Ortho 1

🧠 1. GROWTH & DEVELOPMENT

Big Picture:

Orthodontics starts with understanding how the face and jaws grow — because timing and method of treatment depend on it.

Key Concepts:

• Types of growth:

  • Sutural growth (e.g. maxilla via sutures)

  • Endochondral growth (e.g. condyle of mandible)

  • Appositional growth (surface bone growth)

• Scammon's growth curve:
  → Neural tissues grow early (brain)
  → Lymphoid peaks in childhood
  → General (skeletal) has a pubertal spurt

• Growth Theories:

  • Moss's Functional Matrix theory → Function drives form

  • Scott’s Nasocapsular theory (for maxilla)

  • Servosystem theory → Feedback from occlusion affects growth

Quick Check:

What kind of growth happens at the mandibular condyle — sutural or endochondral?

😁 2. DEVELOPMENT OF DENTITION & OCCLUSION

Big Picture:

Understanding the normal changes helps detect when something's off — like crowding or malocclusion.

Key Concepts:

• Primate spaces (normal):

  • Maxilla: mesial to canine

  • Mandible: distal to canine

• Leeway space:
  Primary molars are wider than permanent premolars → creates space for alignment

• Terminal plane (for molar occlusion prediction):

  • Flush terminal plane → likely Class I

  • Distal step → likely Class II

  • Mesial step → likely Class I or III

Quick Check:

What does the leeway space help with during mixed dentition?

😬 3. CLASSIFICATION OF MALOCCLUSION

Big Picture:

Malocclusion is not just teeth — it's skeletal, dental, or both. Understanding classifications helps guide treatment.

Key Systems:

• Angle’s Classification (based on molar relation):

  • Class I: MB cusp of max 1st molar in buccal groove of mand 1st molar

  • Class II: Distal relation

  • Class III: Mesial relation

• Skeletal Class I/II/III → Based on jaw base relationship (can match or differ from dental)

• Ackerman-Proffit System → Modern, considers 5 characteristics (alignment, profile, vertical, etc.)

Quick Check:

In Angle’s classification, which class has the lower molar more anterior than normal?

🧰 4. ORTHODONTIC APPLIANCES

Big Picture:

Appliances work by applying controlled forces to move teeth or modify growth. Know the types, uses, and mode of action.

Types:

• Removable appliances: Hawley’s, springs, bite planes

• Fixed appliances: Brackets, archwires, bands

• Functional appliances (in growing patients):

  • Myofunctional: Twin block, Bionator

  • Orthopedic: Headgear, facemask

• Clear aligners: Like Invisalign — segmental movement, esthetic

Quick Check:

Which appliance would you use to correct a skeletal Class II due to a retrusive mandible in a growing child?

📐 5. CEPHALOMETRICS

Big Picture:

It’s how we measure and visualize skeletal and dental relationships on a lateral skull X-ray.

Key Terms:

• Landmarks: Sella (S), Nasion (N), A-point, B-point, Pogonion (Pog)

• Angles:

  • SNA → maxillary position

  • SNB → mandibular position

  • ANB = SNA - SNB → Skeletal class

• Steiner, Tweed, McNamara analyses — each has its own norms

Trick to Remember:

• ANB:

  • 2° = Class I

  • 4° = Class II

  • <0° = Class III

Quick Check:

If SNA is 82° and SNB is 76°, what’s the ANB? What class is it?

⚙️ 6. BIOMECHANICS & TOOTH MOVEMENT

Big Picture:

Teeth move in response to light, controlled forces — too much force = hyalinization, root resorption.

Tooth movements:

• Tipping (most common)

• Bodily movement (translation)

• Rotation, intrusion, extrusion

Anchorage:

• Resistance to unwanted movement
  → Can be reinforced with TADs (temporary anchorage devices)

Types of Forces:

• Light vs Heavy

• Intermittent (e.g. removable), Continuous (e.g. fixed)

• Ideal force = 20–60g for tipping, higher for bodily

Quick Check:

Why do we prefer light forces over heavy ones in ortho?

✅ Summary Mnemonic: "GROW-CLAB"

• G: Growth & development

• R: Relationship of jaws (malocclusion)

• O: Occlusion & dentition development

• W: What appliances to use

• C: Cephalometrics

• L: Light controlled forces (biomechanics)

• A: Anchorage

• B: Biology of tooth movement

🧠 1. GROWTH & DEVELOPMENT — High-Yield MCQ Points

• Mandible grows by: Endochondral growth at condyle

• Maxilla grows by: Sutural growth + surface remodeling

• Peak pubertal growth spurt: Girls (~11–13 yrs), Boys (~13–15 yrs)

• Scammon’s growth curve:

  • Neural: early

  • General (skeletal): spurt at puberty

• Functional Matrix Theory — Moss → function controls growth

• Condylar cartilage is a secondary cartilage

• Growth rotation theories: Bjork, Schudy — often MCQ material

💡 Watch for: "Which growth theory emphasizes soft tissue matrix?" → Moss

😁 2. DEVELOPMENT OF OCCLUSION

• Primate spaces:

  • Maxilla: mesial to canine

  • Mandible: distal to canine

• Leeway space:

  • Maxilla: ~1.5 mm per side

  • Mandible: ~2.5 mm per side → more space in mandible

• Flush terminal plane in primary → likely Class I in permanent

• Incisal liability:

  • Maxilla: ~7 mm

  • Mandible: ~5 mm

💡 MCQ Tip: "Which arch has greater leeway space?" → Mandible

😬 3. CLASSIFICATION OF MALOCCLUSION

• Angle’s Classification:

  • Class I: Normal molar, crowding/rotation

  • Class II div 1: Proclined incisors

  • Class II div 2: Retroclined centrals

  • Class III: Mesial molar relation

• Skeletal class:

  • Based on ANB angle:

    • Normal = 2°,

    • Class II > 4°,

    • Class III < 0°

• Vertical malocclusion:

  • Open bite → tongue habits

  • Deep bite → overeruption, deep curve of Spee

💡 Common Trap: “Patient has Class I molar but retroclined incisors and deep bite” → Still Class I if molar is normal (Angle’s is dental-only)

🧰 4. ORTHODONTIC APPLIANCES

Removable:

• Hawley’s — retention

• Adam’s clasp — retention and anchorage

• Z-spring — labial movement

• Bite plane — deep bite

Fixed:

• Edgewise, PEA, MBT — know MBT = .022” slot, torque in bracket

• Bracket slot sizes: .018" and .022"

Functional:

• Twin Block — best for Class II (growing child)

• Frankel — tissue-borne

• Activator — passive appliance

• Herbst — fixed functional

Orthopedic:

• Headgear → maxillary restriction

  • Cervical pull: low angle

  • High pull: open bite

• Facemask → maxillary protraction

💡 MCQ Tip: “Best appliance for skeletal Class II in a 10-year-old?” → Twin Block

📐 5. CEPHALOMETRICS

• SNA (maxilla): ~82°

• SNB (mandible): ~80°

• ANB = SNA - SNB

  • 2° = Class I

  • 4° = Class II

  • <0° = Class III

• Frankfort Horizontal (FH) = Po–Or line

• Y-axis (growth direction):

  • ↑ = vertical grower

  • ↓ = horizontal grower

Cephalometric analyses:

• Steiner: SNA, SNB, ANB, U1 to NA, L1 to NB

• Tweed’s triangle: FMA, IMPA, FMIA

• McNamara: Linear measurements

💡 Watch for: “Which cephalometric point is used to assess mandibular position?” → SNB

⚙️ 6. BIOMECHANICS & TOOTH MOVEMENT

• Ideal force levels:

  • Tipping: 20–60 g

  • Bodily: 100–150 g

  • Intrusion: 10–20 g

• Tooth movement:

  • Pressure side: bone resorption

  • Tension side: bone apposition

• Lag phase: Initial delay before movement

• Center of resistance: ~mid-root level for single-rooted tooth

• Anchorage types:

  • Simple, compound, reciprocal, reinforced

  • TADs (mini-implants): absolute anchorage

💡 Common trap: “Heavy force causes faster movement” → False; it causes hyalinization

🔁 FINAL REVISION TIPS

🔹 HOT MCQ ZONES:

• Growth theories (Moss, Scott, Enlow)

• Functional appliances (age + skeletal correction)

• Cephalometric norms (SNA, SNB, ANB)

• Tooth movement force values

• Dental development (leeway space, primate spaces)

• Angle's classification vs skeletal class

🔹 TRICKS TO REMEMBER:

• ANB = SNA – SNB

• Leeway space > in mandible

• Frankel = tissue-borne, Herbst = fixed

• Activator = passive, Twin Block = active

• High pull headgear = for vertical growers