Broad-spectrum antifungal used only as a topical agent because of renal toxicity is:

  # Broad-spectrum antifungal used only as a topical agent because of renal toxicity is:

A. Miconazole

B. Nystatin

C. Amphotericin B

D. Clotrimazole

The correct answer is B. Nystatin.

Explanation

Nystatin is a polyene antifungal antibiotic (similar in structure and mechanism to Amphotericin B).

• Mechanism: It binds to ergosterol in the fungal cell membrane, creating pores that cause leakage of intracellular contents (potassium and other ions), leading to fungal cell death.

• Toxicity: While it has a broad spectrum of activity, it is never used parenterally (systemically) because of its severe systemic toxicity, particularly nephrotoxicity.

• Usage: It is not significantly absorbed from the gastrointestinal tract, skin, or mucous membranes. Therefore, it is safe and effective when used topically (e.g., oral suspensions for oral candidiasis, creams for skin infections) to treat local infections without causing systemic side effects.

Why the other options are incorrect:

• A. Miconazole: An imidazole antifungal. While largely used topically (e.g., Daktarin gel), it can be administered systemically (IV) for severe infections (though less common now due to newer drugs). Its primary systemic concern is usually related to hepatic enzymes (CYP450 inhibition), not the severe direct renal toxicity seen with polyenes.

• C. Amphotericin B: Also a polyene antifungal with the same mechanism as Nystatin. It is notoriously nephrotoxic (often called "Ampho-terrible"). However, unlike Nystatin, it is used systemically (IV) for life-threatening systemic fungal infections because it is the "gold standard" for efficacy, despite the risk of kidney damage. The prompt asks for a drug used only topically.

• D. Clotrimazole: An imidazole typically restricted to topical use (troches, creams) because of significant gastrointestinal intolerance and hepatic enzyme induction if given systemically. It is not primarily restricted due to renal toxicity.



Relative inability of a material to deform plastically before it fractures is known as:

  # Relative inability of a material to deform plastically before it fractures is known as:

A. Brittleness

B. Malleability

C. Ductility

D. Pseudoplasticity

The correct answer is A. Brittleness.

Explanation

Brittleness is the property of a material that fractures with little to no preceding plastic deformation.

In terms of a stress-strain curve, a brittle material behaves elastically up to a certain point (the proportional limit) and then fractures almost immediately, without undergoing the "yielding" phase associated with permanent deformation. This means the material absorbs relatively little energy before breaking.

Common examples of brittle dental materials include ceramics, dental stone, and enamel.

Why the other options are incorrect:

• Ductility: This is the opposite of brittleness in tension. It describes a material's ability to withstand significant plastic deformation (permanent stretching) under tensile stress before rupturing. It is often measured by percent elongation.

• Malleability: This describes a material's ability to withstand significant plastic deformation under compressive stress (e.g., being hammered or rolled into a thin sheet) without rupturing. Gold is a classic example of a malleable material.

• Pseudoplasticity: This is a rheological property (flow characteristic) of fluids, not solids. It refers to "shear-thinning" behavior, where a fluid becomes less viscous as the shear rate increases (e.g., silicone impression materials that flow better under the pressure of a syringe).



Nerve supplying posterior one third of the tongue, oropharynx and soft palate is:

  # Nerve supplying posterior one third of the tongue, oropharynx and soft palate is:

A. Lingual nerve

B. Glossopharyngeal nerve

C. Chorda tympani nerve

D. Vagus nerve

The correct answer is B. Glossopharyngeal nerve.

Explanation

The Glossopharyngeal nerve (CN IX) is the primary sensory nerve for the posterior one-third of the tongue, the oropharynx, and the tonsillar region.

• Posterior 1/3 of the Tongue: CN IX provides both general sensation (pain, touch, temperature) and special sensation (taste) to this region (via the lingual branches).

• Oropharynx: CN IX supplies the mucosa of the oropharynx, the palatine tonsils, and the faucial pillars. It acts as the afferent limb of the gag reflex.

• Soft Palate: While the sensory supply to the soft palate is complex (involving the lesser palatine nerves from CN V2), the glossopharyngeal nerve contributes to the sensory innervation of the soft palate via the pharyngeal plexus.

Why the other options are incorrect:

• Lingual nerve: A branch of the Mandibular nerve (CN V3). It supplies general sensation (touch, pain, temperature) only to the anterior two-thirds of the tongue.

• Chorda tympani nerve: A branch of the Facial nerve (CN VII). It carries taste sensation from the anterior two-thirds of the tongue (hitchhiking with the Lingual nerve).

• Vagus nerve: Supplies sensation to the area even more posterior than the posterior third—specifically the epiglottis and the extreme root of the tongue (valleculae). It provides motor supply to the muscles of the soft palate (except the Tensor Veli Palatini), but it is not the primary sensory nerve for the posterior third of the tongue.



MCQs in Orthodontics - Occlusion

MDS Orthodontics: Occlusion

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