Dental Cements Amalgam Composite Gold

Dental cements are widely used in dentistry: Cavity lining: base under restorations Luting: cementation of crowns, bridges, inlays, onlays and orthodontic brackets Some cements are specifically formulated to be used as filling material Certain cements are used for special purposes in endodontics, periodontics and surgery

Requirements of ideal cements A- Biological properties It should be non-toxic, non-irritant to the pulp or other dental tissues It should be bacteriostatic It should provide thermal insulation to the pulp It should provide chemical protection to the pulp It should offer electrical insulation to the pulp from galvanic effect

Requirements of ideal cements B- Rheological properties and film thickness When used as luting for cementaion, the mixed cement should have rheological properties that allow complete sealing of restoration. It should give minimal film thickness to obtain maximum strength for adhesive junction

Film thickness depends on: Powder particles size: fine powder particles allow lower film thickness Viscosity of the mix: powder/liquid ratio ↑ liquid ↓viscosity ↓ film thickness Amount of pressure applied: ↑ pressure ↓ film thickness

Requirements of ideal cements C- Solubility Cements should be insoluble in saliva and liquids taken into the mouth because: Solubility marginal leakage, loosening of restoration and recurrent caries

Requirements of ideal cements D- Mechanical properties Depends on the intended application. If cement used as a base under amalgam, it should have sufficient strength to withstand amalgam condensation. Strength depends on: Chemical composition Powder/liquid ratio

Requirements of ideal cements E- Bonding Cements are usually bond to tooth structure and restorations by either mechanical interlocking or chemical bonding. Cements that offer chemical bonding are described as Adhesive Ideal dental cement should bond to tooth structure and restoration but not to instruments

Requirements of ideal cements F- Optical properties It depends on the intended purpose of application. If cement is used for cementation of translucent restoration, only translucent cement can be used

Classification of cements Oil-based cements Zinc oxide eugenol cement (ZOE) Non-eugenol cement Acid-based cements Zinc phosphate cement (ZPH) Zinc polycarboxylate cement (ZPC) Water-based cements Resin-based cements

Zinc oxide eugenol cement Available in two forms Powder & liquid form: Powder: zinc oxide (main constituent), magnesium oxide (10%), zinc acetate & zinc stearate as accelerator Liquid: eugenol, olive oil (15%) Ready made paste: used as temporary filling and set only when it comes in contact with water

Setting reaction It is a chelation reaction Zinc oxide reacts with eugenol in the presence of water to form zinc eugenolate The set material cinsist of unreacted zinc oxide and free eugenol held in zinc eugenolate matrix Presence of water is essential for setting Temperature and humidity accelerate the setting reaction

Manipulation

Properties Biological: pH is about 7. Eugenol is bacteriostatic, and has obtundent effect (can alleviate pain and pulp irritation) Film thickness: about 40 microns Solubility: highly soluble in oral fluids Strength: compressive strength about 15 Mpa tensile strength about 5 Mpa Bonding: bond to tooth by mechanical interlocking Optical properties: it is opaque due to presence of unreacted zinc oxide

Modification of ZOE Polymer-reinforced ZOE Powder: 80 % zinc oxide, 20 % polymethyl methacrylate Liquid: eugenol and 10% polystyrene Compressive strength 38 Mpa Can be used as a base, final cementation or as temporary filling

Modification of ZOE EBA cement Powder: zinc oxide, 30 % alumina to increase strength, 6% rosin and copolymers to impart plasticity and reduce brittleness Liquid: 37.5% eugenol and 62.5% ethoxy benzoic acid (EBA) Compressive strength 85 Mpa Can be used as a base under amalgam, final cementation or as temporary filling

Modification of ZOE Rapid set ZOE Modification of powder particles size and shape, powder/liquid ratio, and by increasing the amount of accelerators

Applications Temporary cementation of crown and bridges Permanent cementaion (modified reinforced types) Base under restorations Temporary filling material Surgical pack Periodontal pack Root canal sealer

ZOE is contraindicated under composite restoration or other resin based materials because it interfere with the polymerization and cause discoloration of composite

Non-eugenol cements Based on oils other than eugenol. Suitable for patients with sensitivity to eugenol Used for temporary cementation for teeth that are supposed to be covered finally by ceramic restoration (because ceramics are cemented by resin cements)

Zinc phosphate cement ZPH Powder: zinc oxide (main constituent), other oxides: Magnesium oxide: maintain white color of cement and control reactivity of powder Silica and alumina: improve mechanical properties Liquid: aqueous solution of phosphoric acid buffered by small amounts of zinc oxide or aluminum oxide. This allow controlling working time

Setting reaction Acid-base reaction 3ZnO + 2H3PO4 + H2O → Zn3(PO4)2 · 4H2O The reaction is rapid and exothermic (release heat)

Manipulation Evaporation of water from liquid → lower pH → slow down the reaction Water gain by liquid → accelerate reaction → lower working time Powder/liquid ratio: depend on the purpose luting: 2.5:1 base: 3.5:1 Mixing time: 60-90 sec Setting time: usually about 5-9 min The reaction is exothermic, heat accelerate the setting. Therefore cold glass slab and mixing over large area → increase working time

Properties Biological: pH freshly mixed 1.3-3.6 pH after hour 6 pH after 48 hours is neutral Film thickness: 25 microns Solubility: 0.1-0.2 % after 24 hour immersion in water Strength: 50% of strength after 10 min, full strength after 24 hours compressive strength: 95-135 MPa tensile strength: 3-5 MPa Bonding: mechanical interlocking Optical properties: ZPH is opaque Thermal & electrical: ZPH provides good thermal and electrical insulation → used under amalgam

Application Permanent cement Temporary filling Base under metallic restoration (like amalgam)

Zinc polycarboxylate cement (ZPC) Present in the following forms 1- Traditional form: powder: zinc oxide, magnesium oxide, additives like alumina, silica, fluoride and stainless steel fibers liquid: 30-40% aqueous solution of copolymer of polycarboxylic acid (polyacrylic acid), sodium hydroxide, tartaric acid to control setting reaction 2- Pre-proportioned capsules: for mechanical mixing 3- Water stable cement: freeze-dried polycarboxylic acid is powdered and added to zinc oxide powder. The liquid will be distilled water or diluted solution tartaric acid

Setting reaction Acid-base reaction between zinc oxide and ionized copolymer of polyacrylic acid Set cement consist of zinc polycarboxylate (polyacrylate) matrix that holds the unreacted powder particles Setting reaction is more rapid than zinc phosphate

Manipulation Powder/liquid ratio: cementation 1:1 base 2:1 Mixing time: 30-40 sec Setting time: 2.5-6 min Plastic spatula should be used because carboxylic group of cement can react with metal spatula result in tenacious adhesion Working time can be extended by: Using cool glass slab Incorporation of powder to liquid in two halves The mixed cement should be used only as long as it still has glossy surface. loss of gloss → initial setting

Properties Biological: it is acidic but it is less irritant to the pulp than ZPH because: Polyacrylic acid is weaker acid than phosphoric acid Polyacrylic acid chains are too large and lack of mobility required to penetrate through dentinal tubules Film thickness: 25-45 microns Solubility: 0.01-0.02 % after 24 hours immersion in water. Less than ZPH Strength: compressive strength: 55-95 MPa tensile strength: 3.5-7.5 MPa

Properties Bonding: ability to bond chemically to enamel & dentin Carboxylic group bond chemically to the calcium of the tooth Bond strength: to enamel 8 Mpa to dentin 2 MPa Has high bond strength to base metal alloys Optical properties: opaque due to unreacted zinc oxide particles

Applications Permanent cementation Base under restoration Note: ZPC should not be used for temporary cementation because it bonds chemically to tooth structure

Glass ionomer cement (GIC) Present in the following forms 1- Traditional form: powder: calcium fluoroaluminosilicate glass powder. Barium glass added to give radioopacity liquid: aqueous solution of copolymer of acrylic and itaconic acids, tartaric acid not more than 5% to increase working time & decrease setting reaction (sharp setting) 2- Pre-proportioned capsules: for mechanical mixing 3- Water stable cement: freeze-dried polycarboxylic acid is powdered and added to glass powder. The liquid will be distilled water or diluted solution tartaric acid

Setting reaction Acid-base reaction Three stages of setting reaction: Dissolution: dissolution of surface of glass particles by acid releasing Ca++, Al+++ and fluoride ions Migration: migration of ions (Ca++, Al+++ and fluoride) into liquid, Ca++ migrates first followed by Al+++ , sodium form silica gel on surface of glass particles Reaction and precipitation: migrating Ca++ and Al+++ react with carboxylic group of acid to form cross-linked polycarboxylic salt gel Set cement consist of unreacted glass particles surrounded by silica gel embedded in matrix of cross-linked poly salt hydrogel of calcium & aluminum

Properties Biological: has mild effect on the pulp, has anticariogenic effect due to release of fluoride from set cement, fluoride recharge Film thickness: 24 microns Solubility: 1.5% after 24 hours immersion in water GIC should be protected from premature exposure to water or saliva Strength: compressive strength: 90-240 MPa tensile strength: 14-24 MPa

Properties Bonding: chemically bond to tooth structure by reaction of polycarboxylic group with calcium and phosphate content of tooth structure Bond strength is lower than that of ZPC To increase bond strength to dentin, the surface should be treated with conditioner (usually diluted polycarboxylic acid) to remove smear layer. Optical properties: it is translucent. Can be used for cementation of all ceramic restorations, and used as esthetic restorative material for children

Drawbacks of conventional GIC Initial solubility (moisture sensitivity) Low early strength Low abrasion resistance Several modification were made to overcome these drawbacks

Modifications Metal modified GIC (cermet glass ionomer) Fine particles of precious metals (silver, gold or palladium) are sintered with the glass ionomer powder particles, most commonly silver is added Adv: 1) higher abrasion resistance 2) higher flexure strength 3) higher fracture toughness Disadv: 1) more opaque than conventional GIC 2) less fluoride release Uses: 1) core build up material 2) filling material for class I and II in primary teeth

Modifications Light cure glass ionomer (resin modified glass ionomer) RMGIC Polymerizable functional group incorporated to give more rapid curing when activated by light or chemical. These materials set by polymerization reaction in addition to acid-base reaction that continues long after polymerization There are two types: Dual cure resin modified GIC Triple cure resin modified GIC

Dual cure RMGIC Set by: Triple cure RMGIC Conventional acid-base reaction: mixing powder&liquid Polymerization reaction of resin: light curing Triple cure RMGIC Light cure polymerization of resin Chemical cure polymerization of resin

Modifications Nano-ionomer RMGIC that contain nano-sized fillers in a range of 1-100 nm Adv: better esthetic higher wear resistance Easier polishing

Resin-based cements Classified according to their bonding mechanism to tooth structure into: Conventional resin cements Adhesive resin cements

Conventional resin cement Gain their retention through acid etching procedure in conjunction with enamel & dentin bonding agents Self-cure resin cements powder/liquid or two pastes of diacrylate monomer diluted to lower molecular weight dimethacrylate monomer Light-cure resin cements single paste of Bis-GMA or UDMA diluted to lower molecular weight monomer Dual-cure resin cement two paste system of material similar to light-cure but it can polymerize by two mechanisms of setting, light & chemical curing at the same time

Adhesive resin cement Formulated with adhesive promoter: 4 META (4 methaciyoxy ethyl trimellitic anhydride) Phosphonate group: phosphate end of phosphonate group reacts with calcium of the tooth or with metal oxides of restoration surface

Properties Biological: it is irritant to the pulp Deep areas of cavity require pulp protection with calcium hydroxide or GIC liner Film thickness: varies from one product to another Solubility: they are insoluble in oral fliuds Strength: Compressive strength: 180-260 MPa High fracture toughness compared to other cements Bonding: mentioned previously Optical properties: translucent

Other materials related to dental cements Cavity varnish (copalite varnish) composed of synthetic resin dissolved in organic solvent such as acetone, chloroform or ether It is applied to the prepared cavity with brush or cotton pellet, solvent is allowed to evaporate leaving thin coating resin film on surface This may be repeated two to three times to give uniform resin layer Application: Seal dentinal tubules & prevent penetration of chemicals into the pulp Applied over glass ionomer filling to protect it from moisture in the first 24 hours Applied under amalgam to seal the gap between amalgam and tooth until corrosion layer is formed

Calcium hydroxide cement (Dycal) Supplied in either: Two paste: chemically cured Base: mixture of calcium hydroxide, zinc oxide and sulfonamide Catalyst: glycol salicylate, titanium dioxide and calcium sulfate Single paste: light cured

Properties of Ca(OH)2: Fresh mix is highly alkaline with pH about 11-12. when placed in very deep cavity, it stimulates the pulp to lay down dentin, and if applied on exposed pulp it can kill microorganisms remaining in the cavity Solubility: it is highly soluble Strength: very low compressive strength 5 MPa If applied under amalgam, it should be covered with ZPH cement before condensation of amalgam, because it is very weak