Dr. Bahjat Abu HamdanConsultant ProsthodontistDDS, CES, DSO. Paris-France

CENTRIC RELATION, THE BASIC REFERENCE

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.

A. Introduction

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.

A. Introduction

A. Introduction 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.

A. Introduction 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.

Discrepancies between CR and CIPEffects of disharmony between TMJ,s and occlusion

B. 10 factors to manage the occlusion. The 10 must know factors of

occlusion. Understand these factors and you will never have to treat occlusal problems by guessing.

Dawson

B. 10 Factors to manage the occlusion.

B. 10 factors to manage the occlusion. 1. TMJ

B. 10 factors to manage the occlusion. 2. Centric relation

B. 10 factors to manage the occlusion. 3. Vertical dimension

B. 10 factors to manage the occlusion. 4. Neutral zone.

B. 10 factors to manage the occlusion. 5. Masticatory muscles

B. 10 factors to manage the occlusion. 6. Occlusal contact

B. 10 factors to manage the occlusion. 7. Occlusal plane

B. 10 factors to manage the occlusion. 8. Long centric.

B. 10 factors to manage the occlusion. 9.Anterior guidance .

B. 10 Factors to manage the occlusion. 10.Envelope of function

Factors to manage the occlusion.

C. Relevant terms

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).

C. Relevant terms 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.

C. Relevant terms

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.

In CR position loading is distributed between teeth and TMJ,s

In CR registration lateral Pt muscle should passive.

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

C. Relevant terms

C. Relevant termsIn CR the mandible hasPurely rotary move-ment about transverse Horizontal axis.

C. Relevant terms

C. Relevant terms

C. Relevant terms Head position effect on mandible

position.

C. Relevant terms3.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.

C. Relevant terms

Centric occlusion

C. Relevant terms Centric occlusion, coincidence

between CR and ICP

C. Relevant terms 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.

D. Significance.

D. Significance.

D. Significance

D. Significance.

E. Dental procedures which reference MIP or CO?

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.

E. Dental procedures whichreference?..……

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).

E. Dental procedures which reference ?………

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.

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

F. Manipulation of mandible for CRregistration.

  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.

F. Manipulation of mandible for CRregistration

. 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.

F. Manipulation of mandible for CRregistration

F. Manipulation of mandible for CRregistration

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.

F. Manipulation of mandible for CRregistration

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.

F. Manipulation of mandible for CRregistration

F. Manipulation of mandible for CRregistration

G. Articulators… 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.

G. Articulators…

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.

G. Articulators… 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)]

G. Articulators… Intercondylar distance.

G. Articulators… Condylar inclination

G. Articulators…

G. Articulators… 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.

G. Articulators…

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.

THANKS FOR YOUR ATTENTION