Intermaxillary relations

J F McCord1 & A A Grant2

In this part, we will discuss:

 How to determine FWS

 How to relate the mandible to the maxilla at an appropriate OVD in RCP
 How to record other intermaxillary relations
 A range of articulators

Helpful Hints

1. Determine what freeway space is appropriate for each patient.

2. Confirm RCP is reproducible.
3. Ensure the completed intermaxillary records are sealed together and are
unambiguous.

Abstract

In this section, various methods of recording of intermaxillary relations are

discussed, as is the determination of appropriate occlusal vertical dimension.
Consideration is also given to choice of articulator.

Introduction

Recording the jaw relations is a very important procedure in the production of

complete dentures. An error at this stage can result in dentures that are
uncomfortable, or unwearable, and may even have the potential to produce lasting
damage to many elements of the stomatognathic system.
The intermaxillary relations are, of course, three-dimensional. In order to simplify
the recording of jaw relations it is established practice, based on extensive clinical
practice and current physiological knowledge, to consider three elements. The first
of these is in the vertical plane to establish the amount of jaw separation, while the
second and third relate to the horizontal plane (which is concerned with the
anteroposterior relations) and the coronal plane when one considers the lateral
relations of the jaw.

Individuals who have their natural dentition demonstrate a space between the
occlusal surfaces of the teeth of the opposing jaws when they are at rest and with
the head upright. This space, the freeway space (FWS) or interocclusal distance, is
determined by a balance between the elevator and depressor muscles attached to
the mandible, and the 'elastic' nature of the surrounding soft tissue in a natural
dentition. It is usually measured indirectly by noting the difference between the
resting vertical dimension (RVD) of the face using, for example, a Willis gauge,
and subtracting from this the vertical dimension of occlusion (OVD) with the teeth
in occlusion (Fig. 1).

Figure 1: The difference between RVD and OVD

A similar set of circumstances is considered to exist in the edentulous patient –

although the RVD may differ from that which pertained when natural teeth were
present. It is now known that the RVD is not a stable position throughout life for a
given individual.

However, the RVD may be considered as a factor when determining as to whether

a patient will be able to tolerate wearing dentures without intra-oral tissue damage
occurring. RVD should also be taken into account as an important aspect of the
appearance of the denture-wearing patient. For these reasons it is the starting point
from which the OVD is estimated.1
Because of the role played by the 'elastic' properties of the soft tissue environment
of the mouth, the importance of developing the form of the upper denture as
described in Part 5 is emphasised. This must be done prior to determining the RVD
for the edentulous patient. The weight of the soft tissues attached to the mandible
plays a very important role in the RVD as does the position of the head. Tilting the
head backwards pulls the mandible away from the maxilla, and a forward
inclination pushes the mandible and attached structures closer to the maxilla.

Resting vertical dimension (RVD) measurement

Many methods have been advocated for the measurement of the RVD. These
include various facial measurements, swallowing methods, biting force
measurements, phonetic methods, tactile methods and electromyographic
measurements.

We recommend a combination of some of the above for a simplified clinical

determination of RVD.

Two measuring points are required in the midline of the face – one related to the
nose, and one to the chin. These points must be on sites of minimal influence from
the muscles of facial expression to avoid skin movement, and should be chosen
only after careful observation of the patient seated normally in the dental chair with
the head erect. The measurement is made with the patient in a relaxed and
comfortable position, while wearing the previously developed upper base and rim.
A Willis bite gauge may be used for the measurement, as it incorporates a suitable
scale (Fig. 2) or a pair of dividers and an additional scale can be used.

Figure 2: Willis bite gauge, and a similar instrument, both with an integrated
scale, may be used to measure RVD and OVD
It may be helpful if the patient moistens the lips with his or her tongue and brings
them into light contact prior to recording the measurement. Asking the patient to
swallow and relax the jaws is also a useful method. Verification of the measured
value can be attempted by asking the patient to say the letter 'm' and to hold the
facial expression whilst the measurement is made. The general appearance of the
patient's face and its proportions should also be taken into account. Careful
observation to guard against unwanted skin movement should be maintained
during the recording of measurements.

In conventional techniques, once the RVD has been established, the upper and
lower bases and rims are placed in the mouth after the upper rim has been moulded
(see Part 5). The lower rim is reduced in height (usually – or added to if
undersized), until it contacts evenly the upper rim at a vertical dimension of
occlusion some 2–4 mm less than the established RVD. This provides for a
freeway space of 2–4 mm, and establishes the OVD.
In establishing the height of the lower rim, the relative height of both the upper and
lower rims should be considered. As a practical consideration, an element of
reasonable balance between the two rims is desirable. Excessive height of the
lower rim can have the effect of 'walling in' the tongue causing a resultant unstable
lower denture. On the other hand, deficient depth of the lower rim can result in
poor aesthetics and, further, may result in tongue biting. Conventional wisdom,
however, would indicate that the occlusal plane should be below the dorsum of the
tongue at rest.

Errors in OVD

Provision of an appropriate OVD is important because of the consequences which

can stem from an over- or under- estimation of this value.
Excessive OVD may result in increased risk of trauma to the tissues underlying the
dentures as the absence of a freeway space effectively causes continuous clenching
of the teeth. Painful mucosa over the denture bearing areas and muscle soreness,
particularly associated with the masseter muscle, may become evident. The teeth
are liable to contact (causing clicking) during speech and other speech problems
caused by difficulty in bringing the lips together (eg 'p', 'b' and 'm' sounds) may
occur. Poor aesthetics may be apparent and there is a possibility of
temporomandibular joint dysfunction developing (Fig. 3).

Figure 3: Excessive OVD results in the orbicularis oris muscle group straining
to effect a seal
Where there is an under-estimation of OVD, lack of support of the angles of the
mouth (causing dribbling and possibly angular cheilitis) may be apparent.
Masticatory efficiency may be reduced and poor aesthetics, because of a lack of
adequate support of the lips and cheeks may be seen. Chin protrusion on closure of
the jaws may also occur (Fig. 4).

Figure 4: Insufficient OVD may result in an ageing effect of the patients

Care at this stage is required, and, furthermore, it must not be assumed that the
value selected is immutable, as the generally quoted value for the freeway space
(FWS) is an average one and, as such, it should be appreciated that some patients
may require a larger, or smaller, value. For example, where atrophic mucosa exists
in a middle-aged adult an increased FWS might prevent/reduce trauma to the
residual mandibular tissues (Fig. 5).2

Figure 5: Atrophic mucosa: an efficient masticatory apparatus with an

optimal FWS might result in trauma to the mandibular ridge - intentional
increase in FWS might reduce trauma to the denture-bearing tissues of the
mandibular denture
There are several accepted tests which can be applied to verify the established
OVD. However, occlusal rims are so different from the form of teeth to be used
that it is very difficult to apply tests for suitability of the chosen value at this stage.
Further checks on the established OVD will need to be made at a later stage of
denture production – the trial stage – and will be dealt with in Part 8.

Registering the intermaxillary relations

The generally agreed position for recording the antero-posterior position of the
mandible relative to the maxilla is that of the retruded contact position (RCP). The
reasons for this are first that it is a reproducible position in the edentulous patient.
Secondly, abnormal contact between opposing dentures when set up in other than
the retruded relationship results in denture instability. Next, the apparatus used for
reproducing relevant jaw movements (the articulator) operates from the retruded
position, and abnormal temporomandibular joint activity may result from patients
attempting to accommodate incorrect occlusal relations.3

Following adjustment of the occlusal rims to the selected OVD, the rims should be
inserted into the mouth and the patient persuaded to close gently with the mandible
in the retruded jaw relationship. The word 'bite' should not be used, as this suggests
to the patient that forceful closure is required and will result in a mandibular
position that is protrusive.
A number of methods have been suggested to assist the patient to achieve retrusion
of the mandible. Some patients have the capacity to relax the muscles attached to
the mandible so that the operator can readily move the mandible up and down as it
rotates about the condyles. In those circumstances, the mandible is in the retruded
position, and can be guided there during the registration procedure. Other patients
are able to retrude the mandible when the tongue is curled back in the roof of the
mouth to feel the posterior border of the upper base, or a shallow ridge of wax
placed on the palatal area of the base posterior to the first molar region.

In our opinion, the most positive and successful method is by means of the Gothic-
arch (or arrowhead) tracing method, as it readily identifies the most retruded
position of the mandible relative to the maxilla from which lateral excursions can
be made.

Methods of registration
Recording the retruded contact position (RCP) requires upper and lower rims to be
fixed in position with the mandible in its most retruded position and with the jaws
separated by the established OVD.
A variety of methods for securing a record of the retruded jaw relations (RJR) have
been used with varying degrees of success.
These include:

 Wax squash bite (and its predecessor, the T-block system) (Table 1)
 Wax rims or 'Manchester' blocks (Table 1)
 Intra-oral tracing (Gothic-arch tracing) (Table 1)
 Extra-oral tracing.

Wax squash bite

The wax squash bite involves placing a horse-shoe shaped roll of softened wax
between the upper and lower rims and having the patient close the jaws together.
The lower rim is first reduced in height to provide space for the wax. Results using
this method are uncertain because of the lack of control of the vertical dimension,
the common difficulty of obtaining mandibular retrusion, and the fact that the
record takes no account of mandibular movements other than the final act of
closure (Fig. 6). In addition, if the wax wafer is not uniformly softened throughout
its length, an unstable relationship with the underlying tissues is recorded. An
earlier version of this method was the T-block method, in which a T-shaped wax
form was used instead of the simpler horseshoe form (Fig. 7). The 'horizontal'
portion was placed between the rims while the 'vertical' part that protruded
anteriorly was intended to be moulded to provide a form of contouring of the labial
aspects of the rims. This method fell into disuse because of the arbitrary nature of
the moulding procedure that also induced the patient to assume non-RCP posturing
of the jaw, as well as having the same defects as those mentioned above.

Figure 6: Typical example of squash bite - insufficient definitions of denture

geometry and form are prescribed

Figure 7: T-block precursor to the squash bite and popular at the onset of the
NHS
Wax rims
The conventional method that has a higher degree of success also involves the use
of wax interposed between the rims to secure a registration. When the upper rim
(aesthetic control base [ACB]) has been formed, and prescribed to suit the patient,
the lower rim is placed in the mouth and trimmed until it contacts the upper rim
evenly in RCP, at the selected OVD (Fig. 8). This is done by selectively removing
points of first contact. These large wax rims may pose problems in inexperienced
hands. Even in experienced hands it is not always easy to detect premature contacts
along the lengths of the rims bilaterally.

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Figure 8: Conventional upper and lower rims

For these reasons, a simplified lower rim has been developed in the University
Dental Hospital of Manchester. It contains several elements incorporated to ensure
that the carefully established OVD is maintained, and that the bases are maintained
in stable relationship to the underlying tissues during the procedure. The lower
base has attached to it two pillars of wax which are situated in the region of the 2nd
premolar/1st molar teeth positions ( Fig. 9a and b). When the contacts, bilaterally,
are even at the selected OVD, the rims may be sealed with registration paste or
other such medium as regularly used.
Figure 9a: 'Manchester' rims - to simplify complete denture registration
technique;

Figure 9b: Addition of carding wax to the labial segment of the lower rim can
help create a functional modelling of the denture space anteriorly

This method using pillars attached to the lower base – which we call the
Manchester block method – provides control over the OVD, ensures a stable
relationship between the bases and the underlying tissues, and also provides a
record that can be simply returned to the mouth to verify its accuracy. To obtain a
functional impression of the labial component of the lower arch, carding wax,
Plaster of Paris or PVS putty may be attached to the labial aspect of the rim and a
closed-mouth impression used to determine the anterior denture-spaced form.

However, the drawbacks of this procedure comprise uncertainty of achieving the

most retruded mandibular position, as well as a lack of information on eccentric
mandibular movements.
Intra-oral tracing

Our preferred method of obtaining a consistent position of retrusion together with

recognition of mandibular movement other than the final point of closure, is by
means of an intra-oral tracing – often referred to as a Gothic-arch tracing. This
method is based on rotation about the condyles when lateral mandibular excursions
are made. When the mandible moves to the left from a central position, it rotates
about the left condyle, and similarly, a right lateral movement causes rotation
about the right condyle. Between each lateral excursion, the condyles assume their
most retruded position (Fig. 10).

Figure 10: Line drawing of occlusal view of mandible and arcs of movement
about the condyles

This technique uses two pieces of apparatus, one for each arch, both mounted on
rigid stable bases, usually made of light-cured polymethylmethracylate (PMMA).
The upper apparatus comprises a metallic plate that spans the maxillary arch. The
lower has a bar containing an adjustable central-bearing screw (1mm thread)
mounted on wax or compound 'pivots' added to a light-cured PMMA base (Fig.
11). The lower plate lies over the most stable pivotal areas of the arch. The
adjustable central-bearing screw is made to contact the upper plate at right angles
and at the selected OVD. The bases are adjusted so that no contact between them
can occur and the patient can make lateral mandibular excursions with contact of
the central-bearing pin on the upper plate only. The patient is requested to swallow,
to indicate a 'central' (RCP) position, then asked to make three protrusive
movements before returning to RCP. From RCP the patient is asked to make three
left lateral excursions and then to return to RCP. Finally, the patient is asked to
perform three right lateral excursions before returning to RCP. The patient should
then be familiar with the two pieces of apparatus and the practitioner can then
proceed to record the tracing. This is done by coating the upper plate with, eg ink
from a felt tipped pen and then asking the patient to replicate the protrusive and
lateral movements. The alternate lateral jaw movements scribe on the upper plate
two arcs of rotation which intersect in a position corresponding to RCP. Clearly, it
is from this point that an intersection (arrowhead) with the protrusive movement is
also traced ( Fig. 12a). To validate this position a perforated perspex cover slip is
positioned with the perforation over the arrowhead and waxed in place. The patient
is then asked to swallow and confirmation of RCP is achieved by the central
bearing screw engaging the perforation ( Fig. 12b).

Figure 11a: Apparatus for measuring Gothic arch tracing. Upper base plate;

Figure 12a: Typical Gothic arch or arrowhead tracing of the mandibular

movements
Figure 12b: Perspex locator placed over the arrowhead point to confirm
reproducibility of RCP

Full size image (21 KB)

This fixed registration records the vertical and antero-posterior intermaxillary

relations. To record the coronal relationship, Plaster of Paris or PVS putty is then
placed between the bases and the central-bearing screws to ensure an unambiguous
relationship ( Fig. 12c).

Figure 12c: PVS putty moulded between the upper and lower bases to provide
a coronal relationship
 F

Extra-oral tracing
The extra-oral tracing is somewhat similar to that of the intra-oral, except that the
tracing apparatus is attached to plates that protrude between the lips. It is not
considered to be as accurate as that of the intra-oral method for edentulous patients
because the protrusion of the recording apparatus is so far forward of the pivotal
area that tilting and/or deflection of the bases is likely.4 In addition, as this
technique is not universally taught worldwide, it will not be described further.

Further considerations
When these three-dimensional intermaxillary registrations have been completed,
they will be sent to the laboratory along with the ACB and facebow transfer to be
articulated. While teeth have still to be selected (see Part 7) it is appropriate to
consider briefly, the types of articulator on which the casts are to be mounted, as
the proper adjustment of these may require additional records.

Articulators for complete dentures

The usage of articulators to enhance clinical practice has been the subject of a
recent review5and thus we shall confine our discussion to simple basic points.
Articulators in common use for the production of complete dentures comprise (Fig.
13):

 Simple hinge (plane line)

 Moveable, fixed condylar path
  Semi-adjustable.

Figure 13a: Simple hinge articulator.

The simple hinge articulator allows the construction only of a centric occlusion,
whereas the fixed condylar path instrument allows some approximate lateral and
protrusive occlusion to be developed. The semi-adjustable articulator allows the
establishment of more accurate or customised lateral and protrusive as well as
centric occlusion.
Few simple hinge articulators have provision for accepting a facebow record so
that this further limits their usefulness. Both the fixed condylar and the semi-
adjustable types will accept facebow records, and, in addition, the more adjustable
instruments accept protrusive and lateral interocclusal records to allow full benefit
of their capability. Facebows improve the accuracy of occlusal development of
these articulators. Facebows were discussed in Part 6.

With the maxillary cast mounted via a facebow transfer and the mandibular arch
related to the maxillary arch via the gothic arch tracing, the development of
satisfactory eccentric (lateral and protrusive) occlusion and articulation is possible.
In addition, small changes (2–3 mm) in the vertical dimension may be achieved on
the articulator, should this be required, without the need for a new registration.

References
1. Zarb G A, Bolender C L, Hickey J L, Carlsson G E. Boucher's
Prosthodontic Treatment 10th ed. pp 272–281. St Louis: Mosby, 1990.
2. Gonzalez J B. Preventing and Treating Abused Tissue. in Essentials of
Complete Prosthodontics 2nd ed. Winkler S (ed) pp81–87. St Louis:
Mosby, 1988.
3. Grant A A, Johnson W. Introduction to Removable Denture
Prosthodontics 2nd ed. pp61–67. Churchill Livingstone, 1992.
4. Zarb G A, Bolender C L, Hickey J L, Carlsson G E. Prosthodontic
Treatment 10th ed. pp283–295. St Louis: Mosby, 1990.
5. Cabot L B. Using articulators to enhance clinical practice. Br Dent
J 1997; 184: 272–276.

1. Head of the Unit of Prosthodontics, University Dental Hospital of

Manchester, Higher Cambridge Street, Manchester M15 6FH
2. Emeritus Professor of Restorative Dentistry, University Dental Hospital of
Manchester, Higher Cambridge Street, Manchester M15 6FH