1. Jaw Relations
Dr. Hussein KH Almaliky
Third visit in the complete denture construction (clinical step) is to register the jaw
relations and transfer these relations to the articulator. Three types of jaw relationships
will be discussed (maxillo-tempromandibular joint relationship, centric jaw relation,
protrusive and lateral relationships).
Orientation relations
It means these relations that orient the maxilla to the cranium in such way that the
mandible is kept in its posterior position to the cranium can rotate around an imaginary
transverse axis passing through as near the condyles. This axis can be located by means
of the face-bow.
Face-bow transfer: it is a caliper-like device used to record the patient's maxilla/hinge
axis relationship and to transfer this relation to the articulator during mounting of the
maxillary cast.
Hinge axis: it is an imaginary line between the mandibular condyles around which the
mandible can rotate without translator movement. This term is now transferred to as the
transverse horizontal axis. If the face-bow transfers procedure properly done, the arc of
the closure on the articulator should duplicate that exhibited by the patient.
The face-bow transfer should be used when:
1. Cusped posterior teeth are selected.
2. Balanced occlusion in eccentric positions is desired.
3. Interocclusion check records are used for verification of the jaw relationships.
4. The occlusal vertical dimension is subjected to change.
Some authors reported that if the cuspless teeth and a monoplane occlusion are selected, a
face-bow transfer is unnecessary. Other recommends the use of the face-bow, even for
the cuspless teeth to provide more accurate placement of the casts in the articulator than
would be obtained by simple placing arbitrarily.
There are 2 types of the face-bow:
Kinematic face-bow: it is initially used to accurately locate the hinge axis. It is attached
to a clutch which is in turn attaches to the mandibular teeth. As the mandible makes
opening and closing movement, the condyles styli move in an arc. The kinematic face-
bow generally not used for complete denture fabrication because the resiliency of the soft
tissues makes precise location of the rotational centers almost impossible.
Arbitrary face-bow: there are several varieties of arbitrary face-bows, all are based on an
average location of the hinge axis, and it is located over measured points on the face or
by some type of earpiece. One average measurement, placing the rotational point 13 mm

2. anterior to the distal edge of the tragus of the ear, along a line from the superior-inferior
center of the tragus to the outer acanthus of the eye. The condylar styli of the face-bow
are then placed directly over the dots. This technique is used with Hanau H-2 and
Dentatus articulators.
Face-bow registration
True hinge axis must be located on a fully-adjustable articulator.
Arbitrary hinge axis is used on a semi-adjustable articulator, and this is determined by the
manufacturer of the face-bow and articulator system.
In order to understand the maxillomandibular relation and the concepts of the occlusion,
we have to study the mandibular movements. Recording the mandibular movements is
affected by TMJ, muscular involvements, neuromuscular regulation of the mandibular
motion and ligaments.
Horizontal jaw relations
It is the relation between the mandible and the maxillae in the anteroposterior direction
and media lateral direction which includes:
1) Centric jaw relation: a maxillomandibular relationship in which the condyles articulate
with the thinnest avascular portion of their respective disks with the complex in the
anteroposterior position against the slops of the articular eminence. The poison is
independent of tooth contact.
2) Eccentric jaw relation: any position of the mandible other than centric. It includes:
A. Protrusive jaw relation: resulting from protrusion of the mandible when the
condyles move downward, forward.
B. Lateral relation: the relation of the mandible to the maxilla in opposition to the left
and right of the midsagittal plane.
How does the TMJ move during function?
Replaced dentures must work in harmony with the patient's TMJ, which consist of the
condyles that articulate with the temporal bones and are located in the elliptical concave
depressions called the glenoid fossae in which they travel forward, from side to side and
in some instances slightly backward.
Between the dome-shaped concavities in the temporal bones and the condyles are
interposed the interarticular fibrocartilages, the meniscus, which are attached at their

3. margins to the articular capsules. The meniscus divides the joint into upper and lower
compartments. Normally, the movements in the upper compartment is chiefly gliding
anteroposterior motion in which the condyles and the cartilage move as a unit, while the
movement in the lower compartment is hinge-like; therefore, the condylar paths are the
controlling factor in the mandibular movements. These movements are results of action
of muscles of mastication, suprahyoid and infrahyoid muscles.
The muscles that control and move the mandible may be considered in three groups:
1. Closing muscles.
2. Guiding muscles.
3. Opening muscles.
Closing muscles include:
A. Masseter muscle (muscle of mastication).
B. Temporal muscle.
C. Medial pterygoid.
The direction of their fibers is essentially vertical. Their origin is superior to their
insertion on the mandible.
Guiding muscles include:
Lateral pterygoid muscles (muscle of mastication).
The action of these muscles is to pull the mandible forward if they both contract
simultaneously, or to pull the mandible laterally if they contract individually.
Opening muscles include:
A. Suprahyoid muscles.
B. Infrahyoid muscles.
Their origin below the mandible and their action is downward and backward.
The teeth cannot occlude or disclude without the action of 4 paired muscles of
mastication that make it all possible.
Mandibular movements
The mandibular movements are related to 3 planes of skull (frontal, horizontal and
sagittal). The point of intersection of these planes is called center of action.
Basic movements of the mandible include:
1) Rotational movements: these movements take place in the lower compartment of the
TMJ between the superior surface of the condyles and the inferior surface of the articular
disc. Centric relation which is called uppermost, rearmost, midmost or most posterior
position is purely rotary movement about the transverse horizontal axis.

4. 2) Translatory movements: they are also called gliding movements of the mandible, they
take place in the upper compartment of TMJ between the superior surface of the
meniscus and the inferior surface of the glenoid fossa, they are called mandibular border
movement.
Functional movements: they include combinations of rotation and translation movements:
A. Opening and closing movements.
B. Symmetrical forward and backward (protrusion and retraction) movements.
C. Asymmetrical sidewise or lateral shift movements.
Opening and closing movements are considered the most important mandibular
movements and they are divided into:
1) Habitual movement.
2) Border movement.
They take place in 3 dimensional limits. The mandible can move about 10 mm laterally
and open about 50-60 mm. It protrudes approximately 9 mm and retrudes about 1 mm.
These limits are known as border movements of the mandible. It is the most extreme
position to which the jaw is able to move in any direction. The border positions are
limited by nerves, bones, muscles, teeth (if present) and ligaments.
Border movements are subdivided into:
A. Anterior border movement: it appears as one arc in the sagittal plane. The condyles
rotate and translate in this movement.
B. Posterior border movements: it appears as two arcs in the sagittal plane. The condyles
rotate in the opening and closing up to the point of terminal hinge opening and translate
to the point of maximal opening.
Sagittal plane movements
A map of the boundary of the movements of the mandible when viewed from one side of
the head, it is tracing of the maximum vertical and anteroposterior movements of the
mandibular central incisors. It includes:
1. Maximum intercuspation or centric occlusion (CO), this border position is usually
defined as that point where the teeth best interdigitate.
2. If the mandible is retruded farther to its posterior, most superior and most terminal
hinge position, the limits of movement and the border position are determined by
structures of the TMJ. Some have also referred to this position as centric relation (CR).

5. Maximum hinge opening (MHO)
Co ± centric occlusion
B-D ± posterior border movement (two arcs)
E-D ± anterior border movement (one arc)
PR ± postural rest position
From D to E ± protrusive closure
Four movements of prime importance to complete denture service are:
1) Hinge-like movement that is used in opening and closing the mouth for the
introduction of food.
2) Protrusive movement that is used in the grasping and incision of food.
3) Lateral a (right or left) movement that is used in the reduction of fibrous as well as
other types of food.
4) Bennett movement which is the bodily side shift of the mandible which when occurs
may be recorded in the region of the rotating condyle on the working side. This
movement includes:
A. Functional mandibular movements that include all the natural or characteristic
movements occurring during mastication, swallowing, speech and yawing.
B. Parafunctional movements that occur in during clenching, tapping or grinding the
teeth.
Jaw registration of condylar movements
It is a recording of the paths/positions of the condyles during border movements that are
recorded in order to program the articulator to simulate the patient's condylar movements.
It can be recorded by:
1. Pantographic tracing to program a fully-adjustable articulator.
2. Interocclusal records to program a semi-adjustable articulator.

6. Types of articulators:
Class I ± a simple holding instrument, capable of accepting a single static registration;
vertical motion is possible (nonadjustable).
Class II ± an instrument that permits a horizontal as well as vertical motion but does not
orient the motion to the TMJ.
Class III ± an instrument that simulates the condylar pathways by using averages or
mechanical equivalents for all or part the motion. It allows for orientation of the casts
relative to the joints and they may be arcon or nonarcon instruments (semi-adjustable).
Class IV ± an instrument that accepts three dimensional registrations. It allows for
orientation of the casts relative to the joints and simulation of the mandibular movements
(fully-adjustable).