03/05/2023 1

An overview on Mandibular Movements

Roll No.:

2

After fabricating the record bases and the occlusal rims, lets have a look at how to go

about relating them in 3D space.

03/05/2023 3

I have in store for you the following subtopics-

• Definitions• Introduction• Complexity of

Maxillomandibular relations.

• Natural vs artificial dentition

• Mandibular movements

• Determinants of mandibular

movements• Anatomy of TMJ• Types of Mandibular

Movements• Bennett Shift• Border Positions• Condyle Path

4

Maxillomandibular or Intermaxillary Relations

• Boucher classified maxillomandibular relations as:• Orientation jaw relation: Use of a facebow.• Vertical jaw relation:1. At rest.2. At occlusion.• Horizontal jaw relation:1. Centric relation.2. Eccentric relations: Deviations from centrica) Protrusive relation.b) Right and left lateral relation.

03/05/2023 5

Definitions by the Glossary, Eighth edition

Maxillomandibular relationship : Any spatial relationship of the maxilla to the mandible; any one of the infinite relationships of the mandible to the maxillaeMaxillomandibular relationship record : A registration of any positional relationship of the mandible relative to the maxillae. These records may be made at any vertical, horizontal, or lateral orientation maxillomandibular registrationMandibular movement : Any movement of the lower jaw

03/05/2023 6

Complexity of Maxillomandibular

relationshipsMaxillomandibular relations and occlusion create a lot of controversy. Several factors in which there are differences in

1. Interpreting definitions.2. Terminology.3. Clinical results.4. Mechanical instruments like articulators which

reproduce living tissues.5. Evaluating the Jaw relations and occlusion of

natural teeth.

03/05/2023 7

Natural vs. ArtificialTeeth attached to PDL and surrounded by alveolar bone. Premature contact affects the involved tooth and adjacent tissues only.

Natural Dentitio

n

Bases rest on movable and displaceable tissues thus a premature contact affects the entire base in its relation to the supporting tissue.

Artificial Dentitio

n

Conclusion: Natural teeth have a greater influence in mandibular movements than do artificial teeth on their movable bases.

03/05/2023 8

Significance of the knowledge of mandibular function

Understanding the whole stomatognathic system is vital for any treatment plan.

To understand natural occlusion and develop complete denture occlusionTo develop occlusal morphology of artificial restorations ( Crowns, Inlays, etc.)To understand, select and design articulatorsTreatment of TMJ disorders.

03/05/2023 9

Mandibular Movements

Determinants of Mandibular Movements:

The two posterior determinants are the TMJ and associated structures.The anterior determinant are the teeth- Cuspal inclines and other contacting areas of the teeth.The fourth determinant is the neuromuscular component.

03/05/2023 10

The prosthodontist has a control over the anterior determinant as the two

posterior determinants are fixed. The fourth component can be

indirectly altered by modification procedures viz.

occlusal equilibration, restorative procedures,

orthodontic therapy and selective extraction of teeth.

03/05/2023 11

Anatomy of the TMJ

03/05/2023 12

The highlight of anatomy of the TMJ are the condyles which articulate with the temporal bones in the elliptical concavities called the glenoid fossae.

Interarticular fibrocartilages, the menisci lie between the dome shaped concavities and the condyles dividing the joint into upper and lower compartments.Movements in the joint compartments

Upper: Hinge like movement or Rotational

Lower: Anteroposterior gliding or Translation

03/05/2023 13

Variety of MovementsGreat variety of movements seen in mandible.It might appear to lack coordination unless carefully understood.Four important movements of the mandible are :Hinge like

Protrusive

Right or Left lateral while reduction of fibrous foodBennett movement on the rotating condyle

03/05/2023 14

Other movements

Natural or Characteristic movements like that occur during mastication, swallowing, speech and yawning;

Parafunctional movements like clenching, tapping or grinding together

constitute the parafunctional mandibular movements.

03/05/2023 15

Planes and Axes of Mandibular Movements

Planes of the skull: 3 Planes

Horizontal,

Frontal and

Sagittal.

03/05/2023 16

Rotational Centers or Axes of rotation of the mandible: 3 Axes

Transverse, Sagittal andVertical.

03/05/2023 17

Vertical Axis, movement in

lateral direction along the

horizontal plane.

Transverse Axis, movement occurs in a hinge fashion while opening and closing along the sagittal plane.

Sagittal Axis, one condyle moves inferiorly while the other is relatively fixed in Terminal hinge position

03/05/2023 18

A trained individual moves the mandible laterally along the vertical, opens and closes in hinge along the transverse and opens in a non hinge

fashion along the sagittal axis.

03/05/2023 19

Bennett Shift contd.

Bennett’s movement and Bennett’s side shift [Sir Norman Godfrey Bennett, British dental surgeon, 1870-1947]: see LATEROTRUSION.

Laterotrusion : Condylar movement on the working side in the

horizontal plane. This term may be used in combination with terms

describing condylar movement in other planes.

Bennett NG. A contribution to the study of the movements of the mandible. Proc Roy Soc Med (Lond) 1908;1:79-98 (Odont Section)

03/05/2023 20

Four different paths of lateral rotation/ Laterotrusion

• Laterosurtrusion (laterally upwards).• Laterodetrusion (laterally downwards).• Lateroprotrusion (laterally forward).• Lateroretrusion (laterally backward).

03/05/2023 21

The two condyles and the Bennett Shift

•The rotating condyle shifts laterally by about 1 to 4 mm with an average of about 0.75 mm

•The orbiting condyle on the other hand makes one of the four possible types of pathways: 1 Just medially (with no lateral component) 2 Straight line path in case of Progressive shift 3 Lateral shift occurring in the first 2-3 mm of forward movement is termed as Precurrent shift and 4 Shift which occurs before any forward movement of the orbiting condyle is termed as Immediate shift

03/05/2023 22

Bennett Shift

03/05/2023 23

Terminal Hinge AxisTerminal hinge axis: see TRANSVERSE HORIZONTAL AXIS (GPT)

Transverse horizontal axis : An imaginary line around which the mandible may rotate within the sagittal plane. The Terminal Hinge Axis (THA) represents a border position that can be repeated and recorded consistently.

The rotary component lasts only for 12mm after which the mandible is forced to move in translation as the condyles of the mandible slide along the articular eminences.

03/05/2023 24

Border Positions

Definition: Border positions can be defined as the extreme positions of the mandible in any direction in which it moves.(GPT 8)

Physiologic limitations to the movements are through the neuromuscular system which involve nerves, bones muscles, teeth when present and ligaments.

03/05/2023 25

Functional range

Functional Range refers to the full extent over which something is effective. The border positions of the mandible are the only consistently repeatable positions.

03/05/2023 26

Envelope

Envelope of motion in three planes- horizontal, frontal and sagittal.

• It is variable since these movements are influenced by the

1. Size and resistance of the bolus2. Number and size of the teeth3. Excess or lack of saliva4. The musculature and the vigor of the stroke.

03/05/2023 27

Border Positions- Posselt’s envelope of motion

Mandibular Border movements

(I) Shows schematic drawings in A. Sagittal plane B. Horizontal movement area at a definite level of maxillomandibular separation C. Composite of average movement area in the sagittal plane at three different levels.

03/05/2023 28

Posselt’s envelope of motion

03/05/2023 29

03/05/2023 30

Superior contact positions

Anterior border opening

03/05/2023 31

(II) Posterior border : Hinge movement and translation.

Also the relation of condyle to articular eminence

03/05/2023 32

Condyle PathIt is the path travelled by the condyles in the TMJ during the various mandibular movements.Determined by:

1. The bony fossae2. The tone of the muscles 3. The limitations by the attached ligaments4. Shape and the movements of the menisci

03/05/2023 33

Condyle Path cannot be altered by a prosthodontist

It does not follow a straight line but follows the contour of the tissue lined bony surroundings.

It is of a dynamic nature and is not recorded by articulators in which condylar elements travel in a

straight slot or on a flat surface. (Figure)

03/05/2023 34

Hanau Wide Vue

03/05/2023 35

Fully adjustable articulator

Articulators that have individually ground condyle

paths refined to pantographic tracings

record the path in the tracings.(Figure)

Hanau Kinoscope

03/05/2023 36

Pantographic tracings

03/05/2023 37

Carl O Boucher

“It must be recognized that the person operating the instrument is more important than the instrument. If dentists understand articulators and their deficiencies, we can

compensate for their inherent inadequacies”.

03/05/2023 38

Conclusion

A sound knowledge of the

TMJ

Mandibular movements and

Its influences on various maxillomandibular relations is important before we actually record

them.

Prosthodontic research has come a long way in its constant efforts to mimic natural

mandibular movements and incoporate those details into new technology.

References1. Prosthodontic treatment for edentulous patients. Zarb-

Bolender 12th ed, Elsevier.2. Text book of complete Dentures, Rahn and Heartwell 5th

ed. Elsevier.3. Essentials of CD prosthetics, Sheldon Winkler, 2nd ed,

Ishiyaku publications.4. Bennett NG. A contribution to the study of the movements

of the mandible. Proc Roy Soc Med (Lond) 1908;1:79-98 (Odont Section)

5. University of Michigan, school of Dentistry resources 20046. Hanau Spring bow user manual by Whip Mix corp.7. Christensen RL Rationale of the face bow in maxillary cast

mounting. ;J Prosth Dent 9;338, 1960

40