Lower Incisors PDF

Lower Permanent Incisors By Dr. Asmaa Ahmed Foad Mandibular Central Incisor Chronology Appearance of dental organ: 5 miu First evidence of calcification; 3-4month Crown completed: 3-4 years Eruption: 6-7 years Root completed: 9-10 years 1...

Lower Permanent Incisors By Dr. Asmaa Ahmed Foad Mandibular Central Incisor Chronology Appearance of dental organ: 5 miu First evidence of calcification; 3-4month Crown completed: 3-4 years Eruption: 6-7 years Root completed: 9-10 years 1. Labial Aspect: Geometrical Outline: 1. -Trapezoid in shape, the short side is cervically and the long side incisally (fan- shaped) is bilaterally symmetrical 2. -The outline: mesial and distal outlines are nearly straight 3. -Mesial and distal contact areas at the incisal third 4. -Mesio-incisal and disto-incisal angles are sharp 5. -The incisal outline: is straight with a perpendicular angle to the long axis of the tooth 6. -The cervical line is convex toward the root  Surface Anatomy:  Elevations: Labial surface is slightly convex with maximum convexity at cervical 3rd (cervical ridge) In a newly erupted tooth, three mamelons are present with 2 developmental grooves in-between.  Depressions: 2 developmental grooves (mesiolabial- distolabial) developmental grooves.  - The root tapers toward the pointed apex.  - Its apical third may be curved distally or centralized.  Lingual Aspect The geometric outline and outline of the crown are similar to that of labial surface The crown and root converge lingually (lingual convergence) Surface Anatomy: Elevations: The cingulum, mesial, and distal marginal ridges are poorly developed than upper incisors Depressions: The lingual fossa is slightly concave and present in between the marginal ridges, incisal ridge, and cingulum The lingual inclination is a characteristic feature of lower teeth The incisal ridge is lingual to the root axis This lingual inclination facilitates proper occlusion Mesial aspect Geometrical outline: It is triangular in shape. The base is cervically and the apex is incisally The outline: The labial outline is slightly convex starting from the cervical line till the cervical 3rd (poorly developed cervical ridge) Above the cervical ridge, the outline is straight till the incisal edge The incisal edge is lingual to a line bisecting the tooth (due to lingual inclination). The lingual outline is slightly convex at the cervical 3rd (poorly developed cingulum) then becomes slightly concave at the middle third (due to lingual fossa) then becomes slightly convex for incisal ridge. Cervical line: it is convex incisally with its apex below the incisal edge -Mesial contact area at the incisal third -The root: The labial and lingual outline of the root is straight till half of the root, then taper to the apex to the appointed apex Developmental depression present at the middle and apical 3rds of the root Distal Aspect: Similar to the mesial aspect but differs in: 1- The cervical line is shallower 2-The root has well developmental depression 5- Incisal Aspect: It is diamond-in shape The lingual surface is smaller than the labial surface (due to lingual convergence) The crown is tapered lingually Incisal ridge is straight having a right angle to a line bisecting the crown labio-lingually and is located lingually to a line bisecting the crown mesiodistally The labiolingual (thickness) is greater than the mesiodistal dimension (width). Elevations are seen as cervical ridges, marginal ridges, and incisal ridges, the cingulum is centralized Depressions: lingual fossa. Lower Lateral Incisor Mandibular lateral incisor is similar to mandibular central incisor but with some differences: 1-Larger in size 2-The root length is longer 3-The root is thicker and distal developmental depression on the distal surface is more developed 4-Crown is twisted distolingually on the root 5-Crown is not bilaterally symmetrical 6-Incisal ridge is distally inclined 7-Cingulum is distally shifted Chronology Appearance of dental organ: 5 miu First evidence of calcification: 3-4month Crown completed: 4-5 years Eruption: 7-8 years Root completed: 10-11 years  Labial Aspect It differs from the central incisor in the following: 1-Crown is not bilaterally symmetrical 2-The incisal outline slops toward the distal outline 3-The distal outline is shorter than the mesial outline 4- The disto-incisal angle is round while the disto-incisal angle of the lower central is sharp 5-The crown is tilted distolingually 6-The distal contact area is located at a lower level (more cervically) than mesially, at the junction of incisal and middle thirds. o 2- Lingual Aspect o -The mesial marginal ridge (MMR) is longer than the distal marginal ridge (DMR) as the mesial outline is longer than the distal one due to the incisal ridge sloping downward toward the distal side. o -The cingulum is deviated distal to the center of the lingual surface. o 3-Mesial and Distal aspects o 1- The distal surface is shorter in length (cevico-incisally) than the mesial surface of the lower lateral incisor due to distal tilting of the incisal ridge o 2-The distal cervical line is shallower than the mesial (the two cervical lines are shallower than those of the lower central incisor). o 3-The mesial contact area is located at the incisal third but the distal contact area is at the junction of the incisal and middle thirds. Roots Root surface showed longitudinal developmental depression which is deeper distally than mesially. The curvature of cervical lines in all teeth distally is less than mesially. The height of curvature decreased also in lower incisors than in upper incisors. 4- Incisal Aspect It is similar to the incisal aspect of lower central incisors but differs in: The incisal edge is not at a right angle to the line bisecting the crown Labio- lingually Due to the incisal ridge inclined lingually in its distal portion The crown appears to be twisted disto- lingually on the root. -The crown is twisted disto-lingually on its root to allow the incisal ridge to follow the curve of the lower dental arch which is more curved than the upper arch (characteristic feature). The cingulum is shifted distally. Thank you