Quartz 4

L1 fixed dentl prosthesis_integrated

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Fixed Dental Prosthesis Components1

Overview of Prosthesis Components

This section outlines the fundamental components and structural elements involved in a Fixed Dental Prosthesis (FDP).

  • Core Concepts: Detailed examination of the individual parts that constitute a fixed bridge or crown assembly.

  • Clinical Acknowledgements: Content developed with contributions and acknowledgements to Dr. Matsubara.

    • Scheduled for May 11th (distinct from the RPD assessment on May 4th).

Introduction

PVS Monophase Clinical Steps

  • Select correct tray and apply PVS tray adhesive; try-in tray for fit.
  • Prepare, clean, and retract tissues (using cord if needed); isolate and dry the
    • Mandatory completion despite no weighting. field.
  • Load medium-viscosity (monophase) material into the tray and into the syringe.
  • Syringe material around the finish line and prepared teeth, then immediately seat the loaded tray.
  • Hold steady until set, remove the impression, and inspect margins and detail.
  • Rinse, dry, and pour or send to the lab per the manufacturer’s recommended time.

PVS Dual-Phase Clinical Steps

  • Select tray and apply tray adhesive; try-in tray for fit.
  • Prepare, clean, and retract tissues; isolate and dry the field.
  • Syringe low-viscosity (light-body) material around finish lines and critical details.
  • Load heavy- or medium-body material into the tray, then seat the tray while the light wash flows into the detail.
  • Hold until set, remove, and inspect for capture of margins and fine detail.
  • Rinse, dry, and pour or send to the lab per manufacturer’s instructions.

Comparative Accuracy: Dual-phase is generally more accurate for fine margin detail because the low-viscosity wash captures fine anatomy while the heavier body supports dimensional stability.

Impression Techniques Overview2

Putty-Wash 1-Step (Simultaneous) Clinical Steps

  • Select tray and apply tray adhesive; try-in to confirm fit.
  • Prepare, clean, and retract tissues; isolate and dry the field.
  • Mix putty and load into the tray; mix light-body wash and syringe around margins.
  • Syringe wash around the preparation, then seat the putty-loaded tray immediately so putty and wash set together.
  • Hold until set, remove, and inspect for voids and margin capture.
  • Rinse, dry, and pour or send to the lab per recommendations.

Putty-Wash 2-Step (Sequential) Clinical Steps

  • Select tray and apply tray adhesive; try-in tray for fit.
  • Make the first putty impression (without wash) and allow to set; remove and inspect.
  • Create controlled space for wash by trimming relief or using a spacer in the putty impression where the wash will flow.
  • Re-seat the tray with light-body wash injected around the preparation so the wash fills the relieved space, then allow to set.
  • Remove and inspect for complete margin detail and uniform wash thickness.
  • Rinse, dry, and pour or send to the lab per instructions.

Comparative Accuracy: The 2-step putty-wash is generally more accurate because a controlled uniform wash thickness around the preparation improves detail reproduction and reduces distortion.

Monophase Technique

  • Preparation with retraction cord.
  • Preparation covered with impression material.
  • Tray inserted with the same impression material.
  • Note: Not recommended due to lower definition.

PVS Dual Phase Technique3

Dual-Phase: Light-Body & Heavy-Body

  • Preparation with retraction cord.
  • Preparation covered with light-body (LB) material.
  • Tray inserted with heavy-body (HB) material.

Dual-Phase: Putty Wash (One-Step)

  • Preparation with retraction cord.
  • Preparation covered with light-body (LB) material.
  • Tray inserted with putty material.
  • Note: One-step putty impressions can have significantly lower accuracy compared to two-step impressions.

Two-Step Impression with Putty

  • Preparation with retraction cord.
  • Initial impression taken with putty.
  • Putty cut-out performed to create space.
  • Preparation and putty cut-out covered with light-body (LB) material.
  • Note: Provides good accuracy.

Comparison of PVS Monophase and Dual-Phase

  • PVS Monophase: Medium/Heavy body PVS material is used in both the tray and on the preparation.
  • PVS Dual-Phase: Heavy/medium body PVS material is used in the tray, while Light-body PVS material is expressed on the tooth.

Putty Wash Techniques45

Comparison of Putty-Wash 1-Step and 2-Step

  • Putty-Wash 1-Step: Putty is mixed and placed into the tray; light-body PVS is expressed onto the prepared tooth, and the tray is immediately inserted.
  • Putty-Wash 2-Step: Putty is mixed and placed into the tray. The tray is inserted into the mouth, the impression is taken and removed. An area is cut out around the prepared tooth. Light-body PVS is then applied on the prepared tooth, and the impression is taken again using the putty/tray unit.

Common Clinical Error

The Putty-Wash 1-Step is a simultaneous single-step procedure. Students often incorrectly describe it as a two-step sequence; however, the correct method requires simultaneous placement of light body on the preparation and putty in the tray.

Technical Definitions and Requirements

  • PVS Monophase: Medium/Heavy body PVS material in the tray and on the preparation.
  • PVS Dual-Phase: Heavy/medium body PVS material in the tray, with Light-body PVS material expressed on the tooth.
  • Putty-Wash 1-Step: Putty mixed and placed into the tray; light-body PVS expressed onto the prepared tooth and tray immediately inserted.
  • Putty-Wash 2-Step: Putty mixed and placed into the tray. Tray inserted into the mouth, impression taken and removed. Cut-out area created around the prepared tooth. Light-body PVS applied on the prepared tooth, and the impression is taken using the putty/tray unit.

Clinical Assessment Criteria

  • Full marks require specifying the exact impression material used (e.g., Light-body vs. Heavy-body rather than generic “impression material”).
  • Accuracy in the 2-step technique requires a physical cut-out or relief in the putty to ensure proper space for the light-body material.

Module Introduction

This module covers the fundamental components and practical applications of fixed dental prostheses. Students are required to complete a dedicated workbook as part of their studies.

Scope of Study

This module focuses specifically on tooth-supported bridgework (fixed partial dentures). It does not cover implant-supported prostheses such as “All-on-4” or “All-on-6” configurations.

Theoretical Examination

The theoretical component accounts for 50% of the total module grade. The exam is held at the main campus during the main round examination period and typically consists of:

  • Multiple Choice Questions (MCQs)
  • Short Answer Questions (SAQs)
  • Likely conducted as a combined exam with Fixed Partial Dentures (FPD)
  • Combined with the Removable Partial Dentures exam at the main campus.

Practical Assessment6

The practical assessment focuses on bridge preparation and the creation of a provisional bridge. A detailed marking rubric will be provided at a later date.

  • Failure in either the bridge preparation or provisional fabrication requires remediation followed by a resit, as both must be passed independently.

Assessment Schedule and Weighting

  1. Formative Assessment (13/04/26)
    • No weighting applied to the final grade.
  2. Summative Assessment (11/05/26)
    • Accounts for 50% of the module grade.
    • Consists of two distinct components.

Passing Requirements

To successfully pass the module, students must achieve a minimum score of 50% in both the theoretical exam and the summative assessment. Within the summative assessment, both individual components must be passed independently with a score of 50% or higher.

Learning Outcomes7

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

  • Discuss the various components of a fixed partial prosthesis.
  • Discuss the biological, aesthetic, and mechanical principles of tooth preparation.
  • Understand and apply the concept of the Path of Insertion.
  • Discuss different designs and applications of retainers.
  • Discuss different designs and clinical considerations for pontics.
  • Discuss the various types of connectors used in prosthodontics.
  • Understand the mechanical and clinical concepts of Cantilevers.

Exam Preparation

Assessment material may be drawn directly from the mandatory reading: Contemporary Fixed Prosthodontics, Chapter 20.

  • Contemporary Fixed Prosthodontics: Chapter 20, “Pontic Design”

Components of Fixed Dental Prostheses8910111213141516171819202122232425262728

Core Components

  • ==Abutments: The supporting natural teeth.==
  • ==Retainers: The crowns placed over the abutment teeth.==
  • ==Pontics: The artificial teeth replacing the missing natural teeth.==
  • ==Connectors: The elements joining the pontics to the retainers, creating a single rigid unit.==
  • A fixed partial denture (FPD) or bridge functions similarly to a structural bridge, requiring support at both ends (with the exception of cantilever designs).

Tooth Supported Bridgework

(Fixed partial prosthesis)

Implant Supported Bridgework

Biomechanical Considerations of Cantilevers

“To be successful, single abutment cantilevers require a very favorable occlusion.”

  • Forces applied to a cantilever fixed dental prosthesis are resisted on only one side, which leads to imbalance.
  • Vertical forces can cause tipping, and horizontal forces can cause rotation of abutment teeth.
  • By including both adjacent teeth in the prosthesis, it is possible to resist forces much better because the teeth have to be moved bodily rather than merely rotated or tipped.
  • ==Advantages: Easier preparation (no strict path of insertion required on both sides) and more conservative tooth structure preservation (e.g., avoiding preparation of a canine when replacing a lateral incisor).==
  • ==Disadvantages: Induces lateral and rotational forces on the single abutment tooth; periodontal ligaments poorly resist tipping or rotational forces compared to axial forces.==
  • ==Favorable Applications: Cantilevering a lateral incisor from a maxillary canine (with good bone support) or cantilever implant-supported prostheses.==

Clinical Indications and Contraindications

When would we consider restoring teeth via FPDs?

Indications for Fixed Partial Dentures29

  • Patient unable/unwilling to accept removable options.
  • Orthodontic reasons (replacement of missing lateral incisors).
  • When adjacent teeth would also benefit from indirect restorations.
  • Patient not suited for implants (e.g., insufficient bone height/dimensions).

Case Study: Space Limitations Preventing Implant Placement

A middle-aged male patient (50–60 years old) presented with a missing maxillary right lateral incisor (12). Due to crowding, only 5–6 mm of space remained. Since implant placement requires 2 mm of bone between the implant and adjacent teeth, there was insufficient room (only 1-2mm left) for a standard implant. Both adjacent teeth (11 and 13) had large existing restorations. A conventional fixed partial denture was selected over a cantilever design to allow the lab better control over the pontic shape, bulking out the space for a more aesthetic outcome.

  • Young Patients: Suitable for permanent or temporary replacement in young patients with congenitally missing teeth (e.g., lateral incisors) where implant placement is contraindicated due to continued jaw growth (wait until ≥18 years).
  • Resin-Bonded Bridges: Conservative option for temporary replacement when canine substitution is unsuitable.
  • Splinting teeth (Note: Mentioned in textbooks, but suggested to proceed with care).

Contraindications for Fixed Partial Dentures30

Factors requiring careful assessment or caution:

  • Poor periodontal status of abutments (Crown-root ratio, Ante’s law, etc.).
  • Absence of distal abutment in posterior sections.
  • Long span bridges.
  • Poor oral hygiene (OH).
  • Extremely tilted teeth (requires careful assessment rather than being a firm contra-indication).
  • Single Point of Failure: Unlike implants, a bridge mechanically links teeth; failure of one abutment typically necessitates remaking the entire prosthesis.
  • Distal Cantilevers in Posterior: Highly undesirable due to leverage forces; should generally be avoided.

The abutment tooth involves principles of tooth preparation (partial or complete) categorized by the following requirements:

Biological Requirements

  • Conservation of tooth structure
  • Avoidance of overcontouring
  • Supragingival margins
  • Harmonious occlusion
  • Protection against tooth fracture
    • Common Path of Insertion: Bridge abutments must share a common path of insertion to allow seating; this requires visual averaging of the long axes of all abutments during preparation.

Abutment Tooth31

Mechanical Requirements

  • Retention form
  • Resistance form
  • Deformation resistance

Aesthetic Requirements

  • Minimum display of metal
  • Maximum thickness of porcelain
  • Porcelain occlusal surfaces
  • Subgingival margins

Retainers32

Retainers provide stability and retention to the dental bridge.

  • Full coverage restoration: All metal, PFM, or All-ceramic crowns.
  • Partial coverage restoration: 4/5 or 7/8 crowns.

Pontics33

  • Artificial tooth that replaces a missing natural tooth.
  • Suspended: tooth supported.
  • Restores aesthetics and function.
  • Prevents tilting and drifting of adjacent teeth and super-eruption of opposing teeth.

Design Parameters of Pontics3435363738

Design parameters of pontics involve:

  • Height and width of the residual ridge.
  • Dimensions of the edentate space.
  • Shape and texture of the soft tissues.
  • Comfort and support of the adjacent tissues.
  • Aesthetic requirements.
  • Ridge Form: Ideal ridges are smooth and regular with attached gingiva; horizontal or vertical defects may require surgical modification.

Optimal Pontic Design Considerations

Biologic

  • Cleansable tissue surface
  • Access to abutment teeth
  • No pressure on ridge

Mechanical

  • Rigid (to resist deformation)
  • Strong connectors (to prevent fracture)
  • Metal-ceramic framework (to resist porcelain fracture)

Esthetic

  • Shaped to look like the tooth it replaces
  • Appears to “grow” out of the edentulous ridge
  • Sufficient space for porcelain
    • Ceramic Thickness: Maximum veneering porcelain thickness should be approximately 1.2 mm; the framework must provide support to prevent bulk porcelain fracture.

Pontic Design Classification

  1. Mucosal Contact

    • Ridge-lap
    • Modified ridge-lap
    • Ovate
    • Conical

  2. No Mucosal Contact

    • Sanitary (hygienic)
    • Modified sanitary (hygienic)

Classification of Pontic Designs

  • Concave tissue surface.
  • Overlaps the residual ridge bucco-lingually.
  • Contraindicated under all circumstances because the tissue surface is inaccessible to cleaning devices.
Saddle Ridge Lap39
Modified Ridge Lap40
  • Lingual modification to open cervical embrasures and facilitate hygiene.
  • Gentle concavity linguo-facially but is always convex mesio-distally.
  • Ideally suitable for “convex” gingiva profile with no concavities.
  • High aesthetic value.
Conical41
  • Bullet-shape or egg-shape.
  • Convex with only one point of contact with the residual ridge.
  • Used in the posterior region.
  • Not as suitable for broad residual ridges due to food trapping.
Ovate Spheroidal42
  • Best aesthetic; appears to be emerging from the ridge.
  • Relative ease of hygiene despite large tissue contact area.
  • Convex tissue surface in both buccal-lingual and mesio-distal directions.
  • May need surgical augmentation (Costly).
  • Strong pontic design (supported ceramic).
  • Eliminates the potential for unsupported porcelain in the cervical portion of an anterior pontic.
Sanitary Hygienic43
  • 2-3 mm clearance off the ridge.
  • Easy cleaning.
  • Used in posterior regions.
    • Status: Not recommended and rarely used today as it traps food and irritates the tongue.
  • Disadvantages: Poor aesthetics, entrapment of food, sharp line angles.

Aesthetic Considerations for Pontics444546

  • Primarily achieved using Modified Ridge Lap and Ovate pontics.

  • Visual Shadowing: A rounded facial line angle can create an incorrect shadow effect; proper contouring is required to avoid this.

  • Management of soft tissue is essential for Modified Ridge Lap and Ovate pontic designs to achieve optimal aesthetics.

Soft Tissue Management47
Soft Tissue Ridge Augmentation48
  • Surgical augmentation of the soft tissue ridge may be required to support aesthetic pontic placement.
Root and Soft Tissue Simulation49
  • Root surface simulation
  • Soft tissue simulation

Immediate Provisionalization

Following atraumatic extraction, inserting a provisional bridge with an ovate pontic encourages the gingiva to heal into a concave, scalloped shape, preserving interdental papillae.

Substructure Configuration50
  • Correct configuration of the metallic or ceramic substructure in the pontic area is vital for long-term success.

Connectors5152

  • Join individual retainers and pontics together.
  • Must be easy to clean and strong.
  • Types:
    • Rigid: cast or soldered.
    • Non-rigid.

Mechanical Principles (Law of Beams)

Deflection (bending) creates tensile stresses that fracture connectors.

  • Height (Depth): Doubling height reduces deflection to one-eighth (inverse cube relationship); height is the most critical dimension.
  • Span Length: Doubling the span increases deflection by a factor of eight.
  • Non-Rigid Connectors: Used when a common path of placement is impossible or to accommodate mandibular flexure; they act as stress breakers.
  • Cantilever Design: Preferred on vital abutments; contraindicated in deep bites or on root canal-treated teeth with post-cores due to high failure risk.

Cantilever Design

  • Try to put it in the anterior teeth due to decreased occlusal load
    • or if the patient has an open bite as this decreases the occlusal forces
  • The middle tooth often acts as a lever, so it may cause dislodging, this is a class 1 lever by a cantilevered FPD

Footnotes

  1. Original PDF page 1: L1 Fixed Dental Prosthesis, p.1 ↩

  2. Original PDF page 2: L1 Fixed Dental Prosthesis, p.2 ↩

  3. Original PDF page 3: L1 Fixed Dental Prosthesis, p.3 ↩

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