Lecture 13 dental anatomy.pdf

Lecture 13 Lecture(13) MANDIBULAR FIRST MOLAR Principal identifying features 1- Five cusps, 2 buccal, 2 lingual, and one distal. 2- The buccal surface is bulky (lingually inclined)...

Lecture 13 Lecture(13) MANDIBULAR FIRST MOLAR Principal identifying features 1- Five cusps, 2 buccal, 2 lingual, and one distal. 2- The buccal surface is bulky (lingually inclined) with two dev. grooves. 3- The crown is wider Mesio-distally than Bucco-lingually. 4- Occlusal outline is rectangular in shape. 5- Two well developed roots, one mesial, and one distal. Buccal aspect 1- The mesial contact area is at the junction of the occlusal and the middle thirds. 2- The distal contact area is a little lower than the mesial contact area. 3- The cervical line is regular, curving apically.  Lecture 13 4- There are 2 developmental grooves between the cusps acting as lines of division between the buccal cusps. The Mesio-buccal developmental groove is shorter than the disto-buccal d.-g. 5- The Mesio-buccal, disto-buccal, and distal cusps are clearly visible, and the Mesio-lingual, and disto-lingual cusp’s tips are seen. 6- The Mesio-buccal cusp is slightly wider than the disto-buccal cusp, together making 80% of the Mesio-distal width. The distal cusp makes the rest 20%. 7- The buccal cusps are flat occlusally, the distal cusp is rounded. 8- The point of bifurcation of the 2 roots about 3mn below the cervical line.  Lecture 13 Lingual aspect 1- Three cusps seen (Mesio-lingual, Disto-lingual, and lingual portion of the distal cusp). Mesio-lingual cusp is the widest Mesio-distally and has the highest cusp tip and the distal cusp is the lowest. 2- The 2 lingual cusps are pointed, and form obtuse angles at their cusp tips. 3- The lingual developmental groove extends downward for about a 1/3 of the crown length, and acts as a line of division between the lingual cusps.  Lecture 13 Mesial aspect 1- The crown is rhomboidal with a lingual tilt of the buccal outline. 2- The buccal outline of the crown is convex at the junction of the cervical and middle thirds (buccal cervical ridge), then the outline straightens to the buccal cusp tip. 3- The lingual outline is less convex, with the crest of curvature at the center of the middle third. 4- The cervical line is irregular, higher lingually than buccally. 5- The buccal cusp is flat, and the lingual cusp is sharp, with greater cusp height. 6- The mesial marginal ridge is located 1mm below the level of the cusp tips.  Lecture 13 Distal aspect 1- Because the crown is shorter distally, than mesially, most of the buccal, lingual, and occlusal surfaces can be seen from the distal aspect. 2- Distal cusp is located buccal to tooth long axis. 3- Distal marginal ridge is short and curves cervically to form obtuse angle. 4- The cervical line is irregular. 5- Distal root is narrower than mesial root.  Lecture 13 Occlusal aspect:- 1- The crown is rectangular in shape, Mesio-distally longer by 1mm than bucco-lingually. 2- Bucco-lingual measurement of the crown is greater on mesial than on distal. The Mesio-distal measurement is greater on buccal than on lingual. 3- More of the buccal surface of the crown can be seen than of the lingual surface. 4- There are 5 cusps, Mesio-buccal (largest), then Mesio-lingual and disto-lingual, then disto-buccal, then the distal cusp.  Lecture 13 5- The distal contact area is on the distal cusp. 6- There are 4 dev. grooves: a) Central d. g. (centrally) b) Mesio-buccal d. g. divides the Mesio-buccal and disto-buccal cusp. c) Disto-buccal d. g. It divides the disto-buccal and distal cusp. d) Lingual d. g. It divides the Mesio-lingual and disto-lingual cusp. 7- There are 3 fossa: a) Central fossa. Roughly circular bounded by Distal slope of Mesio-buccal cusp, Both mesial and distal slopes of Disto- buccal cusp, Mesial slope of the distal cusp, Distal slope of Mesio-lingual cusp, Mesial slope of the disto-lingual cusp. b) Mesial Δ fossa. It is distal to the mesial marginal ridge. c) Distal Δ fossa. It is mesial to the distal marginal ridge.  Lecture 13 8- There are 3 pits: a) Central pit. In the center of the central fossa. b) Mesial pit. In the mesial Δ fossa. c) Distal pit. In the distal Δ fossa.