5Chemistry of Dental Cements Dental cements are typically a powder/liquid systemThe liquid is an acidThe powder is a basePowder must be insoluble in oral fluids but reactive with acid
6Composition of powderTwo materials used to make powders for dental cements:Zinc oxidePowdered glass
7Zinc oxideThe only insoluble, nontoxic, reactive oxide or hydroxide to react w/an acidCommon additives are aluminum oxide and magnesium oxideHas some antibacterial effectsReactivity is controlled by manufacturing process
8The chemical form- silicon oxide - is very un-reactive Powdered GlassThe chemical form- silicon oxide - is very un-reactiveWhen oxides of sodium, calcium and potassium are added in sufficient quantities, the glass will react with strong acid.Made of small translucent glass particlesContains fluoride to reduce melting temp, improve flow of molten glass, and gives cement ability to release fluoride.Reactivity is determined by composition of glass.
9Dental cement liquids Eugenol Phosphoric acid Polyacrylic acid Composition or strength of acid determines reactivity of the cement liquid.Composition is controlled by the manufacturerLiquids used in dental cements include:EugenolPhosphoric acidPolyacrylic acid
10Eugenol Organic liquid- weak acid Major component of oil of cloves Derived from phenolAntibacterialObtundant -- reduces irritation to pulpInhibits free radical polymerizationInhibits setting of composite restorative materialsEthoxybenzoic acid (organic liquid) added to formulate cements.
11Phosphoric acid Used as 2/3 acid and 1/3 water Very acidic and irritating to tissueAmount of water present affects reactivity of liquid by affecting ionization.Different levels of humidity affect it
12Polyacrylic acid Aqueous solutions 30-50% polyacrylic acid by weight Very viscous liquidDispensingMust be very accurate – independent drops importantDo not dispense liquid until ready to mix cementDo not store in refrigeratorCarboxyl groups bond to calcium in toothWater hardening cementsZinc oxide or glass powder mixed with anhydrous polyacrylic acidCombined powder mixed with companion liquid (mostly water)Polyacrylic acid dissolves in water then reacts with ZO or glass
13Dental cements Combine one of the three cement liquids… EugenolPhosphoric acidPolyacrylic acidWith one of the two powdersZinc oxide powderGlass powder
14Most commonly used Calcium hydroxide Zinc phosphate Used as a base/liner under restorations in deep prepsUsed as for pulp cappingZinc phosphateUsed to lute restorations, ortho bands – also used as a base material under restorationsZinc oxide-eugenol (ZOE)Chalky and white, used when not concerned with aesthetics.Obtundant – kind to pulpGlass ionomerUsed for thermal insulation under restorations, luting agent
15Zinc Phosphate Cement Use B. Related Information 1. Lute inlays, crowns, bridges, ortho brackets, etc.2. Also used as a base material under restorations.B. Related InformationWhen the powder and liquid are mixed, an exothermic (heat-releasing) reaction occurs.To dissipate the heat of this reaction:1. A large portion of the glass slab must be used duringmixing.2. The powder must be added in small increments.3. The mixing time must extend to 1.5 to 2 minutes.
16Zinc phosphate cement/base material MixingSet up time is 5-9 min.Add powder to liquid in small increments
17Mixing for luting consistency Measure the powderMeasure the liquid“fluff powder”Fill scoop; do not packDivide powder into several smallincrementsHold bottle verticallyDispense correct # of drops of liquidAdd powder in small incrementsShould stretch ½ inch
18Glass ionomer Use 1. Base, luting agent, restorative material 2. Thermal insulating material in deep prepsCharacteristics1. High strength, low solubility2. Kind to pulp3. Chemically bond to tooth structure; release fluorideDispensing systems1. Powder/liquid systems2. Disposable capsules – mixed in amalgamator3. Paste/paste systems
19Mixing for base or luting Higher power/liquid ratioMixMeasured in same mannerSetting time is ~ 7 min.Mixing time between secondsAdd about ½ the powder at first, then the restMix is determined by ratio set by manufacturer, not “feel”Clean up with soap and water before cement sets
20Liners Used to protect pulp from chemical irritation Stimulate dentin formation or release fluorideConsiderations:Do not provide thermal insulation (too thin)Too weak to support restorative materials or condensation forces (dental amalgam)Once used under composites to prevent irritation-not much anymore
21Calcium hydroxide liners and bases Promote the formation of secondary dentinComes as paste/paste systemOne is calcium hydroxide, one is salicylate.Titanium oxide is an added filterSetting reaction is accelerated by waterSets very quickly on moist dentin
22Dycal (Calcium Hydroxide) A. UseCalcium hydroxide may be used in pulp capping and as a base/liner under other dental restorative materials in deep preparations.B. Protective PropertiesCalcium hydroxide serves as a protective barrier between tooth tissues (dentin and pulp) and acid-containing cements and restorative materials.C. MeasuringDispense small, but equal, amounts on a paper mixing padD. MixingMix thoroughly with the crook of a small, ball-pointed instrument until a uniform color is achievedMixing should be completed within 10 seconds.
23Calcium Hydroxide, con’t E. ApplicationUse the tip of the ball-pointed instrument to place the mixed material on the floor of the cavity preparation. Avoid placing the mixed material on walls and margins, and avoid placing it in large amounts.F. SettingThe setting time of mixed calcium hydroxide is 2 to 3 minutes on the mixing pad at normal room temperature.The setting time for a pulp capping or base/liner will be greatly decreased in the mouth because of the moisture of dentin.
24Cavity Sealer Resins dissolved in a solvent VarnishesCopal VarnishResins dissolved in a solventPainted onto entire cavity preparationSolvent evaporates, leaving thin resin layerUsed under amalgamsNOT used with composites (interferes with adhesion)
26Zinc-oxide eugenol (ZOE) UseProtective propertiesOne of the least irritating dental materials1. Temporary cement2. Insulating base underpermanent restorations3. Provide obtundantfilling for sensitivetoothThermal traumaSedative, soothing effect on dental pulp
27Measuring ZOE Use scoop provided by manufacturer PowderLiquidUse scoop provided by manufacturerPlace 1 scoop of powder onto glass slab or paper padDispense 2 drops of eugenol by holding dropper perpendicular to slab/padDrops should not touch powder, but should be near to it
28Mixing ZOE cement Hold spatula in “flat” position Draw about half of powder into liquidUse small area of mixing slab/padPush powder into liquid with quick motionContinue incorporating small portions of powderMix should be complete in 1.5 minutesSticky consistency – use for cementing temporary crownThick, putty-like consistency – use for base or temporary filling
29Intermediate Restorative Material Reinforced ZOEIRMStronger, less soluble than ZOETemp restorationsIntermediate basesAdditives include:AluminaResins
30Mixing IRM Measure 2 scoops of powder onto glass slab/paper pad Place 1 drop of liquid onto slab/padHold spatula in “flat” positionDraw about ½ of powder into the liquidUse small mixing area; spatulate with quick motionContinue incorporating powder into the mix by pressing powder into the mixMix must be thick, putty-likeComplete mix in about 1.5 minutes
31Application Gather IRM into one mass on the mixing slab/pad May be rolled with fingers to form a ballUse flat-bladed instrument to carry portions of material to the cavity prepMay dip instrument into excess powder to prevent stickingSets up in about 3 – 3.5 minutesGlass slab may be cleaned with alcohol wipe
32Temporary Cement High flow to permit ease of seating restoration Temp BondPropertiesHigh flow to permit ease of seating restorationStrong enough to withstand forces of chewingAllow restoration to be easily removed
33Temporary Cement Two tubes Catalyst Base MeasuringMixingTwo tubesCatalystBaseSqueeze equal lengths of material onto padMix together in 30 sec.Homogenous colorShould form a string when stretched from mixing padApply thin layer to restoration, sets in 2 min.
34Temporary Crown Temporary crown Crown prep leaves an exposed tooth which can be painful.Temp crowns usually made of plastics and formed in mouth.Also made of metal or plastic formed outside of mouth.Temporary cement used to apply temp crown.Placed at crown prep appointment, lasts few days or weeks.
35How Temporary Restorations are used: Remove all or part or decay from tooth, then allow pulp to heal before determining treatment.Patients with many carious lesions (more than 10) to make the oral environment noncariogenicA temporary filling on an “open” tooth in endodontic therapy.
36Exposure controls/personal protection with Eugenol Respiratory protection: In well ventilated areas respiratory protection is not normally required. In confined, poorly ventilated area respiratory protection may be necessaryHand protection: Wear impervious glovesEye protection: Wear eye protection. e.g. Safety glasses/goggles
37What you need to know to stay safe As with most dental materials …read the label and look for hazardous or toxic products in the materialsBe aware of potential for allergic reactionsFollow OHSA exposure limits
38Generic and brand names of base materials Bases:Shofu base cement (Shofu)Ketac bond capsules (ESPC)Zinc Phosphate (Mizzy)ZOE B&T (Caulk)- Eugenol-containing material
39Generic and brand name Liners Liners:Heavy filled glass ionomers:Fuji IX GP in capsule or powder/liquid form.ESPE: provisional filler, larger non-stress-bearing build upsSHOFULight cured resin modified glass ionomerVitre-bond (3M)Fuji Lining Cement LC (G-C)
40Group Activity Divide up into 5 groups – about 4 to a group Discuss the case study your group is given, and answer thesequestions:What material will you select for your patient?Why did you select that material?How will you mix/apply the material?How long would you expect the material to last?