An examination of the edentulous mouth of an aged Pt who has wore maxillary complete dentures for many years against six mandibular teeth would probably show:
a- Cystic degeneration of the foramina of the anterior palatine nerve.
b- Loss of osseous structure in the anterior maxillary arch.***
c- Flabby ridge tissue in the posterior maxillary arch.
d- Insufficient inter occlusal distance.
Dental decks - page 390
When a patient wears complet maxillary denture agansit the six mandibular anterior teeth its very common to have to do a reline so often de to loss of bone strucutrein anterior maxillary arch.
Anatomical description of the lower maxillary or mandible:
The lower jaw, is odd, medial and symmetrical, located at the lower and posterior part of the face, is in itself the skeleton of the lower jaw. The middle part or body is concave horseshoe-shaped ends or branches rise and rise in a vertical direction forming an angle almost right with the body, whose curve is inscribed in a horizontal plane.
This bone is described as a body, branches, and the angle of the lower jaw.
Place forward the convex face, at the top and horizontally the alveolar edge.
Body of the lower jaw:
The body of the lower jaw, arciform anterior convexity, has an outer face, an inner face and two edges a lower edge, free, and an upper edge or alveolar.
The two faces of the lower jaw body are nearly vertical; however, the outer is slightly inclined at the top, while the internal looks a little down. This inclination of the maxillary faces is due to the fact that the body of the bone comprises two very different parts the actual body, arciform, posterior concavity and the alveolar arch, superimposed on the body, and also arciform. As the radius of the latter is smaller than the radius of the first, the upper or alveolar edge of the lower jaw is included or inscribed in the curve of the inferior or free edge; on the median part of the body, we already observe a kind of withdrawal of the alveolar portion on the lateral parts, the alveolar arch is very loose inwards and seems to be applied on the internal face of the body; the cut opposite clearly shows this particularity of structure.
Faces of the lower jaw:
The external surface of the lower jaw (this qualifier is more accurate than that of the anterior one, usually used), shows on the median line a crest or a vertical furrow more or less marked, trace of the welding of the two halves whose lower jaw is originally composed. This ridge ends, a little above the lower edge of the bone to a tubercle, the lower chin, lower pyramidal eminence, very variable development.
Above the tubercle, the alveolar portion is raised in vertical projections corresponding to the roots of the incisors and the canine; between these rounded projections, furrows respond to the inter-alveolar partitions; the projections corresponding to the canine teeth are more pronounced than the others.
Lateral angles of the chin eminence, sometimes indicated by a more or less protruding tubercle, start from a line, called the external oblique line, which follows first the lower edge of the bone, then rises on the lateral parts which it crosses diagonally to continue with the anterior edge of the ascending branch.
At 25 or 30 millimeters on each side of the chinar symphysis, we see on the external side the mental hole opening of the lower dental canal, through which emerges an arteriole and the bouquet of the lower dental nerve. The mental hole is on the vertical passing through the second small molar it is at approximately equal distance from the alveolar edge and the free edge, however a little closer to the latter, when the alveolar portion is entire.
The inner side also shows on the median line the traces of the weld corresponding to the symphysis; at the lower part of it, we see the roughness of insertion distributed in tubercles or apophyses, the genital apophyses; these symmetrically arranged on each side of the median line are four in number; two superior, acuminate, give insertion to the lower genio-glosses muscles, arranged in crests on each side of the median line, give insertion to the genio-hyoïdiens; almost always these two inferior apophyses are united in a median crest, on the slopes of which the genio-hyoid muscles are inserted.
On each side of the genital apophyses is a line, an internal oblique line, which, at first slightly marked, becomes more accentuated and ascends obliquely on the internal surface of the bone, and finally disappears towards the middle part of the ascending branch. a little behind and below the last molar. This line will not merge back with the anterior edge of the rising branch.
As it gives attachment to the mylo-hyoid muscle, it is still called the mylo-hyoid line, it is especially below the last molars that it becomes prominent.
Anatomical description of the lower maxillary or mandible:
The lower jaw, is odd, medial and symmetrical, located at the lower and posterior part of the face, is in itself the skeleton of the lower jaw. The middle part or body is concave horseshoe-shaped ends or branches rise and rise in a vertical direction forming an angle almost right with the body, whose curve is inscribed in a horizontal plane.
This bone is described as a body, branches, and the angle of the lower jaw.
Place forward the convex face, at the top and horizontally the alveolar edge.
Body of the lower jaw:
The body of the lower jaw, arciform anterior convexity, has an outer face, an inner face and two edges a lower edge, free, and an upper edge or alveolar.
The two faces of the lower jaw body are nearly vertical; however, the outer is slightly inclined at the top, while the internal looks a little down. This inclination of the maxillary faces is due to the fact that the body of the bone comprises two very different parts the actual body, arciform, posterior concavity and the alveolar arch, superimposed on the body, and also arciform. As the radius of the latter is smaller than the radius of the first, the upper or alveolar edge of the lower jaw is included or inscribed in the curve of the inferior or free edge; on the median part of the body, we already observe a kind of withdrawal of the alveolar portion on the lateral parts, the alveolar arch is very loose inwards and seems to be applied on the internal face of the body; the cut opposite clearly shows this particularity of structure.
Faces of the lower jaw:
The external surface of the lower jaw (this qualifier is more accurate than that of the anterior one, usually used), shows on the median line a crest or a vertical furrow more or less marked, trace of the welding of the two halves whose lower jaw is originally composed. This ridge ends, a little above the lower edge of the bone to a tubercle, the lower chin, lower pyramidal eminence, very variable development.
Above the tubercle, the alveolar portion is raised in vertical projections corresponding to the roots of the incisors and the canine; between these rounded projections, furrows respond to the inter-alveolar partitions; the projections corresponding to the canine teeth are more pronounced than the others.
Lateral angles of the chin eminence, sometimes indicated by a more or less protruding tubercle, start from a line, called the external oblique line, which follows first the lower edge of the bone, then rises on the lateral parts which it crosses diagonally to continue with the anterior edge of the ascending branch.
At 25 or 30 millimeters on each side of the chinar symphysis, we see on the external side the mental hole opening of the lower dental canal, through which emerges an arteriole and the bouquet of the lower dental nerve. The mental hole is on the vertical passing through the second small molar it is at approximately equal distance from the alveolar edge and the free edge, however a little closer to the latter, when the alveolar portion is entire.
The inner side also shows on the median line the traces of the weld corresponding to the symphysis; at the lower part of it, we see the roughness of insertion distributed in tubercles or apophyses, the genital apophyses; these symmetrically arranged on each side of the median line are four in number; two superior, acuminate, give insertion to the lower genio-glosses muscles, arranged in crests on each side of the median line, give insertion to the genio-hyoïdiens; almost always these two inferior apophyses are united in a median crest, on the slopes of which the genio-hyoid muscles are inserted.
On each side of the genital apophyses is a line, an internal oblique line, which, at first slightly marked, becomes more accentuated and ascends obliquely on the internal surface of the bone, and finally disappears towards the middle part of the ascending branch. a little behind and below the last molar. This line will not merge back with the anterior edge of the rising branch.
As it gives attachment to the mylo-hyoid muscle, it is still called the mylo-hyoid line, it is especially below the last molars that it becomes prominent.
The mylohyoidal line divides the inner surface of the maxillary into two parts of very different extent, inclination, and relationship. The upper part or buccal is smooth very high in front where it responds to the incisors, it tapers on the lateral parts it offers, on each side of genital processes, a dimple, the sublingual dimple, hollowed by the contact of the bone with the anterior part of the sublingual gland; usually there is a large vascular hole.
The portion of the internal surface situated below the mylo-hyoid line may be called cervical, for it responds to the soft parts of the neck; it is no longer vertical like the preceding one, but oblique at the bottom and forwards. It presents, on each side of the median line, below the sublingual fossa, the oval impression of insertion of the anterior belly of the digastric. Apart from this impression, the cervical portion is excavated by a trough depression which corresponds to the upper part of the submaxillary gland.
On this inner surface of the maxillary a parallel and underlying groove is seen on the mylo-hyoid line; it is the mylohyoidal groove which responds to the nerve and vessels of the same name.
Edges of the lower jaw:
The lower edge of the body is rounded and responds to the skin from which it is separated only by the leaflet it is very thick and describes an elongated curve with lower convexity. The upper or alveolar rim has alveolar cavities adapted to the shape, number and arrangement of the roots of the teeth.
Branches of the lower jaw:
The outer face presents, especially in its lower half, rough lines directed obliquely from front to back and from top to bottom; these lines respond to the insertion of the fibrous laminae included in the masseter muscle; they become even more accentuated as one approaches the angle of the maxillary; often this angle is as if thrown out and attracted upward by the pull of the muscle.
On the part of the internal face which borders the angle, there are series of roughnesses, parallel to the preceding ones, and corresponding to the insertion of the internal pterygoid. Towards the middle part of this face, we see the inner ounce of the dental canal, this orifice, situated at an equal distance from the four edges which limit the ascending branch, is enormous; it opens back and up; the canal which succeeds it, obliquely directed forward and downwards, gives passage to the vessels and lower dental nerves, the anterior lip of the hole is sharp and terminates at the top by a triangular spine, the Spix's spine, to which attaches the sphenomaxillary ligament.
Below the orifice of the dental canal begins the mylohyoid trench traced by the nerve and the mylo-hyoid vessels.
The thin, almost sharp, slightly concave forward anterior edge is continuous with the anterior edge of the coronoid process.
The posterior border, thick and rounded, slightly concave behind, widens upwards where it forms the posterior surface of the condyle.
The lower edge of the rising branch follows the lower edge of the body; it is thinner than this; at the point where it continues with the lower edge of the body, it sometimes bears the imprint of the facial artery.
The upper edge, has two projections separated by a wide notch, the coronoid process in front, the condyle back.
The coronoid process is a triangular bone blade, flattened from inside to outside; its summit, curved backwards and outward, is, in most cases, at the same level as the horizontal led by the condyle; he sometimes stays above, sometimes below. The base of the process continues with the rising branch. The process is engined by the tendino-fleshy insertion of the temporal muscle. Its outer face is smooth; its inner face has a foam projection which descends parallel to the front edge and is lost on the inner part of the last cell, where it joins the inner oblique line. The anterior, convex, sharp edge, forms with this internal crest, foam, a triangular gutter, with apex, superior, whose base responds to the last molar; this gutter is traversed obliquely by a small bony ridge which marks the insertion of the blaster.
The sigmoidal notch, semicircular with superior concavity, separates the coronoid process from the condyle it gives passage to the vessels and masseterin nerves.
The condyle is an eminence of ovoid form, whose major axis is directed from outside to inside and from front to back. The condyle is situated entirely within the plane passing through the ascending branch of the lower jaw; also its projection is almost null on the external face of this branch; on the other hand, it shows itself entirely on the internal face. The cutting edge of the sigmoidal notch will terminate at or near the outer corner of the condyle. The posterior surface of the condyle is broad, triangular with a lower vertex; it presents itself as an enlargement of the posterior border of the rising branch. The anterior surface is excavated by the insertion fossa of the external pterygoid muscle. The articular part, shaped like a donkey, has an anterior convex slope, and a posterior flattened slope which continues the plane of the posterior surface of the condyle. Under the external angle is always noted a tubercle, which receives the insertion of the main beam of the external lateral ligament. The narrowed portion, Intermediate to the condyle and the ascending branch, bears the name of condylar neck.
Angle of the lower jaw:
Almost straight, it is often thrown out by the pull of the masseter; it gives insertion to the maxillary ligament.
Ossification of the lower jaw:
The lower jaw is originally formed of two distinct or half bones. Each of these halves has six points of ossification.
A first point, inferior point, appears at first around the thirty-fifth day, in the form of a bone trail which begins towards the angle of the jaw and extends rapidly to the former third of this one. point forms the lower edge of the jaw. A second, incisive point, appears shortly after it occupies on each side of the symphysis the place where the incisive teeth will develop. A third, additional point of the mental hole, forms a small bone lamella destined to form the mental hole. The fourth or condylar point forms the condyle and the portion of the rising branch of the maxilla that supports the latter. The fifth or coronoid point forms the coronoid process and the segment of the ascending branch that supports it. The sixth, finally, point of the Spix spine, forms the part of the bone between the incisal point and the upper orifice of the dental canal.
The maxillary thus formed is presented as a gutter open at the top and without subdivision. Then the inter) alveolar partitions appear around the dental germs, forming the cells staggered in two series corresponding to the two dentitions. Around the vessels and nerves that go to the dental papilla the bone substance is deposited and forms two superimposed channels of the temporary dentition channel, and the channel of the permanent dentition.
The two halves of the lower jaw join together a little after birth. The trace of this weld is marked by the symphysis of the chin.
Cartilage of Mekel:
The lower jaw develops on the external surface of an arcuate cartilage, on which it appears to be modeled and opposite to which it behaves like the bones of the skull facing the primitive chondro-skull. This cartilage appears from the first month of the intrauterine life in the thickness of the maxillary branch of the facial arch, in the form of a horseshoe, with a posterior concavity, the two extremities of which terminate in the auricular regions. From the tympanic cavity where it originates, Meckel's cartilage passes behind the tympanic circle, within the parotid and external carotid, outside the internal pterygoid muscle, and engages between the maxillary and the mylohyoid muscle. to reach the symphysis of the chin, where its two halves, right and left, meet. The tympanic or auricular end of Meckel's cartilage forms the hammer and anvil.
Architecture of the lower jaw:
It consists of a spongy mass wrapped in compact tissue. The maxilla has the structure of a long bone whose medullary canal is filled by an areolar tissue with thick trabeculae. If we consider the body of the maxillary, we see that its walls are formed by a compact layer of a thickness comparable to that of the diaphysis of long bones; this thickness reaches its maximum along the lower edge where it varies from 3 to 5 mm.
The condyle is formed by a resistant spongy mass, with vertical spans.
As for the alveolar portion, its architecture is very different, as the development of this auxiliary portion of the dental apparatus allowed to predict it is formed by a spongy tissue enclosed in a thin bone shell; its trabecular system is dense and its fibers radiate around the cavity, under dental pressure.
A canal, a lower dental canal, whose formation is controlled by the disposition of the inferior vessels and nerves of the teeth, traverses each half of this canal, which begins on the internal face of the ascending branch, then moves downwards and forwards, then horizontally inwards. before, one centimeter above the lower edge of the bone.
It bifurcates towards the anterior third of the bone its external branch comes to end in the mental hole, while its internal branch continuing the path from the trunk to the symphysis will end under the roots of the incisors. From the upper wall of this canal leave the small canaliculi through which the vessels and dental nerves gain the bottom of the alveoli and the roots of the teeth.
Joints of the lower jaw:
The lower jaw articulates with the two temporals.
Muscle insertions:
the external surface of the body gives insertion to the platys of the neck, tufts of the chin, square of the chin, triangular of the lips.
the internal surface of the body gives insertion to the mylo-hyoid muscle, superior constrictor, genio-hyoid, genio-glosse.
the lower edge of the body gives insertion to the digastric muscle.
the outer side of the branches gives insertion to the masseter muscle.
the angle of the inner side of the branches gives insertion to the internal pterygoid.
the coronoid process gives insertion to the temporal.
the condyle gives insertion to the pterygoid-external.
Variations of the lower jaw
The four genic processes are rarely found.
Between the two superior genic processes is a vascular conduit, constant, obliquely directed downwards and forwards.
Between the two digastric facets, there is sometimes a median tubercle, which responds to the raphe of insertion of the mylo-hyoid muscle.
On the posterior lip of the alveolar border, on each side of the medial incisors, two small holes, orifices of vascular canals are constantly observed.
The mylohyoidal gutter is sometimes transformed into a complete canal. Sometimes, behind the furrow, there is an orifice, a vestige of the canal of the first dentition.
Very rarely the major axis of the condyle is transverse:
The discharge inside the condyle is interesting from the point of view of its fractures in a blow or during a fall on the chin, it is understood that the two thirds internal of the condyles, which have no support, are detached, while the external angle supported by the anterior edge of the notch resists.
The maxillary angle varies with age. He opens and returns to dimensions close to those he had in the child.
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