Luting Agents

viscosity & film thickness ease of use radiopaque marginal seal aesthetics solubility cariostatic biocompatible mechanical properties

dependent in size of powder / filler particles in material must be low to allow seating of restoration without interference viscosity increases as material sets so must seat restoration quickly & maintain pressure film thickness should be thin as possible ideally 25um or less

easy to mix working time should be long to allow for seating of restoration setting time should be short

some ceramic crowns are radiolucent makes it easier to see marginal breakdown

ideally luting agent should bone chemically to tooth & indirect restoration with permanent & impenetrable bond

variation in shade & translucency non staining

this should be low

fluoride releasing & antibacterial important in preventing 2ndary caries in crown margins

non toxic non damaging to pulp via inappropriate pH or heat on setting low TEC

high compressive strength - dentine = 275 MPa high tensile strength - dentine = 50MPa high hardness - dentine = 70k, enamel = 400k YM similar to tooth - dentine = 15GPa no luting agent gets close to tooth values for more than 1/2 physical properties

• dental cement - zinc phosphate / zinc polycarboxylate • GIC - conventional / resin modified • composite resin luting agents - total etch for use with DBA, self etch

acid base reaction powder & liquid excellent clinical service easy to use cheap

zinc oxide >90% magnesium dioxide <10% - gives white colour & increases compressive strength aluminium & silica oxide - improves physical properties & alter shade of set material

aqueous solution of phosphoric acid ~50% oxides which buffer solution: -aluminium oxide; ensures even consistency of set material - zinc oxide; slows reaction giving better working time

initial is acid base reaction followed by hydration reaction resulting in formation of crystallised phosphate matrix

• low initial pH; can cause pulpal irritation as can take 24hrs to return to neutral • exothermic setting reaction • not adhesive to tooth or restoration • not cariostatic • final set takes 24hrs • brittle • opaque

• phosphoric aid replaced by polyacrylic acid • bond to tooth surface similar to GICs • less of a heat reaction • pH low to begin with but return to neutral more quickly & longer chain acids don’t penetrate dentine as easy • cheap

difficult to mix & manipulate soluble in oral environment at low pH opaque lower modulus & compressive strength than zinc phosphate

chemistry is the same but in GIC particle size of glass is less than 20um to allow for suitable film thickness

acid base reaction between glass & acid glass - SiO2, Al2O3, CaF2 poly acid mixture - acrylic, maleic, itraconic acid and their copolymers reaction goes through same dissolution, gelation & hardening stages

cement bonds to tooth surface via: - ion exchange with Ca in enamel & dentine - hydrogen bonding with collagen in dentine results in fairly strong, durable & possibly dynamic bond to tooth no chemical bond to restoration surface surface of restoration should be sandblasted to allow mechanical adhesion

easy to use & durable low shrinkage as no polymer in conventional GIC relatively insoluble once fully set aesthetically better than zinc phosphates self adhesive to tooth surface fluoride release cheap

chemistry same as RMGI filling material glass particle size smaller to allow acceptable film thickness in addition to GIC powder & liquid, the liquid contains a hydrophilic monomer - HEMA; hydroxyethyl methacrylate

as GIC is a water based material