The bite: orthopedic perspectives

THE MAXILLO-MANDIBULAR JOINT

To understand the dynamics of the bite in a mammalian jaw system, it must be seen as one large tooth-lined ball-and-socket type of joint that has been re-engineered to house teeth on its articular surfaces, the upper and lower dentitions. This dentate maxillo-mandibular joint connects the upper and lower jawbones, with the lower dentition acting as the ball and the upper dentition acting as the socket.  It is close packed for bracing within a centrally located slightly indented area where the convex buccal (outer) cusp tips of the lower dentition fit up into the larger concave contours formed by the central grooves and marginal ridges of the upper dentition.  This centrally located area in the middle of the maxillo-mandibular joint is flat enough to allow the mandible some freedom of movement horizontally in all directions. The flat area is very small in carnivores and very large in herbivores. In a healthy natural human bite, it occupies at least 4 square mm, within which the articular surfaces (the bite tables) can withstand maximal compressive loading.  That central bracing area is surrounded by sloping walls that provide continuous support for the mandible in its direction of movement throughout its functional range of motion.  This maxillo-mandibular joint has four characteristics of synovial joints: 

1) The area receiving maximal compressive force responds to loads by deforming to distribute the compressive force onto a larger portion of the joint.  In synovial joints, the progressively increasing resistance to loads is formed by a series of increasingly stiff layers of tissue - plastic lubricating film, fibrous articular covering, calcified cartilage, thin subchondral bone, trabeculae aligned to resist functional forces, and cortical bone.   In the maxillo-mandibular joint, progressively increasing resistance to loads is formed by embedding each tooth in a sophisticated hydraulic shock absorbing system that allows it to move easily from its rest position over small distances in response to even light imposed loads.¹⁰  Each tooth that comes under load shifts out of the way in order to distribute the load onto more teeth, and the collection of teeth gives the bite table resiliency like a big cushion.  During light closure in the center of the maxillo-mandibular joint, the load falls only on the teeth in the middle of the dentition – primarily the first molars and the premolars. More forceful closure depresses those teeth until the load is spread out to include the canines and the second molars.¹¹  

2) Functional forces enhance circulation at the articular surfaces.  In synovial joints, the surfaces are flushed of waste products by weeping circulation due to rubbing of the cartilage that forces fluids out like compressing a sponge when they are in the path of the moving bone, and then allows new fluids to enter that area when the compression has moved on to a different area.  In the maxillo-mandibular joint, each tooth is delicately suspended in its socket by a dynamic viscoelastic shock absorbing system that enables it to respond to imposed loads by intruding the tooth into its socket, compressing the collagenous ground substance, tugging on the principle fibers, driving fluids into nearby vessels, and bending out the socket walls.^1-7  The tooth sockets are flushed of waste products by alternating compression and release of the teeth as the mandible operates like a pump handle that stimulates local circulation in all the teeth and their supporting tissues.  

3) Neuromuscular reflexes protect the articular surfaces by responding to damage by vigilance (increased tonus and decreased functional forces) in the surrounding muscles.  In synovial joints, they react to noxious afferent signals from the joint capsule and ligament attachments.  In the maxillo-mandibular joint, they react to noxious afferent signals from the vast network of mechanoreceptors surrounding the tooth roots.

4) Remodeling of the joint surfaces continuously maintains the goodness of fit between them.  In synovial joints, the bony articular surfaces are shaped by remodeling by osteoblasts and osteoclasts.  In the maxillo-mandibular joint, the bite tables are shaped by the adaptive shifting of teeth and their sockets, and the fit is refined by wear on the biting surfaces. 

This maxillo-mandibular joint also has three unique features due to having articular surfaces composed of lines of delicately suspended rocks. 

1) Each tooth functions like its own joint with its socket, complete with range of motion, source of functional circulation, continuous remodeling, and reflex neuromuscular protections.

2) Each tooth forms an interproximal joint with its neighboring teeth, including a joint space when the teeth are at rest and a central flat contact area surrounded by a periphery that defines a range of motion in all directions.

3) The dentitions respond to compressive force by interproximal bracing.  Teeth at rest are separated by interproximal gaps of three to twenty-one microns.¹²  Biting not only depresses the teeth into their sockets, but it also tips them lingually and mesially (forward) until their interproximal gaps close and the adjacent teeth make physical contact. The friction produced by this interproximal contact locks together groups of neighboring teeth and thereby enables them to function as a single structural unit, like one long tooth with many roots. For that system to function effectively requires interproximal contact areas that fit together like the articular surfaces of interproximal joints between the teeth.  In fact, the shapes of their interproximal contact areas reflect their function as interproximal joints.  Modern and pre-industrial interproximal joints are photographed in chapters 2 and 4 of ETIOLOGY.

THE CENTRAL BRACING AREA

Much like the central bracing areas of synovial joints are shaped by the remodeling of their bony articular surfaces in response to postural forces, the central bracing areas of maxillo-mandibular joints are shaped by remodeling of the tooth sockets in response to biting forces.  Postural forces normally provide the light steady forces that shape bones, but the resting posture of the mandible cannot limit the vertical dimension of the anterior portion of the face, because it has to hang open at rest.  Thus bite forces determine the freeway space and the vertical growth of the anterior portion of the face.  Teeth that receive large compressive forces intrude. Teeth that receive less compressive forces than their inherent eruptive force (probably a few grams) extrude. As a result, bite forces shape the maxillo-mandibular joint like tamping down bricks in sand until they create a central bracing platform with an almost perfect fit between the upper and lower dental arches throughout the area used for mandibular bracing and surrounded by slopes that support the mandible in its direction of movement during chewing. 

The area occupied by the central bracing platform of a maxillo-mandibular joint may be small, but it is never a point.  In all mammalian dentitions, the mandible can move around horizontally at least a small distance before encountering an increase in vertical dimension.  In fact, the feature that made temporomandibular joints (TMJs) so valuable in evolution was their ability to support transverse mandibular movements, which allowed them to rub the teeth together, which creates the potential to use attrition to produce wear facets bordered by edges that stay sharp in spite of abrasion.  The closely fitting facets form effective crushing surfaces, and the edges of the facets retain their cutting ability.  The presence of such wear facets is considered the best indicator of the transition to mammals in the archeological record.  In carnivores, the area occupied by the central bracing platform is small (about 5 mm in tigers) to enable shearing for cutting.  In herbivores, the area occupied by the central bracing platform enables wide lateral mandibular movements to grind food like a mortar and pestle. In rodents, the TMJs and the bite tables have long antero-posteriorly extended channels to enable gnawing at the incisors alternating with power-crushing at the molars.  In hominids, these features of previous mammalian dentitions were combined to produce a new hybrid chewing system with increased adaptability and with the jaw muscles centered over the bolus for power and oriented in all directions for control.  The small flat zone in the middle of the central bracing platform was preserved by the twisting of the mandible on the bolus during power-crushing powered by a force couple consisting of the superior lateral pterygoid muscle on the working (chewing) side and the posterior temporalis muscle on the opposite (balancing) side; and it was able to accommodate the variability in mandibular positions produced by postural changes in head position.^13-14  For example, if the jaw and cervical muscles are fully relaxed, mandibular bracing occurs in the rear portion of the central bracing platform when the head is tipped back (as in drinking), and it occurs in the front portion of the central bracing platform when the head is tipped forward (alert feeding position). 

THE JOINT PERIPHERY

Surrounding the central bracing platform, support and proprioception continue to occur in the direction of movement of the mandible, like a ball riding up the walls of a larger socket.  When the mandible shifts to one side, the lower dentition rides up on the wall of tooth structure on that side (the working side) like riding up the sides of a bowl, which provides sensory feedback from that side, while the teeth on the other side separate and stop providing sensory feedback.  When the mandible moves forward, the lower front teeth ride up onto the backwardly facing slopes of the upper front teeth (anterior guidance), while all the other teeth separate and stop providing sensory feedback. The same dynamic also occurs in the opposite direction.  When the mandible moves backward, the terminal lower molars ride up onto the forward facing slopes of the terminal upper molars (posterior guidance) while all the other teeth separate and stop providing sensory feedback. 

The bite table which supports that normal healthy mandibular range of motion is established during childhood by a chewing pattern that includes wide lateral opening thrusts to prevent erupting teeth from impinging on the mandibular range of motion before the jaw muscles achieve enough strength and consistency to maintain it.³⁵ Later the direction of chewing movements reverses, as seen in a frontal plane, into a normal adult mastication pattern, opening in the midline and then shifting laterally in preparation for a powerful mesial thrust during the final stages of closing.³⁶

In our recent ancestors, the ability of the central bite platform to provide orthopedic support in whatever direction the mandible moved was apparently even more important than the bilateral centric stops that are now considered the cornerstone of a healthy bite. In many healthy Aboriginal dentitions, strong jaw muscle forces made the upper jawbone grow so much wider than the mandible that the upper and lower teeth are unable to achieve bilateral contact simultaneously, but adequate bracing is achieved on one side at a time in a healthy adaptation shown below.^15.  

ALTERNATELY UNILATERAL MANDIBULAR BRACING

 

 

The same functional bite forces that shape our maxillo-mandibular joints also shape our TMJs.  They don't even acquire their contours until they start receiving biting forces, they continue deepening well into adulthood,^16-17  and they can change shape at any time in response to a change in bite forces.¹⁸  When animals are raised on a liquid diet to reduce mechanical loading; their TMJs fail to enlarge, their TMJ cartilage does not thicken properly,^19-21 and their TMJ mechano-receptors fail to mature normally.²²

With the mandible supported simultaneously at maxillo-mandibular and temporomandibular joints that have all adapted their contours to the same functional forces, these three joints also end up perfectly fitting each other during bracing and throughout the normal range of motion of the mandible. For example, lateral excursions of the mandible are supported in perfect harmony by the outer (buccal) cusps of the lower teeth on the chewing side riding up onto the inward facing slopes of the upper buccal cusps and into the central grooves and marginal ridges just as the lateral borders of the condyle on the chewing side ride up onto the inward facing slopes of the disk and lateral walls of the glenoid fossa. Because the maxillo-mandibular and temporomandibular joints were shaped by functional forces in our ancestors, studies have shown that their TMJ and bite contours were more highly correlated with each other than with age or sex,^23-24 unlike modern craniofacial structures. 

This coordinated support for the mandible in its direction of movement even extends to the basal bones. Incising loads the premaxilla and anterior nasal spine and the articular eminence. Anterolateral excursions load the canine prominence, the lateral border of the nasal cavity, and the infraorbital shelf on the working side. Lateral excursions load the anterior aspect of the zygomatic process and the lateral portion of the infraorbital shelf on the working side. Posterolateral excursions load the posterior aspect of the zygomatic process and the maxillary tuberosity on the working side.

During powerful chewing in our ancestors, the point of compression moved through the supporting structural components of the facial skeleton like rhythmic waves of compression.  Power-crushing forces started at the back end of the dentition on the working (chewing) side and spread forward. At each point of compression, the movement of the mandible carried the outer cusps of the lower teeth upward, forward, and medially (toward the midline).  After reaching the midline, the wave of compressive force crossed to the non-working side in a follow-through stroke.  At each location of the mandible, compression drove the teeth into their sockets, bent the membrane bones, and compressed the circum-maxillary sutures.  Then, as the location of the mandible shifted, those teeth and their supporting bones rebounded.  

THE SPHERICAL BITE TABLE

The dynamics of the maxillo-mandibular joint can be seen in the observations of early researchers, who all reported that the contour of an ideal natural bite surface approximated the surface of a sphere with a 4 inch radius,^25-27  which is about the length of the temporalis muscles, the postural muscles from which the mandible hangs.  Their illustrations are shown below.

MONSON'S SPHERE

BONWILLS' TRIANGLE

CURVE OF WILSON

CURVE OF SPEE

Monson also described a cone made of 4" radii as a model along which the teeth are aligned

MONSON'S CONE

Teeth even erupt at angles that resemble the radii of the same sphere.  

ANGLES OF ERUPTION OF THE TEETH

Of course, natural bite table contours are much more complex than the surface of a sphere. The mandible hangs from three slings of muscles; and, even if it just swung passively from these slings, its movement would trace a pattern that has compound curves.  In fact, extremely worn natural dentitions  form longitudinal twists that resemble a propeller blade.^27-28  These so-called helicoidal curves, illustrated below, comprise a registration in tooth structure of the natural functional range of motion of the mandible after overcoming the resistance of the dental interdigitation.   

THE HELICOIDAL CURVE

Even such a featureless bite table would be difficult to restore accurately with a mechanical articulator, because its surface angle changes continuously. For example, the curve of Wilson is flat at the second molars, it slopes in one direction at the first molars, and it slopes in the opposite direction at the third molars, as illustrated below.  

A CHANGING CURVE OF WILSON

MODERN OCCLUSION

Modern human bites have much more complex surfaces.  A typical modern bite table, seen below, looks more like a mountain range than the smooth curves of a ball in a socket.²⁹ 

THE MODERN OCCLUSAL INTERFACE

 

Jagged bite features themselves are not necessarily problemmatic.  They don't always restrict horizontal jawbone growth, numerous point contacts can still create a stable bracing platform, and most chewing pathways are smoothed by the bolus anyway.  The problemmatic features of modern bites include loss of stability, restrictions to the mandibular range of motion, and displacement of the location of the central bracing platform.

LOSS OF BITE STABILITY

A sudden loss of bite stability occurs whenever people transition from a traditional rural to a modern urban life style.^32-33  EThis has been well documented by traditional bite measurement techniques that only look at the central biting position; however the stability of healthy bites extends far beyond the central bracing area.  It is surrounded by group function in every direction of mandibular movement, making it even difficult to distinguish between the central bracing area and the surrounding group function.  The mandible can still brace in lateral, anterior, and even more posterior positions.  In contrast, even modern bites that appear perfectly stable after having just been restored in textbook prosthodontic fashion confine the stability to a small area, so that minor changes of the closing trajectory can alter the location of the bite contacts.  

Some modern dentitions even develop balancing side interferences, which are never found in healthy natural bites.  Such contacts are fundamentally anti-orthopedic, because the support for the mandible and the associated proprioception occur in the direction opposite the direction of movement of the mandible.  When the afferent sensory feedback comes from sensory nerves on the other side of the joint, it appears to upset the smooth functioning of the neuromuscular reflexes.

RANGE OF MOTION RESTRICTIONS

When the teeth fail to receive enough functional forces to align them in harmony with a healthy functional mandibular range of motion, the mandibular range of motion can be restricted by the teeth. The range of motion restrictions produced by the interfering teeth then get embedded in the neuromuscular system by an adaptive firing pattern (engram) that results in a narrowed mandibular range of motion.  In steeply interdigitated teeth,  chewing movements may be confined to mashing the bolus in the middle of the central bracing area. 

Restrictions to the mandibular range of motion are well tolerated during childhood; when a steep, vertically oriented, and often irregular bite surface can be negotiated by a fast and agile neuromuscular system. Young tissues are full of water, enzymes, and elastic fibers that enable them to withstand diverse articular stresses and unanticipated impacts while hyperactive neuromuscular reflexes can cope with frequent sudden changes in firing patterns and strong versatile jaw muscles can deftly work the mandible across a jagged bite table while performing intricate dances to avoid traumatic collisions between irregular overlapping cusps.

With advancing age, changes in the character of the tissues favor a steadier and less ballistic masticatory pattern. Adaptability diminishes as metabolic activity slows and the body becomes less able to rapidly increase local circulation. In muscles, the availability of ATP dwindles and the number of contractile fibers declines. Neuromuscular reflexes become slower due to a delay in processing rate and conduction velocity.  Task performance diminishes due to a loss of coordination and precision of movement.

In our ancestors, these progressive losses of strength and adaptability with age were accompanied by changes in the form of the bite table that made chewing require less strength and adaptability. The size of the bite table diminished due to wear on the tops and sides of the teeth, while bite stability increased due to wear interproximally (between the teeth). Functional mandibular pathways became smoother and steadier. 

In modern adults, progressive losses of strength and adaptability of the jaw system with age continue, but the bite table no longer matures in a manner that makes it progressively more compatible with these losses.  The maxillo-mandibular joint cannot adapt to variations between maxillary and mandibular growth patterns, because the upper and lower dentitions stay locked together by steeply interdigitating teeth. As a result, normal facial growth patterns can create progressive strains between the upper and lower jawbones that are felt in the teeth connecting them. 

DISPLACEMENT OF THE CENTRAL BITE PLATFORM 

The most clinically significant result of the recent change in bite table contours is displacement of the location of the central bite platform, which produces a parallel displacement of the mandible's resting posture, which in turn affects body posture and the growth pattern of the face.

VERTICAL DISPACEMENT

The central bite platform can be displaced inferiorly or superiorly. 

Superior displacement can occur due to extreme bruxism, loss of teeth, or worn out dentures. Superior mandibular displacement due to inadequate dentures led to the discovery of TMJ disorders in the 1930s. Insufficient vertical dimension is ICD 10 code M26.36.  

Inferior displacement of the mandible is a much more common problem, because our weak jaw muscles no longer limit it adequately. While our ancestors maintained a relatively steady face height during adulthood in proportion to body height, our faces on average now grow longer during adulthood due to inferior mandibular displacement, which is usually followed to a somewhat lesser extent by the midface.  Our mandibles shift downward on average at about the same rate as the teeth used to wear down.^37-38 An excessively vertical facial growth pattern can be produced experimentally by anything that weakens or impairs the mandibular elevator muscles. Excessive vertical dimension is ICD 10 code M26.37.  

HORIZONTAL DISPLACMENT

Horizontal displacement is a more persistent problem than vertical displacement of the central bite platform, because horizontal displacement maintains itself by altering the pattern of subsequent facial growth in a manner that accomodates and thereby perpetuates the displacement. For example, a permanent canine can erupt into a position that alters the location at which all subsequent mandibular bracing occurs rather than having its final erupted position corrected by the forces of mandibular bracing. Subsequently, the rest of the dentition realigns to acquire stability only in the displaced location, and the jaw muscles acquire adaptive firing patterns (engrams) to brace the mandible there, which in turn reflexively alters jaw muscle forces to hold the mandible in a posture just beneath that position.  Posture provides the light steady forces that control bone growth.^39-40  As a result, the displaced mandibular posture maintains a displaced mandibular growth pattern.  The effect of horizontal mandibular displacement on facial morphology is most easily seen in unilateral cross-bite, but it probably occurs in a posterior direction unilaterally or bilaterally in most TMJ disorder patients.

DEPROGRAMMING

To detect horizontal displacement of the mandible requires temporarily interrupting the flow of afferent periodontal signals (engrams) that has been continually programming the jaw muscles to direct all mandibular bracing into the current central bite platform. The afferent flow can be interrupted with simple mechanical devices such as cotton rolls, a Kois deprogrammer, a Lucia jig, or even just by anesthetizing the teeth; but the most reliable method is to wear a front flat bite plate appliance during sleep. A full arch flat bite plate appliance can also be used when further reduction of overbite is not desired, but it is less effective, because the neuromuscular system will reflexively locate the mandible where it gets bilateral posterior contacts.  The time required for deprogramming depends on muscle health.  It often occurs overnight in young people with strong healthy jaw muscles.  It may require weeks or even months of nightly appliance wear along with jaw muscle rehabilitation in some chronic TMJ disorder patients.

SWALLOWING

After the jaw muscles are deprogrammed, the most accurate way to identify the best location for the central bracing area is by observing the mandible during swallowing, because swallowing is accompanied by a relatively consistent and uniform pattern of firing activity in the jaw closing muscles. Studies of children with laterally forced bites show that the jaw closing forces are least unbalanced during swallowing.⁴³  However, there is some natural variation in the closing trajectories used during swallowing, producing a central bite platform that occupies an area rather than a point.^44-45  Therefore an ideal bite registration technique for the central bracing area would be to have a patient swallow multiple times in varied head postures with the jaw muscles fully relaxed.

RESTORING BITE STABILITY

To restabilize bites according to orthopedic principles, the concave upper bite surfaces (central fossae and marginal ridges) are constructed to house the lower buccal cusp tips.  The walls of the housing provide group function buccally and clearance palatally.  The housings at the premolars and first molars contact in upright posture, the housings at the second molars contact when the head is extended, and the anterior teeth contact when the head is flexed such as in the alert feeding position.   After the ideal bite is constructed, maintaining it requires biting forces that are strong enough and well localized enough to keep the teeth in their desired positions. Bracing in varied locations can deprive the TMJs and dentitions of a consistent target position to which they can co-adapt and therefore all acquire the goodness of fit that joints normally achieve in their close packed positions. In patients without a single central bite platform, the mandible often seems to look for one, biting more frequently than normal in a wide range of different locations. 

The contour of the bite table surrounding the central bracing platform should distribute the forces of bruxism in a manner that protects the teeth (group function).  Its accuracy can be improved during a provisional restoration phase in which the new bite surface is fabricated in resin and allowed to wear in slightly before duplicating the same contours in gold or porcelain using transfer techniques.

In some cases, bite contours may be customized in order to protect vulnerable articular structures in the TMJs or the teeth. For example, the mandibular range of motion can be limited in specific directions, by steepening cuspal contours in that direction; or it can be facilitated in other directions, such as toward the midline, by shallowing cuspal contours in that direction.

OCCLUSAL SOLUTIONS 

In the near future, bite tables will be digitally engineered by integrating data from mandibular movements recorded under the influence of various degrees of loading with data from tiny vibration sensors that display the actual order and timing of each bite contact while mandibular movements are tracked with micron level precision technology like existing position sensing detectors (PSDs).  I've already shown that vibration sensors can detect the actual timing of each occlusal contact during each closure.  Storing and combining the bite contact and jaw tracking data from multiple biting acts will enable us to produce highly pixellated topographical maps of entire bite interfaces, alter them with the click of a mouse, and reproduce them prosthodontically by computerized milling or molding that maximizes chewing efficiency by creating well defined central bracing areas supported by large numbers of small perfectly fitting facets and surrounded by slopes constructed to fit each individual's mandibular range of motion. 

FOOTNOTES

1. Bien SM. Hydrodynamic damping of tooth movement. J Dent Res 1966;45:907-914.

1. Kardos TB, Simpson LO. A theoretical consideration of the periodontal membrane as a collagenous thixotropic system and its relationship to tooth eruption. J Periodont Res. 1979;14:444-451.
2. Kato H. The function of the tooth supporting structures. Part 2. The dynamics of molars in function and at rest. J Jpn Prosthodont Soc.1982;26:133-147.
3. Ng GC, Walker TW, Zingg W, Burke PS. Effects of tooth loading on the periodontal vasculature of the mandibular fourth premolar in dogs. Arch Oral Biol. 1981;26:189-195.
4. Bien S. Ayres H. Responses of rat maxillary incisors to loads. J Dent Res. 1965;44(3):517-520.
5. Anneroth G, Ericsson SG. An experimental histological study of monkey teeth without antagonist. Odont Revy. 1967;18:345..
6. Moxham BJ. Berkowitz BKB. The effects of external forces on the periodontal ligament – the response to axial loads. In: Berkowitz BKB, Moxham BJ, Newman NH (eds) The Periodontal Ligament in Health and Disease. Pergamon Press, Oxford, 1982 pp 249-268.
7. Neumann HH, DiSalvo NA. Compression of teeth under the load of chewing. J Dent Res. 1957;36:286-290.
8. Korber KH. Periodontal pulsation. J Periodontol.1970;41:382-390.
9. Picton DA. Some implications of normal tooth mobility during mastication. Arch Oral Biol .1964;9:565-573.
10. Riise C, Ericcson SG. A clinical study of the distribution of occlusal tooth contacts in the intercuspal position in light and hard pressure in adults. J Oral Rehabil.1983;10:473-480.
11. Kasahara K. Miura H. Kuriyama M. Kato H. Hasegawa S. Observations of interproximal contact relations during clenching. Intl J of Prosthod. 2000;13(4):289-294.
12. Bakke M, Moller E, Thorsen NM. Occlusal control of temporalis and masseter activity during mastication. J Dent Res. 1982;81:257.
13. Ahlgren J, Sonesson B, Blitz M. An electromyographic analysis of the temporalis function of normal occlusion. Am J Orthod. 1985;87:230.
14. Beyron H. Occlusal relations and mastication in Australian Aborigines. Acta Odont Scand. 1964;22:597-678.
15. Angel JL. Factors in temporomandibular joint form. Am J Anat. 1948;83:223-246.
16. Moffett BC, Johnson LC, McCabe JB, Askew HC. Articular remodelling in the adult temporomandibular joint. Am J Anat. 1964;115:119-142.
17. Petrovic A, Stutzmann J, Oudet C. Control processes in the postnatal growth of the condylar cartilage of the mandible. In: Determinants of Mandibular Form and Growth. McNamara JA Jr. (ed), Monograph 4. Craniofacial Growth Series, Center for Human Growth and Development, University of Michigan, Ann Arbor, pp 101-153, 1975.
18. Kato T, Takahashi S, Domon T. Effects of a liquid diet on the temporomandibular joint of growing rats. Med Princ Pract. 2015;24:257-262. Copray JCVM, Jansen HWB, Duterloo HS. Effects of compressive forces on proliferation and matrix synthesis in mandibular condylar cartilage of the rat in vitro. Arch Oral Biol. 1985;30:299-304.
19. Bouvier M, Hylander WL. The effect of dietary consistency on gross and histologic morphology in the craniofacial region on young rats. Am J Anat. 1984;170:117-126.
20. Bouvier M, Zimmy MI. Effects of mechanical loads on surface morphology of the condylar cartilage of the mandible in rats. Acta Anat. 1987;129:292-300.
21. Ishida T, Yabushita T, Soma K. Effects of a liquid diet on temporomandibular joint mechano-receptors. J Dent Res. 2009;88(2):187-191.
22. Wedel A. Carlsson G. and Sagne S.;Temporomandibular joint morphology in a medieval skull material. Swed Dent J. 2:171-187, 1978.
23. Hodges D. Temporomandibular joint osteoarthritis in a British skeletal population. Am J Phys Anthrop. 1991;85:367-377.
24. Monson GS. Applied mechanics to the theory of mandibular movements. Dental Cosmos 1932;74:1039-1053.
25. Bonwill WGA. Geometrical and mechanical laws of articulators: anatomical articulation. Trans Odontol Soc Pa, 1885;119-133.
26. Spee FG. Prosthetic Dentistry, ed 4, Chicago 1928, Medico-Dental Publishing, pp 49-54.
27. Tobias PV. The natural history of the helicoidal occlusal plane and its evolution in early Homo. Am J Phys Anthropol. 1980;53:173-187.
28. Hall RL. Functional relationships between dental attrition and the helicoidal plane. Am J Phys Anthropol 1976;45:69-75.
29. Osborn JW. Helicoidal plane of dental occlusion. Am J Phys Anthropol 1982;57:273-281.
30. Graf H. Analysis of human jaw movement patterns by graphic computer display. in Kawamura Y and Dubner R (eds) Oral-Facial Sensory and Motor Functions. Quintessence Books. 1981, p 323.
31. Corruccini, R. Anthropological Aspects of Orofacial and Occlusal Variations and Anomalies. in Advances in Dental Anthropology New York: Wiley-Liss, Inc., 1991 pp 295-323.
32. Corruccini RS, Townsend GC, Richards LC, Brown T. Genetic and environmental determinants of dental occlusal variation in twins of different nationalities. Human biology 1990;62(3):353-67.
33. Bakke M, Holm B, Jensen BL, Michler L, et al. Unilateral isometric bite force in 8-68 year old women and men related to occlusal factors. Eur J Oral Sci. 1990;98(2):149-158.
34. Gibbs CH, Wickwire NA, Jacobson AP, Lundeen HC, Mahan PE, Lupkiewicz SM. Comparison of typical chewing patterns in normal children and adults. J Am Dent Assoc. 1982;105(1):33-42.
35. Bakke M. Mandibular elevator muscles: physiology, action, and effect of dental occlusion. Eur J Oral Sci. 1993;101:314-331.
36. Ainamo J, Talari A. Eruptive movements of teeth in human adults. The eruption and occlusion of teeth. Butterworths, London. 1976:97-107.
37. Poole DFG. Evolution of mastication. In: Anderson DJ, Matthews B, eds. Mastication, Bristol, England, 1976, John Wright and Sons.
38. Brace CL. Occlusion to the anthropological eye. In The Biology of Occlusal Development, Monograph 7, Craniofacial Growth Series. University of Michigan, Ann Arbor 1977.
39. Petrovic AG, Stutzmann JJ, Gasson N. The final length of the mandible: Is it genetically predetermined? In Craniofacial Biology, D S Carlson ed. Monograph 10, Craniofacial Growth Series. University of Michigan, Ann Arbor. D S Carlson ed. 1981.
40. McNamara JA. Functional determinants of craniofacial size and shape. In Craniofacial Biology. D S Carlson ed. Monograph 10, Craniofacial Growth Series. University of Michigan, Ann Arbor 1981.
41. Miralles RL, Manns AE, Pasini C. Influence of different centric functions on electromyographic activity of elevator muscles. J Craniomandib Pract. 1988;6(1):26-33.
42. Manns A, Rocabado M, Cadenasso P, Miralles R, Cumsille MA. The immediate effect of the variation of anteroposterior laterotrusive contacts on the elevator EMG activity. J Craniomandib Pract.1993;11(3):184-191.
43. Ingervall B, Thilander B. Activity of temporal and masseter muscles in children with a lateral forced bite. Angle Orthod. 1975;45:249-258.
44. Celar A, Siejka E, Schatz J, Furhauser R, Piehslinger E. Mandibular reference position: chin-point guided closure vs, final deglutition. J Craniomand Pract. 1996;14(1):42-45.