lower second & third molar

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آية ) ْاَلْبقرة (32ُسورة

بسَم ْاَلْله ْاَلرحْمن ْاَلرحيَم

الله صدق

العظيم

Permanent Mandibular

Second & Third Molars

By:Assistant professor of Oral

BiologyFaculty of DentistryMansoura University

General characters of the Permanent Mandibular second Molar:

1. Arch position:

General characters of the Permanent Mandibular second Molar:

2. General form and function:

The second molar resembles the first molar in many respects, although it is more symmetrical, and smaller in all dimensions. It has the least complicated occlusal design of any molar. Normally only four cusps are present, and thus there is no distobuccal groove, and no distal cusp. In mastication, it functions with the other molars in grinding.

Chronology1st.

Molar2nd.

Molar3rd.

molarEnamel organ

appearance

1st. Evidence

of calcificati

on

4 m.i.u

At birth

1 year

2 - ½ 3 years

4 year

8 – 10 years

Enamel completed

2 - ½ 3 years

7 – 8 years 12 – 16 years

Eruption 6 – 7 years 11 – 13 years

17 - 21 years

Root completed

9 – 10 years

14 – 15 years

18 – 25 years

Describe in details the morphological differences between mandibular permanent first and second molars, mentioning their chronology and illustrating your answers with diagrams

Buccal aspect1st. Molar 2nd. MolarCrown:

1. The crown is somewhat shorter cervico-occlusally.

2. The crown is narrower mesiodistally.

3. There are only two buccal cusps, which are about equal in their mesiodistal measurements but mesiobuccal cusp is wider.

4. There is only one buccal developmental groove act as a line of demarcation between the mesiobuccal and distobuccal cusps and it may end in a pit on the middle of the buccal surface.

½

½

⅓

⅓

⅓

Buccal aspect1st. Molar 2nd. Molar

Crown:5- More cervically lacated contact areas..6- Cervical line is nearly straight. It may point sharply toward the root bifurcation7- crown more symmetrical from all aspects.

Buccal aspect1st. Molar 2nd. MolarRoot

1.The root is shorter than those of the first molar.2.The roots are usually straighter and closer together and their axes are nearly parallel.3.The roots are inclined distally in relation to the occlusal plane than is found on the first molar.4.The roots taper apically and more pointed than of the first molar.5.Both roots are flattened MD and M root is slightly longer than D root.6.Longer root trunk.

Lingual aspect1st. Molar 2nd. Molar1- Only lingual cusps

are visible and more pointed than buccal cusps. 2- The main difference is that the lingual convergence of the tooth as a whole, crown & root, is less than what could be found in the first molar.

Lingual aspect1st. Molar 2nd. MolarThis relation resulted in:

1. Mesiodistal calibration at the cervix lingually is always greater than that of the mandibular permanent first molar.

2. Little of the mesial and distal surfaces may therefore be seen from this aspect.

3. The curvature mesially and distally on the crown that representing the contact areas are more noticeable from the lingual aspect.

4. The contact areas are found to be at slightly lower level, especially in the distal contact area, than those of 1st. molar

Mesial aspect1st. Molar 2nd. MolarCrown

1. The cervical ridge buccally is in most cases less pronounced.2. The mesial contact area is larger in size. 3. The occlusal surface may be more constricted buccolingually.4. Cervical line shows less curvature, being straight and regular in outline buccolingually.

BB

L

Mesial aspect1st. Molar 2nd. Molar

Root

1-The M root is less broad and is somewhat pointed apically, permitting part of the distal root to be in sight buccally, while in first molar it appeared lingually.2- The M root has longitudinal depression on its M surface as 1st. molar

B

L

Distal aspect1st. Molar 2nd. Molar1. Absence of distal cusp.

2. DB cusp is the shortest of the four cusps.

3. Absence of distobuccal groove.4. Contact area is larger and is

centered on the distal surface buccolingually and is placed equidistant from cervical line and marginal ridge.

5. The D marginal ridge is concave but less angular than M one and less frequently crossed by a marginal groove

B

L

Occlusal Aspect of

Mandibular first Molar : 1. Geometric outline:

2. Dimensions.

3. Surface outlines:

- Buccal outline.

- Lingual outline.

- Mesial outline.

- Distal outline

4. Surface describtion:

- Cusps. - Ridges.

- Grooves.

- Fossae. - Pits.

1

2 2

34

Occlusal aspect1st. Molar 2nd. Molar• Geometric outline:

The occlusal aspect geometric

outline found to be rectangular in shape.

• Dimensions.

1. The crown is larger MD than BL.

2. The D side is narrower than the M side and the L side is narrower than B side.

• Surface outlines:

1. Prominent cervical bulge can be seen.

2. The D shorter side is more convex (semicircular )than M side which is nearly straight.

Occlusal aspect1st. Molar 2nd. Molar• Surface describtion:

- Cusps. 1. Absence of the distal cusp.2. The four cusps are nearly

equal. The two M cusps are larger than D cusps (MD and BL).

- Ridges.1. Four Δ ridges of four cusps

making transverse ridge between MB and ML cusps and DB and DL cusps.

2. 2 marginal ridges M and D.- Fossae.1. Large central fossa.2. Small M Δ fossa.3. Minute D Δ fossa.- Pits.1. May be present in any of the

fossae.

Occlusal aspect1st. Molar 2nd. Molar

- Grooves.Developmental grooves.1- Cross – shaped groove

(cruciform fissure), dividing the occlusal portion of the crown into four parts that are nearly equal.

2- Absence of the distobuccal developmental groove.

3- The central groove extends from the central fossa to both M and D Δ fossae. Its course is straighter than lower 6.

4- B groove separates the two B cusps. L groove separates the two L cusps.

5- The buccal and lingual developmental groove meet the central developmental groove at right angles at the central pit on the occlusal surface.

Occlusal aspect1st. Molar 2nd. Molar

- Supplemental grooves.1. Many supplemental grooves found to be radiating from the developmental grooves.2. The cusp slopes on occlusal surface are roughened by these grooves.3. The marginal ridge grooves

may be seen and are more in M than D.

Buccal aspect1st. Molar 2nd. Molar 3rd. Molar

Lingual aspect1st. Molar 2nd. Molar 3rd. Molar

Mesial aspect1st. Molar 2nd. Molar 3rd. Molar

Distal aspect1st. Molar 2nd. Molar 3rd. Molar

Occlusal aspect1st. Molar 2nd. Molar 3rd. Molar

Buccal aspect1st. Molar 2nd. Molar 3rd. Molar

Lingual aspect1st. Molar 2nd. Molar 3rd. Molar

1st. Molar 2nd. Molar 3rd. Molar

Mesial aspect

1st. Molar 2nd. Molar 3rd. Molar

Distal aspect

1st. Molar 2nd. Molar 3rd. Molar

Occlusal aspect

1st. Molar 2nd. Molar 3rd. Molar

Lower 6 &7

Buccal aspect Occlusal aspect

34

Lower 6&7

Buccal aspect Occlusal aspect

35

Lower 8

Buccal aspect Lingual aspect

36

Lower 8

Occlusal aspect

37

A QESTION?