Oxygen in histotoxic hypoxia

# The beneficial effect of oxygen therapy in histotoxic hypoxia is about:
A. 0 %
B. 50 %
C. 100 %
D. 30 %

The correct answer is A. 0%

Histotoxic hypoxia refers to hypoxia secondary to the inability of the cells to utilize oxygen.

In histotoxic hypoxia, oxygen therapy is  not beneficial as tissue oxygenation is itself defective. 

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Transposition of Teeth

# The commonest teeth involved in transposition are:
a) Maxillary central incisor and lateral incisor
b) Maxillary canine and first premolar
c) Maxillary 1st premolar and 2nd premolar
d) Maxillary canine and Lateral incisor   

The correct answer is B. Maxillary canine and first premolar. 

Canine-first premolar transposition is the most common  transposition. 21. 

Canine-lateral incisor is the second most common transposition. 

Transposition is never seen in primary dentition. 

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Average Leeway Space

# The average "Leeway space" available in each half of the maxilla is approximately:
a) 0.9 mm
b) 4.0 mm
c) 2.9 mm
d) 6.9 mm 

The correct answer is A. 0.9 mm.

The combined mesiodistal width of the permanent canines and premolars is usually less than that of deciduous canines and molars and this difference is known as Leeway Space of Nance. This space is used by the permanent lower molars during late mesial shift from end-on occlusion to class-I relation. The amount ot leeway space is about 1.8 mm (0.9 mm on each side of arch) in maxillary arch and about 3.4 mm in mandibular arch (1. 7 mm on each side of arch). 

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Ugly duckling stage

# Ugly duckling stage affects:
a) Maxillary anterior teeth
b) Mandibular anterior teeth
c) Both Maxillary and mandibular teeth
d) Cause decrease in vertical height 

The correct answer is A. Maxillary anterior teeth. 

Ugly duckling stage is seen in maxillary central incisor region between 8 -9 years of age. This condition is seen during eruption of permanent canines. The developing canines displaces the roots of central and lateral incisors mesially and causes distal divergence of the crowns of the central incisors resulting in midline diastema. 

This type of malocclusion is not seen in lower arch because lower anteriors erupt almost simultaneously. Also, the path of eruption of mandibular canine is different from that of maxillary canines.

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Canine placement

# Canine placed anterior to the orbital plane:
a) Protraction
b) Abstraction
c) Attraction
d) Expansion

The correct answer is A. Protraction.

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ANB Angle Cephalogram

# An ANB angle 2 ° on the cephalogram usually indicates:
a) An unfavorable relationship of mandible to maxilla
b) A favorable relationship of maxillary alveolar base to mandibular alveolar base
c) Poor cranial growth with poor prognosis
d) Retruded maxillary incisor

The Correct answer is B. A favorable relationship of maxillary alveolar base to mandibular alveolar base.

SNA angle relates maxilla to the cranial base. The mean value is 82°. A Larger value indicates prognathic maxilla while a smaller value is suggestive of retrognathic maxilla.

SNB angle relates mandible to cranial base. Its average value is 80°. Larger values indicate prognathic mandible while smaller values indicates retrusive mandible.

AN B angle denotes the relative position of maxilla and mandible to each other. Mean value is 2° .

An increase in this angle indicates class-II skeletal tendency while an angle that is Less than normal or a negative angle is suggestive of a skeletal classIII relationship.

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Frankfort's horizontal plane

# Frankfort's horizontal plane is formed by joining:
a) Porion and Orbitale
c) Porion and sella
b) Nasion and se lla
d) Porion and Nasion

The correct answer is A. Porion and Orbitale.

FHP or Frankfort horizontal plane =  Formed by joining Porion and orbitale
SN plane or anterior cranial base = Formed by joining nasion and sella
Cranial base length = Nasion and Bolton line
Upper facial height = Nasion to ANS (anterior nasal spine)
Lower facial height = ANS to menton
Total facial height = Nasion to menton

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