# Corona virus is:

  # Corona virus is:

A. Ss DNA virus

B. Ds DNA virus

C. Ss RNA virus

D. Ds RNA virus

The correct answer is C. Ss RNA virus.

Specifically, Coronaviruses (members of the family Coronaviridae) are classified as positive-sense, single-stranded RNA (+ssRNA) viruses.

Virological Characteristics

To understand the classification of SARS-CoV-2 and other coronaviruses, we look at their genomic structure:

• Genomic Material: They contain a single strand of RNA. Because it is "positive-sense," the viral RNA acts like messenger RNA (mRNA) and can be immediately translated into proteins by the host cell's ribosomes upon entry.

• Size: They possess one of the largest genomes among all RNA viruses, typically ranging from 26 to 32 kilobases (kb).

• Structure: The genome is packaged within a helical nucleocapsid and surrounded by an envelope containing the characteristic "spike" (S) proteins, which give the virus its crown-like (corona) appearance under electron microscopy.

---

Comparison with Other Viral Genomes

Virus Type	Genomic Classification	Examples
ssDNA	Single-stranded DNA	Parvovirus B19
dsDNA	Double-stranded DNA	Herpes Simplex Virus (HSV), HPV, Adenovirus
ssRNA	Single-stranded RNA	Coronavirus, Influenza, HIV, Hepatitis C
dsRNA	Double-stranded RNA	Rotavirus



Sublingual nitroglycerine is effective because it is:

  # Sublingual nitroglycerine is effective because it is:

A. Ionic and has high lipid solubility

B. Ionic and has low lipid solubility

C. Non ionic and has high lipid solubility

D. Non ionic and has low lipid solubility

The correct answer is C. Non-ionic and has high lipid solubility.

Pharmacological Principle

For a drug to be absorbed rapidly across the sublingual mucosa, it must pass through the lipid bilayer of the epithelial cell membranes via passive diffusion.

• Non-ionic State: Drugs that are non-ionized (uncharged) are significantly more lipid-soluble than their ionized counterparts. Ionized molecules are polar and struggle to penetrate the hydrophobic core of the cell membrane.

• High Lipid Solubility: Nitroglycerine is a highly lipophilic (lipid-loving) molecule. This allows it to dissolve almost instantly into the membrane and enter the systemic circulation through the dense capillary network under the tongue.

Why Sublingual Administration?

In clinical practice, especially for acute angina pectoris, the sublingual route is preferred for Nitroglycerine because:

1. Bypassing First-Pass Metabolism: If swallowed, Nitroglycerine undergoes nearly 100% hepatic metabolism (first-pass effect) by the enzyme organic nitrate reductase, rendering it ineffective. The sublingual route allows the drug to enter the Superior Vena Cava directly.

2. Rapid Onset: Due to the high lipid solubility and thin mucosal membrane, therapeutic blood levels are reached within 1 to 3 minutes.

3. pH Environment: The pH of saliva (approximately 6.2 to 7.4) ensures that Nitroglycerine remains largely in its non-ionized, absorbable form.

---

Comparison of Solubility Factors

Property	Effect on Absorption	Nitroglycerine Status
Ionization	Ionized = Low absorption; Non-ionic = High absorption	Non-ionic
Lipid Solubility	High lipid solubility = Rapid membrane crossing	High
Molecular Weight	Lower weight = Faster diffusion	Low (227.1 g/mol)



A surgeon was suspicious during a biopsy procedure about the involvement of surrounding cells whether it's malignant or not. Which of the following would aid in quick diagnosis?

  # A surgeon was suspicious during a biopsy procedure about the involvement of surrounding cells whether it's malignant or not. Which of the following would aid in quick diagnosis?

A. Frozen section

B. Punch biopsy

C. Excisional biopsy

D. Incisional biopsy

The correct answer is A. Frozen section.

Clinical Rationale

In an intraoperative setting, the primary requirement for the surgeon is speed to decide the immediate course of action (e.g., whether to extend the surgical margin or perform a radical resection).

• Frozen Section (Cryosection): This technique involves rapidly freezing the tissue sample (usually with liquid nitrogen or a cryostat), slicing it with a microtome, and staining it for immediate microscopic examination. The entire process takes approximately 10 to 20 minutes, providing a "quick diagnosis" while the patient is still on the operating table.

• Punch, Excisional, and Incisional Biopsies: These are methods of obtaining tissue rather than a method of processing it for rapid diagnosis. These samples typically undergo Formalin-fixed paraffin-embedded (FFPE) processing, which takes 24 to 48 hours for a definitive report.

Comparison of Biopsy Techniques

Technique	Description	Clinical Utility
Frozen Section	Rapid freezing and sectioning of fresh tissue.	Intraoperative assessment of margins and malignancy.
Punch Biopsy	Uses a circular blade to remove a full-thickness "plug" of skin.	Commonly used for dermatological lesions (e.g., suspected melanoma or inflammatory conditions).
Excisional Biopsy	Removal of the entire lesion or tumor.	Used for small lesions where the procedure is both diagnostic and therapeutic.
Incisional Biopsy	Removal of only a portion of a large lesion.	Used when the lesion is too large for total excision without a prior diagnosis.

Note for MDS Residents

While frozen sections are highly efficient for identifying malignancy and checking margins (e.g., in Oral Squamous Cell Carcinoma), they have limitations compared to permanent sections:

1. Lower Resolution: Rapid freezing creates "freeze artifacts" (ice crystals) that can distort cellular morphology.

2. Thicker Sections: Cryosections are generally thicker than paraffin sections, making fine nuclear detail harder to appreciate.

3. Technician Dependent: The quality depends heavily on the skill of the pathologist and lab technician during the rapid processing window.

Up to what age is thumb sucking considered to be physiologically normal?

  # Up to what age is thumb sucking considered to be physiologically normal?

A. 1 year

B. 2 years

C. 4 years

D. 5 years

The correct answer is C. 4 years.

In the field of pediatric dentistry and orthodontics, thumb sucking is classified as a physiological sucking habit during infancy and early childhood.

Clinical Rationale

• Physiological Phase (Birth to 3–4 years): Sucking is a natural reflex in infants (nutritive and non-nutritive). Most children naturally decrease this behavior as they develop other coping mechanisms and social awareness.

• The "Threshold" Age: While many children stop by age 2, the consensus in orthodontic literature (including Graber and Moyers) is that the habit is considered physiologically normal up to age 4.

• The Significance of Permanent Eruption: The primary concern for an orthodontist is the transition from primary to mixed dentition. If the habit is discontinued before the eruption of the permanent incisors (typically around ages 5 or 6), the dentofacial changes—such as an anterior open bite or flared maxillary incisors—are often self-correcting.

---

Comparison of Age Milestones

Age	Clinical Significance
0–2 Years	Normal sucking reflex; no intervention required.
2–4 Years	Habit usually wanes; considered normal but should be monitored.
4 Years +	Termed a "persistent habit." Intervention (behavioral or myofunctional) is often considered.
6 Years +	High risk of permanent malocclusion (Posterior crossbite, increased overjet, and Open bite).

Scientific Considerations for MDS Residents

As you are in your third year of MDS, you'll recall that the magnitude of the dental deformity is a result of the Trident of Habits:

1. Duration: How many hours a day (the "6-hour threshold" is critical for tooth movement).

2. Frequency: How many times a day the thumb is inserted.

3. Intensity: The amount of force applied (negative intraoral pressure vs. physical leverage).

Note: If the habit persists beyond age 4, it is no longer considered purely "physiological" and begins to transition into a "psychological" or "learned" habit that requires professional guidance.



All of the following can be measured by a spirometer except:

  # All of the following can be measured by a spirometer except:

A. Vital capacity

B. Tidal volume

C. Expiratory reserve volume

D. Functional residual capacity

The correct answer is D. Functional residual capacity.

Scientific Explanation

A standard spirometer measures the volume of air inspired and expired by the lungs as a function of time. It can directly measure all lung volumes and capacities that are exchangeable with the environment.

Functional Residual Capacity (FRC) is defined as the volume of air remaining in the lungs at the end of a normal tidal expiration. It is calculated as:

FRC = Expiratory Reserve Volume (ERV) + Residual Volume (RV)

Why it cannot be measured by spirometry:

• The Constraint of Residual Volume: A spirometer can only measure air that moves in and out of the lungs. The Residual Volume (RV) is the volume of air remaining in the lungs even after a maximal exhalation. Because RV cannot be exhaled, it cannot be recorded by a spirometer.

• Dependency: Since FRC includes the Residual Volume component, FRC cannot be determined via simple spirometry.

How FRC is measured:

To measure FRC (and consequently Total Lung Capacity and Residual Volume), indirect methods are required that do not rely on airflow alone. These include:

1. Helium Dilution Technique: Uses a closed-circuit system with a known concentration of inert helium gas.

2. Nitrogen Washout Technique: Uses an open-circuit system where nitrogen is washed out of the lungs by breathing pure oxygen.

3. Body Plethysmography: Uses Boyle's Law (P1V1 = P2V2) inside a sealed box to measure thoracic gas volume.

Analysis of Distractors

• A. Vital Capacity (VC): This is the maximum amount of air a person can expel from the lungs after a maximum inhalation (VC = TV + IRV + ERV). Since all these components are exchangeable volumes, VC is easily measured by spirometry.

• B. Tidal Volume (TV): This is the volume of air inhaled or exhaled during a normal breathing cycle. It is the most basic measurement performed by a spirometer.

• C. Expiratory Reserve Volume (ERV): This is the additional amount of air that can be expired from the lungs by determined effort after normal expiration. This is directly measurable by spirometry.



MCQs in Orthodontics - Bracket Positioning and Case Setup

MDS Orthodontics Final Exam

Topic: Bracket Positioning and Case Set-up (MBT™ System)

Based on Chapter 3: Systemized Orthodontic Treatment Mechanics

Progress 0 / 0

Score 0%

MCQs in Orthodontics - MBT Brackets System Appliance Specifications: Variations and Versatility

Appliance Specifications

Variations and Versatility - MDS Orthodontics Exam Series

Score: 0 / 40 Questions Attempted: 0 / 40