Which biomechanical principle explains the differential force theory in orthodontic tooth movement?

 1. Which biomechanical principle explains the differential force theory in orthodontic tooth movement?

a) Hooke’s Law

b) Newton’s Third Law

c) Wolff’s Law

d) Poiseuille’s Law

e) Archimedes’ Principle

The correct answer is:

(a) Hooke’s Law

Explanation:

The Differential Force Theory in orthodontic tooth movement states that different types of teeth require different magnitudes of force to move efficiently while minimizing unwanted side effects. This concept is based on Hooke’s Law, which states that the force applied to a material is proportional to the deformation it experiences, as long as the elastic limit is not exceeded (F = kx).

In orthodontics:

Applying lighter forces to teeth with single roots (e.g., incisors) ensures controlled movement.

Higher forces are required for multi-rooted teeth (e.g., molars) due to their increased root surface area and resistance.

Thus, Hooke’s Law plays a crucial role in explaining how force magnitude should be adjusted based on the tooth’s biomechanical response.

The first evidence of cartilage getting converted to bone in craniofacial skeleton occur during:

 # The first evidence of cartilage getting converted to bone in craniofacial skeleton occur during:

A. Fourth postnatal week

B. Eighth prenatal week

C. Fourth prenatal week

D. Eighth postnatal week

The first evidence of cartilage converting to bone (endochondral ossification) in the craniofacial skeleton occurs during the eighth prenatal week. This timing aligns with the development of the cranial base (e.g., occipital, sphenoid, and ethmoid bones), which undergoes endochondral ossification. While mesenchymal condensations and cartilage models form earlier, the actual replacement of cartilage by bone begins around this period, marking the start of ossification in these regions.

Answer: B. Eighth prenatal week

Simple retraction of maxillary incisors using maxillary molars as anchorage is an example of: PGCEE MDS 2025

 # Simple retraction of maxillary incisors using maxillary molars as anchorage is an example of:  (PGCEE MDS 2025)

a) Simple anchorage 

b) Reciprocal anchorage

c) Stationary anchorage 

d) Intermaxillary anchorage

The correct answer is:

c) Stationary anchorage

Explanation:

Stationary anchorage refers to a type of anchorage where the resistance to unwanted tooth movement is achieved by using teeth that undergo minimal movement, usually due to bodily movement rather than tipping.

• In simple retraction of maxillary incisors using maxillary molars as anchorage, the molars provide resistance while the incisors move posteriorly. The molars remain relatively stable, which characterizes stationary anchorage.
• Other types of anchorage:
  • Simple anchorage – Resistance to movement provided by the PDL of the anchoring teeth.
  • Reciprocal anchorage – Two equal and opposite forces are applied, leading to movement of both units (e.g., space closure between two adjacent teeth).
  • Intermaxillary anchorage – Anchorage derived from teeth in the opposite arch (e.g., elastics from maxillary to mandibular teeth).

Serial extractions are indicated when there is - PGCEE MDS Entrance 2025

 # Serial extractions are indicated when there is -

a) No skeletal discrepancy with dental crowding > 10 mm

b) No skeletal discrepancy with dental crowding between 5 - 7 mm.

c) Skeletal discrepancy >5°

d) Skeletal discrepancy >10° with dental crowding < 5mm

The correct answer is A. No skeletal discrepancy with dental crowding > 10 mm

 Serial extraction is indicated in cases of severe dental crowding. For this reason, it is best used when no skeletal problem exists, and the space discrepancy is large i.e., >10 mm per arch.

If the crowding is severe, little space will remain after the teeth are aligned, which means there will be little tipping and uncontrolled movement of the adjacent teeth into the extraction sites. If the initial space discrepancy is smaller, more residual space must be anticipated.