Permanent maxillary incisors l tooth crown & root morphology MCQs for dental students

Permanent maxillary incisors l Tooth crown & root morphology MCQ (multiple choice question) for dental students 

Maxillary Central Incisor

Chronology

• Eruption >> 7 - 8 years.
• Root completed >> 10 years.

Labial aspect

• The geometric outline of the crown is trapezoidal in shape with short side at cervical line & long side at the incisal edge.
• Mesial Outline is slightly convex from the cervical line to mesial contact area. The mesial contact area near mesio-incisal angle.(sharp)
• Distal Outline is more convex than mesial outline. The distal contact area near junction of middle and incisal thirds.(rounded)
• Incisal Outline is straight and perpendicular to the long axis of the tooth.
• Cervical Outline is semicircular direction mesiodistally & convex root-wards.
• The Root is cone shape with blunt apex which directed distally.

Palatal aspect

• It has the same geometrical outline and outline as the labial surface.
• The mesial and distal sides of the crown and root converge ligually ( the lingual surface is narrower than the labial surface).
• This convergence to accommodate the large arch size facially than lingually.

• Crown Elevation:

1.        Mesial and distal marginal ridges.
2.        Cingulum at the cervical third of the crown lingually.
3.        Incisal ridge.

• Crown Depression:

1.        Lingual fossa is lined by the cingulum cervically, marginal ridges mesially & distally and the incisal ridge incisally.

 

Mesial aspect

• The geometrical outline of the crown is triangular in shape, the base cervically and the apex incisally.
• Labial outline is convex at cervical third ( cervical ridge). Then become straight or slightly convex in the middle and incisal thirds.
• Lingual outline is convex in the cervical third (cingulum). Then concave at the lingual fossa. Then slightly convex again for the incisal ridge.
• The mesial contact area is oval shape and centrally positioned labio lingual in the incisal third.
• The root is cone shape with blunt apex.

 

Distal aspect

• It is similar to the mesial aspect except for :

1.    The curvature of the cervical line is less than on the mesial surface.
2.    Distal contact area is located more cervically than mesial contact area.
3.    The crown slope distolingually to adapt to the dental arch curvature like most         teeth.

 

Incisal aspect

• Traingular in shape with its apex on the lingual surface.
• The labial surface from this aspect is broad and flat.
• The incisal ridge is seen clearly and centered over the root.
• The outline of the lingual surface tapered toward the cingulum.
• The mesio-distal diameter larger than labio-lingual diameter.

 

The Pulp cavity

Labiolingual section: 

• The pulp chamber is very narrow in the incisal portion and then increases in the crown dimention cervically.

Mesiodistal section: 

• The pulp chamber is wider than in the labiolingual dimenstion.There are three rounded pulp horns.

Cervical cross section: 

• The pulp chamber is roughly triangular in shape in young teeth & become rounded or crescent shaped in old teeth.

Maxillary Lateral Incisor

Chronology

• Eruption >> 8 - 9 years.
• Root completed >> 11 years.

 

Labial aspect

• The geometric outline of the crown is trapezoidal in shape with short side at cervical line & long side at the incisal edge.
• Mesial Outline is slightly convex from the cervical line to mesial contact area.  The mesial contact area at the junction of the incisal and middle thirds.
• Distal Outline is more convex than mesial outline. The distal area is located more cervically in the center of the middle third.
• Incisal outline is more curved than the central incisor.
• Cervical outline is convex root-wards.
• The Root tapers from the cervical line till the end of the middle third.Then it curves distally and ends in a pointed apex.

 

Palatal aspect

• It has the same geometrical outline and outline as the labial surface.
• the mesial and distal sides of the crown and root converge ligually ( the lingual surface is narrower than the labial surface).
• This convergence to accommodate the large arch size facially than lingually.
• Crown Elevation:

1.          Mesial and distal marginal ridges are marked.
2.          The cingulum is more prominent.
3.          Incisal ridge.

• Crown Depression:

1.         Lingual fossa is more concave and circumscribed tha that it's found on the central incisor.
2.         Lingual pit below the cingulum at the lingual fossa.
3.         Developmental grooves within the lingual fossa, where it joins the cingulum, which may extend up on the root for part or all of its length.

 

Mesial aspect

• The geometrical outline of the crown is triangular in shape, the base cervically and the apex incisally.
• Labial outline is convex at cervical third ( cervical ridge). Then become slightly convex to the incisal ridge.
• Lingual outline is convex at cervical third (cingulum). Then concave at the lingual fossa. Then slightly convex again for the incisal ridge.
• The mesial contact area is located at the junction of the incisal and middle thirds.
• The root appears longer than the central incisor. It is cone shape with blunt apex. It has developmental depression.

 

Distal aspect

It is similar to the mesial aspect except for :

1. Less curvature of the cervical line.
2. Distal contact area is located more cervically than mesial contact area.

 

Incisal aspect

• Traingular in shape with its apex on the lingual surface.
• It resembles that of the central incisor except the cingulum and the incisal ridge are more prominent.
• The mesio-distal diameter equal labio-lingual diameter.

The Pulp cavity

Labiolingual section:

• The pulp chamber is narrow in the incisal region and then gradually increase at the cervical region.

Mesiodistal section: 

• The pulp chamber is wide. Then the pulp cavity is gradually decrease. The pulp horns appear blunted.

Cervical cross section: 

• The pulp chamber is centered within the root.

Permanent incisors

Overview

• Incisors are teeth with straight cutting edges. There are four incisors per arch and two per quadrant. Their main function is to bite and shear food, articulate speech and support the lips. The central incisors are located in the anteromedial aspect of the upper and lower jaws and the lateral incisors are lateral to the central incisors.

 

The maxillary central incisors have straight edges and are the most prominent teeth in the mouth. The mandibular

central incisors are long, narrow and symmetrical, with straight edges and are the smallest teeth in the dental arch.

 

The mandibular lateral incisors are larger and more rounded than the central incisors. The lateral incisors are narrower than the central ones but are otherwise similar in appearance.

 

Maxillary incisors demonstrate a labial convexity which makes the tooth most prominent in the oral cavity while the labial surfaces of mandibular incisors are relatively flat. The lingual surface of the maxillary and mandibular incisors are composed of cingulum and lingual fossa with varying degrees of prominence and slight variation on the location between each tooth. Mamelons are commonly evident in the incisal edges of the incisors. All the incisors

are single rooted with the roots of maxillary incisors being conical with a blunt apex while mandibular incisor roots are usually flat with a pointed apex.

 

KEY POINTS

Maxillary Central Incisors : 

Tooth Crown 

1. Central incisors are wider mesiodistally than other anterior teeth.
2. Mamelons are rounded projections corresponding to the developmental lobes and are present in the newly erupted central incisors.
3. The cingulum is a smooth, convex area below the cervical line in the lingual aspect.
4.  The cingulum and the prominent ridges give a shovel- or scoop-shaped appearance to the incisor.
5. Contact area on the mesial aspect is present in the incisal third, close to the incisal edge. The distal contact area is located at the junction of the incisal and middle third.
6. Central incisors have two embrasures: labial and lingual. The lingual embrasure is large as a result of the convergence.

root : 

• is conical, and the apical third has a mild distal taper.

Maxillary Lateral Incisors

1. Like the third molars, the maxillary lateral incisors show wide variations in morphology.
2. The mesioincisal angle in the maxillary lateral incisor is more rounded when compared with the central incisor.
3. The labiopalatal inclination is 29°.
4. The root shows distal inclination.
5. Developmental grooves known as palatogingival grooves or palatoradicular grooves, are present on the lingual aspect.

Mandibular Central Incisors

1. The mandibular central incisors are the smallest teeth in the permanent dentition.
2. The mandibular central incisor is symmetrical from the incisal aspect.
3. Root concavities are present both on the mesial and distal root aspects.

Mandibular Lateral Incisors

1. The mandibular lateral incisors have increased mesiodistal and incisocervical height when compared with the mandibular central incisors.
2. The lingual aspect is more prominent in the mandibular lateral incisors than in the mandibular central incisors.
3. The incisal ridge is slightly curved lingually near the distal margin.
4. The crown is not bilaterally symmetrical like the mandibular central incisors.