LUTING AGENTS

•Luting is defined as the use of a moldable substance to seal joints and cement two substances together.

Classification of luting cements

-According to the length of time they are expected to stay in function

1. temporary cements

2.permanent cements

-According to the setting mechanism

1.acid base reaction eg. GIC, ZOE

2.polymerisation reaction eg.resin cements

Requirements and characteristics1. Biocompatibility

2. Interfacial sealing - luting cements should not shrink upon setting

3.Anticariogenic activity

4. Marginal seal – poor marginal fit leads to more cement being exposed on the margins than necessary.

Luting cements being soluble is prone to erosion, leads to staining and recurrent caries.

5. Retention – primary role of luting agents is to provide retention. Lack of retention - main reason for failure of restorations

6.Adhesion – may occur by chemical or physical bonding ,micromechanical interlocking or friction.

7. Mechanical properties

• Permanent luting cements should have 1.high strength ( both static and fatigue ) 2.high fracture toughness 3.high wear resistance

• Temporary cements must have a relatively low strength

8.Handling propertiesDesiarable characteristics- 1.ease of use 2.long working time 3.short setting time.9.Radiopacity –important to allow radiographic diagnostic

10.Viscosity and film thickness- low film thickness is important to allow for correct seating of restoration.

11. Solubility – affects marginal integrity of restoration which may increase plaque accumulation.

12. Esthetics – shade and translucency of cement are important as they affect the final esthetic result .

Temporary cements

Indicated for fixation of temporary restorations

Eg. Zinc oxide eugenol non eugenol cements calcium hydroxide paste

Due to inhibitory effect of eugenol on polymerisation of resins and composites ,temporary cements using nonphenolic components are preferred.

ZINC OXIDE EUGENOL

Composition - Powder ZnO –principal ingredient White rosin-brittleness of

set cement Zn acetate- accelerator

strenght upto 1% MgO –modifier Zn stearate - plastcizer

Liquid Eugenol –reacts with ZnO Olive oil- plasticizer Water- initiator Acetic acid/ alcohol- to

accelerate setting –about 1%

Properties•Biocompatible because of neutral pH •Antibacterial action•Eugenol released from salt matrix contibute to pain relief in preparations with little RDT.•Eugenol is a free radical scavenger. Therefore negatively affect polymerisation of resins.

Advantages Minimal pulp reaction Good sealing properties Adequate strength for luting

single restorations.

Disadvantages Hydrolytic breakdown under

exposure to oral fluids Inflammatory reaction on

soft tissue Potential allergic response May soften and discolour Minimal mechanical

properties for luting

EUGENOL FREE CEMENTS

-Suitable for patients who are sensitive to eugenol

- for cases in which the definitve cementation will use resin materials - available in transparent and opaque chromas.

PERMANENT CEMENTSZINC PHOSPHATE CEMENTComposition :

Powder Zinc oxide –principal ingredient MgO- reduces temperature of

calcification process. Silicon dioxide-inactive filler Oxides of bismuth ,calcium or

barium- impart a smoothness to freshly mixed cement mass

Liquid Phosphoric acid -45-60%

reacts with ZnO Water -30-55% -increases

rate of reaction Aluminium-2.3% essential to

the cement forming reaction Zinc -0.9% -moderates

reaction between powder and liquid and allows adequate working time.

Properties

•Compresive strength: 96-110 Mpa

•pH during cementation :3.5

•Film thickness :10-20um

•Modulus of elasticity -13.7Gpa (stiff and resistant to deformity)

•Retention is mechanical.

•Damage to pulp occurs during first few hours of insertion.

•Mixing time-1.5-2 min

•Working time -5 min

•Setting time- 2.5-8 min

Advantages Most popular for cast

restorations Adequate strength Reasonable working time Excess material can be

easily removed Acceptable effect over

dental pulp Manipulation less critical

than other cements.

Disadvantages Pulp irritation Lack of antibacterial

action Brittleness Lack of adhesion Solubility in acid fluids.

ZINC POLYCARBOXYLATE COMPOSITION

Powder Zinc oxide-main ingredient Stannous oxide-replaces

magnesium oxide Stannous fluoride- 4.5%

improves the manipulation Sodium fluoride- 1%

anticariogenic property. Silica ,alumina,bismuth-filler

Liquid Aqueous solution of

polyacrylic acid Copolymer of acrylic acid Other carboxylic

acid(itaconic acid) –stabilizes the liquid.

Properties: Compressive strength: 50-80 MPa Tensile strength:7-10 MPa Bond strength to tooth structure:9 MPa for enamel and 3.3 MPa

for dentin pH during cementation : 4.8 Film thickness: 13-20 um Modulus of elasticity: 2.4-4.4 GPa Low solubility in oral fluids than ZnPO4 Excellent biocompatibility with pulp Mixing time: 30-60 sec Working time:2.5 min Setting time: 6-9 min

Advantages Low level of irritation Good adhesion to tooth

structure and alloys Good strength ,solubility and

film thickness compared to zinc phosphate

Disadvantages Need for accurate

proportion ,more critical manipulation

Lower compressive strength and greater visco-elasticity than zinc phosphate

Short working time and need clean surface to use adhesion potential (technique sensitive)

Glass ionomer cementcomposition

Powder Acid soluble calcium

fluoroaluminosilicate glass Lanthanum,strontium

,barium ,or zinc oxide provide radiopacity.

Liquid Copolymer of itaconic,maleic

or tricarboxylic acids

Properties

Compressive strength: 127 MPa Tensile strength: 8 MPa Bond to tooth structure:9 MPa for enamel and 3 MPa for dentin. Film thickness:9.5-16um Biocompatibility Microleakage is less due to closing of marginal seal Working time: 2-3.5 min Setting time: 6-9 min Retention is very high due to chemical bonding Removal of excess is moderately easy.

Advantages Adequate strength Adhesion to tooth structure Sustained fluoride release Less solubility Good esthetic properties

Disadvantages Sensitive to moisture and

dehydration GIC is translucent Post cementation sensitivity

is common.

RESIN MODIFIED GLASS IONOMERCOMPOSITION

Powder Ion-leachable

fluoroaluminosilicate glass particles

Initiators for light /chemical curing

Liquid Water and polyacylic acid or

polyacrylic acid modified with methacrylate and hydroxyethyl methacrylate monomers.

Properties:Compressive strength: 150 MPaTensile strength: 25-35 MPaFilm thickness:20um

Advantages High strength Good retention Low solubility Fluoride release

Disadvantages Post cementation sensitivity

Resin cements

composition-available as powder/liquid or two paste form- resin matrix/ binder-bis GMA/urethane dimethacrylate ,triethylene glycol dimethacrylate-fillers-quartz,colloidal silica/metal oxides

Coulping agents-organosilanes Also contains-hydroquinonesto prevent premature polymerisation Uv absorber improves colour stability

Properties Solubility is very less in oral fluids. Compressive strength: 194-200 MPa Tensile strength:15 MPa Film thickness: >25u Retention is good and occurs by micromechanical bonding Removal of excess is moderately easy.

Advantages Low solubility Good retention Good strength Good aesthetics

Disadvantages More film thickness Microleakage due to

polymerisation Pulp irritation More cost. Low modulus of elasticity, so

cannot support long span prosthesis.

Meticulous and critical manipulation technique

Compomer

this cement lies between the glass-ionomer and the resin composites but with the predominant characteristics of microfilled resin composites.

The term ‘Compomer’ is derived from composite and glass ionomer, having fluoride releasing capability of conventional GIC and durability of composites .

Because of the presence of water, these materials are self-adhesive and an acid–base reaction starts at the time of mixing .

-Tensile strength, -flexural strength superior to GIC -wear resistance of compomer

Compomers for luting purposes are available as a two component system, either powder/liquid or as two pastes

Powder: strontium aluminofluorosilicate, metallic oxides, chemical-activated and/or light-activated initiators.

Liquid: polymerizable methacrylate/carboxylic acid monomers, multifunctional acrylate monomers, water.

Clinical significance of luting agents

Although zinc phosphate cement is still used in clinical practice and even considered the gold standard, advances in dental technology over the last decade have produced new materials, which might eventually replace zinc phosphate cement in the near future .

If the restoration has been designed with conservation of tooth structure in mind and retention is to be derived from the adhesive properties of the cement,

If fluoride release is of paramount importance, a resin-modified glass ionomer is a suitable cement.

Resin-modified polyphosphoric acid cements do not show adequate bond strength to be considered bonding cements at this time

For optimal bond strength, a resin cement in conjunction with a dentin bonding agent will provide the highest retention. -

PULPAL REACTIONS

Ultimately, a postcementation pulpal reaction under clinical conditions is dependent on three factors:

(1) composition of the cement. Postoperative hypersensitivity for most cements can be problematic and is based on their chemistry, while only a few do not present a problem;

(2) the RDT—the larger the RDT the less risk of pulp irritation due to the greater buffering capacity of the uid in the dentinal tubules;

(3) time elapsed from preparation to moment of cementation—the longer this period, the better the pulp is able to recover from the trauma of preparation and therefore can tolerate a subsequent irritation better.

Regarding selection of dental cements for implant-supported restorations if an implant is ideally placed and the occlusion is optimal, the implant-supported restoration should be cemented with definitive dental cements such as glass-ionomer cement and resin cement.