Dental Anatomy II: Lec. 8 Permanent Mandibular First Molar PDF

Dental anatomy II Lec. 8 The permanent mandibular first molar Dr.Ekhlas Saeed Beshr 1  Permanent mandibular molars They are three on each side of the mandible: the first, second, and third molars. They have two roots: mesial and dist...

Dental anatomy II Lec. 8 The permanent mandibular first molar Dr.Ekhlas Saeed Beshr 1  Permanent mandibular molars They are three on each side of the mandible: the first, second, and third molars. They have two roots: mesial and distal roots Third molars and some second molars may have fused roots. In mandibular molars, the mesiodistal dimension of the crown is larger than the buccolingual dimension ,but the maxillary molars are wider buccolingually than mesiodistally. They are the largest and strongest mandibular teeth, because of their bulk and because of their anchorage. The mandibular molars function is grinding and mastication of the food. 2  Permanent mandibular 1st molar The mandibular first molar is the largest tooth in the mandibular arch. It has five cusps: Two buccal( mesiobuccal and distolbuccal) , two lingual (mesiolingual and distolingual( and a distal cusp. It is formed from 5 lobes It has two root: mesial and distal roots which are curved distally 3  The chronology of permanent mandibular first molar The tooth notation The chronology 4  The buccal aspect Geometric shape: trapezoidal The mesial outline is concave until it joins the mesial contact area. distobuccal cusp mesiobuccal cusp The mesial contact area is at the junction of occlusal and middle thirds. The distal outline of the crown is straight until it joins the distal cusp distal contact area. The distal contact area is at the middle third of crown. We can see the three cusps (mesiobuccal, distobuccal and the buccal part of the distal cusp). The tips of two lingual cusps are also seen because they are 5 at higher level than the buccal cusps.  The buccal aspect The mesiobuccal cusp is wider than the distobuccal cusp. The mesiobuccal, distobuccal and distal cusps are relatively flat. distobuccal groove mesiobuccal groove The distal cusp, which is small, is more pointed than the buccal cusps. The distal cusp forms a very small part of the buccal surface, because the major part of the cusp forms the distal part of the crown The two buccal cusps are separated by the mesiobuccal developmental groove The distobuccal and distal cusps are separated by the distobuccal developmental groove. Mandibular right first molar 6  The buccal aspect The mesiobuccal groove is shorter than the distobuccal groove. The mesiobuccal groove ends at the center of the crown cervico- occlusally (at the buccal pit) and it is a little mesial to the root mesiobuccal groove bifurcation. distobuccal groove The distobuccal groove ends at the cervical third of the crown. The buccal surface is convex in the occlusal third, concave in the middle third and it is more convex in the cervical third forming the cervical ridge. Mandibular right first molar 7  The roots The roots are well formed and they are wider mesiodistally from the buccal aspect than the lingual aspect. The mesial root is curved distally. The distal root is less curved than the mesial root, and its axis is in a distal direction from the cervix to the apex. It may have a mesial or distal curvature. The point of bifurcation is approximately 3 mm below the cervical line. There is a deep developmental depression on the root trunk, which starts at the bifurcation and ends at or above the cervical line. This depression is smooth with no developmental groove. 8 Mandibular right first molar  The buccal aspect Mandibular right first molar MBDG, Mesiobuccal developmental groove CL, cervical line MR, mesial root DR, distal root DBDG, distobuccal developmental groove DC, distal cusp DLC, distolingual cusp; DBC, distobuccal cusp; MLC, mesiolingual cusp; MBC,mesiobuccal cusp. 9  The lingual aspect Geometric shape: trapezoidal ML cusp DL cusp The surface of the crown is smooth and spheroidal The mesial and distal outlines are similar to the buccal aspect. Only lingual cusps and small part of distal cusp are seen The two lingual cusps are almost of same width and are sharper and longer than the buccal cusps. The two lingual cusps are separated by the lingual developmental groove which runs for a shorter distance on the lingual surface and is in line with the bifurcation of the root. The mesiolingual cusp tip is at a higher level than the distolingual cusp The distal cusp tip is at10 a lower level  The lingual aspect The crown tapers lingually making the lingual surface narrower than the buccal surface, so: 1- a part of distal cusp is seen. 2- a part of the proximal surfaces of the crown can be seen. The cervical line on lingual surface is irregular and curved apically. The roots are about 1 mm longer lingually than buccally, but the length seems more extreme because: - the cusp ridges and cervical line are at a higher level (about 1 mm) - The mesiodistal dimension of the root trunk is less lingually than buccally. 11  The lingual aspect The root bifurcation lingually starts at a point approximately 4 mm below the cervical line. There is a developmental depression on the root trunk. Mandibular right first molar DLC, Distolingual cusp LDG, lingual developmental groove CL, cervical line; MLC, mesiolingual cusp. 12  The mesial aspect Geometric shape: rhomboidal The buccal outline is more convex in the cervical third (the cervical ridge) then slightly convex to the mesiobuccal cusp tip The height of buccal contour is in the cervical third of the crown. The lingual outline is convex from cervix to the mesiolingual cusp tip The height of lingual contour is at the center of the middle third. The buccolingual measurement of the crown and root is greater mesially than distally. Only the mesiobuccal and mesiolingual cusps can be seen from this aspect. The mesiolingual cusp tip is sharp and at a higher level than the flattened mesiobuccal cusp tip. 13  The mesial aspect The mesial contact area is at the junction of occlusal and middle third of the crown cervico-occlusally and in the center of the crown buccolingually. The mesial marginal ridge forms a concave outline. The marginal ridge is placed about 1 mm below the level of the cusp tips. The cervical line on mesial surface may be straight or slightly curved occlusally and is at a higher level lingually than buccally. The mesial surface is smoothly convex except for the shallow concavity just below the contact area, which joins the a depression on the center of the mesial root. 14  The mesial aspect The mesial surface of the mesial root is convex at the buccal and lingual borders. There is a developmental depression for most of the root length. 15  The mesial aspect Mandibular right first molar MMR, Mesial marginal ridge MLC, mesiolingual cusp MCA, mesial contact area CL, cervical line DD, developmental depression CR, cervical ridge MBC, mesiobuccal cusp. 16  The distal aspect Geometric shape: rhomboidal The buccal and lingual outlines are the same as the mesial aspect. The distal surface is shorter and narrower than the mesial surface. Most of the buccal surface and some part of the lingual surface can be seen from this aspect because the crown tapers distally. Note: The buccal surface shows more convergence than the lingual surface. A great part of the occlusal surface and some part of each of the five cusps may be seen because of the distal inclination of the crown. The distal marginal ridge is : - shorter and - at a lower level than the mesial marginal ridge 17  The distal aspect The distal contact area is placed more buccally. The distal cusp ridge of the distal cusp and the distolingual cusp ridge of the distolingual cusp meet at an obtuse angle. Often, a developmental groove or depression is found crossing the marginal ridge at this point. The cervical line is straight. The distal root is narrower buccolingually than the mesial root so the lingual border of the mesial root may be seen from the distal aspect. 18  The distal aspect MMR, Mesial marginal ridge MBC, mesiobuccal cusp DBC, distobuccal cusp DC, distalcusp DBDG, distobuccal developmental groove; DCA, distal contact area CL, cervical line DMR, distal marginal ridge DLC, distolingual cusp MLC, mesiolingual cusp. 19  The occlusal aspect Geometric shape: hexagonal with unequal sides. The mesiodistal measurement of the crown is greater than the buccolingual measurement. The crown is bulkier mesially than distally because the crown tapers in a distal direction. The mesial and distal surfaces converge lingually making the lingual surface of the crown narrower than the buccal surface More of buccal surface can be seen from occlusal aspect and very little of lingual surface. 20  The occlusal aspect Cusps and Cusp Ridges All mandibular molars have four major cusps( MB,DB,ML,DL) and one minor cusp ( distal cusp). Distobuccal Mesiobuccul cusp The size of the mandibular cusps in a decreasing order is: Distal cusp 1- The mesiobuccal cusp is the largest 2- The mesiolingual and the distolingual cusps which are nearly equal in size 3- The distobuccal cusp 4- The distal cusp is the smallest one. The cusp ridges of the buccal cusps and distal cusp are usually flattened. Distolingual cusp The lingual cusps are sharp with well-defined cusp ridges. Mesiolingual cusp 21  The occlusal aspect Fossae There is one major fossa and two minor fossae. The major fossa is the central fossa and the 2 minor fossa are mesial triangular fossa and the distal triangular fossa. The central fossa : is a circular large depression in the center of the occlusal surface. It is bounded buccally by the distal slope of mesiobuccal cusp, the mesial and distal slopes of the distobuccal cusp and the mesial slope of distal cusp. Lingually, it is bounded by the distal slope of mesiolingual and the mesial slope of distolingual cusp. 22  The occlusal aspect The mesial triangular fossa: has the mesial marginal ridge as base, the mesial pit as apex. The distal triangular fossa: is less distinct than the mesial triangular fossa. It has the distal marginal ridge as the base, distal pit as the apex. 23  The occlusal aspect Marginal Ridges The distal marginal ridge is shorter and at a lower level than the well-developed mesial marginal ridge. Pits: There are three pits: 1- The central pit :is at the center of the central fossa. 2- The mesial pit : is in the mesial triangular fossa 3- The distal pit: is in the distal triangular fossa 24  The occlusal aspect Grooves :There are four developmental grooves and some supplemental grooves. 1- The central developmental groove: originates at the central pit and runs in mesial and distal directions. Its mesial course from the central pit is relatively smooth and ends in the mesial triangular fossa. The distal course is irregular and ends in the distal triangular fossa. The central developmental groove seems to be at the center of the crown buccolingually. 25  The occlusal aspect 2-The mesiobuccal developmental groove: joins the central developmental groove just mesial to the central pit and runs mesiobuccally separating the mesiobuccal and distobuccal cusps and ends on the buccal surface in the buccal pit 3-The distobuccal developmental groove joins the central groove, distal to the central pit and runs distobuccally between the distobuccal and distal cusps to end on the buccal surface Distobuccal groove mesiobuccal groove Central groove Central groove 26 Lingual groove  The occlusal aspect 4- The lingual developmental groove: takes a lingual course from the central pit and extends onto the lingual surface separating the two lingual cusps Note : Several supplemental grooves can be seen originating from the developmental groove Distobuccal groove mesiobuccal groove Central groove Central groove 27 Lingual groove  The occlusal aspect Mandibular right first molar 28  The roots There are well developed two roots—mesial and distal. There are developmental depressions on mesial and distal surfaces of both the roots extending for the entire length of roots. 29  Thank you 30