Dental crowns come in various types, each offering unique advantages and disadvantages, from metal and PFM to porcelain and zirconia. Dental crowns, also known as caps, are tooth-shaped coverings or restorations placed over damaged or decayed teeth to strengthen them, improve their appearance, and restore their shape and function. Crowns fully encase the tooth’s visible part down to the gum line and can be made from different materials. Crowns protect cracked, broken, or extensively decayed teeth and are used to cap teeth that have had root canal treatment. They are also sometimes placed as connectors on dental bridges.

Metal Crowns

Metal crowns have a coping or substrate made from metal, usually gold alloy, other alloys, or stainless steel. They are extremely durable, but because metal shows through the biting surface, they are not as aesthetic as other crown types for visible teeth. 

Different types of metal crowns are:

  1. High noble crowns have a substrate of at least 60% pure gold, based on the American Dental Association. This offers corrosion resistance, biocompatibility, strength, and longevity. However, the high gold content makes these more expensive.
  2. Base metal crowns contain non-noble metals like nickel or chromium. They are less expensive but have higher corrosion risks and biological incompatibility over time. Common choices are nickel-chromium alloys or cobalt-chromium alloys.

In general, metal crowns last the longest of any type. Studies show that 96% survive at least 10 years. With high noble metals, some may function well for over 40 years. This makes metal a smart functionality-over-aesthetic choice for chewing surfaces or less visible teeth.

Porcelain-Fused-to-Metal Crowns (PFM) as one of the main types of dental crown 

Porcelain-Fused-to-Metal Crowns

As a hybrid between metal and porcelain crown types, PFM crowns combine a metal coping with a stacked porcelain overlay. This fuses the durability of metal with excellent aesthetics resembling natural teeth. PFMs involve two necessary parts:

  1. Metal coping substrate made from high noble, noble, or base alloys. This core foundation gives shape and strength.
  1. Porcelain covering aesthetically mimics enamel for color, light refraction, and texture. Materials like feldspathic porcelain stack in layers are custom color-matched to surrounding teeth.

PFM crowns provide strength for back molars that undergo heavy chewing forces. Their resemblance to natural dentition also makes them applicable in visible areas. Compared to all-porcelain, they have higher resilience and prevention of wear on opposing teeth. 

University of Oulu in Finland reported a 78% survival rate after 20 years and a 3- to 5-year survival rate of between 92% and 97.6% for PFM crowns.

However, PFM drawbacks include potential dark metal lines visible at the crown margins. Porcelain chipping may also lead to metal exposure over time. Both factors impede aesthetic quality compared to all-ceramic crowns in the long term.

All-Porcelain Crowns 

As the name denotes, all-porcelain crowns contain no metal components. They consist of milled or pressed ceramic materials that mimic natural tooth enamel’s light reflection and translucency. The most common varieties include feldspathic porcelain, leucite-reinforced porcelain, and lithium disilicate glass ceramics.

All-porcelain crowns offer exceptional aesthetics and biocompatibility since they contain zero metal. However, they have lower fracture resistance than metal or PFM crowns. Prudent use focuses them on anterior and premolar teeth that undergo low mechanical stress during biting and chewing. With proper prep and cementation, porcelain crowns have expected lifespans of 7-15 years or longer.  

3 different types of all-porcelain crowns are:

  1. Feldspathic porcelain is a glass-based silica material containing feldspar. It offers excellent aesthetics and shade-matching ability. However, it lacks exceptional strength for high stresses.  
  2. Leucite reinforced has potassium-aluminosilicate particles (leucite) to bolster durability. This gives improved fracture toughness for better longevity.
  3.  Lithium disilicate contains lithium disilicate crystals embedded in the glassy ceramic. These contribute substantial fracture resistance, making the material suitable for single-unit anterior or premolar crowns. 

Researches show that both underlying tooth and crown prep factored in, well-placed porcelain crowns give an average 89.4% 10-year success rate. While not as indestructible as metal crowns, they balance aesthetics, biocompatibility, and adequate strength.

Zirconia Crowns

Zirconia crowns showcase the advanced ceramic zirconium dioxide stabilized with yttrium oxide. This yields exceptional fracture toughness and strength properties exceeding traditional porcelain. Crowns consist of a full-contour monolithic zirconia body or zirconia coping covered by feldspathic ceramic. Custom-milled copings or full bodies are highly durable and suitable for anterior or posterior teeth.

Key advantages include:

  • High strength nearing levels of metals  
  • Full zirconia construction allows lifelike translucency similar to natural teeth
  • Biocompatible and chemically inert for ideal compatibility  
  • Does not cause excessive wear on opposing teeth  

Documented clinical studies found 95-99% of zirconia crowns surviving at the 5 to 7-year mark with likely 10+ year lifespans. This positions zirconia between classic PFM and modern all-ceramic endurance but with superior aesthetics. 

The only downside of zirconia crowns is that they remain higher in cost due to advanced CAD/CAM manufacturing. Over time, this price continues lowering towards competitiveness with other ceramic options as materials and technologies progress. For anyone desiring to maximize aesthetics with strength only second to metals, zirconia crowns should remain strongly considered among crown types.

How Crown Types Compare in Key Metrics

The success of dental crowns depends on choosing crown varieties that suit position and purpose. Useful comparisons in metrics like longevity, aesthetics, and price aid decisions:  

Durability & Lifespan

  • Metal: Greatest durability with 40+ year potential lifespans
  • PFM: High durability with typical 10 to 30-year lifespans  
  • Zirconia: Strongest all-ceramic with 10+ year lifespans
  • Leucite/Lithium Disilicate: Moderate strength with 10-15 year lifespans      
  • Feldspathic: Lower durability, better for low-stress uses

Aesthetics

  • Zirconia/Leucite/Lithium Disilicate: Exceptional shade and light handling  
  • PFM and Feldspathic: Very aesthetic, mimicking natural tooth appearance
  • Metal: Poor aesthetic qualities  

Cost

  • Metal: Least expensive option  
  • PFM: Intermediate pricing  
  • Zirconia/Lithium Disilicate/Leucite: Highest material expenses  

No single crown inherently works best. The choice depends on positioning, visibility, mechanics, prep state, and whether to support a dental bridge. Cost may dictate material as well. Dentists should guide optimal selection for situations and desires, but understanding the strengths of types empowers educated patient decisions, too.

Specialty Options

Beyond the main dental crown categories exist speciality options worth noting:

  1. IPS e.max crowns feature reinforced glass-ceramic for high aesthetic potential plus 405 MPa flexural strength approaching early zirconias. This reasonably broadens placement to premolar sites, too.
  2. BruxZir crowns offer a toughened type of zirconia, delivering over 800 MPa of flexural strength. The tradeoff is slightly lower translucency, falling short of lithium silicate materials. They suit patients with substantial grinding or clenching habits.  
  3. Procera crowns showcase densely sintered, high-purity aluminum oxide coping cores. These integrate well with overlaying porcelain for uncommon resilience in combating fractures. 
  4. Non-prep or no-prep crowns conserve healthy tooth structure, needing only minor reshaping. Limited to teeth with existing size, shape, and positioning that already match the preformed crown shape.

While niche and novel, these emerging crown technologies boost the diversity in strength, resilience, biocompatibility, and conservation of natural dentition. Discussing them with one’s dentist helps make fully informed decisions around crown work.

Conclusion  

Today’s crown manufacturing offers versatile solutions balancing aesthetics, resilience, biocompatibility, and conservation based on positioning and use case scenarios. Keeping up with the latest materials and technologies allows dentists to elevate restorative outcomes through informed, strategic crown planning. With evidence-based selections and quality fabrication, both dentists and patients benefit from the expanding possibilities of durable, lifelike crowns.