articulators & face bows

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Articulators & face-bows

Articulators & face-bowsContentArticulators Uses of articulatorsRequirement of an articulatorClassification of articulatorsFace-bowsArticulator:

It is a mechanical device which represents the tempromandibular joints and jaws to which maxillary & mandibular casts may be attached to simulate some or all mandibular movements.

The articulator helps to maintain the desired maxillomandibular relationship of the casts during tooth arrangement.

It makes it possible to arrange teeth in the absence of the patient.Articulators

Uses of articulatorsDiagnose dental occlusal conditions in both the natural & artificial dentitions.Plan dental procedures that involve positions, contours & relationships of both natural & artificial teeth as they relate to each other.Aid in the fabrication of dental appliances & lost dental parts.Correct & modify completed restorations.Study occlusion & mandibular movements.

Requirement of an articulatorIt should hold casts in the correct horizontal.It should hold casts in the correct vertical relationship.It should provide a positive anterior vertical stop (the incisal pin).It should accept a face-bow transfer record.It should open & close in a hinge movement.It should allow protrusive & lateral mandibular motion.The moving parts should move freely & be accurately machined.

Requirement of an articulatorThe non-moving parts should be of a rigid construction.

If your going to choose balanced occlusion, an articulator should have:Adjustable horizontal & lateral condylar path elements.The condylar elements as a part of the lower member & the condylar path elements as a part of the upper member (Acron-type).

Requirement of an articulatorA mechanism to accept a third reference point from face-bow record.A terminal hinge position locking device.Removable mounting plates that can be repositioned accurately.An adjustable incisal guide table.An adjustable intercondylar width.

Classification of articulatorsThe simplest classification system refers to the degree to which the articulator can be adjusted to conform to the jaw movements of the patient.

Classification of articulatorsClass I Articulators (Non-adjustable)

A simple holding instrument capable of accepting a single static registration. Vertical motion is possible.

Defined as:An articulator that does not allow adjustment to replicate mandibular movements.

10Non adjustable (simple hinge or plane-line articulators)It consists of two arms or bows united by a hinge & a stop or screw to hold the bows a fixed distance apart.

It only simulates the opening & closing movements of the mandible.No eccentric movements possible.These articulators reproduce only one relation, centric occlusion.Therefore, setting the teeth for complete dentures will only be balanced in the centric position.

Class II Articulators (mean-value or Average-value)

An instrument that permits horizontal as well as vertical motion but does not orient the motion to the temporomandibular joints.

Average-value Articulator:An articulator that is fabricated to permit motion based on mean mandibular movements.

They permit not only opening & closing hinge movement around a fixed horizontal axis, but also protrusive, right & left lateral excursions.mean-value articulator

Class II Articulators (mean-value or Average-value)

The condylar sphere if present, is normally attached to the upper member of the articulator & rotates in a groove in the lower member.

The condylar path is fixed in 30 angle, this means that the condylar sphere can be pushed to simulate protrusive & lateral jaw movements.

They are provided with an incisal guide pin, it helps:to hold the articulator open at a definite positionThe teeth are protected against accedental closure

Class II Articulators (mean-value or Average-value)

They have a fixed intercondylar distance.

It may include some provision for Bennett movements.

Some can accept a face-bow.

The relationship of the maxilla to the condyles is established by aligning the occlusal surface of the upper occlusal rim with the incisal pin & with the notches or a bar on the condylar posts at the rear of the articulator in accordance to Bonwill triangle.

Bonwill triangleA 4 inch equilateral triangle bouded by lines connecting the contact points of the mandibular central incisors incisal edge ( or the mid line of the mandibular residual ridge) to each condyle &from one condyle to the other.

Cast is mounted in an average position.

Adjustable articulatorsAn articulator that allows some limited adjustment in the sagittal & horizontal planes to replicate recorded mandibular movements.

Class III articulators (Semi-adjustable)An instrument that simulates condylar pathways by using averages or mechanical equivalents for all parts of motion. These instruments allow for orientation of the casts relative to the joints & may be arcon or nonarcon.

Class III articulators (Semi-adjustable)They are adjusted so that the articulator movements will simulate the jaw movements of the patient.

The condylar paths have a fixed contour which cannot be altered & the distance between the condyles cannot be varied.

Class III articulators (Semi-adjustable)Adjustable horizontal condylar guides.Accept centric relation & protrusive records.Adjustable incisal guide tables.Adjustment for lateral mandibular movements.A face-bow to relate the casts to the hinge axis.

They have a close approximation to the actual mandibular position.Class III articulators (Semi-adjustable)Hanau-H series Articulator:

Accept only one eccentric jaw relationship record, protrusive record.

The record is then used to adjust the horizontal condylar inclination.

It is not capable of accepting lateral jaw relation records.

It is calculated:L= H +12 _____ 8

Class III articulators (Semi-adjustable)Whip-mix Articulator:Accept centric & protrusive jaw records only.It has limited three-position adjustment of the intercondylar width.

Arcon articulatorsArticulator + CondyleIt is used to describe an articulator containing the condylar path elements within its upper member & the condylar elements within the lower member.

Arcon articulator:An articulator that applies the arcon design.This instrument maintains anatomic guidelines by the use of the condylar analogs in the mandibular element & fossae essemblies within the maxillary element.

Examples:Hanau university seriesWhip-mix

Non-Arcon articulatorAn articulator whose fossae assemblies are part of the mandibular member& the condylar analogs in the maxillary member.Examples:Hanau-H seriesThe DentatusGyzi

Class iv articulators (fully adjustable)An instrument that will accept three dimensional dynamic registrations.

Allow for orientation of the casts to the temporomandibular joints & simulation of mandibular movements.

They have a complex condylar mechanism, it is adjustable in the horizontal, sagittal & frontal planes.

Replicate 3-D movement of recorded mandibular movement.

Class iv articulators (fully adjustable)They are all arcon, with adjustable intercondylar distance.

They all accept arbitrary or hinge axis face-bow transfers.

They accept all eccentric jaw relation records.

They can be adjusted to trace the recordings of a pantograph.

Class iv articulators (fully adjustable)Pantograph registers a three dimensional dynamic registration or tracings (pantograms).

Then they are transferred to the articulator in the same relationship in which they exist in the patient.

Examples:Stuart articulatorDenar articulator

Face-bowsFace-bowsA calliper like instrument used to record the spatial relationship of the maxillary arch to some anatomic reference point or points & then transfer this relationship to an articulator.

The anatomic references are the mandibular condyles, transverse horizontal axis & one other selected anterior point.It supports the casts while they are being attached to the articulator.

Types of face-bowsArbitrary face-bows: a. Conventional face-bowb. Earpiece face-bow

Kinematic (hinge bow)

Arbitrary face-bowsA device used to arbitrarily relate the maxillary cast to the condylar elements of an articulator.

They are based on the average location of the hinge axis, has an error of 2mm of the true center of the true center of the opening axis of the jaws.

The arbitrary rotational center is located over measured points on the face or by some types of earpiece.

The arbitrary type is considered adequate for complete dentures.Arbitrary face-bowsConsists of:U-shaped bowGraduated condylar rodsBite forkLocking device

Arbitrary face-bowsIt is placed on the face, with the graduated condylar rods located in a line extending from the outer canthus of the eye to the top of the tragus of the ear & approximately 13mm in front of the external auditory meatus.

Earpiece face-bow (ear-bow)An instrument similar to a face-bow that indexes to the external auditory meatus & registers the relation of the maxillary dental arch to the external auditory meatus & a horizontal reference point.

Earpiece face-bow (ear-bow)Advantages:It is a simple instrument to useDoes not require measurements or marks on the faceConsumes less time for its useIt is accurateBoth the face-bow & the ear-bow may use the infraorbital notch ( infraorbital pointer)or the incisal plane as the anterior reference point(