If the length is doubled, then the flexibility of a wire is increased by:

 # If the length is doubled, then the flexibility of a wire is increased by:

A. 4 times

B. 8 times

C. 2 times

D. 6 times

The correct answer is B. 8 times.

The stiffness of a wire is directly proportional to the fourth power of the radius and inversely proportional to the third power of its length. To put it more simply, flexibility is the direct opposite of stiffness therefore when the wire length is increased by 2 times the flexibility increases 8 fold, and if you increase the radius by 2 fold, the stiffness increase or flexibility decreases by 16 times. 

Stainless steel wire can be hardened by:

 # Stainless steel wire can be hardened by:

A. Tempering

B. Work hardening

C. Annealing

D. Pulse straightening

The correct answer is B. Work hardening.

Cold Working (Strain Hardening/Work Hardening): It is the process of plastically deforming metal at a temperature, lower than at which it recrystallizes new grains. This temperature is usually one-third to one-half of its absolute melting point. Cold working disrupts the regular atomic arrangement and incorporates strain across the grain boundaries. 

Annealing: It is the process of reversing the effects of cold working. In a clinical setting, a wire is considered annealed when it appears red hot.

Hysteresis: The difference between the energy required to activate the wire by deflection and that it releases during deactivation. This is called energy loss or hysteresis. 

Heat treatment: It refers to a general process of using thermal energy to change the characteristics of metallic alloys as tempering, precipitation hardening, or annealing. In a clinical setting, different wires are heat treated according to the manufacturer's recommendations. A wire is considered heat treated when it appears straw-colored. 

Which of the following craniofacial syndromes is not associated with craniosynostosis?

 # Which of the following craniofacial syndromes is not associated with craniosynostosis?

A. Apert syndrome

B. Crouzon syndrome

C. Pfeiffer syndrome

D. Treacher Collins syndrome

The correct answer is D. Treacher Collins syndrome.

Craniosynostosis is a condition in which one or more of the fibrous sutures in a young infant's skull prematurely fuses by turning into bone (ossification), thereby changing the skull's growth pattern. Because the skull cannot expand perpendicular to the fused suture, it compensates by growing more in the direction parallel to the closed sutures. Sometimes the resulting growth pattern provides the necessary space for the growing brain but results in an abnormal head shape and abnormal facial features. In cases in which the compensation does not effectively provide enough space for the growing brain, craniosynostosis results in increased intracranial pressure leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment of mental development combined with a significant reduction in IQ.

In primary multiple suture craniosynostosis features like a cloverleaf skull & sun-setting eyes can be seen. 

Simple craniosynostosis = Premature fusion of only one suture 

Complex/compound craniosynostosis = Premature fusion of more than one/multiple sutures 

Syndromes associated with craniosynostosis are: 

• Apert syndrome 

• Crouzon syndrome 

• Pfeiffer syndrome 

• Chotzen syndrome 

• Craniofrontonasal syndrome 

• Shprintzen-Goldberg syndrome 

• Baller-Gerold syndrome 

• Carpenter syndrome 

Most damaging feature of class III malocclusion is:

 # Most damaging feature of class III malocclusion is:

A. Retroclined upper anterior teeth

B. Crowding of lower incisors

C. Deviated path of closure

D. Reduced overbite

The correct answer is D. Reduced overbite.

Deep bite is the most damaging feature of class II malocclusion. Reduced deep bite is the most damaging feature of class III malocclusion.

Most common site for melanotic neuroectodermal tumour of infancy (MNTI) is:

 # Most common site for melanotic neuroectodermal tumour of infancy (MNTI) is:

A. Maxilla

B. Mandible

C. Ethmoid bone

D. Cervical spine

The correct answer is A. Maxilla.

MNTI is an uncommon osteolytic, pigmented neoplasm, primarily affecting the jaws of new born infant. Its origin is linked to neural crest cells. More than 90% occur in the head and neck region especially the anterior part of the maxillary ridge. They appear as rapidly growing, non-ulcerated, darkly pigmented lesions, with a radiographic appearance of an invasive malignant neoplasm. 

Dimensions of inner bow of facebow are:

 # Dimensions of inner bow of facebow are:

A. 0.045’’ and 1.125 mm

B. 0.06’’ and 0.09’’

C. 0.045’’ and 1.25 mm

D. 0.45’’ and 0.71’’

The correct answer is A. 0.045’’ and 1.125 mm

Face bow and 'J' hook are force delivering units of a head gear. The face bow helps in delivering extra oral force to the posterior teeth. It consists of outer bow or whisker bow, inner bow, junction, force generating unit and anchor unit. 

Outer bow: 

• It is made of round stainless steel wire 0.051 or 0.062 inch. 

• It is contoured around the face 

• It may be short, medium or long in relation to inner bow. 

Inner bow: 

• It is made of 0.045 inch (1.125 mm) or 0.052 inch (1.3 mm) round stainless steel wire. 

• Inserts into the round buccal tube on the maxillary first molars. 

Thesis Topic Ideas for MDS Orthodontics

 Thesis and research is a part of MDS curriculum. Here are some good research topics to consider if you are an MDS Orthodontics Resident.

1. Assessment of the relationship between maxillary and mandibular incisors in Class I, Class II, and Class III malocclusions
2. Evaluation of the effectiveness of different treatment modalities for correcting Class II malocclusion in growing patients
3. Comparison of the effectiveness of fixed and removable functional appliances in correcting Class II malocclusion