BITES AND BODY POSTURE
SUMMARY - Bites affect body posture, because the position into which the interdigitation of the teeth forces the mandible for bracing hundreds of times a day controls mandibular posture, mandibular posture is an integral component of head posture, and head posture determines how the spine aligns beneath it to balance the big weight on top. However, the mandible is the only major bone routinely left out of postural analysis, because dentists don't understand the orthopedic role of the bite, and orthopedists don't understand how to manage a joint surface composed of jagged rocks that are so delicately suspended their sockets that they have individual vascular pulses and so extensively wired with protective neuromuscular reflexes that they occupy an oversized portion of the brain. As a result, we allow developing malocclusions to produce progressively displaced mandibular postures, even while straightening the teeth for esthetics. The progressive mandibular displacement, which continues slowly during adulthood, produces progressive displacement of spinal posture (scoliosis). We need to understand how bites affect body posture so we can incorporate bite treatment into postural treatment.
To understand the relationship between bites and body posture requires seeing how they evolved together. Lloyd DrBrul used to comment, "To understand the teeth, you have to look at the feet." In mammals, the teeth operate collectively to form a structural platform on which the mandible exercises in chewing and braces for stability, and neuromuscular reflexes program the jaw muscles to always hold the mandible in a postural position just beneath the center of that bite platform to protect the teeth. As a result, the face grows around that bite platform as a stable architectural landmark. In humans, the whole bite platform and the jawbones supporting it also grow around the airway passing through their center, making mandibular posture and head posture inversely proportional. In modern humans, the structural platform provided by the biting surfaces of the teeth has shifted downward and backward; which has also shifted mandibular posture downward and backward, which may be an important cause of the accompanying shift of average head posture anteriorly. In many people, the mandibular bracing platform and resting posture have also shifted to one side, which tips the head to the same side as the shift due to increased ipsilateral temporalis muscle tonus. Dentists can help other health care professionals restore postural health by extending or shifting the mandibular bracing position in conjunction with synergistic efforts to improve head and body posture.
THE PROBLEM - The mandible is an integral component of the head posture mechanism, but researchers have been unable to establish any workable connections between dental parameters and posture parameters. It's been known since 1928 that extending the head retrudes the mandible, and flexing the head protrudes the mandible.1. In animals, experimentally changing the bite changes the curve of the spine.2 In humans, even minute changes in the bite can cause immediate changes in postural muscle activity and head posture.3 A literature review found mandibular position associated with the spine in 266 publications, head posture in 216 publications, pelvic tilt in 53 publications, and leg-length discrepancies in 35 publications.4 In growing rabbits, experimentally altering the plane of the bite table can bend the whole craniofacial skeleton.5 However, the only bite parameter that has been correlated with postural parameters is maxillo-mandibular relationship (Angle's class 1, 2, or 3 malocclusion), which is mildly correlated with cervical spine angle. Class 3 bites are associated with more flexed head postures, and class 2 bites (also incisor crowding) are associated with more extended head postures.
The reason for our failure to correlate bites and body posture is that the parameters we use to measure bites tell us nothing about their orthopedic features. Dentists compare bites by measuring static details of the way the teeth fit together and some details of how they slide together, but those details reveal very little information about where the teeth position the mandible relative to the cranial base and the cervical spine or the cross-sectional area of the pharyngeal airway. To understand the role of the bite in body posture requires first understanding the importance of mandibular bracing.
MANDIBULAR BRACING – occurs when the powerful jaw closing muscles immobilize the mandible by clamping it up forcefully against the underside of the cranium. Mandibular bracing served a critical protective role during our evolution by temporarily immobilizing the mandible, because the vital inner ear structures in mammals are located just behind the mandibular condyles, and a blow to the prominent chin could drive the condyles into these delicate structures like little hammers. In carnivores and simians, the posteriorly facing surfaces of the lower canines fit against the anteriorly facing surfaces of the upper canines to brace the mandible anteriorly and medially and thereby protect it from posteriorly and laterally directed forces; and the canines project beyond the bite platform to extend this protection to postural rest. In hominids, the canines withdrew into the bite plane to increase adaptability by removing restrictions to the mandibular range of movement, which left the vital areas behind the mandibular condyles protected only by neuromuscular reflexes, which brace the mandible as soon as danger is sensed. For example, in a motor vehicle accident, you'll clench your teeth before your foot hits the brakes.
Mandibular bracing also serves a stabilizing role in postural dynamics. The braced mandible functions as a handle by which the postural muscles on the front of the body (the anterior kinetic chain) can pull down on the front of the cranium without applying forces to the face, where the sensory systems could not operate effectively if enclosed by bone thick enough for anchoring postural muscles. Therefore, to prevent postural muscle forces from reaching the face, the long rigid mandible transfers them around to the sides of the head, where the zygomatic arches and temporal fossae provide large areas of bone with sufficient structural support for strong muscle attachments.
REFLEX NEUROMUSCULAR CONTROL OF MANDIBULAR POSTURE - Mandibular bracing was so important during evolution that our jaw muscles are programmed to always hold our mandibles in a resting posture just beneath its central bracing platform to ensure fast easy access to mandibular bracing. The distance by which the mandible rests below the central bracing platform (its vertical dimension) depends on the resting tonus of the jaw closing muscles. It may rest several millimeters below the central bracing platform when the jaw closing muscles are relaxed or all the way up against it, even in a clench, when central nervous system tension increases. Whether or not the teeth are in contact, the horizontal dimension of the mandible in its resting posture is a function of the horizontal location of the mandible in its central bracing platform.
This accommodation of mandibular posture to the location of its central bracing platform has been demonstrated in many studies. An immediate increase in freeway space (the space between the teeth when the jaw is at rest in its postural position) follows the first bite contact after placing a bite raising appliance, an immediate return to the pre-treatment freeway space follows the first bite contact after removing the bite raising appliance, and shortening the face surgically or prosthodontically leads quickly to a new mandibular resting posture that maintains the pre-treatment freeway space.6 Children with a unilateral cross-bite that shifts the mandibular bracing position laterally show a parallel shift of mandibular posture, maintained by increased tonus in the ipsilateral posterior temporalis muscle, which normalizes after correction of the cross-bite.7-10 Monkeys fitted with crowns that force the mandible to brace in a laterally displaced position undergo a lateral shift of mandibular posture,11 and monkeys fitted with crowns that force the mandible to brace in an anterior position undergo an immediate increase in the tonus of the superior lateral pterygoid muscles to hold the mandible anteriorly.12-13
MYOFASCIAL CONTROL OF MANDIBULAR POSTURE - However, there is also another influence on mandibular posture - a network of cooperative background tensions that maintain the habitual upright postural stance with a light steady muscle tonus of about one percent of maximum voluntary contractile force. The resulting equilibrium (tensegrity) holds each bone in a resting place, called a neutral zone, balanced between opposing tensions. Neutral zone forces create fields of tension on the surfaces of the bone that either resorb bone or deposit new bone until the surfaces fit the neutral zone forces. If a bone is surgically moved away from its neutral zone, these opposing forces act to move it back in, requiring metal fasteners to stabilize many orthopedic corrections. The mandible rests in a postural neutral zone within the myofascial curtain draping down from the front of the cranium onto the clavicles and shoulder girdle. At least it would rest there if there were no teeth involved.
MANDIBULAR POSTURAL STRAIN - If the mandibular posture determined by the resting myofascial tensions of the rest of the body in its habitual upright stance is not coincident with the mandibular posture determined by the neuromuscular reflexes that program it to remain just below the bite table, a strain is shared between the jaw and postural systems, and the symptoms often switch back and forth between jaw and neck or back muscles. Treatment that relieves symptoms in one set of muscles usually just transfers them to the other set of muscles. Permanently relieving the source of the strain requires correcting the jaw and postural systems together, which requires understanding how they are connected, which requires understanding how they became connected in the first place.
UPRIGHT BODY POSTURE - The mandible became incorporated into the posture mechanism when hominids went upright. The spines of quadrupeds are supported at front and back like a suspension bridge - with the skull hanging from the well supported shoulders and the mandible hanging from the skull. The forward ends of the food and air channels, hanging in sequence from the front of that bridge, are easily kept separated and scarcely affected by movements of the head. The neck muscles assist in mouth opening and closing by extending and flexing the head.
Uprighting a quadruped required revamping the skeleton. The spine developed alternating curves. The foot acquired a concave arch. The rib cage flattened. The pelvis acquired a concave front surface to support the abdomen resting on it and a thick bony crest for enlarged buttock muscles to help balance the weight over the legs. The cranium had to be reshaped so it could be balanced on the top of the spinal column. The face shifted backward until it ran into the airway. Its bones became hollow to reduce the weight anteriorly. The connection between the cranium and the spine moved to a location nearly under the center of mass of the cranium.
FIGURE 1 - RESHAPING THE CRANIUM
APE HOMINID
This reshaping of the cranium made room for expansion of the brain on its back half but also compressed the face under its front half between the unchangeable orientation of the orbital plane (has to keep looking forward toward the horizon) and the forwardly rotating cervical spine. This compression of the face necessitated changes in orofacial and cervical anatomy. The tongue balled up. The structural reinforcement for the mandible moved from its inner border, where it limited the size of the airway, to its outer front end where it formed a chin. The center of rotation of the mandible moved from an axis between the condyles, which could rotate the shortened mandible into the airway space during opening, to an axis between the mandibular foramen, which preserved the airway space and protected the neurovascular bundle where it enters the mandible.
To stabilize the hominid cranium on the top of the spine, it was surrounded by a cooperative system of jaw and cervical muscles that keep it erect by pulling down all around its periphery like stays pulling down on the mast of a sailboat or wire cables pulling down on a radio tower. The jaw and postural muscles developed coordinated firing patterns.13-14 The pull down on each side prevents tipping to the opposite side, and selective relaxation provides the flexibility needed for movement. From side to side, this tower is symmetrical and stable, supported by a series of parallel transversely extending structural components - cranium, shoulders, hips, and two feet side by side. However, from front to back, stability is far more difficult for a body so tall and flat. Symmetry is lost right from the top. In back, thick straps of post-cervical muscles attached to large bony occipital prominences pull straight down on the back of the head. However, in front, thick muscles and large bones could interfere with the freedom of movement necessary for yawning, swallowing, coughing, vomiting, spitting, talking, and turning the head. Therefore, the pull down in back is counterbalanced by multiple small muscles with varied directions of pull connecting a series of generally small parallel bones (clavicles, hyoid, and mandible) to ensure that each bone is capable of independent but coordinated action. The balance between this sophisticated pre-cervical kinetic chain and the simple thick post-cervical muscle mass is illustrated below.
FIGURE 2 - THE HOMINID HEAD POSTURE MECHANISM
THE ROLE OF THE MANDIBLE– Because the airway passes between the jawbones through the center of this mechanism and the whole craniofacial structure grows around the airway passage, the postural locations of the head and the mandible are inversely proportional in a sagittal direction. Moving either one anteriorly or posteriorly moves the other in the opposite direction. For example, surgery to advance the mandible causes the head to shift posteriorly, and surgery to move the mandible posteriorly causes the head to shift anteriorly.16-18. Shifting the head posteriorly shifts the mandible anteriorly (relative to the head) by compressing the tissues behind the mandibular rami. Shifting the head anteriorly shifts the mandible posteriorly (relative to the head), because the mandible is tethered to the clavicles and shoulder girdle and thus cannot shift as far anteriorly as the head. Shifting the mandible posteriorly shifts the head anteriorly by triggering reflex neuromuscular responses that extend the head in order to rotate the mandibular corpus upward and forward away from the cervical spine to restore the lost pharyngeal airway space. The increase in pharyngeal airway space produced by such head extension has been demonstrated with imaging.19-20 The ability of pharyngeal airway blockage to trigger head extension can be inferred from findings that most children with swollen tonsils have extended head posture which normalizes quickly after tonsillectomy.21-23
However, the head cannot just tip back, because visual and vestibular reflexes (the so-called righting reflexes), keep it level with the horizon. The regulatory effect of the visual orientation reflex can be seen in the increased variability of head posture in the blind.24 Also its power to alter muscle resting postures can be seen in its ability to bend the whole cranium in bipedal mice and also to produce extreme head extension in people with palpebral ptosis (eyelid droop).25 As a result of these righting reflexes, the head can only extend by simultaneously translating forward, as illustrated below.
THE RECENT POSTERIOR SHIFT OF THE MANDIBLE - During the last couple of centuries, our sudden dietary change to liquids and refined foods has made this scenario endemic. On average, our bites and mandibular postures have shifted significantly in a posterior direction.26-35 The average mandible now rotates down and back rather than up and forward, as it did in our ancestors. Mandibles have become shorter and more posteriorly positioned. Class 2 bites, in which the lower dentition is located posteriorly relative to the upper dentition, have become twice as frequent as they used to be; and many of those with class 1 bites actually have both an upper and lower dental arch that are located posteriorly relative to the cranial base, because most of the structural components of the craniofacial skeleton (including the bite table) follow the growth of the mandibular corpus, roughly in proportion to their distance from it.
One cause of this posterior shift of the mandible is the failure to stimulate jawbone growth by chewing forces. The role of jaw muscles in mandibular advancement and in upward and forward mandibular rotation can be seen by the extreme posterior and inferior mandibular posture that occurs in people with myotonic dystrophy.
The other cause of this posterior shift of the mandible is a partial maxillo-mandibular synostosis due to retained overbite and steep cuspal interdigitation. In our ancestors, overjet and overbite slowly but steadily disappeared with age. In modern people, they generally persist throughout life, furthering the posterior shift by locking the tooth containing portion of the mandible (the corpus) back behind the upper front teeth.
Much of the facial growth that has been inhibited horizontally has been redirected vertically. When the mandible' cannot grow anteriorly, it grows down and back. In some people, strong jaw closing muscles are able to prevent the downward component but keeps the mandible locked posteriorly back behind a steep and usually deep overbite.
The change toward decreased horizontal growth and the increased vertical growth in modern humans is easy to see in skeletal remains. The comparison below left shows a population before and after they discovered agriculture about 10,000 years ago. The comparison below middle shows the average facial structures of traditional Australian Aborigines and modern Swedes.26-39 The same changes can be seen all over the planet when tribal people abandon their traditional diets and acquire a diet of soft processed foods.
The dependence of this change on jaw muscle strength has been shown by numerous experiments. Very similar changes have been produced in several species of animals just by raising them on soft diets.40-49 The same types of changes can also be seen in natural experiments when people lose jaw muscle strength due to myotonic dystrophy, as seen in the comparison below right.
THE SECULAR CHANGE IN CRANIOFACIAL PROPORTIONS
SOLID LINE NUBIANS BEFORE AGRICULTURE SOLID LINE AUTRALIAN ABORIGINES SOLID LINE NORMALS
DOTTED LINE AFTER AGRICULTURE DOTTED LINE MODERN SWEDES DOTTED LINE MUSCLE DISEASE
ANTERIOR SHIFT OF HEAD POSTURE - The average change toward a more posterior mandibular posture is likely an important cause of the accompanying average change toward a more anterior head posture. In population studies, these two variables are well correlated, and most longitudinal studies have found that the changes in mandibular growth usually come first.50-51 The ability of posterior mandibular posture to cause anterior head posture can be seen in children who experience TMJ ankylosis, which prevents the mandible from advancing and also causes extreme forward head posture, simply as a result of their extreme posterior mandibular posture.
Forward head posture progressively diminishes and then reverses the cervical lordosis by shifting its top end forward over its base, as seen from left to right below. The vertical line rotating from a 12:00 position to a 1:00 position shows the long axis of the cervical spine rotating clockwise to support the forward shifting cranium. The descent of the upper horizontal line shows the loss of vertical height that accompanies the rotation of the cervical spine. The rotation of the lower horizontal line shows the shoulder girdles following the base of the neck anteriorly. Because the upper and inner aspects of the scapulae follow the advancing base of the neck more closely than their outer and lower aspects, the scapulae also often rotate inward around a vertical axis, leaving their lower and outer aspects sticking out like wings (winged scapula).
FIGURE 5
-PROGRESSION OF FORWARD HEAD POSTURE
NORMAL POSTURE FORWARD HEAD POSTURE EXTREME FORWARD HEAD POSTURE
AND BACKWARD JAW POSTURE AND EXTREME BACKWARD JAW POSTURE
EFFECTS ON SPINAL POSTURE - Forward head posture reflexively triggers adaptive realignment of the spine to restore physical balance. Typically the hips rotate down in front to thrust the abdomen anteriorly out beneath the anteriorly shifted head while the chest between them sinks backward, increasing the thoracic kyphosis, as seen from left to right in figure 6.
FIGURE 6 - SPINAL RESPONSE TO FORWARD HEAD POSTURE
NORMAL POSTURE FORWARD HEAD POSTURE
LATERAL DISPLACEMENT OF THE MANDIBLE – Mandibular postures also frequently get displaced laterally. Because the lateral displacement is maintained by increased tonus in the ipsilateral temporalis muscle, (as shown convincingly in children with unilateral cross-bite7-8), and because the temporalis is the postural muscle for the mandible; lateral mandibular displacement tips head posture toward the side of the mandibular displacement, which makes the eye of the opposite side appear higher in photographs. It also compresses the face on the side of the displacement, which frequently makes the eye of that side appear smaller than the eye of the opposite side in photographs.
The lateral displacement of the mandible then disturbs symmetry throughout the spine, just as asymmetry in body posture can produce lateral displacement of the mandible. Crooked body posture and mandibular posture are reflections of each other. Tipped head posture has been correlated with scoliosis, asymmetric firing of neck muscles, shoulder imbalance, lateral displacement of the cervical spine, and increased body sway.52-58
One common cause of lateral mandibular displacement is a misfit between a narrow maxilla and a wide mandible. While the width of the mandible is determined almost entirely by genetics, the width of the maxilla is determined largely by functional forces. Pre-industrial populations who chewed very forcefully sometimes developed maxillae which were so wide that the mandible could only bite on the back teeth of one side at a time, which did not prevent effective chewing. In contrast, animals raised on soft diets develop narrow maxillae like modern children. When the narrow maxilla of a child prevents it from fitting around the lower dental arch to achieve normal interdigitation of the teeth, the mandible shifts to achieve meshing of the teeth for chewing. In unilateral cross bite, it shifts laterally far enough to reverse the interdigitation of the teeth on that side.
A significant lateral displacement of the mandible can even be caused by one malpositioned tooth. For example, a permanent canine enters the mouth of an adolescent as a very large structure at the end of a long eruption pathway which cannot be very precisely controlled and therefore needs to be refined by functional forces as it enters the mouth. If it erupts off to one side and the functional forces produced by the tongue, lips, cheeks, and jaw muscles are too weak to realign it; the displaced canine can shift the habitual bracing position used by the mandible instead of being shifted by it. This displacement of the habitual biting position then causes the rest of the erupting permanent teeth to also acquire interdigitation in the same displaced mandibular position, until it becomes normalized by the neuromusculature. As a result, many people live with a significantly displaced mandibular posture and do not know it.
DEPROGRAMMING THE JAW MUSCLES - To find out if the mandible's central bracing position is displaced from its postural neutral zone requires temporarily deprogramming the jaw muscles to stop them from reflexively aiming all mandibular closing trajectories at the old habitual central bracing platform. This is best accomplished by wearing a flat front bite plate appliance during sleep. The orientation of its bite plate parallel to the superior lateral pterygoid muscles supports their role in determining the horizontal location of the mandible by pulling on its condyles like steering a bike by its handlebars. After deprogramming, the mandible opens and closes on a trajectory determined only by resting myofascial postural forces. The distance and direction between where this deprogrammed mandibular closing trajectory and where the habitual mandibular closing trajectory land on a flat bite table provides a measure of the distance and direction of bite strain.
REHABILITATING THE JAW MUSCLES - Unhealthy jaw muscles may need strengthening or stretching before they can clearly and consistently demonstrate a healthy unstrained jaw closing trajectory. Jaw muscles that have become shortened due to chronic tightening (contracture) may need stretching, and jaw muscles that have become hypotonic or atrophic due to a longstanding reduction of functional forces from protecting an inflamed TMJ or tender teeth may need strengthening. Strengthening the jaw muscles requires a stable bite, because the bite table forms their exercise template. However, even a very stable bite can still hold the mandible in a very displaced location and impair muscle health by displacing the template they exercise against, like riding a bike with the seat much too low or lifting weights with your feet planted off to the side.
EXTENDING THE CENTRAL BRACING PLATFORM - toward the postural neutral zone can be accomplished by reducing (shaving down) portions of teeth that are too high (called equilibration) or building-up portions of teeth that are too low when the mandible is moved toward the neutral zone. Extending the central bracing platform anteriorly in the presence of deep or steep overbite usually requires reducing the contacts between the labial-incisal edges of the lower front teeth and the palatal surfaces of the upper front teeth or building up all the other teeth. Extending the central bracing platform medially from a laterally displaced position usually requires reducing teeth on the side opposite the displacement, as well as any balancing side contacts on the side of the displacement, or building up the teeth on the side of the displacement.
Extension of the central bracing platform must be used to be preserved. Simply providing a pathway along which the mandible can shift does not make it shift. If the jaw muscles do not begin bracing the mandible in the newly extended portion of the bite platform, they may not distribute enough axial forces onto the involved teeth to maintain their positions. For example, if the central bracing platform is extended anteriorly by equilibration of the front teeth and the extension is not used functionally, such as by incising or bracing there, the front teeth may extrude until their incisal edges reach the same location they had before the equilibration, which is controlled by lower lip posture. Synergistic measures to improve head posture can also increase the use of the extended area of the bite platform and thereby help the change "take".
MOVING THE CENTRAL BRACING PLATFORM – may be preferred when simply extending it far enough to fit healthy resting myofascial postural forces threatens to damage teeth or make them too flat to cut and tear food. Moving the central bracing platform requires adding tooth structure behind the mandibular shift in addition to removing tooth structure from the path of the shift. The central bracing position is usually moved together with the surrounding inclines of tooth structure that define a functional range of motion which has been established by the jaw muscles.
However, moving the central bracing platform by means of dental work such as crowns forces us to produce the full bite change at a single appointment, requiring a relatively sudden adaptation by the rest of the postural system, while most postural system corrections occur more gradually. If the jaw muscles do not fully adopt the new bracing platform right away, their tendency to brace the mandible in the position of the old central bracing platform can fracture the added artificial tooth material or stress the periodontal support for the teeth bearing them.
DENTAL WORK – Should recognize the orthopedic role of the bite in body posture. Dentists performing full mouth reconstruction must recognize that stabilizing the existing bite also stabilizes the existing body posture. Conventional orthodontics produces a central bracing platform in whatever location the mandible used for bracing most frequently during the process, therefore jaw muscle strength should be maintained during the process to prevent inadvertent displacement of the central bracing platform. Also, if the patient had a deep or steep overbite before orthodontic treatment, adding a front flat bite plate to the retainer (Hawley), is important to prevent the overbite from recurring post-treatment.
FOOTNOTES
1. Schwartz AM. Positions of the head and malrelations of the jaws. Int J Orthod Oral Surg Radiol. 1928;14:56-68.
2. Ramirez-Yanezgerman G, Mehta L, Mehta N. The effect of dental occlusal disturbances on the curvature of the vertebral spine in rats. J Craniomandib Pract. 2015;33(3):217-227.
3. Bakke M, Moller E. Distortion of maximal elevator activity by unilateral premature tooth contact. Scand J Dent Res. 1980:80;67.
4. Hanke BA, Motschall E, Turp JC. Association between orthopedic and dental findings: what level of evidence is available? J Orofac Orthop. 2007;68:91-107.
5. Sergi H., and Farmand M.:Experiments with unilateral bite planes in rabbits. Angle Orthod vol 45 #2 p 108-114.
6. Hellsing G. Functional adaptation to changes in vertical dimension. J Prosthet Dent. 1984;52;867-870.
7. Troelstrup B, Moller E. Electromyography of the temporalis and masseter muscles in children with unilateral cross-bite. Scand J Dent Res. 1970;78:425-430.
8. Nerder PH, Bakke M, Solow B. The functional shift of the mandible in unilateral posterior crossbite and the adaptation of the temporomandibular joints: a pilot study. Eur J Orthod. 1999;21:155-166.
9. Tecco S, Tete S, Festa F. Electromyographic evaluaton of masticatory, neck, and trunk muscle activity in patients with posterior crossbites. Eur J Orthod 2010;32(6):747-752.
10. Ingervall B, Thilander B. Activity of temporal and masseter muscles in children with a lateral forced bite. Angle Orthod. 1975;45:249-258.
11. Curtis D, Miller AJ, Mielsen OL, Kapila S. Lateral shifts in the occlusion of the Macaca mulatta monkey. J Dent Res. 1989;68:415.
12. Elgoyhen JC, Moyers RE, McNamara JA, Riolo MI. Craniofacial adaptation to protrusive function in young rhesus monkeys. Am J Orthod 1972;62(5):469-480.
13. McNamara JA. Functional adaptations of the temporomandibular joint. Dent Clin North Am. 1975;19:457-471.
14. Zafar H. Integrated jaw and neck function in man: studies of mandibular and head-neck movements during jaw opening-closing tasks. Swed Dent J Suppl. 2000;143:1-41.
15. Eriksson PO, Haggman-Henrikson B, Nordh E, Zafar H. Coordinated mandibular and head-neck movements during rhythmic jaw activities in man. J Dent Res. 2000;79:1378-1384.
16. Phillips C, Snow MD, Turvey TA, Proffit WR. The effect of orthognathic surgery on head posture. Eur J Orthod 1991;13:397-403.
17. Marsan G, Oztas E, Cura N, Kuvat SV, et al. Changes in head posture and hyoid bone position in Turkish class 3 patients after mandibular setback surgery. J Craniomaxillofac Surg 2010;38(2):113-121.
18. Wentzel A, Williams S, Ritzau M. Changes in head posture and nasopharyngeal airway following surgical correction of mandibular prognathism. Eur J Orthod. 1989;11:37-42.
19. Hellsing E. Changes in the pharyngeal airway in relation to extension of the head. Eur J Orthod. 1989;11:359-365.
20. Greene DG et al. Cineflourographic study of hyperextension of the neck and upper airway patency. J Am Med Assoc. 1961;1;176:570-573. Also Muto T, Takeda S, Kanazawa M, et al. The effect of head posture on the pharyngeal airway space (PAS). Int J Oral Maxillofac Surg 2002;31(6):778-84)
21. Linder-Aronson S. Adenoids: Their effect on mode of breathing and nasal airflow and their relationship to characteristics of the facial skeleton and dentition. A biometric, rhino-manometric, and cephalometero-radiographic study on children with and without adenoids. Acta Otolaryngol Scand Suppl. 1970;265:1-132.
22. Linder-Aronson S, Backstrom A. A comparison between mouth and nose breathers with respect to occlusion and facial dimension. Odontol Revy. 1980;11:343-376.
23. Solow B, Greve E. Craniocervical angulation and nasal respiratory resistance. In: McNamara JA Jr (ed) Naso-respiratory function and craniofacial growth. Monograph 9, Craniofacial Growth Series, Center for Human Growth and Development, University of Michigan, Ann Arbor 1979.
24. Nucci P, Curiel B. Abnormal head posture due to ocular problems - a review. Current Pediatric Rev. 2009;5(2):105-111.
25. Dogan S, Erturk N. The studied effect of vision on cranio-cervical posture and its relation to craniofacial and dentoalveolar morphology. Quintessence Int. 1990;21:401-406.
26. Jonke E, Orossinger H, Bookstein FL, Schaefer K. Secular trends in the facial skull from the 19th century to the present, analyzed with geometric morphometerics. Am J Orthod Dentofac Orthoped. 2007;32(1)63-70.
27. Mohlin B, Sagne S, Thilander B. The frequency of malocclusion and the craniofacial morphology in a medieval population in Southern Sweden. Ossa. 1978;5:57-84.
28. Angle L. Colonial to modern skeletal change in the U.S.A. Am J Phys Anthropol. 1976;45:723-735.
29. Carlson D, Van Gerven DP. Masticatory function and post-pleistocene evolution in Nubia. Am J Phys Anthropol. 1977;46(3):495-50.
30. Varrela J. Occurrence of malocclusion in attritive environment: a study of a skull sample from southwest Finland. Eur J Oral Sci. 1990;98:242-247.
31. Lundstrom A, Lysell L. An anthropological examination of a group of medieval danish skulls, with particular regard to the jaws and occlusal conditions. Acta Odontol Scand. 1953;11(2):111-128.
32. Jantz RL. Cranial change in Americans 1850-1975. J Forensic Sci. 2001;46:784-787.
33. Paschetta C, de Azevedo S, Castillo L, Martinez-Abadias N, et al. The influence of masticatory loading on craniofacial morphology: A test case across technological transitions in the Ohio valley. Am J Phys Anthropol. 2010;141:297-314.
34. Varrela J. Dimensional variation of craniofacial structures in relation to changing masticatory-functional demands. Eur J Orthod. 1992;14(1):31-36.
35. Phipps GS, German RZ, Smith RJ. Comparative craniofacial variation in Navajo Indians and North American Caucasians. Am J Phys Anthropol. 1988;76:145-154.
36. Carlson DS. Temporal variation in prehistoric Nubian crania. Am J Phys Anthropol. 1976;45:467-484.
37. Lieberman D, Krovitz GE, Yates FW,et al. Effects of food processing on masticatory strain and craniofacial growth in a retrognathic face. J Human Evol. 2004;46(6):655-677.
38. Rando C, Hellson S, Antoine D. Changes in mandibular dimensions during the mediaeval to post-mediaeval transition in London: A possible response to decreased masticatory load. Arch Oral Biol. 2014;59(1):73-81.
39. de Sousa BS, Bichara LM, Guerreiro JF, Abdo Quintao CC, Normando D. Occlusal and facial features in Amazon indigenous: an insight into the role of genetics and environment in the etiology of dental malocclusion. Arch Oral Biol. 2015;60:1177-1186.
40. Ciochon RL, Nisbett RA, Corruccini RS. Dietary consistency and craniofacial development related to masticatory function in minipigs. J Craniofac Genet Dev biol 1997;17:96-102.
41. Phipps GS, German RZ, Smith RJ. Comparative craniofacial variation in Navajo Indians and North American Caucasions. Am J Phys Anthropol 1988;76:145-154.
42. Larsson E, Ogaard B, Lindsten R, et al. Craniofacial and dentofacial development in pigs fed soft and hard diets. Am J Orthodont Dentofac Orthoped 2005;128(6):731-739.
43. He T, Kiliaridis S. Effects of masticatory muscle function on craniofacial morphology in growing ferrets. Eur J Oral Sci 2003;111:510-517.
44. Katsaros C. Masticatory muscle function and transverse dentofacial growth. Swed Dent J Suppl 2001;151:1-47.
45. Beecher RM, Corruccini RS, Freeman M. Craniofacial correlates of dietary consistency in a nonhuman primate. J Craniofac Genetics Develop Biol 1983;3(2):193-202.
46. Bjork A, Brown T, Skieller V. Comparison of craniofacial growth in an Australian and Danes, illustrated by longitudinal cephalometric analyses. Eur J Orthod. 1984;6:1-14.
47. Ulgen M, Baran S, Kaya H, et al. The influence of the masticatory hypofunction on the craniofacial growth and development in rats. Am J Orthod Dentofac Orthoped 1997;189-198
48. Solow B, Siersbaek-Nielsen S. Growth changes in head posture related to craniofacial development. Amer J Orthod. 1986;89:132-140.
49. Huggare J, Raustia A. Head posture and cervicovertebral and craniofacial morphology in patients with craniomandibular dysfunction. J Craniomandib Pract. 1992;10(3):173-177.
50. Solow B, Siersbaek-Nielsen S. Cervical and cranio-cervical posture as predictors of craniofacial growth. Am J Orthod and Dentofac Orthoped. 1992;101:449-458.
51. Huggare J, Cooke MS. Head posture and cervicovertebral anatomy as mandibular growth predictors. Eur J Orthod. 1994;16:175-180.
52. Lippold C, Danesh G, Hoppe G, Drerup B, et al. Trunk inclination pelvic tilt and pelvic rotation in relation to the craniofacial morphology in adults. Angle Orthod. 2007;77(1):29-35.
53. Lippold C, Danesh G, Schilgen M, et al. Relationship between thoracic, lordotic, and pelvic inclination and craniofacial morphology in adults. Angle Orthod. 2006;76(5):779-785.
54. Fushima K, Akimoto S, Takamoto K, et al. Morphological feature and incidence of TMJ disorders in mandibular lateral displacement cases. J japanese orthodont soc. 1989;48:322-328.
55. Zepa I, Hurmerinta K, Kovero O, Nissinen M, et al. Trunk asymmetry and facial symmetry in young adults. Acta Odontol Scand. 2003;61:149-153.
56. Lippold C, Van den Bos L, Hohoff A, Danesh G, et al. Interdisciplinary study of orthopedic and orthodontic findings in pre-school infants. J Orofac Orthop. 2003;64:330-340.
57. Goldberg CJ , Moore DP, Fogarty EE, Dowling FE. The relationship between minor asymmetry and early idiopathic scoliosis. Stud Health Technol Inform. 2002;88:17-19.
58. Sforze C, Tartaglia GM, Solimene U, et al. Occlusion, sternocleidomastoid muscle activity, and body sway: a pilot study in male astronauts. J Craniomand Pract. 2006;24(1):43-49.
59. Huggare J. Postural disorders and dentofacial morphology. Acta Odontol Scand. 1998;56:383-386.
60. Ferrario VF, Sforza C, Serrao G. The influence of crossbite on the coordinated electromyographic activity of human masticatory muscles during mastication. J Oral Rehabil 1999;26:575-581.