Jaw movements and articulator Flashcards
What is the Terminal Hinge Axis (THA)?
The fixed axis around which the mandible rotates during the initial 20 mm of mouth opening. No translation occurs here.
What happens after 20 mm of jaw opening?
The condyles begin translating — moving forward and downward along the articular eminence.
Which muscle helps open the jaw?
Digastric muscle 🪢 – assists in depressing the mandible (mouth opening).
Which muscle is responsible for protrusion and lateral movement?
Lateral Pterygoid muscle 🔧 – assists in protrusion and moving the jaw side-to-side.
Name the primary muscles of mastication and their functions.
What are the ‘working’ and ‘non-working’ sides?
Working side 🟡 = side jaw moves towards
Non-working side ⚫ = opposite condyle, moves down, forward, medially
What is Immediate Side Shift (ISS)?
A quick medial movement of the non-working condyle at the beginning of lateral movement — now considered possibly inaccurate ❌.
What is Progressive Side Shift (PSS)?
A gradual medial movement of the non-working condyle as the jaw continues its lateral movement ✅.
What is Canine Guidance?
Only the canines contact during lateral movements 🐶, protecting posterior teeth from horizontal forces.
What is Group Function?
Multiple posterior teeth contact during lateral excursions 👥 — can be natural but risky in restored dentitions ⚠️.
When does canine guidance change to group function?
Often occurs if the canine is lost, worn down, or heavily restored 😬.
What is the purpose of an articulator?
Simulates jaw movement
Allows accurate crown/denture/splint fabrication
Assesses occlusion
🛠️ Helps ensure restorations conform to patient’s real jaw movements.
What can a Simple Hinge articulator replicate?
Only opening/closing and ICP
No lateral or protrusive movement ❌
📌 Use: Basic restorations like MCC UL4.
What are the key features of an Average Value articulator?
Pre-set values:
Condylar guidance = 30°
Condyle distance = 110 mm
Condyle to incisal edge = 110 mm
Can replicate:
ICP
Opening/closing
Limited lateral movement
❌ Cannot be customised to patient
🧪 Use: Dentures, basic partials
What can a Semi-Adjustable articulator simulate?
💬
✅
ICP, RCP
Protrusive movements
Lateral excursions (ISS & PSS)
🧪 Use:
FVC with group function
Canine guidance MCC LR3
What records are needed for a semi-adjustable articulator?
📏 Facebow + interocclusal records (e.g., wax bite)
What makes a Fully Adjustable articulator unique?
✅ Can replicate:
Hinge axis
Intercondylar width
All condylar angles
ISS & PSS
ICP, RCP, lateral & protrusive movements
⚠️ Requires axiographic tracing
Rarely used due to complexity + patient record limitations.
What does a facebow record do?
Records the spatial relationship between the maxilla and hinge axis of the TMJ 📐.
What is an interocclusal record?
A wax/silicone record of how upper and lower teeth contact, used for accurate mounting on an articulator 🕯️.
You’re making an MCC for UL4 with no occlusal changes. Which articulator?
Simple Hinge — only ICP matters.
Making an upper partial denture for a patient with group function. Which articulator?
💬 ⚖️ Average Value — sufficient for general movement simulation.
FVC with group function, patient has complex lateral movements. Which articulator?
Semi-Adjustable — allows accurate simulation of excursions.
MCC on LR3, patient has canine guidance. Which articulator?
Semi-Adjustable — to preserve occlusal scheme and avoid interferences.
Name 4 Types of articulators
