Terminal hinge axis--Hobo point--Frankfurt horizontal relations.

Area of Science:

• Dental Anatomy and Biomechanics
• Craniofacial Morphology
• Prosthodontics

Background:

• Accurate determination of the temporomandibular joint's (TMJ) terminal hinge axis (THA) is essential for effective prosthodontic treatment.
• The relationship between anatomical landmarks and reference planes like the Frankfurt horizontal (FH) is critical for articulator programming.

Purpose of the Study:

• To determine the spatial relationship between the terminal hinge axis (THA) and the Frankfurt horizontal (FH) plane.
• To evaluate the positional relationship between the THA and the Hobo point.
• To provide insights for optimizing articulator settings in prosthodontic procedures.

Main Methods:

• Utilized Lauritzen's technique to locate the THA in 50 participants.
• Defined the Hobo point and Orbital point, and placed steel pellets for cephalogram analysis.
• Obtained lateral cephalograms, traced anatomical points (Orbital, THA, Hobo, Porion), and defined the FH plane.

Main Results:

• The Hobo point was predominantly located inferior to the THA in the majority of the study population (20 cases in the fourth quadrant).
• The THA and Hobo points were never found to be identical.
• Significant variability was observed in the positions of both THA and Hobo points relative to the FH plane and to each other.

Conclusions:

• The study highlights that the Hobo point is generally positioned below the THA, contrary to assumptions based solely on FH orientation.
• Kinematic definition of the THA is recommended for prosthodontic procedures.
• Orientation in articulator space should not solely rely on the Frankfurt horizontal plane due to observed anatomical variability.