Dental Articulators and Maxillary Arch

Facebow and Articulators

• A facebow is a caliper-like device used to record the relationship of the jaws to the temporomandibular joint (TMJ)
• It records the opening axis of the jaws and orients casts to match this relationship to the articulator's opening axis (terminal hinge axis) for accurate reproductions
• The facebow transfer process ensures casts are mounted in the correct relation to the inter-condylar axis and to the centers of lateral movements

Methods of Determination of Terminal Hinge Axis Determination

• Mandibular Facebow (Kinematic Method): This locates the precise axis of condyle rotation
• Arbitrary Method (11–12 mm): A point is marked 11-12 mm in front of the tragus of the ear along an imaginary line between the outer canthus of the eye and the ear's upper tragus surface

Functions of Facebow

• Recording Spatial Relationship: Records the spatial relationship between the upper jaw and TMJ for accurate reproduction of occlusal relationships in the dental laboratory
• Replicating Natural Jaw Movements: Helps replicate natural jaw movements, necessary for creating dental restorations that align with a patient's unique occlusion and jaw dynamics

Components

• U-shaped Frame: A primary structure for fitting around the patient's head, ensuring stability during recording
• Transfer Assembly: Attaches to the patient's maxillary teeth, responsible for capturing the spatial relationship of the upper jaw. Often includes a fork or bite fork to securely hold the dental arch
• Earpieces/Ear Bows: Secure the facebow to the patient's head. Often adjustable to accomodate variations in anatomy
• Anterior Reference Points: Markers on the facebow used to orient the maxillary arch in relation to the TMJ (e.g., midline indicators)
• Locking Mechanisms: Adjustments allowing for securing the facebow in the desired position and preventing movement during the recording process

External Auditory Meatus (Ear Canal)

• Purpose: Provides a reference point for hinge axis of the jaw for mounting the upper cast on an articulator to simulate jaw opening and closing motion.
• Significance: Approximates the location of the mandibular condyle in the temporomandibular joint (TMJ)

Nasion (Nasion Point)

• Purpose: Located at the bridge of the nose, where frontal and nasal bones meet
• Significance: Helps ensure the vertical alignment of the facebow in relation to the patient's facial anatomy

Maxillary Bone (Bite Fork)

• Purpose: Positioned in the patient's mouth and placed against the maxillary bone
• Significance: Records the position of the maxillary arch relative to the rest of the head. This aids accurate transfer to the articulator.

Dental Articulators

• Definition: A mechanical instrument that represents the temporomandibular joints and jaws. Maxillary and mandibular casts can be attached to simulate movements
• Functions:
  • Replicating Maxillary Position: Replicates the upper jaw's position to ensure dental restorations harmonize with the mouth
  • Simulating Mandibular Movements: Helps recreate the movements of the lower jaw for accurate representations of natural jaw functions
  • Positioning Dental Models: Aids in studying the occlusion (bite) and designing prosthetics that fits the patient's specific oral anatomy
  • Stable Base: Provides a stable platform to measure relationships between the upper and lower dental arches

Classification of Articulators

• Class I (Simple Hinge): Non-adjustable, simulates basic opening and closing for simple restorative cases
• Class II (Fixed Condylar Path): Simulates a fixed condyle path, typically for single-unit crowns
• Class III (Semi-adjustable Condylar Path): Allows for adjustment of the condyle path, useful in cases with more complex restorations
• Class IV (Fully Adjustable Condylar Path): Permits the most comprehensive adjustment and accurate replication of all aspects of jaw movement, used for complex or extensive restorative cases

Other data about the facebow and articulators

• Different articulators offer varied levels of adjustment and complexity, each suited for particular restorative requirements
• Various components (images present) exist on articulators and should be memorized.