MaxilloMandibular Relationships

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 wont 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
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Where is Centric Relation? Glossary of
Prosthodontic Terms

• Independent of tooth contact
• Clinically discernible when the mandible is
  directed superiorly and anteriorly

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Where is Centric Relation?

• Glossary of Prosthodontic Terms
• Condyles articulate with thinnest, avascular
  portion disks
• Anterior-superior position against slope of the
  articular eminence

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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)
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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

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Anterior-Superior Position

• The articular disk is in a superior-anterior
  position

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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 CRCO

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Centric Relation - Why?

• Convenient - relatively centered (Celenza)
• More reproducible (Grasser)
• Easier to set a stable occlusion

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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)

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Centric Occlusion - Why Not?

• CO may be a dysfunctional position
• Palpate muscles, TMJ to ensure no dysfunction
  (Brill et al)

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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)

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Centric Occlusion - Why Not?

• CO may lead to dysfunction - no studies to
  absolutely prove this hypothesis

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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

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When to Not to Use Centric Relation

• Stable occlusion
• No pathology
• Posterior centric stops present
• No valid reason to change
• Use maximum intercuspation

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Registering Centric Relation

• Bimanual manipulation
• Patient in a slightly supine position

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Registering Centric Relation

• Bimanual manipulation
• Occlusion rim notched to aid stabilizing the
  record bases

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Registering Centric Relation

• Bimanual manipulation
• Index fingers on the rim, thumbs under symphysis

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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

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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

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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
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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
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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

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Registering Centric Relation

• Patient opens, relaxes,
• and slowly closes

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Registering Centric Relation

• Gently arc the mandible in a hinge-like motion
• There should be
• No translation
• No splinting

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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

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Registration Should be Sharp, Not Rounded
57
Registering Centric RelationMounting 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

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Check CR Record

• Take new record, place on articulator
• Release articulator centric locks
• Should arc into record without any translation
• If doesnt take 3rd record to see which one is
  reproducible

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Protrusive Records

• Used to set condylar guidance
• Helps setting teeth for best occlusal contacts

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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
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Setting Condylar Angle
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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 Recordsfor 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