Articulators

A mechanical instrument that represents the A mechanical instrument that represents the temporo mandibular joint and jaws, to which temporo mandibular joint and jaws, to which maxillary and mandibular casts may be maxillary and mandibular casts may be attached to simulate some or all mandibular attached to simulate some or all mandibular movement. movement.

((GPT-8GPT-8))

Plaster Articulator

Philip Pfaff (1756)

Barn door hinge articulator

VIRTUAL ARTICULATORS

Additional Requirements

Adjustable horizontal, lateral condylar guide element & allow protrusive movements

A mechanism to accept the face bow transfer . A terminal hinge locking

positional device . Removable mounting plates

that can be positioned accurately An adjustable incisal guide table Adjustable intercondylar width of the condylar element .

ADVANTAGES

Properly mounted cast allow the operated to better visualize the patient occlusion from the lingual side.

Patient’s co-operation is not required, once the Interocclusal records are obtained from the patients .

Refinement of the complete dentures in the patient’s mouth is extremely difficult because of shifting of denture bases and resiliency of the supporting tissues. This does not take place in the articulator.

Chair side appointment time is reduced .

Patient’s tongue ,saliva, check etc. are not a factors of hindrance under using the articulator .

LIMITATIONS

An articulator is a mechanical device made by metal hence is subjected to error in tooling and there by resulting from fatigue and wear .

Articulator will not duplicate but simulates the condylar movements of TMJ .

Classification

Several classifications of articulators were proposed. The most popular methods of classifying articulators are :

Based on the theories of occlusion Based on the ability to simulate jaw movements. Based on the adjustability of the articulator.

Classification based on

THEORIES of OCCLUSION

Bonwill’s theory of occlusion .

Conical theory of occlusion (R.E.Hall ) .

Spherical theory of occlusion (G.S.Monson 1918 ) .

BONWILL’S THEORY OF OCCLUSION

Bonwill introduced (1864) -“Theory of Equilateral Triangle” .

4" (10 cm ) distance occurs between the condyle and between each condyle & the incisal point.

CONICAL THEORY OF OCCLUSION

R.E.HALL (1915)

Lower teeth move over the surface of the upper teeth as over the surface of a conesurface of a cone, generating an angle of 45° with the central axis of the cone tipped at 45 angle to the occlusal plane.

SPHERICAL THEORY OF OCCLUSION

Monson (1918)

Lower teeth moves over the surface of the upper teeth as over the surface of a sphere with a diameter of 8 " (20 cm).

The center of the sphere is located in the region of Glabella and the surfaces of the sphere passes through the Glenoid fossa along the articulating eminences.

Classification Based

on the ability to simulate

jaw movements

At the international Prosthodontic Workshop on complete denture occlusion at the University of Michigan in 1972, the articulators were classified based on the instrument’s capability, intent, recording procedure and record acceptance. This is the most widely used classification .

Class -I

These are simple articulators capable of accepting a single static registration. Only vertical motion is possible. These articulators are used in cases where a tentative jaw relation is done .

Ex : Barn door hinge articulator .

Class II

These articulators permit horizontal and vertical

movements but they do not

orient the movement of TMJ

with a face bow.

Ex: Mean value articulator

Class III

These articulators permit horizontal and vertical movements. They do accept face bow transfer but this facility is limited. They cannot allow total customization of condylar pathways. These instruments simulate condylar pathways by using average or mechanical equivalents for the whole or part of the condylar motion.

Class IV

These articulators accept three

dimensional dynamic registrations. They

are capable of accurately reproducing the

condylar pathways for each

patient. They allow point

orientation of the casts using

a face bow transfer.

CLASSIFICATION Based

on the adjustability

Based on the adjustability, articulators can be classified as

Non-adjustable Semi-adjustable Fully adjustable

Based on the adjustability of the articulator

Based on the adjustability, articulators can be classified as :

Non-adjustable Semi-adjustable Fully adjustable

FULLYADJUSTABLE

can accept the following five records:

-Face bow record -Centric jaw relation record -Protrusive record -Lateral record-Inter condylar distance record

SEMI ADJUSTABLE

can accept the following three records:

-Face bow record-Centric jaw relation record-Protrusive record

NONADJUSTABLE

can accept one or two of following three records:

-Face bow record -Centric jaw relation record -Protrusive record

Non adjustable articulators They can open and close in a fixed horizontal axis.

They have a fixed condylar path

along which the condylar element

can be moved to simulate some lateral

and protrusive jaw movement.

The incisal guide pins ride on an inclined plate in a fixed inclination.

Semi adjustable articulators

They have adjustable horizontal condylar paths, adjustable lateral condylar paths, adjustable incisal guide tables and adjustable inter condylar distances. The degree and ease of these adjustments differ.

There are two types of semi adjustable articulators.

Arcon articulators Non-arcon articulators

Arcon articulators

The term ‘arcon’ was derived by Bergstrom from the words articulator and condyle.

Example : Hanau University series and Whip mix articulators.

The condylar element is attached to the lower member of the articulator and the condylar guidance is attached to the upper member. This articulator resembles the temporo mandibular joint. (Here, the condylar guidance is the mechanical analog of the glenoid fossa).

Non-arcon articulators

These articulators have the condylar elements attached to the upper member.

The condylar guidance is attached to the lower member.

This articulator is the reverse of the temporomandibular joint.

Examples include Hanau H series, Dentatus and Gysi.

Fully adjustable articulators

These articulators have numerous adjustable readings, which can be customized for each patient. They do not have condylar guidance instead they have receptacles in which acrylic dough can be

contoured to form a customized condylar and incisal guidance. They are not commonly used due to their complexity.

Example: Stuart instrument gnathoscope , simulator by E. Granger.

Mean Value Articulator

It is a non-adjustable articulator. This articulator is designed

using fixed dimensions, which are derived from the average

distance between the incisal and condylar guidance of the

population .

The condylar guidance (equivalent of glenoid fossa) is attached

to the lower member and the condylar element (equivalent of

the mandibular condyle) is attached to the upper member,

hence, it is a non-arcon articulator.

Upper member :

It is a triangular frame with the base of the triangle placed

posteriorly. The apex of the triangle contains a provision to accom

modate the vertical rod (incisal pin). The vertical rod can be locked

in position within the upper member

with the help of a thumbscrew. Two condylar

elements are seen projecting on either side of

the base of the triangle. They articulate with

the condylar guidance of the lower member.

The maxillary cast is attached to the upper

member during articulation ..

Lower member : It is a 'L' shaped frame with a horizontal and

a vertical arm. The horizontal arm is triangular in shape. The apex of

the triangle of the horizontal arm contains

the incisal guide table. The vertical arm

contains the condylar guidance slot

at the upper portion .

A fixed metal bar (horizontal bar) is

present in the vertical arm of the lower

member. The plane of occlusion should

coincide with this horizontal bar during

articulation .

Incisal guide table :

Incisal guide Table is defined as, "That part of the articulator

which maintains the incisal guide angle" - GPT. The incisal

guide table gives the incisal guidance of the articulator. The

incisal guide table can be described as a very short cylinder

whose upper surface is concave. The vertical

rod should rest on the centre of the incisal

guide table during articulation. The depth

of the concavity is designed to have a slope

equal to the average incisal guide angle The

incisal guide angle is fixed and non-customizable.

Condylar guidance :

It is represented by a slot (condylar track) located on the upper

part of the vertical arm of the lower member. The slot is

inclined at an angle equal to the average inclination of the

condylar guidance in the population.

The condylar element of the upper member

passes through this track. A spring is mounted

within this track (condylar guidance) to stabilize the condylar

elements when no movements are made. This condylar

guidance does not accept face-bow transfer .

Incisal rod & Incisal pin :

It helps to keep a fixed distance between the upper and lower

members at the anterior end. The vertical rod has a pointed

tip, which should rest on the center of the incisal guide table

during articulation.

At the midpoint of the vertical rod a hole is provided to fit the

incisal guide pin. The tip of the incisal guide pin is the

anterior reference point in this articulator. The incisal edge of

the maxillary incisors at the midline of the occlusal rim

should touch the tip of the incisal pin during articulation The

upper flat surface of the vertical rod should always be locked

flush with the superior surface of the upper member.

Selection of an articulator for complete dentures

If occlusal contacts are to be perfected in centric relation only ,then a simple hinge articulator can be selected .

If denture teeth are to have cross arch and cross tooth balanced occlusion then minimum requirement is semi adjustable articulator.

If complete control of occlusion is desired , a completely adjustable articulator is selected.

Parts of hanau articulator

Condylar guidance :

The condylar guidance's are the control centers of the Articulator and their adjustably assimilate the multiple function of the glenoid fossa .

The closed condylar guidance track rotates in an enclosed housing which stops the Condylar Element ,preventing the accidental disengagement of the upper member .

DUAL -END INCISAL

PIN :

ADJUSTABLE INCISAL GUIDE :