Which of the following drugs is likely to damage the eighth cranial nerve when administered for a long period of time ?

 # Which of the following drugs is likely to damage the eighth cranial nerve when administered for a long period of time ?

 A. Ethambutol

 B. Isoniazide

 C. Rifampicin

 D. Streptomycin

The correct answer is D. Streptomycin.

Nephrotoxicity, ototoxicity, and contact sensitization (due to this, topical application is not indicated) are common side effects of Streptomycin. 8th nerve is usually affected. Vestibular involvement is more common and cochlear involvement is less common. 

Which of the following structures is not of ectodermal origin?

 # Which of the following structures is not of ectodermal origin?

A. Hunter Schreger bands

B. Enamel spindles

C. Enamel tufts

D. Enamel lamellae

The correct answer is B. Enamel spindles.

Enamel spindles are odontoblastic processes, which extend into enamel. Enamel spindles are mesenchymal in origin.

Malocclusion representing a transverse deficiency is often referred to as:

 # Malocclusion representing a transverse deficiency is often referred to as:

A. Open bite

B. Closed bite

C. Cross bite

D. Deep bite

The correct answer is C. Cross bite.

Patients with maxillary transverse deficiency usually have a narrow palate and a posterior crossbite. If the maxilla is narrow relative to the rest of the face, a diagnosis of transverse maxillary deficiency is justified. Occlusal relationships must be considered in all three planes of space. Lingual posterior crossbite (i.e., upper teeth lingual to lower teeth) is the major deviation from the normal transverse dental relationship and reflects deviations from ideal occlusion in the transverse plane of space.

Ref: Contemporary Orthodontics, William R. Proffit, 6th Edition.

Y shaped occlusal pattern is found in which teeth?

 # Y shaped occlusal pattern is found in which teeth?

A. Mandibular first premolar

B. Mandibular second premolar

C. Maxillary first premolar

D. Maxillary second premolar

The correct answer is B. Mandibular second premolar. 

The three cusp type mandibular second premolar manifests as a Y shaped occlusal pattern. The three-cusp type appears square lingual to the buccal cusp ridges when highly developed. Each cusp has well-formed triangular ridges separated by deep developmental grooves. These grooves converge in a central pit and form a Y shape on the occlusal surface. 

Y axis is used to analyze:

 # Y axis is used to analyze:

A. Maxillary growth

B. Mandibular growth

C. Both maxillary and mandibular growth

D. To design appliance

The correct answer is B. Mandibular growth.

Y-axis is obtained by joining the sella - gnathion line with the F.H. plane. The mean value is 59 degree with a range of 53 to 66 degree. The angle is larger in Class II Facial patterns than in patient exhibiting Class III pattern. In addition, Y axis indicates the growth pattern of the individual. If the angle is greater than normal, it indicates greater vertical growth of mandible. If the angle is smaller than normal, it indicates greater horizontal growth of mandible. 

Perikymata are the external surface manifestations of:

 # Perikymata are the external surface manifestations of:

A. Enamel rods

B. Incremental lines of Retzius

C. Nasmyth’s membrane

D. Pellicle

The correct answer is B. Incremental lines of Retzius.

The number of perikymata gradually decreases form cervical region to occlusal or incisal region because of undisturbed development of enamel prior to birth. Perikymata are usually absent in prenatally developed occlusal parts of deciduous teeth, whereas they are present in postnatal cervical parts. 

Abnormal function of epithelial chloride channel protein is the cause of:

 # Abnormal function of epithelial chloride channel protein is the cause of:

A. Ehlers Danlos Syndrome

B. Marfan Syndrome

C. Cystic fibrosis

D. Diabetes insipidus

The correct answer is C. Cystic fibrosis.

Cystic Fibrosis (Mucoviscidosis) Among the genetic paediatric disorders, cystis fibrosis is the most important. It is fundamentally a widespread disorder in epithelial transport affecting fluid secretion in exocrine glands and the epithelial lining of the respiratory, gastrointestinal, and reproductive tracts.

Cystic fibrosis follows simple autosomal recessive transmission. The primary defect is in the regulation of epithelial chloride transport by a chloride channel protein encoded by the cystic fibrosis gene. The impact of this defect in chloride transport differs in various tissues.