Form and Function
Morphology of permanent dentition
General informationHumans have two generations of teeth : deciduous and permanent By the age of 3 years all deciduous teeth have erupted .By 6 years, the first permanent teeth appear and hence the deciduous teeth are exfoliated one by one replaced by their permanent successors.A complete permanent dentition is present at around 18 years .20 teeth 10 in each jaw. (primary dentition )32 teeth 16 in each jaw.
Differences between deciduous teeth and permanent :1.The deciduous teeth are smaller, although the mesiodistal dimension of the permanent premolars are generally less than those for deciduous molar .2. Deciduous teeth have a greater constancy of shape .3. The crown of deciduous teeth appear bulbous , often having pronounced labial or buccal cingula .4. the cervical margins of deciduous teeth are more sharply demarcated and pronounced , enamel bulging rather than gently tapering .5. the cusps of newly erupted deciduous teeth are more pointed .
6. the crowns of deciduous teeth have thinner enamel ( 0.5-1.0 mm ) than the crowns of permanent teeth (2.5 mm )7. the enamel of deciduous teeth are more opaque , gives the crown a whiter appearance 8. the enamel is softer and more easily worn in deciduous teeth .9. enamel is more permeable in dec. teeth .10. the aprismatic layer of surface enamel is wider in dec. teeth .
11. the enamel and dentine of ALL dec . teeth exhibit neonatal lines .12. the roots of dec. teeth are shorter and less robust than those of permanent teeth .13. the roots of dec. incisors and canines are longer in proportion to the crown than those of permanent ones.14. the roots of the dec. molars are widely divergent extending beyond the dimensions of the crown.15. the pulp chambers of dec. are proportionally larger in relation to the crown than those of permanent teeth. the pulp horns in dec. are more prominent. 16. the root canals of dec. are extremely fine .17 . the dental arch for dec. dentition are smaller .
Proximal Contact AreasAll teeth contact adjacent teeth at a proximal contact area except:distal of the last tooth In the archdiastemaspathology (caries)faulty restorations
Importance:Ensures food will not be packed between teeth causing inflammation to the supporting tissues thereby causing gingivitis & periodontitis It helps stabilize the dental arches by the combined anchorage of all the teeth in either arch in positive contact with each other (exception - third molars.)Each tooth is individually supported by these contact areas.
CONTACTS are OBSERVED from 2 views-Labial /buccal aspect- demonstrates the cervicoincisal/cervico-occlusal position
Incisal /occlusal aspect- demonstrates the facio-lingual position
Anterior teeth have contacts that are generally centered faciolingually when view from the incisalPosterior teeth have contacts that are generally located buccal to the center of teeth when viewed from the occlusal
Proximal ContactsMaxillaryMesialDistalCentral incisorIncisal 1/3Junc of incisal/middle 1/3Lateral incisorJunc of incisal/middle 1/3Middle 1/3CanineJunc of incisal/middle 1/3Middle 1/31st preMiddle 1/3Middle 1/32nd preMiddle 1/3Middle 1/31st molarMiddle 1/3Middle 1/32nd molarMiddle 1/3Middle 1/33rd molarMiddle 1/3n/a
Proximal ContactsMandibularMesialDistalCentral incisorIncisal 1/3Incisal 1/3Lateral incisorIncisal 1/3Incisal 1/3CanineIncisal 1/3Middle 1/31st preMiddle 1/3Middle 1/32nd preMiddle 1/3Middle 1/31st molarMiddle 1/3Middle 1/3 2nd molarMiddle 1/3Middle 1/33rd molarMiddle 1/3n/a
Contact area move cervically from anterior to posterior in each quadrantOn individual teeth the distal contact is more cervically located then the mesial contactContacts increase in size from anterior to posterior
2**Note: Contacts on incisors in incisal1/3,Where as contacts on molars in middle /3
LMAXILLARY CENTRAL INCISORabial It is the widest tooth in the maxillary arch.The mesial margin is straight and meets the incisal edge at right angle. The distal margin is shorter and more rounded. The distoincisal angle is more rounded than the mesioincisal angle.
Mesial margin straight & meets at 90 degree
Distal margin shorter & rounded
Distoincisal angle more rounded, making an obtuse angleMesioincisal angle rounded, making somewht 90 degrees
The labial surface is marked by two developmental groove and has convexity in cervical third.Mesiodistally the crown is narrowest cervically, & becomes broadest in the incisal 3rd.
Convexity in cervical third
Wht is perikymata????15
Lingual aspectThe crown profile is same as that of labial surface except that there is a broad depression in the central portion called the lingual fossa and a well developed cingulum.Maxillary incisor with a deep & large lingual fossa & prominent mesial & distal marginal ridges are called as SHOVEL SHAPED INCISORDue to the distal displacement of the cingulum, the mesial marginal ridge is slightly LONGER than the distal marginal ridge
Lingual fossaCingulumMarginal ridgesLingual ridge
The lingual fossa is bordered by mesial and distal marginal ridges on the sides and the cingulum cervically.
The cervical line on labial and lingual surface is convex apically.
Cervical line convex
Lingual aspectLabial aspect
Mesial aspectFrom this aspect the crown appears WEDGE SHAPED, with base of traingle at cervix & apex towards the incisal edge.From the mesial aspect the labial margin is convexThe lingual margin is S shaped, being convex near cingulum and concave in the middle
Labial margin convexConvex near cingulumConcave in the middle
Mesial curvature of cervical line (3.5mm) is the most pronounced compared to any other tooth.
The cervical line on the mesial and distal surface is convex incisally
Distal aspectDistal aspectDistal surface is very similar to the mesial surface.when central incisor viewed from distal aspect, the crown gives the impression of somewhat thicker towards the incisal 3rd, this is because the distoincisal angle is slightly lingually positioned than mesioincisal angle.
Incisal aspectThe crown and incisal margin are centered over root
Crown profile is almost bilaterally symmetrical
The incisal margin of newly erupted teeth show three elevations called mamelons. The middle One is smallest.They correspond to the developmental lobes.
RootThe root is straight and tapers from the cervical line to the apex giving it a conical shape
The root ends in a blunt apex.Root : crown ratio is 1.3:1.05
Straight conical blunt root
10.5Curvature of Cervical Line M DLabiolingualDiameter atCervical LineLabiolingualDiameter atCrest of CurvatureMesiodistalDiameter atCervical LineMesiodistalDiameter of crownRootLengthCrown Length
Average Dimensions in millimeters
Maxillary Lateral IncisorThe general shape is similar to maxillary central incisors except that they are shorter and narrower.
Next to third molars maxillary lateral incisors are the teeth that show most variation in crown size, shape and form
Maxillary central incisor bigger and lateral incisor smaller
The mesioincisal and distoincisal angles are more rounded than the corresponding angles of the maxillary central incisor
Distoincisal angle more roundedMesioincisal angle more rounded
Maxillary Lateral Incisor
Maxillary Central IncisorMesioincisal angleDistoincisal angle
On the lingual aspect the marginal ridges and cingulum are more prominent
Prominent cingulumProminent marginal ridges
MAXILLARY CENTRAL INCISORMAXILLARY LATERAL INCISORLABIALVIEW1.CROWN IS LARGERCROWN IS SMALLER2.MESIOINCISAL ANGLE AT 90 DEGREE & DISTOINCIAL ANGLE SLIGHTLY ROUNDEDMESIOINCISAL ANGLE IS ACUTE & DISTOINCISAL ANGLE ROUNDED3.MESIAL CONTACT AREA AT INCISAL 3rdDISTAL CONTACT AREA AT JUNC OF INCISAL & MIDDLE 3rd.
LINGUALVIEW1.LINGUAL FOSSA LARGER & SHALLOWERLINGUAL FOSSA SMALLER & MORE CONCAVE.2.LINGUAL PITS ARE LESS FREQUENTLINGUAL PITS ARE COMMON3.CINGULUM IS POSTIONED SLIGHTLY DISTALLYCINGULUM IS CENTERED
PROXIMALVIEW1.CERVICAL LINE CURVATURES ARE MORECURVATURE IS LESS 2.ROOT IS EVENLY TAPEREDROOT IS MORE CONVEX
INCISAL1.CROWN WIDER MESIODISTALLY THAN FACIOLINGUALLYCROWN SAME BOTH MESIODISTALLY & FACIOLINGUALLY2.CROWN OUTLINE IS TRIANGLULARCROWN OUTLINE IS ROUNDED OR OVAL3.CINGULUM SLIGHTLY DISTALCINGULUM CENTERED4.INCISAL RIDGE SLIGHTLY CURVED MESIODISTALLYINCISAL RIDGE RELATIVELY STRAIGHTER MESIODISTALLY
Mandibular central incisor and lateral are similar in anatomy and complement each other in function.
Labial aspectLabial surface of mandibular central incisor is very small. It is the narrowest tooth mesiodistally of all the permanent teeth
Narrowest tooth in the dentition
It is bilaterally symmetrical,that it is difficult to tell the sides. The only differnce is the greater mesial than distal curvature.
It is the only incisor where both mesioincisal and distoincisal angles are sharp and at right angles
Both mesioincisal and distoincisal angles are sharp
Lingual aspectThe lingual aspect is concave from the incisal edge to the cervical lineCingulum is smooth, barely visible & no development lines mark the cingulum.Marginal ridges almost absentThe surface is smooth and devoid of any