Lec.10 Mand. 1st Molar PDF Dental Lecture Notes

Permanent Mandibular molars Lec.10 1st Stage Dr. Faten S.M  Permanent mandibular molars are larger than any other mandibular teeth. They are three in number (mandibular first molar , mandibular second molar and mandib...

Permanent Mandibular molars Lec.10 1st Stage Dr. Faten S.M  Permanent mandibular molars are larger than any other mandibular teeth. They are three in number (mandibular first molar , mandibular second molar and mandibular third molar) on each side of the mandible.  *All mandibular molars have crowns some what longer mesiodistally than buccolingually  *Each mandibular molar has two roots, one mesial and one distal.  *The crown of the molars are shorter cervico-occlusaly than anterior teeth  MANDIBULAR FIRST MOLAR  1. it is the largest tooth in the mandibular arch.  2. It has five well-developed cusps: two buccal, two lingual, and a distal cusp.  3. It has two well-developed roots, one mesial and one distal.  4. The dimension of the crown mesio-distally is greater by about 1 mm than the dimension bucco-lingually.  Eruption time: 6-7 years.  Root completed: 9-10 years. Buccal Aspect  1. The crown of the mandibular first molar is roughly trapezoidal  2. The mesial outline of the crown is concave at the cervical third. The distal outline of the crown is straight above the cervical line  3. All five of its cusps are in view from buccal aspect. The lingual cusps may be seen because they are higher than the others.  4. The mesio-buccal cusp, disto-buccal cusp , are flat.The distal cusp which is small, is more pointed than either of the buccal cusps.  5. The mesiobuccal cusp is usually the widest mesiodistally of the three cusps.  6. The two buccal cusps make up the major portion of the buccal surface of the crown. The distal cusp provides a very small part of the buccal surface.  7. These three cusps have the mesiobuccal and distobuccal grooves. The mesiobuccal groove is the shorter one  8.The mesial root is curved mesially from a point shortly below the cervical line to the middle third portion. Then it curves distally to the tapered apex  9. The distal root is less curved than the mesial root. The root may show some curvature at its apical third in either a mesial or a distal direction.  10. The point of bifurcation of the two roots is located approximately 3 mm below the cervical line. Lingual Aspect  1. From the lingual aspect, three cusps may be seen: two lingual cusps and the lingual portion of the distal cusp.  2. The mesiolingual cusp is the widest mesiodistally, with its cusp tip higher than the distolingual cusp.  3. The lingual developmental groove serves as a line of demarcation between the lingual cusps.  4. The mesial outline of the crown from this aspect is convex from the cervical line to the marginal ridge. The crest of contour mesially, which represents the contact area, is somewhat higher than the crest of contour distally.  5. The distal outline of the crown is straight immediately above the cervical. The cervical line lingually is irregular.  6. The roots of the mandibular first molar appear somewhat different from the lingual aspect. They measure about 1 mm longer lingually than buccally  Mesial Aspect  1. When the mandibular first molar is viewed from the mesial aspect, two cusps and one root only are to be seen: the mesiobuccal and mesiolingual cusps and the mesial root.  2. The buccolingual measurement of the crown and root is greater at the mesial portion than it is at the distal portion. Therefore, the mesial portions of the tooth are broader and the mesial cusps are higher  3. Contact area located at occlusal third.  4. The buccal outline of the crown of the mandibular first molar is convex above the cervical line. Lingual outline is straight and then convex above cervical line.  5. The cervical line mesially is irregular and tend to curve occlusally about 1 mm.  6. The buccal outline of the mesial root drops straight down from the cervical line buccally to a point near the junction of cervical and middle thirds of the root.  7. The lingual outline of the mesial root is nearly straight from the cervical line lingually to the point of junction of middle and apical thirds of the root. Distal Aspect  1. We see more of the tooth from the distal aspect because the crown is shorter distally than mesially  2. The distal root is narrower buccolingually than the mesial root.  3. The distal cusp is placed a little buccal to center buccolingually.  4. the distal contact area is placed just below the distal cusp.  5. The distal marginal ridge is short.  6. The cervical line distally extends straight and irregular.  7.The apical third portion of the root is more rounded than is found on the mesial root. Occlusal Aspect  1. It is somewhat hexagonal from the occlusal aspect. The crown measurement is 1 mm or greater mesiodistally than buccolingually.  2. The buccolingual measurement of the crown is greater on the mesial than on the distal. Also, a measurement of the crown at two buccal cusps and the distal cusp, shows greater measurement than the mesiodistal measurement of the two lingual cusps.  3.The mesiobuccal cusp is slightly larger than either of the two lingual cusps, which are almost equal to each other in size; the distobuccal cusp is smaller than any one of all cusps  4.There is a major fossa and there are two minor fossae. The major fossa is the central fossa.  5. The two minor fossae are the mesial triangular fossa, and the distal triangular fossa  6. The developmental grooves on the occlusal surface are the central developmental groove, the mesiobuccal developmental groove, the distobuccal developmental groove, and the lingual developmental groove.  7. Supplemental grooves short grooves and developmental pits are also found.  8.The mesial triangular fossa of the occlusal surface is a smaller concave area than the central fossa.  9. The distal triangular fossa less distinct than the mesial fossa. Pulp cavity of permanent mandibular first molar Buccolingual Section  1-The pulp chambers of the mesial root are square to rectangular  large pulp chamber  3-The mesial root usually has a more complicated root canal system because of the presence of two canals  4- One or both of the mesial canals may be significantly curved.  5-The two canals may join each other in the apical region to exit in a common foramen , or they may have separate apical foramina  6-The apical foramen usually appears to exit on the tip of the broad mesial root, but in some roots one of the two canals exits on the side of the root tip  7-The distal root usually has one large pulp chamber, which is very wide in the buccolingual dimension. The apical foramen of a root with a single canal usually appears to be located at the apex of the root, Mesiodistal Section  1-The pulp horns may be prominent, The pulp chambers are usually rectangular (excluding the pulp horns)  2-The mesial root and canal usually show considerable curvature, the apical foramen usually appears to exit at the tip of the root.  3-The distal root is usually straighter and tends to be a little shorter than mesial root ,  4- The distal canal is usually larger than the mesial canal Cervical Cross Section  The cervical cross section of the mandibular first molar is generally quadrilateral in form.