Permanent mandibular premolars l tooth crown & root morphology MCQs for dental students

tooth crown morphology for mandibular premolars  

Introduction in mandibular premolars tooth crown and root morphology :

• The mandibular premolars are four in no.: two are situated in the right side of the mandible and two in the left side. They are immediately posterior to the mandibular canines and anterior to the molars.

 

Mandibular First Premolar

• The mandibular. first premolar is the smallest premolar in the human dentition, it has a large buccal cusp, which is long, well formed and functional and small, nonfunctioning lingual cusp that looks like cingulum found on maxillary canines.
• This tooth is situated between the canine and second premolar and has some characteristics common to each of them.

Characteristics that Resemble those of the Mandibular Canine

1. The buccal cusp is long and is the only occluding cusp.
2. The buccolingual measurement is similar to that of the canine.
3. The mesiobuccal cusp ridge (mesial slope) is shorter than the distobuccal cusp ridge (distal slope).

The characteristics that resemble those of the second mandibular premolar are:

1. The tooth has more than one cusp.
2. The outline of crown and root from the buccal aspect resembles that of the second premolar, but the buccal cusp of the 1st premolar is longer & pointed .
3. The contact areas, mesially and distally, are near the same level.

Principle identifying features : 

1. Marked lingual inclination of the crown.
2. Two cusps, the buccal is larger, and the lingual one looks like a more developed cingulum.
3. Diamond occlusal outline.
4. Single rounded root.
5. The presence of mesiolingual developmental groove.

Buccal Aspect

1. The crown is pentagonal, with a prominent middle buccal ridge which is continuous from the cusp tip to the cervical line.
2. The distal slope of the buccal cusp is longer than mesial slope.
3. The contact areas are broad, and at the same level.
4. The tip of the buccal cusp is sharp and located mesial to the long axis of the crown.

Lingual Aspect

1. The crown and root taper lingually, and the occlusal surface slope greatly toward the lingual in a cervical direction down to the short lingual cusp.
2. The lingual cusp is less developed (resembling a strongly developed cingulum), but it has pointed tip.
3. A characteristic of the lingual surface of the mandibular first premolar is the mesio lingual developmental groove. This groove located at the mesio lingual angle & it extends into mesial fossa of the occlusal surface.

Mesial Aspect

1. The outline form is rhomboidal.
2. Buccal cervical ridge located at cervical area of the buccal surface.
3. The lingual outline is less convex than the buccal, with a crest of curvature in the center of the middle third.
4. The height of the lingual cusp is 2/3 of the buccal from the cervical line to the cusp tip.
5. The mesial marginal ridge is low &part of the occlusal surface can be seen from this aspect.
6. The cervical line on the mesial surface is curving occlusally.

Distal Aspect

1. The distal marginal ridge is higher than the mesial one.
2. Curvature of the cervical line is nil.

Occlusal Aspect

1. The occlusal outline form is diamond-shaped.
2. The buccal cervical ridge is prominent.
3. The mesial  & distal marginal ridges are well developed.
4. Mesiolingual developmental groove at the lingual side extending to the mesial fossa.
5. There is a big buccal triangular ridge and a small lingual triangular ridge united together forming a transverse ridge.
6. There are two triangular fossae, mesial and distal fossae with their corresponding pits.
7. Central developmental groove crossing the transverse ridge.

Mandibular second premolar

• Mandibular 2nd premolar is two types:

1. Two cusps type.
2. Three cusps types.

The main difference between the two types:

The buccal aspect:

• no difference.

The lingual aspect:

• Two cusps type:

1. Lingual cusp is slightly shorter & narrower than buccal cusp.
2. No mesiolingual developmental groove.

• Three cusps type:

1. Two lingual cusps, the mesiolingual is larger than distolingual.
2. Lingual developmental groove located between the lingual cusps.

 

The mesial aspect & The distal aspect:

• No difference.

The occlusal aspect:

• two cusps type:

1. occlusal outline is more rounded than 3 cusps type.
2. the presence of transverse ridge like the mandibular 1st premolar
3. The central developmental groove is U or H shape.
4. NO mesio lingual groove.

• Three cusps type:

1. The occlusal outline is square.
2. no transverse ridge.
3. The central developmental groove is Y shape.
4. Lingual develop. groove separating the ML & DL cusps.