Learning Objectives
- Clearly define "bioactive" and "regenerative" as they relate to dental crown and bridge luting agents.
- Identify the key characteristics of an ideal dental cement.
- Trace the historical development of common luting agents for crowns and bridges.
- Understand the chemical composition of bioactive cements.
- Recognize the benefits of using bioactive dental cements.
- Familiarize yourself with the three bioactive cements currently available in the U.S.
- Learn the protocols for using bioactive luting agents with various direct and indirect dental restorative materials.
- Examine the current clinical data on the 2-3 year performance of bioactive cements.
Ideal Cements
Today's dental professionals have a wide array of materials for placing indirect restorations, thanks to advancements in dental material science. These options offer excellent restorative choices for crowns and onlays, featuring diverse physical properties and aesthetic profiles. The materials include:
- Zirconia
- Lithium disilicate
- Feldspathic porcelain
- Porcelain fused to metal
- Gold
- Composite
Choosing the appropriate material depends on several factors such as the tooth's position in the mouth, required strength, aesthetic considerations, extent of tooth reduction, interaction with other dental prostheses, biological forces, and patient preferences. After selecting the most suitable material, choosing the right luting material is crucial for successful restoration cementation. Ideally, a dental cement should possess numerous qualities, including:
- Strong adhesion to tooth structure and restorative materials
- Non-irritating to pulp and gingival tissues
- Minimal post-cementation sensitivity
- Insolubility in oral fluids
- Resistance to fracture
- Low film thickness for precise seating
- Low viscosity for easy seating
- Capable of dual-cure or self-cure for reliable setting
- High conversion rate for superior physical properties
- Aesthetic appearance under translucent porcelain restorations
- Easy and consistent mixing
- Simple clean-up
- Distinct radiopacity on x-rays
- Ideally, not requiring etch, prime, or bond
Historically, no cement has met all these criteria perfectly, often requiring compromises when cementing fixed restorations. The most commonly used cements, ranked from lowest to highest bond strength to tooth structure, include:
- Zinc phosphate
- Polycarboxylate
- Glass ionomer
- Reinforced glass ionomer
- Resin-modified glass ionomer
- Self-adhesive resin
- Bonded resin with adhesive
Recently, "bioactive" or "regenerative" cements have been introduced. Bioactive cement can actively elicit a response from tooth tissues. Regenerative cement fosters an environment that promotes tooth tissue healing, particularly by protecting the pulp and generating new hydroxyapatite. This type of cement can promote the formation of new hydroxyapatite when immersed in oral fluids containing inorganic phosphates. These bioactive cements add several new desirable characteristics to the list of ideal cement qualities:
- Release of calcium and fluoride ions over time
- Anti-cariogenic activity
- Alkaline pH upon setting
- Promotion of pulpal healing
- Elimination of post-cementation sensitivity
- Insolubility in oral fluids
- Promotion of remineralization and new hydroxyapatite formation
- Ability to seal gaps at the restorative margin with new hydroxyapatite
Bioactive cements facilitate ionic exchange by donating calcium ions to the tooth structure, stimulating repair through the formation of new hydroxyapatite crystals at restoration margins. In a hydrophilic environment (such as saliva), these cements stimulate odontoblasts in the dentin with calcium, in the presence of inorganic phosphates and active pyrophosphatase. Consequently, bioactive cements can strengthen, protect, desensitize, and remineralize the tooth.
Teeth are fundamentally composed of collagen and hydroxyapatite, making them susceptible to damage and degradation from various oral conditions. Mechanical, chemical, or biological challenges can compromise their integrity. Research shows that the primary reason for replacing fixed restorations is bacterial ingress and recurrent caries at the interface between the tooth structure and the cemented restoration. An ideal luting agent would prevent or repair this ingress, and bioactive cements are the current best solution for achieving this goal.
Available Bioactive Cements in the U.S.
There are three bioactive cements currently available in the United States:
- Ceramir (Doxa Dental)
- TheraCem (Bisco)
- Activa (Pulpdent)
These cements meet the criteria for bioactivity, though each has distinct components, formulations, and chemical structures.
Ceramir (Doxa Dental)
Ceramir, developed by Doxa Dental, is a unique glass ionomer and calcium-aluminate cement that contains no resin, aiming to reduce pulp sensitivity. It exhibits minimal post-cementation sensitivity and is hydrophilic, containing high levels of calcium which contribute to its white appearance. It has the highest bond strength to zirconia among bioactive cements due to its ability to promote nano-crystal formation, which is not impeded by phosphates from saliva and blood. This eliminates the need for cleansing with a phosphate scavenging agent before cementation.
Ceramir is packaged in capsules containing the powder and liquid components, activated in a conventional triturator. The cement has a film thickness of 10-15 microns and does not require etching, priming, or bonding of the tooth or restoration. However, sandblasting the interior of fixed restorations can enhance bond strength. Ceramir is not a dual-cure formulation, requiring chemical setting until an advanced gel stage is reached for clean-up.
The chemistry of Ceramir consists of two stable mineral hydrates:
- Katoite: 10-40 nanometer crystals of calcium-alumina-hydrate
- Gibbsite: an amorphous gel of aluminum hydroxide
Ceramir bonds to tooth structure through a process called "nanostructural integration," placing it in a new category of dental materials known as Nanostructurally Integrating Bioceramics (NIB). This process eliminates shrinkage, unlike resin-based cements. In the presence of inorganic phosphates in the oral environment, Ceramir provides calcium ions that participate in forming hydroxyapatite crystals, the body's natural bioceramic material. This enhances stability and biocompatibility.
Ceramir's calcium-aluminate system demonstrates high water turnover during hardening, bonding a significant amount of water within the cement, which strengthens it. Optimal performance is achieved at body temperature and humidity, conditions naturally found in the oral environment. As it sets, Ceramir initially dissolves and then recrystallizes, precipitating nano-crystals onto the tooth, mimicking natural tooth structure and resulting in chemical bonding and interlocking at the nano-particle level.
Being set in oral fluids allows Ceramir to interact with phosphates, forming hydroxyapatite that maintains the marginal seal of the restoration, prevents bacterial ingress, inhibits recurrent caries, and seals restoration margins. Studies show new hydroxyapatite deposition as Ceramir interacts with saliva and odontoblasts, confirming its bioactive and regenerative properties. Its alkaline pH upon hardening inhibits bacteria and protects the pulp from inflammation. The high pH and calcium ion release contribute to Ceramir's bioactivity. Hydroxyapatite formation at tooth/restoration interfaces has been confirmed by scanning electron microscope and x-ray diffraction studies, as well as spectroscopy testing.
Ceramir also has thermal characteristics similar to tooth structure, minimizing expansion and contraction changes and gap formation from thermal cycling. These characteristics, along with its ability to seal restorative interfaces and prevent bacterial ingress, make Ceramir exceptionally kind to the dental pulp. Studies have shown low pulpal sensitivity and excellent pulp responses in long-term follow-ups.
TheraCem (Bisco)
TheraCem, developed by Bisco, is derived from TheraCal LC, a light-cured calcium hydroxide liner used for pulpal protection. TheraCem is a dual-cured, self-adhesive resin cement suitable for permanently luting various indirect restorations such as crowns, bridges, inlays, onlays, and posts. It offers protection for pulpal tissues in deep preparations prone to inflammation and sensitivity.
TheraCem rapidly transitions to an alkaline state upon setting:
- pH 4 at initial mix
- pH 8 within 5 minutes
- pH 10 within 30 minutes
TheraCem releases calcium and fluoride over time, enhancing pulpal health and promoting hydroxyapatite deposition. It does not require additional etching, priming, or bonding, simplifying placement and reducing the risk of errors. It is dispensed from an automix dual-barrel syringe for accurate mixing and has dual-cure chemistry, allowing for a quick 2-second tack cure for easy clean-up before full set. Its shear bond strength is 26.8 MPa to Zirconia and 34.5 MPa to Lithium Disilicate.
A unique feature of TheraCem is the incorporation of Portland cement filler, containing calcium silicate that releases calcium and fluoride in oral fluids, preserving tooth structure at the tooth/restoration interface. This also acts as a pulpal medicament, promoting pulpal healing and reducing post-cementation sensitivity and recurrent caries. TheraCem is highly radiopaque, making it easily visible on x-rays, and its calcium and fluoride-releasing capabilities can be recharged over time with calcium and fluoride-containing products like MI Paste (GC America).
Activa Bio-Active Cement (Pulpdent)
Activa Bio-Active Cement, developed by Pulpdent, is a distinct bioactive luting agent composed of three key components:
- Bioactive ionic resin
- Patented rubberized resin
- Reactive glass filler
This cement is free from Bisphenol A, Bis-GMA, and BPA derivatives. It includes a rubberized resin designed to absorb shock, providing superior resistance to chipping and fracturing compared to other dental cements. Despite its resilience, Activa remains durable, insoluble, and resistant to wash-out. Its fracture resistance, measured by the deflection at breakage test, is 2-3 times higher than composite resins and 5-10 times higher than resin-modified glass ionomers. Clinical performance data over two years show excellent retention and no post-cementation sensitivity. Activa is suitable for use with all types of dental restorative materials.
Similar to other bioactive cements, Activa releases calcium, phosphate, and fluoride, promoting the formation of new hydroxyapatite. This helps resist bacterial ingress, prevent secondary caries, and eliminate post-cementation sensitivity. Activa can be tack-cured for 2 seconds after seating to facilitate removal, and it sets through three mechanisms:
- Light cure
- Self-cure resin chemistry
- Self-cure glass ionomer reaction
Summary
Recent statistics from Glidewell Dental Laboratories, a leading provider of indirect restorations in the United States, indicate a significant shift in the prescription for crowns and bridges. While porcelain fused to metal was once the standard for fixed restorative applications, nearly 95% of full coverage restorations and onlays now use Zirconia or Lithium Disilicate. These materials eliminate the need for non-esthetic metals and reduce the high cost of gold and precious metals in lab bills. CAD/CAM systems facilitate the milling of these materials, ensuring their continued use in the foreseeable future.
Bioactive cements are proving to be excellent choices for permanently luting these advanced restorative materials. Current two-year clinical performance reports for Ceramir, TheraCem, and Activa show promising results, indicating their potential as reliable luting agents. These cements represent a new paradigm in dental cementation, actively preventing secondary caries, maintaining marginal seals, desensitizing teeth, and promoting new hydroxyapatite formation.
This home study course is intended for educational purposes and to aid in dental professionals' relicensing. It provides general information on treatment protocols and does not endorse any specific brand of dental material.
Quiz For Crown & Bridge Cements
