In prosthodontics, replacing the missing, without affecting the other components of the masticatory system has two main reference the maximum intercupation and the centric relation. In this lecture discussion of centric relation as reference is exposed.

1. CENTRIC RELATION, THE BASIC
REFERENCE

2. A. Introduction.
B. 10 factors to manage the occlusion.
C. Relevant terms.
-Centric relation.
- Maximum intercuspation position MIP.
-Centric occlusion.
D. Significance.
E. Dental procedures which reference MIP or CO ?
F. Manipulation of mandible for CR registration.
G. Articulators.

3.  Masticatory system is composed of 2 main
parts;
 1. Active part represented by the NM system.
 2. Passive part represented by the TMJ and
the teeth.
 The NM system is controlled by the CNS.
 These 2 elements are connected instantly by
sensitive receptors.

5.  In the absence of pathology, these elements work in
synergy and harmony.
 Maintaining this comfort done by balanced
distribution of the elevator muscle forces between
the teeth and the TMJ.
 Pathology and disturbances affect mainly the teeth so
that the relationship in the same and opposite jaw.
 Disturbances of the occlusion affect the existent
harmony with the TMJ and the NM system.
 This disharmony leads to pathologic manifestations in
the TMJ and the muscles.

6.  Treating the affected teeth or replacing the
missing ones need to integrate them in the
masticatory system. The treatment reference
could be;
 The MIP or the occlusion in centric relation CO.
 In 10% of population the MIP coincide with the
CR (occlusion in CR position)
 Discrepancies between MIP and CR is frequently
present and may lead to pathologic conditions in
certain situation.

8.  The 10 must know factors of occlusion.
Understand these factors and you will never
have to treat occlusal problems by guessing.
Dawson

21.  1. Centric relation: 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 shapes
of the articular eminencies.
 This position is independent of tooth contact.
 This position is clinically discernible when the mandible is
directed superior and anteriorly.
 It is restricted to a purely rotary movement about the
transverse horizontal axis. (GPT-5).

22.  CR is anatomically determined; it is repeatable
and reproducible. Ruth et al
 Okeson, describes it as the most orthopedically
and musculoskeletally stable position of the
mandible.
 others consider it to be the essence of optimal
temporomandibular joint form and function.
 It is the most reliable reference point for
accurately recording the relationship of the
mandible to the maxilla.

23.  Therefore, a determination of the CR is a
prerequisite for the analyses of dental
interarch, condylar position, and skeletal
relationships.
 A properly aligned condyle-disc assembly in
centric relation can resist maximum loading
by the elevator muscles with no sign of
discomfort.

26.  At the most superior position, the condyle
disc assembly are braced medially, thus CR
also the midmost position.

28. In CR the mandible has
Purely rotary move-ment
about transverse
Horizontal axis.

32.  Head position effect on mandible position.

33.  3.centric occlusion; the occlusion of opposing
teeth when the mandible is in centric relation.
This may or may not coincide with the
maximal intercuspal position.

34. Centric occlusion

35.  Centric occlusion, coincidence between CR
and ICP

36.  CR position and MIP are well reproducible
reference positions of the mandible.
 When using the "freedom in centric" concept,
the occlusal range is about 0.5 mm.
 Retruded contact position is very close to
MIP in most people. Therefore it can be used
as a "therapeutic compromise" for occlusal
rehabilitation.
 Utz KH1, Duvenbeck H, Oettershagen K.

41.  Regarding dental procedures, the mandible
can assume two well-known positions as a
reference for treatment: centric relation (CR)
and maximum inter cuspation (MIC).
 These usually are not coincident in the
general population.
 The MIC and CR are reproducible.
 10% of the population have coincidence
between CR And MIC.

42.  all simple procedures related to occlusal
surfaces where the ( VDO) and the MIC
position are not affected, in this case the
reference is MIC.
Fillings and single crown.
Missing tooth replacement of limited span
( FPD or RPD).

43.  In which cases CR is considered as basic
reference?
 Missing of all the upper or lower posterior teeth
or both.
 Cases where the VDO is affected.
 Severe dental wear.
 Missing of all the upper or lower teeth or both.
 Signs and symptoms in masticatory system
(TMJ, NMS, Teeth) where the OCC. Is involved.
 Cases need full mouth rehabilitation.
 In orthodontic treatment where discrepancy
between CR and MIC position is more than 3mm.

44.  All the cases where the CR is the reference
the MIP will coincide with CR position.

45.  Avoiding damage caused by premature
contact or occlusal interference put the
codyles away from their position in CR
 The ability of the dentist to modify the
occlusion and reprogram the condylar
position and muscle response is easily
demonstrated clinically in occlusal treatment
procedures.

46.  . After several jaw closures the muscles
reprogrammed the condylar position to
complement the prevailing occlusion.
 This manipulation should avoid tooth
contact. Otherwise prematurity will affect
again the position of the condyles in CR.
 This manipulation should be achieved
without pain or stress which indicates
relaxation of the lower lateral pt muscle
responsible for mandible deviation.

48.  So that closure of the mandible is achieved by
elevator muscles.
 Guiding the mandible to CR position should
never let the Pt. feels any stress or discomfort
in the TMJ, otherwise a iatrogenic TMD may
occur.

49.  Kontor et al, researched reproducibility and
spatial patterning of CR record by using
 1. swallowing.
 2.Chin-point guidance.
 3.Chin-point guidance with anterior jig.
 4.Bilateral manipulation. ( Dawson )
 Bilateral manipulation allowed the greatest
reproducibility, followed by chin point
guidance. Swallowing was the least
consistent.

52.  Achieving dental work or occlusion analysis in
the laboratory require mounting the models on
the articulator.
 An instrument which simulates closely the
mandible and TMJ movements.
 Different types of articulators are exposed, the
development of these instruments is closely
related to the continual development in
understanding the anatomy, physiology,
biomechanics of occlusion, NMS, TMJ,and
mandibular movements.

53.  Improperly using the most sophisticated
articulator results in poor job quality but
attentive using of simple instrument can give
acceptable results.
 Without exact information we are only
guessing.
 Therefore, for an articulator to be acceptable, it
must be anatomically correct and
 should allow enough adjustment to
accommodate a majority of patients.

54.  The following parameters need be
considered:
 1. Intercondylar distance
 2. Condylar inclination
 3. Mandibular arc of closure
 4. Hinge axis position [Centric Relation (CR)
and Centric Occlusion (CO)]

55.  Intercondylar distance.

56.  Condylar inclination

58.  Why use a semi adjustable articulator?
 • Greater accuracy
 • Savings in chairside adjustment time
 • Eliminate iatrogenic occlusal interferences
 • Improved doctor/laboratory relations
 • Increase patient’s perception of care and skill
level
 • Revenue source for the practice and laboratory
 …and finally, because it is the right thing to do.

59.  Chairside refinement is the last step to
integrate the prosthesis in the masticatory
complex which result in patient comfort due
to the synergy between the different
components of the masticatory system. This
adjustment is controlled by the nervous
sensitive receptors.

60. THANKS FOR
YOUR ATTENTION