Permanent mandibular lateral incisors l tooth crown & root morphology revision for dental students

Permanent mandibular lateral incisors l tooth crown & root morphology revision

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comparison between mandibular lateral and central incisors :

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Morphology – Mandibular Lateral Incisor

Labial Aspect

1. Anatomical features of mandibular lateral incisors appear similar to mandibular central incisors with long but larger crown and two shallow developmental depressions on the incisal third of the tooth.
2. Labial surface of the crown appears convex on the cervical and middle third of the crown that gradually taper and become flat at the incisal third of the crown.
3. Crown appears asymmetrical due to extra bulge and curvature seen on the distal portion of the crown.
4. Incisal edge often appears slanted / tilted toward the distal aspect of the tooth.
5. Distoincisal line angle appears more rounded than the sharp (90 degree) mesioincisal line angle.
6. Mesial contact area is located on the incisal third towards the incisal ridge and distal contact area is placed in the incisal third towards the cervical third of the tooth.
7. Narrow root with a pointed apex that curve slightly to the distal aspect or remain almost straight.

Lingual Aspect

1. Lingual outline is the inverse of the labial outline of the crown. Anatomical features appears similar but less prominent in comparison to the maxillary lateral incisors.
2. Asymmetrical crown shows less conspicuous smooth cingulum , marginal ridges and V-shaped lingual fossa on the lingual aspect of the tooth.
3. Cingulum is located more distally exhibiting a larger mesial marginal ridge than distal marginal ridge.
4. Lingual convergence and longitudinal depressions are evident on the lingual aspect of the tooth root.

Mesial Aspect

1. Mesial aspect shows a “twisted” appearance of the crown on its root as the distal end of the incisal ridge is placed lingual to the labiolingual long axis of the tooth. This gives an impression of a part of the distal marginal ridge to be seen beyond the lingual outline of the mesial marginal ridge.
2. Labial outline appears nearly flat in the middle and incisal third of the crown. Labial crest of curvature is located near the cervical region and lingual crest of curvature is placed on the cingulum of the tooth.
3. Cervical line curves incisally to upper level on both mesial and distal aspects of the crown (mesial cervical line of curvature is deeper than distal cervical line of curvature).
4. Root appears to be straight from the cervical to middle third tapering at pointed apex. Longitudinal depression is evident on the root surface.

Distal Aspect

1. Distal outline of this tooth resembles the distal aspect of the mandibular central incisor. As the distal marginal ridge is located at a higher level, less of the mesial portion of the tooth is seen.
2. Narrow root outline and longitudinal depression is prominent on the distal surface of the root. The apex of the root will be in line with the labiolingual axis of the tooth.

Incisal Aspect

1. Broader labiolingual measurements of the crown are seen from the incisal aspect of the crown. Asymmetrical crown of the mandibular lateral incisor from the incisal aspect gives a “twisted” or “rotated” appearance.
2. Labial outline appears convex in the incisal third of the crown and crest of the cingulum on the lingual aspect will be slightly distal to the mesiodistal axis of the crown.
3. Incisal ridge is located lingual to the labiolingual bisector of the crown outline. Prominent distolingual twist is evident. (Distal half of the incisal ridge is bent lingually to the labiolingual axis of the crown).
4. Mesial contact area is centred labiolingually but the distal proximal contact appears lingual to the labiolingual bisector of the crown.
5. When viewed from the incisal aspect, the crown and root is not perpendicular to the incisal ridge as seen in the central incisor.

Steps in Carving Mandibular Lateral Incisor

• Step 1: Draw a mid-line on all 4 sides of the wax block and divide the block as shown in the diagram (crown and root length)
• Step 2: Mark the five aspects of the tooth as Labial – L, Mesial – M, Distal – D, Incisal – I and Lingual – Li

Carving – Labial Aspect

• Step 3: Mark the mesio-distal dimensions of the crown and at cervix. Join the points as shown here on the labial and lingual aspects of the crown (Note that the incisal edge is slanting from mesial to distal).
• Step 4: Remove the shaded portion of the block from the mesial and distal aspects of the crown. (Wider mesiodistal dimensions as compared to mandibular central incisor)
• Step 5: Divide the crown into three equal thirds (cervical, middle and incisal third) from above to below on all sides and mark the labio-lingual dimension of the crown on the mesial and distal aspects as shown. Place the lingual outline 1.0 mm away from the midline at the incisal edge (lingual inclination)
• Step 6: Remove the shaded portion of the tooth from the labial and lingual aspects of the crown (remove wax more on the middle and incisal third of the tooth to maintain the convexity on the cervical third and create lingual fossa on the lingual side) (Remove about 1-1.5 mm from the lingual aspect of the tooth)

Carving – Incisal Aspect

• Step 7: View the incisal aspect of the tooth with the central incisal ridge
• Step 8: Mark lines as shown here up to 1 mm from the edge of the incisal ridge to the lingual aspect and mark lines as shown in the labial aspect of the crown
• Step 9: Remove wax from the shaded portion of the tooth in order to obtain the lingual convergence and smooth rounded labial surface. Remove more wax from the distolabial and mesiolingual aspect of the tooth to produce a distolingual tilt.

Shaping and Contouring of the Crown

• Step 10: Round the disto-incisal angle of the crown and the cingulum area to provide a complete lingual convergence
• Step 11: Round the cervical third of the labial aspect and cingulum portion of the crown. Make the necessary changes as shown in the picture to obtain the exact shape

Carving – Root

• Step 12: Mark the outline of the root on the labial and lingual portion of the tooth. Reduce from the mesial and distal aspects of the block. Reduction is made more on the lingual side of the tooth. Finally, make a distal tilt in the apex of the root portion of the tooth

• Step 13: Mark the outline of the root on the mesial and distal portion of the tooth. Reduce from the labial and lingual aspects of the block.

• Step 14: Mark the cervical line on the labial, palatal, mesial (3.0 mm) and distal (2.0 mm) of the tooth. Remove wax to a small extent above and below the cervical line to obtain the cervical constriction. Mark the lingual fossa as V-shaped on the lingual aspect of the crown. Provide a distal curvature on the apex of the root (only at the apical third). Lingual reduction of the root – Lingual Convergence is made.

Final Step

• Draw the cervical line and cervical constriction with the adequate measurements on all sides of the crown
• Provide a smooth finish to remove sharp edges
• Polish each side of the tooth with a soft cloth and soap water