Mandibular 2nd premolars

Mandibular 2nd premolars

1. Mandibular 2 nd premolars Dr . Samah khaled

2. Fifth tooth from midline. 1 per quadrant. Contacts lower 1 st premolar from mesial. Lower 1 st molar from distal. It is a successional tooth Do you remember the predecessor? Mandibular 2 nd deciduous molar

3. They are transitional teeth . 1 st premolar reflecting the transition from the canine . 2 nd premolar showing the change toward the molars. So its function is in grinding with the molars , while 1st premolar functions much like the canine.

4. Chronology First evidence of calcification 2 1\4- 2 1\2 y Crown completed 6-7 y Eruption 11-12 y Root completion 13-14 y

5. Buccal aspect 1. Geometrical outline Trapezoidal with shortest of uneven sides cervically. (Pentagonal) 2. Outlines Nearly straight from cervical line to contact area mesially . Straight or slightly concave distally. Occlusally the cusp: Tip of the buccal cusp is shorter and less sharp . Cusp tip is centered mesio -distally. This makes the two slopes nearly equal in length 3. Contact area: Both mesial and distal, are broad and at the same level at the junction between middle and occlusal thirds .

6. Buccal aspect 4. Surface anatomy (anatomical landmarks). Cervical ridge present in the cervical third of the buccal surface. Buccal ridge is a continuous ridge from the cusp tip to the cervical margin, which denotes strong development of the middle buccal lobe. Two developmental grooves mark the union of the developmental lobes. 5. The cervical line: The cervical line is curved rootwise . 6. Root Broader mesiodistally with blunter apex It often has a slight distal inclination in the apical third.

7. Lingual aspect The lingual lobes show greater development , which makes the cusp or cusps longer . Less of the occlusal surface is seen from this aspect. lingual cusps are not as long as the buccal cusp, so part of the buccal portion of the occlusal surface is seen. In the three-cusp type, mesiolingual and distolingual cusps are present, with the former being larger and longer . A groove is between them, extending a very short distance on the lingual surface and usually centered over the root.

8. Lingual aspect The two cusp type displays a single lingual cusp. There is no lingual groove , but a depression is often found toward the distal portion of the surface. The single cusp is approximately the same height as the mesiolingual cusp of the three cusp type . The height of contour of the lingual surface is found in the occlusal third of the crown.

9. Mesial aspect Geometric form: Rhomboidal Outline: Buccal outline: Convex from cervical line till the cusp tip. 2. The lingual outline: (represented by the mesiolingual cusp) is convex. In the three cusp type, the disto -lingual cusp is not visible from the mesial aspect. Crest of curvature: Just below the junction of the middle and cervical thirds . The crest of curvature of the lingual outline is found in the occlusal third , a location which is unique to the mandibular second premolar.

10. The tip of the buccal cusp is not centered over the root (buccal to midline) . The contact area is located toward the buccal , at the junction of the occlusal and middle thirds . It is larger in size than the mesial contact of the first premolar. It is also roughly circular in outline. The marginal ridge is nearly horizontal , and a little of the occlusal surface is visible. No mesiolingual developmental groove . The cervical line shows less depth in its occlusal curvature. Mesial aspect

11. Mesial aspect Crest of curvature of the lingual surface is out of the lingual outline of the root (out of root confines)(lingual overhang). The lingual cusps are short, so the buccal cusp is the only occluding cusp. Can’t be called bicuspid.

12. Distal aspect Resembles the mesial surface, except for: The distal marginal ridge is more cervically placed, resulting in more of the occlusal surface being visible from this aspect . In the three cusp type, the tips of both the mesio -lingual cusp and the disto -lingual cusp are visible. The contact area is shared with the first molar, it is larger and somewhat ovoid, wider buccolingually

13. Occlusal aspect • The geometric outline: Square The mesio -distal dimension of the crown is even greater through the lingual line angle area than it is through the buccal portion (no lingual convergence). The Y pattern of the occlusal table is formed by a combination of the central and lingual grooves . • Buccal cusp is largest , then mesio -lingual , then disto -lingual. There is no transverse ridge on the Y type. • There are two fossae , the mesial and distal triangular fossae. Both are linear and are relatively shallow and irregular. They are located just inside the marginal ridges, and are also bounded by two cusp ridges of each appropriate cusp.

14. There are three pits present on the occlusal table: Mesial pit: in the deepest portion of the mesial triangular fossa, which is about midway from buccal to lingual just inside the mesial marginal ridge, point of union of 3 grooves. Distal pit: in the depth of the distal triangular fossa is similar to that of the mesial pit, and it is also the point of union of 3 grooves. Central pit: the deepest of the three pits; located toward the lingual, and more than halfway from mesial to distal, since the ML cusp is wider than the DL cusp. The central pit is located along the central groove, where it joins the lingual groove. The central pit is thus the junction of two primary grooves.

15. Two cusp types (H type) • The geometric outline: Rounded. There is lingual convergence, making the lingual portion narrower, but the taper is never to the degree of the first premolar. The lingual cusp is placed directly opposite the buccal cusp so create a transverse ridge between triangular ridges. These teeth do not have either a lingual groove or a central pit. The buccal cusp is larger and somewhat higher than the lingual cusp. The lingual cusp of the H type is larger and sharper than in the U type, and on both types it is offset to the mesial. The H pattern is formed by the central groove , portions of the four triangular grooves, and the secondary grooves of the buccal and lingual cusps. The central groove runs roughly in a straight line between the two pits.

16. Two cusp type (U type) The U pattern is formed by the central groove, portions of the two buccal triangular grooves , and the secondary grooves of the buccal cusp. The central groove extends from the mesial pit to the distal pit, and in the process forms the lower portion of the "U". It can thus be characterized as crescent shaped. The only two pits, the mesial and distal pits , are the point of union of many grooves. The two cusp type has two fossae. They are roughly circular in shape, and are termed mesial and distal fossa. They are bounded by the transverse ridge , and appropriate marginal ridges and cusp ridges .

17. Pulp cavity The root is normally single, and tapers evenly to the apex which is relatively blunt. It often has a slight distal inclination in the apical third. The root is slightly wider and longer than that of the first premolar. The lingual pulp horns are higher in level and more developed. The general shape of the root from all aspects, as well as in mid root, cross section, ovoid

18. Clinical considerations 1. Congenitally missed. 2.Malformed teeth such as: Gemination. Abnormal root form. 3. Supernumerary teeth. 4. Early loss of predecessor tooth. 5. Relation to mental foramen.

19. Congenitally missed .

20. Gemination

21. Macrodontia

22. Supernumerary teeth Sometimes it is associated with syndromes such as Supernumerary teeth are associated with Gardner’s syndrome, Cleidocranial dysplasia, Down’s syndrome.

23. Thank you