Introduction to Fixed Prosthodontics

Introduction to Fixed Prosthodontics

• Fixed prosthodontics is a specialized area of dentistry focused on tooth replacement and restoration using artificial substitutes that are not removable.
• Its goal is to restore function, aesthetics, and comfort.

Indications for Fixed Prosthodontics

• One or two adjacent teeth missing in the same arch.
• Healthy supportive tissues.
• Suitable abutment teeth present.
• Patient's good health and desire for the prosthesis.
• Patient's oral hygiene skills and motivation.

Contraindications for Fixed Prosthodontics

• Diseased or missing supportive tissues.
• Lack of suitable abutment teeth.
• Patient's poor health.
• Lack of patient motivation.
• Poor oral hygiene habits.
• Inability to afford treatment.

Terminology

• Crown: An artificial replacement restoring missing tooth structure. It usually encompasses most or all of the remaining tooth structure and is made of materials like cast metal, porcelain, or combinations.
• Full Metal Crown: A full coverage all-metal restoration rebuilding the clinical crown of a natural tooth. Mainly used in posterior teeth.
• Jacket Crown (Ceramic Crown): A non-metallic restoration rebuilding the prepared teeth mainly for esthetic purposes.
• Veneered Metal Crown: A full cast metal crown with acrylic or porcelain facing on the labial or buccal surface.
• Full Veneered Metal Crown: A full cast metal crown with all surfaces faced with porcelain.
• Post Crown: A full-coverage crown that gains retention from a post inserted into the prepared root canal. It has a radicular portion inside the root canal.
• Three-Quarter 3/4 Crowns (partial Veneered Crown): Restoration of the occlusal or incisal surface and three axial surfaces (excluding the facial surface). Retention is achieved with prepared proximal surfaces (grooves).
• Reverse Three-Quarter Crowns: Restore all surfaces except the lingual/palatal surface, often used on lower premolars.
• Seven-Eighths Crowns: An extension of three-quarter crowns to include a major portion of the facial surface, excluding the mesio-buccal cusp of maxillary molars.
• Pinledge Retainer: Modification of an anterior three-quarter crown preparation for primary retention and resistance. Achieved by long parallel pins in the lingual/palatal surfaces
• Inlay Retainer: A classic intracoronal cast restoration covering the proximal and occlusal surfaces, but not the cusps entirely.
• Onlay Retainer: Modification of the inlay with cusp overlays on the occlusal surface to protect the remaining tooth structure.
• One-half crown veneers: Restore the occlusal and mesial surfaces, along with portions of facial and lingual surfaces, using a modified form of three-quarter crown.
• Laminates: Veneer restorations restoring a tooth's facial surface for aesthetic purposes. They are fabricated from resin or dental porcelain and bond to etched enamel with a composite resin.
• Bridge: A fixed partial denture, or fixed prosthesis that replaces missing teeth by spanning the edentulous space and anchored at one or both ends to the adjoining teeth. Abutment tooth supports and retains the bridge. The retainer (attachment) rebuilds the prepared tooth to connect the pontic to the abutment. The pontic (dummy) is the replacement for the lost tooth. The connector joint unites the pontic(s) with retainer(s).
• **Pier Abutment:**An isolated tooth where adjacent anterior and posterior teeth are missing.
• Fixed Fixed Bridge (Rigid Bridge, Fixed Rigid Bridge, Stationary-Fixed Bridge): A bridge where both abutment pieces and pontics are soldered together and the bridge is cemented to the abutment teeth.
• Fixed Supported Bridge: A bridge not joined to a terminal abutment tooth, but connected by a non-rigid connector enabling movement.
• Removable Bridge: A bridge where each retainer consists of two parts; one fixed to the abutment and the other soldered to the pontic, allowing for removal at the patient's will for cleaning.
• Cantilever Bridge: A bridge with a pontic supported by a double retainer at one end only, while the other end is unsupported.
• Spring Cantilever Bridge: A cantilever bridge where the pontic is on the end of a slightly resilient curved arm deriving support from an abutment remote from the edentulous space.
• Immediate Bridge: A bridge constructed before tooth extraction and seated immediately after.
• Temporary Bridge: A temporary restoration for the protection of the prepared teeth until a permanent restoration is completed.
• Minimum-preparation bridge (resin bonded bridge, adhesive bridge, Maryland bridge): A bridge attached to the surface of minimally prepared natural teeth.
• Implant supported bridge: A single implant can support a single tooth, or a series of implants can support a prosthesis that replaces multiple teeth.

Classification of Bridges

This section details the criteria for classifying bridges based on several factors, including: location, number of teeth, type of reduction, and support.

Treatment Planning

• This involves a logical sequence of treatment to restore patient dentition to good health and optimal appearance.
• It's based on patient history, clinical examination, diagnostic cast analysis, and radiographic evaluation.
• Key aspects of treatment planning include: identifying patient needs, correcting existing diseases, preventing future diseases, restoring function, improving appearance, treatment of symptoms, stabilization of deteriorating conditions, etc.
• The process of diagnosis and treatment planning for a prosthesis must evaluate certain factors such as abutments, biomechanical forces, retainer selection, pontic selection, and connector selection.

Biological Considerations of Fixed Prosthodontics

• Success of the restoration depends on maintaining the health of oral tissues, the integrity and durability of the prosthesis, and aesthetics.
• This section discusses pre-op, operational and post-op considerations.
• The oral cavity has several structures prone to damage, including pulp, dentine, the periodontium (gingiva and the periodontal ligament), soft tissues (lips, cheeks, tongue), and the TMJ.
• Care should be taken to minimize damage during prosthetic procedures.

Mechanical Considerations of Fixed Prosthodontics

• Retention is the ability of a preparation to resist the crown restoration from removal along its insertion path.
• The resistance is the ability of a preparation to resist dislodgement of a restoration by inclined, or horizontal, external forces.
• The path of insertion refers to the imaginary line along which a restoration can be inserted and removed without causing lateral forces to the abutment.
• Several factors affect retention and resistance, including the magnitude of dislodging forces, the geometry of the tooth preparation, taper, surface area, stress concentrations, type of preparation, roughness of the restoration, and specific materials involved.

Marginal Integrity

• The longevity of a restoration is greatly influenced by the adaptation of the margins to the finish lines of the preparation.
• Proper marginal integrity relates to the border where the prepared tooth structure and the unprepared tooth structure meet. Features of appropriate finish lines include distinct, uniform, and smooth contours that follow the alveolar bone crest and the free gingival margin .
• Different configurations of finish lines exist and are classified based on a variety of factors, such as location and shape.
• Criteria for successful finish lines consider acceptable marginal adaptation, a tissue-tolerant surface, adequate contour, and adequate strength of the restoring material.

Bite Registration

• Bite registration is a process that ensures accurate reproduction of the prepared tooth's relationship with the opposing dentition to create a duplication of the patient's intraoral relationships for the laboratory.
• Materials used for bite record include zinc oxide and eugenol, elastomers, wax, auto-polymerizing resins, impression plaster, and scanning bite registration.
• Several techniques exist for recording the bite, such as using a preformed or custom-made tray.
• Accurate recordings are crucial to guarantee accurate articulation of casts.

Temporary Restorations

Temporary restorations are used to protect prepared teeth until permanent restorations are fabricated and have the advantages of easier handling, biocompatibility, dimensional stability, adequate strength, and good patient acceptance.

• Various materials are used for temporary restorations, including preformed or custom-fabricated materials, such as aluminum shells, polycarbonate crowns, stainless steel, or transparent resin crowns.
• Temporary restorations need suitable properties - convenient handling, biocompatibility, dimensional stability, adequate strength, good esthetics, good patient acceptance, and chemical compatibility with provisional luting agents.

Full Veneer Metal Crowns

• Full veneer metal crowns are a widely used fixed restoration in dentistry, where all the facial surface is covered with ceramic materials.
• They combine the strength of the metal coping with the cosmetic qualities of ceramic.
• A deep facial reduction provides space for the metal coping and porcelain, and a shallower reduction is required on the other surfaces.
• Various procedures are used for preparation, including occlusal reduction, placement of depth orientation grooves, and appropriate finish line configuration.

Porcelain Fused to Metal Crowns

• Porcelain fused to metal (PFM) restorations consist of a metal coping overlaid with a porcelain layer. They combine the strength of a metal framework with the aesthetic qualities of porcelain.
• Preparation involves careful reduction of the tooth structure to provide proper space for the metal and porcelain layers.
• Factors like marginal integrity and retention are crucial for long-term success.
• The preparation typically involves specific methods for incisal, labial, and proximal reduction.

Complete Ceramic Crowns

• Complete ceramic crowns (PJC) are also known as porcelain jacket crowns, a primarily cosmetic restoration made from ceramic.
• Preparation involves creating a shoulder-type finish line or similar method on the prepared tooth.
• Advantages include superior esthetics, tissue response, and high retention.
• Disadvantages include the inherent brittleness of ceramic materials and the need for precisely controlled preparation.

Fluid Control & Tissue Isolation

• Techniques for controlling oral fluids during procedures include mechanical and chemical methods. Mechanical methods utilize rubber dams, cotton rolls, and saliva evacuators. Chemical methods may use local anesthetics, medications to inhibit saliva production, or soft tissue retraction pastes. Proper fluid control is important for accurate impressions, and for preventing damage to tissues.
• Biologic width is the crucial area for maintaining periodontal health. Restoration margin location and design can greatly affect this vital area, potentially compromising periodontal health.