MaxilloMandibular Relationships Centric and Protrusive Records This presentation

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

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 Robert W. Loney

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 Robert W. Loney

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 Robert W. Loney

Finding a Treatment Position Acceptable position should be: • Conducive to health • Relatively repeatable • position should be checked before dentures completed Robert W. Loney

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

Centric Relation (CR) • Treatment Position • Centric position of mandible to maxilla • Defined by position of condyles, not teeth • Hinge position Robert W. Loney

Hinge Position is Repeatable • Relatively centered • Patient can find stable occlusal contacts easily • Allows change in vertical dimension Robert W. Loney

Centric Relation • Treatment position • Not necessarily ‘ideal’ or ‘normal’ Robert W. Loney

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 Robert W. Loney

CR and CO have been defined differently by various investigators, and differently over different time periods Robert W. Loney

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

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

Where is Centric Relation? Glossary of Prosthodontic Terms: • Purely rotary movement about transverse horizontal axis Robert W. Loney

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

Why Anterior-Superior? The articular disk is in a anterior-superior position Robert W. Loney

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

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

For the purpose of fabricating complete dentures, the superioranterior position of Centric Relation will be used Robert W. Loney

Clinically dentist cannot determine actual position of condyles at time of jaw relations records Robert W. Loney

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 Robert W. Loney

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

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) Robert W. Loney

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) Robert W. Loney

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 Robert W. Loney

When to Not to Use Centric Relation • • • Stable occlusion No pathology Posterior centric stops present No valid reason to change Use maximum intercuspation Robert W. Loney

Patient Position Centric Relation Patient in a slightly supine position Robert W. Loney

Stabilizing the Record Bases Occlusion rim notched to aid stabilization Robert W. Loney

Centric Relation Bimanual Manipulation Index fingers on the rim, thumbs under symphysis Robert W. Loney

Maxillo-Mandibular Relationships Centric and Protrusive Records Robert W. Loney

Registering Centric Relation • Jiggle mandible • Mandible should freely arc • Allow the patient to close into contact Robert W. Loney

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

Registering Centric Relation • Minimal closing pressure (Yurkstas and Kapur) Robert W. Loney

Recording Centric Position Robert W. Loney

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 Robert W. Loney

Line up Marks • Eliminate all contact with record bases • Must only be wax rim to wax rim contact Robert W. Loney

Videos • Centric Record • Mount Mandibular Cast Robert W. Loney

Review of Centric Record Procedure Robert W. Loney

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

Ensure Proper Notches Too Shallow - no undercuts Robert W. Loney

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

Thin Layer of Material Too Thick Robert W. Loney Good

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

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

Patient Active, Dentist Guides Patient opens, relaxes, and slowly closes Robert W. Loney

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

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 Robert W. Loney

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 Robert W. Loney

Patient Instructions • Never instruct patient to bite firmly • Can cause translation or inaccuracy Robert W. Loney

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 Robert W. Loney

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 Robert W. Loney

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

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 Robert W. Loney

Mounting Mandibular Cast • Stabilize wax rims together with • sticky wax and sticks • sticky wax directly - 4 spots • Critical for accurate mount Robert W. Loney

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 Robert W. Loney

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

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 3 rd record to see which one is reproducible Robert W. Loney

Protrusive Records • Used to set condylar guidance • Helps setting teeth for best occlusal contacts Robert W. Loney

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 Robert W. Loney

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

Record Requirements • Material must interdigitate with the opposing “V-shaped” notches • Record should cover entire rim surface Robert W. Loney

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 Robert W. Loney

Adjust Protrusive Guide for Maximal Interdigitation Robert W. Loney

Protrusive Record Video Robert W. Loney

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

Protrusive Records Monoplane Occlusion • Protrusive record still required • Allows observation of posterior disclussion Robert W. Loney

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 Robert W. Loney

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 Robert W. Loney