Dental Anatomy Lecture 14 - Mandibular First Molar 2023-2024 PDF

Lecture 14 30 April. Al-Noor University Mandibular first College /Dentistry 1st Year molar...

Lecture 14 30 April. Al-Noor University Mandibular first College /Dentistry 1st Year molar Dental Anatomy By: Assist. Lect. Alaa Hussein Ali 2023-2024  Mandibular molars Mandibular molars They are six in number, three on each mandibular quadrant. They are named from the midline, first molar, second molar and third molar. The mandibular first molars are located near the center of mandibular arch and distally to mandibular second premolar. Alaa H. Ali 2  Mandibular first molar Eruption time: 6-7 years Root completed: 9-10 years The mandibular first molar is the largest mesiodistally among all dentition. It has 5 cusps (3 buccal cusps and 2 lingual cusps) developed from 5 lobes with 2 roots (one mesial and one distal). Three buccal cusps (mesiobuccal, distobuccal, distal cusps) and two lingual cusps (mesiolingual and distolingual cusps). The mesiolingual cusp is the longest followed by distolingual, mesiobuccal, distobuccal and finally distal cusp (located on Alaa H. Ali the buccal surface near the distobuccal line angle). The distal cusp may be absent in fifth of the mandibular 1st molar. 3  Mandibular first molar Buccal aspect The crown is wider mesiodistally than occlusocervically. The crown outline is roughly trapezoidal with the occlusal and cervical outlines represent the uneven sides of trapezoid. Five cusps are visible from this aspect. The mesiolingual cusp is the longest followed by distolingual, mesiobuccal, distobuccal and finally distal cusp (located on the buccal surface near the distobuccal line angle) The mesiobuccal and distobuccal cusps are relatively flat with the distobuccal cusp is sharper than the mesiobuccal cusp, Alaa H. Ali while the mesiobuccal is the wider. 4  Mandibular first molar Buccal aspect There are 2 developmental grooves could be seen on the buccal surface of the crown. The longer developmental groove (mesiobuccal groove) separates between the mesiobuccal and distobuccal cusp, while the shorter (distobuccal) separates between the distobuccal and distal cusps. The mesiobuccal developmental groove may end with pit which is called buccal pit. Alaa H. Ali 5  Mandibular first molar Buccal aspect The crown has greater distal bulge because of the distal cusp and the crown tapers from mesial to distal (gets shorter) making the crown appears to be tilted distally on root base. The mesial contact area is near the junction between middle and occlusal thirds, while the distal contact area is located in the middle third. The mesial outline is concave from the cervical line to the contact area while the distal outline is straight from the cervical line to the distal contact area. Alaa H. Ali The cervical line is nearly straight with little curve. The root trunk is very short (about 3mm) and the bifurcation is near the cervical line. There is a developmental depression on buccal root trunk. 6  Mandibular first molar Buccal aspect The mandibular 1st molar has 2 roots, the longer mesial root and the shorter distal root. The roots are widely separated. The mesial root is curved and the apex is on line with the mesiobuccal groove while the distal root apex is located distally to the distal crown outline (only mesial root is confined within the crown outline). The mesial root is twisted so it may be possible to see the distal surface of this root from the buccal aspect. Alaa H. Ali 7  Mandibular first molar Lingual aspect The lingual half is narrower than the buccal half of the crown. The lingual cusps are visible from this aspect because they are longer than the buccal cusps. The cusp tip of both lingual cusps is more pointed. The lingual developmental groove separates between the lingual cusps but its unlikely to extend onto the lingual surface as the buccal developmental grooves. The mesial marginal ridge is more occlusal than distal marginal ridge. Alaa H. Ali The cervical line is nearly straight. 8  Mandibular first molar Lingual aspect The longer mesial root and the shorter distal root are visible from this aspect. Both roots are narrower lingually. The mesial root is twisted so the mesial surface of the mesial root could be seen from this aspect. The root trunk is longer from this aspect than from buccal aspect because the cervical line is more occlusally positioned as compared to the cervical line from buccal aspect. There is a developmental depression on lingual root trunk. Alaa H. Ali 9  Mandibular first molar Mesial aspect The crown is wider buccolingually than occlusocervically. The crown is tilted lingually on root base. Only mesiolingual and mesibuccal cusps are visible from this aspect and the mesiolingual cusp is longer than the mesiobuccal cusp. The buccal crest of curvature is located in the cervical third and formed by the buccal cervical ridge that runs mesiodistally near the cervical line, while the lingual crest of curvature is located in the middle third. Alaa H. Ali 10  Mandibular first molar Mesial aspect the mesial marginal ridge is concave and more occlusal than the distal marginal ridge. Marginal groove is more likely to be located on mesial marginal ridge than distal marginal ridge. The cervical line is slightly curved. Only the mesial root is visible from this aspect because it is wider and longer than distal root. the mesial root apex is blunt. There is a deep longitudinal developmental depression on the mesial surface of the mesial root and deeper depression on its Alaa H. Ali distal surface. 11  Mandibular first molar Distal aspect The followings are the differences between mesial and distal aspects The crown is narrower in the distal third than in the mesial third that’s why some of the buccal and lingual surfaces could be seen from this aspect. the distal marginal ridge is V shaped and more cervical than the mesial marginal ridge that’s why most of occlusal surface could be seen from this aspect including the triangular ridges of the cusps. Alaa H. Ali There is no developmental groove on distal marginal ridge Five cusps could be seen from this aspect. The depth of curvature of the cervical line is less than on mesial surface and is nearly straight. 12  Mandibular first molar Distal aspect The mesial and distal roots are visible from this aspect. There are developmental depressions on both sides of distal root. The distobuccal developmental groove is visible. Alaa H. Ali 13  Mandibular first molar Occlusal aspect The outline of the crown is roughly pentagon. The crown is wider mesiodistally than buccolingually. The 1 4 buccolingual dimension of mesial half is greater than the 5 distal half. From this aspect, five cusps are visible. The mesiobuccal 2 3 cusp is larger than the distobucal cusp and the mesiolingual cusp is larger than distolingual cusp. Mesial contact area is located buccally to the center of the crown buccolingually, while the distal contact area is located Alaa H. Ali lingual to distal cusp. The buccal surface could be seen from this aspect more than the lingual surface. 14  Mandibular first molar Occlusal aspect Ridges: 1. Triangular ridges: There are 5 triangular ridges, one on each cusp. 2. Transverse ridges: There are 2 transverse ridges. The triangular ridges of mesiobuccal and mesiolingual cusps join to form transverse ridge on mesial half. The triangular ridges of distobuccal and distolingual cusps join to form transverse ridge on distal half. Alaa H. Ali 15  Mandibular first molar Occlusal aspect Fossae: There are 3 fossae on the occlusal aspect 1. The largest central fossa, which roughly circular with central pit. 2. The smaller mesial triangular fossa with mesial pit. 3. The smallest distal triangular fossa with distal pit. Grooves: 1. Central developmental groove: Extends from mesial triangular fossa to distal triangular fossa passing through Alaa H. Ali the central fossa. This groove has zigzag pattern. 2. Mesiobuccal developmental groove: Extends from central groove at the central fossa between the mesiobuccal and distobuccal cusps and extends onto buccal surface. 16  Mandibular first molar Occlusal aspect Grooves: 3. Distobuccal developmental groove: Extends from central groove, distal to the central fossa between the distobuccal and distal cusps and extends onto buccal surface. 4. Lingual developmental groove: Extends from central groove at the central fossa between the lingual cusps but it does not extend onto lingual surface. 5. Marginal ridges groove: The mesial marginal ridge is more to have marginal ridge groove than the distal marginal ridge. Alaa H. Ali 6. Supplemental grooves: Radiates from the developmental grooves, forming small ridges between them and the developmental grooves that act as blades during mastication. 17 Thank you