Permanent maxillary central incisors l tooth crown & root morphology revision

Permanent maxillary central incisors l tooth crown & root morphology  revision

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Morphology of Maxillary Central Incisor

Labial Aspect

1. Trapezoidal in outline with the larger mesiodistal dimensions and cervico-incisal dimensions.
2. Crown appears narrower at the cervical third and broader at the incisal third region.
3. Crown outline at the distal portion appears to be more convex as compared to the mesial portion.
4. Incisal angle is more rounded at the distal side than the incisal angle at the mesial side (almost 90°).
5. Incisal edge may appear straight or show small protuberances (mamelons). This appears more prominent on newly erupted teeth that gradually wear off with age and mastication.
6. Mesial proximal contact (greatest curvature of mesial outline) is situated nearer the incisal third of the crown and distal proximal contact (greatest curvature of distal outline) is located at the level of the junction of the incisal and middle third of the crown.
7. Labial surface appears flat with a slight degree of convexity at the incisal third of the crown. Labial surface may exhibit shallow vertical developmental depressions defining lobe arrangement and few horizontal ridges representing differing rates of enamel formation during normal growth patterns. The raised portions of the ridges (positive anatomy) are termed as “Perikymata” and the horizontal grooves (negative anatomy) are termed as “Imbrication lines.”
8. Cervical outline of crown is slightly concave incisally (semicircular).
9. Cone shaped root with a relatively blunt apex is turned distal to centre line of tooth (distal tilt). Overall, root appears wider labiopalatally.

 

Palatal Aspect

1. Palatal aspect of the crown appears inverse of the labial aspect.
2. Palatal aspect of the crown appears narrower than labial aspect with its incisal ridge centred labiopalatally.
3. Mesial and distal marginal ridges converge towards the cingulum region of the crown (palatal convergence).
4. Well-developed elevated area (cingulum) occupies the cervical third (slightly off-centre – distally) on the palatal aspect of the crown.
5. Broad, shallow M-shaped depression (palatal fossa) is bounded by the incisal ridge - incisally, the longer mesial and shorter distal marginal ridges – mesially and distally respectively and the cingulum– cervical region of the palatal aspect of the crown. Few developmental grooves may be present extending from the cingulum to the palatal fossa of the tooth.
6. Greatest curvature of the cingulum and crest of cervical line on the palatal aspect appears slightly distal to the mesiodistal axis of the crown.
7. Cervical outline of crown is concave incisally.
8. Palatal root appears narrower mesiodistally than labial aspect of the root. Sometimes, mesial portion of the root appears longer and may show longitudinal depression. Distal portion of the root may appear more convex in outline.

Mesial Aspect

1. Wedge shaped (triangular) mesial outline with its base towards the cervical line and apex towards the incisal edge of the crown. Exhibit wide labiolingual dimensions among the anterior teeth.
2. Labial outline of the crown from the crest of the labial cervical ridge to the incisal ridge is relatively flat. Palatal outline of thecrown from the cingulum to the incisal ridge is convex in the
3. cervical third (cingulum& palatal-incisal ridge) and slightly concave (palatal fossa) on the middle and incisal third of the crown (S-shaped).
4. Crown appears to be titled labially to the root axis line in maxillary incisors.
5. Greatest crest of curvature of the crown outline (labial and palatal) is present at the cervical third of the crown (same level) i.e., at the level of crests of the labial and palatal cervical ridges.
6. Cervical line viewed from the mesial aspect curves more incisally than the distal aspect of the crown.
7. Overall, a line drawn along the crown and root at the center of the maxillary central incisor bisect the incisal ridge of the crown and apex of the root.
8. Cone shaped root with smooth convex surface and blunt round apex centered labiopalatally. Longitudinal depression is evident on the mesial root surface of maxillary incisor at the junction of middle and palatal third of the crown.

Distal Aspect

1. Wedge shaped distal outline with its base towards the cervical region and apex towards the incisal edge of the crown. Exhibits greatest labiopalatal width in the cervical third of the crown.
2. Distal aspect appears to be more broader than mesial aspect of the tooth. Cervical line incisally is less curved on the distal side as compared to the mesial surface.
3. Cone shaped root with smooth flat surface and blunt apex centered labiopalatally. Longitudinal depression is absent. Incisal ridge and apex of the root are in line with each other along the long axis of
4. the tooth.

Incisal Aspect

1. Roughly triangular outline with a broad curved labial surface converging towards the palatal aspect of the crown (palatal convergence).
2. Wide labiopalatal and mesiodistal dimensions when viewed from the incisal aspect of the tooth.
3. Mesial half of the crown appears more bulky relative than the distal aspect of the crown.
4. Mesiolabial and distolabial line angles are prominent on the labial aspect of the crown and the surface outline between them is relatively straight.
5. Cingulum forms most of the bulk on the cervical third on the lingual surface of the tooth. Crest of curvature of the cingulum on the palatal aspect is slightly distal to the mesiodistal plane of the crown (Mesial marginal ridge> distal marginal ridge).
6. Interproximal contact areas (greatest curvature mesially and distally) are centred labiopalatally.
7. Incisal ridge is relatively straight, centered parallel to the labiopalatal plane/ perpendicular to the mesiodistal plane and slopes towards the lingual aspect of the tooth.

Steps in Carving of Maxillary Central 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 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 (Trapezoid shape)

• Step 4: Remove the shaded portion of the block from the mesial and distal aspects of the crown (Incisal ridge is longer than the parallel side at cervical region)

Carving – Proximal Aspect

• 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

• Step 6: Remove the shaded portion of the tooth from the labial and palatal 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 palatal fossa on the palatal side). Palatal outline meets at the central axis of the crown. (Remove about 1-1.5 mm more from palatal side)

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 labial and palatal aspect of the crown (Semicircular).

• Step 9: Remove wax from the shaded portion of the tooth in order to obtain the palatal convergence and smooth rounded labial surface , (Distolabial line angle is rounded than Mesiolabial line angle).

Shaping and Contouring of the Crown

• Step 10: Round the Disto-incisal angle of the crown and the cingulum area to provide a complete palatal 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 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 of the tooth on the mesial and distal portion of the tooth. Reduce from the labial and palatal aspects of the block.

• Step 14: Mark the cervical line on the labial, palatal, mesial (3.5 mm) and distal (2.5 mm) of the tooth. Remove wax to a small extent above and below the cervical line to obtain a prominent cervical constriction.

Final Step

• Mark the lingual fossa as M-shaped on the palatal aspect of the crown. Provide a distal curvature on the apex of the root (only at the apical third). 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 except keeping the mesio-incisal angle alone sharp. Polish each side of the tooth with a soft cloth and soap water.