I. Permanent Crown Compositions and Indications
Permanent crowns are generally categorized into metal, metal-ceramic, and all-ceramic compositions.
- Complete Cast Crowns (Full Metal Crowns)
These crowns are composed entirely of metal, such as gold or other alloys.
| Composition | Indications (Clinical Situations) |
|---|---|
| Full Gold Crown (FGC) (A type of Complete Cast Crown) | Longevity and Durability: Full metal crowns have one of the greatest longevities of all dental restorations. Situations requiring high strength and durability. |
| Metal Alloys (Gold, other metals) | Retention and Resistance: Maximum retention and resistance are needed. High displacement forces. Ideal for short clinical crowns in the posterior region, where maximizing retention is critical. |
| Conservative Preparation: Require the least amount of tooth reduction, preserving more natural tooth structure. Cases with limited occlusal clearance where conservative reduction is necessary (1.0–1.5 mm occlusal reduction needed for gold vs. ~2.0 mm for ceramics). | |
| Location: Restoration of posterior teeth, including maxillary molars and mandibular molars and premolars. | |
| Function: Patients who are heavy bruxers, as gold wears at a rate similar to natural tooth enamel and is less likely to fracture or wear the opposing dentition. |
- Porcelain Fused to Metal (PFM) Crowns
PFM crowns consist of a cast metal substructure (coping) veneered with a layer of fused porcelain. Metal alloys include noble or high-noble alloys (e.g., gold) or base metal alloys (e.g., Nickel-Chromium, Cobalt-Chromium).
| Composition | Indications (Clinical Situations) |
|---|---|
| Metal Ceramic (PFM/VITA Metallic Ceramic Crown) | Combined Strength and Aesthetics: Used when both strength and aesthetics are needed. |
| Location/Span: Posterior crowns and bridges where high occlusal forces occur. Anterior crowns when improved aesthetics are desired but a full ceramic crown is not indicated. Long-span fixed partial dentures due to the strength of the metal substructure. | |
| Functional Requirements: Abutments for removable or fixed partial dentures. Teeth receiving heavy load or for patients with parafunctional habits. Used for tooth preparations with reduced height where a full ceramic crown may not have sufficient support. |
- All-Ceramic Crowns
Ceramics are compounds of metallic and non-metallic elements. All-ceramic restorations are indicated when there is a high aesthetic demand or if the patient has a metal allergy. They are often considered more conservative than PFM crowns.
| Composition Type | Specific Examples/Materials | Indications (Clinical Situations) |
|---|---|---|
| Polycrystalline Ceramics | Zirconia (Zirconia Dioxide) | Used for a wide variety of indirect restorations such as crowns and bridges. High-strength material (flexural strength 900–1200 MPa). High translucency zirconia is now available. |
| Glass-Based Ceramics | Feldspathic Ceramics | Used as a monolithic ceramic for single-unit anterior prostheses, veneers, inlays, or onlays. Highly aesthetic due to high glass content. |
| Glass-Based Ceramics (with crystalline fillers) | Leucite Reinforced Glass Ceramics | Generally possess good aesthetic properties. Usually processed via “hot pressing”. |
| Lithium Disilicate Reinforced Glass Ceramics (e.g., IPS Emax CAD) | Suited for single unit anterior crowns due to good flexural strength (360–400 MPa). Also used for occlusal onlays. | |
| Zirconia Reinforced Lithium Silicate (e.g., VITA Suprinity) | Has a high flexural strength (460 MPa). | |
| Resin Matrix Ceramics (Hybrid) | VITA Enamic | Can be used for posterior and anterior crowns. These materials are not brittle and have good shock-absorbing characteristics due to the polymeric matrix. |
II. Temporary/Provisional Crown Compositions
Temporary crowns are placed after tooth preparation to protect the prepared tooth and maintain function while the permanent crown is being fabricated.
| Composition | Typical Use/Clinical Indication |
|---|---|
| Polymethyl Methacrylate (PMMA) | Suitable for long-span provisional restorations. Must generally be used indirectly (laboratory construction) or direct-indirect (reline of a shell) due to its highly exothermic reaction and significant polymerization shrinkage if used directly. |
| Polyethyl Methacrylate (PEMA) | Used for single crowns (direct method), short span bridges, or short term provisional restoration (2-3 weeks). Also used for relining pre-formed or laboratory-made shells. Has minimal exothermic heat compared to PMMA. |
| Bisacryl Composite Resin (e.g., Luxatemp) | Ideal for single crowns (direct method). Suitable for intraoral application with a template or matrix. Advantages include low exothermic reaction and minimal polymerization shrinkage. |
| Light-Cured Composite Resin (e.g., Flowable Composites) | Used for single unit restorations in the direct method. Highly aesthetic and offers controlled setting. Can also be used to repair open margins of bisacryl composite crowns. |
| Preformed Metal Crowns | Used for molar and premolar forms. Very strong and easily adjusted. More suited for children. |