Descriptive Anatomy of Permanent Molars

Maxillary 1st Molar

D. Fikrat Barreman

By Ahmed Reath Jelewi

Permanent Maxillary First Molars

It is the sixth tooth from the median line. It is the largest tooth in the maxillary arch.General Characteristics

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It has large crown with four well-formed cusps (more pronounced than those on the opposing lower molar). General Characteristics

The two buccal cusps are more pointed than the two palatal cusps.

A unique feature of the tooth is the presence of an elevation called tubercle of Carabelli (fifth cusp) .General Characteristics

Cusp of CARABELLI

A unique feature of the tooth is the presence of an elevation called oblique ridge crossing the occlusal surface obliquely. General Characteristics

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The CrownBuccal AspectThe geometric outline of the crown is trapezoidal with the short of the uneven sides cervically.

Distal outline:

Is nearly straight from the cervical line to the mesial contact area then curves distally to be continuous with the mesial slope of the mesiobuccal cusp.

Mesial outline:Is convex from the cervical line to the tip of the distobuccal cusp. The crest of curvature is at the middle of the middle third .The distal side of the crown can be seen from the buccal aspect due to the obtuse distobuccal line angle.

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MESIAL At the junction of the occlusal and middle third.DISTAL At the center of the middle third.Contact Areas:

Two buccal cusps, mesiobuccal and dislobuccal cusps. Each cusp has a tip, a mesial cusp slope and distal cusp slope. The mesiobuccal cusp is broader than the distobuccal cusp.Occlusal Outline:

M.B.CD.B.C

The mesial and distal slopes of the mesiobuccal cusp meet at an obtuse angleWhile the slopes of the distobuccal cusp meet at right angleSo the distobuccal cusp is sharper and at least as long or often longer than the mesiobuccal cusp. Parts of the two lingual cusps can be seen from the buccal aspect.Occlusal Outline:

M.B.CD.B.C

The cervical line is generally irregular and slightly convex toward the root.The Cervical Line

A buccal developmental groove separates the two buccal cusps extending to the middle third.The groove fades out cervically, ending by a transverse dip in enamel mesially and distally. Sometimes the buccal groove ends by a pit. Morphology Of The Buccal Surface Of The Crown:

The roots originate as a common undivided part on the base of the crown, this single common root base is called root trunk. The root trunk of this tooth divides into three roots; two buccal and one palatal. The axes of the roots are inclined distally.The length of root trunk is about 4 millimeters.The Roots

The RootsLeft Right

The mesiobuccal root is slightly longer than the distobuccal one.

The Roots

The mesiodistal diameter of the lingual surface is nearly equal to that of the buccal surface.Lingual Aspect

Lingual Aspect

The Mesial Outline: is almost straight and forms a right angle with the mesial slope of the mesiolingual cusp. The Distal Outline: is smoothly convex and becomes continuous with the distal slope of the distolingual cusp (i.e. semicircular)

M.L.CM.L.CD.L.CD.L.C

The two lingual cusps are the only one to be seen from this aspect (beside the cusp or tubercle of Carabelli when exist).Occlusal Outline:

The Mesiolingual Cusp: is the largest and longest cusp of this tooth. Its mesiodistal width is about three fifth of the mesiodistal crown diameter.The Distolingual Cusp:is spheroidal and smooth. It makes up the remaining two fifth of the crown diameter.

The fifth cusp or tubercle of Carabelli is a small elevation, commonly found in about 60 per cent of cases on the lingual surface of the mesiolingual cusp.It is outlined occlusally by an irregular developmental groove.If it is well developed, its cusp ridge is nearly 1.5 mm cervical to the cusp ridge of the mesiolingual cusp.

Cervical line is irregular.Cervical Line:

A lingual developmental groove divides unequally the two lingual cusps. It ends nearly at the center of the lingual surface. From the end of the lingual groove a shallow depression extends to the center of the lingual surface of the lingual root crossing the cervical line and fades out at the middle third of the root.Morphology Of The Lingual Surface:

The Roots

The three roots are seen lingually.The large palataone l root is conical, ending in a bluntly rounded apex. This apex is on a line with the lingual groove.Parts of the buccal roots are seen from this aspect behind the lingual

The geometric outline is roughly trapezoidal with the uneven short side occlusally.From this aspect the great buccolingual dimension of this tooth is evident as in all upper molars.Mesial Aspect

The crest of curvature is located at the cervical third representing the maximum convexity of the cervical ridge . Buccal Outline:

RightLeft

M.B.CM.B.C

The crest curvature is at the middle third of the crown. Lingual Outline:

LeftRightM.L.CM.L.C

The mesiobuccal cusp is on a line with the long axis of the mesiobuccal root.Occlusal Outline:

RightLeftM.B.CM.B.C

The cervical line is irregular and slightly convex occlusally.The Cervical Line:

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The mesial contact area is just below the marginal ridge, nearly at the junction of the occlusal and middle thirds of the crown and somewhat buccal to the center of the crown.Morphology Of The Mesial Surface:

LeftRight

The Roots

The Root Trunk is a little shorter mesially than buccally (about 3 mm) with a smooth depression at the bifurcation extending occlusally and lingually.The Mesiobuccal Rootis broad and flattened on its mesial surface.

The Palatal Rootis longer and narrower than the mesiobuccal root.The palatal root is the most divergent root in order to follow the bone around the maxillary sinus. It is banana-shaped, extending lingually. The Distobuccal Root can not be seen from this aspect. It is hidden behind the mesiobuccal one.

Distal AspectIt is similar to the mesial aspect with certain variations.The crown tends to converge distally, due to the slant of the buccal side. So, the buccolingual measurement of the crown distally is smaller than that mesially, thus part of the buccal surface can be seen distally.

Is almost straight.Occasionally it may curve apically. The Cervical Line

The root trunk shows the largest length distally reaching 5 mm or more.The distobuccal root is narrower than the other two roots. The Roots

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Occlusal Aspect

The geometric outline of the crown occlusally is somewhat rhomboidal with acute mesiobuccal and distolingual angles and obtuse mesiolingual and distobuccal angles.

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The buccolingual measurement of the crown mesially is greater than distally.The mesiodistal measurement lingually is greater than buccally. Thus,The crown is wider mesially than distally and wider lingually than buccally .

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The maxillary first molar has four well developed cusps named according to their location.A small fifth cusp or tubercle of Carabelli appearing on the lingual surface of the mesiolingual cusp near the mesiolingual line angle. This tubercle may be ill defined or absent.

The mesiolingual cusp is the largest followed in decreasing order of size by the mesiobuccal, distolingual and distobuccal cusp .The fifth cusp (tubercle), if present, is the smallest.

M.LM.BD.BD.L

Each of the four cusps has a definite triangular ridge. Union of the triangular ridges of the mesiolingual and the distobuccal cusps forms an oblique ridge crossing the occlusal surface obliquely (characteristic of maxillary molars).Ridges:

The mesial and distal marginal ridges are continuous with the adjacent cusp ridges.Ridges:

FossaeThere are two types : A - Major fossae: 1- The central fossa 2- The distal fossa

B - Minor fossae:1- The mesial triangular fossa2-The distal triangular fossa

It is near the center of the occlusal surface, and mesial to the oblique ridgeThe central fossa contains in its depth a central developmental pit. It is bounded by the oblique ridge and the distal and mesial slopes of the mesiobuccal and distobuccal cusps respectively. The Central Fossa

The distal fossa is roughly elongated and distal to the oblique ridge. The Distal Fossa

The small mesial and the minute distal triangular fossae are immediately distal and mesial to the mesial and distal marginal ridges respectively .

Developmental GroovesStarting from the central pit of the central fossa the following grooves radiate:Starting from the central pit of the central fossa the following grooves radiate:The buccal developmental groove extends from the central pit buccally and continues between the buccal cusps onto the buccal surface of the crown as the buccal groove.

The central groove extends mesially from the central pit to terminate at the apex of the mesial triangular fossa.The Central Groove

a short developmental groove radiates from the central pit and runs transversely and distally across the oblique ridge to the distal fossa joining the central and distal fossae. This groove is called the transverse groove, of the oblique ridge.

It is irregular developmental groove traverses the distal fossa from the distal triangular fossa lingually between the lingual cusps and continues onto the lingual surface as the 5- lingual groove.The Distal Oblique Groove:

6- the fifth cusp groove (or tubercle) is distinct, this groove separates the tubercle from the mesiolingual cusp and joins the lingual groove.The Fifth Cusp Groove: