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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Treatment of Fordyce's granule

 # If one of your patient is having Fordyce’s granules in his buccal mucosa, what will be your line of treatment?

A. Excision

B. No treatment needed

C. Topical application of steroids

D. Surgery followed by radiotherapy

The correct answer is B. No treatment needed. 

Ref: Shafer's Textbook of Oral Pathology, page no. 25. These glands are innocuous, have no clinical or functional significance, and require no treatment. However, very rarely a benign sebaceous gland adenoma may develop from these intraoral structures.

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Anhidrotic ectodermal dysplasia affects:

 # A known case of anhidrotic ectodermal dysplasia is brought to hospital for treatment. Which area of the body do you find mostly affected in this case?

A. Spleen

B. Skin or ectoderm

C. Kidney

D. Thyroid gland

The correct answer is B. Skin or Ectoderm. 

The most commonly occurring ectodermal dysplasia is called as ‘hereditary hypohidrotic

(anhidrotic) ectodermal dysplasia’. This shows X-linked inheritance. 

Sex—males are affected more frequently than females.

Appearance—it is characterized by hypotrichosis, hypohydrosis and anhidrosis with saddle nose appearance.

Hairs—the hair of scalp and eyebrows tend to be fine, scanty and blond.

Frontal bosses- supraorbital and frontal bosses are pronounced.

Heat intolerance—skin is often dry, soft, smooth and scaly with partial or complete absence of sweat glands. Such patient cannot perspire and they usually suffer from hyperpyrexia and inability to endure warm temperature. 

Sibling appearance—facial appearance of these individual resemble to each other, enough to be mistaken for siblings.

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Nikolsky’s sign is a feature of:

 # Nikolsky’s sign is a feature of:

A. Lichen planus

B. Pemphigus

C. Herpes simplex

D. Lupus erythematosus

The correct answer is B. Pemphigus.

Nikolsky’s sign: It was named after Pytor Vasilyenich Nikolsky who was the first to describe this finding. On applying gentle mechanical pressure (e.g. blowing air or applying pressure with a mirror handle) on affected tissue will result in the formation of a lesion. Nikolsky’s sign is seen both in the skin and oral mucosa. It is seen in pemphigus, paraneoplastic pemphigus, mucous membrane pemphigoid, epidermolysis bullosa, linear IgA bullous disease, lupus erythematosus, graft-versus-host disease and toxic epidermal necrolysis.

Ref: Textbook of Oral Medicine, Oral Diagnosis and Oral Radiology,Ongole and Praveen, 2nd Edition, Page no. 235

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