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ANTHROPOLOG
Y
ORTHODONTIC
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‘Orthodontists are functioning
ANTHROPOLOGISTS. We measure the
bones of the face, skull and teeth and
study the relationship of these structures’
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PRIMATES
Primates are defined as mammals with thumbs and large toes that oppose the
others digits. The ends of the digits are flattened and have nails rather than claws.
MEGAZOSTRODON
Fossil evidence has uncovered a very old, very small, warm-blooded creature
called megazostrodon. It had a sharp snout and pointed ears, nursed its young, and is
the oldest known mammal.
THEORY OF EVOLUTION
Charles Darwin, a close observer of nature, put forward the theory of evolution. It
states that
1.Each individual of a species is different from every other ;
2.Each individual can reproduce in geometric proportion ;
3.Because of a resulting over population, only the most fit will survive.

EARLY PRIMATES
Tree shrews, the most primitive of the primates, are an arboreal variation of the
megazostrodon. Homo sapiens, maturing more slowly than other primates, retained
many primitive features, which may be why the genus has been successful. Hands
and teeth, for example, are quite primitive.
Climatic and geologic changes through millions of years reshaped
environments, and organisms that failed to adapt became extinct.
FROM SHREWS TO HUMANS
The tree shrew developed a shortened snout and an increased cranial capacity.
Being nocturnal, its orbits are large and there is no bony separation from the muscles
of mastication. It does not have stereoscopic vision. The shrew climbs vertically and
scampers along the tops of branches. The large toe is flattened and has a nail, but the
other digits have claws, which make the shrews arboreal existence more secure.
The basic mammalian (Eutherian) Dental formula : I-3, C-1, P-4, M-3 right and left, in
both the upper and lower arches.

TREE SHREW
Dental Formula
Inc.- U-2,l-3
Can.-1
Pre.-3
Molar-3

The next step up the primate ladder, lemur, includes numerous genera and subfamilies
that vary in size from the attractive furry little mouse lemur to the cat-sized, ring- tailed
lemur. lemurs are good climbers, using their tails for balance.
Like the tree shrew, the lemur is almost entirely arboreal. Their digits have flattened
ends on both hands and feet with nails instead of claws, except for the second toe
which is elongated and has a claw with which to scratch and groom. (called the toilet
digit)
The dental formula for lemur, both the upper and lower ; I-2, C-1, P-3, M-3,
The two central incisors are separated by a wide diastema .

The next species in the primate evolution is the TARSIER, which has a combination
of primitive and advanced features.
Dental formula
Upper – I-2, C-1, P-3, M-3 and
Lower – I-1, C-1, P-3, M-3,
All of the incisors and canines are coniform in shape as are the lower premolars and
one of the uppers.
Next among these primates are the MONKEYS, with noticeble differences between
old and new world monkeys. Most old world monkeys are no longer completely
arboreal, instead combining arboreal life with excursions on the ground.
The dental formula for old monkeys is upper and lower :
I-2, C-1, P-2, M-3, this is the same as that for great apes and hominids.

The smallest of living monkeys
is the marmoset. This new
world creature has two rather
than three molars in each
quadrant.
Dental formula for new world
monkeys is ; upper and lower
I-2, C-1, P-3, M-3.
MARMOSET

There are four living types of anthropoid apes ;
1. Gorilla
2. Gibbon
3. Orangutan
4. Chimpanzee
These apes are sexually dimorphic ; males are larger than the females ;
GORILLA
- Largest of the 4 apes
- Have strong incisors with chisel like edges
- The central is larger than lateral, which slopes gingivally on the distal;
- Both have concave labial surfaces
- There is a diastema between the laterals and canines in both arches.

GIBBON
-World class athlete
-Almost completely arboreal
-Locomotion is primarily brachiation
-Upper centrals are broad and laterals are more pointed
-In upper and lower arches the second molar is larger than the first and third.
ORANGUTAN
-Arboreal
-Locomotion is based on brachiation
-The dentition is similar to that of gorrillas except that the jaws are narrower
-The canines are sexually dimorphic

CHIMPANZEES
-Arboreal and terrestrial
-Legs are not as proportionately diminished as those of gibbon
-Arms are long and strong
-They can ambulate on their feet
-The canines of males are heavier, longer, and more curved.

Comparing chromosomes of the great apes with those of Homo sapiens, the
chimpanzee is the closest match.
The change from arboreal to terrestrial life in Homo sapiens could not have occurred
without changes in anatomy.
Man and elephant are the only mammals with chinbuttons.
The elephant has a very long and mobile lower lip, which aids in guiding the enormous
amount of coarse food ingested daily.
The chinbutton provides necessary muscle attachment for the lip.
The hominid chinbutton provides lower muscle attachment to orbicularis oris, the ring
of musculature that restrains protrusion.

EVOLUTION OF THE JAWS AND OF THE MANDIBULAR JOINT :
The skull and jaws of elasmobranch fishes (sharks and rays ) are composed of
calcified cartilage throughout life. In higher vertebrates the base of the skull, the nasal
capsules, and the skeleton of the lower jaw develop first in cartilage. With
development three further process takes place.

1. Parts of the primordial cartilaginous skeleton are replaced by bone. This takes
place at the base of the skull ; at the front of Meckels cartilage, which becomes
incorporated in the mandible ; at the back of the Meckels cartilage, where the
malleus of the middle ear develops ; at the back of the palato-quadrate bar, where
the incus of the middle ear develops ; and in the face, where the lateral masses of
the ethmoid and inferior turbinates replace parts of the nasal capsule.
2. Over the vault of the skull membrane bones develop in regions where the
cartilaginous skeleton was incomplete. such membrane bones (dermal bones )
include the frontal bones, the parietals,the interparietal part of the occipital. The
squamous parts of the temporal bones. And the greater part of the great wings of
the sphenoid.

3. Membrane bones apply themselves around parts of the cartilaginous skeleton which
latter atrophies. The replacement of the greater part of Meckels cartilage by the
mandible ; the lateral walls of the nasal capsule by the premaxillary, maxillary, lacrimal,
and palatine bones, and the replacement of part of the nasal septum by the vomer are
examples in human ontogeny.
PRIMARY AND SECONDARY JAWS :
In elasmobranch fishes the upper jaw is the palato-quadrate bar which is attached to
the cranial part of the skull in front by ligaments and behind through the intermediary of
the hyomandibular cartilage. The lower jaw skeleton is Meckels cartilage which
articulates with the back of the palato-quadrate bar.

Hence, according to functional requirements, in different species. Varying degrees of
movement could take place between the upper and lower jaws and between the upper
jaw and the cranial part of the skull.
In bony fishes, amphibians and reptiles, a series of dermal bones are laid down around
these cartilaginous primary jaw elements. Around the palato-quadrate bar develop the
palatine and transverse bones which in some species carry teeth. Around Meckels
cartilage develops a complex series of bones of which the most important are the
dentary, splenial, angulare, surangulare, coronoid and goniale. Of these the first two
may carry teeth.

In modern fishes and in the tetrapods a new upper jaw develops outside the palato-
quadrate jaw and its associated dermal bones. The new jaw is made up of a series of
dermal bones which include from before backward the premaxilla, the maxilla, the
jugal, and the quadrato-jugal. The first two of these are associated with teeth. In many
animals the teeth of the lower jaw, carried by the dentary, bite between an outer row of
upper teeth carried on the premaxilla and maxilla and an inner row carried on the
palatine and pterygoids.

PRIMARY AND SECONDARY JAW JOINTS :
In the evolution of the reptiles, the number of dermal elements in the lower jaw
becomes gradually reduced until the dentary comes to make up the greater part of the
jaw with the angulare, surangulare, and goniale much reduced in size. The articulare a
bone which has replaced the back part of Meckels cartilage. Still forms the hindmost
element of the jaw and articulates with the quadrate. This is the condition found in the
mammal like reptiles.
In mammals a new joint (mandibular joint ) has been created between the
dentary, which is now the only bone remaining in the lower jaw and the squamosal part
of the temporal. The articulare in mammals is quite separate from the mandible and
forms the malleus of the middle ear. Its articulation with the quadrate ( incus ) remains
as the malleolar – incudal joint of the middle ear. The angulare becomes the tympanic
plate of the temporal.

The history of the primitive jaw joint illustrates very well two characterstic features of
phylogenetic development :
1. When a new organ develops the old organ is not lost immediately but continues to
function for a period while its successor is in the early period of its functional activity.
2. Later, when the new organ is well established the old organ may take on some other
function.

DEVELOPMENT OF MANDIBULAR FORM :
PHYLOGENY, ONTOGENY, AND FUNCTION
Phylogeny – Evolutionary development and history and
Ontogeny – Origin and development from embryo to adult.
Phylogeny
The major transitions associated with the mandible include :
1. The origin of the vertebrate craniofacial region from a presumed cephalocordate
ancestor,
2. Development of jaws in primitive fish,
3.Development of the mammalian mandible and TMJ joint, and
4.Evolution of modern mammalian mandibular morphologies, including that of
humans.

ORIGINS OF THE VERTEBRATE CRANIOFACIAL REGION
 Craniofacial structure in vertebrates constitutes a unique set of morphologies that
define the taxa and lead some zoologists to prefer the name of Craniata instead of
vertebrata.
 these traits include specializations of the skull, brain, sense organs, and other organ
systems, such as the kidneys.
 the first vertebrates probably evolved during the Cambrian period, about 550 million
years ago, during a time of rapid development of the major eukaryotic phyla.
 possible chordate precursors of the vertebrates exist in the fossil record ; most
impressive is the fossil Pikaia from the Burgess Shale of Alberta dating from the
middle of the Cambrian period.
 this fossil strongly resembles living cephalochordates, such as AMPHIOXUS.

• The first possible vertebrates, from the late Cambrian period, were soft-bodied
wormlike creatures called the conodont animals, named for their often preserved tooth
like elements or condonts.
• the first undisputed vertebrates were jawless or agnathan fish from the Ordovvician
period.
• the majority of these animals were covered with external mineralized plates, or bony
armor.
• Another important insight of developmental biology with profound implications for
vertebrate craniofacial evolution was the discovery of the significance of HOMEOBOX
genes.

Homeobox genes are a multigene family that code for homeodomain proteins, which
function as transcription factors during development. The remarkable feature of
homeobox genes is their highly conserved sequence along with their ubiquity
throughout the animal kingdom.
Homeobox genes play key roles in spatial patterning of the whole organism during
early development, and in similar patterning of various organs later in development.
Gene duplication and functional reassignment of homeobox genes played an
important role in the evolution of the vertebrate head.

ORIGINS OF THE VERTEBRATE MANDIBLE :
The classical hypothesis is that the anterior pharyngeal arches evolved in to
articulated jaws. This was accomplished developmentally by the derivation of the
visceral arches in gnathostomes, ie, jawed vertebrates, from the unmodified branchial
arches of Agnatha.
Functionally the gnathostome jaws allowed feeding specializations, including capture
of larger and motile prey. The initial adaptation may have originated in a feeding
pattern similar to that of living Agnatha and speculated for fossil forms, in which the
animal forces the mouth against a fixed prey object and then closes the incipient jaws.
A plausible suggestion is that jaws developed from specializations of the Agnatha
velum, which is a pumping device that early jawless vertebrates may have used to
pump in water and food particles, much as larval lamprey do today.

The internal hyoid and brachial arches of gnathostomes may have developed later,
providing the pharynx with a crushing or biting function.

EVOLUTION OF THE MAMMALIAN MANDIBLE :
Evolution of mammals from reptilian precursors involved a variety of functional and
morphologic changes, many of which were associated with the craniofacial region,
including increased brain size, enlarged cranium, and reduced complexity of the cranial
vault, as well as development of temporal openings, secondary palate, and palatal
fusion. Heterodonty and more complex masticatory muscles accompanied an increase
in masticatory complexity.
The mammalian mandible was much reduced in complexity from its reptilian precursor.
The mammalian structure now consisted of a single bone, the DENTARY, rather than a
series of bones, several of which formerly made up the mandible and its cranial
articulation.

Specifically, the articular and the quadrate bones become ossicles of the middle
ear, the malleus and the incus. Several other bones of mandible were lost entirely.
In the process of these changes, a secondary jaw joint was formed, which became
the precursor of the SQUAMOSAL – DENTARY JOINT or TMJ in mammals.

MAMMALIAN EVOLUTION AND PRIMATE MANDIBULAR DESIGN :
• Dentary or mandibular adaptation has resulted in a broad array of forms throughout
the mammals, which include a variety of dental specializations.
• it has also resulted in a range of features of the primary components of the mandible,
including the relative size, height, and depth of the corpus and ramus ;
• the elevation of the mandibular condyle ; the fusion or lack there of the symphysis ;
and the size and position of the angular and coronoid processes. Despite these
variations in skeletal morphology, the motor pattern of the masticatory muscles is
similar throughout the mammals.
• like wise, the basic structure of the trigeminal system is generally conservative in
vertebrates.

In hominid evolution, the mandibles of modern humans exhibit several differences
from the mandibles of the various taxa of their early hominid forebears, the
autralopithecines. These differences include ;
1. A smaller overall mandibular size and correspondingly less prognathism and tooth
size ;
2. a difference in the shape of the dental arch from parallel rows of cheek teeth
compared to an overall parabolic shape :
3. overall less robusticity and cortical bone thickness, particularly when comparing
modern humans with robust austalopithecines : and
4. A difference in the shape of the symphyseal cross – section, such that most
australopithecines have bony reinforcement on the internal aspect of the
symphysis, while modern humans have reinforcement on the facial aspect.
The change in human society from a hunting and gathering mode of existence to
agriculture is well documented in the archeological record.

ONTOGENY : DEVELOPMENTAL ORIGINS OF THE MANDIBLE

HOMO SAPIENS :
Advanced Homo erectus forms evolved into or were succeeded by early H. sapiens or
archaic man. The distinctions are blurred. Although in most respects similar to
modern man, the archaic forms had generally longer, lower and broader skulls and
heavy faces, the teeth were slightly larger than those of modern man.
There is evidence, for example, of two populations with different cranial
characteristics developing in, for example, Eurasia (NEANDERTHAL man and
modern man). Despite differences in facial form and cranial profile- long and low as
opposed to short and high cranial vaults.
During this period the typical human face finally developed. Brow ridges were
reduced, the jaws became less prognathic and the definitive chin appeared.

In pongids the symphyseal region is buttressed internally, in modern man externally
by the mental protuberance. Nevertheless the progressive shortening of the face and
the concomitant conversion of the dental arcade from a V – shape into a parabola has
been associated with first the reduction and then the elimination of the internal
buttresses, a more vertical orientation of the bone, and then the development of the
chin as a new external buttress.
One feature observed in some populations of early man, particularly the Neanderthals
known is the presence of grossly enlarged pulp chambers in the teeth and an
associated level of root bifurcation in the post canines.
This condition has been alleged to be an adaptation for heavy tooth wear : the longer
and larger the pulp chamber, the greater the opportunity for secondary dentine
deposition and so the longer the life of tooth.

DRYOPITHECUS PATTERN :
The early evolution of the primate upper molar involved the addition of a fourth cusp,
the hypocone to the distolingual aspect of the trigon. The ridge connecting the
protocone and metacone persisted and in some cases became strengthened to form
the oblique ridge dominating the occlusal surface of this tooth in pongids and man. In
contrast, the primitive lower molar lost one of the original five cusps : the paraconid
disappeared leaving only the protoconid and metaconid on the trigonid.
The two cusps of the talonid, the hypoconid and entoconid persisted, augmented
occlusally by a fifth (distal ) cusp, the hypoconulid. As the primates changed their diet
with increasing body size, so the occlusal profile of the molar teeth changed.
Instead of sharply pointed cusps with well defined ridges on their slopes and deep
basins between them, the cusps became more rounded, the basins shallower and
wider and the difference in level of the occlusal table between trigonid and talonid was
lost.

This change increased the grinding capacity of the teeth, allowing them to move in to
centric occlusion with some cutting action between ridges and then lingually out of
occlusion as the food is ground. This type of four or five cusped molar is found in new
world monkeys, apes and man. It is often loosely referred to as having the
Dryopithecus pattern, a name actually given to the fissure pattern running between the
five cusps found on lower molars and first described from the molars of a fossil pongid
Dryopithecus .

DEVELOPMENT OF THE TMJ :
Phylogenetic considerations
In reptiles and birds, the lower jaw apparatus is formed by a number of discrete bones
composed of the dentary bone, which houses the teeth, and a variable number of
postdentary bones. The articulation between the lower jaw and cranium is formed by
two synovial joints : one between the quadrate and articular bones and the other
between the articular and squamosal bone of the cranium.
One anatomic and functional hallmark of mammals is the development of a single joint
system between the dentary bone, now the mandible in mammals, and the squamous
portion of the temporal bone in the cranium. Two of the bones that form the jaw joints in
reptiles, the quadrate and articular, remain as the malleus and incus bones of the
middle ear in mammals.

Appreciation of the phylogenetic development of the mammalian TMJ has profound
implications for understanding of the morphogenesis, growth, and adaptation of the
human TMJ, primarily because of the nature of the tissues comprising the reptilian and
mammalian jaw joints.
For example, the postdentary bones of reptiles are all derived developmentally from
Meckel’s cartilage. However, the dentary bone, which houses the teeth in reptiles and
expanded to become the mandible in mammals, and the squamous portion of the
temporal bone both form ontogenetically via intramembranous ossification : neither is
preformed in cartilage.

Thus, growth / modeling of the skeletal components of the TMJ, ie, the mandibular
condyle and temporal fossa, take place exclusively intramembranously, in the complete
absence of a primary cartilaginous anlagen that typically provides a template and
mechanism for subsequent skeletal growth in post cranial bases. Growth related
cartilage found in various regions of the mandible and especially at the mandibular
condyle throughout ontogeny arise secondarily, and are dependent on local epigenetic
circumstances for their appearance and maintenance.

EVOLUTION OF HUMAN FACE :
The nonprimates like dog, sheep etc. skeleton projects in front of the cranial region of
the skull. During the primate evolution the facial skeleton becomes gradually more
bent downwards until in man it lies below the overhanging frontal region of the
cranium. This change is associated with an increased in the relative prominence of
the brain and bending of the axis of the cranial base in the region of the pitutary
gland. The alteration appears to be associated with gradual attainment of eruct
posture.
Throughout the primitive evolution there has been a reduction of the importance of
the sense of smell with a reduction in the size and complexity of the nasal cavities
and snout. This reduces the space available for the teeth, but is compensated by the
development of the alveolar process.

Forward migration of the eyes from submammalian lateral position to the forward
position associated with stereotypic vision also reduces the size of upper nasal cavity.
As a consequences a typical nasal bone such as the facial ethmoid comes to contribute
to the medial wall of the orbital cavity.
The reduction of the elongated facial skeleton reduces the space available for the
tongue. This part is compensated by for the remodeling of the chin area, the anterior
supporting internal structure- simian shelf- being replaced by the external chin.
In anthropoid apes, mastication is almost a continuous dynamic activity and the whole
masticatory apparatus, dental skeleton and muscular is highly developed. This is seen
as exaggeration of the crests of muscle attachments. With the growth of brain and
cranium in man there is no longer a necessity of the crests.

With the change in the eating habits the dentition is well developed and what remains
of the supra orbital crests become submerged in the developed and forward placed
vertical forehead. The direction of facial growth throughout the primate series and
especially man becomes more vertical. In the later the vertical component is greater
than the forward component. This is noticeable in the alveolar process associated with
an increasing frequency of the crowded misplaced teeth.
One of the secondary consequence of the predominance of vertical growth in the
disengagement of the larynx from the nasal cavity, an important factor in the
development of speech.

DERMATOGLYPHIC PATTERN WITH MALOCCLUSION :
Dermatoglyphics, proposed by Cummins and Midlo ( 1926 ) implies the study of
patterned traceries of fine ridges on digits, palms and soles.
Dermal ridges appear during 12th week of intrauterine life and are completed by 24
weeks of intrauterine life. Thereafter, they remain constant throughout life.
Interest of dermatoglyphics in medicine was aroused when abnormal dermal patterns
were noted in Downs syndrome. A number of disorders like Turners syndrome,
Klinefelters syndrome, Leukemia, rubella syndrome, thalidomide drugs in pregnancy
also exhibit unusual dermatoglyphic findings.
Thereafter based on the fact that development of teeth, alveolus and palate occurs at
the same time as the development of dermal patterns, Studies were done correlating
dermal patterns with normal occlusion and malocclusions since they are both
genetically governed structures.

1. In normal occlusion as the total finger ridge count increases, the space discrepancy
decreases in the maxilla and as angle tab increases the cumulative mesiodistal
crown width decreases in both the maxilla and mandible.
2. In class I malocclusion, as the total finger ridge count increases, the intermolar
width decreases in the mandible and as the a-b ridge count increases in the right
hand, the palatal vault also increases in height. As angle atd increases in the right
hand, the arch length decreases in the maxilla and as angle atd increases in the
left hand, the arch length decreases in the mandible.

3. In class II div. I malocclusion, as the total finger ridge count increases the
cumulative mesiodistal crown width increases and the arch length and arch perimeter
decreases in the mandible. As the a – b ridge count increases in the left hand, the
intermolar width decreases in both the maxilla and mandible. In the left hand, as angle
tab increases the intermolar width decreases in the mandible and as angle atd
increases, the intercanine width also increases in the mandible.
4. In class III malocclusion as the a – b ridge count increases in the right hand, the
height of palatal vault also increases and the intermolar width decreases in the
mandible. As the a – b ridge count increases in the left hand, the intercanine width and
arch length also increases in the mandible. In the right hand, as angle atd increases,
the intercanine width also increases in the maxilla and as angle tab increases, the
intercanine and intermolar widths also decrease in the maxilla.

FOSSIL TEETH REVEAL RECENT
ORIGIN OF HUMAN GROWTH PATTERN
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