Patient with maxillary complete denture and natural mandibular anterior teeth. After years, comes to you to do distal extension for posterior mandibular teeth. You will see:
a- Bone resorption on maxillary anterior region***
b- Severe bone loss of mandibular posterior teeth.
The lower jaw is located at the lower and anterior part of the face. The lower maxilla or mandible is an odd and symmetrical bone, constituting alone the lower jaw. It is divided into three parts: a middle part, the body, and two lateral parts, the rising branches, which rise at the two posterior extremities of the body.
Body of the lower jaw:
The body of the maxillary is shaped like a horseshoe. It has a convex anterior surface, a concave posterior surface, an upper or alveolar edge and a free lower edge.
- Front side:
In its middle part, a vertical line, index of the weld of the two parts of the bone, the symphysis chin. The symphysis of the chin ends below on the summit of a triangular projection with a lower base, the chin eminence.
On each side of the chin, a protruding line is called the external oblique line, which goes backwards and upwards and continues with the outer lip of the anterior edge of the maxillary ramus. It gives insertion to the triangular muscles of the lips, square of the chin and platys.
Above the outer oblique line is the mental hole. This orifice is located equidistant from the two edges of the jaw and on a vertical passing sometimes between the two premolars, sometimes by one or other of these two teeth. It delivers passage to the vessels and the mental nerves.
- Posterior face:
The posterior surface of the maxillary body presents on the median part, and near the inferior border, four small superimposed projections called genital apophyses, two on the right, two on the left; they are the upper and lower apophyses. The superior genital processes give insertion to genio-glosses muscles; and the inferior ones, to the genio-hyoid muscles. Quite often, the lower genital apophyses, and sometimes even the four apophyses, are fused into one.
On the apophyses geni, on each side, a protruding line (a ridge), the internal oblique line or mylo-hyoid. The inner oblique line is worn up and back and terminates on the ascending branch of the lower jaw, forming the inner lip of its anterior border; it gives attachment to the mylo-hyoid muscle. Below it runs a narrow furrow, called the mylo-hyoid groove, where the vessels and nerve of the same name run.
The inner oblique line divides the posterior surface of the maxillary body into two parts. One, superior, excavated especially forward, higher forwards than behind, is called sublingual fossa; it is related to the sublingual gland. The other, lower, is higher behind than before; it is largely occupied by a depression, the submaxillary fossa, in relation to the submaxillary gland.
- edges:
The upper or alveolar edge of the body of the lower jaw is hollowed out with cavities, intended to receive the roots of the teeth. These cavities, called dental cavities, are in all similar, as a general disposition and as a number to the alveoli already described on the upper jaw.
The lower edge is thick, foamy, smooth. It presents, a little outside the median line, an oval surface, slightly depressed, the digastric fossa, on which is inserted the anterior belly of the digastric. It is not unusual to find on this edge, near its posterior extremity, a very marked gutter on certain subjects: it is the facial gutter of the maxillary, determined by the passage of the facial artery, at the moment when it leave the neck area to enter the area of the face.
The rising branches of the lower jaw are rectangular, higher than wide, obliquely directed, elongated from top to bottom, and they have two faces, one external, the other internal, and four edges.
- Face:
On both sides, one looks out (outer face), the other inside (inner face)
- External side:
We see in its lower part rough ridges, oblique bottom and back, on which are inserted the tendinous blades of the masseter. These roughnesses are especially marked in the lower part of this face.
- Internal side:
There are also rough, oblique ridges on the lower part of the inner side. They are determined by the insertion of the internal pterygoid muscle. At the middle part of this face is the entrance orifice of the inferior dental canal, into which the vessels and inferior dental nerves engage. The orifice of the dental canal is placed on the extension of the alveolar rim and responds in the middle of a led line of the tragus to the antero-inferior angle of the masseter. It is limited forward by an acute triangular projection, the spix spine or lingula mandibulae (species of triangular lamella), on which the sphenomaxillary ligament is inserted. At the back of the orifice of the dental canal, there is sometimes another projection, smaller than the previous one, the antilingula. It is at the orifice of the dental canal that the mylo-hyoid sulcus (or mylohyoidal groove), traversed in the fresh state, begins by the nerve and the mylo-hyoid vessels.
edges:
The four edges of the ascending branch of the lower maxillary are distinguished in anterior, posterior, superior and inferior:
- The front edge, oblique from top to bottom, and back to front. It is between two ridges or lips, one internal and the other external. The inner lip limits down, with the outer lip, a gutter that increases depth and width from top to bottom. Its lower end is in more or less direct continuity with the internal oblique line of the maxillary body. Above, the inner lip rises on the inner face of the ascending branch and the coronoid process forming a relief, the temporal crest.
It is seen in the gutter that at the bottom of the two lips of the anterior border there is an oblique ridge downwards and outwards; it is the buccal crest; it gives insertion to the whirlpool.
The two crests of the anterior border give insertion to tendinous bundles of the temporal muscle.
- The posterior border is also oblique at the bottom and in front. It is thick and foamy and describes a very elongated S curve. It is related to the parotid gland, hence the name of parotid edge under which it designates certain authors.
- The lower edge continues forward with the lower edge of the maxillary body; it forms back, when meeting with the posterior edge of the ascending branch, the angle of the jaw or gonion. It is often hollowed out in its anterior part of a transverse depression due to the passage of the facial artery. (The mandibular angle varies greatly according to age: very open in the newborn, where it measures from 150 ° to 160 °, it gradually fades as the subject develops. adult, it is only 115 ° to 125 °)
- The upper edge directed back and forth has two projections, one posterior, the condyle of the lower jaw, the other anterior, the coronoid process, separated from each other by a deep notch called sigmoid notch .
The condyle of the lower jaw is an oblong eminence, flattened in the anteroposterior direction, the long axis of which runs obliquely outwards inwards and a little before and backwards. It overflows much more on the inner side than on the outer side of the ascending branch of the lower jaw. It is known to have an upper face in the shape of a donkey, whose two anterior and posterior sides articulate with the temporal one. The posterior slope continues downwards with a triangular surface, the lower vertex merges with the upper end of the posterior edge of the ascending branch.
The condyle moreover in most cases, below its external end, a small roughness determined by the insertion of the lateral ligament external of the temporomaxillary joint. The condyle is connected to the ascending branch by a narrowed part, the neck of the condyle. It is dug, inside and in front, of a rough dimple where the external pterygoid muscle is inserted. On the inner side of the neck of the condyle, there is a projection, a kind of internal pillar of the condyle, formed by the internal lip of the insertion fossa of the external pterygoid and which extends downwards and forwards to the vicinity of Spix's spine.
The sigmoidal (or semi-lunar) notch, in the shape of a crescent with concavity directed upwards. It separates the two bone projections (and coronoid process) from each other and communicates the masseterin regions on the outer side of the maxillary branch and the zygomatic fossa on the other side. of the branch. It is by this notch that the nerves and the masseterine vessels pass.
The coronoid process gives insertion to the temporal muscle. It has the shape of a triangle whose summit, directed at the top, is smooth and whose base is one with the branch of the maxilla. From both edges, the anterior continues with the anterior edge of the branch, the posterior is directed obliquely towards the neck of the condyle forming the front slope of the sigmoidal notch.
The lower jaw is located at the lower and anterior part of the face. The lower maxilla or mandible is an odd and symmetrical bone, constituting alone the lower jaw. It is divided into three parts: a middle part, the body, and two lateral parts, the rising branches, which rise at the two posterior extremities of the body.
Body of the lower jaw:
The body of the maxillary is shaped like a horseshoe. It has a convex anterior surface, a concave posterior surface, an upper or alveolar edge and a free lower edge.
- Front side:
In its middle part, a vertical line, index of the weld of the two parts of the bone, the symphysis chin. The symphysis of the chin ends below on the summit of a triangular projection with a lower base, the chin eminence.
On each side of the chin, a protruding line is called the external oblique line, which goes backwards and upwards and continues with the outer lip of the anterior edge of the maxillary ramus. It gives insertion to the triangular muscles of the lips, square of the chin and platys.
Above the outer oblique line is the mental hole. This orifice is located equidistant from the two edges of the jaw and on a vertical passing sometimes between the two premolars, sometimes by one or other of these two teeth. It delivers passage to the vessels and the mental nerves.
- Posterior face:
The posterior surface of the maxillary body presents on the median part, and near the inferior border, four small superimposed projections called genital apophyses, two on the right, two on the left; they are the upper and lower apophyses. The superior genital processes give insertion to genio-glosses muscles; and the inferior ones, to the genio-hyoid muscles. Quite often, the lower genital apophyses, and sometimes even the four apophyses, are fused into one.
On the apophyses geni, on each side, a protruding line (a ridge), the internal oblique line or mylo-hyoid. The inner oblique line is worn up and back and terminates on the ascending branch of the lower jaw, forming the inner lip of its anterior border; it gives attachment to the mylo-hyoid muscle. Below it runs a narrow furrow, called the mylo-hyoid groove, where the vessels and nerve of the same name run.
The inner oblique line divides the posterior surface of the maxillary body into two parts. One, superior, excavated especially forward, higher forwards than behind, is called sublingual fossa; it is related to the sublingual gland. The other, lower, is higher behind than before; it is largely occupied by a depression, the submaxillary fossa, in relation to the submaxillary gland.
- edges:
The upper or alveolar edge of the body of the lower jaw is hollowed out with cavities, intended to receive the roots of the teeth. These cavities, called dental cavities, are in all similar, as a general disposition and as a number to the alveoli already described on the upper jaw.
The lower edge is thick, foamy, smooth. It presents, a little outside the median line, an oval surface, slightly depressed, the digastric fossa, on which is inserted the anterior belly of the digastric. It is not unusual to find on this edge, near its posterior extremity, a very marked gutter on certain subjects: it is the facial gutter of the maxillary, determined by the passage of the facial artery, at the moment when it leave the neck area to enter the area of the face.
The rising branches of the lower jaw are rectangular, higher than wide, obliquely directed, elongated from top to bottom, and they have two faces, one external, the other internal, and four edges.
- Face:
On both sides, one looks out (outer face), the other inside (inner face)
- External side:
We see in its lower part rough ridges, oblique bottom and back, on which are inserted the tendinous blades of the masseter. These roughnesses are especially marked in the lower part of this face.
- Internal side:
There are also rough, oblique ridges on the lower part of the inner side. They are determined by the insertion of the internal pterygoid muscle. At the middle part of this face is the entrance orifice of the inferior dental canal, into which the vessels and inferior dental nerves engage. The orifice of the dental canal is placed on the extension of the alveolar rim and responds in the middle of a led line of the tragus to the antero-inferior angle of the masseter. It is limited forward by an acute triangular projection, the spix spine or lingula mandibulae (species of triangular lamella), on which the sphenomaxillary ligament is inserted. At the back of the orifice of the dental canal, there is sometimes another projection, smaller than the previous one, the antilingula. It is at the orifice of the dental canal that the mylo-hyoid sulcus (or mylohyoidal groove), traversed in the fresh state, begins by the nerve and the mylo-hyoid vessels.
edges:
The four edges of the ascending branch of the lower maxillary are distinguished in anterior, posterior, superior and inferior:
- The front edge, oblique from top to bottom, and back to front. It is between two ridges or lips, one internal and the other external. The inner lip limits down, with the outer lip, a gutter that increases depth and width from top to bottom. Its lower end is in more or less direct continuity with the internal oblique line of the maxillary body. Above, the inner lip rises on the inner face of the ascending branch and the coronoid process forming a relief, the temporal crest.
It is seen in the gutter that at the bottom of the two lips of the anterior border there is an oblique ridge downwards and outwards; it is the buccal crest; it gives insertion to the whirlpool.
The two crests of the anterior border give insertion to tendinous bundles of the temporal muscle.
- The posterior border is also oblique at the bottom and in front. It is thick and foamy and describes a very elongated S curve. It is related to the parotid gland, hence the name of parotid edge under which it designates certain authors.
- The lower edge continues forward with the lower edge of the maxillary body; it forms back, when meeting with the posterior edge of the ascending branch, the angle of the jaw or gonion. It is often hollowed out in its anterior part of a transverse depression due to the passage of the facial artery. (The mandibular angle varies greatly according to age: very open in the newborn, where it measures from 150 ° to 160 °, it gradually fades as the subject develops. adult, it is only 115 ° to 125 °)
- The upper edge directed back and forth has two projections, one posterior, the condyle of the lower jaw, the other anterior, the coronoid process, separated from each other by a deep notch called sigmoid notch .
The condyle of the lower jaw is an oblong eminence, flattened in the anteroposterior direction, the long axis of which runs obliquely outwards inwards and a little before and backwards. It overflows much more on the inner side than on the outer side of the ascending branch of the lower jaw. It is known to have an upper face in the shape of a donkey, whose two anterior and posterior sides articulate with the temporal one. The posterior slope continues downwards with a triangular surface, the lower vertex merges with the upper end of the posterior edge of the ascending branch.
The condyle moreover in most cases, below its external end, a small roughness determined by the insertion of the lateral ligament external of the temporomaxillary joint. The condyle is connected to the ascending branch by a narrowed part, the neck of the condyle. It is dug, inside and in front, of a rough dimple where the external pterygoid muscle is inserted. On the inner side of the neck of the condyle, there is a projection, a kind of internal pillar of the condyle, formed by the internal lip of the insertion fossa of the external pterygoid and which extends downwards and forwards to the vicinity of Spix's spine.
The sigmoidal (or semi-lunar) notch, in the shape of a crescent with concavity directed upwards. It separates the two bone projections (and coronoid process) from each other and communicates the masseterin regions on the outer side of the maxillary branch and the zygomatic fossa on the other side. of the branch. It is by this notch that the nerves and the masseterine vessels pass.
The coronoid process gives insertion to the temporal muscle. It has the shape of a triangle whose summit, directed at the top, is smooth and whose base is one with the branch of the maxilla. From both edges, the anterior continues with the anterior edge of the branch, the posterior is directed obliquely towards the neck of the condyle forming the front slope of the sigmoidal notch.
Inner conformation of the lower dental canal:
The lower jaw gives us the general structure of all the flat bones: it is constituted by a central mass of spongy tissue, circumscribed, in all its extent, a remarkably thick and very resistant envelope of compact tissue. The central tissue itself is very dense and it is, so to speak, only in the vicinity of the dental canal that it truly deserves the name of spongy tissue.
At the level of the condyle, the peripheral shell of compact tissue becomes extremely thin. The bone projection is almost entirely composed of spongy tissue, the spans of which for the most part affect a vertical direction. This vertical direction is very clear at the neck. The coronoid process differs from the condyle in that it has only a thin layer of spongy tissue, enveloped by a very thick and dense layer of compact tissue.
Each half of the lower jaw is traversed in most of its extent by a long canal called the lower dental canal. This channel begins, at the top, on the internal face of the branch at a point near its center, immediately behind Spix's spine. From there, it moves obliquely downwards and forwards, approaches the horizontal reaching the roots of the teeth, and, having reached the height of the second premolar, divides into two branches, the outer one, the other internal: its external branch or chin channel, oblique upwards and outwards, comes to open on the external surface of the bone by the mental hole described above; its internal branch or incisal canal, continuing its course towards the symphysis, terminates below the roots of the incisive teeth. The lower dental canal is located 8 or 9 millimeters above the lower edge of the maxilla. Seen in section, it has the appearance of a circle or oval with a large vertical axis, placed in the spongy tissue of the bone: it measures, according to the subjects and according to the points where it is examined, 2 or 3 millimeters in diameter. From the upper wall are numerous ascending canaliculi, which terminate on the other hand in the alveolar cavities. In the fresh state, the dental canal is traversed by the nerve and the inferior dental vessels, and the aforementioned canaliculi give way to the collateral branches which this nerve and these vessels send to the roots of the teeth.
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