Dental Adhesion: Principles and Components

Adhesion vs. Joint

• Adhesion includes one interface and an adhesive substance
• Dental joints possess two interfaces joined by an adhesive

Bonding Components

• Chemical adhesion involves chemical bonds between the adhesive and the adherend
• Mechanical attachment relies on physical interlocking or entanglement

Cohesion

• Cohesion is the attraction between similar atoms or molecules within a material
• Cohesive failure results from a break within the material itself

Dental Adhesion

• Adhesion is the force that binds two dissimilar materials
• It is easier to achieve on enamel than on dentin

Enamel vs. Dentin

• Enamel consists mostly of hydroxyapatite, which has a high surface free energy
• Dentine has two substrates: hydroxyapatite and collagen, which have low surface free energy

Importance of Adhesion

• Adhesion is essential in medicine to do no harm, provide aesthetic dentistry, and maintain sound tooth structure

Main Problem with Adhesion

• Creating interfaces increases the chance of failure
• Adhesive failure at any interface will cause the joint to fail

Steps to Good Adhesion

• Use a good adherend, ensure good wetting, achieve intimate adaptation, proper bonding and good curing

Intimate Contact Factors

• Achieved by surface wettability, adhesive viscosity, and surface roughness/morphology

Best Impression Material

• There is no single best material, selection is case-dependent and based on patient characteristics and treatment needs
• Instructions should be followed when using impression materials

Requirements of a good impression material

• Biocompatibility is needed, be fluid enough to adapt to oral tissue, viscous enough to be contained in a tray, transition and set, be cost effective, resistant to distortion or tearing on removable, dimensionally stable for cast pouring

Setting Reaction Classification

• Physical materials include impression compound and agar
• Chemical setting materials include alginate, elastomers, and zinc oxide eugenol

Viscosity Classification

• Low viscosity materials are light-bodied for thin areas and fine detail
• Medium viscosity materials are regular-bodied, for general impressions
• High viscosity materials are heavy-bodied/putty, used for bulk material or tray support

Composition Classification

• Hydrocolloids consist of agar and alginate
• Elastomers are a type of material
• Rigid materials are ZOE and impression compound

Elasticity Classification

• Elastic materials include hydrocolloids and elastomers
• Inelastic materials include zinc oxide eugenol, impression plaster, impression compound, and wax

Reversible Materials

• Impression compound and agar are reversible materials

Viscosity

• A measure of a material's resistance to flow, often measured at 20 degrees

Hydrocolloids

• The two types of hydrocolloids are agar and alginate
• They start as a solution and become a gel
• A colloidal system contains a dispersed phase and a dispersion phase, typically water
• During the sol-to-gel transition, the concentration of the dispersed phase increases, trapping water within the fibril network

Alginate vs. Agar

• Agar forms secondary bonds and is reversible
• Alginate forms primary bonds and is irreversible

Agar Components

• Consists of seaweed, borax, and potassium sulphate

Agar Setting

• Liquefaction occurs with heat in water baths
• Transition occurs just above body temperature
• Transforms from sol to gel via temperature change and secondary bonds
• It can be heated and used to take impressions again
• Sterilization can create issues

Advantages and Disadvantages of Agar

• Nontoxic and non-irritant.
• Low tear resistance, low dimensional stability,biosafety issues

Alginate Components

• Composed of calcium sulfate as the reactor, sodium and potassium alginate as salts, fillers like silicate powder, and sodium phosphate

Alginate Reaction

• Calcium sulfate + sodium alginate → calcium alginate + sodium sulfate

Sodium Phosphate

• Functions as a retarder by slowing down the chemical reaction between other components
• This increases working time

Advantages of Alginate

• Offers a fast set, is cheap, possesses good fluidity, and causes minimal tissue displacement

Disadvantages of Alginate

• Problems with dimensional stability, compatibility with gypsum, and accuracy
• exhibits low tearing resistance, and potential biocompatibility issues, distortion, and poor mix

Alginate Setting

• Involves an irreversible sol-to-gel phase transition through a decomposition reaction
• pH changes, indicated by a color change from 11 to 7

Altering Setting Time of Alginate

• Altering the temperature will affect the setting time
• Altering the mixing time or water to powder ratio should be avoided, as it changes tear strength and elasticity
• Fast setting occurs in 1.5 – 3 min; normal setting takes 3 - 4.5 min
• Setting time is dependent on the amount of retarder

Dimensional Stability of Hydrocolloids

• The solution traps water in a network of fibers
• Syneresis occurs if water evaporates in a dry environment and the material shrinks
• Expansion and swelling occurs if placed in a wet environment
• Impressions from alignate should be made withing 30 minutes to prevent issues

Types of Elastomers

• Condensation, addition, polyether and polysulphide

Addition vs. Condensation Elastomers

• Condensation elastomers lose by-products, leading to poor dimensional stability
• Polysulfide's by-product is water; condensation silicone's by-product is ethanol

Indications of Elastomers

• Appropriate for high-quality impressions e.g. restoration

Main Components of Polysulfide

• Base paste contains liquid prepolymer with multifunction mercaptan groups and a small amount of sulfur
• Catalyst lead dioxide filler and a retarder like oleic or stearic acid

Reaction of Polysulfide

• Condensation that produces water

Advantages and Disadvantages of Polysulfide

• Advantage is excellent tear strength
• Disadvantages are unpleasant taste and smell, being hydrophobic and requiring excellent moisture control, as well as low dimensional stability

Main Components of Condensation Silicone

• Includes hydroxyl terminated polydimethyl siloxane base paste
• Includes catalyst - tru and tetra functional alkyl silicates and stannous octoate

Reaction of Condensation Silicone

• Occurs in the presence of stannous octoate
• Reaction includes condensation reaction and ethanol by-product

Advantages and Disadvantages of Condensation Silicone

• Advantage is accuracy casting up quickly
• Disadvantages are shrinkage and dimensional stability, and it's hard to mix accurately

Main Components of Addition Silicone

• Base consists of polymethylhydrosiloxane and fillers
• Catalyst consists of divinylpolysiloxane and paltinum salt

Reaction of Addition Silicone

• Reaction includes addition polymerization and releases hydrogen, though not considered a by-product due to its low molecular weight
• BUT, it must be released before casting the model to prevent bubbles

Advantages and Disadvantages of Addition Silicone

• Advantages = high dimensional stability, good eleastic recovery, variety of forms, eleastic recovery.
• Disadvantages = hydrophobic so needs moisture control, latex gloves contain sulphur which can inhibit setting, and hydrogen bubbles released

Main Components of Polyether

• Base consists of polyether prepolymer, colloidal silica filler, and a plasticizer like glycol ether
• Catalyst consists of alkyl aromatic sulfonate, fillers and plasticiser

Reaction of Polyether

• Involves addition polymerization, produces no other products and occurs via cationic polymerization

Advantages and Disadvantages of Polyether

• Advantages = hydrophillic, dimensional stability, non toxic non irritant.
• Disadvantages = very stiff can fracture if thin margins present in crown construction, hydrophillic so absorbs water and must be sent dry

Viscoelastic Behavior

• Viscoelastic behavior describes materials exhibiting both viscous and elastic characteristics when undergoing deformation.
• Elastic recovery is determined based on the speed of the load applied
• Rapid movement exhibits elastic recovery

Removing Viscoelastic Materials

• Use a short quick snapping motion for removal
• Slower removal will deform the material for permanent deformation that does not return to its original shape

Main Components of Zinc Oxide Eugenol

• Paste 1 contains zinc oxide and a plasticizer, such as olive oil and water
• Paste 2 contains eugenol, filler, rodin, and resinous balsam

Setting of Zinc Oxide Eugenol

• 1st reaction is the hydrolysis of zinc oxide to its hydroxide form
• 2nd reaction is eugenol (acid) + zinc hydroxide (base) → zinc eugenolate (salt) and water

Properties of Zinc Oxide Eugenol

• High viscosity will compress tissues; low viscosity will not

Metal Characteristics

• Features strong bonds, high melting and boiling points, good stiffness, and electrical and thermal conductance
• Corrosion occurs and is biocompatible enough for mouth but not the most biocompatible material. opaque/non aesthetic and is ductile malleable

Classifying Metals

• Metals can be classified by hardness yield and strength, noble metal content, use, major elements, and principle three elements

Metal uses

• Instruments, framework for removable and fixed prosthesis, direct and indirect restorations, orthodntic appliances and dental implants and abutments

Metals by Noble Metal Content

• High noble must contain ≥ 40% Au and ≥ 60% noble metal by weight
• Noble must contain ≥ 25% noble metal by weight
• Predominantly metal based contains < 25% noble metal by weight
• Titanium and titanium alloys must contain ≥ 85% titanium by weight

Metals By Dental Applications/Use

• Metals include all metal fixed prosthesis and removable partial dentures
• can be metal ceramic prosthesis

Metal Alloys

• All can be classified by major elements gold, palladium, nickel, cobalt and titanium based.

Force Applied To a Metal

• It can undergo elastic deformation without changing shape or under plastic deformation molecules move cause shape deformation
• The metal will continue to resist force until there is bond breakage and catastrophic fail
• The metals can withstand a lot of energy before reaching this catastrophic fail

Youngs Module E

• can be calculated by elastoc modulus and then by ratio of elastic stress to the elastic strain

Galvanic Current

• Occurs when different metals in dental restorations interact with saliva, creating a small electrical current

Metal Requirements

• Requirements are being economical, biocompatible, high strength and high stiffness
• It also needs to have Biocompatibility, Tarnish and corrosion resistance, thermal properties, mechanical propertues, fabrication and porceralin bonding

Metal Requimentes

• High noble alloys include gold and palladium
• Palladium and platinium inc hardness, elastic module and melting temp
• Copper alloy needs head treatment and increases hardness but color changes
• Use silver palladium
• Silver neutralizes gold and zinc acts as oxygen scavenger
• Predominantly metal based alloys for all metal restoration use nickel and cobalt based alloys which includes cobalt chromium, nicek chromium and chromium oxide

Metals for RPD

• These should have flex in some areas and and stiffness in others, formerly used two alloys but that caused now use with different thockness

Titanium Alloys

• Titanium alloys are needed for for metal prothesis' where it requires to be stiff, high E, rigidbute als sufficiently ductile and flexible to engage undercuts with very high biocompatibility

Considerations of Metal Alloys for Ceramic Prostheses

• They need to bond to dental proccerlain by oxide formation on surface
• solidus temp needs to be high enough to resist softening during sintering, and to have CTE compatible with dental porcerlain
• corrosion can be induced in manufacture to create oxide layer

Metals in Ceramic Restorations

• High noble use gold platnium palladium, gold palladium.
• Base metal alloys use nickel chromium and cobalt chromium of the hard and stiff type
• It is possible to make a metal infrasctructure that is 0.1 - 0.2mm thick
• Metal alloys use a low fusing ceramic to minimize or low CTE demands low expansion porcerlains with melting temp increased makes them resistant to sag deformation with titanium alloys

What is Passivation?

• Initial corosion but then the metal becomes very stable and very biocompatible

Rise of The rise of non noble metals

• Increased in 1973 due to a steep rise in the cost of noble metals and silver
• Advantages = desirable properties, low cost, increased strength and hardness
• Uses for metal crowns metal ceramic crowns long span bridges resin bonded fixed partial dentures which may include nickel chronium cobalt

Conventional Casting Techniques

• Sprue, brush, wax elimination, casting, wax version of restoration made, covered in investment material, placed in furnace in investment ring melts wax, molten metal inserted and cooled.

Nickel Chromium

• May have excessive oxide formation possible difficulty finishing and polishing, but biocompatibility and nickel allergy can elecit allergic response in sensitive individuals and more and more cases of allergic dermatitis

Titanium

• There is an intrest as an alternative to gold with great biocompatibility which makes it a widespread implant material

Titanium Alloy Type

• Alpha, near alpha, alpha beta and beta exists
• Tl 6al4V is alpha beta alloy and increased strnegth but lower biocompatibility due to v and al

Gold Classifications

• Dental golds can be classified by ADA specification No 5 into high gold alloys, low gold alloys and white gold alloys

Gold Forlay

• note soft and medium for inlay gold alloy, hard and extra hard for crowns and bridges

Type 1 Gold

• Composition is 83% gold, weak soft, highly ductile and only placed in areas with low occlusal stresses

Type 2 Gold

• Composition is 77% gold, harder, has good strength and moderate occlusal stresses with less yellow than type 1 and has les gold content

Type 3 Gold

• Type of gold with 75% gold, harder with higher strength and more higher strength and with high occlusal stresses and for crowns and bridges

Type 4 Gold

• Type of gold that is extra hard with high occlusal stresses and crowns bridges rpd frameworks with lowest gold content and crowns/bridges/rpd frameworks

Type of Gold

• Gold's strength increases from type 1-4 (hardness and strength dec the opposite) - strength decreasing from 1 - 4. hardness increase

Dental Ceramics

• These derived from the word kermikos - burn stuff and desirable properties are gained by firing at high temperature.
• used for crowns/bridges/inlays/onlays/veneers are used for implants and abutments

General Ceramic Properties

• exhibit High melting temp, thermal and electrical insulators, transparency due to no free electrons interfering with incident light, and low tensile and high compressive strength which makes them chemically intert after forming from oxidation making them hard and dense

Other Ceramic Properties

• exhibit Ceramics wear down opposing teeth if patient has some kind of parafunction - ceramic can wear down the opposing teethand ceramics have zero metal elastic, plastic deformation beforee failure

Ceramic Limitations

• There is NO plastic or elastic deformation
• ceramics down have the plastic phase, will fracture as soon as stress gets too high and in any clinical application catastrophic failure insetad deformation like in metals

Ceramics vs. Toughness

• Strength can be the commonly used term, also know as the fracture strength to assess the point at which material fractures
• can be tested with different shape sizes or the material can be externally tested or environmentally tested

Metallic/Non-Metallic Element

• Ceramics must have metallic and non metallic elements that is ionic and covalent
• Contains no free electrons
• Two phases: glass and crystal phases

Ceramics Glass Element

• The glass phase has less organized structures, amorphous phase with decreased mechanical properties, but increased optical properties

Ceramics Crystal Element

• The crystal phase has increased mechanical properties, but decreased optical properties and has organized phases

Material Type

• More glass phase means a weaker translucent material

Ceramic Compositions

• Feldspar is 80%, anhydrated aluminum silicate
• Silica is quartz and 15%
• Kaolin is at 4% and includes hydrated aluminium silicare, opaque filler, for colouring pigments and glass fillers,

Glass Modifiers

• Na k ca produce dental porcerlain with different firing temps and increases fluidity of glass

Steps to dental Ceramics

• phases consist of compaction, firing glazing and cooling and consists of predominately glass, particle filled glass and poly crystaline

Mostly Glass Ceramic

• This is mostly predominately glass is called porcelin which is best looking, relatively weak and has low flexural strength and is most suitable for veneering for crowns and all ceramics

Survival rate

• On inlays, onlays, veneers, restorations the survival rate can be 92%, 94%, and 95% at (8 years for inlats onlays and 11 year crowns) is a fedspathic proceralin restorations have good long term success rates when bonded to and supported by primarly enamel structures

Mechanical

• Materials need high cte and glass requires alloys to produce compressive stressed when cooling with glazing which is seals surface defects and gives it a better finish is metal metal infrastructiure → mechanical properties to be a veneering

High Fusion

• requires a high sintering for the predominately glass ceramic at the right temperature and there are different processing levels to consider and layering and CAD CAM technology. and high Fusion, the fusing medium for a complete or fixed teeth

Filled Glass Ceramic material

• In cases of a added particle ceramics and leucite which has a transluceny to porcerlain and there are metal veneers for a metallic restorations. In order to strengthem this class of material, lithium disilicate and ceramic can be used to compete with enax

Zirconia with Prothesis

• Can combine monolithic al ceramic and multi ceramic for any sort of reconstruction and all ceramics or CAD CAM tecniques

Poly Crystal Properties

• Used for aliminua structures where no glass exists, ytzp
• Alumina is 99% aluminum oxide and is slip casted for anteriors and can be reinforced
• It creates strong structures and all ceramics with the alumina structure is for all the muti layers on prothesis