Permanent Dentition - Molars PDF

RAK Medical and Health Sciences University RAK College of Dental Sciences Academic Year 2023-24 Oral Biology and Tooth Morphology DOB126 Semester I- Lecture 5 Permanent Dentition- Posterior Teeth- Molar...

RAK Medical and Health Sciences University RAK College of Dental Sciences Academic Year 2023-24 Oral Biology and Tooth Morphology DOB126 Semester I- Lecture 5 Permanent Dentition- Posterior Teeth- Molars Learning Outcome-2 & 16 Explain dental annotations, describe the morphological and chronological features of primary and permanent teeth, and practically carve crowns of selected permanent teeth in wax. Apply knowledge to distinguish abnormal oral structures and develop robust knowledge for future management Dr. Sivan Padma Priya Assistant Professor, RAKCODS, RAKMHSU  Permanent molars ✓ The name molar comes from the Latin word for “grinding” ✓ There are three types of molars: the first molar, second molar, and third molar ✓ The first and second molars are also called the 6-year and 12-year molars because of the approximate eruption ages ✓ There are 12 molars, three in each quadrant, in the permanent dentition ✓ The molar crowns have four or five short, blunt cusps, and each molar has two or three roots that help to support the larger crown ✓ Eruption of the mandibular molars precede the maxillary molars ✓ First permanent molars erupt distal (posterior) to the second primary molars, therefore they are not succedaneous (have no predecessors) ✓ The location of first permanent molars is at the center of the fully developed adult jaw posterio-anteriorly ✓ Because of their significant positions and timing of eruption they are considered as the cornerstones of the dental arches ✓ Each maxillary molar has three well-separated and well-developed roots (trifurcated) ✓ Lower molars have two roots (bifurcated)  Upper right first molar ✓ The largest tooth in the maxillary arch B ✓ Four well-developed functioning cusps; mesiobuccal, distobuccal, mesiolingual, distolingual and cusp of tubercle of carabelli (supplemental cusp) ✓ Cusp of carabelli is found on the mesio- lingual (or mesiopalatal) cusp (non functional cusp)  Upper right first molar ✓ Three roots; mesial, distal and palatal B root, the latter being the largest root, followed by the mesial root ✓ The root have their greatest spread parallel to the line of greatest force brought to bear against the crown in a buccolingual direction Occlusal aspect: Disto-buccal Buccal Mesio-buccal cusp ridge groove cusp ridge Transverse groove of Bu Central pit the oblique ridge Distal marginal ridge Mesial triangular fossa Distal triangular M Mesial marginal D fossa ridge Oblique ridge Mesio-lingual cusp ridge Distal fossa Pa Disto-lingual Central fossa cusp ridge Cusp of carabelli Palatal groove Cont’d ✓ The bucco-lingual width > B mesio-distal width D M ✓ The crown converge toward distal ✓ The disto-buccal and the mesiolingual cusp ridges form oblique ridge and is divided by a transverse groove P ✓ The buccal groove extends from the buccal surface to the occlusal surface and joins the central groove Cont’d ✓ All cusps slope downward B toward the grooves D M ✓ The two lingual cusps are divided by the distal oblique groove ✓ The mesiolingual cusp is the largest followed by the mesiobuccal cusp P Cont’d Buccal aspect: ✓ The crown is trapezoidal in shape ✓ The distal side can be seen because of the obtuse distobuccal line angle ✓ Mesiobuccal cusp is broader than the distobuccal cusp ✓ The buccal developmental groove divides the two buccal cusps at equidistant Buccal aspect: ✓ The cervical line is not smooth and shows convexity toward the roots ✓ All of the three roots may be seen from this aspect and the lingual/ palatal root is the longest Cont’d ✓ The point of root bifurcation is about 4mm above the CEJ ✓ The common root base is called the trunk ✓ A shallow depression continues from the CEJ to the bifurcation point as a deep groove ✓ The distal side is convex and reaches the contact area in the middle of the tooth Cont’d ✓ The mesiobuccal root extends halfway in a mesial direction then curves distally, while the distal root is straight for half its length, then curves mesially ✓ The mesiobuccal root may have two pulp canals Cont’d Mesial aspect: ✓ The cusps; mesiobuccal, mesiolingual and cusp of carabelli are seen from this aspect ✓ The lingual surface curves outward and the crest of curvature is in the middle1/3 ✓ The mesial marginal ridge is irregular and its outline curves cervically ✓ The mesial contact area is at the junction of the middle and the occlusal 1/3s Cont’d Mesial aspect: ✓ The palatal root is long and narrow (banana-shaped) ✓ The mesiobuccal root is flat but broad and block the distobuccal root from view ✓ The level of bifurcation is closer to the CEJ than is found between the roots buccally Cont’d Distal aspect: ✓ Because of the crown convergence some of the buccal part is seen ✓ The distal surface is generally convex ✓ The distal marginal ridge curves sharply cervically more than the mesial ✓ The cervical line is almost straight Cont’d Distal aspect: ✓ Although all roots are visible, only the outline of the mesiobuccal root is seen ✓ Distal root is narrower at the base than either of the others ✓ The bifurcation is more apical than either of other two areas Cont’d Lingual aspect: ✓ The two lingual cusps are longer than the buccal cusps, therefore they block the latter from view ✓ A lingual groove divides the lingual cusps ✓ A short groove is always present on cusp of carabelli ✓ The mesiolingual cusp is 3/5 width of the crown and supports the cusp of carabelli Cont’d Lingual aspect: ✓ The distolingual cusp is spheroidal and smooth ✓ The lingual root is broad with a furrow extending most of its length and it tapers to a blunt apex ✓ The lingual portion of the root trunk is continuous with the entire cervical portion of the crown lingually  Left side Non-functional cusps are Buccal of Upper and Lingual of Lower (BULL)  Upper right second molar The 2nd molar is similar to the with the following differences: Occlusal aspect: Rhomboidal shape (acute angles are less and obtuse angles are more) BL (buccoLingual) diameter is the same as , but MD (MesioDistal) diameter is 1mm less The distal cusps are smaller and less developed No evidence of fifth cusp  Upper right second molar Buccal aspect: ✓The crown is shorter cervico- occlusally and narrower mesio- distally than the 1st molar ✓The disto-buccal cusp is smaller ✓The roots are about the same length but curve distally more than in 1st molar ✓The apex of the mesiobuccal root is on a line with the buccal groove of the crown instead of the tip of the MB cusp as in 1st molar Cont’d M Mesial aspect: ✓ The roots are not as divergent as in , confined within the buccolingual outline of the crown ✓ The buccolingual dimension is about the same as the 1st molar Distal aspect: D ✓ Because of the smaller distobuccal cusp, more of the mesiobuccal cusp may be seen ✓ The mesiolingual cusp can be seen from this aspect Cont’d Lingual aspect: ✓ No cusp of Carabelli ✓ The distolingual cusp of the crown is smaller ✓ The apex of the lingual root is in line with the tip of the distolingual cusp in some variety  Maxillary third molars ✓ Often appear as developmental anomaly ✓ Vary considerably in size, contour and relative position to the other teeth ✓ They resemble the second molar and supplement their function ✓ As a rule, the crowns are smaller, roots are short and fused ✓ The predominating morphology of the occlusal surface is that of heart-shaped type ✓ All third molars (Mandibular &Maxillary) show wide variation in development than any other teeth ✓ People sometimes refer to this tooth as the “wisdom” tooth because it erupts last. Compare the buccal views of the upper molars. A, first molar; B, second molar; C, third molar ❖What are the differences you notice in the roots form?  Upper right third molars In comparison with the second molar : ✓ The crown is shorter cervico-occlusally and narrower mesiodistally ✓ The roots are usually fused and shorter cervico-apically, ending in a taper apex ✓ Only one large lingual cusp is seen from the lingual aspect. However, in some cases a poorly developed distolingual cusp is present ✓ Mesial aspect show tapered, fused roots and a bifurcation near the apical 1/3  Clinical considerations with maxillary molars ✓ The roots of the maxillary molars may penetrate the maxillary sinus as a result of accidental trauma or during an extraction ✓ Because the maxillary molar roots are close to the sinus, some patients confuse the pain caused by a sinus infection with pain related to their maxillary teeth and vice versa ✓ The maxillary third molars may fail to erupt and may remain impacted within the alveolar bone ✓ If the maxillary first molar is lost, the second molar can tip and drift into the open space, causing difficulty in chewing and furthering periodontal disease.  Mandibular First Molar Occlusal aspect: MBDG DBCR MBCR DBDG SG DCR MTF DTF MMR DP MP DMR CF CDG DLCR MLCR LDG Cont’d ✓ Five cusps present; MB, DB, D, ML, DL cusps B ✓ The MD width > BL width M D (opposite to ) ✓ BL width on the mesial is greater than on the distal ✓ All five cusps are functional cusps; The MB cusp is the largest followed by ML+DL, DB, D L cusp Cont’d ✓ The occlusal grooves extend from the buccal and lingual surfaces and have the same names; MB, DB, L developmental groove and join each other forming Y-shape ✓ Each of the groove join the central developmental groove ✓ There is a large central fossa and 2 triangular fossae (mesial>distal) ✓ There is a deep central pit where grooves merge Cont’d Buccal aspect: ✓ The buccal cusps are flat and separated by MB and DB grooves ✓ The mesial side from contact area to the cervix is concave but the distal side is straight from cervix to the contact area, D M where it becomes convex ✓ The MB cusp is the widest mesiodistally of the 3 cusps ✓ ½ of the M root curves mesially then it curves distally ✓ The distal root is less curved and slants in a distal direction Cont’d Lingual aspect: ✓ 3 cusps may be visible; 2 lingual cusps+lingual portion of the distal cusp ✓ The lingual cusps are pointed and their D M ridges are high enough to hide the buccal cusps ✓ The tip of the ML cusp is at higher level than DL cusp ✓ There is a lingual development groove separating the lingual cusps. Li ✓ There is a developmental depression extending from CEJ to the bifurcation point Cont’d Mesial aspect: ✓ Two cusps (MB+ML) and 1 root (M) are seen ✓ The entire crown has a lingual tilt from this aspect with relation to the root axes ✓ The buccal outline is convex immediately above the cervical line (buccal cervical ridge) Li ✓ There are usually two root canals on the mesial root ✓ The buccal and lingual root outlines are convex and the root is slanted in a buccal direction, although the outline is almost straight from cervix to the point of junction M of the middle and apical 1/3 Cont’d Distal aspect: ✓ Because the crown converge distally, some portion of the buccal aspect is seen ✓ Also the distal side is shorter, therefore some parts of the cusps are seen ✓ The distal cusp is placed a little buccal ✓ The distal contact area is centered on the D distal root and is placed just below the distal cusp ridge of the distal cusp, at a higher level from the cervical line than that is found on the mesial ✓ The cervical line is relatively straight  Mandibular Second Molar Occlusal aspect: ✓ Generally the crown is smaller than that of 1st molar , however, it is not uncommon to find Mand 2nd molar with crown larger than 1st molar and longer roots ✓ Four cusps present, the DB cusp is larger than that of 1st molar and the distal cusp is not present ✓ The buccal and lingual developmental grooves meet the central developmental groove at right angles at the central pit ✓ The slopes of the cusps are not smooth as found in the 1st molar because of the many radiating supplemental grooves Cont’d Buccal aspect: The crown is shorter cervico- occlusally and narrower mesio- distally A single development groove demarcates the MB cusp from DB cusp Roots inclined distally and closer to each other The buccal furcation is about 3mm from CEJ Cont’d Lingual aspect: Li The crown and the root slightly converge lingually The M&D contact areas are noticeable from this aspect and at lower level than that of the 1st molar The lingual groove divides the two lingual cusps and continues onto the occlusal surface Cont’d M Mesial aspect: Differs slightly from 1st molar The buccal cervical ridge is less pronounced The cervical line shows less curvature (regular in outline bucco-lingually) The mesial root is pointed apically and usually has one pulp canal D Distal aspect: Except for the absence of the distal cusp and the disto-buccal groove, no other differences from 1st molar The contact area is centered B-L and cervico-occlusally  Mandibular Third Molar Occlusal aspect: Quite similar to that of the 2nd molar, when it is normally developed There is tendency toward a more round outline and smaller B-L measurements distally Buccal aspect: The crown is wider at the M-D contact area than at cervix The 4 cusps third molars have fair alignment and good occlusion with other teeth