16.2 Removable Complete Dentures: Impression, Occlusion, and Delivery

Removable Complete Dentures: Impression & Delivery Principles

Fabricating successful complete removable dentures requires thorough anatomical evaluation, precise border molding, accurate jaw relation records, and proper post-delivery tissue management. Complete dentures rely entirely on mucosal support, neuromuscular control, and atmospheric seal for retention and stability.

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Anatomical Landmarks & Tissue Support Areas

Understanding which anatomical structures bear forces and which must be relieved is critical to prevent tissue necrosis and denture displacement.

Maxillary Anatomical Landmarks

• Primary Support Areas: Hard palate (palatal vaults horizontal to occlusal load) and post-extraction alveolar ridges. Dense submucosa over keratinized epithelium handles vertical masticatory loads.
• Incisive Papilla: Overlaying the nasopalatine canal (containing nasopalatine nerves and vessels). Must be relieved in custom trays; serves as a landmark for setting maxillary central incisors (labial surfaces are placed 8–10 mm anterior to the center of the papilla).
• Maxillary Tuberosity: Posterior termination of the maxillary alveolar ridge. Provides resistance to lateral displacement. Bulbous or undercut tuberosities may require surgical reduction.
• Posterior Palatal Seal (PPS) Area: Soft tissue area at or near the vibrating line (AH line) between the hard and soft palates. The PPS compensates for volumetric acrylic polymerization shrinkage (~7%) and maintains atmospheric peripheral seal during function.
• Fovea Palatinae: Bilateral mucosal indentations formed by coalescence of mucous gland ducts. Located on the hard/soft palate border, serving as a visual landmark 1–2 mm posterior to the vibrating line.

Mandibular Anatomical Landmarks

• Buccal Shelf: Primary stress-bearing area of the mandibular denture. Bounded medially by the crest of the residual ridge, laterally by the external oblique ridge, and distally by the retromolar pad. Covered by dense cortical bone and aligned perpendicular to vertical masticatory forces.
• Retromolar Pad: Primary posterior support landmark. Contains glandular tissue, fibers of the temporalis tendon, buccinator, and superior constrictor muscles, and the pterygomandibular raphe. Must be covered by the denture base to preserve bone height and maintain posterior seal.
• Genial Tubercles & Lingual Frenum: Bony spines serving as insertion for genioglossus muscles. Severe ridge resorption exposes genial tubercles, requiring relief to prevent denture dislodgement and pain during tongue movement.

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Impression Techniques & Border Molding

Complete denture impressions require a two-stage technique: primary preliminary impression followed by custom tray border molding and wash impression.

┌───────────────────────────┐     ┌───────────────────────────┐     ┌───────────────────────────┐
│   Preliminary Impression  │ ──► │  Custom Tray Border Mold  │ ──► │  Secondary Wash Impression│
│ (Alginate in Stock Tray) │     │ (Green Stick Compound)    │     │ (PVS / Polyether Wash)    │
└───────────────────────────┘     └───────────────────────────┘     └───────────────────────────┘

1. Preliminary Impression: Taken with irreversible hydrocolloid (alginate) or impression compound in a stock tray to construct a diagnostic cast.
2. Custom Impression Tray: Fabricated on diagnostic casts using light-cured resin, incorporating 2–3 mm wax relief over non-bearing structures (e.g., incisive papilla, mid-palatal raphe).
3. Border Molding (Functional Margin Record):
   • Performed sequentially in sections using low-fusing green stick thermoplastic compound.
   • Captures the active extension and width of the vestibules (recording buccinator, orbicularis oris, and frenal attachments in motion).
   • Mandibular Lingual Extension: Evaluated by asking the patient to push the tongue against the upper lip (determines mylohyoid and sublingual fold boundaries).
4. Secondary Wash Impression: Taken using Polysulfide, Polyether, or Addition Silicone (PVS) light-body material under light passive pressure to capture micro-detail without tissue displacement.

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Jaw Relation Records & Vertical Dimension

Transferring the spatial relationship of the maxilla and mandible to an articulator requires establishing vertical and horizontal record planes.

     ┌─────────────────────────────────────────────────────────────┐
     │    Vertical Dimension of Rest (VDR) [Muscles Relaxed]       │
     └──────────────────────────────┬──────────────────────────────┘
                                    │
                                    │  Minus 2 - 4 mm
                                    │  Interocclusal Rest Space
                                    ▼
     ┌─────────────────────────────────────────────────────────────┐
     │  Vertical Dimension of Occlusion (VDO) [Teeth in Contact]   │
     └─────────────────────────────────────────────────────────────┘

Formulations of Vertical Dimension

$\text{VDO} = \text{VDR} - \text{Interocclusal Rest Space (2 to 4 mm)}$

• Vertical Dimension of Rest (VDR): The involuntary postural position of the mandible when the patient is sitting upright and the masticatory muscles are in a state of minimal tonic contraction.
• Vertical Dimension of Occlusion (VDO): The distance between two fixed anatomical points (typically tip of nose to chin) when the teeth or occlusion rims are in contact.
• Interocclusal Rest Space (Freeway Space): The 2–4 mm vertical gap between occlusal surfaces when the mandible is in VDR.

Diagnostic Errors in VDO Setting

• Excessive VDO (Increased VDO / Lack of Freeway Space):
  • Symptoms: Teeth clicking during speech ("s" sounds), facial muscle fatigue, inability to close lips comfortably, rapid alveolar ridge resorption, pain under denture bases.
• Insufficient VDO (Decreased VDO / Excessive Freeway Space):
  • Symptoms: Reduced lower facial height, sunken cheeks, angular cheilitis (pooling of saliva at commissures infected with Candida albicans), reduced masticatory efficiency, temporomandibular joint discomfort.

Centric Relation (CR)

• Definition: The maxillomandibular relationship in which the condyles articulate in their most anterior-superior position in the articular fossae against the posterior slopes of the articular eminences.
• Clinical Significance: CR is an anatomical, repeatable, joint-guided reference position independent of tooth contact. It is the mandatory starting horizontal record for edentulous patients.

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Occlusal Concepts in Complete Dentures

Unlike natural teeth, which function independently, complete denture teeth act as a unified unit attached to a mobile acrylic base resting on fluid-filled mucosa.

Bilateral Balanced Articulation

• Definition: Simultaneous, even bilateral contact of anterior and posterior teeth in centric, protrusive, and lateral excursive movements.
• Purpose: Prevents tipping, unseating, or dislodgement of the denture bases during mastication or parafunctional movements.

Christensen's Phenomenon

Definition: The visual space (gap) created between the posterior occlusal surfaces of upper and lower occlusion rims or teeth when the mandible is protruded.

• Cause: As the mandibular condyle moves forward, it slides down the articular eminence (condylar guidance angle), depressing the posterior mandible relative to the anterior maxilla.
• Compensation: To maintain balanced contact during protrusion and eliminate this gap, prosthodontists introduce a Compensatory Curve (incorporating the anteroposterior Curve of Spee and mediolateral Curve of Wilson) or incline the posterior teeth.

                       Christensen's Phenomenon
                       
        Maxillary Arch   ───┬───┬───┬───┬───┬───►
                            │   │   │   │   │   ▲ (Posterior Gap
        Mandibular Arch  ───┴───┴───┴───┴───┴───►  during Protrusion)

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Post-Delivery Complications & Tissue Responses

Post-delivery adjustments require differential diagnosis between mechanical instability, occlusal trauma, and tissue pathology.

Pressure Sore Spots & PIP Application

• Discomfort caused by localized pressure peaks or overextended flanges.
• Diagnosed clinically by applying Pressure Indicating Paste (PIP) to the dry denture interior, seating the denture, and adjusting areas where paste is completely wiped away to bare acrylic.

Epulis Fissuratum

• Etiology: Hyperplastic fibrous tissue overgrowth occurring in the vestibular mucosa.
• Cause: Chronic irritation from an overextended or knife-edged denture flange on a severely resorbed ridge.
• Management: Surgical excision of the hyperplastic lesion followed by border reduction, tissue conditioning, and eventual denture reline/remake.

Inflammatory Papillary Hyperplasia

• Etiology: Multiple red, cobblestone-like nodular projections on the hard palatal vault mucosa.
• Cause: Combination of poor oral hygiene, continuous 24-hour denture wear, palatal relief chamber suction, and secondary Candida albicans infection.
• Management: Anti-fungal therapy (nystatin suspension or clotrimazole troches), strict instruction to remove dentures at night, tissue conditioning, and surgical removal (electrosurgery/laser) in severe refractory cases.