Environmental Conditions as Epigenetic Modulator of Craniofacial Growth and Development Phenotypes a Mini Review
Daniela Becerra G*
1Department o Morphology and Orthodontic, Dentistry Faculty, Universidad de los Andes, Chile
Submission:January 20, 2021;Published: February 11, 2021
*Corresponding author: Daniela Becerra Giaverini, Dentistry Faculty, Universidad de los Andes, Álvaro del Portillo 1223, Las Condes, Santiago, Chile (ZC)
How to cite this article: Daniela Becerra G. Environmental Conditions as Epigenetic Modulator of Craniofacial Growth and Development Phenotypes a 0010 Mini Review. Adv Biotech & Micro. 2021; 16(2): 555931.DOI:10.19080/AIBM.2021.15.555931
Abstract
Environmental variation is translated into phenotypic variation based on how the same genotype can produce a variety of phenotypes across a range of environmental circumstances. Traits showing greater phenotypic variation are either under less direct genetic control and/or mature less rapidly. As expected, the vertical aspects of mandibular growth, which are the least mature in the craniofacial complex, showed the most pronounced effects, developing three types of phenotypes, where normodivergent and hypodivergent have a good facial, but hyperdivergents are the real problem, because they decrease their growth, they are increasing the incidence and prevalence, and with them, are increasing bad functional and esthetics on the population. The environmental conditions that are associated to hyperdivergent phenotype are masticatory loading during early facial growth and airway obstructive problems.
Introduction
It seems reasonable to expect that complex, highly intrincated objects will function less if they are modified, because even small alterations are likely to have potential deleterious consequences. If we compare primates in general with human linage in particular, heads appear to be no less morphologically conservative than the rest of the body, and possible even more evolvable, despite its complexity [1]. Comparison of genetic and craniofacial variation among human population suggest that most changes in craniofacial from among recent humans occurred from random, unselected genetic changes rather than from natural selection [2, 3]. Has been seen during the process of growth and development, that regulation of local growth (of different craniofacial modules) occurs through interactions between genes (that cause skeletogenic cells to synthesize, resorb, or otherwise modify skeletal tissue), and stimuli from other genes or cells. Such interactions between cells and their environment (which includes other cells) are generally categorized as epigenetic interactions, of which are several types that regulate most bone growth. Then, we have secondary epigenetic interactions between bone and neighboring tissues. Such interactions preserve functioning during complex growth, even when the growth involves many different tissues that grow all at different rates under different mechanisms of control [4]. These interactions also permit morphological variations that range from minor differences between members of the same species to novel phenotypes [2,3].
Craniofacial Phenotypes
Most craniofacial, dentoalveolar, and occlusal traits show a quantitative, often normal, distributions of phenotypes. Traits showing such distributions are polygenetic, due to the actions and interactions of multiple genes [5]. It follows that variation in such traits must be due to genetic, epigenetic, and environmental influences. The relative contribution of genes to phenotypic expression varies depending on the environments in which they are expressed. The way in which environmental variation is translated into phenotypic variation is based on the norm of reaction [6], which states that the same genotype can produce a variety of phenotypes across a range of environmental circumstances. Traits showing greater phenotypic variation are either under less direct genetic control and/or mature less rapidly than traits showing less phenotypic variation. For example, modern day Finns exhibit substantially larger gonial and mandibular plane angles, with a 6% decrease in mandible length, despite overall skull size increases, compared to Finnish samples from the 15th and 16th centuries [7]. Since the time span was insufficient for genetic changes to have occurred, the same genotypes must have been adapting to different environmental factors. As expected, the vertical aspects of mandibular growth, which are the least mature in the craniofacial complex, showed the most pronounced effects [8].
This is how we stablished different phenotypes for traits that are genetical controlled in craniofacial structures, in which vertical aspect of mandible is the latest trait in mature. That suppose then three types of phenotypes, where normodivergent and hypodivergent are forward rotators, in other words with normal facial growth, and both phenotypes have a harmonic development [9,10]. Hyperdivergents are the real problem, because we have seen that over time, they are increasing the incidence and prevalence, and with them, are increasing bad functional and esthetics consequences, with significant decreases of the posterior aspect of manbible [8,11,12].
Hyperdivergent Etiology
The etiology of hyperdivergent phenotype appears to be environmental, due to postural adjustments related with compromised airways and weak masticatory musculature. Changes in diet and food processing technology post industrial revolution, have contribute to some proportion of variations in facial size and shape [2]. Human diets since the Middle Paleolithic have changed substantially in content [13-15] and in how they are processed through cooking, soaking, leaching, and grinding [16- 18]. Food processing improves digestibility, but also makes food softer and smaller in particle size, requiring less occlusal force per chew and fewer chewing cycles per unit of food [1,19, 20]. In turn, softer and more processed foods are widely hypothesized to lead to less facial growth, especially in the lower face and the alveolar crests, because of the potential effects of force-generated strain [21,22]. While one might expect nutritional improvements since the Middle Paleolithic to contribute to increases in overall cranial size [23], the evidence points to a trend towards smaller facial size, with the most dramatic decreases occurring after the Neolithic. Comparisons of Nubian populations prior to and after the introduction of agriculture show significant reductions in many mid- and lower facial dimensions including infraorbital height (7.8%), masseter origin length (26.3%), mandibular corpus length (22%), and mandibular symphysis thickness (15.3%)-despite concurrent increases in brain size [24,25].
Environmental conditions that can modulate craniofacial phenotypes
No human studies have examined the effects of masticatory loading during early facial growth, when such effects are likely to be greatest, and none have quantified strains or site-specific growth rates. Most experimental data on facial growth responses to masticatory loading come from studies on non-human anthropoids and other mammalian models. One primate study [22,26,27] compared 19 adult squirrel monkeys (Saimiri sciureus) raised on soft food diets with 24 controls raised on hard food diets; another study [22, 23] compared 16 adult baboons (Papio cynocephalus) who were raised on a hard diet for two years with 24 baboons raised on a soft diet. In both studies, animals who chewed harder food had significantly wider and taller faces, thicker mandibular corpora, and taller palates. However, primates raised on softer food often had serious malocclusions from narrowed maxillary arches, rotated, and displaced teeth, crowded premolars, and palatal arching, suggesting abnormal growth patterns. A related study on macaques obtained similar results, but also showed that Haversian remodeling rates were higher in monkeys fed hard food [28]. Experiments on non-primates reveal a similar picture [1,2,29].
On the other hand, airway problems have been associated with hyperdivergent phenotypes. On this pathway, there is some statistical support for an association between craniofacial disharmony and pediatric sleep-disordered breathing, however, in children with obstructive sleep apnea and primary snoring, compared with the controls, could be regarded as having marginal clinical significance (e.g., an increased ANB angle of less than 2º) [30]. Evidence for a direct causal relationship between craniofacial structure and pediatric sleep-disordered breathing is unsupported by Katyal´s (2013) meta-analysis. There is strong support for reduced upper airway sagittal width in children with obstructive sleep apnea (representing adenoid hypertrophy) [3,31]. Besides these results, there are some promising studies that have statistical results not only on the sagittal plane, but also on the vertical plane, that is what we expose in this new way of understanding craniofacial growth, were vertical plane affects directly sagittal plane. The investigation group of the author have preliminar results were the saggital of the upper airway is associated to hyperdivergent pediatric population.
Conclusion
Environmental conditions such as obstructive airway and weak muscles can modulate craniofacial phenotypes. When these variables are present, the face turn to limit it´s growth on the vertical posterior aspect of mandible due to be the latest craniofacial trait on mature and generate an hyperdivergent phenotype.
References
- Lieberman DE (1993) Life history variables preserved in dental cementum microstructure. Science 261(5125): 1162-1164.
- Lieberman D, Krovitz GE, Mcbratney-Owen B (2004) Testing hypotheses about tinkering in the fossil record: the case of human skull. J Exp Zool 302(3):284-301.
- Lieberman D (2011) The evolution of human head. The Belknam press of Harvard University press. Cambridge, MA
- Moss ML (1968) The primacy of functional matrices in orofacial growth. Dental Practitioner 19(2): 63-73.
- Moss ML (1962) The functional matrix. In: Vistas in Orthodontics. Lea & Febiger, Philadelphia 85-98.
- Waddington CH (1941) Canalization of development and the inheritance of acquired characteristics. Nature 150: 563-565.
- Varrela J (1990) Effects of attractive diet on craniofacial morphology: a cephalometric analysis of a Finnish skull sample. Eur J Orthod 12(2) :219-223.
- Buschang P, Helder J, Carrillo R (2013) The Morphological Characteristics, Growth, and Etiology of the Hyperdivergent Phenotype. Seminars in Orthod 19 (4): 212–226.
- Naini FB, Donaldson AN, McDonald F, Cobourne MT (2012) Influence of chin height on perceived attractiveness in the orthognathic patient, layperson, and clinician. Angle Orthod 82(1): 88-95.
- Maple JR, Vig KW, Beck FM, Larsen PE, Shanker S (2005) A comparison of providers' and consumers' perceptions of facial-profile attractiveness. Am J Orthod Dentofacial Orthop 128(6): 690-696.
- Nanda SK (2002) Patterns of vertical growth in the face. Am J Orthod Dentofacial Orthop 93(2): 103-116.
- Schudy FF (1964) Vertical growth versus anteroposterior growth as related to functional and treatment. Angle Orthod. 34, 75-93.
- Stiner MC (2001) Thirty years on the broad spectrum revolution and paleolithic demography. Proc Natl Acad Sci 98(13): 6993–6996.
- Richards MP, Pettitt PB, Stiner MC, Trinkaus E (2001) Stable isotope evidence for increasing dietary breadth in the European mid-Upper Paleolithic. Proc Natl Acad Sci 98: 6528-6532.
- Rangel RD, Oyen OJ, Russell MD (1985) Changes in masticatory biomechanics and stress magnitude that affect growth and development of the facial skeleton. Prog Clin Biol Res 187: 281-293.
- Corruccini RS, Beecher R (1982) Occlusal variation related to soft diet in a nonhuman primate. Science 218 (4567): 74-76.
- Wrangham RW, Jones JH, Laden G, Pilbeam D, Conklin-Brittain N (1999) The raw and the stolen. Cooking and the ecology of human origins. Curr Anthrol 40(5): 567-594.
- Brace CL, Smith SL, Hunt KD (1991) What big teeth you had grandma! Human tooth size, past and present. In: Kelley, M.A., Larsen, C.S. (Eds.), Advances in Dental Anthropology. Wiley-Liss, New York, USA.pp. 33-57.
- Shiau YY, Peng CC, Hsu CW (1999) Evaluation of biting performance with standardized test-foods. J. Oral Rehabil 26(5): 447-452.
- Lucas PW, Luke DA (1984) Chewing it over-basic principles of food breakdown. In: Chivers DJ, Wood BA, Bilsborough A (Eds.), Food Acquisition and Processing in Primates. Plenum, New York, USA. pp. 283-302.
- Lukacs JR (1989) Dental Paleopathology: methods for reconstructing dietary patterns. In: Iscan MR, Kennedy KAR (Eds.), Reconstruction of Life from the Skeleton. Alan R Liss, New York,USA. pp. 261-286.
- Corruccini RS, Beecher RM (1984) Occlusofacial morphological integration lowered in baboons raised on soft diet. Journal of Craniofacial Genetics and Developmental Biology 4(2): 135-142.
- Corruccini RS, Beecher RM (1984) Occlusofacial morphological integration lowered in baboons raised on soft diet. J Craniofac Genet Dev Biol 4(2): 135-142.
- Kiliaridis S, Engstro¨m C, Chavez LME (1992) Influence of masticatory muscle function on craniofacial growth in hypocalcemic rats. Scand J Dent Res 100(6): 330-336.
- Carlson DS (1976) Temporal variation in prehistoric Nubian crania. Am J Phys Anthrop 45(3): 467-484.
- Carlson DS, Van Gerven DP (1977) Masticatory function and Post-Pleistocene evolution in Nubia. Am J Phys Anthrop 46(3): 495-506.
- Beecher RM, Corruccini RS, Freeman M (1983) Craniofacial correlates of dietary consistency in a nonhuman primate. J Craniofac Gen Dev Biol 3(2): 193-202.
- Bouvier M, Hylander W (1981) Effect of bone strain on cortical bone structure in macaques (M mulatta). J Morphol 167(1): 1-12.
- Toro-Ibacache V, Zapata V, O Higgins P (2016) The relationship between skull morphology, masticatory muscle force and cranial skeletal deformation during biting. Annals of Anatomy 203: 59–68.
- Katyal V, Pamula Y, Martin AJ, Daynes CN, Kennedy JD, et al. (2013) Craniofacial and upper airway morphology in pediatric sleep-disordered breathing: Systematic review and meta-analysis. Am J Orthod Dentofacial Orthop 143(1): 20-30.
- Flores-Mir C, Korayem M, Heo G, Witmans M, Michael P, et al. (2013) Craniofacial morphological characteristics in children with obstructive sleep apnea syndrome: A systematic review and meta-analysis. JADAA 144(3): 269-277.