Dental Neuroimaging. Chia-shu Lin

relationship between oral and systemic diseases (Lynch et al. 2006), the primary task for dentists is to fix the structural deficits of the oral cavity, such as restoring a decayed tooth or replacing the missing teeth with a denture. All the jobs require dentists to be capable of performing complicated surgical skills.

      An over‐focus on the surgical skills of dental treatment, however, had gradually received criticism since the early days when dental education became an independent discipline. As pointed by Eugene Talbot early in 1900:

      The result is that study of the general diseases which affect the mouth, jaws and teeth have been neglected. Limitations of a dental education have prevented the dentist from associating local diseases with systemic causes.

      (Talbot 1900)

      The statement corresponds to the degree delivered for this new profession, namely Doctor of Dental Surgery (DDS), at Talbot's time. He further showed the concern that ‘… the graduate of dental surgery is not competent to associate systemic diseases with their effects on the teeth, nor is he capable of appreciating systemic lesions due to overtreatment of pathologic conditions of the teeth’ (Talbot 1900). The gap between a dentist and medical knowledge would make dentists ignore the systemic condition of patients – moreover, the ignorance may further exacerbate systemic health when dentists ‘overtreat’ patients (Talbot 1900).

      1.1.3.2 Brain and Neuroscience: Is It Neglected in Dental School?

      According to the Basic Science Survey Series of the American Dental Education Association (ADEA), neuroscience is widely taught in most dental schools in North American. In 2014, among 66 dental schools, 31 (47%) offered neuroscience as a standalone course, with the others integrated the neuroscience topics into other courses (Gould et al. 2014). It is also noteworthy that in most dental schools, the course was delivered by teachers from medical schools, who may not tailor‐make the course for dental students (Gould et al. 2014). The average year of teaching of the teachers is relatively high (23.1 years), suggesting fewer younger teachers are involved in the field (Gould et al. 2014). Critically, the topics to be delivered significantly varied between courses. Some topics, such as the knowledge of cranial nerves, were taught averagely for three hours. In contrast, issues of the neuropathic mechanisms of pain, including nerve regeneration, neuralgia, allodynia and hyperalgesia, were taught less than half an hour (Gould et al. 2014). Topics related to the human brain were taught in most of the courses. Nevertheless, among the 31 independent neuroscience courses, almost half of them focused on neuroanatomy, which emphasizes the knowledge of brain structure rather than the link between the brain and oral functions. This alienation reflects that many courses were taught by personnel outside the dental schools and may not provide what dentists need to know for their clinical careers.

Therefore, for teaching neuroscience and brain science in dental schools, the real challenge is not the time and classes allocated for teaching, but how these materials are taught. Non‐dental school faculties mainly taught the courses, and the topics were less tailored for dentistry. For example, in some syllabi of the neuroscience courses, the issue ‘pain’ is taught alongside somatosensation. Nowadays, we have much evidence showing that pain, as a more generalized cognitive–affective experience, is associated with the brain mechanisms of attention, emotional and cognitive processing (see Chapter 6). In this case, a focus on the brain and mental functions, such as the modulatory effect of attention and cognitive appraisal on pain, should be tailored for dental students since it is highly associated with the clinical management of patients.

      1.1.4 The ‘New Engagement’: Modern Cross‐Disciplinary Research of Dentistry and Brain Science

      Instead of being a comprehensive textbook on the neurobiology of dentistry, this book aims to outline the ‘new engagement’ between dentistry and brain science, with neuroimaging as a critical approach to bridge the two fields. Here, we discuss the trend of cross‐disciplinary research between dentistry and brain science, according to two brief bibliometric surveys. Firstly, a survey based on PubMed was performed by the keywords ‘dental’ and ‘brain’ and the search was limited to titles and abstracts of the literature (tooth[mesh] OR oral[mesh] OR dental[mesh] OR dentistry[mesh] OR teeth[tiab] OR tooth[tiab] OR oral[tiab] OR dental[tiab] OR dentistry[tiab] AND brain[tiab]). The findings revealed that by December 2020, 20261 research papers had been documented in PubMed. The number of publications shows a pronounced rise in recent years, which almost doubled within 10 years. For example, between 1980 and 1989, the number of publications n = 1566. This number rose from 1990 to 1999 (n = 2684) and almost doubled from 2000 to 2009 (n = 4721). From 2010 to 2019, the number doubled again to n = 9331. As discussed in Section 1.2, the increasing number of publications on the brain topic corresponds to the increasing number of publications on neuroimaging, which has become a pivotal method in studying the human brain.

      A second survey was conducted by searching for the past and current research projects funded by the National Institutes of Health (NIH), USA, using the online platform of Research Portfolio Online Reporting Tools (RePORT) report. From 2020 to February 2021, the keywords ‘dental’ and ‘brain’ have led to 106 projects, with 39 projects funded by the National Institute of Dental and Craniofacial Research (NIDCR). This number is almost twice the number of sponsored projects (53) in the whole 1990s when the NIDCR funded 29 projects. The results suggest an increasing trend of cross‐disciplinary research between oral and brain sciences. Critically, not all the projects were granted by the NIDCR, which specializes in orofacial medicine. Several projects were supported by the National Institute of Mental Health and the National Institute on Aging, highlighting the importance of oral issues in cognitive deficits and aging.

      

      1.1.5 Summary

       From a functional perspective, the brain, behaviour and oral health are directly linked because the brain plays a crucial role in maintaining oral functions, and the integrity of mental functions is critical to maintaining oral health.

       The alliance between the research on dentistry and the brain has a long history. It contributes to tackling unsolved challenges (e.g. orofacial pain) and new challenges (e.g. aging and oral functions).

       Topics of neuroscience and the brain are not neglected in dental education. However, many courses are taught by non‐dental school faculties, and the topics were less tailored for dentistry.

       Recently, cross‐disciplinary research on oral and brain sciences has quickly emerged in the number of publications and research grants.

1.2 What Is Neuroimaging?

      1.2.1 Introduction

In Section 1.1, we have highlighted a significant overlap between dentistry and brain science. Though the two fields are closely linked from a functional perspective, there exists a vast difference between research approaches of the oral cavity and those of the brain. Dentists can visually examine the oral structure, and oral functions can be quantified with a chairside set of assessments. In contrast, brain functions and mental status, sometimes metaphorized as a ‘black box’, can hardly be examined directly at the chairside. Therefore, a pivotal step to facilitate the investigation of the brain is to develop the technology for quantifying brain structure and functions. Neuroimaging, defined as a non‐invasive approach of ‘visualizing the central nervous system, especially the brain, by various imaging modalities’ (MeSH 2012), is such a technological breakthrough that revolutionizes the research approaches of the brain.

      A common myth is that neuroimaging or ‘brain scan’ would be a kind of ‘modern magic’. The impression is strengthened by some sci‐fi movies, where ‘peeking into the brain’ is taken as an icon of something futuristic. Contrary to the popular myth,