University of Michigan classification with examples
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Articulator classification
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Here is the complete University of Michigan (International Prosthodontic Workshop, 1972) classification of articulators:
University of Michigan Classification of Articulators (1972)
Proposed at the International Prosthodontic Workshop on Complete Denture Occlusion, University of Michigan, 1972. Articulators are classified based on instrument capability, intent, recording procedure, and record acceptance into 4 classes.
Class I - Simple Holding Instruments
A simple holding instrument capable of accepting only a single static registration. It cannot orient movement to the TMJ.
Subdivision A - Vertical motion is possible but only for convenience (not joint-related).
- Examples: Slab articulator, Barn Door articulator, Corelator (Denar Corp.), Verticulator (Jelenko)
Subdivision B - Vertical motion is joint-related; rotates on the terminal arc registered by a face-bow.
- Example: Centric Relator (Denar Corp.)
Used for tentative jaw relation work, simple bite registrations.
Class II - Arbitrary / Non-TMJ Instruments
These permit horizontal and vertical movements but do NOT orient movement to the TMJ (no facebow transfer).
Subdivision A - Eccentric motion based on averages or arbitrary values; no facebow transfer; based on Bonwill's triangle.
- Examples: Gysi Simplex articulator, Mean-Value articulator (Gysi)
Subdivision B - Eccentric motion based on spheric theory of occlusion; no facebow transfer.
- Examples: Monson's articulator, Hall articulator
Subdivision C - Eccentric motion is determined by the patient using engraving methods; no facebow transfer.
- Example: Gnathic Relator, House's articulator
These instruments cannot replicate patient-specific TMJ anatomy.
Class III - Average / Semi-Adjustable Instruments (with Facebow)
These simulate condylar pathways using averages or mechanical equivalents for all or part of condylar motion. They accept facebow transfer and have mounting plates for unlimited case load. Can be arcon or non-arcon.
Subdivision A - Accept a facebow transfer and a protrusive interocclusal record; use averages for the rest.
- Examples: Hanau H articulator (Rudolph Hanau, 1923), Hanau H2, Bergstrom articulator (ARCON)
Subdivision B - Accept facebow transfer, protrusive interocclusal records, AND some lateral interocclusal records; use equivalents for remaining motion.
- Examples: Trubyte articulator (Gysi), Tripod articulator (Stansberry), Ney articulator, Hanau 130-21, Teledyne articulator, Panadent articulator, Whip-Mix articulator, Denar Mark II, Dentatus articulator
The workhorse class for most prosthodontic cases.
Class IV - Fully Adjustable / Special Instruments
These accept three-dimensional dynamic registrations and allow full orientation of casts to the TMJ with replication of all mandibular movements.
Subdivision A - Condylar paths formed/engraved by registration from the patient (stereographic or pantographic records).
- Examples: TMJ Stereographic instrument, Denar Combi articulator
Subdivision B - Condylar paths can be angled and customized by selection from various curvatures, by modification, or both.
- Examples: Stuart articulator, Denar D5A articulator
Used for complex restorative cases, full-mouth rehabilitation, and temporomandibular disorder cases requiring precise condylar path replication.
Summary Table
| Class | Facebow | Eccentric Motion | Basis | Examples |
|---|---|---|---|---|
| I | No | None / limited | Single static record | Slab, Barn Door, Centric Relator |
| II | No | Yes | Arbitrary / Average / Engraved | Gysi Simplex, Monson's, Gnathic Relator |
| III | Yes | Partial (averages) | Average values + patient records | Hanau H, Hanau H2, Whip-Mix, Denar Mark II |
| IV | Yes | Full | 3D dynamic patient records | Stuart, Denar D5A, Denar Combi |
Clinical Relevance:
- Class I: Simple occlusal adjustments, study models
- Class II: Older designs, limited clinical use today
- Class III: Most routine prosthodontic work (removable and fixed)
- Class IV: Complex full-mouth rehabilitation, gnathologic restorations
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