Permanent Maxillary and Mandibular First and Second Premolar PDF

LEARNING OUT COME (LO 1) Permanent Maxillary and Mandibular First and second Premolar The student should be able to: ❖Distinguish the chronological and morphological details of the permanent maxillary and mandibular Premolars ❖Distinguish the characteristic features from different aspects of the tee...

LEARNING OUT COME (LO 1) Permanent Maxillary and Mandibular First and second Premolar The student should be able to: ❖Distinguish the chronological and morphological details of the permanent maxillary and mandibular Premolars ❖Distinguish the characteristic features from different aspects of the teeth (Buccal, Lingual, Mesial, Distal & Occlusal). ❖Identify & differentiate maxillary from the permanent mandibular First and second premolars ❖Distinguish a few common variations in tooth morphology. POSTERIOR PERMANENT DENTITION They include the premolars and molars. The crown of each posterior tooth has an occlusal surface, bordered distally and mesially by marginal ridges. The occlusal surfaces have two or more cusps. Each cusp has a sloping area, or cusp ridge. Each shallow, wide depression on the occlusal table is called a fossa. MAXILLARY FIRST PREMOLAR General features: 15 Li 14 A maxillary first premolar is larger than a maxillary 2nd PM. Each maxillary first premolar has two sharply defined cusps (buccal and lingual) and two roots (facial and lingual). Both maxillary PMs erupt earlier than the mandibular premolars. Palatal cusp PMs develop from four lobes; mesio-buccal, middle buccal, Buccal cusp disto-buccal and lingual lobe.  Cont’d  Occusal aspect:  Theocclusal shape forms a hexagon, circumscribed by cusps and marginal ridges.  Buccaland lingual cusps are pyramid shaped with their sides sloping toward the central Pits groove. Triangular  The slope from the buccal cusp ridge tip to the central groove and the slope from lingual cusp tip to the central groove forms a triangular ridge. Mesial marginal developmental groove  Cont’d  Occusal aspect:  Two fossae exist, the mesial and distal triangular fossae.  Severalgrooves separating the two cusps at their base (central, mesiobuccal, distobuccal, distolingual and mesial marginal Pits developmental grooves) Triangular  There may be pits, a meeting ridge point of grooves e.g mesial and distal pits in the triangular Mesial marginal fossae. developmental groove Cont’d Buccal triangular Tip of buccal ridge cusp Disto-buccal Mesio-buccal cusp ridge cusp ridge Distal triangular Mesial fossa triangular Distal marginal fossa ridge Mesial marginal ridge Disto-lingual Mesio-lingual cusp ridge cusp ridge Distal Mesial developmental developmental groove groove Lingual triangular Tip of ridge lingual cusp  Cont’d M Contact area Buccal  Buccal aspect: lobe  The crown is trapezoidal in shape. Depress-  Prominent middle buccal lobe extending ions from the cervix to the tip of the cusp with sallow depressions on either side.  Themesial outline is slightly concave Mesial from the cervical line to the contact area. slope Distal slopes  Cont’d M Contact area  Contact area: Mesially, represented by a Buccal lobe broad curvature, the crest of which lies halfway point between the cervical line and Depress- the tip of the buccal cusp. The distal ions contact is broader and is more occlusally.  The mesial slope of the buccal cusp is straight and longer than the distal slope. Mesial  Themesio-distal width is 2mm less at slope cervix than its greatest mesio-distal width. Distal slopes  Cont’d B Buccal  Thebuccal surface is convex showing a long root cusp resembling canine. Buccal  Thecontinuous ridge from the cusp tip to the ridge cervical margin is called the buccal ridge.  Thefirst PM has a bifurcated root (two roots, one buccal and one lingual and 2 root canals). Lingual D When one root is present (fused root), 2 pulp root canals are found. Bifurca-  The roots are shorter in length and resemble tion area the roots of the molars.  Cont’d B Buccal root  Thelingual root is smooth and convex and its Buccal apex is more blunt than the buccal root apex. ridge  The buccal root is tapered. Lingual D root Bifurca- tion area  Cont’d Li  Lingual aspect:  The crown tapers toward the lingual Cervical because the lingual cusp is narrower mesio- line distally.  Lingual cusp is smooth and spheroidal from the cervical portion to the area near the cusp. Mesial M  The cusp tip is pointed with mesial and interradi- distal slopes. cular groove  Cervicalline is regular and with slight Mesial curvature to the root. groove  Cont’d Li  Mesial Aspect:  Mesialgroove extending from occlusal Cervical line surface crossing marginal ridge onto the mesial surface.  Deep groove extending from CEJ to the bifurcation (mesial inter-radicular groove). M Mesial interradi- cular groove Mesial groove  Distal Distal aspect: depression  The distal surface of the crown is convex Root trunk and smooth, and it has no groove or depression.  No distal groove crossing the distal marginal ridge.  The curvature of the cervical line is less on the distal than the mesial.  Distal depression  The root has a depression which extends into the bifurcation. Root trunk  The root trunk is flattened on the distal surface above the CEJ line.  Maxillary Second Premolar  The maxillary second PM looks like the first PM with the following differences :  2nd PM has only one root and one pulp canal. B  2nd PM is less angular (more rounded).  The mesial buccal cusp slope is shorter than the distal buccal cusp slope (the opposite is true of the 1st PM).  Maxillary Second Premolar Both cusps are about the same level (lingual is slightly shorter). The mesial surface of the crown has no groove or concavity. B The buccal cusp is not as long as that of the 1st PM. The buccal ridge is less prominent. Cont’d  The central development grooves are shorter and more irregular.  A shallow depression is evident on the mesial surface of the root.  The distal root depression is deeper than the mesial depression on 2nd Max. PM. Li D M Shallow depression Mandibular First Premolar Occlusal aspect: Buccal triangular ridge Buccal cusp Mesio-buccal Disto-buccal cusp ridge cusp ridge Distal marginal Mesial marginal ridge ridge Mesio-lingual developmental Lingual cusp groove Central developmental groove  Occlusal aspect:  The occlusal aspect is diamond-shaped and resembles the mandibular canines  The buccal ridge is prominent  The mesiobuccal and distobuccal line angles are prominent  The marginal ridges are well developed  The lingual cusp is small  The occlusal surface show heavy buccal triangular ridge  Irregular mesial and distal fossae Buccal aspect: B Develops from 4 lobes Have a sharp pointed buccal cusp, located mesial to the center of the crown Very prominent buccal ridge extending to the buccal cusp with 2 depressions on either side of the ridge The mesial cusp slope is shorter than the distal and usually shows a concavity  B The mesial and distal outlines are slightly concave above the cervical line to the contact point The cervix is narrow mesiodistally when compared with the width at the contact area  Li Lingual aspect: The crown and the root taper toward lingual surface The lingual cusp is small and the major portion of the crown is made of the buccal middle lobe (i.e resemble the canine) The occlusal surface slopes toward the lingual in a cervical direction Mesial aspect: M Thecrown is characteristic from this aspect, Rhomboidal in shape The buccal cusp is centered over the root The tip of the lingual cusp will be on a line approximately with the lingual border of the root The root is broad, tapering only at the apical 1/3 and has a deep developmental groove, which bifurcates at apical 1/3.  M The buccal outline from this aspect is curved from the cervical line to the tip of the cusp. The crest of the curvature is in near the cervical 1/3 (a character of all post. teeth) The buccal triangular ridge is parallel to the mesial marginal ridge Distal aspect: Overall shape is the reverse of the mesial D aspect The distal marginal ridge is higher above the cervix and it does not have the extreme lingual slope of the mesial marginal ridge Most of the distal surface is smooth and convex The distal contact area is broader than the mesial and located at a point midway between D the buccal and lingual crests of curvature The surface of the root is more convex than that is found on the mesial surface A shallow developmental depression is centered on the root  Mandibular Second Premolar Occlusal aspect: Mand 2nd PM assumes two forms; one with 2 cusps and another form with 3 cusps (the most common pattern, buccal, mesiolingual and distolingual cusps) B The 3 cusps type appears more angular and the 2 cusps form appears more rounded ML DL  Mandibular Second Premolar The buccal cusp is the largest, next is the mesiolingual cusp and the distolingual is the smallest Each cusp has well developed triangular ridges separated by deep developmental grooves B ML DL  There are two triangular fossae; one mesial and one distal and there is no transverse ridge on the 3 cusp variety, but would be present in 2 cusp PM  Supplemental grooves and depressions are seen radiating from the developmental groove Buccal surface: Resembles the Mand 1st PM but slightly shorter and broader mesiodistally The mesiobuccal and distobucal cusp ridges present with less degree of angulation  Both contact areas are at higher level The root is broader than the 1 st PM mesiodistally and ends in a blunt apex Lingual aspect: The lingual lobes are more developed (cusps are longer than that of 1st PM) Partof the buccal cusps may be seen from this aspect In case of 3-cusp type, there is great variations from that of 2-cusp form. In the former, the mesio-lingual cusp is larger and longer and there is a groove separating it from the disto-lingual cusp that extends a short distance on the lingual surface No development groove in 2-cusp type The lingual surface is smooth and having a bulbous form above the cervical margin Theroot portion is smooth and convex Mesial aspect: M  It differs from the 1st PM in the following:  Less of the occlusal surface may be seen  The lingual lobe development is greater  The marginal ridge is at right angles to the long axis of the tooth  No mesio-lingual developmental groove on the crown  The root is longer and slightly convex D Distal aspect: More of the occlusal surface may be seen The crowns of all posterior teeth are tipped distally to the long axes of the roots Mirror image photograph showing 44 with mesiolingual and distolingual cusp. Photograph of mandibular cast showing 44 with typical “Y” shaped occlusal groove with 3 cusps resembling mandibular second premolar.