Maxillo-Mandibular Relations and Vertical Dimensions: Study Notes

MMR Records: Maxillo-Mandibular Relations and Vertical Dimensions

  • Purpose of MMR records:
    • Determine VDR and OVD
    • Create CR (centric relation) records
    • Create protrusive records (jaw records at wax denture try-in or jaw records appointment)
    • Perform tooth selection (refer to Lecture 6)
    • Record Posterior Palatal Seal
    • Transfer maxillo-mandibular relationship to articulator for balanced occlusion

Vertical Dimension Concepts

  • Key dimensions:

    • Vertical Dimension of Rest (VDR): vertical separation of jaws when opening/closing muscles are in tonic (rest) contraction.
    • Occlusal Vertical Dimension (OVD or VDO): vertical distance when the teeth are in occlusion.
    • Relationship: the difference between rest position and occlusion is the free-way space.

  • Definitions and relationships:

    • VDR and OVD are two measurable lengths used to establish MMR records.
    • In the absence of pathology, physiologic rest position is fairly constant and can be recorded accurately.
    • The vertical separation between arches is determined to establish balanced occlusion.

  • Key formula:

    • VDR - OVD = \, \text{Free-way space}
    • Range of free-way space: 2\,\text{mm} \leq \text{Free-way space} \leq 4\,\text{mm}

  • Physiologic Rest Position (PRP):

    • The vertical separation of the jaws when the mandible is at rest with the opening/closing muscles in tonic contraction.
    • Used to determine OVD.

Practical Goals of Complete Denture Occlusion

  • Limit trauma to remaining supporting structures
  • Preserve remaining tissues
  • Enhance denture stability
  • Restore esthetics, speech, and mastication

Occlusion Terminology and Concepts

  • Balanced Occlusion: maintaining simultaneous contacts in centric and eccentric positions.
  • Lingualized Balanced Occlusion: a form of balanced occlusion focusing on lingual contact of upper teeth with mandibular teeth.
  • Protrusion: anterior-posterior movement of mandible forward.
  • Balancing side / Working side: balancing side contacts during movement; working side is the side toward which the jaw moves.
  • Centric: a defined jaw relation used as a reference point for occlusion.

Establishing Jaw Relation Records

  • To obtain balanced occlusion, transfer the patient’s maxillo-mandibular relation to the articulator.
  • Records required:
    • VDR and OVD (VDO)
    • Facebow record
    • Protrusive (jaw) record
    • Tooth selection (lect. 6)
    • Posterior Palatal Seal record

Determination of Vertical Dimension: VDR, VDO, and Related Terms

  • VDR is determined via multiple methods to ensure accuracy:
    • Facial measurements
    • Tactile sense of comfort
    • Phonetics (e.g., phonetic practice like saying mm-mm)
    • Facial expression (relaxed facial expression when jaws are at rest)
    • Anatomic landmarks (average measurements, with caveats)
    • Establishing a tentative VDR by comparing results from several methods
  • Tentative VDR: no single method is valid for all patients; use several methods and compare results

Facial Measurements and Landmarks for VDR

  • Steps used to establish tentative VDR include:
    • Facial measurements: patient sits comfortably; maxillary record base in place; reference points on nose and chin; patient swallows and relaxes; measure distance between references to estimate VDR
    • Tactile sense
    • Phonetics: repeat “mm-mm” and relax
    • Facial expression: observe relaxed expression when jaws are at rest
    • Anatomic landmarks: average measurements (note potential validity issues)

Freeway Space and OVD Determination

  • Free-way space (Interocclusal Rest Space): difference between VDR and OVD.
  • Definition:
    • ext{Free-way space} = VDR - OVD
  • Clinical note: Free-way space typically ranges from approximately 2\text{ mm} to 4\text{ mm} in many patients.

Wax Rim Contouring and Occlusal Plane

  • Procedure:

    • Place maxillary record base and wax rim; contour for proper phonetics, esthetics, lip support, and occlusal plane.
    • With lips at rest, the wax rim should project约1–2 mm below the lip line (before and after adjustment).

  • Occlusal plane alignment:

    • Adjust the wax rim plane to be parallel to Camper’s plane ( ala of the nose to the superior border of the tragus of each ear )
    • Also adjust to be parallel to the interpupillary line.

  • Camper’s plane: defined by the ala of the nose and the tragus.

  • Interpupillary line: line between pupils; used for orientation.

  • Fox Plane: an instrument to help orient the occlusal plane with reference to lip corners.

The Occlusal Plane, Midline, and Landmark Lines

  • Occlusal plane: the plane defined for the occluding surfaces.
  • Landmarks used:
    • Midline on the wax rim
    • Canine line determined by landmarks (ala of the nose, lip commissures at rest, and smile line)
    • Lip commissures at rest and smile line help determine canine line
    • Patient phonetics: have patient say “eeeee” to help establish smile line and lip movement
  • Facial landmarks help locate midline and canine positions for proper esthetics and function

Midline and Canine Line Identification

  • Mark the midline on the wax rim.
  • Mark midline, smile line, and canine lines:
    • Canine line is approximated by landmarks: ala of the nose and lip commissures at rest
    • Lip commissures at rest and smile line assist in determining canine position
    • The patient’s “eeeee” phonation helps refine canine and incisor positions via soft tissue guidance

Methods for Obtaining the Occlusal Vertical Dimension (OVD)

  • Methods include softening wax rims and allowing patient to bite down to seat the rim at the desired position.
  • Specific technique:
    • Soften the mandibular wax rim in a warm water bath.
    • Have the patient bite down on the softened rim and repeat until the patient achieves the previously determined VDO position.
    • Relationship: VDR − OVD = Free-way space.

Interocclusal Rest Space and Speaking Tests

  • Interocclusal rest space refers to the distance between opposing teeth when mandible is in physiologic rest.
  • Speaking tests for verifying OVD:
    • Assess “s” sounds and closest speaking space (lip/lingual contact) during speech.
    • Clinically test by counting from 60 to 70 while monitoring occlusal fit.

Clinical Consequences of Inadequate or Excessive Rest Space

  • Inadequate rest space (Excessive VDO):

    • Clicking of teeth
    • Facial distortion and tense appearance
    • Difficulty closing lips and swallowing; soreness under denture;
    • Increased ridge resorption due to trauma

  • Excessive rest space (Overclosed VDO):

    • Potential TMJ damage due to over-closure; restricted tongue space
    • Facial distortion with chin closer to nose; commissures turn downward; lips appear thinner and less full
    • Muscles of facial expression may lose tone; face appears flabby; angular cheilitis can occur

Facebow Records and Hinge Axis Concepts

  • Purpose of facebow:

    • Records the orientation of the maxilla to the terminal hinge axis
    • Provides the same relative opening axis on the articulator as the mandible has to the TMJ

  • Hinge axis definitions:

    • Hinge Axis: a hypothetical line through the two mandibular condyles around which the mandible rotates
    • Arbitrary Hinge Axis: estimated axis location; e.g., earbows use external auditory meatus as reference; typically within about +6 mm of true axis
    • True Hinge Axis: difficult to determine in many patients, especially edentulous; requires special equipment

  • Denar Hanau Ivoclar Facebow: a brand/model used to orient the maxilla to the transverse axis of the mandible in three dimensions and transfer this orientation to the articulator

Facebow Transfer Record: Armamentarium and Procedure

  • Armamentarium includes:
    • Compound, Water bath, Alcohol torch, Vaseline, Red-handled knife, Facebow
  • Steps:
    • Place notches in the maxillary wax rim as shown
    • Index wax rim to bite fork with compound; apply a thin Vaseline layer; temper and center midline; soften compound
    • Place compound on bite fork and align with midline; place four notches on the wax rim
    • Mark the third point of reference: using Denar facebow, this point is 43 mm above the level of the lateral incisor (in edentulous patients, this point is represented by the wax rim)
    • Place facebow in position; align ears; ensure bow is parallel to the interpupillary line; position the 3rd point of reference (points a, b, c)
    • Tighten bolts in sequence (1-2); carefully remove the facebow from the patient
    • Mount the maxillary cast onto the bite fork and attach facebow to the articulator with the jig; note V-notches for lab remount
    • The bite fork record is indexed to the maxillary wax rim

Mounting, Articulator Setup, and CR/CO Concepts

  • Mountings should be finished smoothly and neatly; casts should appear well-polished

  • After acquiring VDO, the mandibular cast is mounted using CR records:

    • Centric Occlusion (CO): occlusion of opposing teeth when the mandible is in centric relation; may not coincide with maximum intercuspation
    • Centric Relation (CR): maxillomandibular relationship where condyles articulate with the thinnest avascular portion of the discs, with the mandible in anterior-superior position against the slopes of the articular eminences
    • CO is tooth-to-tooth in a functional position; CR is bone-to-bone relation and a static reference point
    • In complete denture occlusion, CR ≈ CO (CR = CO in complete dentures), and CR should be recorded at the proper VDO

  • Requirements for a reliable CR record:
    1) Record the horizontal relation of the mandible to the maxilla at the proper VDO
    2) Apply equal vertical pressure on the record base while recording
    3) Avoid distortion of the record until casts are mounted
    4) A record that cannot be repeated or verified is unacceptable

  • Verification and preparation steps:

    • Check interferences between record bases and adjust as needed before final recording
    • If retention is lacking, apply a thin layer of powder adhesive to the record base, tap off excess, moisten the surface, and use denture adhesive if needed
    • Before making the final CR record, ensure posterior casts do not touch

Centric Relation Records: Technique and Practical Details

  • Two-phase approach to CR records:
    1) Get the mandible retruded using a gentle, bimanual technique
    2) Position the condyle-disc assembly in the uppermost anterior position and have the patient practice closing gently in a retruded position before final recording

  • Practical cues for the patient:

    • Instruct the patient to bring the tongue back, touch the roof of the mouth in the back, and close gently
    • Use both hands to stabilize the mandibular record base during retrusion (fingers on buccal shelf areas; thumbs on mandibular borders)

  • Margin notes: maintain good support and avoid forcing the mandible during retrusion

  • Final CR record considerations:

    • CR records should be repeatable and verifiable; accuracy is critical for proper mounting and subsequent occlusal arrangement

Protrusive Records: Purpose and Setup

  • Protrusive records capture anterior guidance and condylar paths necessary for balanced occlusion in eccentric movements
  • Procedure details:
    • The mandible must be protruded a minimum of 5-6\,\text{mm} during recording
    • Loosen centric locking pins before taking the protrusive record
    • Set condylar inclination by rotating the condyle until the teeth seat completely into the protrusive record
  • Use protrusive records to calibrate the articulator so that eccentric movements mimic the patient’s mandible-to-maxilla movements

Summary: Practical Sequence for Maxillo-Mandibular Records (MMR)

  • Steps used in clinical practice (as summarized in the module):
    • 1) Seat the patient comfortably; establish lip contour, midline, and occlusal plane; contour maxillary wax rim for phonetics
    • 2) Establish (a) VDR and (b) VDO
    • 3) Obtain a facebow transfer record and mount the maxillary cast
    • 4) Obtain a tentative CR record at the proper VDO
    • 5) Use the CR record to mount the mandibular cast on the articulator
    • 6) Obtain a protrusive record to set condylar inclinations
    • 7) Finalize mounting and proceed to denture fabrication with balanced occlusion in mind

Reading and Study References (Lecture Context)

  • Complete Denture Clinical Syllabus (PDF on CCLE): P 28-34 (MMR) and P 34-36 (Tooth Selection); P 36-37 (Mounting casts with MMR records)
  • Reading assignments on CCLE for Lectures 8 and Immediate Complete Denture practice (P42-45, P46-52, P52-57)

Quick Recall Questions (From Objectives)

  • Describe three methods used in determining the vertical dimension of rest on a patient.
  • Define the occlusal plane and its landmarks; describe the methods used to determine the plane of occlusion in edentulous patients.
  • What clinical problems arise if the plane of occlusion is too low or too high?
  • What is the purpose of condylar settings on your articulator? How is it transferred to the articulator in edentulous patients? How is the Bennett angle set?
  • Define centric relation and centric occlusion; what is the difference between them?
  • What clinical problems occur when the vertical dimension of occlusion is closed excessively compared to the vertical dimension of rest?
  • Why do we use centric relation when making complete dentures?

Practical Exam and Lab Notes

  • Practical exam: Anatomic setup (Open book) on CCLE; date: July 19, 2019; 2:00–5:00 PM; complete anatomic setup in 3 hours
  • Practical focus: Mastery of MMR, tooth selection, mounting casts with MMR records