Although the concept of bone remodeling is in complete contrast, the current perception of the malocclusion etiology is genetic. However, studies and works proving environmental factors as the main cause for malocclusion are coming into light. In order to understand how the environment is involved, looking into the past is mandatory. 

Malocclusion is becoming so common in our modern society that everyone thinks having a brace is a step strictly required throughout the life. It is thought to be genetic, where the term genetic literally means relating to origin, or arising from a common origin. But interestingly, if we look to our ancestors (our origin), there is very little sign of malocclusion [1]. Figure 1 shows the difference of a prehistoric skull against a modern one: the difference in the palate shape and airways size is massive. So, is it really genetic?

In 1939, dentist Weston A. Price published Nutrition and Physical Degeneration, describing his travel around the world among both civilized and isolated groups [2]. Interestingly, as Figure 2 highlights, he found out that malocclusion was a problem uniquely present in the civilized groups, together with caries and improper development of the facial structure (and many other problems, reason why he talks about physical degeneration). Although Dr. Price thought that everything was connected to the type of diet (that is partially true, due to the important role that nutrition covers in the total body health), the important thing to highlight is the difference in the level of civilization among the several groups he studied: malocclusion was present only in modernized groups. So, do you still think it is genetic?

A further milestone has been put by John Mew in 1958, when he set the ‘Tropic Premise’, which suggested that malocclusion was a ‘Postural Deformity’ and that irregular teeth were not necessarily inherited [3]. He then developed the Bioblock therapy [4] and founded  the London School of Facial Orthotropics, that is still nowadays considered controversial to the common orthodontics. Indeed, while common orthodontics simply straights teeth, the aim of Orthotropics is to guide facial growth (that essentially means the craniofacial development).

John Mew treated several cases of patients (like the one shown in Figure 3) that were suggested to have surgery for their improper development of the facial structure. He used postural appliances with the aim of exploiting the ‘Tropic Premise’: the ideal development of the jaws and teeth is dependent on correct oral posture with the tongue resting on the palate, the lips sealed and the teeth in light contact. So, what are the factors that affects oral posture in modern society?

In Figure 4, analyzing the skull of our ancestors with the one of our time, the first notable thing is the different shape, especially of the facial bones. We are assisting to a down-siding of the entire craniofacial structure, with the maxilla that drops down and back. This reduces the eye support, flattens the cheekbones, narrows the nasal airway, lengthens the mid facial third, and lowers the palate, which narrows and create malocclusion [5]. Thus, malocclusion is just a consequence of the craniofacial development.

Although it is a very slow process, bones always remodel according to force stimuli in order to address the mechanical stress applied [6]. In particular, high-frequency low-amplitude postural strains are the main responsible for bone remodeling [7].  Everyday our body fights an invisible constant force, the gravity, that is the actual responsible of the down-siding of the maxilla. But then, what are the missing forces that counteract this phenomena? What are the differences with our ancestors?

In a simplistic view, maxilla is primarily remodeled by forces coming from tongue and teeth (through masseter muscles). So the causes of malocclusion have to be found in the modern lifestyle, in particular in:

• Increasing of bottle-feeding over breast-feeding that influences the swallowing pattern and all oral muscles [8,9,10,11].
• Use of pacifiers/dummies that mainly affect tongue posture [12,13,14,15].
• Trend towards industrial soft high-calorie food that hits chewing effort and muscles action [16,17,18].
• Reduced nasal airways, increasing of allergies and nasal congestion that leads to mouth breathing affecting both tongue posture and muscles action [19,20,21,22,23].
• Trend towards an earlier or too early weaning, influencing swallowing pattern [24,25].

Figure 5 shows a couple of brother and sister. They were breast-fed for different  periods of time, leading to different weaning. This difference had effects on the tongue posture and  the function of all the oral muscles of the two individuals: notice the tongue thrust of Miranda (on the left) and how this affected the development of the maxilla that dropped down and back creating a long and kind of smashed face, together with malocclusion. Gwithian (on the right) has been breast-fed longer, with a later weaning with respect to Miranda. The facial shape is completely different: maxilla is correctly developed, creating space for all the teeth. Notice as well the difference of the cheekbones, that provide eyes support.

To have a further confirmation of what is going on in our modern society, it is sufficient to look in the past: indeed, malocclusion had an exponential increase with the Industrial Revolution. Women started to give up their mother role inside the family to work in industries, leaving the care of the new born child to older relatives. Thus, bottle-feeding became a necessity as well as pacifiers and early weaning. Furthermore pollution increased, together with food processing and less contact with the nature, leading to an increase of the allergies and other pathologies.

So, every alteration in the lifestyle has good and bad sides. While recent thoughts were that malocclusion was genetic, indeed it is not. It is an environmental problem, due to consequences of civilization. This finds further confirmation from the isolated groups in the world, where the civilization is still not influent: they present minimal sign  of malocclusion and a complete different facial and physical development. However, avoidance of pacifiers and bottle-feeding, together with a proper food diet during the weaning phase, are proper actions that can prevent the insurgence of bad habits maintained for the entire life of the individual, affecting occlusion, craniofacial development and his entire health.

References

[1] Boyd, Kevin L. “DARWINIAN DENTISTRYPART.” Journal of American Orthodontic Society (2012): 28-33.

[2] Price, Weston A., and Trung Nguyen. Nutrition and physical degeneration: a comparison of primitive and modern diets and their effects. EnCognitive. com, 2016.

[3] Mew, John RC. “The postural basis of malocclusion: a philosophical overview.” American journal of orthodontics and dentofacial orthopedics 126.6 (2004): 729-738.

[4] Mew, John. “Bioblock therapy.” American journal of orthodontics 76.1 (1979): 29-50.

[5] Mew, M. “Craniofacial dystrophy. A possible syndrome?.” British dental journal 216.10 (2014): 555-558.

[6] Chen, Jan-Hung, et al. “Boning up on Wolff’s Law: mechanical regulation of the cells that make and maintain bone.” Journal of biomechanics 43.1 (2010): 108-118.

[7] Fritton, Susannah P., Kenneth J. McLeod, and Clinton T. Rubin. “Quantifying the strain history of bone: spatial uniformity and self-similarity of low-magnitude strains.” Journal of biomechanics 33.3 (2000): 317-325.

[8] Jacinto-Gonçalves, Suzane Rodrigues, et al. “Electromyographic activity of perioral muscle in breastfed and non-breastfed children.” Journal of Clinical Pediatric Dentistry 29.1 (2005): 57-62.

[9] Inoue, Naohiko, Reiko Sakashita, and Tetsuya Kamegai. “Reduction of masseter muscle activity in bottle-fed babies.” Early human development 42.3 (1995): 185-193.

[10] Suzely, AS Moimaz, et al. “Association between breast-feeding practices and sucking habits: a cross-sectional study of children in their first year of life.” Journal of Indian Society of Pedodontics and Preventive Dentistry 26.3 (2008): 102.

[11] Peres, Karen Glazer, et al. “Effects of breastfeeding and sucking habits on malocclusion in a birth cohort study.” Revista de saude Publica 41.3 (2007): 343-350.

[12] Larsson, E. “Artificial sucking habits: etiology, prevalence and effect on occlusion.” The International journal of orofacial myology: official publication of the International Association of Orofacial Myology 20 (1994): 10-21.

[13] Odont, Erik Larsson. “Sucking, chewing, and feeding habits and the development of crossbite: a longitudinal study of girls from birth to 3 years of age.” The Angle orthodontist 71.2 (2001): 116-119.

[14] NIHI, Valdeane Simone Cenci, et al. “Pacifier-sucking habit duration and frequency on occlusal and myofunctional alterations in preschool children.” Brazilian oral research 29.1 (2015): 00-00.

[15] Pages, Leader. “Breastfeeding: reducing the risk for obstructive sleep apnea.” (1999).

[16] Kiliaridis, Stavros. “Masticatory muscle function and craniofacial morphology. An experimental study in the growing rat fed a soft diet.” Swedish dental journal. Supplement 36 (1985): 1-55.

[17] Beecher, Robert M., and Robert S. Corruccini. “Effects of dietary consistency on craniofacial and occlusal development in the rat.” The Angle Orthodontist 51.1 (1981): 61-69.

[18] Gomes, SG Farias, et al. “Masticatory features, EMG activity and muscle effort of subjects with different facial patterns.” Journal of oral rehabilitation 37.11 (2010): 813-819.

[19] Bresolin, Dante, et al. “Mouth breathing in allergic children: its relationship to dentofacial development.” American journal of orthodontics 83.4 (1983): 334-340.

[20] Souki, Bernardo Q., et al. “Prevalence of malocclusion among mouth breathing children: do expectations meet reality?.” International journal of pediatric otorhinolaryngology 73.5 (2009): 767-773.

[21] Harari, Doron, et al. “The effect of mouth breathing versus nasal breathing on dentofacial and craniofacial development in orthodontic patients.” The Laryngoscope 120.10 (2010): 2089-2093.

[22] Faria, Patrícia Toledo Monteiro, et al. “Dentofacial morphology of mouth breathing children.” Brazilian dental journal 13.2 (2002): 129-132.

[23] Luzzi, Valeria, et al. “Allergic rhinitis as a possible risk factor for malocclusion: a case–control study in children.” International journal of paediatric dentistry 23.4 (2013): 274-278.

[24] Karjalainen, S., et al. “Association between early weaning, non‐nutritive sucking habits and occlusal anomalies in 3‐year‐old Finnish children.” International Journal of Paediatric Dentistry 9.3 (1999): 169-173.

[25] Kobayashi, Henri Menezes, et al. “Relationship between breastfeeding duration and prevalence of posterior crossbite in the deciduous dentition.” American Journal of Orthodontics and Dentofacial Orthopedics 137.1 (2010): 54-58.

Other websites

[26] The Human Body, Hunter-Gatherer Vs. Modern (2016)

[27] Can you tell the difference between Orthotropics and Orthodontia? Dr. Karen O’Rourke, DDS

[28] Brazil, by David Lazar