Permanent maxillary lateral incisors l tooth crown & root morphology revision

Permanent maxillary lateral incisors l tooth crown & root morphology revision

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comparison between upper lateral and central incisors 

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Morphology of Maxillary Lateral Incisor

Labial Aspect

1. Maxillary lateral incisor appears long and narrow as compared to maxillary central incisor (overall smaller size of the crown).
2. Trapezoidal in outline with shorter parallel side towards the cervical region of the tooth.
3. Labial surface appears more convex with rounded (curved) incisal edge as compared to the maxillary central incisor.
4. Distoincisal and mesio incisal line angles appear more rounded (less symmetrical).
5. Mamelons are less commonly seen in this tooth.
6. Mesial proximal contact is located at the level of the junction of the incisal and middle thirds of the crown and distal contact is at a level near the middle of the middle third of the crown. Crest of curvature is elliptical and slightly distal to mesiodistal bisector of the crown.
7. Overall the root appears to be longer than the crown length. Cone shaped root converging evenly toward the apex for the cervical two thirds of its length. There is usually a characteristic curve of the root toward the distal aspect in its apical third of the crown (distal tilt).

Palatal Aspect

1. Morphology of maxillary lateral incisor appears similar to the maxillary central incisor except that cingulum of the maxillary lateral incisor is limited to the cervical third of the crown, centred
2. on the root axis with a very deep depression or even a pit, deep in the fossa behind the cingulum at the junction of the “V” shaped palatal pits. Sometimes, accessory lingual ridges may become evident.
3. Deep, smaller triangular (V-shaped) fossa lodges the incisal two thirds of the palatal surface of the crown bounded by incisal ridge - incisally, mesial & distal marginal ridge mesially and distally, cingulum on the cervical region of the tooth.
4. Presence of developmental groove extending out of the palatal fossa between a marginal ridge and the cingulum, usually on the distal side of the cingulum is evident. This groove may be quite
5. deep and may even run through the cement enamel junction onto the root (palatogingival groove).
6. Narrow root with lingual taper and mesial developmental depression is evident.

Mesial Aspect

1. Wedge shaped crown with an incisal ridge that is in line with midpoint or slightly labial to the labiopalatal diameter of the crown is evident.
2. Labial crown outline is convex from labial cervical ridge crest to incisal ridge. Palatal crown outline is convex in the cervical third and slightly concave from the cingulum area to the incisal region.
3. Crest of curvature of labial and palatal aspects of the crown are located on the cervical third of the crown. A line drawn through the center of the root bisects the incisal ridge of the crown.
4. Curvature of the cervical line is deeper on the mesial surface than on the distal surface of the crown.
5. Long conical root with its blunt apex located labial to the labiopalatal bisector of the crown is evident. Developmental depression is present occasionally on the mesial aspect of the
6. crown.

Distal Aspect

1. Wedge shaped crown with an incisal ridge that is in line with midpoint to the labiopalatal diameter of the crown.
2. Overall, the labial and palatal aspect is underdeveloped with prominence of curvatures from cervical to incisal region of the teeth.
3. Incisal ridge and root apex is not in line with one another.
4. Cervical line curves for a shorter distance incisally to a greater extent on the distal surface.
5. Long conical root with its blunted apex located labial to the labiopalatal bisector of the crown is evident. Absence of any developmental depressions.

Incisal Aspect

1. Crown is wider mesiodistally as compared to that of the maxillary central incisor. Rarely, labiopalatal and mesiodistal dimensions of the crown remain the same.
2. Labial outline is more convex than that of the maxillary central incisor and the Mesiolabial & distolabial line angles are more rounded (less prominent).
3. Crown appears more smooth-edged and converges from labial aspect toward the palatal aspect of the tooth (palatal convergence). Incisal ridge crosses approximately midway between the labial and palatal outline. However, it usually shows some curvature with the convexity toward the labial aspect of the crown. Crest of the palatal outline of the cingulum is distal of the mesiodistal bisector of the crown.

Steps in Carving Maxillary 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)(Shorter crown length)
• Step 2: Mark the five aspects of the tooth as Labial – L, Mesial – M, Distal – D, Incisal – I and Palatal - P

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 palatal aspects of the crown

• Step 4: Remove the shaded portion of the block from the mesial and distal aspects of the crown (Incisal edge is longer than the other parallel side at cervix) (Lateral incisor is smaller in dimensions as compared to central incisor mesio-distally)

• 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-palatal dimension of the crown on the mesial and distal aspects as shown. (Lateral Incisor is smaller in dimensions as compared to central incisor labiopalatally)

• Step 6: Remove the shaded portion of the tooth from the labial and palatal aspects of the crown (remove more wax on the middle and incisal third of the tooth to maintain the convexity on the cervical third and create palatal fossa on the palatal side of the tooth. Check if palatal outline meets at the central axis.

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 palatal and labial aspect of the crown

• Step 9: Remove wax from the shaded portion of the tooth in order to obtain the palatal convergence and smooth rounded labial surface. Wax is removed more on the labial surface to obtain a rounded surface as compared to central incisor (Ovoid outline with distolingual rotation)

Shaping and Contouring of the Crown

• Step 10: Round the Disto-incisal angle of the crown and the cingulum area to provide a palatal convergence

• Step 11: Round the cervical third of the labial aspect and cingulum portion of the crown and make the necessary changes as shown in the picture to obtain the exact shape. (More rounded distolingual line angle with slightly round mesiolingual line angle)

Carving – Root

• Step 12: Mark the outline of the root on the labial and palatal portion of the tooth. Reduce from the mesial and distal aspects of the block. Reduction is made more on the palatal 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 portion on the mesial and distal portion of the tooth. Reduce from the labial and palatal aspects of the block. (Labial outline must be straight while the palatal outline is S-shaped)
• 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.

Final Step

1. Mark the lingual fossa as V-shaped on the palatal aspect of the crown.
2. Provide a distal curvature on the apex of the root (only at the apical third).
3. Draw the cervical line and cervical constriction with the adequate measurements on all sides of the crown.
4. Provide a smooth finish to remove sharp edges except keeping the mesio-incisal angle alone sharp and more rounded disto-incisal angle.
5. Polish each side of the tooth with a soft cloth and soap water.