Prof. A. El-sahn (9)

The premolars are so named because they are situated in front of the permanent molars. The premolars are so named because they are situated in front of the permanent molars. They replace the deciduous molars, so they are succedaneum teeth (no premolars in the deciduous dentition). They replace the deciduous molars, so they are succedaneum teeth (no premolars in the deciduous dentition). Prof. A. El- Sahn GENERAL CHARACTERISTICS GENERAL CHARACTERISTICS

They have usually two cusps, buccal and lingual, so they are called bicuspid. They have usually two cusps, buccal and lingual, so they are called bicuspid. B BB B L L L L This term, which is widely used, is misleading, since mandibular premolars may show a variation in the number of cusps from one to three. This term, which is widely used, is misleading, since mandibular premolars may show a variation in the number of cusps from one to three. B L Prof. A. El- Sahn

The lingual cusp developed from the lingual lobe, which is represented by the cingulum in anterior teeth. The lingual cusp developed from the lingual lobe, which is represented by the cingulum in anterior teeth. Prof. A. El- Sahn The middle buccal lobe of the premolars is highly developed. The middle buccal lobe of the premolars is highly developed. They are developed from four lobes as anterior teeth, three buccal and one lingual except the lower second premolar, which may develop from five lobes. They are developed from four lobes as anterior teeth, three buccal and one lingual except the lower second premolar, which may develop from five lobes. It corresponds to the middle labial lobe of the canine.

The premolars differ from the anterior teeth in the following: a)The premolars are wider bucco- lingually than mesio-distally. b) They have occlusal surfaces with well-developed cusps instead of incisal edges. Prof. A. El- Sahn DM L L M B B D

c)Their marginal ridges are part of the occlusal surface and are oriented nearly in a horizontal plane instead of vertically as in anterior teeth. d)Their crown and roots are shorter than those of the maxillary canines. d)Their crown and roots are shorter than those of the maxillary canines. Prof. A. El- Sahn

e)The contact areas of premolars (and molars) are nearly at the same level, broad and are more cervically than those for anterior teeth. Prof. A. El- Sahn

g)Their cervical line is less curved proximally. f)Proximally, the crests of curvatures of both buccal and lingual surfaces of the crown are more occlusal than the corresponding crests of curvature in anterior teeth. Prof. A. El- Sahn BBLL

The premolars assist the canines in tearing of food by the sharp cusp tips of first premolars and assist the molars in mastication of food. The premolars assist the canines in tearing of food by the sharp cusp tips of first premolars and assist the molars in mastication of food. The premolars function with molars in maintaining the vertical dimension of the face. The premolars function with molars in maintaining the vertical dimension of the face. They support the corners of the mouth and cheeks to keep them from sagging. They support the corners of the mouth and cheeks to keep them from sagging. Prof. A. El- Sahn FUNCTION OF PREMOLARS PM

MAXILLARY PREMOLARS Prof. A. El- Sahn first second

There are four maxillary (upper) premolars: two in each side of the maxillae; the first and the second. There are four maxillary (upper) premolars: two in each side of the maxillae; the first and the second. The first and second upper premolars are posterior to the upper canines. The first and second upper premolars are posterior to the upper canines. Prof. A. El- Sahn

The maxillary first and second premolars are more alike than the mandibular premolars. The maxillary first and second premolars are more alike than the mandibular premolars. Prof. A. El- Sahn second first first maxillary mandibular second

The maxillary first premolar is larger than the second premolar, unlike the mandibular premolars. The maxillary first premolar is larger than the second premolar, unlike the mandibular premolars. Prof. A. El- Sahn

The maxillary first premolar has a longer crown and a shorter root than the second premolar. The maxillary first premolar has a longer crown and a shorter root than the second premolar. Prof. A. El- Sahn first first

The cusps of maxillary and mandibular first premolars are more sharp than the second premolars. The cusps of maxillary and mandibular first premolars are more sharp than the second premolars. Prof. A. El- Sahn Mand. first MAX. first

MAXILLARY FIRST PREMOLAR Prof. A. El- Sahn

The maxillary first premolar is the fourth tooth from the midline. The maxillary first premolar is the fourth tooth from the midline. Its mesial side is in contact with the distal side of the adjacent canine. Its mesial side is in contact with the distal side of the adjacent canine. Prof. A. El- Sahn

It has a mesial depression extending from the root area to the cervical half of the crown, which is called the "canine fossa". It has a mesial depression extending from the root area to the cervical half of the crown, which is called the "canine fossa". Prof. A. El- Sahn D M M

Its crown is angular with prominent buccal line angles. Its crown is angular with prominent buccal line angles. L B D M

Prof. A. El- Sahn Maxillary first premolar has two well-formed roots in about 60% - 61% of the cases, a buccal and a lingual root. Maxillary first premolar has two well-formed roots in about 60% - 61% of the cases, a buccal and a lingual root.

Initial Calcification 18 – 21 months after birth Completion of Crown 5 – 6 years Eruption 10 – 11 years Completion of Root 12 – 13 years CHRONOLOGY Prof. A. El- Sahn

BUCCAL ASPECT The Crown Its geometric outline is roughly trapezoidal with the smallest of the uneven sides is cervically. Prof. A. El- Sahn

Mesial outline is slightly concave from the cervical line to the mesial contact area. Distal outline is nearly straight from the cervical line to the distal contact areas. BUCCAL ASPECT Prof. A. El- Sahn DM

The junction of mesial and distal surfaces and cusp slopes is more broad, bulging and angular, and more than the second premolars. The junction of mesial and distal surfaces and cusp slopes is more broad, bulging and angular, and more than the second premolars.

Mesial: Is relatively broad. It is usually in the middle third just cervical to the junction of the occlusal and middle thirds. Prof. A. El- Sahn Contact Areas Distal: Is broader than the mesial contact area. It is in the middle third, slightly more cervically than the mesial contact area. The two contact areas are nearly at the same level more than those found on anterior teeth.

Occlusal Outline The tip of the buccal cusp is slightly distal to the vertical axis of the tooth because its mesial slope is longer than the distal slope. The tip of the buccal cusp is slightly distal to the vertical axis of the tooth because its mesial slope is longer than the distal slope. Prof. A. El- Sahn D

The mesial slope is nearly straight or slightly concave, and is sometimes notched, while the distal slope is convex. The mesial slope is nearly straight or slightly concave, and is sometimes notched, while the distal slope is convex. This is the only tooth, considering canine and other premolars, on which mesial cusp slope is longer than the distal slope. This is the only tooth, considering canine and other premolars, on which mesial cusp slope is longer than the distal slope. Prof. A. El- Sahn D M

The buccal cusp is relatively long, and pointed, and resembles that of maxillary canine. The buccal cusp is relatively long, and pointed, and resembles that of maxillary canine. Prof. A. El- Sahn

Cervical Line It shows little curvature towards the root. It shows little curvature towards the root. Prof. A. El- Sahn

This ridge is due to strong development of the middle lobe. This ridge is due to strong development of the middle lobe. Morphology of the buccal surface The buccal surface is convex. The buccal surface is convex. Prof. A. El- Sahn There is prominent elevation in the middle of the crown running from the cusp tip to the cervical margin, it is called the buccal ridge. There is prominent elevation in the middle of the crown running from the cusp tip to the cervical margin, it is called the buccal ridge.

The one on the mesial side is deeper. The one on the mesial side is deeper. Two shallow vertical developmental depressions mesial and distal to the buccal ridge (B.R.). Two shallow vertical developmental depressions mesial and distal to the buccal ridge (B.R.). Prof. A. El- Sahn The mesio-buccal and disto- buccal line angles are prominent. The mesio-buccal and disto- buccal line angles are prominent. The cervical ridge ( C.R.) occupies the cervical third of the buccal surface.. The cervical ridge ( C.R.) occupies the cervical third of the buccal surface.. C. R. B. R. DM D.DM.D.

It is conical in form with pointed apex. It is conical in form with pointed apex. Its apical third may curve distally and sometimes curve mesially. Its apical third may curve distally and sometimes curve mesially. Its buccal surface is convex. Its buccal surface is convex. Prof. A. El- Sahn D D D M M M The Root

The crown is a little narrower lingually than buccally because of the lingual convergence of the proximal sides. The crown is a little narrower lingually than buccally because of the lingual convergence of the proximal sides. The mesial and distal outlines of the lingual portion of the crown are convex. The mesial and distal outlines of the lingual portion of the crown are convex. The Lingual Aspect Prof. A. El- Sahn The Crown

Occlusal Outline The lingual cusp is shorter than the buccal cusp by about 1 mm. The lingual cusp is shorter than the buccal cusp by about 1 mm. The mesial and distal slopes of the lingual cusp meet at the cusp tip at a somewhat rounded angle but is still a sharp cusp compared The mesial and distal slopes of the lingual cusp meet at the cusp tip at a somewhat rounded angle but is still a sharp cusp compared to the molars. to the molars. Prof. A. El- Sahn -1 mm.

The slopes of the lingual cusp are continuous with the convex proximal outlines of the crown lingually. The slopes of the lingual cusp are continuous with the convex proximal outlines of the crown lingually. Prof. A. El- Sahn DM The lingual surface is convex in all directions. The lingual surface is convex in all directions. The mesial slope is shorter than the distal and the cusp tip is mesial to the buccal cusp tip. The mesial slope is shorter than the distal and the cusp tip is mesial to the buccal cusp tip.

Cervical Line It shows slight curvature towards the root. It shows slight curvature towards the root. Prof. A. El- Sahn

The lingual portion of the root (if the tooth is single rooted) or the lingual surface of the lingual root (if two roots are present) is convex and narrower mesio-distally than the buccal portion. The lingual portion of the root (if the tooth is single rooted) or the lingual surface of the lingual root (if two roots are present) is convex and narrower mesio-distally than the buccal portion. The Root The lingual root (if two roots are present) is shorter than the buccal root by about 0.8 mm. The lingual root (if two roots are present) is shorter than the buccal root by about 0.8 mm. L Prof. A. El- Sahn 0.8 mm. B

The apex of the lingual root tends to be more blunt than the buccal root apex. The apex of the lingual root tends to be more blunt than the buccal root apex. The apical end of the lingual root may bend mesially or distally. The apical end of the lingual root may bend mesially or distally. The Root ( cont.) Prof. A. El- Sahn

Cont. will be … next Wednesday !!!.

Geometrically, the crown is roughly trapezoidal with the small uneven side occlusally. Geometrically, the crown is roughly trapezoidal with the small uneven side occlusally. The Mesial Aspect Prof. A. El- Sahn The Crown

The buccal cusp tip is directly below the center of the buccal root (in two- rooted tooth),and is nearer the center of the root trunk than is the lingual cusp. The buccal cusp tip is directly below the center of the buccal root (in two- rooted tooth),and is nearer the center of the root trunk than is the lingual cusp. Prof. A. El- Sahn +1 mm. LB The buccal and lingual cusps are long and sharp. The buccal and lingual cusps are long and sharp. The buccal cusp is longer than the lingual cusp by about 1 mm. The buccal cusp is longer than the lingual cusp by about 1 mm.

Buccal Outline Is convex from the cervical line to the tip of the buccal cusp. Is convex from the cervical line to the tip of the buccal cusp. The crest of curvature is usually at the junction of the middle and cervical third (or it may be located within the cervical third) making the cervical ridge. The crest of curvature is usually at the junction of the middle and cervical third (or it may be located within the cervical third) making the cervical ridge. Prof. A. El- Sahn L B

Lingual Outline Is smoothly convex line from the cervical line to the tip of the lingual cusp. Is smoothly convex line from the cervical line to the tip of the lingual cusp. The crest of curvature is usually at the center of the middle third. The crest of curvature is usually at the center of the middle third. Prof. A. El- Sahn L

The tip of the lingual cusp may be on a line with the lingual border of the lingual root. The tip of the lingual cusp may be on a line with the lingual border of the lingual root. As in all posterior teeth, the distance between the tips of the buccal and lingual cusps is less than the bucco-lingual measurement at the cervix. As in all posterior teeth, the distance between the tips of the buccal and lingual cusps is less than the bucco-lingual measurement at the cervix. Prof. A. El- Sahn L B

Both cusp tips are located well within the boundary of the root contour. Both cusp tips are located well within the boundary of the root contour. Prof. A. El- Sahn This is an important relationship for good support for large chewing area. This is an important relationship for good support for large chewing area.

It is more occlusally positioned than the distal marginal ridge. It is more occlusally positioned than the distal marginal ridge. The mesial marginal ridge is horizontally concave from buccal to lingual and forms the occlusal border of the mesial surface. The mesial marginal ridge is horizontally concave from buccal to lingual and forms the occlusal border of the mesial surface. Prof. A. El- Sahn The mesial marginal ridge is at about the level of the junction of the middle and occlusal thirds. The mesial marginal ridge is at about the level of the junction of the middle and occlusal thirds. Distal aspect

The mesial marginal ridge is usually crossed by a developmental groove. The mesial marginal ridge is usually crossed by a developmental groove. Prof. A. El- Sahn This marginal ridge developmental groove crosses the marginal ridge immediately lingual to the mesial contact area and extends for a short distance on the mesial surface. This marginal ridge developmental groove crosses the marginal ridge immediately lingual to the mesial contact area and extends for a short distance on the mesial surface. LB

Prof. A. El- Sahn This groove is continuous with the central groove of the occlusal surface. This groove is continuous with the central groove of the occlusal surface. The marginal ridge groove serves as a spillway for food during mastication The marginal ridge groove serves as a spillway for food during mastication

Cervical Line It slightly curves occlusally in a curvature averaging about 1 mm. It slightly curves occlusally in a curvature averaging about 1 mm. Prof. A. El- Sahn

Morphology Of The Mesial Surface On the mesial surface of the crown a mesial developmental depression is found. On the mesial surface of the crown a mesial developmental depression is found. This depression is cervical to the mesial contact area and is centered on the mesial surface between the two mesial line angles. This depression is cervical to the mesial contact area and is centered on the mesial surface between the two mesial line angles. Prof. A. El- Sahn

This depression is continuous with the developmental depression on the mesial surface of the root (or root trunk) forming what is sometimes called "canine fossa". This depression is continuous with the developmental depression on the mesial surface of the root (or root trunk) forming what is sometimes called "canine fossa". Prof. A. El- Sahn canine fossa This depression is a distinguishing feature of the maxillary first premolar, which is not found on any other premolar.

The Mesial Contact Area It is relatively broad. It is relatively broad. It lies in the middle third just cervical to the junction of the occlusal and middle thirds. It lies in the middle third just cervical to the junction of the occlusal and middle thirds. Bucco-lingually, it lies buccal to the junction of the buccal and middle thirds. Bucco-lingually, it lies buccal to the junction of the buccal and middle thirds. Prof. A. El- Sahn LB O C

Most maxillary first premolars have two roots (about 61%), one buccal and one lingual which are distinguishing characteristic of this tooth. Most maxillary first premolars have two roots (about 61%), one buccal and one lingual which are distinguishing characteristic of this tooth. The Root Prof. A. El- Sahn BBLL

In the two-rooted type The root trunk is long in this tooth, making up about half of the tooth length. The root trunk is long in this tooth, making up about half of the tooth length. The bifurcation mesially begins at a more occlusal point than distally. The bifurcation mesially begins at a more occlusal point than distally. Prof. A. El- Sahn

The mesial surface of the roots is smoothly convex. The mesial surface of the roots is smoothly convex. Prof. A. El- Sahn The root trunk shows a deep developmental depression on its mesial surface, at or below the bifurcation, which is continuous with the mesial depression on the crown. The root trunk shows a deep developmental depression on its mesial surface, at or below the bifurcation, which is continuous with the mesial depression on the crown.

In single-rooted teeth (about 38%), the relatively straight buccal and lingual outlines of the root end in a blunt apex above the center of the crown. (about 38%), the relatively straight buccal and lingual outlines of the root end in a blunt apex above the center of the crown. The mesial surface of the root portion is convex buccally and lingually with prominent developmental depression for most of the root length. The mesial surface of the root portion is convex buccally and lingually with prominent developmental depression for most of the root length. Prof. A. El- Sahn

Distal Aspect The distal aspect of this tooth is similar to its mesial aspect, with the following differences: Prof. A. El- Sahn The Crown The distal surface is convex except for a small flat area just cervical to the contact area and buccal to the center of the distal surface. The distal surface is convex except for a small flat area just cervical to the contact area and buccal to the center of the distal surface.

There is no deep developmental groove crossing the distal marginal ridge. If a groove is found, it is shallow and insignificant. There is no deep developmental groove crossing the distal marginal ridge. If a groove is found, it is shallow and insignificant. Prof. A. El- Sahn The distal contact area is slightly buccal to the mesial contact area. The distal contact area is broader than the mesial one. The distal contact area is slightly buccal to the mesial contact area. The distal contact area is broader than the mesial one. The cervical line is less curved on the distal than on the mesial surface. The cervical line is less curved on the distal than on the mesial surface. The distal marginal ridge is slightly more cervically than the mesial one. The distal marginal ridge is slightly more cervically than the mesial one.

The bifurcation of the roots is near the apical third, so the root trunk is longer distally and the divided part of the root is shorter (about the apical third) than mesially. The bifurcation of the roots is near the apical third, so the root trunk is longer distally and the divided part of the root is shorter (about the apical third) than mesially. Prof. A. El- Sahn The Root D D M M

On the middle third of the root trunk or root (on both double - and single - rooted teeth) there is a depression less deep than those on the mesial side. On the middle third of the root trunk or root (on both double - and single - rooted teeth) there is a depression less deep than those on the mesial side. Prof. A. El- Sahn The distal surface of the root near the cervix is usually convex or flat. The distal surface of the root near the cervix is usually convex or flat.

Occlusal Aspect The geometric outline of the occlusal surface is roughly hexagonal (six-sided). The geometric outline of the occlusal surface is roughly hexagonal (six-sided). The six sides are made up of two buccal, two lingual and two proximal sides. The six sides are made up of two buccal, two lingual and two proximal sides. Prof. A. El- Sahn D M L B

than the distal side and the mesio-lingual side is shorter than the disto-lingual side. than the distal side and the mesio-lingual side is shorter than the disto-lingual side. The two buccal sides (mesio-buccal and disto- buccal) are nearly equal, the mesial side is shorter The two buccal sides (mesio-buccal and disto- buccal) are nearly equal, the mesial side is shorter Prof. A. El- Sahn D M L B The bucco-lingual dimension of the crown is much greater than the mesio-distal The bucco-lingual dimension of the crown is much greater than the mesio-distal The rounded hexagonal shape is not equilateral. The rounded hexagonal shape is not equilateral. The crown is wider on the buccal than on the lingual due to lingual convergence of the proximal sides. The crown is wider on the buccal than on the lingual due to lingual convergence of the proximal sides. dimension. dimension.

Both the buccal and lingual cusps have mesial and distal cusp ridges (or slopes) which meet at the cusp tip and merge with the marginal ridges. Both the buccal and lingual cusps have mesial and distal cusp ridges (or slopes) which meet at the cusp tip and merge with the marginal ridges. Prof. A. El- Sahn L B MD The lingual cusp ridges are curved, forming a semi-circular outline, and the crest of curvature is at the tip of the lingual cusp, which is mesially placed in relation to the buccal cusp. The lingual cusp ridges are curved, forming a semi-circular outline, and the crest of curvature is at the tip of the lingual cusp, which is mesially placed in relation to the buccal cusp.

The two cusps are sharper than those of the maxillary second premolar and the buccal cusp is larger than the lingual. The two cusps are sharper than those of the maxillary second premolar and the buccal cusp is larger than the lingual. Prof. A. El- Sahn Buccal and lingual triangular ridges extend from the buccal and lingual cusp tips respectively to the central developmental groove. Buccal and lingual triangular ridges extend from the buccal and lingual cusp tips respectively to the central developmental groove. maxillary second The buccal triangular ridge is more prominent than the lingual triangular ridge. The buccal triangular ridge is more prominent than the lingual triangular ridge. MD L B

The mesial marginal ridge is shorter bucco-lingually than the more convex distal marginal ridge, and is usually crossed by the mesial marginal ridge groove. The mesial marginal ridge is shorter bucco-lingually than the more convex distal marginal ridge, and is usually crossed by the mesial marginal ridge groove. Prof. A. El- Sahn DM L L B B Marginal ridges: Central developmental groove: The central developmental groove runs across the central part of the occlusal surface. The central developmental groove runs across the central part of the occlusal surface. This groove is longer than that of the maxillary second PM. This groove is longer than that of the maxillary second PM.

The central groove ends mesially and distally in-pits in the mesial and distal triangular fossa, where it meets the supplemental grooves of the fossae. The central groove ends mesially and distally in-pits in the mesial and distal triangular fossa, where it meets the supplemental grooves of the fossae. Prof. A. El- Sahn DM The mesial marginal groove connects the central developmental groove in the mesial triangular fossa and is considered a mesial extension of that groove. The mesial marginal groove connects the central developmental groove in the mesial triangular fossa and is considered a mesial extension of that groove.

Triangular Fossae There are two triangular depressions or fossae just distal and mesial to the mesial and distal marginal ridges, which form their bases. There are two triangular depressions or fossae just distal and mesial to the mesial and distal marginal ridges, which form their bases. Prof. A. El- Sahn DM The Mesial Triangular Fossa : Is slightly smaller and less deep than the distal one. Is slightly smaller and less deep than the distal one.

In this fossa (M), the mesial end of the central groove meets two collateral supplemental grooves, which are called the mesio- buccal and mesio-lingual supplemental grooves. In this fossa (M), the mesial end of the central groove meets two collateral supplemental grooves, which are called the mesio- buccal and mesio-lingual supplemental grooves. The point of union is called the mesial developmental pit. The point of union is called the mesial developmental pit. Prof. A. El- Sahn D M ML MB B L

The Distal Triangular Fossa: Is just mesial to the distal marginal ridge. Is just mesial to the distal marginal ridge. In this fossa the central developmental groove meets its two collateral supplemental grooves at the distal developmental pit. In this fossa the central developmental groove meets its two collateral supplemental grooves at the distal developmental pit. Prof. A. El- Sahn D M The disto-lingual supplemental groove of the distal triangular fossa is very short. The disto-lingual supplemental groove of the distal triangular fossa is very short. The distal marginal ridge may be crossed by a marginal groove similar to that of the mesial marginal ridge. The distal marginal ridge may be crossed by a marginal groove similar to that of the mesial marginal ridge.

Contact areas from the occlusal aspect Mesial contact area is buccal to the junction of the buccal and middle thirds. Mesial contact area is buccal to the junction of the buccal and middle thirds. Distal contact area is slightly buccal to the mesial contact area (the opposite of second premolars). Distal contact area is slightly buccal to the mesial contact area (the opposite of second premolars). Prof. A. El- Sahn

Variations The buccal root may be divided into a mesio and disto-buccal root giving a total of three roots (and three root canals). The buccal root may be divided into a mesio and disto-buccal root giving a total of three roots (and three root canals). There may be just a single longitudinally grooved root. There may be just a single longitudinally grooved root. Prof. A. El- Sahn

Maxillary 1 st Premolars Pertinent Data Universal Code International Code Palmer Notation Number of Roots (40%) 2 (60%) RightLeft Number of Root Canals 22 Number of pulp Horns Number of Developmental Lobes Number of Cusps 2 2

Maxillary First Premolars Pertinent Data MesialMesial Middle third DistalDistal Location of proximal contact areas: FacialFacial Jun. of Middle & Cervical third LingualLingual Center of Middle third Height of contour: Middle third