Maxillo-Mandibular Relationships Centric and Protrusive Records This presentation includes images from the UCLA/APC/Ivoclar Educational Curriculum

No Easily Determined Reference Position Unlike dentate patient where existing teeth establish: Vertical height Position of maximum intercuspation Fine sensory input to find maximum intercuspation

Require a Reference Position to Set Teeth When remove dentures, no easily determined position to set teeth Differences in dentures and wax rims confuse some patients Without rims, no way to record centric position

Difficulties Maxillo-mandibular Relationships Difference in sensation (no teeth, changed lip support, height, contact with tissue) Edentulous patients have more difficulty determining where their teeth should contact No periodontal membrane

Finding a Treatment Position Acceptable position should be: Conducive to health Relatively repeatable position should be checked before dentures completed

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

Centric Relation (CR) Treatment Position Centric position of mandible to maxilla Defined by position of condyles, not teeth Hinge position

Hinge Position is Repeatable Relatively centered Patient can find stable occlusal contacts easily Allows change in vertical dimension

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

Centric Occlusion (CO) Occlusion of opposing teeth when mandible in centric relation Treatment position for Complete Dentures Sometimes coincident with ‘maximum intercuspation’ in natural dentitions

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

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

Where is Centric Relation? Glossary of Prosthodontic Terms: Anterior-superior position against slope of the articular eminence

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

Why Anterior-Superior? Thickening (buttressing) bone is present where joint articulation occurs Thickest part of eminence is anterior portion of fossae

Why Anterior-Superior? The articular disk is in a anterior-superior position

Why Anterior-Superior? Cartilage covers articular surfaces Fibrocartilage on anterior surface of glenoid fossae Articular cartilage on superior and anterior of condyles

Why not Posterior Position? Neurovascular supply of retro-discal pad is posterior to disk If condyles articulated in a posterior position – impingement

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

Clinically dentist cannot determine actual position of condyles at time of jaw relations records

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

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

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)

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

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

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

Patient Position Centric Relation Patient in a slightly supine position

Stabilizing the Record Bases Occlusion rim notched to aid stabilization

Centric Relation Bimanual Manipulation Index fingers on the rim, thumbs under symphysis

Maxillo-Mandibular Relationships Centric and Protrusive Records

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

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

Registering Centric Relation Minimal closing pressure (Yurkstas and Kapur)

Recording Centric Position

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

Line up Marks Eliminate all contact with record bases Must only be wax rim to wax rim contact

Videos Centric Record Mount Mandibular Cast

Review of Centric Record Procedure

Reference Notches In Wax Rims Two sharp “V”-shaped notches in molar/premolar region of each side Depth: 1-2 mm 1-2 mm

Ensure Proper Notches Too Shallow - no undercuts

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

Thin Layer of Material Too Thick Good

Thin Layer Want flat record, no excess on sides of rims Material over sides of rim can cause deflection when checking record

Stabilize the Mandibular Record Base Index fingers on flange (or recess in rim), thumbs under symphysis

Patient Active, Dentist Guides Patient opens, relaxes, and slowly closes

Recording Should Feel Relaxed Gently arc mandible in a hinge-like motion There should be NO: Translation Muscle splinting

If Mandible Has Retentive Rim or Natural Dentition Implants, single denture, very retentive record base Don’t need to stabilize Operator places hands extraorally Ensure no translation

Patient Instructions Close until rims are almost touching (1 mm separation) Stop as soon as this position has been reached Some patients may not be able to determine contact

Patient Instructions Never instruct patient to bite firmly Can cause translation or inaccuracy

Ensure Accurate Record Keep hands on mandible to ensure no translation during setting Hold position until set 1-2 min Remove both rims together Separate rims

Ensure Accurate Record Registration Should be Sharp, Not Rounded Ensure record is repeatable by repeating with record in place If not repeatable, take another record and check repeatability again prior to mounting

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

Prior to Mounting Mandibular Cast Ensure Only wax-rim to wax-rim contact Casts should not contact Record bases should not contact If other contacts, mounting will be incorrect

Mounting Mandibular Cast Stabilize wax rims together with sticky wax and sticks sticky wax directly - 4 spots Critical for accurate mount

Mounting Mandibular Cast Use mounting plaster After set, remove record & adjust incisal pin to allow contact between rims Occlusion rims should be touching evenly, over entire occlusal surface

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

Take New Record to Check CR Take new record, place on articulator Release articulator centric locks Should arc into record without any translation If not the same, take 3rd record to see which one is reproducible

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

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

Protrusive Records Close w. mandible positioned anteriorly Posterior separation critical to capture Not repeatable – determined by amount of protrusion

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

To Set Condylar Inclination Condylar elements unlocked Instrument protruded, rims closed into record Only wax-rim to wax-rim contact on articulator – otherwise can’t set properly

Adjust Protrusive Guide for Maximal Interdigitation

Protrusive Record Video

Protrusive Records Lateral component of condylar guidance (Bennett Angle) set arbitrarily at 15°

Protrusive Records Monoplane Occlusion Protrusive record still required Allows observation of posterior disclussion

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

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