Morphology of Permanent Incisors PDF

MORPHOLOGY OF PERMANENT INCISORS Dr. Firas Alsoleihat, BDS, PhD Department of Conservative Dentistry Introduction  Human dentition is diphyodont  Primary (deciduous/ predecessor) dentition Formula: I 2/2 C 1/1 M 2/2 Eruption: 6 months - 28±4 months Sheddi...

MORPHOLOGY OF PERMANENT INCISORS Dr. Firas Alsoleihat, BDS, PhD Department of Conservative Dentistry Introduction  Human dentition is diphyodont  Primary (deciduous/ predecessor) dentition Formula: I 2/2 C 1/1 M 2/2 Eruption: 6 months - 28±4 months Shedding: 6 to12 years  Secondary (permanent/successor) dentition Formula: I 2/2 C 1/1 P 2/2 M 3/3 Eruption: 6 to (18-25) years Stages of human dentition  Edentulous stage: 0 - 6 months  Eruption of primary dentition: 6 months-2.5 years  Functioning primary dentition: 2.5 – 6 years  Mixed dentition: 6 – 12 years  Permanent dentition: 12+ years  Full permanent dentition: (18-25)+ years Dental terms  Dental arch: maxillary and mandibular  Tooth class  Incisor: incisal edge  Canine: one pointed cusp  Premolar (bicuspid): 2 cusps  Molar: 3 or more flattened cusps  Identification traits  Set traits  Arch traits  Class traits  Type traits Glossary Terms related to anterior teeth  Anterior teeth  Surfaces  Line angle  Point angle  Incisal edge  Cusp  Cingulum  Fossa  Ridge and marginal ridge  Cervical line  Lobe  Mamelon  Lingual pit  Developmental groove  Division into thirds  Contact point  The permanent incisors  Eruption sequence  41/31, 11/21, 42/32, 12/22  Functions  Cutting  Esthetics  Speech  Class traits  Incisal 2/3 flattened MD & compressed LL  Long horizontal MD biting edge  2 or more mamelons  Marginal ridges parallel to long axis  Chronology Maxillary Central Maxillary Lateral incisor Incisor First evidence of First evidence of calcification:3-4mo calcification:1yr Enamel completed:4-5yr Enamel completed: 4-5yr Eruption: 7-8yr Eruption:8-9yr Root completed:10yr Root completed:11yr The permanent maxillary incisors  Arch traits  Crown Wider MD Smaller height / width proportion Greater MD / LL proportion  Root Greater MD / LL proportion Conical root in central incisors  Type traits  Size  Height / width proportion in crown  MD / LL proportion in crown and root  The permanent maxillary central incisors  Labial aspect  The widest MD of all incisors – type trait  3 mamelons Middle is the smallest in width Mesial has a raised shoulder Distal has a low shoulder  2 labial lobe grooves  About 90º mesioincisal line angle – type trait  Rounded distoincisal line angle  Mesial contour straight, distal is somewhat rounded and both converge cervically  Mesial height of contour (contact point) within incisal third  Distal HOC at junction between incisal & middle thirds  CEJ convex cervically  Root is conical & inclined distally The permanent maxillary central incisors  Lingual aspect  Scoop-like surface  Lingual fossa bordered by (all more prominent in max.) Mesial & distal marginal ridges Cingulum  CEJ more convex than labial& summit toward distal  Root is narrower seen from lingual  Mesial aspect  Chisel-shaped  Labial HOC in the cervical third  CEJ curved incisally (the most pronounced) – type trait  Incisal edge coincides with long axis  Root is conical The permanent maxillary central incisors  Distal aspect  CEJ is less curved than seen from mesial Little differences exist between the mesial and distal aspects of this tooth. The crown gives an illusion of being somewhat thicker toward the incisal third when viewed from this side due to the slope of the labial surface disto-lingually, more of that surface is seen from the distal aspect. Most teeth are turned a little on their root bases to adapt to the dental arch curvature. The extent of curvature of the cervical line is less than on the mesial side “most teeth show this characteristic”  Incisal aspect  Triangular outline  Labial outline is slightly convex  Mesial outline is longer than distal  Labial lobe grooves Maxillary central incisor Permanent maxillary lateral incisor The crown closely resembles that of the central incisor. They supplement central incisors in function. Smaller than the central incisor in all dimensions except the root length. They vary in form more than any other tooth in the mouth except for the third molar. If the variation is too great it is considered a developmental anomaly. Peg shaped lateral: a common anomaly where the tooth has a pointed nondescript form. Permanent maxillary lateral incisor In some individuals these teeth are missing. The presence of a palato-gingival groove “palato-radicular groove” (interruption groove) in some individuals may be a predisposing factor to localized periodontal disease. Some of the common malformations: 1. The presence of a large pointed tubercle as part of the cingulum (Tuberculum dentale) 2. A deep developmental groove that extend down on the root lingually with a deep fold in the cingulum. 3. Twisted root. 4. Distorted crown….. The permanent maxillary lateral incisors  Labial aspect  Narrower MD & shorter IC – type trait  More rounded in general MI angle DI angle more rounded M & D outlines  HOCs are farther from incisal edge Mesial HOC is between middle & incisal thrids Distal HOC is at the center of middle third  Root is conical and slightly inclined distally  Labial aspect / Ctd. The tooth is relatively narrow mesio-distally, about 2mm narrower than the central incisor. The cervico-incisal measurement is 2-3mm shorter than the central incisor. the root: is about 1.5 times the length of the crown. Tapers evenly from the cervical line to two thirds its length apically. In most cases, it curves sharply from this area apically in a distal direction and ends in a pointed apex. Sometimes the root ends straight and sometimes curves mesially.  Lingual Aspect  Marginal ridges & cingulum are more pronounced  Lingual fossa is deeper  Developmental groove and pit? Mesial and distal marginal ridges are marked. The cingulum is usually prominent with a tendency to deep developmental grooves within the lingual fossa where it joins the cingulum. The incisal ridge is more developed and the lingual fossa is more concave and circumscribed than the central incisor. It tapers towards the lingual like the central incisor. A deep developmental groove is a common finding at the distal side of the cingulum which may extend to the root.  Mesial Aspect Mesial aspect Cingulum more convex CEJ less curved Similar to a small central incisor except the root appears longer, the crown is shorter, the labio-lingual measurement of the tooth is less. The curvature of the cervical line is marked in an incisal direction though less than that of the central incisor. The incisal ridge appears somewhat thicker than that of the central due to the heavy development. The root appears tapered, cone shaped, with a blunt apex, again this is variable because sometimes it appears blunt, and other times it is pointed. A line drawn through the centre of the root bisects the incisal ridge of the crown.  Distal Aspect The width of the crown distally appears thicker than mesially from the marginal ridge to the labial aspect due to the placement of the crown on the root. The curvature of the cervical line is usually a mm or less than the mesial surface. A developmental groove may be found on this aspect extending towards the root.  Incisal Aspect Incisal aspect Ovoid outline Smaller MD than central Labial outline is rounded ML & DL line angles are more rounded Sometimes it resembles that of a central incisor and sometimes it looks like a small canine. The cingulum may be large as well as the incisal ridge and the labio-lingul width may be greater than usual in comparison with the mesio-distal width. if these variations are present the tooth has a marked resemblance to a small canine. It exhibits more convexity labially and lingually from this aspect than the central incisor. Maxillary lateral incisor The permanent mandibular incisors  Arch traits  Crown Narrower MD Greater height / width proportion Smaller MD / LL proportion  Root Smaller MD / LL proportion Generally oblong in x-section  Type traits (arch trait)  Nearly equal in size & dimensions The permanent mandibular central incisors  Labial aspect  The narrowest MD of all incisors  Bilaterally symmetrical (type trait)  3 mamelons Mesail and distal mamelons are of equal prominence  About 90 º MI & DI angles and are at same level IC (type traits)  Both HOCs are within the incisal third  M & D outlines are almost straight lines  CEJ convex cervically  Root is narrow & conical  Lingual aspect  Shallow fossa & less prominent cingulum & marginal ridges  CEJ summit in the center  The permanent mandibular central incisors  Mesial aspect  Labial HOC within cervical third  From HOC toward incisal edge labial outline is straight  Root Broad & flat A shallow depression in the midportion Ovoid in x-section  Distal aspect  CEJ is less curved  Incisal aspect  Triangular  Labial surface is flat compared to max. incisors  Seldom labial lobe groove  Long axis of incisal edge is perpendicular to LL line (type trait)  Mesial outline = distal outline in length  Pulp  Broad LL and narrow MD  Right and Left: The symmetry of this tooth makes a judgement on right and left unreliable.  Variation: This tooth is consistent in development and is is rarely absent. Mandibular central incisor The permanent mandibular lateral incisors  Labial surface  Slightly wider than central  Lack of bilateral symmetry  MI angle is sharp while DI angle is rounded with the distal HOC being more cervically situated  Lingual & mesial aspects  Nearly identical to that of central  Distal aspect  More of the incisal edge is visible  CEJ is less pronounced  Incisal aspect  The incisal edge is 'twisted' from the 90 degree angle with the LL line  DI angle is more toward lingual  Pulp  Similar to that of central The permanent mandibular lateral incisors  Right and Left: Two significant features assist in identification, even in a worn tooth. The incisal edge is 'twisted' relative to the labiolingual bisecting line anticipating the curvature of the dental arch. Also, the cingulum will be shifted toward the side from whence the tooth has come.  Variation: This tooth is stable, but variations in root length and direction are occasionally seen.  Comparative Anatomy: Incisors of Interest in other Species  In the animal kingdom, incisors have a variety of functions, such as fur combing in lemurs, tree chopping in certain rodents, and meat stripping in the carnivores.  Rodent incisors are deeply implanted in the jaws, are curved, and continue to grow throughout life. The enamel is limited to the labial surface. In life, the diastem between the incisors and molars is filled by the cheeks and tongue, effectively creating separate incising and grinding chambers. There is a sphincter muscle to facilitate this action.  The lagomorphs, the rabbits and hares, have a very small second incisor immediately behind the main one on each side.  Comparative Anatomy: Incisors of Interest in other Species  Lemurs have comb-like lower incisors adapted to grooming--a paramasticatory adaptation.  The Aye Aye, unlike humans and the majority of living primates have two upper and two lower incisors in each quadrant of the jaw. A curious adaptation in the Aye Aye of Madagascar is the acquisition of continuously growing rodent-like incisors.  Comparative Anatomy: Incisors of Interest in other Species  Sheep have no upper anterior teeth at all. There is instead a horny pad which meets the six lower incisors (and two canines) to 'crop' the grass on which the animal feeds. The ruminants, such as cows, crop and swallow. Later they regurgitate the contents of the caecum to chew their cud. A large volume of saliva buffers and protects the teeth.  Comparative Anatomy: Incisors of Interest in other Species  The most extreme adaptation is the Monodon, the narwhale. It is a rare example of a unilateral tooth. In the adult male, there is a large left incisor which reaches a length of nine to twelve feet and is grooved in a left handed spiral. The one to the right is vestigial. Rare males have two tusks; the incisors tusks of females calcify, but do not erupt and thus remain edentulous. It has no other teeth besides the tusks. The narwhale has another distinction: it is the most extreme example of dental sexual dimorphism in mammals.  Comparative Anatomy: Incisors of Interest in other Species  The largest incisors are the tusks of elephants and their extinct relatives, the mammoth and mastodon which died out at the end of the last Ice Age. The tusk incisors grow from persistent pulps and continue to grow throughout life. They have an enamel tip upon eruption; however, cement covers the remainder of the crown part of the tusk and extends onto the root. The adult tusks have deciduous predecessors.  Comparative Anatomy: Incisors of Interest in other Species  Horses have three incisors per quadrant. Their unusual design and wear throught life permits their use in judging the age of an animal. When the teeth first erupt they have a central pit. With wear the enamel becomes worn off the area around the pit so that the enamel bordering the central (the mark) becomes isolated from the enamel of the crown surface by exposed dentin. With further wear the bottom of the pit (the mark) is reached and passed, so that in old animals the central part of the occlusal surface is made up of secondary dentin filling in the roof of the pulp cavity. Mandibular lateral incisor Incisal relationship  Class I  Class II  Class III  Overjet  Reverse overjet  Overbite