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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