Registering Centric Relation
Dr. Muaiyad. Malimoud. Buzayan, BD8
AF AAMP “SA
Centric relation: Centric occlusion:
1-there is no teeth intercuspation. 1-Sometimes, there is maximum
2-it’s a maxillomandibular relation, (bone intercuspation.
to bone relation). 2-teeth to teeth relation.
3-from which lateral jaw movement can 3-there is no free way space.
4-the condyles are in the most retruded
(recently became mast Gloomy of
hustbadanticzs) unstrained position in the
Variability of rest position:
Short term variables that affect the position. the RVD is :
1. Head posture: increased by tilting head backward
2. Stress: decreased by stress
3. Pain decrease by pain in the mouth or belong to it. The amount of
jaw separation at rest is reduced by pain
4. Drugs such as adrenalin and caffeine. and emotional stress
5. Respiration: increases during inspiration
Long term variables of the vertical dimension:
1. Age and health status
A decrease in the rest vertical dimension usually accompany
prolonged period of edentulism.
Mainly abnormal habits are usually associated with muscular
h_ pertonicity with a resultant decrease in the vertical dimension of
Jaw relation (llltlxlllﬂlllillltllblllal‘ relatioiisliip):
Delinition: _ An__' spatial relationship of the maxillae to the mandible; any
one of the mfmite relationships of the mandible to the maxillae
Clinical signiﬁcance of jaw relation
1- To re-establish the functional position of the mandible (in
Verticalanterioposterior and lateral directions)
2- It is essential for proper mastication. comfort. esthetics and phonetics
3- Functional efficieiicy
4- Structural balance (maintaining the health of the TM] and suppoiting
5- Getting stable and 'ell-functioning complete denture.
centric relation is a reference point in recording inaxillo-mandibulzir
relations and during the time frame of denture construction.
ll it can be '€l‘lfl€d and repeated.
t it‘s a fiiiictional position.
Jaw relation registration
Before we register the jaw relation we need to clinically
Clinical methods for recording vertical dimension of the rest
1- Facial measurement after swallowing and relaxing:
a. Patient is asked to sit upright and comfortably. eyes looking straight ahead.
b. Insert maxillary occlusal rim ( not the lower).
c. Place two points of reference.
d. Instruct the patient to wipe his lips with his tongue. to swallow and to drop
his shoulders — rest position.
e. Measure - repeat and take average.
2- Tactile sense:
This method is entirely depending on patient tactile sensation. The patient is
instruct to keep his mouth open widely until he feels tired in the muscle of the
mandible then he request to close his mouth gradually to the degree when he
feel comfort and mandible in relaxed position. then a measurement is taking
between the two ordinary placed points on the face.
Like telling the patient to say M many times, however. Can’t
consider as reliable method for determining vertical dimension
of the rest position.
3- Measurement of anatomical landmark (Willis measurement):
It has been known that when the mandible in rest position the
distance between pupils of the eyes to part of the lips, when the
patient looking forward is equal to the distance from anterior
nasal spine to the lower border of the chin.
5- Facial expression:
> is one of the most widely used method, it depend on the
experience of dentist or operator at rest position, the face
appear without distortion at the comer of the mouth or at the
comer of the eyes,
> In case of low vertical d1'111e1251'on the corner of the mouth drop
down more, the chin become closer to the nose, the lips
> In the contrary with increased facial vertical dimension, stress
appear clearly in the face, the corner of the mouth become ﬂat
and pushed laterally, the lip can not brought together
METHODS OF DETERMINING VDO
a) Mechanical methods
1- Ridge relation
. —. Distance from incisive papilla to mandibular incisors.
B. Parallelism of ridges.
2- Pre-extraction records:
A. Proﬁle photographs
C. .-rticul.1ted casts
D. Facial measurements
3- Measurement from fonner dentures
b) Physiological methods
1. Power point
2. Physiological rest position
5. Swallowing threshold
6. Tactile sense or neuromuscular perception
Patienfs perception of comfoit.
A- MECHANICAL METHODS
1. RIDGE RELATION: Defined as positional relationship of
the mandible ridge to the maxillary ridge.
a) Distance from the incisive papilla to the mandibular incisors:
* The distance of the papilla from the incisal edges of lower anterior teeth
averages approximately 4mm in natural dentition.
The incisal edges of the maxillary central incisors are an average 6mm
below the incisive papilla. Based on this Value VDO can be calculated.
b) Parallelism of the ridges:
- Sears suggested that correct vertical dimension of occlusion is
at a point where the jaws are parallel.
1- Pre-extraction record
Profile photographs: are made and enlarged to life size.
Radiography: cephalometric proﬁle.
Articulating casts: after teeth have been removed and
edentulous cast have been mounted in the aiticulator,
the inter arch measurements are compared with the
articulating casts for the same patient’s made before
3. MEASUREMENT OF THE FORMER DENTURES:
- A Boley’s gauge is used to measure the distance between the
border of the maxillary and mandibular denture, when the
dentures are in occlusion. This measurement is used to
determine the VDO.
B- PHYSIOLOGIC METHODS
BOOS BIMETER (POWER POINT)
Boos (1940) stated that maximum biting force occurs at VDO. A device that
measures the biting force (Bimeter) is attached to the mandibular record base and
a metal plate to maxillary A screw is turned to adjust the vertical relation. The
maximum power point on the gauge indicates the correct VDO.
NlSWONGER’S METHOD (193-I):
- Two markings are made. one on the upper lip below the nasal septum. and the
other on the chin. The patient is told to swallow and relax. The distance between
the marks is measured. The occlusal rims are adjusted until the distance between
the marks is 2-4 mm less during occlusion.
- Disadvantage- The marks move with the skin.
0 The dentist asks the patient to speak certain words and then makes certain observations
of the relationship of the occlusion rims to each other and to the lips.
1- Using ‘m’ sound:
0 The patient repeats the letter ‘in. When the lips just touch. ask the patient to hold the
jaws still. The distance between tip of the nose and chin is measured (VDR). The
occlusion rims are adjusted and again measured. The second measurement should be 2-
4mm less than the first measurement (VDO)
2- Using for v sounds:
0 The maxillar_v incisors/ occlusion rims should lightl_v contact the lower lip at the
vermillion border when pat pronounces these words.
3- SILVERMAN’S CLOSEST SPEAKING SPACE
- The 2mm space between the incisors at correct VDO when patient pronounces words
- The closest speaking space measures vertical dimension when the mandible and
muscles involved are in physiologic function of speech.
- In normal relaxed position the lips are even anterioposteriorly and in
slight contact. If the face appears strained the vertical height may be
more. If the corners of the mouth droop, making the chin appear too
close to the nose, then vertical dimension may be too less.
- The technique is based on the fact that when a person swallows, the
teeth come together with a very light contact at the beginning of the
swallowing cycle. If the occlusion rims do not come into contact during
swallowing then the VDO is less.
- Cones of soft wax having excessive height are placed on the lower
base. Salivation is stimulated (using candy) and the patient is instructed
to swallow. The repeated swallowing reduces the height of the wax to
the occlusal vertical dimension.
TACTILE SENSE AND PATIENT- PERCEIVED COMFORT
The patients tactile sense is used as a guide to the determination of the
correct vertical dimension. Using a central bearing plate attached to
mandibular occlusion rim and central bearing screw attached to maxillary
occlusion rim. VD is increased too high. Then in progressive steps the screw
is adjusted downward until the patient signifies over closure. The procedure is
then reversed until the patient signifies that it’s just right.
ELECTRON YO GRA PH Y
- Rest position can be determined by recording the minimal
activity of muscles of mastication.
Clinical methods to obtain centric relation:
1- Retruding mandibular method:
Guidance by hand. It can be 1- chin guide tech. 2- bimanual tech.
Operator stands in front of patient and catching the chin of the patient by
index and thumb finger and ask the patient to close and open until closing in
2- Tongue method:
Asking the patient to raise his tongue back as possible to the soft palate. This
movement will bring automatically the mandible to the centric relation and
3- Swallowing method:
This is based on principle that when patient swallow his own saliva 9 the
mandible becomes into centric relation.
-1- Fatigue of muscle:
Instruct the patient to open his mouth widely and keep his position several
months until fatigue of muscle begin. this is can be shown by tendency of
, atient to close his mouth.