BITES AND BODY POSTURE
THE PROBLEM - Bites affect body posture, because the location of the bite platform onto which the interdigitation of the teeth forces the mandible for bracing hundreds of times each day reflexively controls mandibular posture, mandibular posture affects head posture, and the posture of the head determines how the spine aligns beneath it to balance the big weight on top. However, the mandible is the only bone routinely left out of postural analysis, because dentists don't understand its orthopedic role, and orthopedists don't understand how to manage joint surfaces composed of jagged rocks that are so delicately suspended in 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. Without understanding how bites affect growth, we allow children to develop strained facial growth patterns, even while straightening their teeth within their crooked jawbones. The strained growth patterns continue during adulthood, producing a progressive scoliosis. Medical authorities point out that postural strains can cause bite problems, but they fail to point out that strained bites can cause postural problems.
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 braces, and neuromuscular reflexes program the jaw muscles to always hold the mandible in a postural position just beneath that platform to ensure fast easy access to to it for bracing to protect the vital structures behind the mandibular condyles. As a result, the mammalian face grows around the bite table. In humans, the face also grows around the airway passing between the mandible (surrounding it on front and both sides) and the cervical spine (behind it). If the mandible shifts back toward the cervical spine, the head extends and shifts forward to pull the mandible forward to open the airway. In the last couple of centuries, as we adopted a diet of processed foods and liquids, our mandibles have shifted backward, which may be an important cause of the accompanying forward shift of our head postures. Many mandibles have also shifted to one side, which tips the head to that side 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 meaningful correlations 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, 5 In humans, even minute changes in the bite can cause immediate changes in postural muscle activity.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 However, the only bite parameter that has been correlated with postural parameters is maxillo-mandibular relationship (Angle's class 1, 2, or 3 malocclusion). Class 3 malocclusions are correlated with more flexed head postures, and class 2 malocclusions (also incisor crowding) are correlated with more extended head postures, but those correlations are weak and non-specific.
The reason for the failure to correlate bites and body posture is that the parameters used 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 tell us nothing 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 posture and TMJ disorders requires recognizing that mandibular posture is under two different and sometimes competing influences - one from the myofascial tonus of the postural system and one from reflexes designed to protect the teeth. When these influences are not aligned, mechanical strain is shared by the jaw and postural systems, and successful treatment requires addressing both. Treating the pain in one set of muscles usually just transfers it to a different set of muscles.
MYOFASCIAL TONUS - is a network of cooperative myofascial tensions (tensegrity) that maintains your habitual upright postural stance with a light steady skeletal background muscle tonus of about one percent of maximum force and the steady support of the fascia that has formed around it. Collectively these forces maintain an equilibrium (tensegrity) that holds each bone in a resting place, called a neutral zone, balanced between opposing tensions. The neutral zone is maintained by 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 postural 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.
PROTECTIVE REFLEXES -The myofascial influence on mandibular posture can be overridden by protective neuromuscular reflexes that ensure fast easy access to mandibular bracing. During evolution, our teeth were the fragile components of the jaw system, and the jaw muscles were strong. Mandibular bracing, when the powerful jaw closing muscles immobilize the mandible by clamping it up forcefully against the underside of the cranium through the medium of the bite table, served a critical protective role; 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 them 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 thereby protect it from posteriorly directed forces; and the canines project beyond the bite platform to extend this protection to the mandible's postural resting position. 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.
As a result of these protective reflexes, your jaw muscles only allow you to brace and work your mandible on its most stable bite platform, even if that is uncomfortable for them; and your jaw muscles keep the posture of your mandible just beneath that most stable bite platform for quick access to bracing, even if that requires continually straining. Because of the jaw muscle programming to fit the bite, the strained mandibular posture will feel perfectly normal.
The distance (vertical dimension) by which the mandible rests below its most stable bite platform depends on the resting tonus of the jaw closing muscles. It may hang several millimeters below the bite platform when the jaw closing muscles are relaxed, or it may keep the mandible close to the bite platform, even with the teeth touching, when central nervous system tension increases their tonus.
The accommodation of mandibular posture to the location of its most stable bite 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, which is maintained by increased tonus in the ipsilateral posterior temporalis muscle, and the tonus 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
POSTURAL STRAIN - If the mandibular posture determined by your neutral zone forces is not coincident with the mandibular posture determined by your protective reflexes, a strain is shared between your jaw and postural muscles, and symptoms often switch back and forth between them. 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 harmonizing the jaw and postural systems, which requires understanding how they are connected, which requires understanding how they became connected in the first place.
UPRIGHT BODY POSTURE - For evolution, balancing the heavy head on top of an upright spinal column was an enormous feat that required changing all the structures supporting the body and also incorporating the mandible into the posture mechanism. The spines of quadrupeds are supported at front and back like a suspension bridge. 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 to produce a biped 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. Its center of mass shifted posteriorly by shortening and hollowing out the facial bones, and its connection to the spine shifted anteriorly to a location almost directly under its center of mass.
APE HOMINID
This reshaping of the cranium made room for expansion of the brain on its back half; but it 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; necessitating a number of changes in orofacial and cervical anatomy. The tongue balled up and moved toward the cervical spine, leaving only a narrow passage in which the airway and alimentary canal must cross. To safeguard the exposed entrance to the pharynx, an oropharynx developed between the soft palate and the epiglottis, a secondary palate developed the ability to separate the nasal passage from the mouth as needed, and the larynx descends during infancy to a location below the sharp bend in the airway, creating space for multiple pharyngeal muscles to separate the air and food channels and facilitate speech. The structural reinforcement for the mandible moved from its inner border, where it limited the size of the airway passage, 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 passage during opening, to an axis between the mandibular foramen, which preserved space for the passage and protected the neurovascular bundle where it enters the mandible.
To stabilize the hominid cranium on the top of the spine, the surrounding muscles keep it erect by pulling down all around its periphery. Thus, 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. At the front of the cranium, the sensory systems could not operate effectively if enclosed by bone thick enough for anchoring postural muscles, so the long rigid mandible absorbs them all and 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.
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, and 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; but 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.
The location of the airway passage within that pre-cervical kinetic chain makes the postural locations of the head and the mandible inversely proportional in a sagittal plane. 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.
BACKWARD MANDIBULAR POSTURE AND FORWARD HEAD POSTURE - Most clinically relevant, shifting the mandible posteriorly (backward jaw posture) shifts the head anteriorly (forward head posture) 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 pharyngeal airway space that gets lost when the mandible shifts posteriorly. The increase in pharyngeal airway space produced by 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, head posture 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 inferred from the increased variability of body sway in people standing on a force table when they are blindfolded and by 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 produce extreme head extension in people with palpebral ptosis (eyelid droop).25 As a result of these righting reflexes, head extension is always accompanied by anterior head translation, and backward jaw posture causes forward head posture, as illustrated below.
THE RECENT POSTERIOR SHIFT OF THE MANDIBLE - During the last few centuries, our dietary change to soft foods has made this scenario endemic. Most people have both backward jaw posture and forward head posture. On average, mandibles have become shorter, and mandibular postures have become displaced posteriorly.26-35 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, except when the tongue intervenes to protect the airway. In most people, the facial growth that is inhibited horizontally is redirected vertically, so the mandible rotates down and back rather than up and forward, as it did in our ancestors.
The same general change in facial shape due to soft foods can be seen in skeletal remains from all over the world, when tribal people abandon their traditional diets and acquire a diet of processed foods. The illustration below left compares a population before and after they discovered agriculture about 10,000 years ago. The illustration below middle compares the average facial structures of traditional Australian Aborigines and modern Swedes.26-39 The illustration below right compares a patient who has muscular dystrophy with an average growth pattern for the same age. The dependence of this change on jaw muscle strength is supported by the fact that very similar changes have been produced in several species of animals just by raising them on soft diets.40-49
SOLID LINE NUBIANS BEFORE AGRICULTURE SOLID LINE AUTRALIAN ABORIGINES SOLID LINE NORMALS
DOTTED LINE AFTER AGRICULTURE DOTTED LINE MODERN SWEDES DOTTED LINE MUSCLE DISEASE
The same average change in craniofacial proportions has been accompanied by increased variability, even in populations that have not experienced significant genetic mixing. Asymmetry has increased dramatically, especially in people with weak muscles. People with strong muscles more frequently maintain symmetry, and their strong muscles prevent excessive lengthening of the face; but their biting forces are usually confined to the posterior teeth, which intrudes those teeth and allows the front teeth to extrude, leaving the mandible locked back posteriorly behind a steep and often deep overbite.
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 their upper and inner aspects 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.
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 below.
NORMAL POSTURE FORWARD HEAD POSTURE
LATERAL DISPLACEMENT OF THE MANDIBLE – In many people, the mandibular posture following the most stable bite has also shifted laterally, accompanied by posterior displacement on the side of the shift. Because the lateral displacement is maintained by increased tonus in the ipsilateral temporalis muscle, (as shown 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 displacement, which makes the opposite eye appear higher in photographs. This feature is consistent enough to be predictive. A photograph of the head in the habitual postural stance can predict the side to which the mandible is advanced. Lateral mandibular displacement also typically compresses the face on the side of the displacement, making the eye of that side appear smaller than the eye of the opposite side.
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 bite forces. Pre-industrial populations who chewed very forcefully sometimes developed maxillae which were so wide that the mandible could only contact the back teeth of one side at a time. In contrast, animals raised on soft diets develop narrow maxillae like modern children. When a child's narrow upper dental arch prevents it from fitting around their lower dental arch to achieve a stable bite, the mandible looks for one. In unilateral cross bite, it shifts laterally far enough to reverse the interdigitation of the teeth on that side.
Lateral displacement of the mandible can 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 needs to be refined by functional forces as it enters the mouth. If it erupts off to one side and functional forces are too weak to realign it, it can realign them. It can shift the bracing position used by the mandible, which 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.
The lateral displacement of the mandible then disturbs symmetry throughout the spine. 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
DEPROGRAMMING THE JAW MUSCLES - To find out if your current bite platform is displacing your mandible from its myofascial neutral zone requires temporarily deprogramming your jaw muscles to stop them from reflexively aiming all mandibular closing trajectories at your old bite platform by wearing a flat front bite plate appliance during sleep. The orientation of its bite table 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 bicycle 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 the habitual mandibular closing trajectory land on a flat bite platform 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 an unstrained jaw closing trajectory. Jaw muscles that have become shortened (contracture) due to chronic tightening 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, which requires a stable bite.
EXTENDING THE BITE PLATFORM - toward the postural neutral zone can be accomplished by grinding down portions of teeth that are too high when the mandible is moved toward its neutral zone position. Extending the bite 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 posterior teeth. Extending the bite 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.
Any extension of the bite 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 using 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 bite 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 BITE PLATFORM – by also adding tooth structure behind the shift may be preferred when simply extending the bite platform threatens to damage teeth or make them too flat to cut and tear food. The bite platform 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 bite platform by means of dental work such as crowns forces the treating dentist 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 bite platform right away, their tendency to brace the mandible in the old bite 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 platform in body posture. Dentists performing full mouth reconstruction must recognize that stabilizing the existing bite platform also stabilizes the existing body posture, and changing the existing body posture requires at least altering the existing bite platform. The jaw and postural systems are fully integrated, and making a change anywhere ina fully integrated biological system requires making some changes everywhere; but most modern bites lock the articulating upper and lower jawbones together in a position that is precisely fixed in three dimensions. Conventional orthodontics produces a bite platform in whatever location the mandible used for bracing most frequently during the process, therefore jaw muscle strength and healthy functional activities should be maintained during the process to prevent inadvertant displacement of the bite platform. Also, if the patient had a deep or steep overbite before orthodontic treatment, adding a front flat bite plate to the retainer (Hawley), can prevent a growth restricting 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.