GENERAL FEATURES OF MOLARS
- There are twelve permanent molars three in each quadrant. They are the largest and strongest teeth in the mouth by their crown bulk size and their root anchorage in the bone.
- The molars have No deciduous predeccesors. Generally the lower first molars are formed from five lobes, but second and some third molars may have only four. Each cusp of a molar is formed from its own lobe.
- The most developed of the molar is the first molar. The third molar exhibits the most variable morphology in the mouth.
- Molars are used in grinding food, but most important they support and maintain the vertical dimension of the face.
MAXILLARY FIRST MOLAR
The normal location of the first permanent molar is at center of the fully developed adult dental arch antero-posteriorly. Table XV shows the chronology of the first maxillary molar.
It is the largest tooth in maxillary arch. It has four well developed cusps (two buccal and two lingual) and a fifth supplemental nonfunctioning elevation which is called Tubercle of Carabelli. This fifth cusp serves to identify the maxillary first molar. The crown of this tooth is wider buccolingually than mesiodistally.
There are three wel developed and widely separated roots, two buccal and one palatal (lingua). They give this tooth the maximum anchorage against forces.
- The crown is roughly trapezoid. The cervical line is the shortest of the uneven sides. The tips of all cusps are usually visible from this aspect. Part of the distal side is seen due to the obtuse distobuccal line angle.
- The mesial outline of the crown follows a nearly straight path downward and mesially, curving occlusally as it reaches the crest of contour of the mesial surface which is the contact area. The contact area is just Cervical to the junction of the occlusal and middle thirds. Then, the mesial outline curves occluaslly and distally and becomes corresponding with the outline of the mesial slope of the mesiobuccal cusp.
- The distol outline is convex, from the cervical line to the contact area is in the center of the middle third then it curves occlusally and mesially to outline and distal slope of the distobuccal cusp.
- The cervical line is slightly curved with the curvature root wise. This line is not so smooth and regular as found in some other teeth.
- Although the mesiobuccal cusp is broader than the distobuccal cusp, the distobuccal cusp is usually sharper and longer. The mesial slope of the mesiobuccal cusp meets its distal slope at an obtuse angle. The mesial slope os the distobuccal cusp meets its disal slope at approximately right angle.
- Separating the two buccal cusps is the buccal developmental groove. This shallow groove runs in occluso-apical direction parallel to the long axis of the distobuccal root. It terminates at a point nearly half the distance from its origin as a horizontal groove.
- The buccal surface is characterized by buccal ridges on each buccal cusp. They are convex areas which extend cervically about half its length. It is also characterized by the buccal cervical ridge which extends horizontally from mesial to distal in the entire cervical third.
- The molar roots originate as a single root on the base of the crown, and then they divide into three roots. The common root base is called root trunk. Usually the palatal toot is the longest and the two buccal roots are approximately equal in length. The root are about twice as long as the crown and their greatest extremities mesiodistally is less than the calibration of the crown mesiodistally.
- There is a deep developmental groove buccally on the root trunk which starts at the bifurcation and progresses downward to end in a shallow depression at the cervical line.
- All three roots may be seen from the buccal aspect. The point of bifurcation of the two buccal roots is located approximately 4.mm above the cervical line. The roots are not straight; the buccal roots are curved halfway between the point of bifurcation and the apices.
- The mesiobuccal root curves distally starting at the middle third to the apex. Its long axis at an acute angle distally with the cervical line. It has a tendancy toward curvature mesially at the middle third.
- It is Trapezoid in shape. The crown surface shows more convexity occlusocervically than the buccal surface. The hight of contour is located in the middle third of the surface. The lingual cusps are the only ones to be seen from this aspect. The mesiolingual cusp is much larger. Its mesiodistal width is about 3/5th of the mesiodistal diameter of the crown, the distolingual cusp making up the remaining 2/5th.
- The mesial outline is straight from the cervical line to the contact area and meets the mesial slope of the mesiolingual cusp at 90o. The two cusp slopes meet at obtuse angle. The distal outline of the crown is smoothly curved. The cervical line is slightly convex rootwise in an irregular manner.
- The fifth cusp (Tubercle of Carabelli) appears attached to the mesiolinguall surface of the mesiolingual cusp. The fifth cusp is separated from the mesiolingual cusp by an irregular developmental groove. This is called the fifty cusp developmental groove.
- The distolingual cusp is smooth and spherioidal without angulation on the mesial and distal slopes. The lingual developmental groove separates the two large lingual cusps and runs cervically to end at the center of the lingual surface of the crown. From this point a shallow depression extends cervically and continues in an apical direction on the lingual root till the middle third.
- All three roots are visible from the lingual aspect. The lingual portion of the crown lingually. The lingual root is conical with blunt rounded apex. The apex of the lingual root is on line with the lingual groove of the crown.
- It is trapezoid in shape with the smallest uneven side located occlusally. The buccal outline of the crown starting from the cervical line is curved with the crest of curvature within the cervical third. As it progresses downward, it becomes less convex to circumscribe the mesiobuccalcusp. Only the mesiobuccal, mesiolingual and the fifth cusps are seen. Also only two roots are seen, the mesiobuccal and the palatal roots.
- The lingual outline is curved with the crest of curvature located near the middle third. If the tubercle is well developed, the lingual outline dips inward to illustrate it. If it is undeveloped the lingual outline continues from the crest of curvature as a smooth curved arc to the tip of the mesiolingual cusp.
- The mesial marginal ridge, which is confluent with the mesiobuccal and mesiolingual cusp ridges, is irregular and curved cervically about one-fifth the crown length. The cervical line is irregular, curving occlusally not more than 1mm.
- The mesial contact area is above the marginal ridge approximately cervical to the junction of the middle and occlusal thirds of the crown and some what toward the buccal side. Just above it, a shollow concavity is found which may continue to the mesial surface of the root trunk at its cervical third.
- The mesiobuccal root is broad and flattened on its mesial surface. The width of this root at the point of bifurcation is about 2/3rds of the crown width at the cervical line buccalingually. The buccal outline of this root is curved, but its lingual outline is straight to end at a blunt apex.
- The lingual or (palatal) root is longer than the mesiobuccal root by 1.0mm but it is narrower from this aspect. Its buccal outline is concave and its lingual outline is convex. At its middle and apical thirds, it is outside of the confines of the greatest crown projection. It is banana shaped.
- The level of the bifurcation is a little closer to the cervical lie than is found between the roots buccally. There is smooth depression extends from the bifurcation to the cervical line.
The gross outline of this aspect is similar to that of the mesial aspect, but the following variation is noted.
- The buccolingual measurement of the crown on the distal aspect is less than that of the mesial asplect.
- The distal marginal ridge dips sharply in a cervical direction exposing part of the four cusps.
- The cervical line is almost straight.
- The distalsurface is generally convex except for a small concave area near the distobccal root at the cervical third. This concavity continues over the distobuccal root and end at the bifurcation point.
- The distobuccal root is narrow at its base than either of the others. Its outline follows a concave path from the cervical line for a short distance than makes a convex arc to the blunt apex. The lingual outline of this root is slightly concave from the apex to the bifurcation.
- The bifurcation is more apical. The area from the cervical line to bifurcation is 5mm or more in extent.
- It is Rhomboidal in outline, the crown is wider mesialy than distally, and wider lingually than buccally (this the only molar that is wider lingually than buccally).
- The mesiobuccal and distolinguall angles are acute in comparison to the mesiolingaul and distobuccal angles which are comparatively obtuse.
- The four major cusps are well developed. The tubercle of Carabelli on the lingual surface of the mesiolingual cusp is small and nonfunctional. It may be indistinct, and instead, a developmental line in the enamel is present.
- The mesiolingual cusp is the largest cusp, followed by the rounded mesiobuccall, the sharp distobuccal, the small distolingual , and the nonfunctional fifth cusp (tubercle of Carabelli).
- The occlusal surface is within the confines of the cusp ridges and the marginal ridges.
- There are two major fossae, a central fossa which is triangular concave area mesial to the oblinque ridge, and a distal fossa which is to the distal marginal ridge.
- The central development pit lies in rteh central fossa. The buccal developmental groove radiates from this pit buccally between the two bucclcusp. The central development groove proceeds in a mesial direction originating in the central pit and termination at the mesial triangular fossa. The mesial pit is found in the mesial triangular groove and crosses the mesial marginal ridge.
- From the mesial pit the following developmental grooves radiate.
- The central developmental groove to the central fossa.
- The mesiobuccal groove.
- The mesiolingual groove.
- Another developmental groove may be seen radiating from the central pit distally and crosses the oblique ridge to end at the distal fossa. This is called the Transverse groove of the oblique ridge.
- From the distal pit the following developmental
- The distal groove that joins the distal triangular and distal fossa.
- The distal marginal groove that may extends over te marginal ridge into the distal surface.
- The distolingual groove.
- The distobuccal groove.
- The oblique ridge traverses the occlusal surface from the top of the mesiol;ingual cusp to the top of the distobuccal cusp. It is reduced in height in the center of the occlusal surface and is some times crossed by the transverse groove of the oblique ridge.
- The mesial and distal marginal ridges are irregular elevations of enamel which are confluent with the adjacent cusp ridges.
- It contains a pulp chamber and three or four root canals.
- In buccolingual section yhe chamber is broad and rectangular in shape and the two pulp horns are prominent and extend to the mesiobuccal and mesiolingual cusps. The floor is smooth with canal openings widening out as they enter the pulp chamber. The lingual canal is large and accessible, while the mesiobuccal canal is small and shorter and it may have supplementary branches and multiple foraminae, but mostly the mesiobuccal root has two root canals which either oopen in one or two aical foramina. The disto buccal root has only one root canal.
- In mesiodistal section The pulp chamber is not wide, and the pulp horns extend to the mesio-buccal and distobuccal cusps. The mesiobuccal and distobuccal canals are narrow and tapering to the apex. The pulp chamber the two root canals are centered within the tooth outlines.
- In cervical cross section The outline is rhomboidal in shape with rounded corners. The canals of this tooth form a triangular patern. A line drawn between the mesiobuccal and the palatal canals makes the base of the triangle.
- In midroot cross section The palatal root canal is rounded in outline. The distobuccal canal is oval and smaller. The mesiobuccal canal or canals are elongated oval or kidney shaped. ■
MAXILLARY SECOND MOLAR
This tooth assists the maxillary first molar in function, and it has the same from with some varioations.
- The crown is a little shorter cervico-occlusally (by about 0.5mm) narrower mesiodistally (by 1mm), but of the same measurement bucco-lingually.
- The buccal groove is located further distally, with a resultant larger and longer mesiobuccal cusp, and a shorter, smaller and sharper distobuccal cusp.
- The buccal roots are about the same length. They are more nearly parallel ad are inclined distally more than those of the maxillary first molar so that the end of the distobuccal root is slightly distal to the distal extremity of the crown.
- The apex of the mesiobuccal root is on a line with the buccal groove of the crown instead of the tip of the mesiobuccal cusp as found on the first molar.
- The mesilingaul cusp is smaller and not well developed as in the first maxillary molar. No fifth cusp is present.
- The distolingual cusp is smaller.
- The buccal cusps may be seen between the lingual cusps.
- The apex of the lingual root is in line with the distolingual cusp instead of the lingual groove as was found on the first molar.
- There is no developmental groove on the palatal root.
No tubercle of Carabelli. It shows less divergent roots (being within the confines of buccolingual crown outline). In addition the cervical concavity is not present.
It is similar to the mesial except that the distobuccal cusp is smaller than in the first molar. The apex of the lingual root is in line with the distolingualcusp.
The crown is more constricted mesiodistally and has no tubercle of Carabelli. There are two major types of crown from:
- Rhomboidal form which is most frequent type resembling the maxillary first molar except that:
- The rhomboid form is more accentuated.
- The acute angle is less acute, and the obtuse angles are greater.
- The distobuccal and distolingual cusps are smaller.
- Heart shaped form resemble the maxillary third molar. The distolingaul cusp being poorly developed or sometime missing.
It is common to find supplemental grooves as well as grooves and pits on the occlusal surface of the maxillary second molar which make the surface more wrinkled.
It is similar to the first maxillary molar both in the mesiodistal and buccolingual cross sections. It is not common to find two root canals in the mesiobuccal root.
MAXILLARY THIRD MOLAR
The maxillary third molar is the most variable tooth in the upper arch. It v aries in size, shape, contour and surface details. The most common crown shape is the hear-shape, which is generally smaller and more rounded in all dimensions than the second molar and also the crown is shorter and narrower.
The distolingual cusp is very small and poorly developed or may be absent presenting an occlusal table with three cusps. The groove pattern is variable and may show many supplementary grooves and the distolingual groove is absent.
The root form and number are extremely variable, but are smaller in all dimensions. The most common is the three root type where they are often fused
Due to the variation in shape of this tooth the pulp cavity also subjected to great variation in shape and size. However, the pulp cavity roughly follows the shape of the tooth.