Arch length space for the eruption of permanent mandibular second and third molars is created by:

 # Arch length space for the eruption of permanent mandibular second and third molars is created by:

A. Apposition of the alveolar process

B. Apposition of the anterior border of ramus

C. Resorption of the anterior border of ramus

D. Resorption at the posterior border of ramus

The correct answer is C. Resorption of the anterior border of ramus.

Nowhere is there a better example of remodeling resorption than in the backward movement of the ramus of the mandible. The mandible grows longer by apposition of new bone on the posterior surface of the ramus. At the same time, large quantities of bone are removed from the anterior surface of the ramus. In essence, the body of the mandible grows longer as the ramus moves away from the chin, and this occurs by removal of bone from the anterior surface of the ramus and deposition of bone on the posterior surface. 

In infancy, the ramus is located at about the spot where the primary first molar will erupt. Progressive posterior remodeling creates space for the second primary molar and then for the sequential eruption of the permanent molar teeth. More often than not, however, this growth ceases before enough space has been created for the eruption of the third permanent molar, which becomes impacted in the ramus. 

Ref: Contemporary Orthodontics, Proffit, 4th Edition, Page no 47

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Facial plane in Lateral Cephalogram:

 # In a lateral cephalogram, facial plane runs from:

A. Nasion to pogonion

B. Nasion to gnathion

C. Sella to gnathion

D. Nasion to ANS

The correct answer is A. Nasion to Pogonion. 

Facial plane: It is a line from the anterior point of the frontonasal suture (nasion) to the most anterior point of the mandible (pogonion). 

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Condition always present in a class II div 2 malocclusion

 # Which of the following conditions is always present in a class II div 2 malocclusion?

A. Open bite

B. Crossbite

C. Deep bite

D. Closed bite

The correct answer is C. Deep Bite. 

Some children exhibit a skeletal vertical deficiency (short face), almost always in conjunction with an anterior deep bite and some degree of mandibular deficiency and often with a Class II, division 2 malocclusion. Skeletally, the condition often can be described as Class II rotated to Class I. The reduced face height is often accompanied by everted and prominent lips that would be appropriate if the face height were normal. Children with a vertical deficiency can be identified at an early age. 

Ref: Contemporary Orthodontics, Proffit, 4th Edition, page no. 534

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Center of rotation in simple tipping

 # When a simple tipping force is applied to the crown of an incisor, the center of rotation is usually located:

A. At the apex

B. At the incisal edge

C. At the cervical line

D. One third the root length from the apex

The correct answer is D. One third the root length from the apex.

Center of rotation-the point around which rotation actually occurs when an object is being moved. If a force and a couple are applied to an object, the center of rotation can be controlled and made to have any desired location. 

The center of resistance( Cp)f or any tooth is at the approximate midpoint of the embedded portion of the root. lf a single force is applied to the crown of a tooth, the tooth will not only translate but also rotate around Cp (i.e., the center of rotation and center of resistance are identical), because a moment is created by applying a forcea t a distance from Cn. The perpendiculadr istancef rom the point of force application to the center of resistance is the moment arm. Pressure in the periodontal ligament will be greatest at the alveolar crest and opposite the root apex. 

Ref: Contemporary Orthodontics, Proffit, 4th Edition, Page no. 373

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The ‘ugly duckling stage’ is characterized by:

 # The ‘ugly duckling stage’ is characterized by:

A. Distoangular axial inclination of the crown of maxillary incisors

B. Deep overbite

C. Mandibular lateral incisors erupting lingual to mandibular central incisors

D. Maxillary lateral incisors erupting lingual to maxillary central incisors

The correct answer is A. Distoangular axial inclination of the crown of maxillary incisors.

In some children, the maxillary incisors flare laterally and are widely spaced when they first erupt, a condition often called the "ugly duckling" stage. The position of the incisors tends to improve when the permanent canines erupt, but this condition increases the possibility that the canines will become

impacted.

Ref: Contemporary Orthodontics, Proffit, Fourth Edition, Page no. 101

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Orthodontic correction of which of the following is most easily retained?

 # Orthodontic correction of which of the following is most easily retained?

A. Anterior crossbite

B. Spacing

C. Diastema

D. Crowding

The correct answer is A. Anterior Crossbite.

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Earliest radiographic sign of osteomyelitis

 # The earliest radiographic sign of osteomyelitis is:

A. Solitary or multiple small radiolucent areas

B. Increased granular radiopacity

C. Blurring of trabecular outlines

D. Formation of sequestrum appearing as radiopaque patches

The correct answer is C. Blurring of Trabecular outlines.

Radiographic Features

Radiodensity—about 10 days after acute infection, the density of trabeculae will be decreased, with blurred and fuzzy. For the radiographs to reveal any changes, there must be a loss of from 30 to 60% in the calcium content.

Trabecular pattern—the earliest radiographic change is that trabeculae in the involved area are thin, of poor density and slightly unsharp or blurred. The trabeculae soon lose their continuity as well as the little density present. Individual trabeculae become fuzzy and indistinct.

Ref: Textbook of Oral Medicine, 2nd Edition, Anil Govindrao Ghom

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