Permanent Dentition- Posteriors Premolars PDF

RAK Medical and Health Sciences University RAK College of Dental Sciences Academic Year 2023-24 Oral Biology and Tooth Morphology DOB126 Semester I- Lecture 4 Permanent Dentition- Posterior Teeth- Premolars...

RAK Medical and Health Sciences University RAK College of Dental Sciences Academic Year 2023-24 Oral Biology and Tooth Morphology DOB126 Semester I- Lecture 4 Permanent Dentition- Posterior Teeth- Premolars Learning Outcome-2 & 16 Explain dental annotations, describe the morphological and chronological features of primary and permanent teeth, and practically carve crowns of selected permanent teeth in wax. Apply knowledge to distinguish abnormal oral structures and develop robust knowledge for future management Dr. Sivan Padma Priya Assistant Professor, RAKCODS, RAKMHSU  Posterior Permanent Dentition They include the premolars and molars. Occlusal surface has two or more cusps- Each cusp has a sloping area, or cusp ridge. Fossa- shallow, wide depression the central fossa, is located where the cusp ridges converge in a central point, where the grooves meet. Triangular fossa- is located near the marginal ridges  Posterior Permanent Dentition Ridges: Marginal ridges- Distal and mesial Triangular ridge-is formed by the cusp slopes. Transverse ridges are formed by the union of two triangular ridges on posterior teeth. Oblique ridges: characteristics of the maxillary molars Developmental pits is a sharp pinpoint depression where two or more grooves meet and located in the deepest portion of the fossa. Roots vary from one to three or more. Each root may have only one canal or more.  Premolar Functions: Masticate food Maintain the vertical dimension of the face (between the nose and chin). First premolars assist the canines in shearing or cutting food Support the corners of the mouth and cheeks to keep them from sagging.  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 Palatal cusp than the mandibular premolars. PMs develop from four lobes; Buccal cusp mesio-buccal, middle buccal, disto- buccal and lingual lobe.  Occusal aspect: The occlusal shape forms a hexagon, circumscribed by cusps and marginal ridges. Buccal and lingual cusps are pyramid shaped with their sides Pits sloping toward the central groove. The slope of the buccal and lingual Triangular ridge cusp tip to the central groove forms a triangular ridge. Mesial marginal developmental groove  Occusal aspect: Two fossae exist, the mesial and distal triangular fossae. Grooves separating the two cusps at their base (central, mesiobuccal, distobuccal, distolingual and mesial marginal developmental grooves) Pits Pits, a meeting point of grooves Triangular ridge e.g mesial and distal pits in the triangular fossae. Mesial marginal developmental groove  Buccal triangular ridge Tip of buccal cusp Disto-buccal cusp Mesio-buccal ridge M cusp ridge cal es io b uc bu t o cc Distal triangular fossa Di s al Mesial triangular fossa l Distal marginal ridge Dista Mes i Mesial marginal ridge al Di al s to gu Disto-lingual cusp lin lin Mesio-lingual cusp ridge g o ua l esi ridge M Distal developmental Mesial developmental groove groove Lingual triangular ridge Tip of lingual cusp  Buccal aspect: B The crown is trapezoidal in shape. Buccal root Prominent middle buccal lobe extending from the cervix to the tip of the cusp with sallow depressions on either side. Buccal ridge The mesial outline is slightly concave from the cervical line to the contact area. M Contact area Buccal lobe Mesial slope Depressions Distal slopes  M Contact area Contact area: Mesially, - halfway between the cervical line and the Buccal lobe tip of the buccal cusp. The distal contact is broader and more Depressions occlusally placed. The mesial slope of the buccal cusp is straight and longer than the distal slope. The mesio-distal width is 2mm less at cervix than its greatest Mesial slope mesio-distal width. Distal slopes  The buccal surface is convex showing B Buccal root a long cusp resembling canine. The continuous ridge from the cusp tip to the cervical margin is called the Buccal ridge buccal ridge. The first PM has a bifurcated root (two roots, one buccal and one lingual and 2 root canals). When one Lingual root D root is present (fused root), 2 pulp canals are found. The buccal root is tapered. Bifurcation area The lingual root is smooth and convex and its apex is more blunt than the buccal root apex.  Lingual aspect: Li The crown tapers toward the lingual because the lingual cusp is Cervical line narrower mesio-distally. Lingual cusp is smooth and spheroidal from the cervical portion to the area near the cusp. Cervical line is regular and with slight curvature to the root. M Mesial Mesial Aspect: interradicular Mesial groove in the crown extend groove from occlusal surface crossing the mesial marginal ridge. Deep groove extending from CEJ Mesial groove to the bifurcation (mesial inter- radicular groove). Distal aspect: The distal surface of the crown is convex and smooth, and it has Distal depression no groove or depression. No distal groove crossing the Root trunk distal marginal ridge. The curvature of the cervical line is less on the distal than the mesial. The root has a depression which extends into the bifurcation. 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.  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 Woelfels Dental Anatomy-8th edition 2012—page no 95 Woelfels Dental Anatomy-8th edition 2012—page no 95  Mandibular First Premolar Occlusal aspect: Buccal triangular ridge Buccal cusp Mesio-buccal cusp Disto-buccal cusp ridge ridge Mesial marginal Distal marginal ridge ridge Mesio-lingual developmental groove Lingual cusp 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 The crown 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: D Overall shape is the reverse of the mesial 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  D The distal contact area is broader than the mesial and located at a point midway between 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) The 3 cusps type appears more angular and the 2 cusps form appears more rounded B 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 1st PM mesiodistally and ends in a blunt apex Lingual aspect: The lingual slobes are more developed (cusps are longer than that of 1st PM) Part of 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 The root 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 D The root is longer and slightly convex 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  Mandibular Premolar Occlusal view-Mandibular Premolars -Three types H-shaped groove pattern: On two-cusp type mandibular Fist premolars Y-shaped groove pattern: On three-cusp type mandibular second premolars U-shaped groove pattern: On two-cusp type mandibular second premolars Woelfels Dental Anatomy-8th edition 2012—page no 109 Woelfels Dental Anatomy-8th edition 2012—page no 112 Woelfels Dental Anatomy-8th edition 2012—page no 107  Clinical Considerations with Posterior Teeth The pits and grooves make them susceptible to caries development. This occurs because of increased plaque retention and the thinness of the enamel forming the walls of the pits and grooves. The pits and grooves need to be carefully checked for decay with an explorer and mirror and possibly a chemical caries indicator. (called disclosing agents) Posterior teeth with deep pit and groove patterns better placed with dental sealants. (Called Pit and fissure Sealants)