Centric Relation .pptx

Centric relation

1. Nishu Priya 2 nd year PGT In Prosthodontics CENTRIC RELATION

2. CONTENTS Definitions Chronological changes of definitions of centric relation Theories Muscles involved in centric relation Factors influencing centric relation records Significance of centric relation Complications in recording centric Complications in recording centric Recording of centric relation Methods to returde the mandible Difficulties in retruding Methods of recording centric relation Errors Conclusion References

3. introduction The relationship among occlusion, condylar position and temporomandibular disorders (TMDs) has been part of an extensive discussion in dentistry. There is hardly any aspect of clinical dentistry that is not adversely affected by a disharmony between the articulation of the teeth and the centric relation position of the temporomandibular joints. Centric relation (CR) is the most controversial concept in dentistry. The concept of CR emerged due to the search for a reproducible mandibular position that would enable the prosthodontic rehabilitation. This term is derived from the word ‘center’ or ‘center oriented relation’.

4. DEFINIT I ONS CENTRIC RELATION - A maxillomandibular relationship, independent of tooth contact, in which the condyles articulate in the anterior-superior position against the posterior slopes of the articular eminences; in this position, the mandible is restricted to a purely rotary movement; from this unstrained, physiologic, maxillomandibular relationship, the patient can make vertical, lateral or protrusive movements; it is a clinically useful, repeatable reference position. (GPT-9) The definition of centric relation has evolved over the years and with advanced understanding of mandibular movement it may change again in future

5. 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 CENTRIC RELATION RECORD - A registration of the relationship of the maxillae to the mandible when the mandible is in centric relation. The registration may be obtained either intraorally or extraorally TERMINAL HINGE AXIS /TRANSVERSE HORIZONTAL AXIS –an imaginary line around which the mandible may rotate within the sagittal plane

6. CONTROVERSIES REGARDING CENTRIC RELATION The rearmost position is relative term which denotes that the condyles can go backwards as far as the temporomandibular ligaments would permit without any strain. It does not literally means the most retruded position in the glenoid fossa, since such a position will produce considerable amount of strain in ligaments and cause pain. Understanding various terms used in definitions

7. The term Unstrained refers to the strain of the ligaments and not the strain of the muscles since it’s the ligament that limits the mandibular movements and not the muscles  hence only ligaments can suffer strain if the head of the condyle is taken posteriorly beyond the centric relation position. During normal contraction of muscle, strain always occurs. The closing and retruding muscles are under some degree of strain in centric relation as centric is a power position. The rest position of the jaws is the only position where there is a minimum tonic contraction of the muscles and truly an unstrained position.

8. The most anterior superior position of the condyle is the position used by the head of the condyle when the mandible is in its retruded position, from where there is an anterior superior bracing of the condyle against the distal slope of the articular eminence. Anterior superior bracing against the distal slope of articular eminence is an intra-articular position that cannot be clinically visualized.

9. CHRONOLOGICAL CHANGES IN DEFINITIONS OF CENTRIC RELATION 1920 Mc Collum Rearmost position 1952 G r ai n g er U pp e r mo s t, Rearmost position 1969 S t u a r t RUM position

10. 1977 Ame r i c an Equillibrum Society Most anterior and uppermost position of condyle opposite the slope of articular eminence 1978 Cele n z a 1987 Am e r i c an Equillibrum Society Condyle disc assembly braced superiorly and anteriorly against the posterior slope of articular emi n ence Revised - Thinnest avascular portion of the disc in the anterior, most superior position of dorsal slope of eminence Celenza, F. V., and Nasedkin, J. N.: Occlusion: State of the Art. Chicago, 1978, Quintessence Publishing Co., Inc.

11. Musculoskeletally stable position- okeson condyles are in their most supero -anterior position in the articular fossae, resting against the posterior slopes of the articular fossae with the discs properly interposed. This is the position the condyles assume when the elevator muscles are activated with no occlusal influences.

12. T H E O R I E S MUSCLE THEORY LIGAMENT THEORY OSTEOFIBER THEORY Defense reflex -- external pterygoid muscles to contract halt the jaw Ferrei n Ligaments become tens e -- determines the limits of the retrusive movement. Meyer Retrusive terminal stop formed by the soft tissues of the posterior part of the roof of the glenoid fossa. Sazier Innervated posterior zone of disc provides biofeedback– retrusive movement MENISCUS THEORY Saizar, P.: Centric relation and condylar movement: Anatomic mechanism. J PROSTHET DENT 26~581, 1971.

13. SIGNIFICANCE OF CENTRIC relation Bone to bone relation (constant) Repeatable and recordable and thus serves as a reliable guide for developing c entric occlusion Related to the terminal hinge axis , in centric relation, condyles exhibit pure rotation without any translation More definite than vertical relation since it is independent of tooth contact Yurkstas AA, Kapur KK. Factors influencing centric relation records in edentulous mouths. J Prosthet Dent 2005; 93: 305- 10

14. Reference relation: The maxillo-mandibular musculature is so arranged that a patient can easily move his mandible into centric relation. Thus CR serves as a reference relationship for establishing an occlusion. When the CR-CO of artificial teeth do not coincide or a freedom from centric is not present, the stability of the denture bases is in jeopardy and the edentulous patient is subjected to unnecessary pain or discomfort. CR is the horizontal reference position of the mandible that can be routinely assumed by edentulous patients under the direction of the dentist. This makes it possible to verify the relationship of casts on the articulator when they are mounted in Centric Relation.

15. Functional movements like chewing and swallowing can be carried out since it is the most unstrained position. When a bolus of food is prepared for swallowing  the teeth attempt to masticate it  with strong muscular force against the bolus  condyles following the paths of movement that the anatomic structure of the joint dictates, i.e., in an upward and backward direction. The condyle tries to seat itself in the glenoid fossa as far as it will go by its own muscular power. If the teeth intervene before this position is reached, there is a lateral component of force registered upon the teeth which subsequently causes pain in the temporomandibular region. The degree of this lateral force is directly proportional to: 1. The amount of force applied by the muscles during mastication 2. The degree the jaw is out of centric relation.

16. CONCEPTS OF CENTRIC RELATION Position Anatomic: Centric relation is the most retruded relation. A border position is determined by the ligaments. Pathophysiologic: Centric relation is the most posterior unstrained jaw relation. A position that is not a border position and is established by muscle action. Douglas Allen Atwood , JPD ;1968;20 ;21 S. David and R.M.J Gray; 2001; BDJ; 191; 235. Anatomically –when the head of the condyle is against the most superior part of the distal facing incline of the glenoid fossa. Conceptual –with the articular disc in place, when the muscles that support the mandible are at their most relaxed and least strained position. Geometrical- with the intra-articular disc in place, when the head of the condyle is in terminal hinge axis.

17. CENTRIC RELATION AND CENTRIC OCCLUSION Numerous studies have reported that the majority of patients with a natural dentition show discrepancies between the occlusal position of the mandible in CR and MI. This discrepancy is present in at least 90% of dentitions. In dentulous individuals, occlusion in centric relation is not and need not be centric occlusion, although it would be ideal to have centric occlusion at centric relation . After the removal of teeth, centric occlusion is lost, while centric relation remains and serves as a reliable guide to develop centric occlusion in artificial dentures. When centric occlusion does not coincide or is not identical with centric relation, the condyles do not remain in their upper most position in the glenoid fossae, but take a position either anteriorly or laterally. This referred as “centric slide”.

18. THE CONCEPT OF LONG CENTRIC Dawson: freedom to close the mandible either into centric relation or slightly anterior to it without varying the vertical dimension at the anterior teeth. Long centric refers to freedom from centric, not freedom in centric. The principal concern regarding long centric is the restrictive effect that can result from the lingual inclines of the upper anterior teeth. If no horizontal freedom is provided for a slightly protruded postural closure, the lower incisal edges will strike the lingual inclines of the upper anterior teeth.

19. Key elements of the procedure to establish myostablized centric relation Orthostatic position of the patient and the practitioner Cervical support Head and mandibular stabilization by the practitioner Rotation movement executed by the patient with tactile control of the practitioner Patient education: perception of the premature contact, creation of confidence Reproducibility of rotation movements without translation (tactile sensation) Myostabilized centric relation November 2011 international journal of stomatology & occlusion medicine  4(3):87-94

20. Factors influencing centric relation records Resiliency of the supporting tissues Stability of the recording bases Temporomandibular joint and its associated neuromuscular mechanisms Character of the pressure applied in making the recording Technique used in making the recording and the associated recording devices used Skill of the dentist Yurkstas AA, Kapur KK. Factors influencing centric relation records in edentulous mouths. J Prosthet Dent 2005; 93: 305- 10 Health and cooperation of the patient Maxillomandibular relationship Posture of the patient Character or size of the residual alveolar arch Amount and character of the saliva Size and position of the tongue

21. RECORDING OF CENTRIC Relation Assisting the patient to retrude the manible Recording the centric Verifying the record

22. METHODS to RETRUDE THE MANDIBLE Simplest, easiest and most efficient Let your lower jaw relax, pull it back, and close on your back teeth RE L AX A TI ON OF JAW PUSHING UPPER JAW Get the feeling of pushing your upper jaw out and close your back teeth together Automatically pull the lower jaw backward Protruding and retruding of mandible – repeatedly - finger on the point of the chin - mandible strike its retruded position STRETCH AND RELAX MOVEMENTS

23. Tip of tongue - posterior border of the maxillary record base - close until the rims come into contact Disadvantage : likehood of displacing the mandibular record base by the action of tongue RETRUSION OF TONGUE Gentle tapping of occlusal rims rapidly and repeatedly retrudes the mandible Disadvantage: Difficult to record and patient can easily tap in a slightly protrusive or lateral position RAPID TAPPING OF THE OCCLUSAL RIMS Tilting the head backwards - place tension on the inframandibular muscles and tend to pull the mandible to a retruded position Disadvantage: Insertion and removal of occlusal rims from mouth is very difficult HEAD POSITION

24. S W A L L O W I NG Swallowing usually brings the mandible to a retruded position . Unreliable – since person can swallow when mandible is not completely retruded The temporalis muscle - contraction can be felt when the mandible is in or near retruded position by placing finger tips on each side of the head. TEMPORALIS MUSCLE CHECK Total relaxation of the patient on the chair automatically brings mandible to retruded position GENERALIZED RELAXATION OF THE PATIENT Boucher’s Prosthodontic Treatment for Edentulous patients.9 th edition,277-291

25. Postural relaxation of the patient Pure hinge axis movement imposes an important decrease of postural muscular activity, both cervical and mandibular. Therefore it is essential to offer occipital support to the patient in order to relax the cervical muscles which are maintaining head position. It is important to observe the patient’s head position without any flexure or extension of the cervical spine. The aim is to achieve a natural head position. To make it easier for the practitioner the patient is placed in a chair inclined approximately 30° from the horizontal.

26. COMPLICATIONS IN RECORDING CENTRIC O ne joint can be displaced downward by uneven pressure (record are made) Y et the condyles be in their most retruded position S ituation on articulator – cannot occur - a deflective occlusal contact - instability, soreness and resorption St ru c t u r e of TMJs Hanau U neven resiliency in the soft tissues - the mucosa and tissue of TMJs U ndue pressure - excessive displacement of soft tissues Realeff effect Boucher’s Prosthodontic Treatment for Edentulous patients.9 th edition,277-291

27. DIFFICULTIES IN RETRUDING Biological Problem Psychological problem Mechanic al problem

28. Biological problem Denture wearers with marked attrition of posterior teeth Edentulous for a long time Patient having only anterior teeth Lack of muscle co-ordination Lack of synchronization between the protruding and retruding muscles due to “HABITUAL” eccentric jaw positions adopted by the patient to accommodate malocclusion Involuntary forward movement of the mandible. Causes

29. Psychologi c al problem Patient and dentist The more the dentist – irritated by – apparent inability of the patient to retrude the mandible - more confused the patient The dentist must be prepared to spend adequate time securing the CR record Poorly fitting of base plates Displacement of the soft tissue (excessive pressure during registration) Tissue depth is uneven Mechanical problem

30. RECORDING THE CENTRIC RELATION MINIMUM CLOSING PRESSURE HEAVY CLOSING PRESSURE Two basic concepts Record - minimal closing pressures - tissue supporting the bases will not be displaced Objective - opposing teeth to touch uniformly and simultaneously at their first contact Record - heavy closing pressure - tissues under the recording bases will be displaced Objective - same displacement of the soft tissue . Thus occlusal force will be evenly distributed over the supporting residual ridges Minimal closing pressures – produce best result for most patients

31. Methods of recording centric relation Static methods Functional methods BOUCHER’ S Interocclusal record with/without central bearing devices and tracing devices Chew-in technique Needle House technique Patterson technique

32. Physiological or inter-occlusal check record method Functional methods HEARTWELL Chew-in technique Needle House technique Patterson technique Graphic methods Intraoral devices Extraoral devices

33. PHYSIOLOGIC METHOD Proprioceptive impulse of patient Kinethetic sense of mandibular movement Visual acuity and sense of touch Based on Tactile or interocclusal check record method Pressure less method Pressure method T yp e s

34. Tactile or interocclusal check record method Phillip Pfaff – 1756 Also known as the 'mush', 'biscuit' or 'squash bite‘ Indications: Abnormally related jaw Supporting tissues that are excessively displaceable Large tongue Uncontrollable or abnormal mandibular movements

35. YEAR AUTHOR MATERIAL AND METHOD 1954 Brown Repeated closure into softened wax rims 1957 Greene Patients hold their jaws apart for 10 seconds to fatigue the muscles Snap the rims together. Made lines in the rims to orient them after removal from the mouth. Gradually, these procedures evolved - Small amounts of wax, compound, plaster and Zinc-Oxide Eugenol Impression paste were placed between the occluding rims equalize the pressure of vertical contact MATERIALS

36. YEAR AUTHOR MATERIAL AND METHOD 1932 Schuyler Viscosity – not uniform - uneven pressure transmitted to the record Bases - disharmony of occlusion. Modeling compound - softened more evenly, cools slower, and doesn’t distort as much as wax. 1939 Wright Factors -Resiliency of tissue Saliva film Fit of bases Pressure applied ZERO PRESSURE 1955 Trapozzano Wax “Check-bite method most prefered technique 1955 1964 Pay ne H i c k e y Dental plaster because less material had to be placed in the patient’s mouth for the record Which material is best?

37. YEAR AUTHOR MATERIAL AND METHOD 1932 Schuyler Consider a record secured on compound or wax occluding Rims sufficiently free from error to compete with the restorations without additional checks 1954 Simpson Wax records were unscientific Gysi Tested this method on manikins and never got the same recording twice with wax or compound, He concluded that the uneven cooling of the material produced distortion Critisicm

38. STATIC OR PRESSURELESS METHOD Nick and Notch method Nick - Anterior - prevent lateral movement Notch – Posterior - anteroposterior movement

39. FUNCTIONAL METHOD Utilize the functional movements of the jaws to record the centric relation. The patient is asked to do the movements in Protrusion Retrusion Right lateral Left lateral Types: -Needles House Method -Patterson method -Mayer’s method

40. AUTHOR MATERIALS Greene Plaster and pumice mixture Needles Mounted three studs on maxillary rims Patterson Corborandum and plaster mixture Meyer Soft wax occlusal rims, tin foil placed Boose Gnathodynomometer Shanahan Cones of soft wax Historical background

41. Earliest graphic recordings were based on studies of mandibular movements by Balkwill in 1866. The intersection of the arcs produced by the right and left condyles formed the apex of what is known as GOTHIC ARCH TRACING “Gothic” name originate from ancient Gothic people’s houses (Barbarian tribes of Rome) GOTHIC ARCH TRACING GRAPHIC METHOD

42. GRAPHIC METHO D S I n t r ao r al Tracings E x t r ao r al Tracings

43. Intraoral Tracings A central bearing and tracing device. Pointed screw in bearing Tracing device - maxillary rim Plate mounted - mandibular rim. Plate is covered with a marking substance. The central bearing pin is connected to the proper vertical relation Patient -lateral and protrusive movements. Gothic arch form is traced on the plate.

44. Types of intraoral tracers

45. Bearing-tracing device is strong enough to resist biting pressures and can be held in position by means of a locking disk More accurate ADVANTAGES Relative difficulty in visualizing the tracing Since the intraoral tracings are small, it will be difficult to find the true apex. DISADVANTAGES

46. Extraoral Tracings Similar to intra oral tracer. It has same central bearing device attached to occlusal rims & another attachment projects outside the mouth. Extra oral tracing pointer & recording plates are attached to these projections. Size of tracing pattern is larger so apex can be identified easily

47. Larger than its intraoral counterpart - apex is more discernible Visible - Patient can be guided and directed more intelligently during the mandibular movements The stylus can be observed in the apex of the tracing during the process of injecting plaster A D V A N T A G E S The lips and cheek may interfere as recording device is placed extraorally DISADVANTAGES

48. Pantography Used clinically to measure mandibular movement Graphic record in three planes Types- Mechanical (by McCollum and Staurt ) Electronic It has six tracing platforms and styli to graph gothic arch as well as jaw and condylar movements. A vertical and a horizontal tracing table are located on each side of the patient's face overlying the TM joints, and a pair of horizontal tables, approximately at the level of the plane of occlusion, is located below the eyes. The tracing procedure is carried out to record terminal hinge axis as the reference point and lateral border paths are traced whilst the jaw is gently guided.

49. AUTHOR METHODS Gysi (1929) Gothic tracing technique - five-degree error wax and compound bites - 25-degree error Brown needle point tracing is unreliable and recommends repeated closures into wax under close observations National Society of Denture Prosthetics Needle point tracing - both scientific and practical. This society recognizes no other means of verifying centric jaw relationships Payne 1955 Intra-oral tracer - difficult to see and does not work as well where flat ridges or flabby tissue occur. Extra-oral tracing provides visibility but retain the other difficulties if central bearing plates are used. The more equipment we put into the mouth, the more difficult it is for the patient Kingery(1952) Several drawbacks in the use of the central bearing point central bearing point allows for no control over the amount of closing pressure applied by the patient COMPARATIVE EVALUATION OF DIFFERENT METHODS

50. Kapur et al -The intra-oral and extra-oral tracing procedures were more consistent as compared to the wax registration method. - In patients with flabby ridges, the intra-oral and extra-oral tracing procedure became less consistent as compared to the wax registration method. Thakur M Gothic arch method- more technique sensitive and required greater chair-side time both for the dentist as well as for the patient. -Incorporation of errors due to mishandling of the device -fatigue of muscles and jaws from repeated efforts to guide the mandibular movements conventional method > gothic arch Abbad Intraoral digital tracing technique > conventional intraoral tracer technique. Consistency of reproducibility - supine position is significantly higher than upright position. Thakur M, Jain V, Parkash H, Kumar P. A comparative evaluation of static and functional methods for recording centric relation and condylar guidance: A clinical study. J Indian Prosthodont Soc. 2012;12:175–81

51. Arrow head tracing A planar tracing that resembles an arrowhead or gothic arch made by means of a device attached to the opposing arches; the shape of the tracing depends on the location of the marking point relative to the tracing table, i.e., In the incisal region as opposed to posteriorly; the apex of a properly made anterior tracing is considered to indicate the centric relation position (GPT-9) Measured across a single plane

52. Classical, pointed form Seen as a well-defined apex with a symmetrical left and right lateral component The symmetry indicates an undisturbed movement sequence in the joints and uniform muscle guidance It reflects a healthy TMJ Classical flat form Similar to typical arrow point Except that it has more obtuse left and right lateral tracings. This type of arrow point signifies a marked lateral movement of Condyle in the fossa. Weak Gothic arch tracing A lax and negligent performance of the movements. Apex - Round Form The registration must be repeated: Stronger movements must be demanded from the patient

53. Asymmetrical form The left and right lateral tracings meet in an arrow point; however their inclination to the protrusive path is not symmetrical. One of the lateral tracing is shorter. Indicates an inhibition of the forward movement; either in the left or right joint. Miniature form Similar to the typical arrow point Extension of tracing is very limited. This can be due to : - restricted mandibular movements improper seating of record bases painfully fitting record bases during registration. Indication of a long period of edentulousness with an inhibition in condylar movements Vertical line beyond arrow point (Dorsally Extended) By forcible retraction or pushing of the mandible. Gothic arch was obtained with a protruded mandible An artifact - forward displacement of upper occlusal rim o r backward dislodgement of lower occlusal rim

54. Double Arrow Point Record of habitual and retruded centric relation. Allow patient training and repeat till a single gothic arch is obtained. It is also seen when vertical dimension is altered during registration Interrupted Gothic Arch Break or loss of continuity of lateral incisal path of Gothic arch. This happens due to posterior interference at the heels of occlusal rims during lateral movements. Check for posterior clearance before recording. Atypical Form Protrusive component does not meet at apex but on one of the lateral path. This may happen in dentulous because of a faulty m uscular pattern due to par functional habits like bruxism. It is also seen in very old edentulous patients, who are using complete denture with incorrect centric relation

55. ERRORS IN CENTRIC relation record ER R O R S POSIT I ONAL ERRORS T E CH N ICAL ERRORS

56. Positional errors Failure of the operator in his registration of the correct horizontal relationship Failure of the operator to record equalized vertical contact Application of excessive closure pressure by the patient at the time of recording Changes in the supporting area

57. Technical errors Ill fitting occlusion rims: if record bases are not stable Indiscriminate opening and closing of the occluding device (articulator) The slight shifting teeth which occurs between the stage of final arrangement in wax and the transfer to a permanent base material A movement by the tooth or several teeth either horizontally, or vertically, introduces an error

58. Consequences of recording incorrect centric relation TMJ dysfunction Mucosal ulceration and irritation Spasm of muscles Resorption of bone

59. CONCLUSION Centric relation is a most reproducible , reliable, repeatable , recordable, and reference position . Centric relation should coincide with centric occlusion otherwise will affect the stability of the dentures. Correct recoding of horizontal jaw relation, verified for accuracy as it affects the health, comfort, function of the muscles, and Temporomandibular joint. It is apparent from dental literature that with many opinions and much confusion concerning centric r elation records, a certain technique might be required for an unusual situation or a problem patient. In the final analysis, skill of the dentist and co-operation of the patient are probably the most important factors in securing an accurate Centric Relation record.

60. REFERENCES Celenza, F. V., and Nasedkin, J. N.: Occlusion: State of the Art. Chicago, 1978, Quintessence Publishing Co., Inc. Saizar, P.: Centric relation and condylar movement: Anatomic mechanism. J PROSTHET DENT 26~581, 1971. Boucher’s Prosthodontic Treatment for Edentulous patients.9 th edition,277-29 Yurkstas AA, Kapur KK. Factors influencing centric relation records in edentulous mouths. J Prosthet Dent 2005; 93: 305- 10 Squire, BE : Joint Compliance – Its role in centric relation. J Gnath 3:61,1984 E.G.R. Solomon, Manual of maxilla-mandibular relations

61. Sharry JJ Complete denture prosthodontics 3rd edition Heartwell CM,Rahn AO Syllabus of complete dentures 4th edition Winkler’s Essentials of complete denture prosthodontics 2nd edition Posselt, Franzen. Registration of the condyle path nclination by intraoral wax records: variations in three instruments. J Prosthet Dent 1960;10:441-54. Badel T, Panduric J, Kraljevic S, Dulcic N. Checking the occlusal relationships of complete dentures via a remount procedure. Int J Periodontics Restorative Dent 2007; 27:181192. Gutowski A. Remounting and occlusal adjustment of complete dentures. J Gnathol 1990;9:9–22. Myostabilized centric relation November 2011 international journal of stomatology & occlusion medicine  4(3):87-94