Porcelain Crowns
The journey of dental ceramics, utilized for the restoration and replacement of lost tooth tissue or teeth, has undergone a significant transformation since the early days of porcelains. Presently, the focus with dental ceramic restorations is on reinstating aesthetics, natural appearance, anatomy, function, and the mechanics of the teeth. The range of options includes types without metal and with metal, crowns, inlays, fixed bridges, and more—all falling under the umbrella term ‘fixed prosthesis.’
Deciding the most suitable ceramic material for individual patients requires the expertise of a dentist, while the dental technician takes on the responsibility of preparing the prosthesis with precision based on the provided measurements from the dentist.
Introduction
Dental ceramics are essentially crafted from metallic oxides that undergo high-temperature sintering, either individually or in combination, resulting in a solid piece with minimal pores and remarkable mechanical resilience. The microstructure achieved post-sintering depends on the types and ratios of the metal oxides, leading to a composition that can be entirely crystalline, glass-ceramic, or predominantly vitreous.
In contemporary classification, ceramics are grouped based on their microstructural composition and their response to acid attacks:
- Vitreous ceramics primarily composed of silica (feldspathic): susceptible to acids
- Vitreous ceramics composed of silica with filled crystals (leucite and lithium disilicate, lithium silicate): acid-sensitive
-
Polycrystalline ceramics (zirconia): acid-resistant
Ceramic-metal prostheses, crafted from a material that has proven quite effective in dental treatments, are undergoing a transformation with the regular advent of technological progress and superior materials capable of meeting all criteria for patient restorations. This evolution is causing ceramic-metallic restorations to gradually fade away, making room for the newest development: total ceramics. The primary drawback lies in the high cost, making it an ideal choice for oral restoration that may not be accessible to every patient. Consequently, some patients choose the incorporation of metal into their mouths, accepting a compromise in aesthetics and resistance.
It’s worth mentioning that metal-free ceramics exhibit superior biocompatibility and lower chemical reactivity, offering a stark contrast to the potential harm posed by metal in the oral cavity. Over the past two decades, ceramics have become the prevailing choice, surpassing the utilization of porcelain-metal combinations. Patient awareness regarding the material’s advantages becomes imperative to rationalize the higher cost.
Despite their artificial nature, these materials closely imitate natural teeth, establishing them as the preferred ceramics for oral use. Additionally,
it’s important to acknowledge that ceramic materials are inherently of inorganic origin.
Clinical uses
In clinical settings, metal-porcelain units find applications in crowns and bridges, with the coefficient of linear thermal expansion of porcelain adjusted by manufacturers using leucite. This adjustment aims to prevent significant disparities that might create stress concentration zones and lead to material fractures during cooling. Initially, the dental technician employs an oxidation treatment on the metal alloy infrastructure to establish a chemical bond between the two.
Inlays and metal-free porcelain onlays: Despite initial contradictions, modern techniques and adhesives have advanced, ensuring reliable adhesion between porcelains and enamel, resistant to chewing forces.
Pure porcelain facets or veneers: Clinical trials reveal survival rates of these restorations ranging from 82% to 96% over 10 to 21 years, provided they are prepared and cemented exclusively to enamel. Instances of increased peeling and fracture failures were observed when preparation and grinding exposed 50% or more dentin.
Feldspathic ceramics
Read Less
Containing glass, these ceramics contribute to the prosthesis’s translucency and natural appearance. However, their delicacy and fragility preclude their placement without metal support. A metal structure is essential to provide the necessary support in the oral cavity.
This requirement has spurred modifications in ceramics to bolster their resistance, resulting in the evolution of total ceramics.
Aluminous ceramics
Read Less
In 1965, McLean and Hughes ventured into the realm of metal-free ceramics, achieving success with aluminum oxide. While they crafted a robust ceramic, it retained a considerable level of opacity, leading to reduced translucency and a loss of natural appearance. To counteract this, patients had to treat additional teeth to avoid an artificial look. Consequently, this material is specifically utilized for the framework, constituting the internal aspect of the crown. A separate layer, composed of a distinct translucent ceramic, is applied over it.
Zirconium ceramics
Read Less
This marks the pinnacle of innovation and excellence in ceramic materials. These state-of-the-art ceramics are composed of highly sintered zirconium oxide (95%), partially stabilized with yttrium oxide (5%). Known chemically as zirconia or ZrO2, the standout feature of this material is its exceptional toughness, attributed to its entirely crystalline microstructure. It also boasts a reinforcing mechanism referred to as ‘resistant transformation.’
Discovered by Garvie & colleagues in 1975, this ceramic showcases an ability to withstand substantial mechanical stress within the oral cavity, effectively handling the forces exerted by chewing muscles.
Due to its outstanding mechanical and optical properties, it finds application in extensive prosthetic restorations, bridges exceeding 3 units, crowns, prostheses on implants, implants, orthodontic brackets, endodontic posts, inlays, and onlays.
These materials exhibit resistance to fracture, high precision in marginal adjustment, and remarkable aesthetics, contributing to a noteworthy clinical survival rate.
Conclusions
As demonstrated, there exists no ceramic material that perfectly satisfies all requirements. It’s undeniable that nothing can replicate the distinct qualities of natural tooth enamel. The ideal scenario would entail achieving tissue regeneration through the utilization of biodegradable ceramics, which remain in the body solely for the duration of their required function, gradually disappearing as tissues undergo regeneration. While experimental creation of dentin has been achieved, its practical application in everyday clinical scenarios remains a considerable distance away.
Dental ceramics have undergone significant evolution, undergoing substantial changes in both mechanical and optical properties, striving to closely mimic a natural tooth in terms of color, texture, and resistance to wear and tear, including forces encountered during chewing.
With noteworthy strides in dental adhesives, these porcelain crowns can now be applied to incisors and canines, particularly in the creation of aesthetic veneers, provided they are bonded to tooth enamel. However, their resistance diminishes when adhered to dentin.
Zirconias, boasting the mentioned characteristics, prove to be an exceptionally hard and highly resilient element. This makes them suitable for crafting large bridges in posterior areas, individual crowns, and structures for implants, including the implants themselves. However, their cementation presents significant difficulties.
Dental ceramics have gradually overcome their limitations, evolving into highly coveted restorative elements for dentists, patients, and dental technicians alike.
Currently, various types of ceramics, each with distinct characteristics, empower dentists to restore teeth with outstanding naturalness. Dentists have access to a diverse range of ceramic materials, each with unique compositions and properties. Being well-versed in these options is crucial when selecting the specific ceramic that aligns with the individual needs of each patient.
Other Dental Insurances We Accept
