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Maxillary Premolars Dr.\Manar A. Selim Oral Biology Department Faculty of Dentistry  General features of premolars: - They are eight in number, four in each dental arch, two in each quadrant. - The premolars are situated in the dental arch distal to the canines and mesial to...

Maxillary Premolars Dr.\Manar A. Selim Oral Biology Department Faculty of Dentistry  General features of premolars: - They are eight in number, four in each dental arch, two in each quadrant. - The premolars are situated in the dental arch distal to the canines and mesial to the first molars. Premolars Bicuspids - They are called bicuspids because each of them has two cusps. - Like anterior teeth the premolars are developed from four lobes (3 buccally & 1 lingually) except the lower second premolar when it has three cusps. -Lower second premolar: When lower second premolar has three cusps, developed from five lobes (3 buccally & 2 lingually). - The first premolars have sharp cusps to assist the canines in tearing of food. - While the second premolars have more rounded cusps to assist the molars in grinding of food. - The crowns and roots of the premolars are shorter than those of the canines. But their crowns are slightly longer than those of the molars. premolar molar canine Marginal ridges: - The marginal ridges of the premolars-like those of the molars-are in a horizontal plane related to the occlusal surface of the crown rather than of the lingual surface as in case of the anterior teeth.  - In the maxillary premolars the first premolar is larger than the second premolars. maxillary first premolar maxillary second premolar  However, the lower first premolar is smaller than the lower second premolar. Mand. second premolar Mand. first premolar Posterior teeth differ from the anterior teeth in the following: 1-They have greater buccolingual dimension. 2-Their crowns are shorter cervico-occlusally. Ant. teeth Post. teeth  3- They have larger contact areas which are nearly at the same level. 4- They have less curvature of the cervical line from all aspects. Ant. teeth Post. teeth  Maxillary First Premolar Chronology: Appearance of enamel organ 7 months IUL First evidence of calcification 1 1/2- 1 3/4 years Crown completed 5-6 years Eruption 10-11 years Root completed 13 years Chronology: 4 4 5 5 Appearance of enamel organ 7 m i.u.l. 7 m i.u.l 8 m i.u.l 8 m i.u. l Beg. Of calcification 1 1/2- 1 ¾ y 1 ¾-2 y 2-2 1/4 y 2 ¼- y 2 1/2 y Crown completed 5-6 y 5-6 y 6 -7 y 6 -7 y Eruption 10-11 y 10-11 y 10-12 y 11-12 y Root completed 13 y 13 y 13-15 y 14 y Maxillary First Premolar The maxillary first premolar has two sharp well developed cusps. The buccal cusp is longer than the lingual cusp. About 80% of the maxillary first premolars have two roots one buccal and one lingual root and 20% have one root. Whether it is double or single rooted the maxillary first premolar has two root canals.  Buccal surface - The buccal surface is roughly trapezoidal with the short of the uneven sides cervically and the long side occlusally. It is generally convex. - The maximum convexity is located at the cervical third (cervical ridge). - The middle buccal lobe is highly developed and represented on the buccal surface as a ridge called buccal ridge. - The mesial slope of the buccal cusp is longer than the distal slope contrary to the cusp of the maxillary permanent canine.  Buccal surface - The mesial outline of the crown is slightly concave from the cervical line to the mesial contact area, which lies just cervical to the junction of the occlusal and middle thirds. Then the outline from the mesial contact area to the cusp tip is straight line. - The distal outline is straight from the cervical line to the distal contact area which lies nearly at the same level of the mesial contact area (at the junction of the occlusal and middle thirds). Then the outline from the distal contact area to the cusp tip is slightly convex.  Buccal surface - Two developmental depressions, the mesiobuccal and distobuccal, are located on both sides of the buccal ridge and mark the union of the developmental lobes. - The cervical line shows little curvature towards the root.  Buccal surface - If two roots, only the buccal root could be seen as the lingual root is shorter and narrower than the buccal root. - The root is slender, conical with pointed apex. Its apical third shows distal inclination.  Lingual surface - The lingual surface is narrower than the buccal surface because of the convergence of the proximal surfaces lingually. - The lingual cusp is shorter than the buccal cusp with a pointed tip. - Both cusps with their mesial and distal slopes can be seen from the lingual aspect.  Lingual surface - The maximum convexity of the lingual surface is located at the middle third. - The mesial and distal slopes of the lingual cusp meet at a 90˚ angle. - The mesial and distal outlines of the crown lingually are convex. - The root is smooth and convex with blunt apex.  Mesial surface - The mesial surface is trapezoidal in shape with the short side occlusally and the long side cervically. - The buccal outline is convex from the cervical line to the tip of the buccal cusp, the crest of the convexity is located in the cervical third marking the cervical ridge. The cusp tip is on line with the apex of the buccal root.  Mesial surface - The lingual outline is smoot and convex from the cervical line to the lingual cusp tip. The crest of this convexity lies in the middle third. - The tip of the lingual cusp is on a line with the lingual margin of the lingual root. The lingual cusp is shorter than the buccal by about 1 mm.  Mesial surface - There are two features on the mesial surface of the maxillary first premolar: 1- The presence of a mesial developmental depression just cervical to the mesial contact area, that continues cervically to include the cervical line and then joins a deep developmental depression present on the root trunk. 2- The presence of a well defined developmental groove that cross the mesial marginal ridge to end on the mesial surface. This developmental groove is continuous with the central groove present on the occlusal surface. This groove is called mesial marginal developmental groove.  Mesial surface Cervical line curves occlusally and decreased distally. Most maxillary first premolars have two roots one buccal and one lingual. The root trunk is long making about half of the root length.  Mesial surface The buccal outline of the buccal root is straight above the cervical line with tendency toward lingual inclination. The lingual outline of the lingual root is also straight and may show buccal or lingual inclination.  Mesial surface The mesial surface of the root trunk is smooth and convex buccal and lingual to the deep developmental depression. Even when one root only is present, the developmental depression is still very noticeable for most of the root length. A Single root ends with a blunt apex.  Distal surface - The distal surface is generally convex except for a flattened area cervical to the distal contact area. - The root trunk is also flattened with no developmental depressions. - There is no developmental groove crossing the distal marginal ridge and the length of the root trunk is longer distally.  Distal surface - The cervical line distally is nearly straight. - The bifurcation is near the apical third of the root.  Occlusal surface - The occlusal surface is hexagonal in shape. The sides of this hexagonal form are: the mesiobuccal and distobuccal, the mesiolingual and distolingual, the mesial and the distal. - A central developmental groove divides the occlusal surface evenly buccolingually. Buccolingually is greater than mesiodistally. The crown is wider buccally than lingually due to lingual convergency.  Occlusal surface - Distal to the mesial marginal ridge lies a triangular depression called mesial triangular fossa. - Similarly mesial to the distal marginal ridge there is a distal triangular fossa. - The triangular ridge of the buccal cusp is more prominent than the triangular ridge of the lingual cusp.  Pulp Cavity of Maxillary first premolar - Mesiodistal section: narrow pulp chamber and narrow root canal. - Buccolingual section: The pulp chamber is wider buccolingually than mesiodistally with two pulp horns of which the buccal one is usually longer. - In midroot cross section: The two canals appear rounded and constricted with the lingual one slightly larger.  Maxillary Second Premolar Chronology: Appearance of enamel organ 8 months IUL First evidence of calcification 2-2 1/4 years Crown completed 6-7 years Eruption 10-12 years Root completed 13-15 years  The maxillary second premolar resembles the maxillary first premolar to a great extent but they differ in many respects. The crown of the maxillary second premolar is rounded from all aspects. The crown is smaller both cervico-occlusally and mesiodistally. maxillary second premolar maxillary first premolar  Maxillary Second Premolar The buccal and lingual cusps are nearly of the same length. In 80% of the cases it is single rooted. 20% of the cases it is double rooted. maxillary second premolar maxillary first premolar  Buccal surface - The buccal cusp of the upper second premolar is shorter and less pointed with the mesial slope shorter than the distal slope ( contrary to the upper first premolar). - The buccal ridge of the crown is less pronounced. - The crown and root are thick at the cervix. maxillary second premolar maxillary first premolar  Lingual surface - The lingual cusp is as long as the buccal cusp making the crown of the upper second premolar longer from this side. maxillary second premolar maxillary first premolar  maxillary second premolar maxillary first premolar  Proximal surfaces - From the mesial and distal aspects it is obvious that the buccal and lingual cusps have the same length. - The cusp tips are farther apart increasing the length of the occlusal surface buccolingually. maxillary first premolar maxillary second premolar  Proximal surfaces - The mesial and distal surfaces are convex with no developmental depressions as found on the first premolar. - There is no developmental groove crossing the mesial marginal ridge. - A shallow developmental groove may be found on the single tapered root. maxillary first premolar maxillary second premolar  Occlusal surface - The occlusal surface is rounded or oval with short central developmental groove. - Multiple supplemental grooves are seen radiating from the central groove and ending in shallow depressions which may extend to the cusp ridges giving the occlusal surface a wrinkled appearance. maxillary second premolar - The occlusal surface is wider buccolingually because the cusps are farther apart.  Pulp Cavity of Maxillary Second Premolar: - Mesiodistal section: reveals narrow pulp chamber that extends apical to the cervical line then it becomes constricted and tapers as a root canal to the apex of the root. - Buccolingual section: The pulp chamber and root canal are rather wide buccolingually. Thank You