28. Landmarks for restoration of masticatory system – constant reference points (bioconstants).
Covers the constant reference points, called bioconstants, used to rebuild the bite in edentulous patients. It goes through facial planes and lines such as Camper's line and the Frankfort plane, with a table of their definitions and uses. It then describes intraoral landmarks and rules for upper and lower rim heights and the freeway space, shown in a second table. The note closes with jaw bioconstants, including Bonwill's triangle, the Balkwill angle and the transverse hinge axis, and explains why these anchors remain stable after tooth loss.
Topic 28 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 5 sections, about 194 words (3 min of reading), with 13 flashcards.
In this note
Introduction
Facial planes and lines
Points and distances inside the mouth
Bioconstants of the jaws
Why bioconstants work
Introduction
When teeth are lost, so are the clues to where they stood and how high the bite was. To rebuild them, prosthetics uses bioconstants: landmarks of the face, skull and mouth that change little or not at all after tooth loss. They are the constant reference points for restoring the masticatory system, especially in edentulous patients.
Bioconstants of the jaws
Bonwill's triangle: the two condyles and the contact point of the lower central incisors form an equilateral triangle with sides of about 10 cm. Average-value articulators are built on it.
Balkwill angle: the angle between Bonwill's triangle and the occlusal plane, about 22–26°.
Transverse hinge axis: repeatable, so it is the main reference for mounting casts with a facebow.
Rest vertical dimension: constant through life, governed by muscles, not teeth (topic 13).
Condylar path inclination (about 33°) and Bennett angle (15–17°): average values when they can't be recorded.
Why bioconstants work
They are anchored in parts of the body that tooth loss doesn't change: the skull, the TMJs, the muscles and the face's soft-tissue landmarks. Used together, they let the clinician rebuild the height, position and plane of teeth that are no longer there, and check the result phonetically and esthetically.
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