Lin

Samras Johnson Vanathaiya, Copyeditors Aravind Kannankara and Rathi Aravind, and Editorial Publication Coordinator Susan Engelken. I have been much benefited from their professional assistance in preparing this book.

      Finally, I am lucky to see things just because I stand on the shoulders of many giants – the researchers and clinicians who devote themselves in oral medicine and neuroscience. This book will just be empty without their pioneering works. They are the true explorers in this new frontier.

      About the Companion Website

      This book is accompanied by a companion website.

       www.wiley.com/go/lin/dental‐neuroimaging

      The companion website includes:

       Video courses From Tools to Discovery

       Lists of suggested readings for each chapter

       Tables of updated information of neuroimaging literature associated with dentistry

Part I Methods of Neuroimaging and Assessment of Oral Functions

1 Introduction to Neuroimaging and the Brain–Stomatognathic Axis

1.1 Why Do Dentists Need to Understand the Brain?

      1.1.1 Introduction

If we look into any textbook of clinical dentistry – be it oral pathology, prosthodontics, periodontics or orthodontics – we may not feel surprised that the word ‘brain’ would appear just very few times in the whole book. Traditionally, dentists are trained as an expert in treating oral diseases and the topics related to the brain, and its relevant disorders are usually categorized as systemic issues. The dichotomy of ‘dental vs. systemic’ suggests that the brain and behaviour issues are beyond the spotlight of dentists. Such alienation is even pronounced if we hold a ‘pathological perspective’ on the association between the brain and dentistry: oral diseases are usually not the primary aetiology of neurological/mental disorders, cardiovascular, gastrointestinal or endocrinal diseases (Figure 1.1). Therefore, there is no urgent need for dentists to learn the knowledge of the human brain.

      However, the association between the brain and dentistry may show a different story if we adopt a ‘functional perspective’. Here, the brain, behaviour and oral health are directly linked if we consider that the brain plays a crucial role in maintaining oral functions, and the integrity of mental functions is critical to maintaining oral health. If we adopt the view that the brain and mental functions guided by the brain are essential to all human behaviours (e.g. from eating to toothbrushing), we may find that the brain has an essential and more dominant role in oral health (Figure 1.1).

      In the following sections, we elaborate on this functional perspective by revisiting three lines of evidence. Historically, we see that dentistry and brain science are the ‘old alliance’ for more than 100 years. Educationally, we discuss the role of neuroscience in the curriculum of dental education. Finally, the new engagement between dentistry and the brain via neuroimaging methods is highlighted.

      1.1.2 The ‘Old Alliance’ Between Dentistry and Brain Science

The first evidence of the alliance between dentistry and brain science exists in an article published 130 years ago entitled Reflex Neurosis in Relation to Dental Pathology. The author mentioned that ‘… pain in a tooth is not indicative of the source of trouble, … The cause may be remote or in another tooth’ (Hayes 1889), a phenomenon now we may consider as heterotopic pain. Subsequently, the author put forward some insightful speculation on orofacial pain:

Figure 1.1 The association between the brain and the stomatognathic system. The traditional perspective highlights the brain as a ‘systemic factor’ associated with oral health, just like the factors related to other body systems. The functional perspective highlights that the brain and mental functions guided by the brain play an essential role in stomatognathic functions.

      Cerebral diseases, for example, insanity, softening of the brain, tumors and inflammation may produce odontalgia, but clinical reports reveal comparatively few, inasmuch owing to their obscurity positive diagnosis is often rendered difficult.

      (Hayes 1889)

      Though not scientifically accurate from the modern view, the statement points out the complex association between the brain and orofacial pain, which has confused dentists for more than one century. The alliance becomes cemented due to the challenge of treating orofacial pain, and new technologies, including neuroimaging, have provided new insights into this field (see Chapter 6). Our second evidence comes from the issues of infection control, especially the brain abscess secondary to dental infection. At present, dentists have been highly aware of infection control within the oral cavity. However, new challenges have emerged, such as the recent debates on the neuroinflammatory mechanisms that may underlie the link between neurodegenerative disorders and periodontal diseases (see Chapter 7). Finally, the third evidence of the old alliance has an even longer history. Back in 1790, when the terms ‘brain science’ and ‘dentistry’ have not yet popularized, in an article entitled ‘Pathological Observations on the Brain’, the author reported a potential association between epileptic signs and symptoms and irregular behaviour in eating and drinking (Anderson 1790). The finding echoes the link between the brain and oral sensorimotor functions, extensively studied in animal research (Lund 1991). New issues have emerged in modern days. For example, can older individuals be benefited from oral functional training to improve mastication and swallowing (Sessle 2019)? Can patients with neurodegenerative disorders, who have deficits in mental functions, also improve their oral functions? There are more challenges to meet for the old alliance between dentistry and brain science.

      1.1.3 Dental Education: The Role of Neuroscience and the Brain

      In the previous section, we have briefly discussed how the research of the brain has been linked to issues of oral health. However, the discussion may not be complete without looking into dental education for the following questions: has the role of brain science been recognized in dental education?

      1.1.3.1 The Tradition of ‘Dentists as Surgeons’

A discussion of early dental education will not be complete without mentioning the contribution from Pierre Fauchard, widely recognized as the Father of Modern Dentistry, with the first textbook of dentistry Le Chirurgien Dentiste (‘The Surgeon Dentist’) published in 1728. As the name suggests, dentistry is the discipline of managing dental diseases with a surgeon's training. Notably, in this book, Fauchard has extended the professional domain of dentists from ‘teeth’ to the oral cavity (including the soft tissue). The new profession, a ‘surgeon dentist’, is different from a ‘toothpuller’ in the