Malocclusion (HM) is a rising public health epidemic that is seen mainly within industrialized/industrializing cultures. To date, there is no published evidence that malocclusion had ever been a significantly observed human trait prior to the Industrial Revolution in Europe and North America during late 18th/early to mid/late 19th-Centuries; its relatively recent appearance as a common human phenotype suggests that intensifying industrial environmental pressures upon the human genome must somehow be contributory.
The concept of a genome-environment mismatch is one explanation for the high rates of non-communicable disease (NCDs) now seen in industrialized populations that were seldom, if ever, significantly prevalent within ancestral populations.1 Evidence from various academic disciplines suggests a correlation between risk for NCD’s (e.g., type 2 diabetes, obstructive sleep apnea, cardiovascular disease, and some cancers) and changed dietary practices associated with industrialization.2 The environmental-genomic mismatch hypothesis can also help explain the relatively recent increasing prevalence of certain chronic diseases of oral origin; the so-called plaque-mediated dental diseases, caries and periodontal disease, are both oral infirmities that have plagued mankind since the advent of agriculture some 10-12,000 years ago, but along with recently emerged HM, have only begun increasing in frequency over the past 250-300 years, and mainly in cultures consuming an industrial-type diet. Given additional evidence that mandibular retrognathia is now a very common human trait known to be associated with increased risk for many potentially devastating NCDs such as obstructive sleep apnea, 3,4 etc., it is urgent that we identify possible environmental-genetic (i.e., epigenetic) mechanisms that might help explain the relatively sudden appearance of malocclusion in humans living in industrialized cultures.
Once disease-producing epigenetic mechanisms can be identified, healthcare researchers and clinicians can begin to work collaboratively with anthropologists (and others) towards developing preventive and curative strategies aimed at eliminating human malocclusion (HM), and its associated negative systemic health consequences, as a common disease phenotype.
In a collaborative effort to explain why/how industrial intensification seems to coincide with high prevalence of malocclusion, this article’s authors, Marianna Evans, an orthodontist-periodontist from the University of Pennsylvania School of Dental Medicine and Kevin Boyd, a pediatric dentist and dental Sleep Medicine consultant at Lurie Children’s Hospital in Chicago, as consulting Visiting Consulting Scholars at the University of Pennsylvania’s Museum of Anthropology and Archaeology, under the tutelage of museum curator Professor Janet Monge, have been analyzing, via direct and 3-D radiographic measurements, pre-industrial child and adult specimens from within the Penn Museum’s crania collections. From collected craniomentric data, two separate, but related research questions will be discussed:
1. By comparison to pre-industrial adult/pre-adult crania samples, precisely which specific skeletal landmark structures of modern (mid-late 20th-/early 21st-Century) crania can be shown to have been diminished over the past few centuries in concert with industrial intensification; and 2. At which stage of pre- and/or post-natal craniofacial-mandibular growth and development might skeletal malocclusion, most notably, mandibular retrognathia, be earliest detected?
The craniofacial skeletal landmarks most pertinent to the Penn Museum projects’ research questions involve skeletal structures that are most directly affected by the vital functions of breathing and chewing: specifically:
1.) Upper and lower anterior facial heights; 2.) Bi-zygomatic width to bi-orbital width ratio; 3.) Intranasal width; 4.) A-point distance to/from N-perpendicular to Frankfort Horizontal (FH); 5.) Mandibular plane angle to FH; 6.) Intra-canine, P3/P4, M1 and M3 widths; 7.) ANS (Ho)-PNS distance; 8.) Palatal vault depth/length/width volume; and 9.) Posterior nares/choanal area. In addition to using validated metrics for measuring the posterior nares (choanae) and palatal vault depth cranial areas, other respiratory and masticatory-influenced skeletal dimensions will be measured with the use of currently accepted cephalometric normative standards (e.g., Steiner, Downs, McNamara, etc.) as a validated method for measuring representative samples of ancestral non-Western-exposed vs. modern Western-exposed crania.
Preliminary data from the Penn Museum projects seem to indicate:
1. Certain malocclusion traits in pre- versus post-industrial crania, vary most markedly in the anterior-posterior dimensions of the mandible and maxilla relative to the anterior cranial base (i.e., industrial intensification tends to coincide with more retrusive/retro-positioned upper and lower jaws)5; or otherwise stated, retrognathic malocclusion phenotypes are common in industrialized cultures, and conversely, extremely rare in non-industrialized cultures; and 2. Retrognathic HM phenotypes are likely first detectable in infancy/early childhood, and possibly even during in utero fetal development.
EVOLUTIONARY ORAL MEDICINE
The emerging discipline of Evolutionary Medicine (EM), also known as Darwinian Medicine, is a new approach providing a useful framework for understanding modern systemic diseases from an evolutionary, rather than from a ‘proximate cause’ perspective.6 For example, within a traditional medical educational framework, a proximate cause for development of a fever might be best explained as a bodily response to an internal microbial exposure (e.g., bacteremia); however, an explanation developed from an EM perspective would be predicated upon an understanding of the reasons for why the fever mechanism had evolved over the span of deep evolutionary time. To date, the best supported hypothesis for why the fever response initially evolved and has apparently been allowed (by natural selection) to persist to the present day, is centered around the observation that, as long as an elevated body and blood temperature is above the survival threshold of a blood borne pathogen, but remains below the survival threshold of the human host, the pathogen will die and the host will be spared.
The EM educational framework model is now taught in many US and worldwide medical school curriculums; and there is now even a M.Sc. level graduate program in the UK at Durham University (https://www.dur.ac.uk/ev.med/. Evolutionary Oral Medicine (EOM), or Darwinian Dentistry, is the branch of EM whose goals are to understand the evolutionary origins of oral diseases and to use this understanding for development of diagnostic, preventive, clinical treatment and research strategies. In an effort to introduce and develop an academic forum for the EOM model, that might be integrated at some point into teaching curriculums of dental, medical and anthropology programs, Dr. Rick Wilson, also a Visiting Consulting Scholar at the U Penn Museum, has led a collaborative effort resulting in establishment of an online EOM forum for clinicians and researchers interested in cross disciplinary information exchange. Information about EOM (ckwilsondmd.typepad.com/rick_wilson_dmds_blog/2015/11/evolutionary-oral-medicine-inaugural-symposium.html) and free membership can be found online (http://evolutionaryoralmedicine.ning.com/main/invitation/new) for interested healthcare professionals and anthropologists. To date, there are already 128 members.
Ever accumulating published evidence regarding the positive association between craniofacial-respiratory morphology deficiencies (i.e., skeletal malocclusion) in early childhood and risk for susceptibility to negative systemic health consequences, seems to suggest that prospective and randomized study of airway health-focused orthodontic (AHFO) regimens would obviously not be ethically possible. But available published case study data and circumstantial evidence render implementation of specific AHFO treatments as being scientifically and medically defensible; and it seems reasonable to suggest that specific SDB/OSA-associated co-morbidities, such as neurological (e.g., ADD/ADHD, cognitive dysfunction, etc.) and peripheral (e.g., appetite hormone dysregulation, type 2 diabetes, impaired somatic growth, etc.) systemic illness symptoms, might also be improved in conjunction with appropriate orthodontic/dentofacial orthopedic interventions. Given recent evidence7,8 that clearly shows a relationship between impaired naso-respiratory competence and risk for negative neuro-behavioral, neuro-cognitive and neuro-anatomical sequelae, it might soon become a medically-indefensible position to describe as harmless (i.e., unnecessary to treat) certain malocclusion phenotypes that might first become evident, and appropriately treated, in early childhood (i.e., in the primary/early mixed dentition). OH
Oral Health welcomes this original article.
1. Boyd, KL, (R)evolutionary Health Care. ICAN: Infant, Child, & Adolescent Nutrition. 2012 4: 332.
2. Bateson, P, Gluckman, P and Hanson, MJ, The biology of developmental plasticity and the Predictive Adaptive Response hypothesis. Physiol. 2014 592(11):2357-68.
3. Luqi Chi, et al, Heritability of craniofacial structures in normal subjects and patients with sleep apnea. SLEEP 2014;37(10):1689-1698.
4. Luqi Chi, et al, Identification of craniofacial risk factors for obstructive sleep apnoea using three-dimensional MRI. European Respiratory Journal;2011 (8)
5. Festa F, et al, Maxillary and mandibular base size in ancient skulls and of modern humans from OPI, Abruzzi, Italy: A cross-sectional study.
6. Nesse, RM, Evolution: medicine’s most basic science. Lancet. 2008; 372:S21-S27.
7. Bonuck, K et al, Sleep-Disordered Breathing in a Population-Based Cohort: Behavioral Outcomes at 4 and 7 Years. 2012 Pediatrics 129, Number 4, April.
8. Hoogman, M et al, Subcortical brain volume differences in participants with attention deficit hyperactivity disorder in children and adults: a cross-sectional mega-analysis. Lancet Psychiatry 2017 Published online February 15, 2017.
About the Authors
Dr. Marianna Evans is a board-certified dual specialist in orthodontics and periodontics practicing in the greater Philadelphia area. She divides her time between private practice, teaching at the University of Pennsylvania Department of Orthodontics, and clinical research. A published researcher, Dr. Evans lectures frequently on airway orthodontics and periodontal plastic surgery. She co-founded the OrthoPerio Institute and recently developed 4D Morphotropic OrthodonticsTM, an airwayfocused preventative orthodontic technique.
Dr. Kevin Boyd is a board certified Pediatric Dentist in Chicago. He teaches in the Pediatric Dentistry residency program at Lurie Children’s Hospital and serves as a dental consultant to their sleep medicine clinic. Dr. Boyd is a visiting scholar at the University of Pennsylvania Museum of Archeology and Anthropology conducting research in post-industrial evolution of the human face and airway-related structures. He lectures worldwide on pediatric OSA, evolutionary oral medicine and early age orthodontics.