Horizontal jaw relations Department of Prosthodontics Dentistry Explorer

Horizontal jaw relations Department of Prosthodontics Dentistry Explorer

Consists of – – Centric jaw relations – Eccentric jaw relations Dentistry Explorer

CENTRIC JAW RELATION "The maxillo-mandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective discs with the complex in the antero-superior position against the slopes of the articular eminences. “ – (GPT -8) Dentistry Explorer

CONTROVERSIES REGARDING CENTRIC RELATION • Mc. Collum 1920 rear most condylar position • Granger 1962 up most, rear most position • Stuart 1969 RUM position • Celenza 1978 condyle disc assembly braced superiorly & anteriorly against the posterior slope of the eminentia Dentistry Explorer

HOW TO UNDERSTAND CR WITHOUT GETTING CONFUSED WITH THE CONTROVERSIES IN ITS DEFINITION? ? ? Dentistry Explorer

FUNCTIONAL VS. MORPHOLOGICAL DEFINITION § Centric is best understood if we define it as “when it is required to select one mandibular to maxilla/condyle –fossa relationship that is most conducive to comfort , function & health of the odontostomatognathic system, without any controversy it would be CR position”. § It is a FUNCTIONAL definition, while GPT definition is a MORPHOLOGICAL definition. § The functional definition tells us why centric is necessary & the morphological definition helps us in securing the functional position. Dentistry Explorer

METHODS OF RETRUDING THE MANDIBLE - Chin point guidance – Guichet - Bimanual method –Peter Dawson - Three finger method –Peter Thomas - Anterior deprogrammer –Long Williamson Dentistry Explorer

DIFFICULTIES IN RETRUDING THE MANDIBLE • Biological causes : – lack of co-ordination between groups of opposing muscles. – habitual eccentric jaw relation § Physiological causes : § inability of the patients to follow the instructions § Mechanical causes : § poorly fitting base plates Dentistry Explorer

METHODS OF RECORDING CENTRIC RELATION • Physiologic methods • Functional methods • Graphic methods • Radiographic methods • Other methods Dentistry Explorer

PHYSIOLOGIC METHOD • Tactile or Inter occlusal check record • Pressure less method • Pressure method Dentistry Explorer

TACTILE OR INTER-OCCLUSAL CHECK RECORD METHOD • In this method, a tentative CR is recorded • The casts are articulated based on the tentative jaw relation • Teeth arrangement is done & an inter-occlusal registration is made • The tentative jaw relation is verified with the interocclusal record & errors are corrected Dentistry Explorer

RATIONALE BEHIND BOTH THE METHODS There are two schools of thought regarding pressure used while recording CR : • Minimal closing pressure: tissues are not displaced • Heavy closing pressure: produce the same displacement of tissue that occurs during mastication Dentistry Explorer

STATIC OR PRESSURELESS METHOD • Its called as the “NICK & NOTCH” method Dentistry Explorer

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PRESSURE METHOD • After establishing the VD, the upper occlusal rim is inserted in the pts’ mouth. • The lower rim is fabricated of excess height. • The entire lower rim is softened in a water bath & inserted into the pts’ mouth. • The pt is guided to close in CR. • After the pt. closes his mouth till the predetermined VD, both the rims are removed, cooled & articulated. Dentistry Explorer

FUNCTIONAL METHODS • Needle House method • Patterson's method • Meyer’s method Dentistry Explorer

NEEDLE - HOUSE METHOD Dentistry Explorer

PATTERSONS METHOD Dentistry Explorer

GRAPHIC METHODS • Intra oral tracing method • Extra oral tracing method Dentistry Explorer

INTRA ORAL TRACING • The central bearing device is located intra orally & is more simple compared to the extra oral arrow point tracing. • The tracer is placed within the mouth. • The tracer is not visible during the procedure & the size of the tracing is very small making it difficult to determine the apex of the tracing Dentistry Explorer

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EXTRA ORAL TRACING • They are similar to the intra oral tracers • Additionally, they have attachments that project outside the mouth • The size of the tracing pattern is larger, &the apex can be identified easily Dentistry Explorer

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OTHER METHODS • Using strips of celluloid • Deep heating or pooling method • Pantographs Dentistry Explorer

PANTOGRAPHS • Consists of six styli & tracing tables attached to the maxilla & mandible by means of a special kinematic face bow & clutches • Two tables are adjacent to each condyle & two anteriorly on either side of the mouth • The tracings produced are called “Pantograms” • Pantograms are used to program on a fully adjustable articulator Dentistry Explorer

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SIGNIFICANCE OF CR • It is a repeatable, reproducible & recordable position • It is a definite learned position • It acts as a centre from which all movements can be made • It is a definite entity , so it used as a reference point in establishing CO • It is helpful in adjusting condylar guidance in an articulator to produce balanced occlusion Dentistry Explorer

RELATION BETWEEN CR & CO • CR & CO need not be the same in a dentulous patient. • Edentulous people who wear complete dentures are provided with CRO so that they can learn to pull the mandible back & close into a repeatable position enabling the dentures to remain tightly secured. • CRO is the simultaneous even contact between maxillary & mandibular teeth into maximum interdigitation with the mandible in CR. Dentistry Explorer

FACTORS INFLUCENCING THE CR RECORDS • • The resiliency of the supporting tissues The stability of the recording bases The TMJ & its associated NM mechanisms The technique used The skill of the dentist The health & co-operation of the patient The posture of the patient The size & position of the tongue Dentistry Explorer

COMPLICATIONS IN RECORDING CR • Biological factors : Realeff (Resiliency and like effect) TMJ’s structure § Mechanical factors : Cast mounting procedure Denture processing Dentistry Explorer

ECCENTRIC JAW RELATION “Any relationship of the mandible to the maxilla other than Centric Relation”. • It includes : Protrusive jaw relation Lateral jaw relation Dentistry Explorer

PROTRUSIVE JAW RELATION • When the mandible is protruded there is a wedge shaped space between the upper & lower occlusal surfaces of the occlusal rims or dentures. • This is known as “Christensen’s phenomenon”. • It is caused by the downward & forward movement of the condyles. Dentistry Explorer

LATERAL JAW RELATION • Lateral movements are complex activities in most humans. • They are of paramount importance because they influence the inter-cuspation of teeth in working mastication. • Bennett movement is the bodily wide shift of the whole mandible that occurs in lateral movements. • L = (H/8 + 12) Dentistry Explorer

METHODS OF SEALING THE RECORD BLOCKS • The record blocks can be fused together using a heated instrument • ZOE impression paste can be used • Staple pins are also used Dentistry Explorer

ERRORS IN REGISTERING JAW RELATIONS • Record bases that do not fit accurately • A shifting of the record bases over displaceable tissues (Realeff) • Excessive pressure exerted by the patient during the recording • Patient not registering CR because of systemic factors • Interference of heels of the casts during mounting Dentistry Explorer

CONCLUSION § “Establishing the jaw relation” is an important step in fabrication of complete dentures. § There are many methods of obtaining jaw relations. § In the final analysis, it is the experience and judgment of the operator which helps in determining what is right for the patient. Dentistry Explorer

BIBLIOGRAPHY: 1. Prosthodontic treatment for edentulous pts- Zarb Bolender 2. Essentials of complete denture prosthodontics. Sheldon Winkler 3. Clinical dental prosthetics - H. R. B. Fenn 4. Syllabus of complete dentures- Charles M. Heartwell 5. Fabrication of complete dentures- Swenson Dentistry Explorer

CONTD… 6 7 Impressions for complete dentures- Bernaud Levin Pre-extraction records for CD fabrication JPD 2004; 91: 55 -8 8 Physiologic jaw relation and occlusion of CD JPD 2004; 91: 203 -5 9 Factors influencing CR records in edentulous mouths JPD 2005; 93: 305 -10 10 The Glossary of Prosthodontic Terms-8 JPD 2005; 94 Dentistry Explorer