LEC 9 - The Maxillary 1st Premolars PDF

Lecture 9 - The Permanent Maxillary 1st Premolars OUTLINE 1. Overview Video presentation. 2. Tooth Numbering system 3. Detailed Description Of The Maxillary first Premolar From All Aspects 4. Labial Aspect 5. Lingual Aspect 6. Mesial Aspect. 7. Distal Aspect 8. Incisal Aspect OVERVIEW VIDEO...

Lecture 9 - The Permanent Maxillary 1st Premolars OUTLINE 1. Overview Video presentation. 2. Tooth Numbering system 3. Detailed Description Of The Maxillary first Premolar From All Aspects 4. Labial Aspect 5. Lingual Aspect 6. Mesial Aspect. 7. Distal Aspect 8. Incisal Aspect OVERVIEW VIDEO PRESENTATION.  https://www.youtube.com/watch?v=IdIvaVgeIPw  https://www.youtube.com/watch?v=87Dhc2YlHsw  INTRODUCTION  The maxillary premolars are developed from the same number of lobes as anterior teeth—four.  The primary difference in development is the well-formed lingual cusp, developed from the lingual lobe, which is represented by the cingulum development on incisors and canines  The middle buccal lobe on the premolars, corresponding to the middle labial lobe of the canines, remains highly developed, with the maxillary premolars resembling the canines when viewed from the buccal aspect  INTRODUCTION  The buccal cusp of the maxillary first premolar, especially, is long and sharp, assisting the canine in tearing tooth  The mandibular first premolar assists the mandibular canine in the same manner  The second premolars, both maxillary and mandibular, have cusps less sharp than the others, and their cusps articulate with opposing teeth when the jaws are brought together; this makes them more efficient as grinding teeth, and they function much like the molars, but to a lesser degree  INTRODUCTION  The maxillary premolar crowns are shorter than those of the maxillary canines, and the roots are also shorter. The root lengths equal those of the molars  The crowns are a little longer than those of the molars  When premolars have two roots, one is placed buccally and one lingually MAXILLARY FIRST PREMOLAR  TOOTH NUMBERING  Universal: 5,12  Palmer: 4 4  FDI System: 14, 24  The maxillary first premolar has two cusps, a buccal and a lingual  The buccal cusp is usually about 1 mm longer than the lingual cusp  The crown is shorter than that of the canine by 1.5 to 2 mm on the average  Although this tooth resembles the canine from the buccal aspect, it differs in that the contact areas mesially and distally are at about the same level  The root is shorter than canine  If the buccal cusp form has not been changed by wear, the mesial slope of the cusp is longer than the distal slope  Generally, the first premolar is not as wide in a mesiodistal direction as the canine  Most maxillary first premolars have two roots and two pulp canals  When only one root is present, two pulp canals are usually found The maxillary first premolar has some characteristics common to all posterior teeth. Briefly, those characteristics that differentiate posterior teeth from anterior teeth are as follows: 1. Greater relative faciolingual measurement compared with the mesiodistal measurement 2. Broader contact areas 3. Contact areas more nearly at the same level 4. Less curvature of the cervical line mesially and distally 5. Shorter crown cervico-occlusally than that of anterior teeth DETAILED DESCRIPTION OF THE MAXILLARY FIRST PREMOLAR FROM ALL ASPECTS BUCCAL ASPECT  BUCCAL ASPECT  The crown is roughly trapezoidal D M  The crown exhibits little curvature at the cervical line  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  BUCCAL ASPECT  The mesial slope of the buccal cusp is rather straight and longer than the distal D M slope, which is shorter and more curved  This arrangement places the tip of the buccal cusp distal to a line bisecting the buccal surface of the crown  The mesial slope of the buccal cusp is sometimes notched; in other instances, a concave outline is noted at this point  BUCCAL ASPECT  The distal outline of the crown below the cervical line is straighter than that of the D M mesial, although it may be some- what concave as well  The distal contact area is represented by a broader curvature than is found mesially  The width of the crown of the maxillary first premolar mesiodistally is about 2 mm less at the cervix than at its width at the points of its greatest mesiodistal measurement  The buccal cusp is long, coming to a pointed tip and resembling the canine in this respect, although contact areas in this tooth are near the same level  BUCCAL ASPECT  The buccal surface of the crown is convex, showing strong development of the D M middle buccal lobe  The continuous ridge from cusp tip to cervical margin on the buccal surface of the crown is called the buccal ridge  The roots are 3 or 4 mm shorter than those of the maxillary canine, although the outline of the buccal portion of the root form bears a close resemblance LINGUAL ASPECT  LINGUAL ASPECT  The gross outline of the maxillary first premolar is the reverse of the gross outline from the buccal aspect  The crown tapers toward the lingual because the lingual cusp is narrower mesiodistally than the buccal cusp  The cusp tip is pointed, with mesial and distal slopes meeting at an angle of about 90 degrees  Lingual ridge LINGUAL ASPECT  Naturally, the spheroidal form of the lingual portion of the crown is convex at all points  Sometimes the crest of the smooth lingual portion that terminates at the point of the lingual cusp is called the lingual ridge  The mesial and distal outlines of the lingual portion of the crown are convex  The cervical line lingually is regular, with slight curvature toward the root  LINGUAL ASPECT  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, depending on the posing of the tooth and the line of vision  The lingual portion of the root, or the lingual portion of the lingual root if two roots are present, is smooth and convex at all points  The apex of the lingual root of a two-root specimen tends to be blunter than the buccal root apex MESIAL ASPECT  BR Buccal root LR Lingual LR BR root 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 measurement from the tip of the buccal cusp to the tip of the lingual cusp is less than the buccolingual measurement of the root at its cervical portion  MESIAL ASPECT  Most maxillary first premolars have two roots, one buccal and one lingual; these are clearly outlined from the mesial aspect  The buccal outline of the crown curves outward below the cervical line  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  MESIAL ASPECT  The lingual cusp is always shorter than the buccal cusp, the average difference being about 1 mm, This difference, however, may be greater  From this aspect, it is noted that the cusps of the maxillary first premolar are long and sharp  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 depression  This mesial concavity continues apically beyond the cervical line, joins a deep developmental depression between the roots, and ends at the root bifurcation  MESIAL ASPECT LC BC  On single-root specimens, the concavity on the crown and root is also plainly seen, although it may not be as deeply marked  Maxillary second premolars do not have this feature  Another distinguishing feature of the maxillary first pre- molar is a well-defined developmental groove in the enamel of the mesial marginal ridge  This groove is in alignment with the developmental depression on the mesial surface of the root but is not usually connected with it  Mesial developmental depression Mesial marginal ridge MESIAL ASPECT Developmental groove  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  The root trunk is long on this tooth, making up about half of the root length Root trunk  MESIAL ASPECT  Generally speaking, when bifurcated, the root is bifurcated for half its total length  Except for the deep developmental groove and depression at or below the bifurcation, the mesial surface of the root portion of this tooth is smoothly convex buccally and lingually  Even when only one root is present, the developmental depression is very noticeable for most of the root length  In such cases, roots with buccal and lingual outlines ending in a blunt apex above the center of the crown are seen DISTAL ASPECT  DISTAL ASPECT  The anatomy of the crown and root of the maxillary first premolar differs from that from the mesial aspect as follows:  The crown surface is convex at all points except for a small, flattened arc just cervical to the contact area and buccal to the center of the distal surface  The curvature of the cervical line is less on the distal than on the mesial surface, often showing a line straight across from buccal to lingual  DISTAL ASPECT  The anatomy of the crown and root of the maxillary first premolar differs from that from the mesial aspect as follows:  A deep developmental groove crossing the distal marginal ridge of the crown is not evident. If a developmental groove should be noticeable, it is shallow and insignificant  The root trunk is flattened on the distal surface above the cervical line with no outstanding developmental signs  The bifurcation of the roots is abrupt near the apical third, with no developmental groove leading to it such as that found mesially OCCLUSAL ASPECT OCCLUSAL ASPECT  OCCLUSAL ASPECT  The occlusal aspect of the maxillary first premolar resembles roughly a six-sided or hexagonal figure  The six sides are made up of the mesiobuccal, which is mesial to the buccal ridge; mesial; mesiolingual, which is mesial to the lingual ridge; distolingual; distal; and distobuccal  This hexagonal figure, however, is not equilateral, The two buccal sides are nearly equal, the mesial side is shorter than the distal side, and the mesiolingual side is shorter than the distolingual side  OCCLUSAL ASPECT  The crest of the distal contact area is somewhat buccal to that of the mesial contact area, and the crest of the buccal ridge is somewhat distal to that of the lingual ridge  The crests of curvature represent the highest points on the buccal and lingual ridges and the mesial and distal contact areas  OCCLUSAL ASPECT  Close observation of the crown from this aspect reveals the following characteristics :  The distance from the buccal crest (A) to the mesial crest (C) is slightly longer than the distance from the buccal crest to the distal crest (D)  The distance from the mesial crest to the lingual crest is much shorter than the distance from the distal crest to the lingual crest  The crown is wider on the buccal than on the lingual  The buccolingual dimension of the crown is much greater than the mesiodistal dimension  OCCLUSAL ASPECT  The occlusal surface of the maxillary first premolar is circumscribed by the cusp ridges and marginal ridges  The mesiobuccal and distobuccal cusp ridges are in line with each other, and their alignment is in a distobuccal direction  In other words, even though they are in the same alignment, the distobuccal cusp ridge is buccal to the mesiobuccal cusp ridge  OCCLUSAL ASPECT  The occlusal surface of this tooth has no supplemental grooves in most cases, a fact that makes the surface relatively smooth  A well-defined central developmental groove divides the surface evenly buccolingually  It is located at the bottom of the central sulcus of the occlusal surface, extending from a point just mesial to the distal marginal ridge to the mesial marginal ridge, where it joins the mesial marginal development groove  OCCLUSAL ASPECT  This latter groove crosses the mesial marginal ridge and ends on the mesial surface of the crown  Two collateral developmental grooves join the central groove just inside the mesial and distal marginal ridges  These grooves are called the mesiobuccal developmental groove and the distobuccal developmental groove OCCLUSAL ASPECT References – Wheeler's Dental anatomy, physiology and occlusion 10th edition by Stanley J Nelson, 2015, Elsevier Dental Anatomy Coloring Book by Margaret J. Fehrenbach, 3rd edition, 2018, Mosby ANY QUESTIONS!!!