DENT1001: Mandibular First Molars

• The lecture covers DENT1001 Dental Anatomy, specifically focusing on mandibular first molars.
• Dr. Murat Kurt, a professor in the Department of Prosthodontics at Bahçeşehir University, presents the information.

Textbook

• Wheeler's Dental Anatomy, Physiology, and Occlusion, 11th Edition by Stanley J. Nelson is the textbook for the course.

Mandibular 1st Molars

• These are the three most posterior teeth in each lower quadrant.
• They are named first (six-year) molar, second (twelve-year) molar & third molar (wisdom tooth).
• They are the largest and strongest teeth in the mandibular arch.
• The crowns are much larger than premolars in all dimensions except occlusogingivally.
• General size decreases from the first molar through the third molar.

Proportions

• Crowns are wider mesiodistally than buccolingually.
• Viewed from the occlusal aspect, crowns are rectangular or pentagonal.
• From proximal aspect, crowns are rhomboidal & inclined to the lingual.
• The presence of four or five major cusps, including two lingual cusps of approximately the same size is a key characteristic.
• Two roots are typically present.

Buccal Aspect

• The crown is roughly trapezoidal with cervical and occlusal outlines representing the uneven sides.
• All five cusps can be seen if the tooth is posed vertically.
• The lingual cusps may be visible due to their greater height.
• The mesiobuccal, distobuccal & distal cusps are relatively flat
• The distal cusp, being small, is more pointed than the others.
• Flattened buccal cusps are typical.
• The mesiobuccal cusp is usually the mesiodistally widest.
• This has some curvature but is relatively flat.
• The distobuccal cusp is almost as wide, with a more curved cusp ridge.
• Mesiobuccal & Distobuccal grooves provide key points of demarcation.
• Mesiobuccal groove is shorter with terminus centrally located cervico-occlusally.
• Distobuccal groove has terminus near distobuccal line angle at cervical third of the crown
• The distal cusp provides a small part of the buccal surface, major portion makes up distal portion of crown
• The distal cusp ridge is rounded occlusally and is sharper than the buccal cusps
• The cervical line is commonly regular, dipping apically toward the root bifurcation.
• The mesial outline is slightly concave cervically from the contact area, & convex occlusally to the contact.
• The height of contour of the mesial outline is located at the junction of the occlusal & middle thirds.
• The roots are well-formed and constant in development.
• The mesial root curves mesially below the cervical line to the middle third portion.
• It curves distally to tapered apex, which is located directly below the mesiobuccal cusp.
• The crest of curvature of the mesial root is mesial to the crown cervix.
• The distal outline is generally more convex than the mesial outline.
• In the occlusal portion, it is rounded, and cervical to the contact area it is straight to slightly convex.
• The height of contour is found slightly more cervically than mesial margin, still at junction of occlusal & middle thirds.
• The distal root is less curved, distal direction from cervix to apex.
• The apical third may show curvature in either mesial or distal direction.
• Crest of curvature mesially is mesial to the crown cervix
• Distal outline of the mesial root is concave from the bifurcation of the root trunk to the apex.
• The apex is usually more pointed & located below or distal to the distal contact area of the crown
• Considerable variation is evident in comparative lengths of mesial and distal roots
• Both roots are wider mesiodistally at the buccal than they are lingually.
• The point of bifurcation of two roots is approximately 3 mm below the cervical line.
• Deep developmental depression is evident buccally on root trunk starting at bifurcation, progressing cervically, & terminating near cervical line.

Lingual Aspect

• Three cusps may be seen: two lingual cusps and the lingual portion of the distal cusp.
• The two lingual cusps are pointed
• Cusp ridges are high enough to hide the two buccal cusps from view
• Mesiolingual cusp is widest mesiodistally, tip somewhat higher than distolingual cusp.
• Distolingual cusp is almost as wide mesiodistally as the mesiolingual cusp.
• The lingual developmental groove serves as a line of demarcation between the lingual cusps.
• Some teeth show no groove but show a depression lingual to the cusp ridges.
• The angle formed by the cusp ridge of the mesiolingual cusp and cusp ridge of the distolingual cusp is more obtuse than angulation at cusp tips.
• Angle formed by the distolingual cusp ridge of mesiolingual cusp and the mesiolingual cusp ridge is more of obtuse than at lingual cusp tips
• The entire distal margin is convex from the contact area occlusally
• Height of contour of distal outline is at junction of occlusal and middle thirds.
• The mesial outline is convex occlusal from the contact area which is the crest of curvature, at the junction of occlusal and middle thirds.
• Mesial outline cervically from contact area is concave.
• The cervical line is shorter mesiodistally and is located at a more occlusal level than on the buccal surface.
• The cervical line is usually irregular and nearly straight, although it can project in the bifurcation area.
• The surface of the crown lingually is smooth and spheroidal on each of lingual lobes.
• The surface is concave at the side of the lingual groove above the center lingually.
• Surface of the crown becomes almost flat as it approaches the cervical line below this point
• The root bifurcation lingually starts approx. 4 mm below cervical line
• The depression is rarely reflected in the cervical line or the enamel of the lingual surface of the crown.
• The roots appear different from lingual aspect.
• Measure about 1 mm longer lingually than buccally, but the length seems extreme.
• This impression is derived from the fact that cusp ridges/cervical lines are higher (1 mm).

Mesial Aspect

• Viewed with mesial surface at right angles to the line of vision, two cusps & one root are seen: mesiobuccal/lingual cusps & mesial root.
• Crown from mesial/distal aspect is roughly rhomboidal, entire crown has a lingual tilt in relation to the root axis.
• Crowns of maxillary posterior teeth have the center of the occlusal surfaces between cusps in line with the root axes.
• The buccal outline of the mandibular first molar is convex above the cervical line.
• Above the cervical ridge, the buccal contour may be slightly concave or flat or less convex, outlining the mesiobuccal cusp
• The lingual outline of the crown is straight in a lingual direction, starting at the cervical line.
• Lingual curvature is pronounced between this point and the tip of the mesiolingual cusp.
• The crest of the lingual contour is located at the center of the middle third of the crown.
• The mesial marginal ridge is confluent with the mesial ridges of the mesiobuccal and mesiolingual cusps.
• Marginal ridge is placed approx. 1 mm below the level of the cusp tips.
• Contact area is almost centered buccolingually & placed below the crest of the marginal ridge about one-third the distance from the marginal ridge to the cervical line.
• Cervical line mesially is rather irregular & tends to curve occlusally about 1 mm toward center of the mesial surface of the tooth.
• The cervical line may assume a relatively straight line buccolingually. The mesiobuccal cusp is located directly above buccal third of the mesial root.
• The tip of mesiolingual cusp is directly above the lingual third of the mesial root.
• The buccal outline of the mesial root drops straight down from the cervical line to a point near the junction of cervical and middle thirds of the root.
• A gentle curve starts lingually from this point to the apex, under the mesiobuccal cusp. The cervical line is usually shorter 1 mm in first molar than second. Can vary. The first molar root is usually shorter 1 mm. Can vary. The buccolingual measurement of crown and root of the molar is greater by 2 mm. Lingual cusp is longer than the buccal cusp.

Distal Aspect

• The distal cusp is in the foreground on the crown.
• The distal cusp is slightly buccal to the center buccolingually, with the distal contact area appearing on its distal contour.
• The distal marg. ridge is typically short, consisting of the distal cusp ridge of the distal cusp and distolingual cusp ridge of distolingual. These cusp ridges dip sharply in a cervical direction, meeting at obtuse angle. Distal contact area is placed just below the distal cusp ridge The distal cusp is placed higher than area mesially. Often a, developmental groove or depression is crossing the marginal ridge. Contact area is centered over the distal root Arrangement is buccal to the center point of the distal marginal ridge.
• The distal surface is similar in outline to the mesial, wider buccolingually at the cervical than at the occlusally.
• The distal surface is generally smaller than the mesial, especially in the buccolingual dimension.
• The cervical line distally usually extends straight across.
• Cervical line distally dips rootwise below the contact area.
• The apical third portion of the root is more rounded as it tapers to a sharper apex than is found on the mesial root.
• The lingual border of the mesial root may be seen from the distal aspect. if the specimen held with its distal surface of crown at right to the line of vision. Much of occlusal surface and some of five cusps be seen which favourably compares to mandibular premolar 2

Occlusal Aspect

• The mandibular first molar is somewhat hexagonal

• The crown measurement is greater by 1 mm or more mesiodistally than buccolingually.

• The mesiobuccal cusp is slightly larger than either of the two lingual cusps The lingual cusps are almost of equal size The distobuccal cusp is smaller than any of those

• The distal cusp is the smallest in most cases

• when the tooth is posed with the line of vision is Parallel with the long axis then great part buccal is visible Small portion of the lingual is visible,

• no part of mesial is visible

• There is a major fossa, the central fossa is roughly circular, placed centrally on the occlusal surface

• Two minor fossae are:

• mesial triangular fossa (immediately is distal to the mesial marginal ridge Distal triangular fossa immediately mesial to the distal marginal ridge

• Developmental grooves are"

• central developmental

• mesiobuccal developmental

• distobuccal and the lingual

• supplemental grooves pit are also grooves, most supple is tributary to. developmental.

• The lecture thanks the audience and indicates the next lecture will cover maxillary & mandibular 2nd and 3rd molars.