6.2 Maxillomandibular Relationships, Vertical Dimension & Occlusion Schemes

Establishing accurate maxillomandibular relations is critical in complete denture therapy. Because the edentulous patient lacks natural occlusal stops and periodontal mechanoreceptors, the clinician must re-establish the vertical dimension of occlusion, guide the mandible into a reproducible reference position in centric relation, and design an occlusal scheme that stabilizes the prostheses during functional and parafunctional movements.

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Vertical Jaw Relations: VDR, VDO, and Freeway Space

Vertical jaw relations establish the vertical separation of the maxilla and mandible during resting tonicity versus tooth contact:

                     VERTICAL DIMENSIONS OF THE JAW

   Upper Facial Point (e.g., Subnasale)
         |
         |   ============================= 
         |   Vertical Dimension of Rest (VDR)
         |   (Muscles in passive tonic equilibrium)
         |   ============================= 
         |                ↕  FREEWAY SPACE (Interocclusal Rest Space)
         |                   Normal: 2.0 to 4.0 mm
         |   ============================= 
         |   Vertical Dimension of Occlusion (VDO)
         |   (Teeth or occlusion rims in contact)
         v   ============================= 
   Lower Facial Point (e.g., Gnathion)

1. Vertical Dimension of Rest (VDR)

• Definition: The postural relationship of the mandible to the maxilla when the patient is resting comfortably in an upright position and the elevator and depressor muscles are in a state of minimal, passive tonic contraction.
• Properties: Governed by muscle tone and gravity; remains relatively stable throughout adult life, even after tooth loss.
• Clinical Determination:
  • Facial Measurements (Niswonger / Willis Method): Using a Willis gauge or millimeter ruler, measure between subnasale (base of nose) and gnathion (most inferior point on chin). In harmonious facial proportions, this equals the distance from the outer canthus of the eye to the rima oris (corner of the mouth), or from the pupil to the commissure.
  • Physiological Relaxation: Patient swallows and lets the jaw relax, or repeatedly phonates the letter "m" (e.g., repeating "Emma") until the mandible drops into its resting posture.

2. Vertical Dimension of Occlusion (VDO)

• Definition: The vertical distance measured between two arbitrary facial points (nose and chin) when the teeth or occlusion rims make maximum contact in centric occlusion.
• The Formula:

$\text{Freeway Space (Interocclusal Rest Space)} = \text{VDR} - \text{VDO} = 2.0\text{ to }4.0\text{ mm}$

3. Closest Speaking Space of Silverman

• During the pronunciation of sibilant sounds ("s", "z", "ch", "sixty-six", "Mississippi"), the incisal edges of the maxillary and mandibular anterior teeth should approach each other closely without touching, maintaining a clearance of 1.0 to 2.0 mm.
• This is the definitive phonetic test to verify that VDO has not been excessively opened.

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Clinical Consequences of Altered Vertical Dimension

Altering the vertical dimension beyond physiological tolerances produces severe pathological, functional, and esthetic consequences:

                   CLINICAL PATHOLOGY OF ALTERED VDO

         EXCESSIVE VDO                           INSUFFICIENT VDO
   (Freeway Space < 2.0 mm)                (Freeway Space > 4.0 mm)
              ↓                                       ↓
   * Teeth click during speech             * Angular cheilitis (salivary pooling)
   * Muscle fatigue & spasm                * Pseudo-prognathic facial collapse
   * Accelerated bone resorption           * Cheek and lip biting
   * Inability to close lips at rest       * Reduced masticatory efficiency
   * Strained facial appearance            * TMJ pain & retrodiscal loading

1. Excessive VDO (Increased VDO / Insufficient Freeway Space < 2.0 mm)

When the VDO is set too high, the freeway space is encroached upon or eliminated entirely:

• Teeth Clicking During Speech: The anterior teeth collide during normal speech because the closest speaking space is violated.
• Muscular Fatigue and Pain: The masseter, temporalis, and medial pterygoid muscles remain under continuous isometric stretch, causing severe fatigue, stiffness, and spasm.
• Accelerated Alveolar Bone Resorption: Continuous non-physiological pressure transmitted through the denture bases stimulates rapid osteoclastic resorption of the residual alveolar ridges.
• Generalized Ridge Soreness: Patient complains that "the entire gums ache everywhere," rather than reporting a localized sore spot.
• Esthetic Impairment: Strained facial appearance; mentalis muscle hyperactivity with chin dimpling; inability to close the lips comfortably at rest (lip incompetence).

2. Insufficient VDO (Decreased VDO / Excessive Freeway Space > 4.0 mm)

When the VDO is over-closed, the lower third of the face collapses:

• Angular Cheilitis (Perlèche): Deep folds develop at the labial commissures due to facial collapse. Saliva pools continuously in these macerated skin creases, fostering opportunistic superinfection with Candida albicans and Staphylococcus aureus.
• Facial Collapse (Aging Appearance): Sunken lips, loss of vermilion border visibility, prominent protruding chin, and deepened nasolabial and mentolabial grooves, creating a characteristic pseudo-Class III (prognathic) appearance.
• Cheek and Lip Biting: The flaccid buccinator musculature loses tonic tension and folds inward between the occlusal tables during mastication.
• Decreased Masticatory Efficiency: Chewing power is reduced because the masticatory muscles operate at a mechanically disadvantaged shortened length.
• TMJ Symptoms: Deep condylar displacement into the glenoid fossa can compress sensitive retrodiscal tissues, generating joint pain and acoustic clicking.

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Horizontal Jaw Relations: Centric Relation (CR)

Definition of Centric Relation

According to the Glossary of Prosthodontic Terms (GPT-9), Centric Relation (CR) is:

"A maxillomandibular relationship, independent of tooth contact, in which the condyles articulate in the anterior-superior position against the posterior slopes of the articular eminences; in this position, the mandible is restricted to a purely rotary movement; from this unstrained, physiologic, maxillomandibular relationship, the patient can make vertical, lateral or protrusive movements; it is a clinically useful, repeatable reference position."

Earlier editions (GPT-5 to GPT-8) also described the thinnest avascular portion of the discs as interposed; GPT-9 (2017) dropped that phrase.

Critical Biomechanical Properties of CR

1. Reproducibility: CR is a bone-to-bone, disc-interposed reference position. Because it is independent of teeth, it is the only reproducible, repeatable, and verifiable horizontal reference position available in edentulous patients.
2. Rotational Axis: In centric relation, the mandible rotates around the transverse horizontal hinge axis during the initial 20 to 25 mm of interincisal opening before anterior translation begins.
3. Treatment Reference: In complete denture prosthodontics, the artificial teeth are arranged so that maximum intercuspation coincides precisely with Centric Relation (Centric Occlusion = Centric Relation).

Methods of Recording Centric Relation

• 1. Gothic Arch (Needle Point / Arrow Point) Tracing:
  • Mechanism: An intraoral or extraoral tracing device consisting of a central bearing pin on one arch and a recording plate coated with wax or ink on the opposing arch. Mandibular lateral and protrusive movements generate a characteristic arrow-point tracing.
  • The Apex: The sharp apex of the arrow point indicates true Centric Relation. Highly objective; eliminates subjective operator pressure and soft-tissue displacement errors.
• 2. Bimanual Manipulation of Dawson:
  • Clinician positions four fingers of each hand along the lower border of the mandible (angle and ramus), with both thumbs resting lightly over the symphysis of the chin. The fingers lift the condyles anterosuperiorly against the eminence while the thumbs guide the mandible without posterior displacement.
• 3. Chin Point Guidance:
  • Clinician places the thumb and index finger on the patient's chin, guiding the mandible upward and backward. Caution: excessive posterior force can displace the condyles postero-inferiorly into retrodiscal tissues.
• 4. Swallowing / Tongue-Retraction Method:
  • Patient is instructed to place the tip of the tongue onto the posterior border of the upper occlusion rim and swallow gently, seating the condyles into their anatomical position.

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Complete Denture Occlusion Schemes

The choice of occlusal scheme depends on ridge anatomy, muscular coordination, and skeletal jaw relationships:

                      COMPLETE DENTURE OCCLUSION SCHEMES

    Bilateral Balanced           Lingualized Occlusion           Monoplane (0°)
    (Anatomic: 30° - 33°)        (Mortar and Pestle)           (Neutrocentric: 0°)

          /\   /\                    /\                          |       |
         /  \ /  \                  /  \ (Lingual Cusp)          |       |
        +----+----+                +----+                        +-------+
        |    |    |                |    |                        |       |
        +----+----+                +----+                        +-------+
         \  / \  /                 (____) (Shallow Fossa)        |       |
          \/   \/                 /      \                       |       |
      [Working & Balancing]     [Zero Buccal Deflection]       [Zero Shearing Vectors]

1. Bilateral Balanced Occlusion (Anatomic / Semi-Anatomic)

• Concept: Simultaneous bilateral contact of maxillary and mandibular teeth in centric relation and across all eccentric excursions (working side, non-working/balancing side, and protrusive movement).
• Tooth Selection: Anatomic teeth (30° to 33°) or semi-anatomic teeth (20°).
• Christensen's Phenomenon:
  • When flat occlusal rims or teeth move into protrusion, the downward and forward incline of the articular eminence causes a wedge-shaped separation (gap) between the posterior teeth.
  • In balanced occlusion, this gap is compensated by incorporating the Curve of Spee (anteroposterior compensating curve) and the Curve of Wilson (mediolateral compensating curve), maintaining simultaneous posterior balance during incisal biting.
• Hanau's Quint Laws of Articulation: Balance is governed by the dynamic interaction of five variables (Thielemann later expressed the relationship as balanced articulation $= \frac{C \times I}{H \times O \times K}$):
  1. $C$ = Condylar Guidance: Fixed by the patient's TMJ anatomy; cannot be altered by the dentist.
  2. $I$ = Incisal Guidance: Controlled by the clinician; kept as low as possible in complete dentures to minimize tipping levers.
  3. $H$ = Cusp Angle (Height): Angle of the tooth cusps.
  4. $O$ = Plane of Occlusion: Oriented parallel to Camper's line.
  5. $K$ = Compensating Curve: Curve of Spee and Wilson.
• Indications: Well-preserved residual ridges, repeatable centric relation, Class I jaw relationships.
• Contraindications: Severely resorbed, flat, or knife-edge ridges (steep cuspal inclines generate destructive lateral shearing vectors that dislodge the denture bases).

2. Lingualized Occlusion

• Concept: Formulated by Alfred Gysi and popularized by S.H. Payne. Prominent maxillary lingual cusps (anatomic 30° or semi-anatomic 20°) act as the primary functional elements, articulating against shallow, widened central fossae of mandibular teeth (0° to 10° or 20°).
• Buccal Cusp Clearance: The maxillary buccal cusps are ground out of contact (raised 1.0 mm above the occlusal plane), eliminating all lateral incline interference.
• Biomechanics: Functions on a mortar-and-pestle principle. Masticatory forces are concentrated strictly vertically onto the center of the mandibular residual ridge, eliminating lateral tipping torque.
• Indications:
  • Severely resorbed, flat, or knife-edge mandibular ridges.
  • Displaceable, flabby alveolar ridges.
  • Discrepancies in ridge relationship: Class II and Class III malocclusions, crossbites.
  • Patients requiring natural esthetics with compromised ridge stability.
• Advantages: Combines the cutting penetration of cusped teeth with the lateral freedom of non-anatomic teeth; forgiving of minor centric discrepancies; easy to adjust.

3. Monoplane / Non-Anatomic (Neutrocentric) Occlusion

• Concept: Devised by M.M. DeVan. Non-anatomic flat (0-degree) teeth are arranged on a single flat occlusal plane oriented parallel to the residual ridges. No compensating curves are placed, and no eccentric balance is attempted.
• Kinematics: Pure vertical chewing strokes without lateral shearing vectors. During protrusion, posterior separation occurs (Christensen's phenomenon is accepted).
• Anterior Tooth Arrangement: Anterior teeth are arranged with zero vertical overlap (zero overbite) and 1.5 to 2.0 mm of horizontal overlap (overjet) to prevent posterior dislodgement during incisal contact.
• Indications:
  • Severely atrophic, flat mandibular ridges.
  • Extreme skeletal Class II or Class III malocclusions.
  • Patients with neuromuscular disorders (e.g., Parkinson's disease, post-stroke ataxia, severe dyskinesia) who exhibit erratic masticatory strokes and cannot achieve a reproducible centric relation.
• Limitations: Compromised esthetics; reduced masticatory efficiency (crushing rather than shearing food).

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Occlusion Schemes Comparison Matrix