permanant maxillary first premolar.pdf

Almaaqal University Dental Anatomy Dr. Bahaa Altememi College of dentistry lec. 7 The Permanent Maxillary first Premolars The maxillary first premolars are two in number: one in the right maxilla and one in the left max...

Almaaqal University Dental Anatomy Dr. Bahaa Altememi College of dentistry lec. 7 The Permanent Maxillary first Premolars The maxillary first premolars are two in number: one in the right maxilla and one in the left maxilla. They are posterior to the canines and immediately anterior to the premolar The premolar succeed the deciduous first molars (There are no premolars in deciduous dentition) They are also called bicuspid The buccal cusp is usually about 1 mm longer than the lingual cusp Most maxillary first premolars have two roots about 80% and two pulp canals. When only one root is present, two pulp canals are usually found anyway Function like canine tearing only Chronology eruption 10-11 years Root completed 12-13 years 1 Almaaqal University Dental Anatomy Dr. Bahaa Altememi College of dentistry lec. 7 DETAILED DESCRIPTION OF THE MAXILLARY FIRST PREMOLAR FROM ALL ASPECTS: Buccal Aspect: From the buccal aspect, the crown is roughly trapezoidal Cusp tip tilt distally The mesial outline of the crown is slightly concave from the cervical line to the mesial contact area. The contact area is represented by a relatively broad curvature, the crest of which lies immediately occlusal to the halfway point from the cervical line to the tip of the buccal cusp. The distal outline of the crown below the cervical line is straighter than that of the mesial, although it may be somewhat concave also. The distal contact area is represented by a broader curvature than is found mesially, and the crest of curvature of the contact area tends to be a little more occlusal when the tooth is posed with its long axis vertical. Even so, the contact areas are more nearly level with each other than those found on anterior teeth. The buccal surface of the crown is convex, showing strong development of the middle buccal lobe. The continuous ridge from cusp tip to cervical margin on the buccal surface of the crown is called the buccal ridge. Also there is two shallow developmental groove and two mesial and distal lobes Mesial slope look longer than distal slope ? 2 Almaaqal University Dental Anatomy Dr. Bahaa Altememi College of dentistry lec. 7 3 Almaaqal University Dental Anatomy Dr. Bahaa Altememi College of dentistry lec. 7 Lingual aspect The mesial and distal outlines of the lingual portion of the crown are convex; these outlines are continuous with the mesial and distal slopes of the lingual cusp and straighten out as they join the mesial and distal sides of the lingual root at the cervical line. The cervical line lingually is regular, with slight curvature toward the root and the crest of curvature centered on the root. Because the lingual portion of the crown is narrower than the buccal portion, it is possible to see part of the mesial and distal surfaces of crown and root from the lingual aspect. Because the lingual cusp is shorter by about 1mm than the buccal cusp, the tips of both cusps, with their mesial and distal slopes, may be seen from the lingual aspect. The lingual cusp is smooth and spheroidal from the cervical portion to the area near the cusp tip. The cusp tip is pointed, with mesial and distal slopes meeting at an angle of about 90 degrees. The apex of the lingual root of a two root specimen tends to be more blunt than the buccal root apex. 4 Almaaqal University Dental Anatomy Dr. Bahaa Altememi College of dentistry lec. 7 Mesial Aspect - The mesial aspect of the crown of the maxillary first premolar is also roughly trapezoidal. However, the longest of the uneven sides is toward the cervical portion and the shortest is toward the occlusal portion. - The cervical line curvature occlusally is less (about 1 mm on the average) than the cervical curvature on the mesial side of any of the anterior teeth. - From the mesial aspect, the buccal outline of the crown curves outward below the cervical line. The crest of curvature is often located approximately at the junction of cervical and middle thirds. From the crest of curvature, the buccal outline continues as a line of less convexity to the tip of the buccal cusp, which is directly below the center of the buccal root. - The lingual outline of the crown may be described as a smoothly curved line starting at the cervical line and ending at the tip of the lingual cusp. The crest of this curvature is most often near the center of the middle third. The tip of the lingual cusp is on a line, in most cases, with the lingual border of the lingual root. - A distinguishing feature of this tooth is found on the mesial surface of the crown. Immediately cervical to the mesial contact area, centered on the mesial surface and bordered buccally and lingually by the mesiobuccal and mesiolingual line angles, is a marked depression called the mesial developmental depressioncalled canine fossa. This mesial concavity continues apically beyond the cervical line, joins a deep developmental depression between the roots, and ends at the root bifurcation - Another distinguishing feature of the maxillary first premolar is a well- defined developmental groove in the enamel of the mesial marginal ridge. 5 Almaaqal University Dental Anatomy Dr. Bahaa Altememi College of dentistry lec. 7 This marginal groove is continuous with the central groove of the occlusal surface of the crown, crossing the marginal ridge immediately lingual to the mesial contact area and terminating a short distance cervical to the mesial marginal ridge on the mesial surface.This groove is called the mesial marginal developmental groove. - The root trunk is long on this tooth, making up about half of the root length and the root is bifurcated for half its total length. Also we can see the shadow of root trunk of distal side. 6 Almaaqal University Dental Anatomy Dr. Bahaa Altememi College of dentistry lec. 7 Distal Aspect The differences between distal and mesial aspects are: Distal contact more occlusally and more extended The curvature of the cervical line is less on the distal than on the mesial surface. There is no deep developmental groove crossing the distal marginal ridge of the crown, and if a developmental groove is present, it is shallow and insignificant. The bifurcation of the roots is abrupt with no developmental groove leading to it such as that found mesially. The root trunk distally more longer so the bifurcation more apically 7