L2 Classification and Clinical rationale_integrated

Fixed Partial Prosthesis¹

Classification and Clinical Rationale

This section covers the foundational classifications and the clinical reasoning behind the application of fixed partial prostheses.

Focus of Lecture

This lecture focuses primarily on resin-bonded bridges (RBBs) as a less invasive alternative to conventional fixed partial dentures.

Acknowledgements to Dr. Matsubara

Learning Outcomes²

Upon completion of this module, students should be able to:

• Understand and discuss the advantages and disadvantages of different types of Fixed Partial Dentures (FPD).
• Discuss the differences between various types of bridges.
• Discuss tooth preparation techniques specifically for bonded bridges.
• Discuss the application and properties of fibre-reinforced bonded bridges.
• Discuss the concept of the Shortened Dental Arch (SDA).
• Discuss the clinical rationale of prosthetic treatment using FPD, including factors that affect the overall prognosis of the treatment.
• Understanding the classification and historical development of resin-bonded fixed partial dentures
• Differentiating between cement-retained and resin-bonded prostheses
• Mastering preparation principles for various RBB designs (metal-ceramic, all-ceramic, fiber-reinforced)
• Selecting appropriate abutment teeth based on biomechanical principles
• Managing soft tissue and impression techniques for fixed prosthodontics

Clinical Resources and Reading

• Practical Guidance: Practical advice for successful clinical treatment with resin-bonded bridges.
• Required Reading: King, S., Sood, B., and Ashley, M. P.

Classification³

Prosthodontics is broadly categorized into two main branches: Dental Prosthodontics and Maxillofacial Prosthodontics.

Dental Prosthodontics

Dental prosthodontics is further divided into Fixed and Removable Dental Prostheses:

Fixed Partial Dentures (FPDs)

FPDs represent one of several options for tooth replacement, alongside complete dentures, removable partial dentures, and implant-supported prostheses.

• Fixed Dental Prostheses

  • Tooth supported (crown & bridge)
    • Cement-retained
    • Resin-bonded
  • Implant supported (crown & bridge)
    • Screw-retained
    • Cemented

• Removable Dental Prostheses

  • Partial
  • Complete

Fixed partial prostheses can be classified according to the materials used in their construction:

Material⁴

• Acrylic or composite (typically used for temporary bridges)
• Cast metal: gold alloy
• Metal-ceramic (Porcelain-Fused-to-Metal or PFM)
• Resin-Veneered
• All ceramic (e.g., zirconia)
• ==Temporary/Provisional: Luxatemp and similar materials for interim restorations==
• ==Metal: Base metal or noble metal frameworks used for substructures==

Cement-retained Fixed Partial Dentures (FPD) utilize different luting protocols based on the restorative material:

Metal-ceramic Systems

• These are cemented using conventional luting materials, such as:

Mechanical Retention

Conventional cement-retained FPDs rely heavily on the mechanical retention provided by the preparation shape (parallel walls and geometric resistance form). The cement layer is secondary to the macro-mechanical design.

• Glass Ionomer Cement (GIC)
• Resin-Modified Glass Ionomer Cement (RMGIC)
• Zinc phosphate

Cement-Retained FPD⁵

All-ceramic Systems

• These may be clinicaly managed using two primary methods:
  • Cemented with conventional luting material
  • Bonded with resin cement

Early Bonded Fixed Partial Dentures (FPD)

Early iterations of bonded restorations utilized various materials for temporary or immediate replacement:

• Extracted natural teeth
• Acrylic teeth

Resin-Bonded FPD⁶⁷

Evolution of Bonded Techniques

• Etched Cast: Development of mechanical retention through metal etching.
• Rochette Bridge (1970s): Early design utilizing macroscopic mechanical retention.
• Maryland Bridge: Refinement of the etched-metal technique for improved resin bonding
  • ==Rochette Bridge Limitation: The perforations weakened the metal structure, leading to long-term failures.==
  • ==Maryland Bridge Innovation: Developed at the University of Maryland using electrochemical etching to create micromechanical retention without perforations.==.

Clinical Advantages

Traditional Approach^89101112

• Minimal Tooth Preparation: Requires minimal removal of tooth structure, typically with a wing thickness of 0.8mm.

• Simplified Procedures: Supragingival preparation allows for easy impression making.

• Efficiency: Interim restorations are not usually required between preparation and cementation.

• Minimal removal of tooth structure

• Supragingival preparation, easy impression making

• Interim restoration not usually required

Clinical Disadvantages

• Reduced restoration longevity compared to conventional FPDs
  • Survival rate: Approximately 87% at 5 years (compared to >90% for conventional bridges)
  • Nickel allergies (specifically for metal wings)
• Limited ability to correct space discrepancies
• Requirement for good alignment of abutment teeth
• Compromised esthetics in the anterior region (potential for metal show-through)

Clinical Indications

• Short edentulous spaces (replacement of a single tooth)

• Healthy or unrestored abutment teeth with sufficient enamel surface for bonding

• Significant clinical crown length to provide adequate surface area

• Temporary restoration or space maintenance

• Patients with an open bite

  • Young patients with continued growth where implants are contraindicated
  • Temporary space maintenance after orthodontic treatment prior to implant placement

• Short edentulous space (one tooth)

• Healthy/Unrestored abutments (enamel surface)

• Significant clinical crown length

• Temporary restoration - space maintenance

• Open bite

Contraindications

• Damaged or heavily restored abutments
• Large edentulous areas (multiple missing teeth)
• Unfavorable angulation or rotation of abutment teeth
• Parafunctional habits or heavy occlusal forces
• Deep bite (insufficient clearance)
• Mobile teeth
• Known alloy allergy

Design and Construction

• Cantilevered Design: Often preferred for anterior replacements.

Survival Characteristics

Based on research published on 10 April 2015 regarding the survival of 771 resin-retained bridges at a UK dental teaching hospital (King, P. A., Foster, L. V., Yates, R. J., Newcombe, R. G. & Garrett, M. J.):

• Cumulative Survival Data: Analysis of time to failure or censoring.
• Comparison Groups:
  • Cantilever designs
  • Other designs (e.g., fixed-fixed)
  • Statistical tracking of censored data for both cantilever and other designs.

Principles of Stability and Retention

To ensure the long-term success of the prosthesis, the design must incorporate:

Metal-Ceramic

• Stability and Retention: Achieved through specific preparation features that secure the framework against dislodging forces.
• Single Path of Insertion: The preparation must be designed to allow the prosthesis to seat in only one direction, which enhances the mechanical retention of the resin bond.

Structural Preparation Features

1. Guide Planes

   • Designed to provide the maximum surface area of enamel contact.
   • Establishes a definitive Path of Insertion (POI).
   • Provides resistance against horizontal movement.

2. Axial Grooves

   • Supplement the preparation to increase resistance against horizontal displacement.

3. **Rest Seats

4. ==Palatal Preparation: Extend approximately 2 mm from the incisal edge to avoid the “grey line” (metal show-through). Use a dark object behind the incisor to evaluate translucency.==

5. ==Cementation Protocol: Sandblast metal retainers and use dual-cure or chemical-cure adhesive resin cement containing MDP (e.g., Panavia).==**

   • Specifically incorporated to provide resistance against vertical occlusal forces, preventing the prosthesis from being driven gingivally.

All Ceramic

Further considerations for all-ceramic resin-bonded restorations.

Clinical Performance

All-ceramic RBBs have a 5-year survival rate of 88–92%, with a debonding rate of 12.2% and a fracture rate of 4.8% (typically at the connector).

Principles of Tooth Preparation

• Intra-enamel preparation
• Supragingival margins
• Maximize surface area for retainers
• Bracing of abutments
• Single path of insertion
• Clearance for retainers
• Rest seats
  • ==Connector dimensions: Minimum 2 mm horizontal width and 3 mm vertical height to prevent fracture==
  • ==Interproximal wrap-around: Essential to maximize bonded surface area; failure may result in 50% failure rate within 3 years==

Retainer Types

• Inlay
• Onlay

Clinical documentation and visual evidence of all-ceramic resin-bonded fixed partial dentures.

Concluding clinical observations regarding all-ceramic resin-bonded FPDs.

Fiber-reinforced bonded bridges can utilize either a natural tooth or an acrylic tooth as a pontic.

Commercial Fiber Systems

• everStick® Product Range:
  • everStick® NET
  • everStick® ORTHO
  • everStick® POST 1.2
  • everStick® PERIO
  • everStick® C&B
• Ribbond®: Utilizes a Leno weave structure

Ribbond Architecture

Utilizes a "lock stitch Leno weave" designed to prevent fiber pull-out. The weave pattern creates friction that tightens under tension rather than separating. .

Fiber-Reinforced^131415161718

Fiber Composition and Architecture

• Types of Fibers:
  • Glass
  • Polyethylene
  • Kevlar
• Structural Configurations:
  • Woven
  • Braided
  • Unidirectional

Fiber-reinforced bonded bridge.

Dimensional Specifications

• Minimum Thickness/Width: 3 mm

Direct Fiber-Reinforced Technique

1. ==Measurement: Cut ribbon using sharp scissors and an aluminum strip guide.==
2. ==Base Layer: Apply 0.5 mm of packable composite (not flowable) to the etched tooth.==
3. ==Fiber Placement: Soak ribbon in unfilled resin (dipping resin) before adapting to the composite.==
4. ==Pontic Attachment: Use a 3 mm groove with an undercut in the pontic tooth for mechanical retention.==
5. ==Finishing: Overlay ribbon with flowable composite to prevent tongue irritation (ribbon is not polishable).==

Implant Supported Bridge¹⁹

An implant-supported bridge is a restorative solution used to replace multiple missing teeth by anchoring a dental bridge to dental implants rather than natural teeth.

This approach provides a stable and durable prosthetic result, preserving the integrity of adjacent natural teeth and maintaining alveolar bone structure through functional stimulation.

Clinical Application

Implant-supported bridgework represents an alternative to tooth-supported FPDs, particularly in cases where abutment teeth are sound and preservation of tooth structure is desired.

Clinical Rationale²⁰²¹

The clinical rationale for fixed partial prostheses involves a comprehensive assessment of the patient’s oral health status and the functional or aesthetic

Managing Unrealistic Aesthetic Expectations

Scenario: A 60-year-old patient presents requesting replacement of a missing anterior tooth, bringing a photograph from age 20 expecting identical replication. Clinical Considerations:

• Perioral soft tissue changes (gingival recession, facial sagging) alter the overall appearance regardless of prosthetic replication.
• Aging changes lip support and smile dynamics.
• Red Flag: Patients expecting 40-year-old aesthetics on 60-year-old facial structures may require referral for complex oral rehabilitation or specialist care. Management: Clinicians must communicate that restoration of single teeth cannot reverse overall facial aging. implications of missing dentition.

The loss of teeth leads to several physiological and functional degradations:

Consequences of Tooth Loss²²²³²⁴

• Masticatory Efficiency: Reduced ability to chew, which can subsequently affect systemic health.
• Bone Structure: Loss of quality, width, and height of the alveolar bone.
• Soft Tissue: Loss of soft tissue volume.
• Aesthetics: Compromised facial and dental appearance.
• Phonetics: Compromised speech, particularly regarding dental consonants.
• Occlusal Instability: Shifts in the bite and tooth alignment
  • Migration of adjacent teeth and supereruption of opposing teeth
  • Loss of vertical dimension.

Occlusal and Muscular Changes

Tooth loss contributes to significant occlusal changes, including:

• Occlusal interferences.

• Unbalanced muscle contraction.

• Development or exacerbation of temporomandibular disorders (TMD).

• Occlusal interferences.

• Unbalanced muscle contraction.

• Temporomandibular disorders (TMD).

Shortened Dental Arch Concept

According to Witter et al. (1999), the shortened dental arch concept evaluates the functional requirements of the dentition, often categorized by the number of occluding pairs (e.g., 3, 4, or 5 pairs).

• The SDA concept defines a functional dentition of no more than 20 teeth with intact anterior teeth but reduced posterior occluding pairs.
• Modern soft diets do not require a complete dental arch (32 teeth).
• Occluding Units Calculation: Premolars count as 1 unit each; Molars count as 2 units each.
• Distal extension cantilevers to replace second molars (7s) or bilateral free-end RPDs may represent overtreatment if functional goals are already met.

When considering intervention, the following diagnostic questions must be addressed:

• Is there a need for improved aesthetics?
• Does the patient need to improve masticatory function?
• Is there a need for improved occlusal stability?

Rationale for Intervention²⁵²⁶²⁷

Clinical Assessment: Need vs. Demand

It is essential to distinguish between the clinical need for treatment and the patient’s personal demand for services.

Aesthetic Considerations

Aesthetic planning requires balancing three distinct perspectives:

1. What the patient wants.
2. What the patient needs.
3. What the patient can realistically get.

Critical Evaluation Questions

• What is the patient’s expectation?
• Can that expectation be achieved?
• What is technically possible in this specific case?

Aesthetic and Structural Factors

Key factors in the aesthetic evaluation include:

• Lip support.
• High smile line considerations.

Clinical Rationale of Tooth Supported Bridgework^{282930313233343536}

Management of Occlusal Forces

NEVER OVERLOAD ABUTMENT TEETH!

• Direction of Occlusal Forces:

  1. Mandibular stability
  2. Axial occlusal load
  3. During lateral excursions: no interference in the working side
  4. During lateral excursions: disocclusion in the non-working side
  5. During protrusion: disocclusion of posterior teeth

• Intensity of Occlusal Forces:

  • Parafunctional habits
  • Age, Gender

Assessing Potential Abutment Teeth

• Crown/Root Ratio
• Root configuration
• Periodontal Ligament Area

Ante’s Law

“Root surface area of the abutment teeth has to equal or surpass that of the teeth being replaced with pontics”

• Contraindicated Scenario: The combined root surface area of the canine and second molar (Ac + A2m) is exceeded by that of the teeth being replaced (A1p + A2p + A1m). A fixed partial denture would be a poor choice in this situation.
• Favorable Scenario: The combined root surface area of the second premolar and the second molar (A2p + A2m) is greater than that of the first molar being replaced (A1m).

Crown-to-Root Ratio

• Minimum requirement is 1:1.
• Reference: Shillingburg 1997.
• Optimal crown-to-root ratio is 2:3.
• Assessment is measured from the alveolar crest to the incisal edge versus the crest to the apex on periapical radiographs.

Root Shape and Angulation

• Evaluation of root morphology and alignment (The Tooth Dance).

Root Configuration Principle

The more difficult a tooth is to extract, the better it functions as an abutment. Favorable features include broad roots in a labiolingual direction, multi-rooted teeth, and divergent or curved roots rather than conical formations.

Root Surface Area Measurements (mm²)

Mandibular Teeth

• Central Incisor: 154 (1.0)
• Lateral Incisor: 168 (1.1)
• Canine: 268 (1.7)
• First Premolar: 180 (1.2)
• Second Premolar: 207 (1.3)
• First Molar: 431 (2.8)
• Second Molar: 426 (2.8)

Maxillary Teeth

• Central Incisor: 204 (1.1)
• Lateral Incisor: 179 (1.0)
• Canine: 273 (1.5)
• First Premolar: 234 (1.3)
• Second Premolar: 220 (1.2)
• First Molar: 433 (2.4)
• Second Molar: 431 (2.4)

Source: JEPSEN A. Root surface measurement and a method for x-ray determination of root surface area. Acta Odontol Scand. 1963.

Length of Edentulous Area

Ante’s Law The total root surface area (periodontal membrane) of the abutment teeth for a FPD must be equal to or greater than the root surface area of the teeth being replaced (Irvin Ante, 1926).

Clinical Configurations:

1. Replacement of first molar (Abutments: A2p, A2m)
2. Replacement of first and second premolars (Abutments: Ac, A1m)
3. Replacement of multiple units (Abutments: Ac, A2m)

Mechanical and Biological Risks

Increasing the length of the edentulous span increases the risk of:

• Fracture of a porcelain veneer
• Breakage of a connector
• Loosening of a retainer
• Unfavorable soft tissue response
• Fracture of abutment
  • Span length increases deflection; because porcelain is a brittle material that cannot flex, this significantly increases the risk of veneer fracture.

Anatomical Considerations

• Dental arch shape
• Opposing arch

Biomechanics of Arch Shape and Retention

• Secondary Retention: Secondary retention (R) must extend a distance from the primary interabutment axis equal to the distance that the pontic lever arm (P) extends in the opposite direction.
• Leverage and Stress: The retainers on secondary abutments will be placed in tension when the pontics flex, with the primary abutments acting as fulcrums.

Risks of Secondary Abutments

Secondary retainers must be equally or more retentive than primary retainers. Because deflection causes tensile forces that may debond secondary retainers first, these teeth face a significantly increased risk of undetected caries.

• V-Shaped Arches: Replacing four incisors using only canines as abutments creates lever arms that produce heavy torquing forces.
• Opposing Arch Management: Overerupted teeth may require opening the vertical dimension, reduction, or orthodontic intrusion to create prosthetic space.

*Source: Fundamentals of Fixed Prosthodontics

Impression and Soft Tissue Management

• Objectives: Exact duplication of prepared and uncut surfaces, clear identification of finishing lines, and freedom from bubbles (which create cement layer vulnerability).
• Biological Width: Normal crest patients allow 0.5–1.0 mm subgingival margins; high crest patients (<10%) are at high risk for persistent inflammation if margins are deep.

Double Cord Retraction Technique

1. First Cord: Size 000 or 00 placed with a rotational motion to avoid hooking fibers.
2. Second Cord: Larger size (0 or 1) placed over the first.
3. Timing: Leave in place for 5 minutes for adequate displacement.
4. Note: Use a single cord for shallow sulci in the anterior region.*

Footnotes

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