Bite force relation to face shape and ethnic origins face variations


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Here are some evidences of bite force potential in relation to jaw shape. There are also information about different types of ethnic origins and face shapes.
It was mostly gathered on the Internet medical resources. I didn't thought to publish it so I didn't bother mentioning the sources.

 

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found in all Asia except the west and south (India), in the northern and eastern Pacific, and in the Americas. The skin is brown to light, hair coarse, straight to wavy, and sparse on the face and body. The face is broad and tends to flatness. The eyelid is covered by an internal skinfold in the central populations but such folds are less marked or absent elsewhere. The teeth often have crowns more complex than in other people, and the inner surfaces of the upper incisors frequently have a shovel appearance.
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Jutting lower face (lower jaw, lower lip)
The Mongoloid lower face, lower jaw, and lower lip, like those of the Negroid, jut out farther than those of the Caucasian. Also like the Negroid, the lower jaw is often wider and more muscular than that of the Caucasian
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The heaviest jaws and greatest bigonial diameters are found in the northwestern European borderlands, and in eastern Europe, where mongoloid influence is strong.
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The Mongolian race includes most Asiatics, the Finnish tribes, the Lapps and the Eskimo; it has an almost square skull (exceedingly brachycephalic), flat nose, flat projecting malar bone, somewhat broad alveolar arch, and projecting chin. The American race has a higher forehead, highly developed superciliary arch, deeply sunken bridge of the nose, cheek-bones strongly projecting sidewards, and high, broad, and strong lower jaw.



Mongoloid Crania – Bass 1995:91-92
• Projecting zygomatics – “flat” face – pencil across nasal aperture – try to insert finger between pencil and zygomatics
• Edge-to-edge bite – upper & lower incisors will meet
• Shovel shaped incisors
• Inferior zygomatic projection – zygomatics dip below lower edge of maxillae
• Nasal “overgrowth” – nasals project forward beyond their junction with the frontal portion of the maxillae
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It was remarked in a
former chapter that as man gradually became erect, and continually
used his hands and arms for fighting with sticks and stones, as well
as for the other purposes of life, he would have used his jaws and
teeth less and less. The jaws, together with their muscles, would then
have been reduced through disuse, as would the teeth through the not
well understood principles of correlation and economy of growth; for
we everywhere see that parts, which are no longer of service, are
reduced in size.

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From the correlation which exists, at least in some cases,*(4) between the development of the extremities and of the jaws, it is possible that in those classes which do not labour much with their hands and feet, the jaws would be reduced in size from this cause. That they are generally smaller in refined and civilized men than in hard-working men or savages, is certain. But with savages, as Mr. Herbert Spencer*(5) has remarked, the greater use of the jaws in chewing coarse, uncooked food, would act in a direct manner on the masticatory muscles, and on the bones to which they are attached. In infants, long before birth, the skin on the soles of the feet is thicker than on any other part of the body;*(6) and it can hardly be doubted that this is due to the inherited effects of pressure during a long series of generations.
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head large and brachycephalic; face broad; cheek-bones prominent; mouth large and broad; jaw mesognathic; teeth strong and snow-white; chin broad; nose broad and flat; forehead low and little arched; ears large; eyes considerably wide apart, deep-sunken, and dark-brown to piercing black
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It's really quite pointed, and this is usually considered a Caucasoid trait. This is one of the traits that forensic anthropologists look for. It's also fairly small, the jaw is fairly small compared to the Native American, where it comes way down, very strong and square. This square jaw is one of the traits that is used to identify Native Americans.
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SHovel tooth:
In the final analysis, it was found that shovelling had relatively high positive or negative associations with the latitude, average temperature in the coldest month, lifeway that included milking, etc. By taking account of these and the results by previous authors, it was suggested that the development of shovelling was primarily associated with a facial structure resisting powerful biting forces, which was in turn a result from adopting a hunting lifeway with a heavy reliance on meat-eating.



The group with the highest incidence consisted of such Mongoloids as American Indians, Eskimos, Mon golians, part of the Japanese and part of the Chinese;

Suzuki and Sakai (1966) furthermore reported that the mesiodistal crown diameters of the well developed shovel-shaped incisors were significantly larger than those of the non-shovel shaped ones.

The function of shovelling is presumably to strengthen the structure of the anterior teeth mechanically.


Dahlberg (1951) reported on morphological features of the teeth of American Indians: the tooth size was large; shovelling was highly developed; the frequencies of three-cusped maxillary second and third molars were high

These two reports are very interesting. Notwithstanding the fact that both American Indians and Aleuts have highly-developed shovelling

In the two preceding chapters shovelling was considered to be a structure for strengthening the incisor

In general, the characteristics of Mongoloid skulls, especially the facial flatness, have been considered to be those which were produced through adaptation to severely cold environments (Coon et al., 1950; Yamaguchi, 1970, 1977; Hylander, 1977). Particularly, the crania of Eskimos have such peculiarities as large spacious orbits, a narrow nasal aperture, reduced nasal bones, increased facial flatness, an enlarged zygomaxillary region, high temporal lines, a shallow glenoid and canine fossa, a robust mandible with a wide, low, oblique ascending ramus, a high incidence of palatal and mandibular tori, increased thickness of the tympanic plate, sagittal keeling, a weakly developed brow, pronounced gonial eversion and a high incidence of third molar agenesis (Hylander, 1977). To explain these characteristics, two major hypotheses have been proposed at present (Hylander, 1977). One is the "cold adaptation hypothesis" by Coon et al. (1950) that postulates that such peculiarities are a result of an adaptation to minimize heat loss in the cold environment of the Arctic. The other is the hypothesis proposed long before by that it is a structure for resisting powerful biting forces (Hylander, 1977). Hylander (1977) assumed a negative attitude to the former because of the scarcity of evidence favoring it. Instead, he took up a position sustaining 's hypothesis and claimed that the peculiar structure of Eskimo skulls was especially adapted to gen erate and dissipate large vertical biting forces. Further, Hylander (1977) asserted that the low prognathism typical of Eskimos could be viewed as an adaptation to reduce the bending moments acting on the facial skeleton in order to dissipate more effectively the excessively large biting forces in the anterior region of the Eskimo skull. Hylander's statement seems useful also for explaining the relation between the structure and func tion of shovelling. In the facial skeleton of the modern Japanese skull, in which shovel ling is not as highly developed as that of Eskimos and the flatness of the zygomaxillary region is extraordinarily weak among Mongoloid populations (Yamaguchi, 1973), it has been demonstrated through biomechanical experiments that the region in which the strain caused by biting forces is greatest is the lower frontal part of the upper jaw (Endo, 1965, 1969). Endo considered that such a facial skeleton was possibly adapted to occlude chiefly using the cheek teeth.

Taking the above and the conclusions of the two preceding chapters (2. and 3.) together, shovelling should be considered basically as part of the facial structure asso ciated with powerful biting forces.

However, why is the habitat of people with such a facial structure restricted to the severely cold regions at present? If there is any reason why the biomechanically strong structure cannot occur in other than severely cold regions, this facial structure itself should be regarded as part of adaptation to the cold.

First, shovelling is primarily part of the facial structure resisting powerful biting forces, and, second, one of the causes by which such a structure is generated seems to be hunting activity directly or indirectly associated with heavy meat-eating.

Taking these results and previous studies on the facial structure of the Eskimo skull and the food habits of hunter-gatherers into account as a whole, it was inferred that shovelling was primarily part of the facial structure resisting powerful biting forces, and one of the causes of the need for such a powerful biting mechanism was possibly hunting activity directly or indirectly associated with heavy meat-eating.
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Many studies have looked into the range of normal chewing and maximal bite forces in man. Mean values have ranged from 216 to 740 N with lower values of 108 to 293 N in the incisor region. The recording instruments and the method of use, whether unilateral, bilateral and the number of tooth contacts have varied considerably, hence the diversity of the results. The greatest unilateral force recorded is 1550 N for Eskimos and with a bilateral sensor 4346 N.


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Muscle tenderness was associated with a `long face' type of craniofacial morphology and a lower bite force. Headache was associated with a larger maxillary length and increased maxillary prognathism. A high score on Helkimo's Clinical Dysfunction Index was associated with smaller values of a number of vertical, horizontal, and transversal linear craniofacial dimensions and a lower bite force.

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Although the reasons for growth differences are not well understood, these differences affect the entire craniofacial complex. The muscles of mastication act in different directions in horizontal and vertical growers, and produce different muscular pressures and tensions in the two types of growth. This results in different apposition and resorption of surface bone, and, therefore, different mandibular morphology in horizontal and vertical growers.


Strong – and weak – muscle factors
Why are these differences in mandibular morphology important? In horizontal growers, the angles at which the muscles work produce much masticatory force. In vertical growers, the angles at which the muscles work produce much less force.12 Therefore, horizontal growers can be referred to as strong-muscled patients, and vertical growers can be referred to as weak-muscled, patients. In Figure 5, the morphological differences are highlighted between the two growth patterns as viewed on lateral cephalometric x-rays. The morphological differences are numerous, but five are especially diagnostic.

First, strong-muscled patients have relatively acute gonial angles; in weak-muscled patients, the gonial angle tends to be obtuse.13, 14 Second, the shape of the lower border of the mandible differs in the two types of patients. In strong-muscled patients, a double curvature on the lower border consists of a concavity near the gonial angle and a convexity near the anterior portion of the lower border. Weak-muscled patients lack this double curvature and instead exhibit a concave lower border. Third, strong-muscled patients have a radiopaque symphysis; in weak-muscled patients, this area is more radiolucent.2 Fourth, the more acute the symphyseal inclination, the more the patient tends to be strong-muscled. This can be quantified by a simple cephalometric measurement of the angle between Go-Gn and the chin line (the line from pognion (Po) to infradentale (Id) – the most anterosuperior point on the mandibular alveolar ridge) (Fig. 6). 11 A range of 70° ± 4° is normal: 65° or less indicates that the patient is strong-muscled; 75° or more indicates that the patient is weak-muscled


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Maximal voluntary contraction was positively
correlated to molar
contact and negatively to anterior face height,
mandibular inclination,
vertical jaw relation and gonial angle. Relative
loading of the muscles was
markedly increased during resting posture. It was
concluded that reduced
occlusal stability and long-face morphology were
associated with weak
elevator muscle activity with disposition overload and
tenderness. The
results also indicated that increase of occlusal
stability might lead to
increased muscle strength and possibly reduce risk of
physical strain.

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Determination of the force: Assessing a patient’s occlusal force capability pre-operatively is currently difficult due to the lack of suitable equipment. Studies such as Carlsson and Haraldson (1985) have shown that biting forces increased by 85% from the pre-prosthetic levels, during the first 2 months of prosthesis function. Thus initial bite force assessment may not predict the eventual level that may develop.

Wolff’s Law (1949) states that, “Every change in the use or static relations of a bone leads not only to a change in its internal structure and architecture but also to a change in its external form and function.” Given that the masseter and the medial pterygoid muscles are the principle muscles of mastication enclosing the angle of the jaw, it is postulated by the authors that the bony morphology underlying the gonial angle may provide a reliable expression of the inherent muscular biting power of any individual. A larger muscular force would theoretically produce a more acute angle and a weaker force a more obtuse one.



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Abstract. The existence of an interaction among bite force magnitude, jaw muscle size (e.g., cross-sectional area, thickness), and craniofacial morphology is widely accepted. Bite force magnitude depends on the size of the jaw muscles and the lever arm lengths of bite force and muscle forces, which in turn are dictated by craniofacial morphology. In this study, the relative contributions of craniofacial morphology and jaw muscle thickness to the bite force magnitude were studied. In 121 adult individuals, both magnitude and direction of the maximal voluntary bite force were registered. Craniofacial dimensions were measured by anthropometrics and from lateral radiographs. The thicknesses of the masseter, temporal, and digastric muscles were registered by ultrasonography. After a factor analysis was applied to the anthropometric and cephalo-metric dimensions, the correlation between bite force magnitude, on the one hand, and the "craniofacial factors" and jaw muscle thicknesses, on the other, was assessed by stepwise multiple regression. Fifty-eight percent of the bite force variance could be explained. From the jaw muscles, only the thickness of the masseter muscle correlated significantly with bite force magnitude. Bite force magni-tude also correlated significantly positively with vertical and transverse facial dimensions and the inclination of the midface, and significantly negatively with mandibular inclination and occlusal plane inclination. The contribution of the masseter muscle to the variation in bite force magnitude was higher than that of the craniofacial factors.



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The correlation between maximum bite force and facial morphology was studied in 54 boys, 8 to 16 years old, and 66 girls, 7 to 17 years old. Bite force was measured at the first molars with a miniature bite force recorder. Facial morphology was evaluated on profile cephalograms. In addition, the number of teeth in contact in the intercuspal position was recorded with occlusal foils. In the girls, maximum bite force was correlated to the inclination of the mandible, the size of the gonial angle, and the ratio between posterior and anterior face heights. The correlations implied a large bite force with a small mandibular inclination and gonial angle, a large posterior face height in relation to the anterior face height, and a small bite force with the opposite facial characteristics. These correlations were nonexistent or weaker in boys. In both sexes, bite force was correlated to the number of occlusal contacts. Elimination of the influence of age and occlusal contact in the group of girls by the use of partial correlations reduced the correlation between bite force and facial morphology. A significant correlation to the size of the gonial angle remained, however, and the correlation to mandibular inclination was close to significance. In addition to the correlations found to facial morphology, the study clearly demonstrated the need to take gender and occlusal contacts into consideration in future studies of masticatory muscle function and strength in relation to facial morphology.



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ISOMETRIC BITE FORCE AND ITS RELATION TO CRANIOFACIAL MORPHOLOGY
Taek-Woe Lee, Ki-Soo Lee
This study was undertaken to grope the correlation of the maximal bite force and tooth craniofacial structure. The maximal bite force of 76 adult male, aged 18-28 (mean aged: 23.4 ±2.2) years, was estimated and cephalometric headplates were measured, tabulated and statistically analyzed.

The results were as follows.

1. 59.61kg of bite force in first molar, 45.38kg in premolar and 17.10kg in central incisor were arranged.

2. The bite force was negatively correlated to genial angle, mandibular plane angle, the angle between occlusal plane and mandibular plane, the angle between palatal plane and mandibular plane, and positively correlated to posterior height of face, length of mandibular body,length of ramus, facial depth in craniofacial structure.

3. The group with strong bite force showed small genial angle, mandibular plane angle, the angle between occlusal plane and mandibular plane, the angle between palatal plane and mandibular plane, and long posterior height of face, length of mandibular body, length of ramus,facial depth. So they manifested the tendency to brachycephalic pattern, on the other hand, the group with weak bite force manifested the tendency to dolichocephalic pattern.

4. There is no correlationships between bite force and mesial inclination of premolar axis in this subject.

5. It is considered bite force have an effect upon craniofacial pattern, especially upon the lower face .



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The objectives of this study were to record the molar bite force values with the Digital bite force meter produced by Dr. Somkiat Dujnungkunakorn in 1997. To compare the difference in bite force values among subjects that have vary craniofacial skeletal structures and analyze the relationship between the masticatory bite force and craniofacial structures. The study was carried out in 90 Thai subjects ; craniofacial skeletal type I ( ANB 0 – 4 degrees) = 30 subjects, craniofacial skeletal type II ( ANB >4 degrees ) = 30 subjects and craniofacial skeletal type III ( ANB < degrees ) = 30 subjects ; age range 17 – 44 years, 32 males, 58 females. Bite force values between male and female were significantly different at 0.05 level. The mean value for the maximum bite force in males was 533 N and 393 N in females . The mean value for the bite force in total subjects was 445 N, 428 N in subjects that have craniofacial skeletal type I, 434 N in type II and 473 N in type III subjects. When considering the bite force in relation to skeletal type, there was no statistical significant difference between bite force and craniofacial skeletal type I,II and III at 0.05 level. There was a highly significant but weak positive correlation between bite force and bizygomatic breadth , lower anterior facial height, lever arm length, Mandibular length, Upper anterior facial height, and upper posterior dental height. ( p < 0.01) . There was a positive correlation between bite force and load arm length, lower molar arch width, Midface length, and Upper molar arch width ( p < 0.05 ) . The bite force was inversly correlated to the mandibular angle and Mandibular plane to palatal plane. ( p < 0.05 ). 4136323 DTOD/M : ÊÒ¢ÒÇÔªÒ

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Diagnosis and treatment planning/surveying/fixed considerations




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Author(s): DiPietro GJ, Moergeli JR.
Title: Significance of the Frankfurt-mandibular plane angle to Prosthodontics
Reference: J Prosthet Dent 1975; 36: 624-635.
Introduction:
This article discussed the way to determine the Frankfurt-mandibular plane angle (FMA), it looked at the associations between radiographic measurements and observations made clinically, and it identified where all this ties in with Prosthodontics.

Synopsis:
BackgroundThere are three craniofacial types of cephs, which include: the AP facial, the vertical facial, and a combination of the two. This article focuses on the vertical facial types.

Frankfurt- mandibular plane angle
The FMA is formed by the intersection of the Frankfurt horizontal plane (which is a line that is made between the porion and the orbitale) and the mandibular plane (which is a line that extends through the menton and gonion angle). A normal range of this angle adopted by orthodontists is 25+-5 degrees. A “high-angle” (open bite skeletal pattern) is where the angle is 30 degrees or more and a “low-angle” (closed-bite skeletal pattern) is when the angle is 20 degrees or less.

Clinical Factors related to FMA—Biting Force

Biting forceHigh FMA typically show a decreased biting force whereas a low FMA has an increased biting force. Low angle patients have infra-erupted teeth and usually are characterized by having small teeth. They are also predisposed to a decrease in VDO. These patients are also more likely to return to the former occlusion if the VDO has been opened during treatment. The low angle patients require a more rigid prosthesis usually because of this. This is not evident in high angle patients. The increased biting force in these low angle patients cause more stress to the residual ridge also. High FMA patients display the opposite characteristics.

Alveolar Bone Growth
A high FMA usually shows an increase in the alveolar bone growth and a low FMA has a decrease in the bone growth. Low angle patients typically have flat, broad palatal vaults, shallow buccal vestibules, and high muscle attachments. High FMA patients are the opposite. Stability and retention may be a problem for the low FMA person. Planes of the FaceA convex profile is usually seen with a high FMA and a low FMA results in a concave profile. The low angle patients have exceedingly little mesial drifting of the natural teeth. Mesial drifting is more likely to occur in the high FMA.

Tongue Conditions

High FMA patients tend to exhibit an extension of the tongue, which may affect the wearing of different kinds of prosthetic appliances. A retracted tongue position related to the low FMA also needs to be addressed.

Position of the Glenoid Fossa
The glenoid fossa in high FMA patients usually is positioned in a more superior and posterior position. The low FMA patient’s glenoid fossa is usually situated more anterior and inferior. Conclusions:
The FMA is important and has an important application to the field of Prosthodontics in diagnosis and treatment planning. More research also needs to be accomplished to determine the role of the FMA in other areas of Prosthodontics also.

other areas of Prosthodontics also.

Comments:
Older article.Relates the information of the topic to Prosthodontics nicely. The authors have good explanations and definitions. It is presented in a straightforward manner and is easy to understand.

One-Liner:
An article discussing the frankfurt-mandibular plane angle (FMA) determined from cephalometric radiographs and how these diagnostic tools can be used in Prosthodontics. Patients with low FMA angles depict an increased biting force, infra-erupted teeth, small teeth, and are predisposed to a decrease in VDO.

Keywords: Removable partial dentures, cephalometrics, Frankfurt-mandibular plane angle

Summary written by: Pedar Didriksen, 3/2/00


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"Steeply inclined mandibular plane, a small posterior face height and an increased gonial angle were strongly related to short, thin masseter muscles of low volume." "Long thick muscles of high volume were related to the converse features".

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Maxillofacial morphology and masseter muscle thickness in adults

M Kubota*, H Nakano, I Sanjo, K Satoh, T Sanjo, T Kamegai and F Ishikawa

Department of Orthodontics, School of Dentistry, Iwate Medical University, 1-3-27 Chuo-dori, Morioka, Iwate 020, Japan, *Corresponding author


The aim of this study was to investigate how the thickness of the masseter muscle relates to the maxillofacial morphology, including the thickness of alveolar process in the mandibular incisor region, and the thickness of the mandibular symphysis.

The subjects consisted of 80 adult male volunteers (mean age: 23 years 8 months).

The relationship between masseter muscle thickness and the maxillofacial skeleton was investigated by measuring the former by ultrasonography and the latter by roentgenographic cephalometry. The data were initially analysed using a multiple regression analysis. Thereafter, correlation coefficients were obtained by a simple regression analysis. The following results were found:

1. The thickness of the masseter muscle (mean ± SD) was 15.8 ± 3.0 mm in the relaxed state and 16.7 ± 2.7 mm at maximal clenching.

2. Masseter muscle thickness was negatively correlated with the mandibular plane angle.

3. Masseter muscle thickness was positively correlated with the mandibular ramus height (Cd-Go), and the thickness of the alveolar process and that of the mandibular symphysis.

It is therefore suggested that masticatory function influences the morphology of the mandible.

Pages 535-542

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This individual was 5 feet 4 inches tall, with a brain size of about 850 cc's, and the near complete skeletal remains clearly showed that he walked fully erect. His total features, including brain size and height, fall completely within the range of modern human beings of that age. This specimen had a large brow ridge and a sloping forehead. In this connection Arthur Custance published a paper which certainly showed beyond reasonable doubt that "a diet of fruit, tough seeds, fibrous material, etc. in the formative years, especially if there was a lack of bone hardening content, would result in constant heavy chewing which would cause depressing of the forehead, render the brow ridges more prominent and force outward the zygomatic arch, thus accentuating the cheek bones.23


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In fact, our typical patient is between 30 and 60 years old. In the upper dental arch nature has provided a suture line front to back between the two bones that form the palate. This allows for an easy widening process and as the palate expands, the cheekbones as well, creating more prominence.

Q: What type of facial changes are possible?
A: One can experience any or all of the following: The stimulation of a stronger jawline. Intensified cheekbone prominence.

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They had advanced cheekbone arches, which meant they had stronger jaw muscles and consequentially could bite harder.


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Since they do not chew on hard foods, the cheek and jaw to which the chewing muscles attach will recede. If the cheekbone recedes, it will not stick out, so people's faces will get much narrower. In addition, the lower jaw will become thin. The area from the eyes to the cheeks, and up to the mouth will become more narrow, and recede back into the face.


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The lower jaw is held in place with the help of a bone on each side of the face called the Zygomatic arch. The Zygomatic arch is shown in yellow color on the drawing. This arched bone allows muscle formation to adhere to it and it is this muscle that joins the jaws and head together and gives them strength. While this bone serves a very important function and should be strong, in the Tervuren the Zygomatic should not be pronounced, or bowed out from the head.

If the zigomatics are not held close in to the head, this is an indication that the head itself is likely wider than the standard calls for. Additionally, the greater the size and protrusion of a bone, the more muscle mass can be attached to it. Therefore, pronounced zigomatics would give both the head and jaws too much power. The Tervuren should not have a broad head or great power in its jaws like the Bull-type breeds or the Rottweiler, for example. Or, even so much as the German Shepherd Dog. The Tervuren working style is that of a very agile dog that is quick and has fast reactions. So while the jaws themselves are to be strongly built and it's bite is certainly effective, it's working style should not be that of a dog with massive gripping power.

By having a Zygomatic that lies close to the head, both the head width is kept in check, and there will be a corresponding reduction of muscle mass, which also helps keep the cheeks flat.



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Zygomatic arch: very pronounced. The development of the zygomatic arch determines the width of the face. Underdeveloped arches will result in narrow faces, which is not characteristic of this breed. It also supports the strongly developed temporal muscles, which close the jaw and the masseter muscles, which move the jaw from side to side. These muscles must be developed to aid the dog in holding, but are never prominent.
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Muscle variables significantly correlated with widths of the bizygomatic arch and temporal fossa but not with the cranium width. Masseter volume significantly correlated with cross-sectional areas of the zygomatic arch and mandibular ramus. Masseter orientation was almost perpendicular to the zygomatic arch and mandibular antegonial region. The zygomatic arch angle significantly correlated with the antegonial angle. The results of the study suggest that the masticatory muscles exert influence on the adjacent local skeletal sites.


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The Temporal Process of the zygomatic runs lateral and posterior toward an articulation with the zygomatic process of the temporal bone. Together these two processes assist in forming the zygomatic arch which serves as the attachment for the masseter muscle in life, one of the primary muscles used in mastication. The temporal muscle runs beneath the arch and is also a primary mover of the mandible in chewing. The Maxillary Process of the zygomatic articulates with the zygomatic portion of the maxilla by way of the Zygo-Maxillary Suture.

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The zygomatic arch is enlarged to provide a larger surface area of attachment for the masseter and zygomaticomandibular muscles. The zygomatic arch also is expanded laterally to increase the temporal fossa. This lateral expansion limits the horizontal movement of the jaw. Having larger muscles allows the giant panda to crush the tough bamboo stalks.

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The great site of the temporal in robust and a second chewing muscle, the masseter, causes the cheekbones (the zygomatic arch) to be exaggerated and flared forward.

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The earliest biological manifestations of technological progress. Our (Homo sapiens) modern masticatory system copies all these distinctively hominid traits, but it is very much reduced. This reduction is developmentally and functionally integrated (cfr Calcagno and Gibson, 1988). First of all our teeth have smaller working surfaces and shorter roots. Consequently the alveolar module of the jaws is constricted. The masticatory musculature is also reduced. This in turn is reflected in the "gracilisation" of the maxillar and mandibular bones, in the restriction of the muscular attachments on the braincase and zygomatic arch, and in the evident reduction of the bony structures which have to provide a proper rigidity and resistance of the braincase (Russell, 1985). The shape of the modern human skull is evidently modified by the influence of food technology.

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Cheekbones (Zygomatic arches): determine facial width. More prominent in Mongoloids. Width between eyes greater in mongoloids.

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The width of the zygomatic arches suggest that it has very powerful jaw muscles for dealing with its large prey.
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Relating these observations to bone structure, Marsh et al (1989) found a correlation between a deficiency in masseter, temporalis, medial and lateral pterygoid muscles and a reduction in height of the coronoid and condylar processes, medial and lateral pterygoid plates, and length of the zygomatic arch, all origins and insertions for theses muscles.

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Masseters attach from the dentary (specifically, the masseteric fossa) to the zygomatic arch and onto the maxilla in front of the arch, providing crushing force.
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Larger zygomatic arches due to masseter muscle growth for more chewing power.

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The increasing muscle development which rose up under the zygomatic arch naturally forced the latter outwards and required a stronger form.

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Maximum voluntary bite forces were primarily correlated with variables relating to jaw size[mdash ]both before and after surgery.
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It is concluded that: (1) independent of chronological age, children with larger faces have larger moment arms and require less muscle activity to attain any given force.

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Bite force magnitude also correlated significantly positively with vertical and transverse facial dimensions and the inclination of the midface, and significantly negatively with mandibular inclination and occlusal plane inclination.

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Bite force changes bone structure. The harder we have to bite, the larger our jaws have to be; but because we no longer have to bite or chew large pieces of meat our bones have shrunk."

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In the girls, maximum bite force was correlated with the inclination of the mandible, the size of the gonial angle, and the ratio between posterior and anterior face heights. The correlations implied a large bite force with a small mandibular inclination and gonial angle, a large posterior face height in relation to the anterior face height, and a small bite force with the opposite facial characteristics.

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3. The group with strong bite force showed small gonial angle, mandibular plane angle, the angle between occlusal plane and mandibular plane, the angle between palatal plane and mandibular plane, and long posterior height of face, length of mandibular body, length of ramus,facial depth. So they manifested the tendency to brachycephalic pattern, on the other hand, the group with weak bite force manifested the tendency to dolichocephalic pattern.


5. It is considered bite force have an effect upon craniofacial pattern, especially upon the lower face .



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It is basic that we recognize the reciprocal nature of the reaction between vertical and horizontal growth. Effective condylar growth (horizontal growth) moves the chin forward, not downward.

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Fma = angle: plus il est petit, plus la mach est horizontal

Clinical Characteristics High FMA Low FMA
Bite Force Decreased Increased
Muscular line of force Arcuate Vertical
Molar position Anterior to line
of force Direct in line
of force
Size of masticatory muscles Hypotrophic Hypertrophic
Mandibular bony processes Underdeveloped Well developed
Height of alveolar bone Increased Decreased
Palatal vault High and narrow Broad and flat
Buccal vestibules Deep Shallow
Muscle attachments Base of ridge Crest of ridge
Residual ridge relation Divergent Parallel
Lip length Short Long
*Excerpted from DiPietro and Moergeli.5




High Frankfort Mandibular Angle
A high FMA skeletal relationship develops when the anterior components of vertical growth are proportionally greater than condylar growth. This results in a steeper diagonal growth pattern with anterior face height significantly greater than posterior face height. The mandible tends to be retrognathic with the maxilla in a near normal position anteroposteriorly. The maxillae are narrow with well-formed arches, deep vestibules, and a high palatal vault with limited bony palatal bearing area


Furthermore, these patients generally present with more hypotonic muscles of mastication resulting in decreased bite force.11

The retrognathic mandible is generally small and tapering.

Low Fma:
Patients with a low FMA are brachycephalic (short head) and present with a skeletal deep bite and a less convex facial profile.

The mandible is well formed and less likely to exhibit the keyhole effect.
Because patients with low FMA's often have well-formed mandibles
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brachyfacial (brachyprosopic) A facial pattern characterized by a broad, square face; preferred term is euryprosopic.


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The brachycephalic headform establishes a face that is more broad, but somewhat less protrusive.
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Mongoloids have a euryprosopic or wide face and a brachycephalic head.

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Mongoloids- Wide cheek bones, short stature, epicanthic fold of the eyes (common), straight black hair, mostly situated around the regions of eastern Asia. In this review, the Pacific Islanders (Filipinos and so forth) are not tended to be included in as a part of the Mongoloid category.

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Mongoloid: Projecting zygomatics (wide, pronounced cheek bones), edge-to edge bite, shovel shaped incisors

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This distinction is more challenging because anthropologists have traditionally grouped Native Americans and Asians into "Mongoloids" because of shared features such as a "flat, moonlike face, nasal overgrowth, and zygomatic (cheekbone) projection" (Bass, 1995). This research focuses on the morphometric distinction between Native American and Asian populations. The


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Dolichocephalics tend to a retrusively placed mandible and lower lip with a retrognathic (convex) facial profile. Posture of the head is more slumped. The maxillary arch and palate is longer, narrower and deeper
In brachycephalics, the lower jaw tends to be variably more protrusive, with a greater tendency for a straighter or even concave facial profile and a more prominent appearing chin. The mandible is more prominent in appearance. Posture of the head is more erect. The maxillary arch and palate is shorter and more shallow.



Overall, in dolichocephalics, there is a tendency towards mandibular retrusion and placement of molars in a Class II position.
Brachycephalics have a rounder, wider brain. This results in a more posterior placement of the maxilla. The horizontal length of the nasomaxillary complex is relatively short (but wider).
Overall, in brachycephalics, there is a tendency toward a prognathic profile and a Class III molar relationship.


For example, a retrusive mandible can be compensated for by an increase in the horizontal dimension of the mandibular ramus

The more open ("flat") cranial base flexure that usually characterizes the dolichocephalic headform in many Caucasian groups sets up a more protrusive upper face and a more retrusive lower face. A Class II tendency is built in.
The more closed, upright basicranial flexure that usually characterizes the brachycephalic head sets up a correspondingly wider, flatter, more upright type of face. The face appears flatter, broader, and squared.
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The increasing muscle development which rose up under the zygomatic arch naturally forced the latter outwards and it developed a stronger form.

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Tearing flesh from the bone in the absence of knives tends not.only to strengthen the masseter muscles and enlarge the zygomatic arch somewhat as a direct consequence,
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In the skull there's this thing called the zygomatic arch, which is behind the eyes, and your jaw fits in there, and if you have a really big zygomatic arch, then that means that a lot of muscle is in there

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The cheekbones and jaws of the Eskimo are very massive, possibly under the influence of the intense chewing he has to practice, which also results in a tremendous development of the chewing muscles. Eskimo teeth are often worn down to the gums, like animal teeth, from excessive use.
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The powerful jaw of these animals in chewing, gives rise to a terrific pressure upwards against the face, and the brow ridges make a strong upper border which absorbs it.
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Race forensic tres credible:
As are shape of the jawbone, or mandible. Mongoilids and ameridians tend to exhibit a more robust, square mandible, whereas negroids show a more oblique mandibular angle, and caucasauds a medium mandibular angle
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chin: It may be due to a reduction
in face size, to reduce chewing stress of the mandible
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Subjects with large masseter and medial pterygoid muscle volumes had flat mandibular and occlusal planes, and small gonial angles.
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In addition, a larger posterior cranial base, a smaller gonial angle, and an increase in mandibular length contributed to the increase in mandibular prognathism found in the Chinese sample.


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Des capteurs (dans les os) mesurent en permanance la pression sur l'os et l'obligent à mettre de la matière là ou elle est la plus forte
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Fifty-five per cent of the bite force could be explained by variations in the posterior facial height, gonial angle, antero-posterior size of the maxilla, and posterior length of the cranial base. The result showed a larger bite force implies a greater posterior facial height, smaller gonial angle, larger maxilla and straighter posterior length of the cranial base. This study suggests that among Indonesians, maximum bite force could be explained by craniofacial morphology as found in Caucasians. In addition, we proposed a clinical standard of the OLC for the comprehensive evaluation of occlusion.
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Two groups of men with opposite facial morphology were then selected: all men with a steep mandibular plane (higher than the mean plus one standard deviation) entered a first group (10 'long face' subjects), while all men with a relatively more horizontal mandibular plane (lower than the mean minus one standard deviation) entered a second group (13 'short face' subjects). Mean EMG potentials computed in the two groups were compared by using Student's t -test for independent samples. All the EMG potentials recorded during maximum voluntary clench in the 'long face' men were lower than that recorded in the 'short face' men, with statistically significant differences for all four analyzed muscles (p < 0.05). In conclusion, a non-invasive three-dimensional method confirmed that facial morphology and muscular function are significantly related, at least in men with a sound stomatognathic apparatus.

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The buccal cortical bone was thicker in short-faced individuals than in the average and long-faced groups and lingual cortical bone thickness of the M1 and M2 sections was greater.

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The amount of force is variable in accordance with the skeletal pattern of the patient, the type of movement desired and the size of the cusps. Normally, in brachyfacial cases, due to their strong musculature, it is necessary to use more force (greater activation) than in dolicofacial cases.

However, in a brachyfacial pattern with strong musculature this movement would be expected.


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brachyfacial (brachyprosopic), chemoprosope

A facial pattern characterized by a broad, square face; preferred term is euryprosopic.

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Q: Have you had problems with appliance breakage?

A: We have seen a few cases of appliance breakage in patients with brachyfacial types and strong musculature. In patients who have strong musculature, upon the doctor's request, Align can have the Aligners fabricated with a more durable material.

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However, point A of brachyfacial individuals was located in a more forward position (p = 0.05) and they had larger maxilla than dolichofacial individuals (p = 0.02).

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Brachyfacial pt. Typically has: flat mandibular plane, may have excessive overbite, short lower face, prominent chin, strong mandible, usually don’t have an esthetic problem like dolicofacial, molars usually undererupted that’s why pt. Has a short face
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Dolichofacial patients with weak musculature or vertical growth problems
tend to have high Mandibular Plane Angles. Brachyfacial types with strong musculature and deep
bites tend to have square jaws which result in low Mandibular Plane Angles.


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A large angle is indicative of a
"strong" and "square" mandible; a small angle represents a lower jaw with a short ramus and
vertical growth pattern.

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The face is short and
wide, the mandible is "strong" and "square", and
the dental arches are also broad when compared
to the ovoid Class I and the narrow Class II,
Division I, arches.
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Theoretically, differences in musculature tend to account for these
difficulties. Brachyfacial types exhibit powerful masseter, temporal, and pterygoid muscles that
resist mandibular change, as opposed to weak muscles seen in dolichofacial cases.
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Patients with
brachyfacial, square jaws and long corpi are able to afford wider incisors than are those with
dolichofacial, vertically angled jaws.

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The formula shows that a
patient with a brachyfacial pattern, i.e., wide
mandible, low mandibular plane, and
prognathic mandible will have a wider
mandibular arch than the dolichofacial patient
with a narrow, retrognathic mandible and a
high mandibular plane angle.



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Two groups of men with opposite facial morphology were then selected: all men with a steep mandibular plane (higher than the mean plus one standard deviation) entered a first group (10 ‘long face’ subjects), while all men with a relatively more horizontal mandibular plane (lower than the mean minus one standard deviation) entered a second group (13 ‘short face’ subjects). Mean EMG potentials computed in the two groups were compared by using Student's t -test for independent samples. All the EMG potentials recorded during maximum voluntary clench in the ‘long face’ men were lower than that recorded in the ‘short face’ men, with statistically significant differences for all four analyzed muscles (p < 0.05). In conclusion, a non-invasive three-dimensional method confirmed that facial morphology and muscular function are significantly related, at least in men with a sound stomatognathic apparatus.



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Based on biomechanical studies of extant great ape and human mandibles, Daegling (1993) hypothesized that decreased wishboning stress at the symphysis in conjunction with maintained levels of vertical bending stress was important in the origination and evolution of the human "chin" or mentum osseum.

This result supports one aspect of Daegling's hypothesis (the maintenance of vertical bending stress levels), while refuting the other key element (decrease in wishboning stress levels). From this, we conclude that factors other than facial/mandibular proportions and/or habitual bite force levels were important in the origin and early evolution of the "chin."


 

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