PART II **PFM Crowns** *Synonyms* - Metal ceramic - VITA Metallic Ceramic (VMK) Crown (historical) # **PART II: PFM Crowns** ## **Synonyms** - Metal ceramic - VITA Metallic Ceramic (VMK) Crown (historical) > [!info] > VMK (Vita Metall-Keramik) is a historical term from the company that first introduced layering ceramics. **Porcelain Fused to Metal crown - PFM** --- **Definition** > Complete-coverage cast metal substructure (metal coping), veneered with a layer of fused porcelain to mimic the appearance of a natural tooth GPT-9 Porcelain Fused to Metal crown on dental model # **Porcelain Fused to Metal crown - PFM** ## **Definition** > Complete-coverage cast metal > [!info] > Modern alternatives exist where the metal infrastructure is replaced with a strong ceramic like zirconia, creating a layered all-ceramic crown that follows similar fabrication principles. substructure (metal coping), veneered with - ==Smooth all transitions between planes and margin types.== - ==Ensure all line angles are rounded, especially for modern CAD/CAM fabricated copings.== - ==Verify from an occlusal view that the entire margin is visible, which confirms the absence of undercuts.== - ==**Avoiding Gutter Margins:** To prevent creating a weak, unsupported lip of enamel at the margin, avoid cutting with the very tip of the bur. Instead, approach from the side and use the side of the bur to plane the tooth structure down to the finish line.== a layer of fused porcelain to mimic the appearance of a natural tooth **Porcelain Fused to Metal crown - PFM** **General Features** - Complete-coverage cast metal substructure with a mechanically & chemically bonded ceramic veneer - Range of designs depending on the material coverage - Variable extent of ceramic veneer Diagrams illustrating different designs of PFM crowns with varying ceramic veneer coverage on buccal (B), lingual (L), and mesial (M) surfaces. ## **General Features** - Complete-coverage cast metal substructure with a mechanically & chemically bonded ceramic veneer - Range of designs depending on the material coverage - Variable extent of ceramic veneer - ==**Full Ceramic Coverage:** The entire visible surface of the crown is covered in porcelain. This is used when aesthetics are the primary concern, such as on anterior teeth.== - ==**Partial Ceramic Coverage:** Only a portion of the crown (e.g., the buccal/facial surface) is covered in porcelain, while other areas (e.g., occlusal and lingual surfaces) remain as metal.== - ==**Benefits of Partial Coverage:**== - ==**More Conservative:** The metal portion requires less tooth reduction (0.5-1.0 mm) compared to the porcelain portion (at least 1.5 mm).== - ==**Wear Resistance:** A metal occlusal surface is more wear-resistant for the crown itself and is less abrasive to the opposing natural teeth compared to an unpolished or adjusted ceramic surface. This is particularly beneficial for patients with bruxism.== **Porcelain Fused to Metal crown - PFM** **General Features** - One of the most widely use crown in the past. - Long history of clinical success and have been considered the gold standard. *Contemporary Fixed Prosthodontics 4th Ed* - One of the most widely use crown in the past. - Long history of clinical success and have been considered the gold standard. # Porcelain Fused to Metal crown - PFM ## Indications When both strength and aesthetic are needed: - **Posterior crowns and bridges**: high occlusal forces occur - **Anterior crowns**: When improved esthetics are desired but full ceramic is not indicated - **Long-span fixed partial dentures**: due to the strength of the metal substructure - **Tooth preparations with reduced height**: Where a full ceramic crown may not have enough support - **Teeth receiving heavy load**: parafunction habits. - **Abutments for removable or fixed partial dentures** ## Contraindications - **Patients with metal allergies**: especially to base metals (nickel, cobalt) - **Highly aesthetic cases**: Where maximum translucency is required - **Minimal tooth reduction cases**: Requires more tooth reduction than all-metal crowns; Young patients whose pulp chambers are large - **Deep bite or limited interocclusal space**: Risk of porcelain fracture - **Parafunctional habits without protection**: Increased risk of porcelain fracture ## **Indications** When both strength and aesthetic are needed: - **Posterior crowns and bridges**: high occlusal forces occur - **Anterior crowns**: When improved esthetics are desired but full ceramic is not indicated - **Long-span fixed partial dentures**: due to the strength of the metal substructure - **Tooth preparations with reduced height**: Where a full ceramic crown may not have enough support - **Teeth receiving heavy load**: parafunction habits. - **Abutments for removable or fixed partial dentures** > [!info] > These are called ## **Contraindications** - **Patients with metal allergies**: especially to base metals (nickel, cobalt) - **Highly aesthetic cases**: Where maximum translucency is required - **Minimal tooth reduction cases**: Requires more tooth reduction than all-metal crowns; Young patients whose pulp chambers are large - **Deep bite or limited interocclusal space**: Risk of porcelain fracture > [!tip] Clarification > While a deep bite with limited space is a consideration, it is not an absolute contraindication. A PFM with a metal palatal/lingual surface can be an ideal choice, as it requires less reduction (0.5 mm) than an all-ceramic crown (at least 1.0 mm). - **Parafunctional habits without protection**: Increased risk of porcelain fracture **Porcelain Fused to Metal crown - PFM** **Advantages** **Strong and durable**: metal substructure provides excellent fracture resistance, suitable for posterior regions and bridges. **Good Aesthetics**: porcelain overlay mimics natural tooth color (though not as translucent as all-ceramic). **Versatility**: suitable for single crowns, multi-unit bridges, and implant-supported restorations. **Predictable Marginal Fit**: especially when fabricated using traditional casting techniques and noble alloys. **Proven Clinical Track Record**: well-documented long-term success. **Functional Performance**: handles well heavy occlusal loads **Adjustable Shade and Contour**: through layering and staining techniques. ## **Advantages** - **Strong and durable**: metal substructure provides excellent fracture resistance, suitable for posterior regions and bridges. - **Good Aesthetics**: porcelain overlay mimics natural tooth color (though not as translucent as all-ceramic). - **Versatility**: suitable for single crowns, multi-unit bridges, and implant-supported restorations. - **Predictable Marginal Fit**: especially when fabricated using traditional casting techniques and noble alloys. - **Proven Clinical Track Record**: well-documented long-term success. - **Functional Performance**: handles well heavy occlusal loads - **Adjustable Shade and Contour**: through layering and staining techniques. **Porcelain Fused to Metal crown - PFM** **Disadvantages** **Aesthetic Limitations:** less translucent than all-ceramic crowns; may show dark margin **Metal Allergies:** possible hypersensitivity to base metals like nickel or cobalt. **Porcelain Fracture Risk:** Chipping or delamination of the veneering porcelain can occur, especially under high stress or trauma. **Tooth Reduction Requirement:** requires more tooth reduction than full-metal crowns overall **Potential for Opposing Tooth Wear:** porcelain can be abrasive to natural enamel if not properly polished or glazed. **Subgingival Margin Challenges:** may compromise periodontal health if margins are deep or poorly contoured. **Cost:** more expensive than other crowns (metal crowns or monolithic ceramic crowns) ## **Disadvantages** - **Aesthetic Limitations:** less translucent than all-ceramic crowns; may show dark margin - **Metal Allergies:** possible hypersensitivity to base metals like nickel or cobalt. - **Porcelain Fracture Risk:** Chipping or delamination of the veneering porcelain can occur, especially under high stress or trauma. - **Tooth Reduction Requirement:** requires more tooth reduction than full-metal crowns overall - **Potential for Opposing Tooth Wear:** porcelain can be abrasive to natural enamel if not properly polished or glazed. - **Subgingival Margin Challenges:** may compromise periodontal health if margins are deep or poorly contoured. - **Cost:** more expensive than other crowns (metal crowns or monolithic ceramic crowns) > [!info] > This is due to the skilled labor involved in layering porcelain. However, a PFM is typically less expensive than a full gold crown. **Porcelain Fused to Metal crown - PFM** Material Science **Metal Alloy: requirements** - Allow for casting in thin section (0.3 mm) - Porcelain-metal compatibility - Thermal match between metal and porcelain: the metal should have higher melting temperature than porcelain for thermal stability while porcelain firing; - Colour preservation: some components of the alloy affect porcelain color; - Thermal contraction: if the porcelain shrinks slightly less than metal, the ceramic will be in a state of beneficial residual **compressive stress** at room temperature. - High alloy rigidity is required to prevent flexing (modulus of elasticity) # **Material Science** ## **Metal Alloy: Requirements** - ==**Sufficient Rigidity:** Must have a high modulus of elasticity to resist flexing under load, which would otherwise cause the brittle porcelain to fracture.== - Allow for casting in thin section (0.3 mm) - Porcelain-metal compatibility - Thermal match between metal and porcelain: the metal should have higher melting temperature than porcelain for thermal stability while porcelain firing; - Colour preservation: some components of the alloy affect porcelain color; - Thermal contraction: if the porcelain shrinks slightly less than metal, the ceramic will be in a state of beneficial residual **compressive stress** at room temperature. - High alloy rigidity is required to prevent flexing (modulus of elasticity) **Porcelain Fused to Metal crown - PFM** Material Science **Metal Alloys** **Classification:** Noble and Base metal - Based on the electrochemical character of the alloys - Gold-based alloys are the gold-standard alloys for PFM **NOBLE METAL ALLOYS:** - **High-noble metal (gold-based):** - Noble metal content: 60% (>40% gold) - e.g. Gold-Platinum-Palladium; Gold-Palladium-Silver, Gold-Palladium - **Noble metal (Palladium-based):** - Noble metal content: 25% (no gold requirement) - e.g. Palladium-Silver, Palladium-Copper-Gallium *Indium, tin and iron promote bonding of porcelain by the formation of stable adherent oxides* Palladium and platinum are generally added to serve as hardening elements in alloys with high gold content ## **Metal Alloys** ### **Classification: Noble and Base metal** - Based on the electrochemical character of the alloys - Gold-based alloys are the gold-standard alloys for PFM ### **NOBLE METAL ALLOYS:** - **High-noble metal (gold-based):** - Noble metal content: 60% (>40% gold) - e.g. Gold-Platinum-Palladium; Gold-Palladium-Silver, Gold-Palladium - **Noble metal (Palladium-based):** - Noble metal content: 25% (no gold requirement) - e.g. Palladium-Silver, Palladium-Copper-Gallium > [!tip] Key Feature > All noble alloys for PFMs must contain a small amount of **non-noble metal** (e.g., tin, indium). This is essential for forming an oxide layer on the coping's surface, which is required for chemical bonding with the porcelain. *Indium, tin and iron promote bonding of porcelain by the formation of stable adherent oxides* Palladium and platinum are generally added to serve as hardening elements in alloys with high gold content **Porcelain Fused to Metal crown - PFM** Material Science **Metal Alloys** *Classification: Noble and Base metal* **BASE METAL ALLOYS:** - Noble metal content: <25% (no gold requirement) - e.g. Nickel-Chromium, Cobalt-Chromium - Casting is more technique sensitive - Higher Hardness and Modulus of elasticity - Burnishing and finishing are more difficult - Less flexure – long span bridge ### **BASE METAL ALLOYS:** - Noble metal content: <25% (no gold requirement) - e.g. Nickel-Chromium, Cobalt-Chromium - Casting is more technique sensitive - Higher Hardness and Modulus of elasticity - Burnishing and finishing are more difficult - Less flexure – long span bridge - ==Clinicians must check for patient **nickel allergies**.== - ==These alloys are also more difficult for the dentist to adjust intraorally compared to gold alloys.== **Porcelain Fused to Metal crown - PFM** Material Science **Bonding to porcelain** - **Mechanical:** - rough metal surface (sandblasting/oxidizing) provides micromechanical retention - ceramic locking on cooling - **Chemical:** fusion of ceramic to metal oxide layer Diagram illustrating mechanical bonding with arrows indicating forces and a cross-section showing metal, oxide layer, and opaque layers. ## **Bonding to Porcelain** - **Mechanical:** - rough metal surface (sandblasting/oxidizing) provides micromechanical retention - ceramic locking on cooling - **Chemical:** fusion of ceramic to metal oxide layer > [!info] Compression Stress Mechanism > During cooling after firing, the metal alloy shrinks slightly *more* than the porcelain. Because the two are bonded, this differential shrinkage places the porcelain layer under a state of **residual compressive stress**. This internal compression makes the porcelain significantly more resistant to cracking and chipping. **Porcelain Fused to Metal crown - PFM** Contemporary Fixed Prosthodontics 4<sup>th</sup> Ed Diagram showing a cross-section of a PFM crown with labels for "Metal" and "Porcelain", and a fracture line indicated. Below, a flowchart illustrates the sequence: "Uneven porcelain thickness" → "Lack of proper support" → "Increased potential for fracture". **Porcelain Fused to Metal crown - PFM** Wax-up complete anatomical contour Cut back consistent amount for ceramic veneer **EVEN THICKNESS OF PORCELAIN** Contemporary Fixed Prosthodontics 4<sup>th</sup> Ed # **Fabrication and Preparation of PFM** ## **Fabrication Principles** - **Wax-up complete anatomical contour** - **Cut back consistent amount for ceramic veneer** - **EVEN THICKNESS OF PORCELAIN** > [!info] Coping Design > A properly designed coping provides uniform support for the porcelain layer. If the coping is thin or flat, it can create areas of thick, unsupported porcelain that are prone to fracture. **Porcelain Fused to Metal crown - PFM** Occlusal contact in centric ≠ Metal-porcelain junction at least 1.5 mm away from the junction Occlusal analysis is necessary to determine the PFM crown design - Occlusal contact in centric ≠ Metal-porcelain junction - at least 1.5 mm away from the junction - Occlusal analysis is necessary to determine the PFM crown design > [!tip] Modern Workflow > Many labs now use CAD/CAM technology to design and mill a wax pattern of the coping, which is then invested and cast using traditional methods. The porcelain layering, however, remains a manual process performed by a skilled technician. **Porcelain Fused to Metal crown - PFM** **Always check if the patient accepts a compromised aesthetic** *Contemporary Fixed Prosthodontics 4th Ed* Diagram showing cross-sections of a PFM crown with labeled layers: Porcelain, Metal-porcelain junction, Metal. Two additional images below show a PFM crown from occlusal and buccal views, with a 1 mm measurement indicated on the occlusal view. **Always check if the patient accepts a compromised aesthetic** **Porcelain Fused to Metal crown - PFM** Fabrication of PFM Diagram showing cross-section of PFM crown with labeled thicknesses: 1.5 mm for metal, 2.0 mm total thickness, and layered structure with metal (0.3 mm), opaque (0.2 mm), and ceramic (0.5/1.0 mm). **Porcelain Fused to Metal crown - PFM** Reduction depends on coverage material **PFM: Full coverage with ceramic** **PFM: Partial coverage with ceramic** **Anterior:** - Incisal reduction: 2mm - Margin: Shoulder, at least 1.0-1.5 mm - Axial reduction (metal-ceramic): 1.5mm Diagram showing two tooth preparations: one for full ceramic coverage (labeled with 1.5 mm and 2.0 mm reductions) and one for partial ceramic coverage (labeled with 0.5 mm, 1.0 mm, 1.5 mm, and 2.0 mm reductions). ## **Tooth Reduction Guidelines** Reduction depends on coverage material. ### **PFM: Full coverage with ceramic** - **Anterior:** - Incisal reduction: 2mm - Margin: Shoulder, at least 1.0-1.5 mm - Axial reduction (metal-ceramic): 1.5mm **Porcelain Fused to Metal crown - PFM** Reduction depends on coverage material **PFM: Full coverage with ceramic** - **Occlusal Surface (metal-ceramic)** - Non-functional cusp: 1.5 mm - Functional cusp: 2 mm - **Margin**: Shoulder, at least 1.5 mm - **Axial reduction (metal-ceramic)**: 1.5 mm **PFM: Partial coverage with ceramic** - **Occlusal Surface**: - Non-functional cusp: 1 mm - Functional cusp: 1.5 – 2.0 mm - **Margin**: Chamfer or shoulder: 0.5 and 1.5 mm - **Axial reduction (metal only)**: 1 mm **(metal-ceramic)**: 1.5 mm Diagram showing PFM crown reduction measurements for full and partial coverage. - **Posterior (Occlusal Surface - metal-ceramic):** - Non-functional cusp: 1.5 mm - Functional cusp: 2 mm - **Margin**: Shoulder, at least 1.5 mm - **Axial reduction (metal-ceramic)**: 1.5 mm ### **PFM: Partial coverage with ceramic** - **Occlusal Surface**: - Non-functional cusp: 1 mm - Functional cusp: 1.5 – 2.0 mm - **Margin**: Chamfer or shoulder: 0.5 and 1.5 mm - **Axial reduction (metal only)**: 1 mm - **Axial reduction (metal-ceramic)**: 1.5 mm # Porcelain Fused to Metal crown - PFM ## Margin Design ### Metal collar - Conservative - More accurate fit - Unaesthetic - Subgingival placement in some cases - More suitable posteriorly ### Ceramic shoulder - Balanced compromise of aesthetic and conservation - Suitable for anterior teeth - Equigingival labial margin is possible ## **Margin Design** ### **Metal collar** - Conservative - More accurate fit - Unaesthetic - Subgingival placement in some cases - More suitable posteriorly ### **Ceramic shoulder** - Balanced compromise of aesthetic and conservation - Suitable for anterior teeth - Equigingival labial margin is possible - ==**Requirement:** This design requires a **shoulder margin** with at least 1.5 mm of reduction to provide enough bulk for the porcelain. It cannot be done with a chamfer or feather edge.== - ==**Instruction:** The dentist must specifically request a # Porcelain Fused to Metal crown - PFM ## Preparation Armamentarium - Silicone putty - Round-end tapered diamond bur - course - Fine grid (red band) - Football-shaped diamond - sickle and periodontal probe ## **Preparation Armamentarium** - Silicone putty - Round-end tapered diamond bur - course - Fine grid (red band) - Football-shaped diamond - ==**Needle Bur:** A thin, pointed bur recommended for safely breaking interproximal contacts without damaging the adjacent tooth.== - sickle and periodontal probe **Porcelain Fused to Metal crown - PFM** Posterior Crown – Partial coverage with ceramic Occlusal reduction - Occlusal orientation grooves - Bur: tapered carbide or diamond (1mm diameter) - Follow anatomic configuration and cusp inclines ## **Posterior Crown Preparation (Partial Ceramic Coverage)** ### **Occlusal reduction** 1. ==Create **orientation grooves** on the cusp ridges and in the central groove, sinking the bur to the desired depth (e.g., 1.0 mm for metal).== 2. ==Join the grooves, ensuring the reduction follows the original **anatomic planes** of the cusps and grooves. The final surface should not be flat.== - Occlusal orientation grooves - Bur: tapered carbide or diamond (1mm diameter) - Follow anatomic configuration and cusp inclines **Porcelain Fused to Metal crown - PFM** Posterior Crown Occlusal reduction Three images showing occlusal reduction on a posterior tooth for a PFM crown: top view with reduction lines, top view after reduction, and side view showing reduction depth. **Porcelain Fused to Metal crown - PFM** Posterior Crown Buccal reduction ### **Buccal reduction** **Porcelain Fused to Metal crown - PFM** Posterior Crown Buccal reduction Four images showing dental crown preparations from different angles, illustrating buccal reduction for a posterior crown. **Porcelain Fused to Metal crown - PFM** Posterior Crown Lingual reduction Metal + Ceramic Metal ### **Lingual reduction** 1. ==This surface is more conservative as it will be covered only by metal.== 2. ==A **single plane of reduction** is sufficient, following the path of insertion.== 3. ==The margin is prepared as a **chamfer** (approx. 0.5 mm).== - Metal + Ceramic - Metal **Porcelain Fused to Metal crown - PFM** Posterior Crown Interproximal reduction Two images showing a dental crown preparation with interproximal reduction, marked with a black line indicating the reduction area. ### **Interproximal reduction** **Porcelain Fused to Metal crown - PFM** Posterior Crown Interproximal reduction Three images showing a dental crown from different angles, highlighting interproximal reduction. **Porcelain Fused to Metal crown - PFM** Posterior Crown Finishing Shoulder with bevel finishing line ### **Finishing** - Shoulder with bevel finishing lin # **Provisional (Temporary) Restorations** ## **Definition** Also known as **interim** or **temporary** restorations, these are fixed or removable prostheses designed to enhance aesthetics, stabilize the teeth, and provide function for a limited time between tooth preparation and final crown delivery. They serve as a diagnostic tool and a trial for the final restoration. ## **Aims and Requirements** A good provisional restoration must satisfy biological, mechanical, and aesthetic needs. ### **Biological Requirements** - ==**Pulp Protection:** The most critical function. After preparation, dentinal tubules are exposed. The provisional must seal these tubules to prevent post-operative sensitivity and protect the pulp from thermal, chemical, and bacterial irritation.== - ==**Maintain Periodontal Health:** The provisional must have:== - ==A good marginal fit (no gaps or overhangs).== - ==Proper contours that support the gingiva.== - ==A smooth, polished surface to prevent plaque accumulation and gingival inflammation.== - ==**Prevent Decay:** A well-sealed provisional prevents leakage and recurrent decay on the prepared tooth.== ### **Mechanical Requirements** - ==**Positional Stability:** Must have accurate **interproximal contacts** to prevent drifting of adjacent teeth and **occlusal contacts** to prevent super-eruption of the opposing tooth. This is especially critical if the patient has recently undergone orthodontic treatment.== - ==**Occlusal Function:** Allows the patient to chew comfortably.== - ==**Strength:** Must be strong enough to withstand occlusal forces for the duration of its use.== ### **Aesthetic Requirements** - ==Should provide an acceptable appearance, especially for anterior teeth.== ## **Diagnostic Use: Cracked Tooth Syndrome** A provisional crown is an excellent diagnostic tool for suspected cracked tooth syndrome. 1. A provisional crown is placed over the suspected tooth, providing full cuspal coverage. This holds the cracked segments together and prevents them from flexing during biting. 2. The patient wears the provisional for several weeks. 3. If the biting pain resolves, it confirms that cuspal coverage is the correct treatment, and the dentist can confidently proceed with the final crown. 4. If the pain persists, the crack may be too deep, and the tooth may require root canal treatment or extraction. e **Porcelain Fused to Metal crown - PFM** **Classical preparation** *(wing preparation)* **Contemporary PFM Preparation** *(Wingless preparation)* - Shoulder blending interproximally from wide labial margin to narrow palatal margin - Easier to prepare ## **Preparation Styles** ### **Classical preparation** *(wing preparation)* ### **Contemporary PFM Preparation** *(Wingless preparation)* > [!info] > Emphasizes **smooth, rounded line angles** and flowing transitions. This reduces stress concentration within the restoration and is more compatible with digital scanning and milling technologies. - Shoulder blending interproximally from wide labial margin to narrow palatal margin - Easier to prepare **Porcelain Fused to Metal crown - PFM** Anterior Crown – full coverage with ceramic Incisal reduction Three dental models showing incisal reduction for PFM crowns, with a diagram illustrating the reduction pattern. ## **Anterior Crown Preparation (Full Ceramic Coverage)** ### **Incisal reduction** 1. ==Create orientation grooves using the bur width as a guide (for 2.0 mm reduction).== 2. ==When reducing, tilt the bur slightly towards the **palatal/lingual** to create a facial bevel, which preserves more tooth structure on the facial surface and improves aesthetics.== **Porcelain Fused to Metal crown - PFM** **Anterior Crown** **Buccal reduction** Anterior tooth preparation for PFM crown showing buccal reduction with 1/3 and 2/3 depth markings, multiple views including labial, occlusal, and cross-sectional perspectives. ### **Buccal reduction** 1. ==This surface requires a **two-plane reduction** to conserve tooth structure and create space.== 2. ==**Occlusal Third:** The first plane follows the natural inclination of the buccal cusp.== 3. ==**Cervical Two-Thirds:** The second plane is aligned with the planned **path of insertion** of the crown.== 4. ==The margin is prepared as a **shoulder** to accommodate the bulk of the metal and porcelain (approx. 1.5 mm).== 1. ==Requires a **two-plane reduction** following the natural contour of the tooth.== 2. ==**Incisal/Middle Third:** Follows the flatter, more vertical contour of this area.== 3. ==**Cervical Third:** Follows the more convex contour near the gumline and is aligned with the path of insertion.== **Porcelain Fused to Metal crown - PFM** Anterior Crown Buccal reduction Three views of a prepared anterior tooth for a PFM crown, showing buccal reduction with a marked reduction line. **Porcelain Fused to Metal crown - PFM** Anterior Crown Lingual reduction 1 ### **Lingual reduction 1** > [!warning] > The lingual surface is reduced to create clearance for the restoration in both centric occlusion and during protrusive movements. It is critical to check that the planned **metal-ceramic junction does not fall on a functional contact point**. The lab should be instructed to either extend the porcelain past the contact or keep the entire contact area in metal. **Porcelain Fused to Metal crown - PFM** Anterior Crown Interproximal reduction ### **Interproximal reduction** 1. ==Use a needle bur to carefully break contact with the adjacent teeth.== 2. ==Use a tapered diamond bur to extend the buccal shoulder and lingual chamfer into the interproximal areas, creating a smooth transition.== 3. ==Ensure the walls have the correct taper and there are no undercuts.== **Porcelain Fused to Metal crown - PFM** Anterior Crown Lingual reduction 2 Three images showing dental preparations for an anterior crown, illustrating lingual reduction from different angles. ### **Lingual reduction 2** **Porcelain Fused to Metal crown - PFM** Anterior Crown Finishing Two images showing the finishing stage of an anterior PFM crown, highlighting the contour and margin detail. ### **Finishing** - ==All line angles should be rounded and smooth.== - ==The margin should be a continuous, well-defined shoulder or deep chamfer.== - ==The critical retention and resistance form comes from the **cervical third** of the preparation, which should have a taper between **6 and 20 degrees**. The reduction in the incisal two-thirds is primarily for material space.== > [!tip] Subgingival Margin Refinement > When placing a subgingival margin, a good technique is to first prepare the margin at the gingival level (equigingival). Then, pack a retraction cord to displace the tissue, and carefully refine the margin 0.5 mm below the retracted gumline. When the cord is removed, the tissue will rebound to cover the finish line. This provides better visibility and control than trying to cut subgingivally from the start. **References:** Shillingburg, H.T., Hobo, S., Whitsett, L.D., Jacobi, R. and Brackett, S.E. (1997) *Fundamentals of fixed prosthodontics*, 3rd Edition, Quintessence SF Rosenstiel, MF Land, R Walter (2022) *Contemporary fixed prosthodontics* Kenneth J. Anusavice (2003) *Phillips' Science of Dental Materials* The Glossary of Prosthodontic Terms: Ninth Edition. *J Prosthet Dent*. 2017 May;117(5S):e1-e105 Goodacre et al. Tooth preparations for complete crowns: An art form based on scientific principles *J Prosthet Dent* 2001;85:363-76 Kontakiotis et al. A prospective study of the incidence of asymptomatic pulp necrosis following crown preparation *International Endodontic Journal*, 48, 512–517, 2015. Edelhoff and Sorensen Tooth Structure Removal Associated with Various Preparation Designs for Posterior Teeth. *Int J Periodontics Restorative Dent* 2002;22:241–249 J Valderhaug et al. Assessment of the periapical and clinical status of crowned teeth over 25 years. *J Dent*. 1997 Mar;25(2):97-105. # **References** - Shillingburg, H.T., Hobo, S., Whitsett, L.D., Jacobi, R. and Brackett, S.E. (1997) *Fundamentals of fixed prosthodontics*, 3rd Edition, Quintessence - SF Rosenstiel, MF Land, R Walter (2022) *Contemporary fixed prosthodontics* - Kenneth J. Anusavice (2003) *Phillips' Science of Dental Materials* - The Glossary of Prosthodontic Terms: Ninth Edition. *J Prosthet Dent*. 2017 May;117(5S):e1-e105 - Goodacre et al. Tooth preparations for complete crowns: An art form based on scientific principles *J Prosthet Dent* 2001;85:363-76 - Kontakiotis et al. A prospective study of the incidence of asymptomatic pulp necrosis following crown preparation *International Endodontic Journal*, 48, 512–517, 2015. - Edelhoff and Sorensen Tooth Structure Removal Associated with Various Preparation Designs for Posterior Teeth. *Int J Periodontics Restorative Dent* 2002;22:241–249 - J Valderhaug et al. Assessment of the periapical and clinical status of crowned teeth over 25 years. *J Dent*. 1997 Mar;25(2):97-105. 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