DIFFERENCE BETWEEN MANDIBULAR FIRST MOLAR AND

SECOND MOLAR

The Permanent Mandibular Molars:

A. Introduction:1. The permanent mandibular molars are the three most posterior teeth in each lower quadrant.

Like their maxillary counterparts, they are named first(six-year) molar, second (twelve-year) molar, and third molar (wisdom tooth).

They are the largest and strongest teeth in the mandibular arch. Mandibular molar crowns are much larger than those of mandibular premolars in all dimensions except occlusogingivally, where they are slightly shorter.

Their general size normally decreases from first molar through third molar.

FUNCTIONS:

2. The mandibular molars function with the maxillary molars in grinding, and their form, root structure, and bone support are suited to this role.

3. A review of the features which serve to differentiate mandibular and maxillary molars includes:

a. Crowns which are wider mesiodistally than buccolingually.

b. Crowns which are rectangular or pentagonal from the occlusal aspect.

c. Crowns which are rhomboidal and inclined to the lingual, from a proximal aspect.

d. The presence of four or five major cusps, of which there are always two lingual cusps of approximately the same size.

e. The presence of two roots in most cases.

Permanent Mandibular First Molar:1. General characteristics:a. Arch position -The initial permanent tooth to erupt, the mandibular first molar is located sixth from the midline, and distal to the second deciduous molar. Hence it is not a succedaneous tooth.

Because of its normal eruption time, it is often called a "six year" molar.

The first molars are also thought of as the cornerstones of occlusion in the mandibular arch.

It shares a mesial contact with the deciduous second molar for approximately five years, until that tooth is replaced by the second premolar. There is no distal contact, until eruption of the permanent second molar occurs at about age twelve.

Universal number:

Mandibular right first molar - #30

Mandibular left first molar - #19

c. General form and function - The first molar is the largest and strongest tooth in the lower arch. It normally exhibits five functional cusps, and two well developed roots.

The crown is wider mesiodistally than buccolingually, and, in fact, the mesiodistal dimension is greater than that of any tooth in the mouth.

The crown is relatively short occlusocervically, the only dimension which is normally less than that of the teeth anterior to it.

It displays a trapezoidal outline from the buccal and lingual, and exhibits a rhomboidal form from either proximal aspect.

From the occlusal, the general outline is pentagonal.

In mastication, it functions with the other molars in grinding.

Development Table: (Mandibular First Molar)

Initiation of calcification...........At birth

Completion of enamel ........ 2 1/2 to 3 years

Eruption ..........................6 to 7 years

Completion of root ............ 9 to 10 years

Permanent Mandibular Second Molar:

1. General characteristics:Arch position - The second molar is the seventh tooth from the midline in each mandibular quadrant.

The mesial contact is shared with the permanent Mandibular first molar, while distal contact with the permanent third molar occurs if and when that tooth erupts.

It is also known as the "twelve year" molar, due to its normal time of eruption.

Universal number:

Mandibular right second molar - #31

Mandibular left second molar - #18

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.

The second molar complements the other molars in their grinding function.

Development Table: (Mandibular Second Molar)*

Initiation of calcification ..2 112 to 3 years

Completion of enamel .... 7 to 8 yearsEruption ................... 1 I to 13 yearsCompletion of root ....... 14 to 15 years

Mandibular first molar

Occlusal border is divided into three parts by two buccal grooves.

Three cusps are present buccally.

Occlusal border is divided into two parts by one buccal groove.

Two cusps are present bucally.

BUCCAL SURFACE

The surfaces is irregular as three ridges are present on this surface.

It is wider mesio-distally.

The surfaces is irregular as three ridges are present on this surface.

It is wider mesio-distally.

•The mesio-buccal cusp is wider than disto-buccal cusp

•Both are of equal height and width.

b. Mesial outline - The mesial outline is slightly concave from the contactarea cervically, and convex occlusal to the contact.

b. Mesial margin - The mesial margin is similar to the first molar's. It isconvex in the occlusal portion, and concave In the cervical portion. Distal margin -Again, this outline is similar to that of the first molar. Itis generally convex, and more so than the mesial margin

a. General considerations - The buccal is largest lateral surface of notonly the mandibular 1st molar, but of any tooth in mouth. It is trapezoidalin outline, with the greatest mesiodistal width at the occlusal.

a. General considerations - The buccal surface is trapezoidal like that ofthe first molar, but is shorter occlusogingivally, and narrower mesiodistally.

c. Distal outline - The distal margin is generally more convex than themesial outline. In the occlusal portion, it is more rounded, and cervical tothe contact area it is straight to slightly convex, as compared to the concavityof the mesial margin. d. Cervical outline - The cervical line exhibits slight, but regular curvatureapically, and sometimes displays a sharply pointed projection over the bifurcationarea.

d. Cervical margin - The cervical line normally has little curvature likethat of the first molar, but some specimens may exhibit a sharp dip over thebifurcation area.e. Occlusal margin - This margin is separated into two nearly equal halvesby the buccal groove. The two buccal cusps, the mesiobuccal and distobuccalm, are about equal in length as are their cusp outlines

Occlusal outline -!t is divided into three portions by two grooves, as they pass ontothe buccal surface. They are termed buccal (mesiobuccal) groove, anddistobuccal groove.

Mandibular first molar

Lingual surface is smaller than buccal surface.

Buccal profile and proximal surfaces are visible from lingual aspect.

Lingual surface is almost same as buccal surface.

Buccal profile and proximal surfaces are not visible from lingual aspect.

{LINGUAL SURFACE}

LINGUAL SURFACE: General

considerations – • The lingual

surface is also roughly trapezoidal in outline.

• Both proximal surfaces can be seen from this aspect. The lingual surface is, in fact, generally smaller than the buccal surface.

General considerations –

• The lingual surface is also trapezoidal in outline.

• It is also shorter occlusocervically, and narrower mesiodistally than

the first molar.

Mesial outline - The mesial outline is convex occlusal from the contact area. From the contact area cervically, it is concave.

Mesial, distal, and cervical outlines are similar to those of the lingual surface of the first molar.

Distal outline - The entire distal margin is convex, The height of contour of the distal outline is also at the junction of the occlusal and middle thirds.

d. Cervical margin - The cervical line is shorter mesiodistally, and is located at a more occlusal level, than on the buccal surface. It is usuallyirregular and nearly straight.

d.Cervical margin- same as first molar

c. Occlusal margin - The occlusal outline is usually broken by the lingual groove passing onto the lingual surface. The mesiolingual and distolingual cusps, and a small portion of the distal cusp are visible from this aspect.

c. Occlusal margin - The occlusal outline is divided approximately in halfby the lingual groove. Only the two lingual cusps are visible

Mandibular first molar

Mandibular first molar

MESIAL ASPECT:Mesial surface is said to be rhomboidal,Only the two mesial cusps are visible from this aspect.

Mesial aspect is similar to the first molar except:a. It is smaller in size but more convex in all directions.

The buccal margin is usually convex from gingival toocclusal, but is most convex at the cervical third crest of curvature, especially if the tooth has a buccocervical ridge

. The cervical outline is straighter, but like the first molar is more cervicallypositioned on the buccal as compared to the lingual.c. The mesial contact area is definitely ovoid than first molar

c. Lingual outline - The lingual outline is straight, or slightly convexd. Cervical margin - CEJ may be either relatively straight, or slightlycurved occlusally, but it is always located at a more occlusal level on thelingual side.e. Occlusal margin - This margin is concave. A mesial marginal groove is usually present.

DISTAL ASPECT:The distal surface is similar in outline to the mesial, but wider buccolingually at the cervical than at the occlusal.It is smaller than mesial surface, in buccolingual dimension.b. Buccal margin - The buccal margin is similar to that of the mesial aspect.

The distal aspect is comparable to the first molar except:a. There is no distal cusp contour, and no distobuccal groove.b. Since there is no distal cusp, the buccal surface shows much less convergencetoward the distal.

c. Lingual outline – same as mesial aspect.d. Cervical outline -The cervical line is relatively straight, although it may curve occlusally to a slight degree..

c. The contact area is wider buccolingually than occlusocervically, but ismore irregular in its configuration

e. Occlusal outline - it is shorter than on the mesial, but similarly concave. The distal marginal ridge is notched by the distal marginal groove

Contact area on mesial surface is smaller than distal surface as mesial surface is in contact with premolar tooth.

Contact area on mesial as well as distal surfaces are equal as both the surfaces are having contact with molar tooth.

{MESIAL AND DISTAL SURFACES}

Mandibular first molar

Occlusal surface shows five cusps.

Occlusal surface presents more complicated pit and groove and cusp and ridge pattern.

Occlusal surface shows four cusps.

Occlusal surface presents simple pit and groove and cusp and ridge pattern.

{OCCLUSAL SURFACE}

Outline is trapezoidal hence all four angles are not equal.

Disto-bucco triangular groove is absent.

Outline is rectangular hence all the angles are almost equal.

Disto-buccal triangular groove is present

Mandibular first molar

Mesial and distal branches are separated and wide.

Branches are thick & wide.

Mesial and distal branches lie close together.

Branches are thin and narrow.

THE ROOT

There is greater tendency for formation of curve at the apex of two roots.Root is bifurcated close to cervix hence trunk is short.

Ther e is lesser tendency for formation of curve at the apex of two roots.Root is bifurcated away from cervix hence trunk is larger.

Variations and Anomalies of first molar:

a. The first molar exhibits few developmental anomalies. However, on rare occasions, the crown may lack a distal cusp.

b. Mulberry molar - The mulberry molar, along with Hutchinson's incisor,are a consequence of congenital syphilis. On the first molars, the cusps are more centrally positioned on the occlusal table, creating a gnarled appearance.

c. Occasionally, the first molar exhibits three roots, when the mesial root has buccal and lingual branches

Variations and Anomalies of second molar:

a. Crown anomalies are uncommon, although five-cusp specimens are occasionally seen.

b. Root anomalies are more common, and may be manifested in fused roots or irregular curvatures.

SUBMITTED BY:

SAURABH J.KAPOOR (INTERN) 2004 BATCH

REFERENCES:WHEELERS DENTAL ANATOMY BIVIJI S DENTAL ANATOMYCONCISE DENTAL ANATOMYGOOGLE.COM