What is Proportional Limit?

# The proportional limit is defined as:
A. The maximum stress in a structure
B. The minimum force required to cause a structure to break
C. The maximum stress that can be induced without permanent deformation
D. The maximum elongation under tension that
 can be measured before failure

The correct answer is C. The maximum stress that can be induced without permanent deformation.

Stresses above proportional limit cause plastic deformation. This stress is called yield strength or proof stress. It  is the greatest stress, produced in a material such that stress is directly proportional to the strain. 

Phillip's Science of Dental Materials, 12th ed. Page no 57.

Most Common reason for removal of Impacted Mandibular third molars:

# Most common reason for the removal of impacted mandibular third molars is:
 A. Referred pain
 B. Recurrent pericoronitis
 C. Chronic periodontal disease
 D. Orthodontic treatment


The correct answer is B. Recurrent Pericoronitis

Pericoronitis is an inflammatory lesion occurring around the impacted or partially erupted tooth. An incomplete eruption of the tooth provides a large stagnation area for food debris under the gingival flap. This becomes infected easily and results in inflammation of the pericoronal flap. It exhibits chronic inflammation for a long period. If the debris and bacteria are deeply entrapped, an abscess may form which is called a pericoronal abscess. It is a mixed infection and various bacteria of the dental plaque (particularly anaerobes) play a significant role in the development of pericoronitis.

Clinical Features: The mandibular third molar is the commonly involved tooth. Pain and swelling of the pericoronal tissue around the affected tooth, difficulty in chewing, and difficulty in opening the mouth are the usual complaints. The patient may be mildly ill with fever, malaise, and regional lymphadenopathy.

Management: Entrapped food debris must be removed. When the upper tooth is involved, it should be grounded or extracted if it is malposed. Radiograph helps in assessing the position of the involved tooth. If impacted, the tooth must be removed. And if it is in a favorable position, surgical removal of the pericoronal flap is advocated after acute symptoms subside. The administration of antibiotics helps to relieve the symptoms and prevents the spread of infection to the adjacent tissue spaces.

Ref: Shafer's Textbook of Oral Pathology, 7E, Page: 400

AIIMS MDS Nov 2007 MCQs - Part 2

# In lead poisoning, gingival discoloration presents as:
A. Blue black line
B. Yellow line
C. Grayish black line
D. Steel gray line

# Dilaceration occurs due to:
A. Trauma to the tooth germ during root development
B. Abnormal displacement of the tooth germ during root development
C. Abnormal displacement of enamel epithelium during tooth development
D. Abnormal displacement of ameloblasts during tooth development

AIIMS MDS Nov 2007 MCQs - Part 1

CLICK HERE TO REVEAL ALL ANSWERS AFTER YOU HAVE MARKED ALL YOUR ANSWERS IN A SEPARATE PAPER AND CHECK YOUR SCORE.

# Which one of the following is a junction of frontal,parietal, temporal and greater wing of sphenoid bone?
A. Pterion
B. Lambda
C. Vertex
D. Inion

# A non synovial joint with dense connective tissue between two bony surfaces is termed as:
A. Synchondrosis
B. Syndesmosis
C. Symphysis
D. Suture

Radiographically, driven snow appearance is seen with:

# Radiographically, driven snow appearance is seen with:
A. Adenomatoid odontogenic tumor
B. Calcifying odontogenic cyst
C. Calcifying epithelial odontogenic tumor
D. Keratocyst

The correct answer is C. Calcifying Epithelial Odontogenic Tumor

- Scattered flecks of calcification throughout the radiolucency has given rise to the descriptive term driven snow appearance.

- Lesion appears as diffuse or well circumscribed unilocular radiolucency.

- Combined radiolucency and radioopacity with irregular bony spicules producing honeycomb pattern

- Scattered flecks of calcification give driven snow appearance

- Sometimes, lesion is totally radiolucent and in association with unerupted tooth

Zones of Dentinal Caries

ZONES OF DENTINAL CARIES
ZONE 1	Normal Dentin
Zone 2	Subtransarent Dentin	Zone of demineralization (by acid from caries) Damage to the odontoblastic process is evident. However, no bacteria are found in the zone. Stimulation of the dentin produces pain, and the dentin is capable of remineralization.
Zone 3	Transparent dentin	Softer than normal dentin Further loss of mineral from the intertubular area. Stimulation of this region produces pain. There are no bacteria present. The collagen cross-linking remains intact in this zone, can serve as a template for remineralization. The intact collagen of the intertubular dentin, and thus this region remains capable of self-repair, provided the pulp remains vital.
Zone 4	Turbid dentin	Turbid dentin is the zone of bacterial invasion  Widening and distortion of the dentinal tubules which are filled with bacteria. There is very little mineral present and the collagen in this zone is irreversibly denatured. The dentin in this zone will not self-repair. This zone cannot be remineralized and must be removed prior to restoration
Zone 5	Infected Dentin	The outermost zone, infected dentin, consists of decomposed dentin that is teeming with bacteria. There is no recognizable structure to the dentin. Absence of collagen and mineral content. Great numbers of bacteria are dispersed in this granular material. Removal of infected dentin is essential to sound, successful restorative procedures as well as prevention of spread of the infection

# Whenever the caries cone in enamel is larger or at least the same size as that in dentin, it is called as:

# Whenever the caries cone in enamel is larger or at least the same size as that in dentin, it is called as:
A. Residual caries
B. Recurrent caries
C. Forward caries
D. Backward caries

Forward Caries. Forward caries is where the caries cone in enamel is larger or at least the same size as that in dentin.

Backward Caries. When the spread of caries along the DEJ exceeds the caries in the contiguous enamel, caries extends into this enamel from the junction.

Ans is C: Forward caries (Ref: Sturdevant's Art and science of operative dentistry 4th ed., p 274)