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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