Dental Anatomy Lecture 15: Mandibular Second Molar PDF

Lecture 15 7 May. Al-Noor University Mandibular College /Dentistry 1st Year second molar Dent...

Lecture 15 7 May. Al-Noor University Mandibular College /Dentistry 1st Year second molar Dental Anatomy By: Assist. Lect. Alaa Hussein Ali 2023-2024  Mandibular second molar Eruption time: 11-13 years Root completed: 14-15 years It has 4 cusps (2 buccal cusps and 2 lingual cusps) developed from 4 lobes. The longest cusp is the mesiolingual cusp followed by the distolingual cusp then the mesiobuccal cusp and the shortest is the distobuccal cusp. The mandibular second molar has 2 roots, one mesial and one distal. Alaa H. Ali 2  Mandibular second 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. Four cusps are visible from this aspect. The mesiolingual cusp is the longest followed by distolingual, mesiobuccal and distobuccal cusp. The two buccal cusps are relatively flat but the mesiobuccal cusp is wider than the distobuccal cusp. There is one buccal developmental groove separates between Alaa H. Ali the buccal cusps and may end with buccal pit. 3  Mandibular second molar Buccal aspect The crown has no distal bulge as compared to mandibular 1st molar because there is no distal cusp in mandibular 2nd molar. 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 cervical line is nearly straight with little curve. The root trunk is longer than that of mandibular 1st molar. There is a developmental depression on buccal root trunk. The mandibular 2nd molar has 2 roots. The longer mesial and Alaa H. Ali the shorter distal roots are more parallel and less separated as compared to mandibular 1st molar and the apices are pointed and directed toward the centerline of the tooth. Or both roots are curved toward the distal. 4  Mandibular second 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. Mesiolingual cusp is slightly wider than distolingual cusp. 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 groove. The mesial marginal ridge is more occlusal than distal marginal ridge. The cervical line is nearly straight. Alaa H. Ali The longer mesial and the shorter distal roots are visible from this aspect. Both roots taper lingually. The mesial root is not twisted as mandibular 1st molar. There is a developmental depression on lingual root trunk 5  Mandibular second 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. The buccal cervical ridge is more prominent than that of mandibular Alaa H. Ali 1st molar. The mesial marginal ridge is more occlusal than the distal marginal ridge. 6  Mandibular second molar Mesial aspect Only the mesial root is visible from this aspect because it is wider and longer than distal root. There is a deep longitudinal developmental depression on the mesial surface of the mesial root and deeper depression on its distal surface. Marginal groove is more likely to be located on mesial marginal ridge than distal marginal ridge. Alaa H. Ali 7  Mandibular second 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. Four 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. The distal marginal ridge is more cervical than the mesial marginal ridge. The mesial and distal roots are visible from this aspect. Alaa H. Ali There are developmental depressions on both sides of distal root. 8  Mandibular second molar Occlusal aspect The outline of the crown is roughly rectangle because of the buccal cervical ridge is more prominent on mesiobuccal cusp than distobuccal cusp The crown is wider mesiodistally than buccolingually. The buccolingual dimension of mesial half is greater than the distal half. Four cusps are visible. The mesiobuccal cusp is larger than the distobucal cusp and the mesiolingual cusp is larger than distolingual cusp. Alaa H. Ali 9  Mandibular second molar Occlusal aspect Mesial contact and distal contact areas are located buccally to the middle of the crown. The mesial contact area is more buccally then distal contact area. The buccal surface could be seen from this aspect more than the lingual surface. Fossae: There are 3 fossae on the occlusal aspect 1. The largest central fossa, which is roughly circular with Alaa H. Ali central pit. 2. The smaller mesial triangular fossa with mesial pit. 3. The smallest distal triangular fossa with distal pit. 10  Mandibular second molar Occlusal aspect Ridges: 1. Triangular ridges: There are 4 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 11  Mandibular second molar Occlusal aspect Grooves: 1. Central developmental groove: Extends from mesial triangular fossa to distal triangular fossa passing through the central fossa. 2. Buccal developmental groove: Extends from central groove at the central fossa between the mesiobuccal and distobuccal cusps and extends onto buccal surface. 3. Lingual developmental groove: Extends from central groove at the central fossa between the lingual cusps but it is unlikely to extend onto lingual surface. The lingual groove lines up with the Alaa H. Ali buccal groove to form cross pattern (+). 4. Marginal ridges groove: The mesial marginal ridge is more likely to have marginal ridge groove than the distal marginal ridge. 5. The mandibular 2nd molar has more supplemental grooves. 12 Thank you