factors influencing centric relation/ orthodontic straight wire technique

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FACTORS INFLUENCING
CENTRIC RELATION
RECORDS IN EDENTULOUS
MOUTHS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

INTRODUCTION
DEFINITION OF CENTRIC RELATION AND
CENTRIC RELATION RECORD
SIGNIFICANCE OF CENTRIC RELATION
CLASSIFICATION OF DIFFERENT METHODS OF
RECORDING CENTRIC RELATION.
• ARTICLE
• CONCLUSION.
• REFERENCES

INTRODUCTION:
Centric relation is the starting point of occlusion. If we were asked to
select the one arch to arch relationship that is most important to the
comfort, function and health of the gnathostomatic system, we would
have to say without reservation “ Centric relation”.

CENTRIC RELATION:
Acc. to GPT-8
The maxillomandibular relationship in which the condyles
articulate with the thinnest avascular portion of their
respective disks with the complex in the anterior-superior
position against the slopes of the articular eminences. This
position is discernible when the mandible is directed superior
and anteriorly and is restricted to a purely rotary movement
about the transverse horizontal axis.
Acc. to Boucher:
The most posterior relation of the lower to the upper jaw from
which lateral movements can be made at any given degree of
jaw separation. www.indiandentalacademy.comwww.indiandentalacademy.com

CENTRIC RELATION RECORD
Acc. to GPT-8
It is a registration of the relationship of the maxilla to the
mandible when the mandible is in centric relation. The
registration may be obtained either intraorally or extraorally.

SIGNFICANCE OF CENTRIC RELATION:
 Artificial teeth are best set to occlude evenly at centric relation.
 This position is more definite than the vertical relation and
is independent of presence or absence of teeth.
 It is recordable and reproducible over a period of time.
 Centric relation serves as a reference relation for establishing
occlusion.
 When centric relation and centric occlusion of natural teeth do
not coincide, the periodontal structures around the natural teeth
are endangered and also there is instability of the dentures and
the patient will be subjected to pain and discomfort.www.indiandentalacademy.comwww.indiandentalacademy.com

Errors in mounting the casts on the articulator can be
detected, when centric relation is used as a horizontal
reference position.
An accurate centric relation record properly orients the
lower cast to the opening axis of the articulator and the
mandible.
Accurately recorded centric relation when transferred to the
articulator, permits proper adjustments of the condylar
guidance for the control of eccentric movements of the instruments.

CLASSIFICATION OF DIFFERENT
METHODS OF RECORDING CENTRIC
RELATION
DIRECT RECORDING
GRAPHIC RECORDING
FUNCTIONAL RECORDING
CEPHALOMETRICS

DIRECT RECORDING
DIRECT RECORDING
Teeth & Occlusion
as predominating factor
Supporting tissues
as predominating factors
Wax
Compound
Wax
Compound
PlasterPlaster

GRAPHIC RECORDING
GRAPHIC RECORDING
Extra Oral
Graphic Recording
Intra Oral
Graphic Recording
Plaster Recording
Graphic recording
Graphic recording
With indicators

FUNCTIONAL RECORDING
FUNCTIONAL RECORDING
MANDIBULOGRAPHING
PHONETIC
RELATOR

FACTORS INFLUENCING CENTRIC
RELATION RECORDS
1.The resiliency of the supporting tissues.
2. The stability of the recording bases.
3. The temporomandibular joint and its associated
neuromuscular mechanisms.
4. The character of the pressure applied in making the
recording.
5. The technique used in making the recording and the associated
recording devices used.www.indiandentalacademy.comwww.indiandentalacademy.com

6. The skill of the dentist.
7. The health and cooperation of the patient.
8. The maxillomandibular relationship.
9. The posture of the patient.
10. The character or size of the residual alveolar arch.
11. The amount and character of the saliva.
12. The size and position of the tongue.

THE RESILIENCY OF THE SUPPORTING TISUUES:
Hanau has pointed out the “ resilient and like effect” Realeff, of the
supporting tissues as a chief source of error in registering
maxillomandibular relationships.
In order to minimize this factor, Hanau & Wright advocated that the
registration of centric relation should be made under minimum pressure.

STABILITY OF RECORDING BASES:
It is essential that both the retention and stability should be good if
accurate results are to be obtained.
STABILITY: Is the ability of a denture to remain stationary in relation to
the surrounding musculature and opposing occlusal forces. This is
unobtainable with complete dentures owing to the slight compressibility
of even normal mucosa when subjected to masticatory pressure, but a
denture is considered to be clinically stable if it remains stationary in
relation to its bony support within the bounds of compressibility of
normal mucosa.

THE TEMPOROMANDIBULAR JOINT & ITS ASSOCIATED
NEUROMUSCULAR MECHANISMS:
The patients with neuromuscular disorders
Senile patients
THE CHARACTER OF PRESSURE APPLIED IN MAKING
THE RECORDING:
Trapozzano stated that the use of the central bearing point will
produce equalization of pressure. Equalization of pressure with the
central bearing point will result only if two conditions are present:
1. If normal ridge relation exists & the central point of bearing can be
placed in the center of the maxillary and mandibular foundation bases.
2. If mucosal resiliency is extremely slight.

According the available dental literature, most clinicians were in
agreement that the amount of pressure exerted during registrations was
a major influencing factor on reliability of the various recordings.
The literature, however considered no quantitative experimental
evidence regarding the influence that the different factors played on
the reliability of various techniques of registering centric relation.
THE TECHNIQUE USED IN MAKING THE RECORDING
AND THE ASSOCIATED RECORDING DEVICES USED:
Payne has called attention to the fact that the introduction of any
apparatus into the mouth may lead to discrepancies. “The more
equipment we put into the oral cavity, more difficult it is for the
patient.”

THE SKILL OF THE DENTIST:
The adaptability of the dentist to a particular technique and his ability to
gain mastery over that technique.
THE HEALTH & CO-OPERATION OF THE PATIENT:
The physical and mental health of the patient determines the extent to
which the patient co-operates with the dentist.
MAXILLOMANDIBULAR RELATIONSHIP:
In Class II & III conditions, which are associated with unequal jaw sizes
would create problems in recording centric relation.

Wright described the four factors, he believed affected the accuracy of
records:
• Resiliency of the tissues.
• Saliva Film
• Fit of the bases
• Pressure applied.

ARTICLE
This study was carried out to evaluate the effect of
various factors on the reliability or duplicability of two
methods used in recording centric relation.
The wax recording and the intraoral tracing procedures
were the two methods studied.

EXPERIMENTAL PROCEDURE
Thirty-five edentulous patients were selected at random.
Stabilized recording bases made from the reinforced shellac
base plates with zinc oxide and eugenol paste linings over tin
foil that was burnished on the final casts were prepared for each
patient.

An evaluating tripod was used
to record the amount of
deviation in each recording
procedure. It consisted of a
tripod instrument similar to the
Hooper duplicator, modified to
facilitate the accurate recording
of changes exhibited by various
registrations.
A Hanau type of mounting ring
was attached to the upper
element by means of a center
bolt, machined so that one full
revolution would raise or lower
the ring by 1.0 mm.

The three legs of the tripod
were tipped with pointed tool
steel cylinders, which could be
moved up and down
independently.
The base of the instrument had
a mounting table and three
projecting arms with 1.0 mm.
grids inscribed on the steel
squares fixed at their
extremities.
The exact center of the grid was
pitted and the pointed ends of
the tripod fitted exactly in the
center of each grid.www.indiandentalacademy.comwww.indiandentalacademy.com

The variations noted during the experimental procedures were
recorded on millimeter graph paper.
Any change in the original occlusal vertical dimension was noted
by adjustments needed on the center adjustment screw whereas the
registration of so-called ‘‘tilting’’ where one or more legs did not
touch the grid was recorded by means of a machinist’s ‘‘filler
gauge’’ placed between the leg of the tripod and the grid.
A geometric projection was accomplished to transpose the values at
each leg of the tripod to a single value of deviation at the exact
center of the evaluating tripod. These single ‘‘center’’ values were
used in the statistical analysis.

WAX RECORD PROCEDURE:
Variables tested
1. Consistency of wax
a. Recording waxes of different hardnesses
b. Variation in degree of softness of wax on both sides
c. Variation in degree of softness of wax on each side
2. Amount of occlusal contact
a. Recording wax over the entire ridge
b. Recording wax in posterior portion
(1) with anterior freedom
(2) without anterior freedomwww.indiandentalacademy.comwww.indiandentalacademy.com

PROCEDURE:
Hard wax occlusion rims were prepared on the upper and lower
stabilized base plates utilizing a previously determined occlusal
vertical dimension which was held constant throughout the
experimental procedure.
The approximate center of the lower arch was determined
geometrically, and a hole was made through the lower cast with a
No. 10 round bur.
The lower cast was mounted to coincide with the center of the
evaluating tripod at a point equidistant from the recording points or
center points of the arms of the instrument.
The upper cast was mounted in the instrument by means of a
‘‘control’’ standard wax record technique.

The mandibular occlusion rim was shortened approximately 2 mm,
and keys were cut into the upper and lower occlusion rims.
Two small rectangular pieces of softened beeswax were then placed
in the molar and bicuspid regions of the lower occlusion rim.
These were pooled with a wax spatula and tempered in warm water.
Extreme care was taken to make certain that they approached the
same consistency.
The patient was asked to raise and retrude the tip of his tongue and
touch the posterior palatal edge of his upper baseplate.
He was then instructed to close until the previously determined
occlusal vertical dimension was reached.

The vertical dimension of occlusion was checked by means of nose
and chin guide points. No contact existed in the anterior region
from cuspid to cuspid. This record was used to mount the upper
cast.
Three more records were made in a similar manner, and the
deviations were recorded.
The mean and standard deviation of the values were calculated for
the control wax recording procedure. They were used to compare
with the standard deviations of the results obtained when each
variable was introduced.
Five patients were used for each variable studied, and triplicate
records were obtained.
The order of presentation was carefully randomized so as to
preclude the influence of learning and fatigue.www.indiandentalacademy.comwww.indiandentalacademy.com

This is a bar graph
illustrating the
standard deviation of
the records obtained
by means of various
wax recording
procedures.
The means, standard
deviations and critical
rates were evaluated.

The control wax recording
method showed the least
variability when compared
to the records obtained
with the use of a
moderately hard or a hard
wax for registration.
There was significant
difference between records
when soft wax was pooled
on both sides rather than
when it was slightly
warmed on one or both
sides.

The soft wax procedure
showed the least variation
when the occlusal contact
was small and limited to
the bicuspid and molar
regions on each side,
together with a small
amount of freedom in the
anterior region.
Variation between records
increased when contact
existed over the entire
ridge in soft wax, and also
when there was posterior
contact without anterior
freedom.

VERTICAL DISCREPANCIES IN WAX
RECORDING PROCEDURES
The control soft wax recording
procedure showed the least amount
of vertical discrepancies (17 per
cent); whereas the moderately hard
and hard wax showed vertical
discrepancies amounting to 27 per
cent and 40 per cent, respectively.
When the recording material was
softened but slightly or un-evenly,
the percentage of change was 37
per cent and 23 per cent.
This indicated that the vertical
equalized relationship was greatly
influenced by the degree of
softening of the recording wax.

It was also apparent that the
percentage of records showing
vertical discrepancies was
influenced by the amount of
occlusal contact.
Vertical discrepancies were
observed in 67 per cent of the
records where occlusal contact
was made in soft wax over the
entire rim; 80 per cent when
anterior contact existed on
occlusion rims formed of hard
wax; but, only 17 per cent when
the recordings were made in soft
wax without anterior contact.

INTRAORAL TRACING PROCEDURE
VARIABLES TESTED
1. Location of the central bearing point
a. Bearing point centralized to tracing plate
b. Bearing point located 6.0 mm. anterior to the center
c. Bearing point located 6.0 mm. posterior to the
center
d. Bearing point located 6.0 mm. lateral to the center
2. Inclination of the central bearing point
a. Perpendicular to the tracing plate
b. Inclined 15 degrees posteriorly
c. Inclined 15 degrees anteriorly
d. Inclined 15 degrees laterallywww.indiandentalacademy.comwww.indiandentalacademy.com

3. Inclination of the tracing plate
a. Tracing plate parallel to the bearing portions of the
lower posterior ridge
b. Tracing plate inclined 15 degrees anteriorly
c. Tracing plate inclined 15 degrees posteriorly
d. Tracing plate inclined 15 degrees laterally
4. Amount of pressure exerted
a. Extremely light contact
b. Deliberate heavy contact
5. Type of ridge
a. Well-developed
b. Flat

PROCEDURE:
The lower cast was mounted as previously described.
The upper cast was mounted with the use of a control intraoral
tracing procedure.
This consisted of placing a tracing plate parallel to the bearing
portion of the lower ridge.
An effort was made to divide the maxillomandibular space evenly.
The central bearing point was positioned as close as possible to the
center of the lower bearing area. It was also placed perpendicular to
the tracing plate. www.indiandentalacademy.comwww.indiandentalacademy.com

A thin film of blue inlay wax was coated on the rigid mandibular
tracing plate.
The patient was instructed to exert light pressure and to move his
jaw from one side to the other with an occasional protrusive
movement.
In this way a needle-point tracing was obtained.
When a definite apex was scribed, an aluminum disc with a small
hole in the center was placed so that the apex of the needle-point
tracing coincided with the center of the hole. This disc was luted in
position with sticky wax, and the recording rims were returned to
the patient’s mouth.

He was then requested to engage this small hole in the disc with the
central bearing point and to hold the two recording rims together as
lightly as possible.
Quick setting impression plaster was then injected between the two
recording rims from a plaster syringe. The plaster was allowed to
set, and the recording rims were removed.
The initial mounting was then made with the aid of this recording.
Three other recordings were made in the same manner.
The mean and standard deviation of the values were calculated for
each procedure used.
Again 5 patients were evaluated for each variable studied.www.indiandentalacademy.comwww.indiandentalacademy.com

RESULTS:
Standard deviations were computed
for each of the variables studied
The control mounting procedure
showed the least amount of deviation,
and the variation between records
increased with the introduction of
variables. It was apparent that the
control intraoral tracing procedure
evidenced the least variation. It was
also apparent that the records which
showed the greatest variation were
obtained when the central bearing
point was inclined posteriorly.

The influence of the location of
central bearing point was
studied in subjects with different
types of ridges: flat and well-
developed.
The group with flat ridges
showed slightly more variation
than did the subjects with well-
developed ridges.
The laterally displaced central
bearing point resulted in greater
variability in patients with flat
type ridges than in those with
well-developed ridges.

This is a bar graph illustrating
the percentage of records that
show vertical discrepancies.
When the central bearing
point was located laterally,
anteriorly, or posteriorly, the
percentage of records
showing vertical
discrepancies amounted to 67,
73, and 57 per cent,
respectively.

Inclination of the central
bearing point resulted in
changes of 40 per cent
(lateral), 40 per cent
(anterior), and 20 per cent
(posterior).
The percentage of records
showing vertical
discrepancies was 40, 20, and
40 percent with the lateral,
anterior, and posterior tilting
of the tracing plate.

The percentage of records
that showed vertical
discrepancies amounted to 57
per cent when the
registrations were made under
deliberate heavy pressure
exerted by the patient.
When minimal holding
pressure was used, none of
the 15 records obtained
showed detectable vertical
discrepancies.

The placement of the central
bearing point in the lateral
and posterior position
resulted in vertical
discrepancies in 53 and 60
per cent of the records
studied.
In well-developed ridges,
vertical discrepancies of 80,
33, and 46 percent were
shown with lateral, posterior,
and anterior placement of the
central bearing point.

DISCUSSION:
The purpose of this study was not to evaluate the accuracy of one
recording procedure over another, but to emphasize the fact that
there are many variables which can enter into any recording
procedure when care is not taken in its execution.
According to the results of this study, it is not desirable to exert any
closing pressure in the anterior region and the recording medium
should be placed only in the bicuspid and molar regions of the
residual ridge. The softer the wax, and the more nearly
homogeneous both sides were made, the more duplicable the
recording procedure became.
In the intraoral tracing procedure, the data seemed to indicate that
the duplicability was greatly influenced by the position of the
central bearing point, the inclination of the central bearing point,
and the relative tilt of the tracing plate. It was also influenced by the
amount of closing pressure exerted by the patient.www.indiandentalacademy.comwww.indiandentalacademy.com

CONCLUSION:
Many prosthodontist feel that recording centric relation is the most
difficult, yet the most important step in treating edentulous patients
with complete dentures.
“In normal cases, the occlusion, the temporomandibular joints, the
bone, the soft tissues and the musculature all produce the same
relationship to each other and any one of the many registrations
techniques may be used.” A certain technique might be required for
an unusual situation or a problem patient.
In the final analysis, the skill of the dentist and the co-operation of
the patient are probably the most important factors in securing an
accurate centric relation record.

REFERENCES:
1. Boucher’s prosthodontic treatment for edentulous patients, 11th
edition.
2. Fenn, Liddelow & Gimson’s Clinical dental prosthesis, 3rd
edition.
3. Complete denture prosthodontics. Dr. John Joy Mannapallil.
4. JPD 1957, Vol. 7(6) : 771-786.
5. JPD 1982, Vol. 47(2) : 141-144.
6. JADA 1923, Vol. 10 : 776-784.
7. JADA 1939, Vol. 26 : 542-555.
8. JADA 1929, Vol. 16 : 199-223.
9. JPD 2004, Vol. 91(3) : 206-209.
10. JPD 1955, Vol. 5 : 325-332.www.indiandentalacademy.comwww.indiandentalacademy.com

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