Dental Restorative Materials and Techniques

• Restorative materials and techniques are used in dentistry.

Dental Material Requirements

• Dental materials must be biocompatible with pulp tissue.
• They should not produce allergic reactions.
• The materials must maintain esthetics and function.
• They should have an adequate shelf life and be economical.
• Easy to use with minimum equipment.
• Adequate setting characteristics to meet clinical requirements.
• Should possess elastic properties with freedom from permanent deformation.
• Should possess dimensional stability.

Glass Ionomer Cement

• Other names include polyalkenoate cement, man made dentin, dentin substitute, alumino silicate polyacrylic cement, and Ion leachable glass.

Glass Ionomer Cement Composition: Powder

• Made up of 35-50% Silica.
• Made up of 20-30% Alumina.
• Made up of 3-6% Sodium fluoride.
• Made up of 1.5 – 2.5% Aluminium fluoride.
• Made up of 4-12% Aluminum phosphate.
• Traces of barium, strontium.

Glass Ionomer Cement Composition: Liquid

• Made up of 45% Polyacrylic acid.
• Made up of Itiaconic acid, maleic acid, tricarboxyllic acid - 5% (reduce the viscosity)
• Contains Tartaric acid which increases the working time and shortens the setting time.
• Contains 50% water.

Glass Ionomer Cement Classification

• Type I is luting cement.
• Type II is restorative cement.
• Type III is liners and bases.
• Type IV is pit and Fissure sealant.
• Type V is orthodontic cement.
• Type VI is core build up.
• Type VII is high strength.
• Type VIII is for ART.
• Type IX is pediatric GIC

Factors affecting Setting Time of Glass Ionomer Cement

• Temperature of the mixing slab.
• Water powder ratio.
• Prolonged mixing time.
• Loss of water from the liquid.

Mechanical Properties of Glass Ionomer Cement

• Compressive strength is 150 MPa, less than silicate cement.
• Tensile strength is 6.6 Mpa, higher than silicate cement.
• Hardness is 49 KHN, less hard than silicate cement.
• Fracture toughness is inferior to composite.

Other Properties of Glass Ionomer Cement

• Solubility and disintegration is like silicates.
• Initial solubility is high due to leaching of intermediate products.
• Complete setting reaction takes place in 24 hours so cements should be protected from saliva.
• Esthetics are inferior to silicates and composites.

Glass Ionomer Cement Adhesion

• Provides good adhesion to enamel and dentine.
• Binds chemically to tooth structure.
• Bonding is due to the reaction between carboxyl ions of the polyacids and calcium ions of the enamel and dentine.
• Bond to enamel is higher than to dentine due to greater inorganic content.

Glass Ionomer Cement Manipulation: Tooth Preparation

• The tooth should be clean for effective adhesion of the cement.
• Smear layer after cavity preparation blocks the tooth surface and should be removed to achieve adhesive bonding.
• Achieved by pumice wash or 10% polyacrylic acid application for 10-15 seconds, then washed with water.

Glass Ionomer Cement Proportioning and Mixing

• Powder and liquid are dispensed just prior to mixing.
• Powder is divided into two equal increments, first increment is incorporated into liquid rapidly with a stiff bladed spatula to produce a homogenous milky consistency
• The remainder of the powder is then added.
• Mixing should be done in a folding method to preserve gel structure.
• Pack the mix immediately into the cavity with a plastic instrument.

Glass Ionomer Cement Protection and Finishing

• It is extremely sensitive to air and water during setting.
• Cement surface is protected with special varnish, unfilled resin, or cocoa butter.
• Excess material is trimmed from margins, hand instruments are preferred to rotary tools to avoid ditching.
• Further finishing is done after 24 hours; restoration is coated with a protective agent to protect trimmed areas.

Advantages and Disadvantages of Glass Ionomer Cement

• Advantages are minimal tooth preparation, tooth colored material, and fluoride reservoir which makes secondary caries less likely.
• Disadvantages are more prone to fracture and less resistance to wear and abrasion.
• It is susceptible to dehydration throughout life span, so it's not indicated for mouth breathers.

Modified Glass Ionomer Cement

• Resin modified materials have small quantity of resin into the liquid formula.
• Less than 1% of photoiniators are used for the setting reaction initiated by light.
• Advantage includes early resistance to water uptake in newly set cement and enhanced translucency
• Resin utilized is hydroxyethylmethacrylate (HEMA), incorporated into the liquid in about 15-25%.

Nano-Ionomer

• Nano-ionomer delivers greater wear resistance, esthetics and polish compared to glass ionomer.
• It offers the same fluoride release as conventional glass ionomer cement.
• Example is Ketac, nano light cured glass ionomer cement.

Metal Modified GIC

• Metal modified GICs were introduced to improve strength, fracture toughness, and wear resistance.
• They maintain the potential for adhesion and anticariogenic property.

Two Methods of Employing Metal Modified GIC

• Silver alloy admixed: Spherical amalgam alloy powder is mixed with the type II of GIC called as miracle mix.
• Cermet: Silver particles are bonded to glass particles and this is done at high sintering temperatures.

Giomers

• Giomers employ pre-reacted glass ionomer (PRG) technology to form a stable phase of GIC in restoration.
• Known as PRG composites.
• Giomer is a hybrid of the words 'glass ionomer' and 'composites'.
• They have the properties of both glass ionomer and resin composites, including fluoride release, fluoride recharge, excellent aesthetics, easy polishibility, and biocompatibility.
• Immediate fluoride release may occur from PRG fillers, in contrast to compomers.

Zirconomer

• This new class of restorative glass ionomer promises the strength and durability of amalgam.
• Protective benefits of glass ionomer while completely eliminating hazard of mercury.
• Reinforced with special zirconia fillers to match the strength and durability of amalgam.
• Features sustained high fluoride release for anti-cariogenic benefits especially in cases with high caries risk.
• Packable and condensable like amalgam without hazard of mercury, or risk of corrosion, expansion, and thermal conductivity.
• High flexural modulus and compressive strength ensures longevity in stress-bearing areas.

Composite Resins

• Applications include restoration of anterior and posterior teeth, to veneer metal crowns and bridges, to build up cores, cementation of orthodontic brackets, pit and fissure sealant, and repair of chipped porcelain restorations.

Classification of Composite Resins by Curing System

• Chemically cured
• Visible light cured
• UV light cured
• Dual cured

Classification of Composites by Filler Particle Size

• Mega fill has very large size.
• Macro fill has 10-100 micrometer.
• Midfill has 1-10 micrometer.
• Minifill has 0.1-1 micrometer.
• Microfill has 0.01-0.1 micrometer.
• Nanofill has 0.005 -0.01 micrometer.

Composite Resin Composition

• Consists of Bis – Phenol Glycedyl methacrylate (BISGMA) resin matrix.
• Triethylene Glycol dimethacrylate (TEGDMA) serves as a viscosity controller.
• Urethane dimethacrylate (UEDMA).
• Includes coloring agents.
• Includes inhibitor as hydroquinone and opacifiers such as titanium dioxide, barium and strontium to produce radiopacity.

Composite Resin Filler Phase

• Addition of filler particles into the resin matrix significantly improves its properties.
• Less resin equates to less curing polymerization shrinkage
• Reduces water sorption.
• Reduces the coefficient of thermal expansion
• Increases mechanical properties like strength, stiffness, hardness and abrasion resistance.
• Filler particles used are colloidal silica, quartz, ceramic materials, barium, strontium and zirconium in composites.

Composite Resin Coupling Agent

• Coupling agents bond filler particles to the resin matrix.
• These agents improve physical and mechanical properties of resin.
• Provides hydrolytic stability by preventing water from penetrating the filler resin interface.
• Common coupling agents are organosilanes, zirconates, and titanates.

Composite Resin Curing Systems: Self-Cured Composites

• Supplied in two pastes: base paste containing the initiator benozyl peroxide and accelerator paste containing activator as tertiary amine as N-dimethyl- P-toluidine.
• Manipulated by mixing proper proportion on a mixing pad with a plastic spatula to avoid metal spatula discoloring the composite.
• Cavity is slightly overfilled because shrinkage occurs towards the center of the material.

Composite Resin Curing Systems: UV Light Activated Composites

• Curing occurs due to activation of Benzoin methyl ether when exposed to UV light.
• Poses a potential hazard to clinician and patient, causing retinal soft tissue damage.
• Requires 60 seconds of curing and can cure up to a thickness of 1.5 mm.

Composite Resin Curing Systems: Dual Cured Composites

• Possess both self and visible curing components in the same material.
• Recommended for ceramic inlays that may be too thick to allow sufficient light to radiate through for adequate monomer conversion.

Different Types of Composites: Conventional Composite

• Contains filler particle size of 8 – 12 micrometers.
• Composite with the largest filler size.
• Has high strength and hardness.
• Has less water sorption and co – efficient of thermal expansion.
• Polishing is difficult and results in a rough surface that tends to retain stain.

Different Types of Composites: Microfilled Composite

• Contain smallest filler particle size 0.04- 0.4 micrometer.
• Has lowest filler content.
• Lowest strength and hardness.
• Highest thermal co efficient of expansion and water sorption.
• Excellent esthetics due to increased smoothness.

Different Types of Composites: Small Particle Composite

• Contains filler particle of size 1-5 micrometer.
• Has good surface smoothness like Microfilled composite.
• Improved physical properties like conventional composites.
• Has the highest compressive strength.

Different Types of Composites: Hybrid Composite

• Has filler particle size of 0.6 -1 micrometer.
• Have smooth finish and better esthetics than small particle composite.
• Still have similar physical properties.

Composite Resin Manipulation: Cleaning and Etching

• The tooth is first cleaned with a mild abrasive.
• Enamel at the cavity margins is acid etched, rinsed, and dried thoroughly.
• Acid etching is an essential pre-requisite for micro-mechanical attachment, 37% orthophosphoric acid is used to demineralize the enamel to a depth of 20-30 mm.
• Acid etching removes pellicle to expose inorganic crystalline component, raises surface energy and surface area.

Composite Resin Manipulation: Bonding and Finishing

• Bonding agents, very low viscosity unfilled resins, are applied and polymerized.
• Allowed to soak into porosities for about 30 seconds before light activation.
• Composite resins are then built over the resin bond in increments.
• Initial contouring is done with a knife or diamond stone.
• Final finishing is done with a rubber impregnated abrasive or rubber cup with polishing pastes or aluminum oxide discs.
• Best finish is obtained when composite is allowed to set against the matrix strip.

Variations in Composite Resins: Flowable Composite

• The term flowable indicates a composite resin which is relatively simple to place into the cavity.
• In contrast to the standard hybrid materials, flowable composites are rather stiff and sticky.
• Mainly used in deciduous dentition where flowability is improved by reducing the filler content.
• Containing fluoride and are ideally suited as caries prevention sealants.

Variations in Composite Resins: Packable Composite

• Achieved by varying particle size and size distribution, water uptake and wear resistance remains the same.
• Difference comes in the feel of the material when being placed in cavity.
• The material is less likely to stick to the packing instruments and can be withdrawn from the cavity during placement.