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COMPREHENSIVE PROSTHODONTICS ANSWERS (25 Marks Each)

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ANSWER 1: SINGLE COMPLETE DENTURE (25 Marks)

Definition

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Introduction and Clinical Significance

• Prevalence: Most commonly seen as a maxillary complete denture opposing a mandibular natural/partially edentulous dentition.
• The mandibular arch retains teeth more often than the maxilla because mandibular bone resorption after extraction can be severe and patients resist lower denture construction.

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Problems Specific to Single Complete Dentures

1. Retention and Stability Problems

2. Combination Syndrome (Kelly's Syndrome)

• Loss of bone from the anterior maxillary residual ridge
• Papillary hyperplasia of the hard palate
• Overgrowth and supraeruption of the mandibular anterior teeth
• Loss of alveolar bone and ridge height under mandibular posterior denture base
• Flabby (fibrous) replacement of anterior maxillary bone
• Occlusal plane discrepancy

3. Occlusal Plane Discrepancy

4. Dual Bite

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Patient Assessment

History

• Duration of edentulousness, previous denture experience
• Systemic conditions (xerostomia, diabetes, medications reducing salivary flow)
• Parafunctional habits

Clinical Examination

• Residual ridge - height, width, shape (assess for flabby ridge anteriorly)
• Maxillary tuberosities - check for fibrous tuberosities
• Frenal attachments
• Palatal vault form (flat, medium, high)
• Opposing natural teeth - periodontal status, occlusal wear, curves of Spee and Wilson, tooth positions
• Interridge distance and interarch space
• Evaluate for existing Combination Syndrome features

Radiographic Examination

• OPG: residual roots, unerupted teeth, bone quality
• PA views of suspect areas

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Treatment Planning

Options for Opposing Arch

1. Accept the natural dentition as is - if well-aligned, adequate periodontal support, no supraeruption
2. Selective grinding/equilibration of opposing natural teeth to establish an acceptable occlusal plane and harmonious centric stops
3. Restoration of opposing teeth to ideal occlusal contacts
4. Fixed partial dentures or implants in posterior mandible to prevent Combination Syndrome
5. Immediate extraction and conventional complete denture - convert to complete denture situations bilaterally (rarely recommended)

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Special Impressions

Maxillary Flabby Ridge Management

• Window technique: A window is cut in the custom tray over the flabby area. The posterior firm tissues are border-moulded and a wash impression with zinc oxide eugenol (ZOE) paste is made. The flabby tissue is then recorded with a low-viscosity material (plaster of Paris or light body silicone) without displacement.
• This ensures no distortion of the unsupported fibrous tissue and avoids forward rocking of the denture.

Border Moulding

Final Impression Material

• Zinc oxide eugenol (Impression paste) for resorbed ridges
• Low-viscosity addition silicone (monophase technique)
• Selective pressure impressions for firm and flabby ridge differentiation

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Jaw Relation Records

Vertical Dimension of Occlusion (VDO)

• Methods: Niswonger's method (VDR - VDO = 2-4 mm freeway space), phonetic method (closest speaking space), aesthetic assessment, pre-extraction records if available

Centric Relation vs. Habitual ICP

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Tooth Selection and Arrangement

Selection Principles

• Anterior teeth: Match natural mandibular teeth in size, form, and color
• Posterior teeth: Select cuspal morphology based on the opposing natural dentition

Occlusal Scheme

• Maxillary palatal cusps occlude in mandibular central fossae
• Reduces lateral forces on the denture base
• Preferred in SCD opposing natural dentition
• Allows centric stops on the complete denture without steep inclines that could displace it

• Simultaneous contact in both centric and eccentric positions
• Reduces tipping forces
• Difficult to achieve accurately when opposing natural dentition

• 0-degree cusp teeth
• Reduces lateral forces
• May compromise aesthetics and masticatory efficiency

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Posterior Palatal Seal (Post-Dam)

• Creates a pressure zone in the soft tissue
• Prevents break of posterior border seal during function
• Location: junction of hard and soft palate, identified by tissue displacement along vibrating line
• Depth: 1-2 mm in the midline (pterygomaxillary notch region), shallowing toward midline (torus palatinus consideration)

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Occlusal Adjustment at Delivery

1. Denture seating - verify full seating without occlusal prematurities
2. Centric relation contacts - articulating paper (Bausch 200 micron) to identify heavy contacts
3. Working and balancing side contacts
4. Protrusive contacts
5. Selective grinding to eliminate deflective contacts

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Follow-Up and Maintenance

• 24-hour review: check for sore spots, retention, speech
• 1-week review: relieve pressure spots, adjust occlusion
• 3-month review: relining assessment, combination syndrome monitoring
• Annual review: assess bone resorption, occlusal changes, denture hygiene

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Prognosis

• Progressive anterior maxillary bone loss
• Supraeruption of mandibular anterior teeth
• Continued resorption beneath the denture base

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References

1. Zarb GA, Hobkirk JA, Eckert SE, Jacob RF. Prosthodontic Treatment for Edentulous Patients: Complete Dentures and Implant-Supported Prostheses. 13th ed. St. Louis: Mosby/Elsevier; 2013. Chapters 7, 16.
2. Boucher CO, Hickey JC, Zarb GA. Prosthodontic Treatment for Edentulous Patients. 9th ed. St. Louis: CV Mosby; 1975.
3. Winkler S. Essentials of Complete Denture Prosthodontics. 2nd ed. Chicago: Year Book Medical Publishers; 1988. pp 157-170.
4. Kelly E. Changes caused by a mandibular removable partial denture opposing a maxillary complete denture. J Prosthet Dent. 1972;27(2):140-150.
5. Glossary of Prosthodontic Terms, 9th Edition. J Prosthet Dent. 2017;117(5S):e1-e105.
6. Swoope CC. Single denture construction. In: Dental Clinics of North America. 1977;21(2):251-263.
7. Saunders TR, Gillis RE Jr, Desjardins RP. The maxillary complete denture opposing the mandibular bilateral distal-extension partial denture. J Prosthet Dent. 1979;41:124-128.
8. Palmqvist S, Carlsson GE, Owall B. The combination syndrome: a literature review. J Prosthet Dent. 2003;90(3):270-275.

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ANSWER 2: IMMEDIATE DENTURES (25 Marks)

Definition

• Defined by the Glossary of Prosthodontic Terms (9th Ed.): "A dental prosthesis made to be inserted immediately following removal of teeth."

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Classification

Type 1: Conventional Immediate Denture

• Better stability and support during the construction phase
• Accurate posterior jaw relation records
• Better occlusal stability

Type 2: Immediate Overdenture

Type 3: Tooth-Supported Immediate Denture

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Advantages of Immediate Dentures

1. Psychological benefit: Patient never has to appear edentulous in public
2. Preservation of appearance: Supports facial contours, prevents collapse of muscles of facial expression and lips
3. Aids in hemostasis: Acts as a surgical dressing over the extraction wounds; pressure from denture reduces bleeding
4. Wound protection: Covers surgical wounds, reduces food contamination, minimizes post-operative pain and swelling
5. Preservation of VDO: Pre-extraction records of jaw relations, tooth position, lip support, and VDO are captured while natural teeth are still present
6. Easier adjustment to dentures: Patient adapts to speech, mastication, and aesthetics immediately - no edentulous phase
7. Preservation of neuromuscular patterns: Reduces loss of muscle memory and proprioceptive pathways
8. Maintains occlusal vertical dimension: Muscles of mastication adapt immediately
9. Guide to tooth position: Natural tooth arrangement guides artificial tooth placement
10. Better aesthetics: Replication of natural tooth position, size, and form is more accurate

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Disadvantages and Limitations

1. Relining required: Inevitably needed within 3-6 months as bone resorbs and healing occurs beneath the denture; the most significant disadvantage
2. Cannot preview aesthetics: Unlike conventional dentures, the patient cannot evaluate aesthetics at the try-in stage (no wax try-in with anterior teeth)
3. Higher cost: Multiple appointments, laboratory fees for reline/rebase
4. Surgical difficulties: Tissue trimming at the time of insertion may be difficult
5. Adjustment of denture required post-extraction: Pressure spots, trimming of alveoloplasty areas
6. Increased post-operative discomfort: More appointments in the post-operative period
7. Not suitable for all patients: Poor systemic health, coagulation disorders, extensive pathology may contraindicate
8. Ridge morphology may change unpredictably: If alveoloplasty is extensive, the fit changes substantially
9. Limited adaptation: Some patients find it difficult to tolerate a new prosthesis during healing

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Contraindications

• Acute infection in the region of extractions
• Blood dyscrasias and coagulation disorders (uncontrolled)
• Severe systemic illness
• Poor patient cooperation
• Extensive cysts or pathology requiring complex surgical management

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Clinical Procedures

Step 1: Preliminary Records

• Alginate impressions (maxillary and mandibular) with natural teeth present
• Face bow record and centric jaw relation record
• Photographs of the patient's face and smile
• Shade and mould selection for anterior teeth based on natural teeth

Step 2: Working Casts and Surveying

• Pour diagnostic casts
• Articulate on semi-adjustable articulator
• Assess ridge contour and interarch space
• Plan alveoloplasty if required (measured on the cast)

Step 3: Laboratory Procedures

• Posterior teeth are set first
• On the cast, the remaining anterior teeth are trimmed with a sharp instrument to simulate post-extraction ridge form
• For each anterior tooth: the tooth outline is traced, the labial surface of the tooth on the cast is removed to simulate the labial plate of bone loss, and the alveolar crest is rounded
• The cast reduction (alveoloplasty simulation): Each tooth is removed from the cast individually; the labial contour is reduced by 2-3 mm to simulate post-extraction ridge resorption; the ridge is smoothened
• Anterior teeth are then set in the modified cast at the pre-determined VDO, following the original tooth arrangement

Step 4: Trial Wax-Up and Wax Try-In (Posterior Only)

• A try-in with posterior teeth set is performed; anterior aesthetics cannot be evaluated at this stage
• VDO, CR, tooth arrangement, and plane of occlusion verified

Step 5: Processing

• The denture is flasked, dewaxed, packed with heat-cured PMMA, cured, deflasked, and finished

Step 6: Day of Insertion

• Extractions are performed atraumatically
• Alveoloplasty if required (to smooth sharp spicules)
• Denture is inserted immediately in the mouth
• Adjustments made for pressure spots
• Occlusion checked

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Post-Insertion Management

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Tissue Conditioning

• Cushion irritated tissues
• Maintain intimate contact with the changing ridge
• Allow minor corrections of fit

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Relining vs. Rebasing

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Special Considerations: Alveoloplasty on the Cast

1. Labial bone loss: ~2-3 mm reduction in the labial surface
2. Undercuts: Severe undercuts (bony prominences, exostoses, tori) must be reduced on cast and surgically at the time of extraction
3. Interproximal papillae: After tooth removal, the interproximal peaks are trimmed to simulate post-healing tissue

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References

1. Zarb GA, Hobkirk JA, Eckert SE, Jacob RF. Prosthodontic Treatment for Edentulous Patients. 13th ed. Mosby/Elsevier; 2013. Chapter 5.
2. Heartwell CM Jr, Rahn AO. Syllabus of Complete Dentures. 4th ed. Philadelphia: Lea & Febiger; 1986. Chapter 18 (Immediate Dentures), pp 335-364.
3. Winkler S. Essentials of Complete Denture Prosthodontics. 2nd ed. Year Book Medical Publishers; 1988. Chapter 22.
4. Boucher CO, Hickey JC, Zarb GA. Prosthodontic Treatment for Edentulous Patients. 9th ed. CV Mosby; 1975. Chapter 11.
5. Swoope CC, Kydd WL. The effect of cusp form and ridge morphology on denture base deformation. J Prosthet Dent. 1966;16:34-43.
6. Glossary of Prosthodontic Terms, 9th Ed. J Prosthet Dent. 2017;117(5S):e1-e105.
7. Atwood DA. Bone loss of edentulous alveolar ridges. J Periodontol. 1979;50(4 Spec No):11-21.
8. Tallgren A. The continuing reduction of the residual alveolar ridges in complete denture wearers. J Prosthet Dent. 1972;27(2):120-132.

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ANSWER 3: PREPROSTHETIC SURGERY IN COMPLETE DENTURE SUCCESS (25 Marks)

Definition and Rationale

• Broad, well-rounded, with a flat or slightly rounded crest
• Covered by firm, keratinized, attached mucosa
• Free from bony irregularities, undercuts, and exostoses
• Have adequate sulcus depth and vestibular height
• Free from pathological lesions

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Classification of Preprosthetic Surgical Procedures

A. Hard Tissue Procedures

1. Alveoloplasty

• Simple Alveoloplasty (Intraseptal Alveoloplasty / Dean's technique): Performed at the time of extractions. The interseptal bone between extraction sockets is compressed medially with finger pressure after socket curettage. Simple, conservative, quick.
• Radical Alveoloplasty (Compressive Alveoloplasty): Removal of the labial cortical plate and reshaping of the alveolar crest. Used for severe labial undercuts. More bone is sacrificed; reserved for cases with significant bony irregularities.
• Correction of undercuts: Local removal of knife-edge ridges or undercuts that would prevent denture insertion.

2. Torus Palatinus Removal

• Torus palatinus: A bony protuberance in the midline of the hard palate
• Contraindicated if small and non-interfering
• Surgical removal indicated when:
  • Torus extends beyond the vibrating line, compromising the posterior palatal seal
  • Large torus causes mucosal ulceration
  • Torus affects denture retention by fracturing the midline of the denture
  • Patient complains of food impaction around torus
• Technique: Midline incision, mucoperiosteal flap reflection, bone removal with bur and mallet/chisel, smoothing with bone file, primary closure

3. Torus Mandibularis Removal

• Lingual exostoses in the premolar region, bilateral in most cases
• Removal indicated when preventing flange extension and causing chronic mucosal trauma
• Technique: Mucosal incision over the crest, reflection of lingual flap, removal with chisel and mallet or surgical bur, bone file smoothing, closure

4. Removal of Exostoses

• Bony outgrowths on the buccal or labial plates of alveolar bone
• Must be removed to allow denture placement and eliminate undercuts
• Technique similar to torus removal

5. Maxillary Tuberosity Reduction

• Enlarged fibrous or bony maxillary tuberosities
• Causes inadequate interarch space (insufficient room for teeth and denture base)
• Fibrous tuberosity: Soft tissue reduction with tissue scissors or scalpel and primary closure
• Bony tuberosity: Osteotomy, bone removal, reshaping, closure

6. Mylohyoid Ridge Reduction

• Sharp, prominent mylohyoid ridge causes discomfort when the lower denture flange presses against it
• Indication: Persistent pain on the lingual flange of the lower denture despite relieving
• Surgical technique: incision at the crest of the ridge, subperiosteal reflection, reduction with bur or bone file

7. Genial Tubercle Reduction

• After severe mandibular resorption, the genial tubercles may become prominent at the crest of the ridge
• Cause instability and discomfort
• Surgical reduction performed under local anesthesia via a midline lingual incision

8. Mental Nerve Repositioning (Anterior Loop Correction)

• Severe mandibular atrophy brings the mental nerve to the crest of the ridge
• Denture pressure causes neuropathic pain
• Surgical repositioning of the nerve anteriorly (mental nerve transposition) creates adequate bone above the nerve for denture support

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B. Soft Tissue Procedures

1. Frenectomy / Frenotomy

• High frenal attachments (labial, buccal, lingual frenula) extending close to the alveolar crest compromise denture retention by breaking the peripheral seal
• Frenotomy: Simple incision and repositioning
• Frenectomy: Complete removal of the frenum
• Techniques: Classical excision, V-Y plasty, Z-plasty, electrosurgery, laser frenectomy
• Lingual frenectomy: Especially important in mandibular dentures; high lingual frenum restricts tongue movement and disrupts lingual border seal

2. Vestibuloplasty (Ridge Extension Procedures)

3. Excision of Flabby Ridge (Hyperplastic Ridge Reduction)

• Flabby (fibrous, hyperplastic) tissue replaces the anterior maxillary bone in Combination Syndrome
• Soft, displaceable tissue causes denture instability and rocking
• Surgical excision followed by healing and proper impression technique
• A minimum of 4-6 weeks healing is required before impressions

4. Papillary Hyperplasia of the Palate

• Inflammatory papillary hyperplasia (IPH): multiple papillary projections on the hard palate
• Caused by ill-fitting dentures, poor denture hygiene
• Treatment:
  • Phase 1: Tissue conditioning (remove denture at night, antifungal agents if Candida infection present)
  • Phase 2: Surgical excision (scalpel, electrosurgery, laser) or dermabrasion
  • Phase 3: New denture fabrication on healthy tissue

5. Epulis Fissuratum (Denture Hyperplasia)

• Fibrous hyperplastic tissue in the labial or buccal vestibule caused by overextended denture flanges
• Surgical excision required, followed by new denture
• Allow 6-8 weeks healing

6. Labial Scar Band Removal

• Scar tissue in the labial vestibule after cleft palate repair, burns, or previous surgery
• Restricts the denture flange; removed surgically

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C. Bone Augmentation Procedures

1. Ridge Augmentation with Hydroxyapatite (HA)

• Particulate HA implanted subperiosteally to increase ridge volume
• Used in severely resorbed ridges (Cawood and Howell Class IV-VI)

2. Onlay Bone Grafts

• Autogenous bone (iliac crest, tibial plateau, mandibular symphysis) or allografts
• Provide hard tissue augmentation before conventional complete denture or implant placement

3. Distraction Osteogenesis

• Used in severely atrophic jaws
• New bone generated in the distraction gap

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D. Pre-implant Bone Augmentation

• Sinus floor elevation (Caldwell-Luc or transcrestal approach)
• Guided bone regeneration with barrier membranes

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Timing of Denture Construction After Surgery

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References

1. Zarb GA, Hobkirk JA, Eckert SE, Jacob RF. Prosthodontic Treatment for Edentulous Patients. 13th ed. Mosby/Elsevier; 2013. Chapter 3 (Surgical Preparation of the Mouth for Complete Dentures).
2. Winkler S. Essentials of Complete Denture Prosthodontics. 2nd ed. Year Book Medical Publishers; 1988. Chapter 2 (Preprosthetic Surgery).
3. Peterson LJ, Ellis E, Hupp JR, Tucker MR. Contemporary Oral and Maxillofacial Surgery. 4th ed. St. Louis: Mosby; 2003. Chapter 12 (Preprosthetic Surgery).
4. Cawood JI, Howell RA. A classification of the edentulous jaws. Int J Oral Maxillofac Surg. 1988;17(4):232-236.
5. Heartwell CM Jr, Rahn AO. Syllabus of Complete Dentures. 4th ed. Lea & Febiger; 1986. Chapters 4-5.
6. Tallgren A. The continuing reduction of the residual alveolar ridges in complete denture wearers. J Prosthet Dent. 2003;89(5):427-435 (reprint of classic article).
7. Devlin H. Complete Dentures: A Clinical Manual for the General Dental Practitioner. Berlin: Springer; 2002. Chapter 2.
8. Winkler S, Ortman HR. A classification of complete denture patients. J Am Dent Assoc. 1970;81(6):1434-1437.

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ANSWER 4: PHONETICS IN COMPLETE DENTURES (25 Marks)

Introduction

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Anatomy of Speech Production

• Lungs (air reservoir and pump)
• Larynx (phonation, voiced vs. unvoiced sounds)
• Velopharyngeal mechanism (nasal vs. oral resonance)
• Tongue (most critical articulator)
• Teeth (especially mandibular and maxillary anterior teeth)
• Lips
• Hard and soft palate

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Classification of Speech Sounds

1. By Air Stream Modification

2. Consonants by Manner of Articulation

3. Consonants by Place of Articulation

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Role of Complete Denture in Phonetics

Anterior Teeth Position

• F and V sounds (labiodentals): The lower lip makes contact with the incisal edges of the maxillary anterior teeth. In a well-made denture, the incisal edges should lightly touch or be slightly contacted by the wet-dry line of the lower lip during normal speech. If teeth are placed too far posteriorly (lingually), F/V sounds are distorted (interdental - teeth too far anteriorly). If placed too far anteriorly, the labial flange may interfere.
• S sound (sibilant): Most diagnostically useful sound. When pronouncing a sustained "S", the teeth come close but do not contact (phonetic closest speaking space or closest speaking space of approximately 1 mm). This verifies the VDO.

Posterior Teeth Position and Palatal Contour

• The palatal contour of the maxillary denture affects resonance and tongue movement for lingual sounds
• An over-thick palate reduces tongue space, affecting T, D, N, L, S, Z
• The palatal contour should match the pre-extraction anatomy as closely as possible

Vertical Dimension of Occlusion (VDO) and Speech

• Too little VDO (over-closed): The freeway space is excessive; clicking sounds during speech as teeth come together excessively
• Too much VDO (over-opened): Teeth contact during "S" production; patients report "choppy" speech, teeth clicking constantly during normal conversation
• Phonetic method of VDO verification: Patient repeats "S" sounds; at correct VDO, a 1-mm space (phonetic freeway space) exists between the teeth

Denture Flanges and Speech

• Excessively thick flanges, particularly in the labial and buccal sulci, alter resonance and lip movement
• The palatal and lingual surfaces of the prosthesis should be contoured to allow adequate tongue placement

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Phonetic Assessment in Complete Denture Construction

1. Pre-operative Speech Assessment

• Document any pre-existing speech difficulties
• Assess natural tooth position relative to lip and tongue at rest
• Photographs: frontal view at rest and smiling

2. At Wax Try-In Stage

3. At Denture Delivery

• Repeat all phonetic tests
• Patients with previous dentures show quicker speech adaptation
• First-time denture wearers may need 4-6 weeks for full adaptation

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Common Phonetic Problems and Solutions

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The S-sound as a Diagnostic Tool

1. Testing VDO: Patient repeats "sixty-six" or "Mississippi" - at correct VDO, minimal/no audible tooth contact occurs
2. Phonetic freeway space: The distance between upper and lower anterior teeth during S production equals the closest speaking space (~1 mm)
3. Anterior tooth position: S production is compromised by poor anterior tooth position

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Neuromuscular Adaptation

• Initial speech difficulty after denture insertion is normal and expected
• The tongue, lips, and buccal mucosa adapt to the new tooth positions and palatal contour within 4-8 weeks
• Patients should be counseled pre-operatively about temporary speech changes
• Reading aloud for 15-20 minutes daily helps accelerate adaptation

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References

1. Zarb GA, Hobkirk JA, Eckert SE, Jacob RF. Prosthodontic Treatment for Edentulous Patients. 13th ed. Mosby/Elsevier; 2013. Chapter 19 (Phonetics and Denture Aesthetics).
2. Heartwell CM Jr, Rahn AO. Syllabus of Complete Dentures. 4th ed. Lea & Febiger; 1986. Chapter 12.
3. Winkler S. Essentials of Complete Denture Prosthodontics. 2nd ed. Year Book Medical Publishers; 1988. Chapter 15 (Phonetics).
4. Silverman MM. The speaking method in measuring vertical dimension. J Prosthet Dent. 1953;3(2):193-199.
5. Pound E. Let /S/ be your guide. J Prosthet Dent. 1977;38:482-489.
6. Frush JP, Fisher RD. The dynesthetic interpretation of the dentogenic concept. J Prosthet Dent. 1958;8(4):558-581.
7. Rothman R. Phonetic considerations in denture prosthetics. J Prosthet Dent. 1961;11(2):214-223.
8. Langer A, Michman J, Seifert I. Factors influencing satisfaction with complete dentures in geriatric patients. J Prosthet Dent. 1961;11(6):1019-1031.
9. Boucher CO, Hickey JC, Zarb GA. Prosthodontic Treatment for Edentulous Patients. 9th ed. Mosby; 1975. Chapter 17.

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ANSWER 5: SURVEYING, RATIONALE OF SURVEYING, AND NOTE ON THE SURVEYOR IN REMOVABLE PARTIAL DENTURES (25 Marks)

Definition

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The Dental Surveyor

Description

1. Base: A flat, horizontal platform
2. Vertical column (post): A rigid vertical support
3. Horizontal arm: Extends from the vertical column; adjustable in height
4. Surveying head (handpiece): The working end, mounted at the end of the horizontal arm; moves only in the vertical plane
5. Table/cast platform: A tilting table on which the cast is placed; can be tilted in any direction and locked at any angle
6. Cast holder/mandrel: Secures the articulated cast to the surveying table

Surveying Tools (Attachments)

1. Analyzing rod (carbon marker): A straight cylindrical rod used to identify the survey line; when moved across the tooth, the bottom edge touches at the widest point of contour (height of contour)
2. Carbon marker (graphite marker): A carbon-coated cylinder; marks the height of contour (survey line/clasp line) on the cast as it is moved vertically along tooth surfaces
3. Undercut gauges: Calibrated rods that measure the depth of undercut available:
   • 0.25 mm undercut gauge (color: red) - used for cast metal clasps (CrCo), wrought wire clasps
   • 0.50 mm undercut gauge (color: green) - used for wrought wire clasps (more flexible)
   • 0.75 mm undercut gauge (color: orange) - used for flexible acrylic clasps
4. Wax trimmer (chisel blade): Used to trim blockout wax to the exact survey line during the laboratory blockout phase

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Rationale of Surveying

1. Determination of the Path of Insertion and Withdrawal

• There is only one path of withdrawal but there may be multiple acceptable insertion paths
• The path must allow the denture to seat fully without binding, and remove without excessive force

2. Identification of the Height of Contour (Survey Line / Clasp Line)

• Supragingival portion (above the survey line): Guides, reciprocal arms, and rigid parts of clasps are placed here
• Infragingival portion (below the survey line - the retentive undercut): Only the retentive tip of the clasp engages the undercut

3. Location of Retentive Undercuts

• Desirable undercuts: Retentive areas for clasp tips (buccal, lingual, or mesiodistal undercuts)
• Undesirable undercuts: Interproximal areas, tissue undercuts, and soft tissue undercuts that must be blocked out to prevent binding of the denture framework

4. Selection of Abutment Teeth

• Whether potential abutment teeth have adequate undercuts for retention
• Whether tooth modifications (enameloplasty, crown restorations with survey crowns) are needed to create or modify undercuts

5. Design of the Clasp Assembly

• The type of clasp arm is selected (circumferential/Akers, bar/Roach clasp)
• The depth of undercut utilized is determined (0.25 mm for cast metal clasps)
• The location of the retentive clasp tip is placed in the correct undercut

6. Preparation of Guiding Planes

7. Determination of the Most Favorable Path of Insertion for Aesthetics and Function

• Which undercuts are engaged (lingual vs. facial)
• Whether diastemas or prominent tissue undercuts are eliminated by posterior tilting
• Aesthetics: a slightly anterior tilt of the cast often moves the anterior survey line gingivally, improving the aesthetic placement of clasps on anterior abutments

8. Blockout of Undesirable Undercuts

• Undesirable undercuts are filled with blockout wax (or blockout resin) parallel to the chosen path
• Ensures the denture framework does not engage tissue undercuts, proximal areas, or cervical embrasures
• Types of blockout:
  • Parallel blockout: All hard and soft tissue undercuts filled parallel to the path of insertion
  • Shaped blockout: For the retentive area, a shaped blockout is created to allow only the designed amount of undercut to remain for clasp retention

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Determining the Optimum Path of Insertion

1. Guiding planes: A tilt that makes the greatest number of proximal surfaces parallel to each other
2. Retentive undercuts: A tilt that places undercuts in favorable positions for clasp retention
3. Esthetic considerations: A tilt that minimizes display of clasps on anterior teeth (moves survey line gingivally on anterior abutments)
4. Interference elimination: A tilt that eliminates or minimizes hard and soft tissue interferences

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Survey Lines and Clasp Design

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Types of Clasps and Undercut Used

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Surveying Procedure - Step by Step

1. Mount the cast on the surveying table
2. Level the cast (horizontal tilt) as the first orientation
3. Place the analyzing rod against the abutment teeth and note the height of contour at the default orientation
4. Tilt the cast anteroposteriorly and laterally to test different paths of insertion
5. Select the optimum tilt based on the four criteria above
6. Mark the survey line on all teeth using the carbon marker
7. Measure undercuts with undercut gauges on potential abutment teeth
8. Mark three reference points with indelible pencil/carbon on the base of the cast to allow re-trimming of the cast to the exact same tilt later in the laboratory
9. Perform blockout of undesirable undercuts parallel to the path of insertion
10. Trim blockout wax to the survey line using the wax trimmer attachment
11. Design the partial denture framework on the surveyed and blocked out cast

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The Ney Surveyor

• Heavy cast iron base
• Precise vertical column and arm
• Full range of interchangeable tools
• Simple, durable, and accurate mechanism

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References

1. McCracken WL. McCracken's Removable Partial Prosthodontics. 13th ed. (Carr AB, Brown DT). St. Louis: Elsevier; 2016. Chapter 5 (Surveying), pp 55-80.
2. Henderson D, Steffel VL. McCracken's Partial Denture Construction. 5th ed. Mosby; 1977. Chapter 4.
3. Kratochvil FJ. Influence of occlusal rest position and clasp design on movement of abutment teeth. J Prosthet Dent. 1963;13(1):114-124.
4. Glossary of Prosthodontic Terms, 9th Ed. J Prosthet Dent. 2017;117(5S):e1-e105.
5. Krol AJ. RPI (rest, proximal plate, I bar) clasp retainer and its modifications. Dent Clin North Am. 1973;17(4):631-649.
6. Roach FE. Principles and essentials of bar clasp partial dentures. J Am Dent Assoc. 1930;17:124-138.
7. Applegate OC. Essentials of removable partial denture prosthesis. 3rd ed. Philadelphia: WB Saunders; 1965. Chapter 6.
8. Stewart KL, Rudd KD, Kuebker WA. Clinical Removable Partial Prosthodontics. 2nd ed. St. Louis: Medico-Dental Media International; 1992. Chapter 4.

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ANSWER 6: IMPLANT-ABUTMENT INTERFACE (25 Marks)

Definition

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Historical Evolution

• Branemark's original design (1965-1980): External hexagon (hex) connection; designed primarily as an anti-rotational feature for single-stage surgery
• Subsequent evolution: Internal hex, Morse taper (conical), internal octagon, trilobe (Tri-channel), spline connections
• The shift from external to internal connections was driven by reducing micro-movements, micro-leakage, and abutment screw loosening

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Components of the Interface

1. Implant Fixture: Titanium or titanium-zirconia endosseous screw placed in bone
2. Abutment: Transmucosal component; connects fixture to prosthetic crown or prosthesis
3. Abutment Screw (retention screw): Fastens the abutment to the implant; most prone to loosening
4. Connection geometry: The interlocking shape at the IAI (hex, taper, spline, etc.)

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Classification of Implant-Abutment Connections

A. Based on Location of Connection

1. External Connection (External Hex)

• The anti-rotational feature (hexagon) is above the implant platform
• Hex protrudes 0.7 mm above the implant head
• Examples: Nobel Biocare Branemark System, Zimmer External Hex
• Advantages:
  • Easy to use
  • Universal compatibility with multiple abutments
  • Well-documented long-term clinical data
• Disadvantages:
  • Greater micro-movement at the interface under lateral loads
  • Higher screw loosening rates
  • Greater micro-leakage (bacterial contamination into the implant-abutment gap)
  • Marginal bone loss of 1.5-2 mm in the first year (Albrektsson criterion)
  • Less vertical height for subgingival placement of the connection

2. Internal Connection

• The anti-rotational feature is within the implant body
• Multiple configurations: Internal hex, internal octagon, tri-lobe, spline
• The abutment engages inside the implant chamber
• Examples: Straumann (Morse taper), ITI Solid Abutment, Ankylos, BioHorizons, Astra Tech (conical seal)

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B. Based on Platform Relationship

1. Flat-to-Flat (Butt Joint / Flat Platform)

• The abutment platform exactly matches the implant platform diameter
• Simple, effective, traditional design

2. Platform Switching (Platform Shifting)

• The abutment diameter is narrower than the implant platform diameter
• Creates an inward step at the IAI
• First described: Lazzara and Porter (2006)
• Rationale:
  • The implant-abutment microgap is moved inward (away from the bone crest)
  • The inflamed connective tissue at the microgap is over the implant platform rather than adjacent to bone
  • This preserves crestal bone by keeping the inflammatory cell infiltrate away from the bone crest
  • Results in significantly less crestal bone loss compared to non-platform-switched implants (multiple RCTs confirm ~0.5-1.0 mm bone preservation)
• Clinical benefit: Maintained peri-implant bone height; better soft tissue volume and papilla height

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C. Based on Connection Angulation

1. Straight (0°) Connection

• Abutment is collinear with the implant axis
• Used for implants placed in ideal positions (parallel to adjacent teeth)

2. Angled Connections (15°, 17°, 25°, 30°)

• Abutment is angled relative to the implant body
• Compensates for implant angulation in bone without tilting the prosthesis
• Used when ideal implant angulation is not achievable due to anatomical limitations (bone defects, proximity to sinus, nerve)

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The Morse Taper (Conical) Connection - In Detail

1. Cold-welding effect: Friction locking eliminates micro-movement at the IAI
2. Near-zero micro-leakage: The conical seal virtually eliminates fluid seepage across the connection
3. No micro-gaps: Unlike external hex connections, the Morse taper creates an intimate seal
4. Minimal abutment screw loosening: The cold-welding reduces rotational micro-movements that unscrew abutment screws
5. Peri-implant bone preservation: Least marginal bone loss of all connections (combined with platform switching)
6. Better soft tissue response: Stable bone = stable soft tissue; ideal papilla height and gingival margin maintained

1. Abutment removal difficulty: Cold-welding may make abutment removal difficult once seated
2. Proprietary systems: Morse taper designs are system-specific; less universal compatibility
3. Less clinical longevity data: Newer systems have shorter follow-up than Branemark-type external hex

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Biological Aspects of the IAI

The Microgap

• The IAI always has a microgap of 2-10 micrometers between abutment and implant surfaces
• This gap is colonized by bacteria within 2 weeks of abutment connection (Quirynen et al., 1994)
• Bacterial colonization leads to an inflammatory cell infiltrate at the microgap (Listgarten, 1996)
• The inflammatory infiltrate expands apically, causing marginal bone loss (crestal bone resorption)

Biological Width at Implants

• Around implants, a similar biological width to teeth is established:
  • Junctional epithelium: ~2 mm
  • Supracrestal connective tissue: ~1-1.5 mm
  • Total: ~3-3.5 mm (similar to natural teeth)
• If the abutment-crown margin encroaches on this space, bone loss occurs to re-establish biological width
• This is why the IAI should be placed at or below the crestal bone level (bone-level implants) with appropriate emergence profile

Crestal Bone Resorption Patterns

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Mechanical Aspects of the IAI

Abutment Screw Loosening

• One of the most common mechanical complications (5-20% incidence)
• Causes:
  • Micro-movements at the IAI (ratcheting effect)
  • Inadequate tightening torque
  • Occlusal overload
  • Off-axis loading (lateral forces)
• Prevention:
  • Proper torque (10-35 Ncm depending on screw size; manufacturer specifications must be followed)
  • Passive fit of the prosthesis
  • Occlusal load distribution
  • Platform switching
  • Internal vs. external connections (internal connections have lower screw loosening rates)
  • Use of torque-limiting devices

Abutment Screw Fracture

• Rarer but more serious complication
• Occurs when fatigue fracture of the screw titanium alloy
• Prevention: Adequate torque, avoiding occlusal overload, proper implant positioning

Fretting Corrosion

• Micro-movements at the IAI create metal wear particles (titanium and oxide debris)
• Can stimulate peri-implant inflammation
• Minimized by Morse taper connections

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Prosthetic Design Considerations at the IAI

Cement-Retained vs. Screw-Retained Prostheses

The Transmucosal Collar and Emergence Profile

• The emergence profile is the contour of the crown/abutment as it emerges from the soft tissue
• A proper convex emergence profile maintains soft tissue contour and papilla height
• An over-convex profile creates excessive pressure on soft tissues and may cause bone loss
• The emergence profile should be designed with a concave to convex transition (S-curve profile) to maintain peri-implant health

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Abutment Materials

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Peri-implant Tissue Health and the IAI

1. Marginal bone stability: Peri-implant bone loss of >0.2 mm/year after the first year is abnormal
2. Peri-implant tissue health: Mucosal seal (junctional epithelium and connective tissue attachment) around the transmucosal collar
3. Success criteria (Albrektsson et al., 1986):
   • No mobility
   • No pain or paresthesia
   • No peri-implant radiolucency
   • Bone loss <0.2 mm per year after the first year
   • No infection

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References

1. Misch CE. Dental Implant Prosthetics. 2nd ed. St. Louis: Mosby/Elsevier; 2015. Chapters 6-8 (Implant Abutment Interface).
2. Misch CE. Contemporary Implant Dentistry. 3rd ed. St. Louis: Mosby; 2008. Chapter 9.
3. Lazzara RJ, Porter SS. Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels. Int J Periodontics Restorative Dent. 2006;26(1):9-17.
4. Branemark PI, Zarb GA, Albrektsson T. Tissue-Integrated Prostheses: Osseointegration in Clinical Dentistry. Chicago: Quintessence; 1985.
5. Albrektsson T, Zarb GA, Worthington P, Eriksson AR. The long-term efficacy of currently used dental implants: a review and proposed criteria for success. Int J Oral Maxillofac Implants. 1986;1(1):11-25.
6. Quirynen M, Bollen CM, Eyssen H, van Steenberghe D. Microbial penetration along the implant components of the Branemark system: an in vitro study. Clin Oral Implants Res. 1994;5(4):239-244.
7. Wilson TG Jr. The positive relationship between excess cement and peri-implant disease: a prospective clinical endoscopic study. J Periodontol. 2009;80(9):1388-1392.
8. Merz BR, Hunenbart S, Belser UC. Mechanics of the implant-abutment connection: an 8-degree taper compared to a butt joint connection. Int J Oral Maxillofac Implants. 2000;15(4):519-526.
9. Dibart S, Warbington M, Su MF, Skobe Z. In vitro evaluation of the implant-abutment bacterial seal: the locking taper system. Int J Oral Maxillofac Implants. 2005;20(5):732-737.
10. Gamborena I, Blatz MB. Evolution: Contemporary Protocols for Anterior Single-Tooth Implants. Quintessence; 2015. Chapter 3.

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Summary: What You Got (6 x 25-mark answers)