Dental cements are a group of materials with a wide range of Dental & Orthodontic applications. Common uses include temporary restoration of teeth, cavity linings to provide pulpal protection, sedation or insulation and cementing fixed prosthodontic appliances.
Traditional cements are presented as separate power & liquid components, manually mixed to form a viscous liquid, which then sets to form a brittle solid after application on the required treatment surface. More advanced cements, such as GIC, can also be presented in capsule form and are mechanically mixed using rotational or oscillating mixing machines.
Ideal Cement Properties
- Non irritant - many cements are acidic and therefore an irritant to the pulp. However, on setting there is a rapid increase in pH and polycarboxylate cements are considered to be the most biocompatible of the cements due to its most rapid rise in pH.
- Provide a good marginal seal to prevent marginal leakage.
- Resistant to dissolution in saliva, or in any oral fluid - a primary cause of failure of cements is due to dissolution of the cement at the margins of a restoration.
- High strength in tension, shear and compression to resist stresses at the restoration-tooth interface.
- Adequate working and setting times.
- Good aesthetics.
- Good thermal and chemical resistance.
- Opacity - for diagnostic purposes on radiographs.
- Low film thickness (ideally 25 microns).
- Retention - if an adhesive bond can be created between the cement and the restorative material, this can greatly enhance the retention. Otherwise, the retention is governed by the geometry of the tooth preparation.
The following table describes the properties of each type of cement in more detail: Â
Dental Applications
How to Cement a Temporary Crown -
Dental cements can be utilised in a variety of ways depending on the composition & mixture of the material. The following categories outline the main uses of cements in Dental procedures.
Temporary Restorations
Unlike composite and amalgam restorations, cements are usually used as a temporary restorative material. This is generally due to their reduced mechanical properties which may not withstand long-term occlusal load.
- GIC - Glass Ionomer cement
- Zinc Polycarboxylate cement
- Zinc Oxide Eugenol cement
- RMGIC
Bonded Amalgam restorations
Amalgam does not bond to tooth tissue and therefore requires mechanical retention in the form of undercuts, slots and grooves. However, if insufficient tooth tissue remains after cavity preparation to provide such retentive features, a cement can be utilised to help retain the amalgam in the cavity.
Historically, zinc phosphate and polycarboxylate cements were used for this technique, however since the mid-1980s composite resins have been the material of choice due to their adhesive properties. Common resin cements utilised for bonded amalgams are RMGIC and dual-cure resin based composite.
Liners and Pulp Protection
When a cavity reaches close proximity to the pulp chamber, it is advisable to protect the pulp from further insult by placing a base or liner as a means of insulation from the definitive restoration. Cements indicated for liners and bases include:
- Zinc oxide eugenol
- Zinc polycaroxylate
- RMGIC
Pulp capping is a method to protect the pulp chamber if the clinician suspects it may have been exposed by caries or cavity preparation. Indirect pulp caps are indicated for suspected micro-exposures whereas direct pulp caps are place on a visibly exposed pulp. In order to encourage pulpal recovery, it is important to use a sedative, non-cytotoxic material such as Setting Calcium Hydroxide cement.
Luting Cements
Luting materials are used to cement fixed prosthodontics such as Crowns & Bridges. Luting cements are often of similar composition to restorative cements, however they usually have less filler meaning the cement is less viscous.
- RMGIC
- GIC
- Zinc Polycarboxylate cement
- Zinc oxide eugenol luting cement
Summary of clinical applications
Composition and classification
ISO classification Cements are classified on the basis of their components. Generally, they can be classified into categories:
- Water-based acid-base cements: zinc phosphate (Zn3(PO4)2), Zinc Polyacrylate(Polycarboxylate), glass ionomer (GIC). These contain metal oxide or silicate fillers embedded in a salt matrix.
- Non-aqueous/ oil bases acid-base cements: Zinc oxide eugenol and Non-eugenol zinc oxide. These contain metal oxide fillers embedded in a metal salt matrix.
- Resin-based: Acrylate or methacrylate resin cements, including the latest generation of self-adhesive resin cements that contain silicate or other types of fillers in an organic resin matrix.
Cements can be classified based on the type of their matrix:
- Phosphate (zinc phosphate, silico phosphate)
- Polycarboxylate (zinc polycarboxylate, glass ionomer)
- Phenolate (Zinc oxideâ€"eugenol and EBA)
- Resin (polymeric)
Resin-based Cements
These cements are resin based composites. They are commonly used to definitively cement indirect restorations, especially resin bonded bridges and ceramic or indirect composite restorations, to the tooth tissue. They are usually used in conjunction with a bonding agent as they have no ability to bond to the tooth, although there are some products that can be applied directly to the tooth (self-etching products).
There are 3 main resin based cements;
- Light-cured - required a curing lamp to complete set
- Dual-cured - can be light cured at the restoration margins but chemically cure in areas that the curing lamp cannot penetrate
- Self-etch - these etch the tooth surface and do not require an intermediate bonding agent
Resin cements come in a range of shades to improve aesthetics.
Zinc Polycarboxylate Cements
Composition:
- Powder + liquid reaction
- Zinc oxide (powder) + poly(acrylic) acid (liquid)= Zinc polycarboxylate
- Zinc polycarboxylate is also sometimes referred to as zinc polyacrylate or zinc polyalkenoate
- Components of the powder include zinc oxide, Stannous fluoride, magnesium oxide, silica and also alumina
- Components of the liquid include poly(acrylic) acid, itaconic acid and maleic acid.
Adhesion:
- Zinc polycarboxylate cements adhere to enamel and dentine by means of chelation reaction.
Indications for use:
- Temporary restorations
- Inflamed pulp
- Bases
- Cementation of crowns
Known contra-indications of dental cements
Dental materials such as filling and orthodontic instruments must satisfy biocompatibility requirements as they will be in the oral cavity for a long period of time. Some dental cements can contain chemicals that may induce allergic reactions on various tissues in the oral cavity. Common allergic reactions include stomatitis/dermatitis, uticaria, swelling, rash and rhinorrhea. These may predispose to life threatening conditions such as anaphylaxis, oedema and cardiac arrhythmias.
Eugenol is widely used in dentistry for different applications including impression pastes, periodontal dressings, cements, filling materials, endodontic sealers and dry socket dressings. Zinc oxide eugenol is a cement commonly used for provisional restorations and root canal obturation. Although classified as non-cariogenic by the Food and Drug Administration, eugenol is proven to be cytotoxic with the risk of anaphylactic reactions in certain patients.
Zinc oxide eugenol constituents a mixture of zinc oxide and eugenol to form a polymerised eugenol cement. The setting reaction produces an end product called zinc eugenolate which readily hydrolyses producing free eugenol that causes adverse effects on fibroblast and osteoclast-like cells. At high concentrations localised necrosis and reduced healing occurs whereas for low concentrations contact dermatitis is the common clinical manifestation.
Allergy contact dermatitis has been proven to be the highest clinical occurrence usually localised to soft tissues with buccal mucosa being the most prevalent. Normally a patch test done by dermatologists will be used to diagnose the condition. Glass Ionomer cements have been used to substitute zinc oxide eugenol cements (thus removing the allergen), with positive outcome from patients.
References
3. Acid-base Cements (1993) A. D. Wilson and J.W. Nicholson
