Hinge axis

Contents

1) Introduction 2) Definitions3) Mandibular movements 4) History 5) Theories of hinge axis 6) Method of locating hinge axis7) Clinical value of hinge axis 8) Summary 9) Reference

Definition

• “Imaginary line between mandibular condyles around which the mandible can

rotate within the sagittal plane” GPT—8

Terminal hinge axis = Transverse axis = Transverse horizontal axis = Transverse

hinge axis

• Pure rotation of condyles prior to translation

Mandibular Movements

• Rotation - the movement of a rigid body in which the parts move in circular paths

with their centers on a fixed line called the axis of rotation.

• Translation - that motion of a rigid body in which a straight line passing through any

two points always remains parallel to its initial position.

• Hinge axis point = posterior reference points - two points, located one on each side

of the face in the area of the transverse horizontal axis, which together with an

anterior reference point, establish the horizontal reference plane.

Rotational movement can occur in all the three reference planes:

Frontal

Horizontal

Sagittal

• In each plane occurs around a point called the axis

Frontal (Vertical) Axis of Rotation

Horizontal axis of rotation

Sagittal Axis of Rotation

Sagittal view Frontal view

Horizontal view

Posselt`s border movements

Posselt’s FigureMP

MO

ICPRCP

HA

MP = Maximal protrusionICP = Intercuspal positionRCP= Retruded Contact position HA = Hinge axisMO = Maximum opening

History

• Campion ( 1902-1905 ) – No axis, but movement is complex one.

Consisting first of rotation and secondly of a forward and downward movement

• Bennett ( 1908 ) - no single fixed rotation, since center of rotation constantly shifted for movements in sagittal plane,

mandible was capable of two independent movements

1. Angular rotation 2. Translation movement

• Gysi ( 1920 ) – Natural condyles are not considered as true rotation points, but as fixed guides of the mandible

"The mandible opens/closes and rotates on another rotational center which has no influence in the setting up of the teeth on articulators. Therefore, need not be considered in the construction of an articulator.”

• Needles ( 1923 ) - agrees with Bennett: Hinge Joint + Sliding Joint. No center of rotation in temporomandibular joint itself.

Instant and constantly shifting centers

• Wadsworth (1925) – Anatomist's conclusion

1st movement around transverse axis passing through condyles which remain seated in fossae.

2nd movement on articular eminence

• Hall ( 1929 ) – concluded that “condyle is not center of rotation”

`

McCollum ( 1939 )• Leading advocate of the hinge-axis theory• Definite opening and closing axis by using facebow • External landmarks are of little use. • Rotation occurs during 0.5 inch at incisors for most people, some can open

1 inch.

Stuart ( 1939 ) • Completed work of McCollum • Pioneers of gnathology • Movements were reproduced on articulator to duplicate the jaw movements

McLean ( 1944 )" The diagnosis of pathological occlusion depended on the fact that the final phase of jaw closure was pure hinge movement.“

Lauritzen ( 1951 )

• He thought articulation would be understood more easily if the joint were regarded as two separate joints• The only movement which could take place in the 'menisco-condylar'

part of the joint while opening and closing - a purely rotational movement. • In all patients, the anterior teeth could be separated by at least 12

mm in the rotational hinge relation.

Posselt (1952) • Hinge opening is obtained if patient is in passive, or trained active motion.• He could not prove this movement was habitual. • Hinge-axis opening = 19.2mm ± 1.9mm.

Kornfield & Granger ( 1955 ) • The only position at which it was possible to locate & reproduce the hinge axis

was at centric relation

Trapozzano ( 1955 )• Hinge-axis represented a border movement that could be recorded

repeatedly with unfailing accuracy

• It was essential to use trained mandibular hinge movement

• Recording was static starting point • Much of concept was based on

asymmetry of condyles• Off-Centre opening and closing

movements were perpendicular to hinge axis

• Movement in one direction in the plane could have only one axis of rotation

Weinberg ( 1959 )

Theories Of Hinge axis

The absolute location of hinge axis

school

The arbitrary

axis school

The non-believers

The split hinge axis

school

Aull ( 1963 )

Four schools of thought

•The hinge axis is a component of every masticatory movement and can not be disregarded.

•If the hinge axis of the articulator is not the same as the hinge axis of the patient then the mechanical reproduction of jaw motions are impossible.

•Believe that there is a definitive transvers axis and should be located

Absolute location of the axis

• The value of actually locating the exact hinge axis is not worth the effort. This group fails to recognize that if the hinge axis of the articulator does not coincide with the hinge axis of the patient, the paths of closure will not be the same.

Arbitrary location of axis

• This group does not believe the hinge axis can be accurately

located or believes other movements are involved and can not be

reproduced by an articulator simulating one axis

Non-Believers in the transverse axis location

• This group believes there are two axis of rotation ( one in each condyle) and they parallel

each other.

1. The horizontal axis is a hypothetical line connecting the two horizontal rotation centers of

the two condyles of the mandible.

2. There is one hinge location!

Split axis theory

METHOODS OF LOCATING HINGE AXIS

Arbitrary methodsKinematic methodsModified methods

1. loma-linda hinge axis device and method2. Buhnergraph intraoral method

3. Technique using geometric principle to locate hinge axis4. Abdal-Hadi’s method for locating arbitrary hinge axis

• Beryon point: 13mm anterior to posterior border of center of tragus on a line joining outer canthus of eye

• Bergstrom point : 10mm anterior to center of spherical insert for external auditory meatus and 7mm below FH plane

• Gysi point: This was on a line from the upper margin of the external auditory meatus to the outer canthus of the eye, 13 mm in front of the anterior margin of the meatus • Commonly used today

Arbitrary Method

Dejoyuex point : 10-11 mm anterior to ear on line to canthus and 5mm below it

Dawson palpatory method

Lauritzen boundner axis: 12mm anteroir and 2mm below portion of FH plane

Two theorems of geometry are used in this technique• 1. A line drawn through the center of a circle perpendicular to chord

meets it at its midpoint• 2. The line joining the center of a circle to the mid point of a chord is

perpendicular to the chord.

Kinematic methods

Instruments

• Buhnerberg instrument

• Pantograph

• Transograph

• Electronic mathematical method

• Stereognathography

• Axitron-computerised axiograph

• Digital recording system

Step wise method of recording

1. Recording hinge axis points

2. Transfer to the articulator

3. Mounting of upper casts and

4. Mounting of lower casts with centric record

• T.M.J instrument

• Hinge axis locator

Hinge axis bow

• Attach the clutch to lower teeth

• The clutch is a device, which relates the face-bow to the mandibular residual alveolar ridge. It is nothing but an occlusal rim made of impression compound with a bite fork attached to it

• the clutch resembles a cap splint with a bite fork attached to it. It is usually fabricated and cast in aluminum.

Axis location

Attach cross bar to clutch and side arms with stylus to cross bar

Guide mandible to terminal hinge closure

Observe the movements of stylus. When stylus rotates without arching movements indicates hinge axis point

At terminal hinge closure stylus should make contact on skin to transfer ink mark.

The two marks are hinge axis points

Low fusing compound to

bite fork of facebow

Slight indentations of maxillary

teeth is obtained

Now position styli on either

sides on posterior reference

points

Position orbital

reference point

Lock face bow and

remove it to clamp it on

transfer board

Axis jig is placed and adjusted to support the

styli

Axis transfer

Loma-linda hinge axis recording device and method

• The opponents of use of a kinematic hinge-axis location for edentulous patients point to its unreliability because of the resiliency of the oral mucosa.• the added weight of the recording clutch which tends to shift the

denture base

Modified method

• Dentist called Buhnergraph

• Buhnergraph instrument consists of a U-shaped piece of aluminum

• Attached to the underside of the lower member of a Whip Mix articulator. On each side is attached an adjustable arm containing a pointed shaft which moves in and out.

Buhnergraph intraoral method

• New arbitrary method• Y = 9.5 c 0.95 (X)

Y = width profile of the face measured from the ectocanthion to the center of the external auditory meatus

X = anterioposterior position

Abdal-Hadi's technique

Clinical value of Hinge Axis

• Allows for correct recording of centric relation and its transfer to the articulator• Starting point of lateral movements• Permits a change in vertical dimension• If transferred to articulator—teeth contact each other in the articulator

exactly as they do in the mouth• Helps in diagnosis and treatment planning

Variables affecting hinge axis location

Patient variables affecting the T.H.A.• locations Condyle • Asymmetry

• Inability to locate a true hinge axis• Myospasm or joint pathosis• Emotional conditions of patient

Factors of the recording system affecting THA• Right angle non-right angle system of the bow• Length of stylus arms and sharpness of styli

• A minimal error of 5 mm can be expected no matter what arbitrary position might be chosen. • Placement of the tragus-canthus line at the superior border of the

tragus of the ear will contribute to greater inaccuracy in most patients.• The largest percentage of true axis locations will be inferior to the

tragus-canthus line at the superior border of the tragus of the ear

summary

• In the final analysis, the true value of our individual work can be measured only by the degree of fineness with which we practice the art of dentistry rather than by the particular school of thought to which we adhere.

conclusion

• Jeffery P. Okeson. Management of temporomandibular disorders and occlusion, 5th edition • Zarb bolender-prosthodontic treatment for edentulous patients-12th

edition• Shillingberg• Heartwell• Terminal hinge movement of the mandible J Prosthet Dent 1957;7:787-97.• Winstanley, R. B. The hinge-axis: A review of the literature. J Oral Rehabil

12:135-159, 1985.• Hinge axis overview ; ashu sharma int journal of clinical dentistry• Vol 5, no, 3 : 2012

reference

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