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Maxillo-Mandibular Relationships

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Presentation on theme: "Maxillo-Mandibular Relationships"— Presentation transcript:

1 Maxillo-Mandibular Relationships
Centric and Protrusive Records

2 Problems Establishing Edentulous Maxillo-mandibular Relationships
Edentulous patients have more difficulty determining where their denture teeth should contact No periodontal membrane Old dentures won’t fit on casts Record base fit and wax rim changes confuse some patients

3 Centric Position Acceptable position should be: Conducive to health
Relatively repeatable position can be checked before dentures completed

4 Conducive to Health Relatively Symmetrical Position
Not ‘absolute’ symmetry Less chance of muscle strain which might occur in non-centered positions

5 Hinge Position is Repeatable
relatively centered patient can find stable occlusal contacts relatively easily allows change in vertical dimension

6 Centric Relation (CR) Centric position of mandible in relation to the maxilla Defined by the position of the condyles, rather than the teeth Hinge position

7 Centric Relation Treatment position
Not necessarily ‘ideal’ or ‘normal’

8 Centric Occlusion (CO)
Maxillo-mandibular position determined by teeth Sometimes considered coincident with ‘maximum intercuspation’ or ‘habitual closure’

9 CR and CO have been defined differently by various investigators, and differently over different time periods

10 Where is Centric Relation? Glossary of Prosthodontic Terms:
Independent of tooth contact Clinically discernible when the mandible is directed superiorly and anteriorly

11 Where is Centric Relation?
Glossary of Prosthodontic Terms: Condyles articulate with thinnest, avascular portion disks Anterior-superior position against slope of the articular eminence

12 Where is Centric Relation? Glossary of Prosthodontic Terms:
Purely rotary movement about the transverse horizontal axis

13 Other definitions of centric relation have included:
Rearmost, Uppermost, Midmost (RUM) Most Posterior

14 Posterior positioning of the condyles is no longer considered desirable (Celenza)

15 Anterior-Superior Position
Thickening (buttressing) occurs in areas of bone where articulation occurs Thickest part of the articular eminence is the anterior portion of the glenoid fossae

16 Anterior-Superior Position
The articular disk is in a superior-anterior position

17 Anterior-Superior Position
The neurovascular supply of the retro-discal pad is posterior to the articular disk If condyles articulated in a most posterior position – impingement

18 Anterior-Superior Position
Cartilage covers articular surfaces Fibrocartilage on anterior , not posterior of the glenoid fossae Articular cartilage on superior and anterior of the condyles

19 Anterior-Superior Position
Posterior-most positions require force Pressure may force condyles down posterior slope, or cause flexure of mandible

20 For the purpose of fabricating complete dentures, the superior-anterior position of Centric Relation will be used

21 Clinically the dentist cannot determine the actual position of the condyles at the time jaw relations records are made

22 Centric Relation - Why? Allows function to all positions
Conducive to health (non-pathologic) Brill et al - pain & loss of occlusal sense when not in CR Renyolds - 24% of normal population has CR=CO

23 Centric Relation - Why? Convenient - relatively centered (Celenza)
More reproducible (Grasser) Easier to set a stable occlusion

24 Centric Relation - Why? OVD can be changed and condylar inclination will not have to be readjusted (arcon articulators) (Celenza) CR is not far from CO at same occlusal vertical dimension (Wilson and Nairn)

25 Centric Occlusion - Why Not?
Position is difficult to determine - not as reproducible Patients cannot tell where centric occlusion or a habitual position is with bulky wax rims in position No habitual position with new wax rims (Crum and Loiselle; Brill et al)

26 Centric Occlusion - Why Not?
CO may be a dysfunctional position Palpate muscles, TMJ to ensure no dysfunction (Brill et al)

27 Centric Occlusion - Why Not?
Not reproducible, so the influence of other variables on the centric record cannot be assessed: Wax consistency Biting force Symmetry of guidance (Yurkstas and Kapur)

28 Centric Occlusion - Why Not?
CO may lead to dysfunction - no studies to absolutely prove this hypothesis

29 When to Use Centric Relation
When entire occlusion being restored No remaining posterior centric stops When complete, fixed, or removable partial dentures involve the entire occlusion

30 When to Not to Use Centric Relation
Stable occlusion No pathology Posterior centric stops present No valid reason to change Use maximum intercuspation

31 Registering Centric Relation
Bimanual manipulation Patient in a slightly supine position

32 Registering Centric Relation
Bimanual manipulation Occlusion rim notched to aid stabilizing the record bases

33 Registering Centric Relation
Bimanual manipulation Index fingers on the rim, thumbs under symphysis

34 Registering Centric Relation
Jiggle the mandible Mandible should freely arc Allow the patient to close into contact

35 Registering Centric Relation
Do NOT push the mandible or dislodge the record base Medium must be dead soft (Yurkstas and Kapur)

36 Registering Centric Relation
Minimal closing pressure (Yurkstas and Kapur)

37 Recording Centric Position

38 Preparing Occlusion Rims
Place 3 widely separated lines between the rims in the centric position CRITICAL! Check that record base heels/rims do not touch

39 Line up Marks Eliminate contact with record bases

40 Registering Centric Relation
Max & Mand Occusion Rims Two sharp “V”-shaped notches in the molar/premolar area of each sided wax Depth 1-2 mm 1-2 mm

41 Ensure Adequate Notch Depth
Too Shallow - no undercuts

42 Registering Centric Relation
Rehearse making the record without recording medium Place occlusion rims intraorally PVS registration material (Memoreg) over entire occlusal rim

43 Thin Layer of Material Too Thick Good

44 Thin Layer Want flat record, no excess on sides of rims
Excess material recording of the sides of the rim can cause deflection when checking record

45 Making the Record Have patient close into record
Ensure smooth arc of closure, no horizontal deviations Use index fingers to stabilize lower record base

46 Alternate Medium Alluwax Must be dead soft

47 Registering Centric Relation
Place Alluwax into a 1-2mm slot in maxillary rim Fill to slight excess Ensure wax is dead soft Hot water bath for softening (use care)

48 Keep Wax Neat

49 Registering Centric Relation
Stabilize mandibular record base using index fingers on the flange (or in a recess in the rim) and the thumbs under the symphysis

50 Registering Centric Relation
Patient opens, relaxes, and slowly closes

51 Registering Centric Relation
Gently arc the mandible in a hinge-like motion There should be: No translation No splinting

52 Registering Centric Relation
Patient slowly closes Operator uses tactile senses to ensure the mandible does not translate

53 Registering Centric Relation
Patient closes until rims are almost touching (1 mm separation) Ask patient to stop as soon as this position has been reached Some may not be able to tell when they contact

54 Registering Centric Relation
Never instruct the patient to bite firmly Causes translation or inaccuracy in the record

55 Registering Centric Relation
Hold position until set 1-2 min Remove both rims together Separate

56 Registration Should be Sharp, Not Rounded

57 Registering Centric Relation Mounting the Mandibular Cast
Ensure record is repeatable Increase the height of incisal pin 1 mm, invert articulator Place wax rims together, lute with sticky wax - 4 spots

58 Registering Centric Relation
Mount the mandibular cast with mounting plaster After mounting, remove the record & adjust the incisal pin to allow contact between rims Occlusion rims should be touching evenly, over the entire occlusal surface

59 Registering Centric Relation
Do not alter incisal pin after rims are contacting Otherwise, height of correct vertical dimension can be lost

60 Check CR Record Take new record, place on articulator
Release articulator centric locks Should arc into record without any translation If doesn’t take 3rd record to see which one is reproducible

61 Protrusive Records Used to set condylar guidance
Helps setting teeth for best occlusal contacts

62 Protrusive Records Protrude a minimum of 5-6 mm
Ease of determination Protrude less than 12 mm Maximum travel of the condylar element on most articulators

63 Protrusive Records Registration material over entire rim
Patient closes with mandible positioned anteriorly

64 Protrusive Records Material must interdigitate with the opposing “V-shaped” notches Record should cover entire rim surface

65 Protrusive Records Condylar elements are released from hinge position
Instrument protruded, and the rims closed into record

66 Adjust Protrusive Guide for Maximal Interdigitation

67 Setting Condylar Angle

68 Protrusive Records The lateral component of condylar guidance (Bennett Angle) can be set arbitrarily at 15°

69 Protrusive Records Monoplane Occlusion
Protrusive record may be omitted If not obtained, set condylar guidance to 0°

70 Protrusive Records Monoplane Occlusion
May be advantageous to alter the occlusal plane angle in patients with steep condylar guidance Improves denture stability Cannot be assessed if the condylar guidance has not been set

71 Maxillomandibular Records for Complete Dentures
Centric Relation Treatment position Operator assists to ensure a hinge position Patient stops closure at initial contact Protrusive Programs articulator to optimize occlusion

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