Mean Value Articulator Classification Classification According to Adjustability of Articulators: Nonadjustable Articulators: Semiadjustable Articulators:

1. Preclinical Prosthodontics
Articulator Introduction
The oral cavity is confined by maxilla and mandible with two temporomandibular joints (TMJs).
During fabrication of prosthesis, some procedures are carried out in oral cavity and some are
performed in dental laboratory in absence of patient. A mechanical device stimulating the two
jaws and the TMJs is needed for ease of work. This device is “articulator”.
Articulator Definition
Articulator is a mechanical device that represents the TMJs and the jaw members to which
maxillary and mandibular casts may be attached to simulate some or all the mandibular
movements.
Mean Value Articulator Classification
Articulators are classified in several ways. The most common classification of articulator is
based on their adjustability. Adjustability of articulator is judged based on their ability to accept
face bow and various occlusal records which modifies condylar and incisal guidance
accordingly.
Read and Learn More: Preclinical Prosthodontics Notes
Articulators can be classified according to:
• According to theories of occlusion
• Based on type of interocclusal records used
• Based on adjustability of the articulators
• Based on University of Michigan workshop.
Classification According to Theories of Occlusion:
• Bonwill theory articulator: This articulator was made by WGA Bonwill. This
articulator is based on Bonwill’s theory of equilateral triangle. According to this theory
the teeth move in relation to each other as guided by the condylar and the incisor
guidance. The equilateral triangle is formed between two condyles and condyles to
midincisal point (of mandible). Theoretically the dimension of equilateral triangle is 4
inch.
• Conical theory articulator: This theory was proposed by RE Hall. According to this
theory the lower teeth move over the surface of upper teeth as over the surface of cone
generating an angle of 45° with the central axis of cone tip 45° to the occlusal plane.
• Spherical theory articulator: This articulator is based on Monson’s theory of spherical
occlusion.

2. Preclinical Prosthodontics

3. Preclinical Prosthodontics
The theory states that the lower teeth move over the surface of sphere of 8 inch which has its
center at the glabella. The surface of
sphere passes through glenoid fossa along and articulating eminence.
Based on Type of Interocclusal Records Used:
• Interocclusal records adjustment: These devices are programmed based on interocclusal
records made up of plaster, bite registration polyvinyl siloxane, zinc oxide eugenol (ZOE)
paste, and base plate wax.
• Graphic records adjustment: These articulators are capable of producing accurate jaw
movements. A transographic record can be used to accurately locate the hinge axis on
articulator.
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Classification According to Adjustability of Articulators:
• Nonadjustable articulators

4. Preclinical Prosthodontics
• Semiadjustable articulators
• Fully adjustable articulators.
Nonadjustable Articulators:
These are simple device to mount the casts. They are simple mechanical device which opens and
close in one direction. They have fixed horizontal axis of rotation. The upper and lower members
are joined together with hinge-like mechanism. Examples are slab articulator and hinge
articulator, mean value articulator.
Semiadjustable Articulators:
They have adjustable horizontal condylar paths. They also have adjustable lateral condylar paths
and incisal guide tables, and adjustable intercondylar distance. They accept face bow record.
These articulators are divided in two types based on arrangement of condylar guidance assembly.
1. Arcon articulator: Term arcon was coined by Bergstrom by combining two words, i.e.
articulator and condyle. In this type of articulator, the arrangement of condylar guidance and
condylar element is similar to arrangement in TMJ. The condylar guidance which represents the
gleaned fossa is attached with upper member of articulator. The condylar element which
represents the human condyle is attached with lower member, e.g. Hanau wide-vue.
Advantages: The face bow transfer, occlusal plane, and the relationship of opposing cast are
preserved when articulator opened and closed.

5. Preclinical Prosthodontics
2. Nonarcon articulators: In this type of articulators the position of condylar guidance and
elements is reverse compared to human TMJ. The condylar guidance is attached with lower
member and condylar element is attached with upper member, e.g. Hanau H2.
Fully Adjustable Articulators:
They have ability to adjust according to patient’s mandibular movements. THey have provision
to customize condylar guidance.
They are highly precise in recording and understanding mandibular movements. Not widely used
due to complexity. Example is Stuart instrument gnathoscope.
Based on University of Michigan Workshop (Based on Ability to Simulate Jaw
Movements):
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Articulators may show single dimensional movement or they can show complex
threedimensional movements. The workshop on complete denture occlusion at the University of
Michigan in 1972 classified articulators based on their ability to simulate jaw movements.

6. Preclinical Prosthodontics
Class I:
Simple device, capable of accepting single static record. Only vertical movement is possible.
Class II:
These articulators perform horizontal and vertical movements but cannot orient the movement to
TMJ with a face bow.
Class IIa:
Limited eccentric motion is possible which is based on average value.
Class IIb:
Limited eccentric motion is possible which is based on theories of arbitrary motion.
Class IIc:
Limited eccentric motion is possible which is based on engraving records obtained from the
patient.
Class III:

7. Preclinical Prosthodontics
They accept the face bow records but the facility is limited. They permit horizontal and vertical
movements.
Class IIIa:
They accept the face bow records. They accept static protrusive records.
Class IIIb:
They accept static lateral, protrusive records.
Class IV:
These articulators accept three-dimensional dynamic records. The point orientation of the cast
can be achieved using face bow
transfer.
Class IVa:
Condylar path is determined by engraving records produced by the patient.
Class IVb:
These articulators are similar to type IVa but they allow angulations in customization of condylar
path.
Uses:
• To diagnose the condition of occlusion in both natural and artificial dentition.
• To plan the treatment based on relationship of opposite natural or artificial teeth.
• To aid in the fabrication of restoration and prosthesis.
• To correct and modify complete restorations.
• To arrange artificial teeth.
Advantages:
• Better visualization of cast and restorations in occlusion, especially from lingual side.
• Chair side and patient appointment time are reduced.
• No interference due to saliva, tongue, and cheek.
• Realeff effect eliminated (discrepancy due to resiliency of mucosa).
• Transfer of work from clinician to technician through articulators and vice versa.
Limitations:
Since it is a mechanical instrument, it is subjected to error resulting from fatigue and wear. It can
simulate but not duplicate the jaw movements/relation.

8. Preclinical Prosthodontics
Ideal Requirements:
• It should hold casts in the correct horizontal and vertical relation.
• Provision to removal and reattachment of casts should be there.
• It should provide a positive anterior vertical stop.
• It should accept face bow transfer record using an anterior reference point.
• It should open and close in hinge movement.
• It should be made of noncorrosive and rigid material that resists wear and tear.
• It should not be bulky and heavy.
• There should be adequate space between the upper and lower member.
• The moving parts should move freely without any friction.
• Condylar guide should allow protrusive and lateral movements.
• Condylar guidance should be adjustable.
• The articulator should be adjustable in horizontal direction.
• The incisal guide table should be customizable (adjustable).
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Mean Value Articulator
Mean value articulator is called as “threepoint articulator” or “free plane articulator”. It is
nonadjustable and nonarcon type of articulator. It is based on Bonwill theory of occlusion.
According to this theory, an equilateral triangle of 4 inch formed between two condyles and from
each condyle to midincisal point of mandibular incisors. It is capable of lateral and protruding
movements
based on the fixed average value in addition to hinge movements. Thus, these cannot be
programmed to suit the individual requirement of a patient. The mean value of incisal guidance
is fixed at 5°. Condylar guidance is fixed at 33° for mean value articulator.

9. Preclinical Prosthodontics
Various Models of Mean Value Articulator:
In mean value articulator, the intercondylar distance is 110 mm, condylar guidance is 30–33°,
and incisal guidance is 5°. These are
mean (average) values adopted for fabrication of articulator so known as mean value articulator.
Parts of Mean Value Articulators:
Incisal Pin/Vertical Rod:
It helps to keep a fixed distance between upper and lower member. It has a pointed tip resting on
the center of incisal guide table. The upper flat surface should be flush with superior surface of
upper member.
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10. Preclinical Prosthodontics
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Condylar Shaft:
This is horizontal shaft attached with upper member of articulator. This attached in condylar
slots. The length is 110 mm which represents intercondylar distance.
Midincisor Pin/Central Pin:
It is the anterior reference point. This is located at midpoint on incisal pin/rod. Relate to anterior
occlusal plane. During mounting of wax occlusal rims this pin coincide with midline of occlusal
rims. It helps during arrangement of maxillary central incisors according to midline and occlusal
plane.

11. Preclinical Prosthodontics
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12. Preclinical Prosthodontics
Horizontal Bar.
Two horizontal bars are attached in posterior region of articulator. Upper bar is supporting bar
and the lower bar is known as horizontal orientation bar/rod. Orientation bar along with the
midincisal pin form the plane of articulator. The plane of occlusion coincides with plane of
articulator.
Upper Member:
This represents maxilla on which maxillary cast may be attached (through mounting ring). It is
triangular shaped. In anterior part incisal pin/vertical rod is attached and in posterior part two
extensions correspondng to condyle elements are attached.

13. Preclinical Prosthodontics

14. Preclinical Prosthodontics

15. Preclinical Prosthodontics
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16. Preclinical Prosthodontics
Lower Member:
It is an “L”-shaped frame with vertical and horizontal arm. Vertical part of “L” frame: Vertical
arm of “L” frame is attached with upper member through condylar slots.
Horizontal bar is also attached on this part of lower member. Horizontal part of “L” frame: In
anterior region, anterior guide table is fixed. In the center, mounting rim is attached on which
mandibular cast is attached.
Incisal Guide Table/Anterior Guide Table:
It has a concave upper surface which gives the incisal guidance. The concavity is designed in
such a way that it gives anterior guidance equal to 5°. Incisal pin/vertical rod is in contact with
center of anterior guide table. The value of incisal guidance is fixed in mean value articulator.
Condylar Guidance:
In mean value articulator condylar guidance is represented by a slot known as condylar
slot/track. Condylar slot together with condylar
elements make condylar guidance. Condylar elements are fixed in condylar slots. Spring
assembly is attached in condylar slots/track to permit movements of condylar elements, when not
in action it holds condylar elements in most posterior part of the slots. In mean value articulator
condylar guidance is fixed at 33°

17. Preclinical Prosthodontics
Mounting Rings/Plates:
They are two in number, each attached with upper and lower member. Mounting plates/rings are
attached with upper and lower member by thumb screws.

18. Preclinical Prosthodontics
Maxillary and mandibular casts are mounted on mounting rings/plates using dental plaster. These
mounting rings are removable so that same articulator can be used with other case or patient with
other set of mounting rings.
Stabilizing Rod:
It is located in anterior part of upper member opposite to vertical rod. It prevents fall of upper
member of articulator while working on it. It stabilizes the upper member.