Dental Anatomy: Face Bow Overview

Face Bow

• Definition: A caliper-like device that records the relationship between the maxilla and the rotational axis of the mandible. It then transfers this relationship to the articulator.
• Types
  • Mandibular Face Bow (Kinematic Face Bow): Used to locate the exact terminal hinge axis before using the maxillary face bow. Consists of:
    • U-shaped bow
    • Clamp - attaches the bow to the mandible.
    • Universal joint - attaches the clamp to the bow.
    • Two pointed condylar rods - attached to the bow.
    • Two screws - used to adjust the position of the condylar rods.
  • Maxillary Face Bow (Arbitrary Face Bow): Records the relationship between the maxilla and the rotational axis of the mandible.
    • Consists of a U-shaped bow, a bite fork (attached to the bow), and condylar rods.
    • Types of maxillary face bows:
      • Facial Face Bow: Uses facial landmarks for orientation.
      • Ear Piece Face Bow: Uses the external auditory canal as a posterior reference point.
    • Orientation on Patient's Face: Condylar rods are positioned 13 mm in front of the tragus on a line called the canthus-tragus line.
    • Orientation on the Articulator: The bite fork is placed on the articulator aligning the condylar rods with the articulator's condylar housing.

Articulators

• Definition: A mechanical device that represents the temporomandibular joints (TMJs) and jaw members. Maxillary and mandibular casts are attached to it to simulate different mandibular movements.
• Types
  • Simple Hinge Articulator (Plain Line Articulator): A simple holding device that allows for vertical movement but no horizontal movement.
  • Mean Value Articulator (Average Value Articulator): Simulates condylar pathways using average measurements. Has a fixed condylar path angle of 33 degrees.
    • Examples: Gysi Simplex Articulator
  • Adjustable Articulator: Allows for customization based on patient-specific records.
  • Semi-Adjustable Articulator: The horizontal condylar path is adjusted using a protrusive record, and the lateral condylar path is adjusted using Hanau's formula.
    • Examples: Hanau (Model H) Articulator, Denar 5a
    • Hanau's Formula: Determines the lateral condylar path: L=H/8+12 (where L is the lateral condylar path and H is the horizontal condylar path).
  • Fully-Adjustable Articulator: All horizontal and lateral inclinations are adjusted using patient-specific records.
    • Examples: Hanau Kinoscope, Dentatus Articulator, Denar 2
• Mounting the Master Cast on the Articulator:
  • The cast is positioned with the midline of the occlusion rim aligned with the incisal indicator pin and the midline marker on the articulator.
  • Cast is placed on the occlusion plane table and secured with wax until the mounting process.

Benefits of Using a Face Bow and an Articulator

• Accuracy: While not perfectly replicating the TMJ movement, articulators provide sufficient accuracy for most cases, improving denture placement, occlusal harmony, and esthetics.
• Mobility: Using an articulator is preferable to making final occlusal adjustments solely intraorally, as dentures rest on movable tissues.
• Easier Adjustment: Face bows and articulators simplify the procedure by providing a stable platform for adjusting occlusal schemes, especially for complete denture cases.
• Occlusion: Articulators aid in proper occlusal schemes with balanced and nonbalanced techniques.

Indexing the Cast

• Indexing allows for accurate remounting of the cast to the articulator for adjustments.
• It is achieved with grooves, notches, or remounting plates.

Conclusion

Articulators are fundamental tools in complete denture fabrication. Though not perfect replicas of the TMJ, they provide necessary accuracy for proper denture placement and occlusal adjustments.