Characteristics of molars in adult teeth

Located in the distal premolar, responsible for chewing. Includes first, second and third maxillary molars, and the volume decreases from the first molar to the third molar. ?

Common features: (two copies and three copies)

1. Big Crown, shelter? Wide face.

2. There are many cusps, usually 4-5 cusps.

3. There are many developmental grooves and accessory grooves, as well as grooves leading to cheeks and tongue, which are convenient for self-occlusion of food when chewing? Surface overflow.

4. There are many roots, usually 2-3.

(a) maxillary first molar ()?

It appears in the oral cavity around 6 years old and is located in the distal part of the maxillary second molar, also known as the six-year-old tooth. It is the largest tooth in the maxillary molar, and the buccal and lingual diameter of the crown is >: occlusion? Root of gum. ?

1, crown?

(1) bite? Face: near, far and middle diameter: occlusion? Gum diameter, occlusion? The edge is longer than the neck edge, the neck edge line protrudes towards the root, the proximal edge is long and straight, and the distal edge is short. ?

2) sharp point, development slot?

① Two buccal tips can be seen, and the proximal buccal tip is slightly wider than the distal buccal tip. (The line connecting the mesial buccal tip and the distal buccal tip is approximately parallel to the neck edge line. )?

② The buccal axis ridge near the middle buccal apex is obvious. ?

③ There is buccal communication between the two tips, and a point gap is formed at the end. (From the middle to the distance, the buccal groove is roughly in the center. )

3) The high point of appearance is in the neck 1/3. ?

(3) Lingual surface:?

1) Appearance: Is it similar to or slightly smaller than cheeks?

2) sharp point, development slot?

① There are two tips of the tongue, the proximal tip is obviously wider than the distal tip, and the fifth tip occasionally appears on the lingual side of the proximal tip (the fifth tip has no occlusal function. There is a crescent-shaped groove between the tongue and the tip of the tongue (called the groove near the base of the tongue). ?

② There is a distal lingual groove between the two tips of the tongue extending to the lingual surface 1/2, and there is no point gap at the end. (Lingual sulcus is in the middle of the lingual surface)

3) The high point of the shape in the tongue surface is 1/3. ?

(4) Adjacent surface:?

1) quadrilateral with buccal tongue diameter >; Bite? The diameter of gum and the outline of buccal surface are slightly inclined to the lingual side in a straight line; The outline of the tongue surface is inclined to the buccal side, showing a convex curve. ?

2) Cheeks are sharp and sharp, the tip of the tongue is blunt, and the connecting line between the two tips of cheeks and tongue is roughly parallel to the neck edge line. ?

3) The proximal neck is flat and the contact area is in occlusion? The junction of cheek 1/3 and middle 1/3 (or occlusion? 1/3 buccal side). The distal face is slightly smaller, and the contact area is at its bite. The junction of 1/3 and tongue 1/3 near the middle (bite? In 1/3). ?

2. root?

There are three roots: mesial buccal root, distal buccal root and tongue root, among which the tongue root is the longest, the distal buccal root is short, the bifurcation between the two buccal roots is small, and the buccal root and tongue root are large. ?

3. medullary cavity?

Features: The pulp chamber is cubic, mainly located in the root column. There are four pulp angles at the top of the pulp chamber, and three or four root canals can be seen at the bottom of the pulp chamber, which communicate with the corresponding root canals. ?

(1) Buccal lingual side sectional view:?

It is a short cube with buccal tongue diameter >; Proximal, distal and middle diameter > height of medullary cavity is depressed at the top of medullary cavity, and the most depressed part is about flush with the neck edge. There are four pulp angles at the top of pulp chamber, the buccal pulp angle is higher than the lingual pulp angle, and the mesiobuccal pulp angle is higher than the distal pulp angle (mesiobuccal pulp angle is higher than the distal pulp angle, mesiobuccal pulp angle is the highest, and mesiolingual pulp angle is the second, both of which are close to 1/3 in the crown. The far buccal pulp angle and the far lingual pulp angle are lower, both located in the crown and neck. ) The pulp chamber floor is about 2mm below the neckline, and 3-4 root canals can be seen. The orifice of lingual root canal is round, and the lingual root canal is straight and long. The orifice of mesiobuccal root is narrow, and 63% of root canals are divided into buccal root canal and tongue root canal. Distal buccal root canal is slightly round with few branches, accounting for about 9%. ?

(2) Near-far-middle section:?

Buccal pulp angle is slightly higher than lingual pulp angle and sharper than lingual pulp angle; The mesiodistal pulp angle is higher than the distal pulp angle, and the lingual root canal is thicker and longer than the buccal root canal. The mesiobuccal root is a double-tube type or a single-tube mixed type. Distal buccal roots are rarely divided into double canals. ?

(3) Tooth neck cross section:?

It is quadrangular or triangular, and the buccal tongue diameter is larger than the proximal and distal middle diameter. There are 3 ~ 4 root canal orifices at the pulp chamber floor, and the lingual root canal orifice is the largest and round. The distal buccal root canal orifice is small and round, which is located on the far lingual side of the proximal buccal root canal. The mesiobuccal root canal orifice is narrow and long, and sometimes the buccal tongue faces two root canal orifices. ?

(2) Maxillary second molar ()?

Similar to twelve-year-old teeth, but smaller in size. Narrow. The buccal and lingual diameter of the crown is obviously smaller than the proximal and distal median diameter, and the whole tooth is round.

1. Crown:

2. Quadrangular type:

(1) bite? Face:

1) Oblique is more obvious, with mesial occlusion? Is the marginal ridge longer than the distal occlusion? Marginal ridge, buccal occlusion? Marginal crest and lingual occlusion? The edge ridges are equal in length.

2) Oblique crest, buccal sulcus and distal lingual sulcus are not so obvious, but partially cross. Is the buccal groove in the far position?

3) The height difference between the proximal end and the distal end on the buccal side and lingual side is quite large. (The buccal side is more obvious than the lingual side)

4) The buccal tip of the tongue is closer, so the inherent occlusal surface becomes narrower. ?

(2) Buccal surface: the appearance is rectangular, and the near-middle buccal tip is obviously larger than the far-middle buccal tip (the far-middle buccal tip is obviously reduced). The distal buccal apex is obviously inclined to the distal lingual side, and the mesiobuccal axis ridge is far away from the mesiobuccal axis ridge, with buccal groove. The spread formed is not as obvious as expected. From the buccal side, the angle between the crown and the proximal edge of the root is close to 180 degrees. ?

(3) Tongue surface: it is large near the middle of the tip of the tongue and small in the distance. ?

(4) Adjacent surface: similar, near middle surface >; Far-middle surface. ?

Tricuspid valve type: three types?

(1) The tip of the tongue has degenerated and still occupies a small position on its lingual side. ?

(2) Distal tip degeneration only occupies a small position on the lingual side. ?

(3) Complete degeneration of the distal tip of the tongue: tricuspid valve (no oblique ridge).

Oblique ridge is unclear or disappeared, the shape and distribution of central fossa and development groove are irregular, and accessory grooves are mostly. ?

2. Roots: three, the roots are long, the roots are relatively close, smaller than the root bifurcation, and the whole roots are inclined to the distal end. The shape of the horizontal section of the tooth neck is short and round at the distal and lingual sides. ?

3. medullary cavity?

There are three types:

The first type: the crown is similar to the first molar, but the distal tip is smaller. The shape of pulp cavity is similar, but smaller. 38% of buccal root canal is divided into buccal root and tongue root. ?

The second type: the tip of the tongue is very small in the distance, located in the corner of the distance. The shape of the crown pulp chamber is the same as that of the crown, and the shape of the root canal is similar to the first one. ?

The third type: tricuspid valve with the tip of the tongue disappearing in the far middle. The shape of the crown pulp chamber is the same as that of the crown, and the shape of the root canal is similar to the first one. ?

③ Maxillary third molar ()?

There are many changes in the shape, size and position of teeth, and their standard shapes are all similar (four-pointed type)?

1. Features:?

(1) bite? There are many accessory grooves on the face, and the sharp ridges are unclear. ?

(2) Most of the roots merge into a cone root, and there are also many branched roots, and the number and shape of the roots vary greatly. ?

2. What is the shape of the pulp cavity of the maxillary third molar?

The pulp cavity changes greatly, but it also has its own characteristics, which are mainly manifested in large pulp cavity, thick root canal and low pulp angle. ?

(4) Mandibular first molar ()?

It is the largest mandibular molar, with the proximal, distal and middle diameter of the crown >: buccal and lingual diameter >; Bite? Gum diameter?

1. Crown?

(1) bite? Face: Rectangular, with the proximal-distal middle diameter larger than the buccal-lingual diameter, and the inherent occlusal surface close to the lingual side.

1)? Edge ridge:

Buccal occlusion? Is the marginal ridge longer than the lingual occlusion? Marginal crest, mesial occlusion? The marginal ridge is long and straight, with distal occlusion? The marginal ridge is short and prominent (the lingual edge line is straight? The buccal border line is convex and curved. )

2)? Tip:

It can be seen that the five tips, the buccal tip is short and round, the tip of the tongue is long and sharp, and the distal tip is the smallest, and the distal tip is located at the junction of the buccal surface and the distal surface. ?

The order of cusp height is: ① proximal cusp ② distal cusp ③ proximal buccal cusp ④ distal buccal cusp ⑤ distal cusp; The order of cusp size is as follows: ① near buccal apex; ② far buccal apex; ③ near apical apex; ④ far apical apex; ⑤ far apical apex. ?

3) Triangular crest:?

The triangular ridge at the distal buccal tip is the longest and the triangular ridge at the distal buccal tip is the shortest. (The triangular ridge on the tip of the tongue is obvious, and the tip of the cheek is round and blunt. )

4) Point gap, nest and development ditch?

Bite? There are two nests on the surface?

Central fossa: large, located in occlusion? Triangular ridge of distal cusp, distal marginal ridge near the second face. The central fossa is located in the center of buccal and lingual direction near the lingual side.

Proximal fossa: small, triangular, on the inner side of the mesial marginal ridge.

Point notch: 3 notches, namely, center notch, far notch and near notch. ?

Development sulcus: 5 sulcus, namely buccal sulcus, lingual sulcus and lingual sulcus. The proximal sulcus, distal sulcus and distal buccal sulcus are distributed in a "big" shape. There are also many ancillary ditches. ?

Buccal sulcus: It extends from the midpoint space to the buccal side and passes between the near buccal tip and the far buccal tip to the buccal surface. ?

Lingual groove: from the middle point gap to the tongue surface through the two gaps of the tip of the tongue. ?

Proximal sulcus: extending from the midpoint gap to the mesial, ending in mesial occlusion? In the marginal ridge. ?

Distal sulcus: extending from the central point gap to the distal end and ending in distal occlusion? In the marginal ridge. ?

Distal buccal sulcus: starting from the distal midpoint gap, passing between the distal buccal tip and the distal buccal tip to the buccal surface. ?

5) Bevel: Does the tongue bevel of the tip of the tongue bite the opposite tooth? There is no occlusal contact between the teeth, and the slopes of the other teeth are occlusal? There is occlusal contact. ?

(2) cheeks?

1) shape: trapezoidal, with nearly medium length and diameter >; Bite? Gum diameter, occlusal surface? The margin is longer than the collar. The edge line of the neck protrudes to the root. The mesial edge is straight and the distal edge is prominent. ?

2) Cusp and development groove: two buccal processes and some distal cusps can be seen on the buccal surface, the volume and height of the three cusps decrease in turn, and the buccal groove and the distal buccal groove communicate between the cusps, forming a point gap at the end of the buccal groove. (The buccal groove is slightly proximal to the distal part, straight to the neck of the tooth, and the buccal groove in the distal part is in the proximal and distal part, oblique to the proximal and distal part. )?

3) The high point of appearance is at the ridge of buccal neck (neck 1/3)?

4) The line connecting the proximal tip and the distal tip is approximately parallel to the neck edge line.

(3) lingual surface?

1) shape, like cheeks, smaller than cheeks, slightly round. ?

2) sharp point, development slot?

It can be seen that the two tips of the tip of the tongue, the proximal tip and the distal tip, are slightly larger than the distal tip of the tongue, and there is a tongue groove between the two tips. (Lingual sulcus is slightly near the middle of mesial direction. )?

3) The high point of contour line is in the middle 1/3. ?

(4) Adjacent surface:?

1) Appearance: quadrangle, neck angle near the middle cheek, tongue biting? Sharp angle, the tip of the tongue is higher and sharper than the tip of the cheek. The line between the neck edge line and the buccal tip of the tongue is roughly parallel. ?

2)? Is the mesial contact area mostly in occlusion? 1/3 on the buccal side. ?

3) The distal intermediate surface is smaller than the proximal intermediate surface. Is the tip of the tongue sharp and the cheek sharp and blunt?

Is the distal contact area in occlusion? The junction of 1/3 and the middle 1/3 is also the cheek. ?

2. root?

Double roots, flat and thick, with short forks. The mesial root is slightly larger than the distal root, and has a root surface groove. 20% of the distal root is divided into two roots: buccal root and lingual root. There are also two "horseshoe roots" that are partially fused on the buccal side and still bifurcate on the lingual side. ?

3. medullary cavity?

Features: Similar to maxillary molars, but with 5 pulp angles, 2-4 root canals can be seen at the pulp chamber floor. ?

(1) buccolingual section:?

It is a short cube, the diameter of pulp chamber near buccal tongue is larger than that of distal buccal tongue, and the lingual pulp angle is larger than that of buccal pulp angle. 95% of the mesial root is divided into two small root canals in the buccal and lingual direction, and most of them have two apical foramens. Sometimes buccal and lingual root canals meet the root tips at 1/3, and an apical foramen leads to the periodontal area. Most of the distal root canals are wide single canals, and about 46% of the root canals are divided into buccal and lingual root canals, usually two apical foramens. ?

(2) Near, far and middle section:?

Proximal-distal median diameter of pulp chamber >: buccal-lingual diameter, with five pulp angles, the proximal pulp angle is higher than the distal pulp angle, and the proximal pulp angle is the highest. The crest of the medullary cavity and the bottom of the medullary cavity both protrude to the medullary cavity, and the most protruding part of the medullary cavity is about flush with the cervical margin. The pulp chamber floor is 2mm below the neck edge, and the distance between the top and bottom of pulp chamber is generally 2? Below mm, the pulp chamber bottom is 2mm away from the root bifurcation. The mesial root canal is small (87% is double-tube or single-tube mixed type). 40% of distal root canals are double-tube or single-tube mixed type). ?

(3) Tooth neck cross section:?

Proximal-distal median diameter of dental pulp cavity >: buccal-lingual diameter, and buccal-lingual diameter of proximal pulp cavity is larger than that of distal pulp cavity. ?

(5) Mandibular second molar ()?

Volume less than

There are two types:

Five-pointed star type: similar, difficult to distinguish in isolated teeth?

Four-pointed type: different from that, there are four points, the distal middle point disappears, the proximal and distal middle diameters are almost the same, and the buccal and lingual diameters are relatively symmetrical.

1, crown: obvious degeneration tendency, round overall.

(1) bite? Face:

1)? Shape: square and round?

2)? Sharp: there are four sharp points, and the tip of the tongue near the middle cheek is often larger than the tip of the tongue far from the middle cheek. (The tip of the tongue moves closer to the center of the occlusal surface, and the inherent occlusal surface becomes smaller. ? )

3) Central fossa: located in occlusion? The center of the face. ?

4) There are four developmental sulcus, which are distributed in an a+ shape, namely buccal sulcus, lingual sulcus, mesial sulcus and distal sulcus, and auxiliary sulcus are distributed on both sides of the developmental sulcus. The whole occlusion? The face looks like a field, which is the characteristic of this tooth. ?

(2) cheeks?

1) shape: trapezoid? The proximal middle edge is straight and the distal middle edge is protruding. ?

The neckline is flat. (The inclination of the neck edge line increases from near middle to far middle)

2) sharp point, development slot:?

You can see that there are two buccal tips, and there is a buccal groove between them and a gap at the end. (The buccal sulcus is in the center of mesial direction. )

3) The high point appears at the neck 1/3, and sometimes the buccal-cervical ridge at the buccal neck 1/3 is obviously prominent (characteristic). ?

(3) Lingual surface:?

1) Appearance: same, similar in size to cheeks. (Lingual sulcus is in the center of proximal and distal direction. )

2) sharp point, development slot:?

There are two tips of the tongue with a groove in the middle. ?

(4) Adjacent surfaces: the height of the buccal tip is not much different, and the inclination of the neck edge line from buccal side to lingual side is small.

2. Roots: proximal roots and distal roots. The degree of bifurcation between the two roots is less than that, and both roots are distal, sometimes converging into a cone. ?

3, medullary cavity:?

The pulp chamber depends on the shape of the crown, one is four corners and the other is five corners, so there can be four or five pulp angles respectively. Similarly, 64% of the mesial root canals are double-tube or single-tube mixed. Distal and middle root canals are mostly single canals. ?

(6) Mandibular third molar ()?

The shape, size and position of teeth can vary. Like a five-pointed star, like a four-cornered man. ?

1, function:

(1) bite? Facial convergence and contraction

(2) The sharp ridge is not obvious, and there are many accessory grooves.

(3) Roots often merge into cones, and some diverge into multiple roots. ?

2. medullary cavity?

Large variation, large pulp chamber and root canal. ?

(7) the difference between upper and lower molars