Adhesion in Restorative Dentistry

• Adhesion to tooth structure continues to be a primary goal in restorative dentistry.
• A new era in dentistry started in 1955 with the introduction of the acid etch technique by Buonocore, based on the adhesion concept.
• Adhesive dentistry is the standard today.
• Traditional mechanical methods of retaining restorative materials have largely been replaced by adhesive methods that conserve tooth structure.
• Most instances of dental adhesion are called dental bonding.

Advantages & Clinical Significance of Adhesion

• Adhesion allows stabilization and long-term retention of restorations.
• It provides better resistance against tooth fracture by allowing better transmission and distribution of functional stresses across the bonded interface.
• The tooth and restoration act as one unit.
• Adhesive restoration has the potential to reinforce the remaining weakened tooth structure.
• Tooth conservation is maximized compared to non-bonded restorations requiring additional removal of sound tooth structure.
• Microleakage, or the clinically undetectable passage of bacteria, fluids, molecules, or ions at the tooth-restoration interface, is reduced.
• Minimizing the ingress of oral fluids and bacteria along the cavity wall reduces clinical problems like postoperative hypersensitivity, marginal staining and recurrent caries.
• Adhesion expands the range of esthetic restorative dentistry by enabling the correction of dimensions and color of teeth, repairing existing restorations, bonding indirect resin-based restorations, and producing esthetic direct restorations.

Adhesion Defined

• Adhesion is derived from the Latin word adhaerere, which means "to stick".
• When two substances make intimate contact, the molecules of one substance adhere to or are attracted to the molecules of the other.
• Adhesion results when unlike molecules are attracted and cohesion results when molecules of the same kind are attracted.
• Making two solid surfaces adhere is difficult because surfaces, even smooth ones, appear rough at a microscopic level and only high spots will be in contact.
• Placing a fluid between surfaces helps flow into irregularities and provide contact.
• The material or film added to produce adhesion is known as the adhesive or adherent and the surface to which it is applied is called the adherend.
• Glass ionomer cement is the only restorative material that possesses an intrinsic self-adhesive capacity to tooth structure.
• Dental adhesion involves adhesive joints, which result from interactions of a layer of intermediate material (adhesive) with two surfaces (adherends) producing two adhesive interfaces.
• An adhesive joint example is bonding resin composite to tooth structure using a bonding agent where the composite and tooth substrates are the adherends and the bonding agent is the adherent or adhesive.

Mechanisms of Adhesion

• Physical Adhesion: Involves relatively weak electrostatic interactions and may be the only type if surfaces are smooth and chemically dissimilar.
• Chemical Adhesion: Involves bonding at the atomic or molecular level across the interface from the adhesive to the adherent.
• Mechanical Adhesion: Occurs where the substrate has undercuts or other irregularities that produce interlocking of the materials.
• Almost every case of dental adhesion is based on mechanical retention from the interlocking of restorative materials in undercuts created in cavities that use macro-mechanical means of retention.
• Retention of adhesive restorations relies on mechanical retention on a microscopic level, where the adhesive flows into the pores of the adherend, hardens and interlocks, producing micro-mechanical retention.

Requirements for Adhesion

• To produce good bonding, the adhesive or adherent should flow easily over the adherend to produce good wetting.
• Wetting is the degree of spreading of one drop of liquid on a solid surface and is measured by the contact angle.
• Contact angle is the angle formed by the adhesive with the adherend at their interface and may be 0 or 180 degrees for maximum adhesion, less than 90 degrees for moderate adhesion, or more than 90 degrees for poor adhesion.
• Sufficient wetting of the adhesive only occurs if its surface tension is less than the surface energy of the adherend.
• Surface energy or surface tension is the increase in energy per unit area of a surface.

Requirements for Successful Wetting of Adhesive

• Intimate molecular contact between adhesive and tooth tissues (adherend).
• Cleanliness of the tooth tissues.
• High surface energy of the tooth tissues to attract the atoms of the adhesive.
• Low-surface tension of the adhesive material (adherent) to properly wet the adherend.
• Low viscosity of the adhesive to penetrate into the microporosities.
• Displacement of air and moisture during the bonding process.

A Successful Adhesive Joint

• Gap free.
• Sufficient bond strength to resist debonding under polymerization shrinkage stresses of resin composite or under function.
• Bond strength measures the bond-bearing capability of the adhesive and is evaluated by the force needed to debond the adhesive.
• Compatible to tooth tissues and restorative material.
• Dimensionally and hydrolytically stable in the complex oral environment which provides bond durability.

History of Adhesive Dentistry

• Experiments on bonding acrylic resin to enamel and dentin began in the 1950s in England with Dr. Oscar Hugger, who developed a monomer based on glycerophosphoric acid.
• In 1955, Dr. Michael Buonocore made the second and more important advance in adhesive dentistry by identifying the occurrence of micromechanical adhesion to enamel via its acid etching.
• His efforts paved the way for development of bonding agents that aimed enamel at the beginning, and then shifted to dentin.
• Japanese researcher Fusayama advocated etching dentin using phosphoric acid in 1979.
• Many scientists initially refused the concept of dentin etching, fearing pulpal irritation.
• Later in the mid 80's, the concept was internationalized, showing it was clear that dentin could be etched if and only if it could be sealed adequately with subsequently applied bonding resins and pulpal problems result from ingress of bacteria, not from acid-etch application.
• Thereafter, the industry shifted from enamel etch to total etch technique, involving enamel and dentin.
• Current adhesives bond to enamel and dentin simultaneously.

Classification of Contemporary Dental Adhesives

• Based on the adhesion strategy, Van Meerbeek in 2001 classified dental adhesives into three main categories: etch-and-rinse adhesives, self-etch adhesives, and glass ionomer adhesives.
• All three categories exhibit a common adhesion mechanism of hybridization which is the process of micro-mechanical interlocking that occurs by infiltration of resin into demineralized substrate.
• The resultant resin-infiltrated layer (hybrid layer) to dentin was first described by Nakabayashi in 1982.
• Etch-and-rinse adhesives are currently available as three-step systems (where etching, priming and bonding to tooth substrates are done individually) and two-step systems (where primer and adhesive are simplified into one bottle).
• Self-etch systems do not comprise a separate etching step and are applied in either a two-step system (with an acidic primer and an adhesive) or an all-in-one adhesive (where primer and adhesive are simplified into one step).
• Self-etch adhesives are further classified according to their aggressiveness or acidity into ultra-mild (pH ≥ 2.4), mild (pH ≥ 2), intermediate (pH = 1.5), and strong (pH≤1).

Bonding to Enamel & Dentin

• The composition and structure of enamel and dentin are different, and thus adhesion to the two tooth tissues is also different.
• Bonding to enamel is easily achieved compared to bonding to dentin.
• Enamel is homogeneous in composition and structure, irrespective of its depth or location and is composed of 96 wt% inorganic hydroxyapatite crystals arranged as enamel rods, and also possesses a high surface-free energy.
• Bonding to dentin suffers from different obstacles, and only recently have dentin adhesive systems reached bond strengths approaching that of enamel.

Problems in Bonding to Dentin

• Heterogeneous composition: Dentin contains a high percentage of water and organic content (30%) as collagen, and only 70 %wt inorganic hydroxyapatite, which are unevenly distributed in intertubular and peritubular dentin.
• Complex histological structure: Dentin is composed of numerous dentinal tubules, each surrounded by a collar of hypermineralized peritubular dentin, with intertubular dentin in between that is less mineralized & contains more organic collagen.
• The dentinal tubules diverge from the dentin-enamel junction to the pulp, so the number and diameter of dentinal tubules increases at pulpal dentin.
• Inherent intrinsic wetness: The dentinal tubules are filled with dentinal fluid, so dentin is under constant wetness.
• Deep dentin has more intrinsic wetness than superficial dentin and is more difficult to bond to.
• The dentinal fluid is under a slight, but constant, outward pressure from the pulp, estimated to be 25 to 30 mmHg.
• Dentin is a dynamic tissue subject to continuous physiologic and pathologic changes in composition & microstructure.
• The presence of more than one type of dentin presents challenges in dentin bonding.
• The smear layer on the cut dentinal surface.
• Smear Layer: Following cutting of dentin with manual & rotary instrumentation, a layer 2-5 microns thick is formed on the surface of dentin and cannot be removed by rinsing.
• It is composed of chips, hydroxyapatite crystals, collagen, saliva, and blood, and incorporates microorganisms.
• The smear layer becomes packed inside the dentinal tubule forming a smear plug.
• In enamel, it is composed of larger apatite crystals tightly bound by salivary glycoprotiens to form a crust over the enamel surface and it also contains microorganisms.

Advantages of a Smear Layer

• Reduces dentin permeability by about 86% through plugging the dentinal tubules, reducing inter-tubular dentin fluid flow, and reducing the the intratubular & intertubular permeability.
• Provides a drier surface for adhesion.
• Minimizes post-operative hypersensitivity.
• Prevents the ingress of irritants from the restorative material to the tubules.

Disadvantages of a Smear Layer

• Incorporates microorganisms.
• Loosely attached to the underlying dentin, providing a weak joint between tooth tissues and the restorative material.
• Current adhesive systems should remove or penetrate through the smear layer to ensure successful bonding.

Bonding to Enamel vs Dentin

• Enamel (Easy)*
• Homogenous in composition & structure.
• 96% inorganic.
• Has Hydroxyapatite crystals (enamel rods).
• High surface energy.
• Dentin (Obstacles)*
• This is a heterogeneous structure.
• Complex histology.
• Inherent wetness.
• Dynamic tissue.

Steps of Bonding to Enamel & Dentin

• The steps of bonding to tooth substrate differ depending on the category of adhesive used.
• Adhesive systems aim to remove, dissolve or modify the smear layer and create microporosities in enamel & dentin for micromechanical interlocking.
• Manufacturer's instructions for application of each adhesive system should be strictly followed, & the use of the adhesive system with its recommended composite is mandatory.

Etch-and-Rinse Adhesives

• (Smear layer removing adhesives)
• Selective acid demineralization aka Conditioning or Etching: conditioning is any chemical alteration on the substrate surface by acids with the objective of removing the smear layer & demineralizing the surface.
• Etching is a form of conditioning used term usually when a strong acid is used, particularly on enamel surfaces.
• Etch-and-rinse adhesives incorporate a separate etching step which is used for total etching of enamel & dentin, followed by thorough rinsing.
• Use of phosphoric acid concentration between 30% & 40% & an etching time of no less than 15 seconds are recommended to achieve the most receptive surface for bonding.
• Acid etchant is supplied in the form of a liquid or colored gel with the gel form preferred because its application is easier to control.

Enamel Etching

• UNCUT ENAMEL*
• Pellicle: Consists of organic material, to which no bonding is possible (must be removed before bonding).
• Aprismatic enamel: Parallel to the surface of the tooth & perpendicular to the underlying prismatic layer that is highly mineralized (absence of prism boundaries, no organic).
• CUT ENAMEL*
• Smear layer: Formed on the cut enamel.

Enamel Etching Goals

• Remove the organic pellicle & prismless enamel in uncut enamel & smear layer in cut enamel.
• Partially dissolves the mineral crystals (dissolution of inorganic component, thereby transforming the smooth enamel surface into an irregular surface with numerous microporosities.
• Enlarging surface area for bonding (MICROPOROSITIES).
• Increasing surface energy (more than twice that of unetched enamel).
• Lowering contact angle of wetting.
• Selective demineralization of enamel surface produces dissolution & microporosities in the interprismatic substance (Interprism etching) as well as microporosities in the enamel prism core (Intraprism etching)

Dentin Etching Goal

• Total removal of the smear layer.
• Remove Smear Plugs.
• Demineralize the superficial dentin surface by removing minerals from the superficial layer and exposing them to a microporous layer of organic collagen fibers and increasing the microporosity of the intertubular dentin.
• When acid etching unplugs the dentinal tubules, it demineralizes the peritubular dentin to a lesser extent producing more funneling of the dentinal tubules.
• The exposed collagen fibrils function as a microretentive network for micromechanichal interlocking of the resin polymers.

Rinsing and Drying

• (Rinsing)*
• The etchant must be rinsed with water for 5-10 seconds (not less than 10 sec) to remove acid remnants and dissolved calcium phosphates.
• (Drying)*
• Air syringe (short intermittent blasts of air)
• Minisponge
• Cotton pellet
• Enamel Drying*
• Dryness until chalky white appearance.
• Dentin Drying*
• Avoid excessive dryness, which leads to collapse of collagen fibers.
• Moist Dentin*
• The abundant intertubular porosity serves as a pathway for the penetration of the dentin adhesive.
• Air Dried Dentin*
• "Swiss Cheese" due to collapse of collagen matrix.
• Inter tubular dentine less able to permit infiltration of resin monomers.

Primer (adhesion-promoting monomers)

• Acid-etched enamel has high surface energy & doesn't need a separate primer application.
• Etching of dentin decreases its surface energy due to the high protein extent exposed after etching.
• Increased permeability & wetness of dentin also hinder adhesion. A primer should be used to:
• to have sufficient wetting to dentin.
• to displace residual water.
• to carry monomer into created microporosities. Effective primers should contain:
• Hydrophilic monomers, e.g. Hydroxyethyl Methacraylate (HEMA), that have an affinity for wet dentin.
• Hydrophobic part that co-polymerizes with the subsequently applied adhesive resin.
• The primer could contain organic solvents, such as acetone or ethanol.
• Because of their volatile characteristics, these solvents act as water-chasers, displacing water from the dentinal surface, and promoting infiltration of monomers.
• A primer application time of at least 15 seconds should be performed.

Wet vs Dry Bonding

• Following etching & rinsing, enamel & dentin present different conditions for priming & bonding:
• (Enamel)*
• Should be dry to achieve good bonding
• (Dentin)*
• A certain amount of water is needed to prevent the collagen fibrils from shrinking. Conventionally, acid etched enamel was dried with short intermittent blasts of air until it showed chalky white appearance, but this collapsed the dentinal unsupported collagen network, preventing proper infiltration of collagen with monomers.
• To overcome this problem in dentin bonding, two different approaches can be followed depending on the primer of the adhesive system:

Dry bonding technique

• Air drying of enamel & dentin
• Applying a water-based primer to re-expanding the collapsed collagen network.

Wet bonding technique

• Leave dentin moist (No collapse of collagen)
• Use a solvent-containing primer (water-chasing capacity) to displace water
• Gentle air-drying with solvent to evaporate by leaving the active primer monomers behind. Enamel doesn't always need a separate priming step, but needs dry bonding for effective wetting of the adhesive. When using wet bonding technique, primers are indicated to be applied on acid etched enamel is to displace residual water through solvent evaporation.

Adhesive Resin “Bonding Agent”

• It is a solvent-free, filled (i.e. containing filler particles) or unfilled solution containing mainly hydrophobic monomers (Bis GMA, UDMA,TEGDMA).
• Light vs Dual Cure: Light cured contains camphoroquinone, while dual cure contains catalyst for self curing.
• It co-polymerizes with the previously applied primer and subsequently applied resin composite.
• When adhesive resin infiltrates the etched enamel, two types of resin tags are subsequently formed:
  • Macro-tags at the prism peripheries with the etched interprismatic substance
  • Micro-tags at the cores of enamel prisms (with intraprism etching).
• Micro-tags contribute more to bond strength because of their greater quantity and larger surface area.
• When filled with primed dentin, it fills up the interfibrillar spaces left between the collagen fibrils leading to hybridization with dentin.
• The hybrid layer occurs mainly with demineralized inter-tubular dentin as well as demineralized peritubular dentin known as tubule wall hybridization.
• The adhesive also enters dentinal tubules forming resin tags.
• Intertubular hybridization is more important than resin tags in the bonding process and contributes more to the bond strength of an adhesive system with the hybrid layer is 10 µm into dentin tubules.
• Peritubular or tubule wall hybridization provides a firm attachment of the resin tag necks to the tubule walls and guarantees proper hermetic sealing of the tubules.
• The resin also infiltrates lateral tubule branches forming submicron lateral resin tag formation.
• A commercial example for three-step etch-and-rinse adhesive system is Scotchbond Multipurpose (3M ESPE).
• In two-step etch-and-rinse adhesives, primer and adhesive bonding components are combined into one solution that should fulfill both functions, and an example is Excite Bond (Ivoclar Viva-dent).

Advantages of Etch-and-Rinse Adhesives

• They provide proven effective bonding with enamel & dentin with sufficient long-term clinical results.
• Three-step adhesives are considered the gold standard for adhesives, and have low technique sensitivity due to separate application of primer & adhesive resin (each is applied to serve a specific function).
• Two-step etch-and-rinse adhesives have more simplified application but are more technique sensitive than three-step adhesives.
• Possibility for particle-filled adhesive where filled adhesives act as shock absorbers & increase the bond strength of adhesives.

Disadvantages of Etch-and-Rinse Adhesives

• They can be time consuming due to the multi-steps required and the separate post-etching rinsing step is required.
• Risk of over-etching dentin due to aggressive etching with phosphoric acid causes demineralization to a depth that might be inaccessible for complete resin impregnation, leading to a porous zone in the hybrid layer.
• Discrepancy between the depth of demineralization and the depth of resin infiltration results is nano-leakage, or the presence of submicrometer-sized gaps within the hybrid layer which, then, compromises the durability of the bond due to hydrolysis of exposed collagen.
• Total removal of smear layer can cause post-operative sensitivity due to dentinal fluid movement & increased dentin permeability.
• This is also sensitive to over-wet or over-dry dentin condition, so over-wetting of dentin should be avoided to prevent dilution of the adhesive when using wet bonding technique and over-drying will cause collagen fiber collapse.

Self-Etch Adhesives (Smear Layer Dissolving Adhesives)

• These do not comprise a separate etching or rinsing step.
• They use acidic primers, called self-etching primers, which simultaneously condition & prime the tooth substrate.
• As a result, the dissolved smear layer & the demineralization products are not rinsed away, and they are incorporated in the adhesive resin & into the hybrid layer.
• The morphological feature of the hybrid layer depends on their aggressiveness or acidity where the more aggressive the adhesive, the deeper is the hybridization.
• Mild self-etch adhesives perform shallow demineralization of dentin producing shallow or thin hybrid layers and there smear plugs are not completely removed, but Hydroxyapatite crystals are available around the collagen fibrils as a result of mild demineralization.
• Strong or aggressive self-etch adhesives produce a thick hybrid layer with long resin tags resembling etch-and-rinse adhesives.
• Intermediary strong self-etch adhesives: Lie between mild & strong adhesives.
• Two-step self-etch adhesives consist of a hydrophilic aqueous acidic primer solution and a separate hydrophobic adhesive resin.
• Despite the shallow hybridization of mild self-etch adhesives, they can reach satisfactory bond strength values, and some comprise monomers that are capable of chemical interaction with hydroxy apatite crystals, e.g. 10-MDP monomer in Clearfil SE.
• A commercial example for two-step intermediary strong self-etch adhesive is AdheSE (Ivoclar Vivadent)
• One-step self-etch adhesives: complex mixtures of both hydrophilic & hydrophobic monomers.

Advantages of Self-Etch Adhesives

• They simplify the clinical application procedure by reducing application steps & omit the post-etching rinsing phase due to simultaneous demineralization & resin infiltration, overcoming the problem of over-etching or incomplete resin impregnation, and it has a time-saving application procedure
• Does not increase permeability of dentin, thus reducing the potential postoperative sensitivity;
• Technique sensitivity from dentin wetness is prevented as both dryness (collapse of collagen) & over-wetting is eliminated.
• Possibility for particle-filled (shock-absorber) adhesive.

Disadvantages of Self-Etch Adhesives

• They produce insufficient long-term clinical results due to incorporation of the smear layer which could complicate the bond durability.
• One-step self-etch adhesives have relatively low bond strength.
• Adhesion potential of mild self-etch adhesives to enamel is weak, because of their mild aggressiveness, so separate pre-etching of enamel with phosphoric acid might be recommended before application of the mild self-etch to enamel and dentin.

Universal Adhesive “Multi-Mode” “Multi-Purpose" Adhesives

• A single-bottle, no-mix system.
• Bonds to direct and indirect restorations and to all surfaces: enamel, dentin, glass ceramics, zirconia, porcelain and composite.
• Etch & Rinse
• Universal adhesive
• Self Etch
• Total Etch E&D
• Selective E Etching
• Contain monomers, carboxylate, and/or phosphate monomers that bond ionically to calcium found in hydroxyapatite for 10-MDP because it's hydrophilic and has mono-etching properties.
• Acidic nature provides the potential to etch and demineralize tooth tissues and bond chemically to metals, zirconia, and to tooth tissues through the formation of non-soluble Ca++ salts.

Glass Ionomer Adhesives (Smear Layer Modifying Adhesives)

• Technology based on glass ionomers and their self-adhesive capacity, where these are resin-diluted versions of resin-modified glass ionomer.
• Consists of conditioning dentin with weak concentration (10-20%) polyalkenoic (polyacrylic) acid for about 20 seconds removes the smear layer but not the smear plugs, and also creates a clean dentin surface, shallow demineralization for hybridization, and sufficient residual hydroxyapatite for chemical bonding.
• The acid is then rinsed with water (20 sec), Air dried (10 sec) & resin-modified glass ionomer bond is placed & CURED (10 sec), which results in a partially demineralized hybrid layer = 1 µm.
• The remaining hydroxyapatite crystals within the hybrid layer function as receptors for chemical bonding with the carboxyl groups of the polyacrylic acid. On top of the hybrid layer, an amorphous, gray "gel phase" represents the reaction product formed through interaction of polyacrylic acid with calcium that was extracted from the dentin surface.

Glass Ionomer Adhesive Bonding

• Chemical adhesion between calcium in hydroxyapatite & carboxylic group of polyalkenoic acid along with limited demineralization of enamel & dentin with subsequent infiltration & micromechanical interlocking termed shadow hybridization.
• Twofold bonding mechanism to have cariostatic potential via fluoride release and and viscous particle-filled adhesive that acts as a shock absorber.

Glass Ionomer Adhesive Negatives

• No long term clinical data and adequate adhesion to enamel requires total smear layer removal.

Etching and Surface Notes

• Remove:* (all smear unit) Etch & Rinse.
• Dissolve:* (demineralize smear layer & superficial dentin without removal of smear plug) = Self Etch
• Modify:* Removal of only smear layer = Universal & G.I
• Etchant used:* Phosphoric acid.
• Other etching methods:* Acids, laser, air abrasion.
• Etching Time:* 15 sec.
• Dental fluorosis:* 60-90 sec .
• Etching %:* 30-40 (37) %
• Enamel Etching pattern:* Inter & intra prismatic.

Hybrid Layer

• Type 1: prism core (Honeycomb)
• Type 2: prism periphery (Cobbelstone)
• Type 3: combination (1+2).
• Type 4: pitted (unfinished Buzzle).
• Type 5: flat, smooth

Smear Layer

• 2-5 microns.
• Tightly attached to high speed cutting.
• Thicker with a diamond versus fissure bur.

Zones of Hybrid Layer

• Top layer (loosely attached collagen).
• Middle layer (collagen fibers separated by spaces of 10-20 nm which OH-apatite is replaced with resin).
• Bottom layer (partially dem.dentin)

Defects in Hybrid Layer

• Reverse hybrid layer where NaOCl will dissolve and remove the exposed dentinal collagen and provide a fresh mineralized dentin surface to which the adhesive resin can be applied.
• Ghost hybrid layer.
• Nano-leakage where the clinically undetectable passage of bacteria, fluids, molecules or ions is allowed to reach the tooth restoration interface.
• Hybridoid layer has the presence of submicron spaces within the hybrid layer, which then, allows dentinal & oral fluids to permeate to the hybrid layer. The cause is from the hydrolysis of exposed collagen and the resultant compromise to durability.
• Water tree.
• Reverse water tree.

Additional Bonding Notes

• Resin layer between 0.02 and 0.4 mm will absorb part of the polymerization shrinkage stress and absorb shocks during function for elastic bonding.
• Wet Bonding: Use acetone/alcohol based Primer and quickly apply with acetone to quickly evaporate with potential change monomer/ acetone ratio.
  • With overly wet primers, the solvent will diffuse into water instead of visa versa, meaning the monomers undergo phase changes forming resin globules, or blisters
• Dry bonding uses water based primer, but with too much, it will dilute the monomer concentration. Over dryness leads to collapse of collagen and ineffective penetration.
• All in one adhesive create water trees, which are very acidic-hydrophilic, where the channels pass from the hybrid layer through the adhesive-composite interface. The cause is absorbing water by leaching of unpolymerized monomers or water filled channels.
• Reverse water tree has water trapped at the adhesive-composite interface in blisters, where Channels pass from the interface downward. Light curing causes heat and reflects the trapped water back into less polymerized subsurface.

Material Properties Notes

• Cementum high organic content must undergo a deproteination step by conditioning the material with NaOCL to remove high organic content and expose inorganic material.

Adhesive Properties

• Generations: 7
• Surface pretreatment, No. of steps
• 1st: Enamel etch 2
• Generations: 2nd Enamel etch 2 3rd Dentin conditioning 2-3 4th Total etch 3 5th Total etch 2 6th Self etch 2 7th Self etch
• Mechanism/Clinical steps: Etch & rinse, self etch, universal, Gl approach
• Type of solvent: Acetone, water, ethanol, Acetone-water, ethanol-water, Acetone-Ethanol
• Fillers content: Unfilled, filled
• Fluoride content: Fl. Free, Fl. Releasing Fl-apatite prevent release of hydrolytic enzymes long term stability.
• Effect on smear layer: Removing, modifying, dissolving.
• Shear bond strength:
  • Category 1: 5-7 Mpa -Category 2: 8-14 Mpa
  • Category 3: above 20 Mpa.