Adhesive Dentistry

DR. FAMUREWA B.A. 1

ADHESIVE DENTISTRY: RECENT ADVANCESby

DR. FAMUREWA B.A.O.A.U.T.H.C.,ILE-IFE.

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DR. FAMUREWA B.A. 2

OUTLINE

• INTRODUCTION• HISTORICAL MILESTONES• DEFINITION OF TERMINOLOGIES• TYPES OF ADHESION IN DENTISTRY• FACTORS AFFECTING ADHESION

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DR. FAMUREWA B.A. 3

OUTLINE

• ADHESION TO ENAMEL– ACID ETCHING– EFFECTS OF ACID ETCHING– PATTERN OF ACID ETCHING

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DR. FAMUREWA B.A. 4

OUTLINE

• ADHESION TO DENTINE– BARRIERS TO DENTINE ADHESION– EVOLUTION OF DENTIN BONDING AGENTS(DBA)CLASSIFICATION OF DBAs.IDEAL REQUIREMENTS OF DBAsCLINICAL INDICATIONS OF DBAs

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DR. FAMUREWA B.A. 5

INTRODUCTION

• ADHESIVE DENTISTRY HAS REVOLUTIONIZED RESTORATIVE DENTAL PRACTICE FOR THE PAST 45 YEARS.

• IMPROVED ADHESIVE MATERIALS HAVE MADE RESIN-BASED COMPOSITE RESTORATIONS MORE RELIABLE & DURABLE.

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DR. FAMUREWA B.A. 6

INTRODUCTION

• THE OBJECTIVE OF THIS PRESENTATION IS TO:– REVIEW THE EVOLUTION OF DBAs– DISCUSS THE COMPOSITION & EFFECTIVENESS OF

VARIOUS DBAs– HIGHLIGHT CURRENT DENTAL ADHESIVES WITH

THEIR CLINICAL USAGES

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DR. FAMUREWA B.A. 7

HISTORICAL MILESTONES

• 1955- M. BUONOCORE ACID ETCHED ENAMEL WITH PHOSPHORIC ACID.

• LATE 1960s- HE SUGGESTED THAT IT WAS THE FORMATION OF RESIN TAGS THAT CAUSED ADHESION OF RESIN TO ETCHED ENAMEL

• 1982- NAKABAYASHI et al REPORTED THE FORMATION OF HYBRID LAYER.

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DR. FAMUREWA B.A. 8

Adhesion can be defined as “the state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking forces or both.”

An adhesive is usually a viscous fluid material that joins two substrates together ,it solidifies and transfers a load from one surface to the other.

Adhesive strength is the measure of the load bearing capacity of an adhesive joint.

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DR. FAMUREWA B.A. 911/30/2011

DR. FAMUREWA B.A. 10

Bonding of resins to tooth structure is a result of four possible mechanisms:

1. Mechanical- penetration of resin and formation of resin tags within the tooth structure.

2. Diffusion –precipitation of substances on the tooth surfaces to which resin monomers can bond mechanically or chemically

3. Adsorption- chemical bonding to the inorganic component(hydroxylapatite) or organic components(type I collagen).

4. A combination of the previous three mechanisms

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Failure of Adhesive joints occur as a result of combined breakdown in three locations:

• Cohesive failure in the substrate• Cohesive failure within the adhesive• Adhesive failure, at the interface of substrate

and adhesive.

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FACTORS AFFECTING ADHESION

• SURFACE ENERGY• WETTING • CONTACT ANGLE

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Surface energy• For adhesion the surfaces must be attracted to one

another at their interface . The energy at the surface is the surface energy, this is because at the surface the atoms are not equally attracted in all directions.

• The increase in surface energy per unit area of the surface is referred as surface energy or surface tension.

• When primary bonding is involved the adhesion is called as chemisorption and when physical forces are involved these are due to Vander waals forces.

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Wetting

• It is difficult to force two solid surfaces to adhere when placed in apposition if the surface molecules of the attracting substances are separated by distances greater than 0.7 nm then the adhesion is negligible.

• The method to overcome this is to use a fluid that flows into the irregularities to provide contact. This is called wetting.

• Wetting is influenced by the cleanliness of the surface.• The extent to which an adhesive wets the surface of an

adherend may be determined by the contact angle between the adhesive and the adherend.

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Contact angle.• A) when contact angle

is 0 the liquid contacts the surface completely and spreads freely and good adhesion.

• B) small contact angle • C) large contact angle

hence poor wetting and poor adhesion.

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Adhesion to EnamelEnamel etching and high surface energy.Clean etched field without moisture and

saliva.Bond strengths 20-25 MPa.

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Acid Etching • Before the introduction of acid etching the use of bonding

agents and leakage of oral fluids within the microscopic space between the prepared teeth and restorative materials was of greater concern for resin composites.

• The first meaningful proof of intra-oral adhesion was reported in 1955 by MICHEAL BUONOCORE, who etched the enamel with acids and then placed the restorative resin which formed resin tags when penetrated into the roughened surface created by the acid.

• This was the effective method to improve the mechanical bonding and to ensure sealed interfacial gaps.

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• Phosphoric acid 30-50% (most commonly used at a conc. Of 37% )

• Citirc acid• Maleic acid• Oxalic acid• Polyacrylic acid.• Pyruvic acid Procedure –Available as gel ( colloidical silica is added) or

liquid form. Applied onto the tooth surface with brushes or when

available in the form syringe it is expressed onto surface. Etching time is -15 sec. Rinse the tooth. If any contamination occurs procedure is to

be repeated.

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EFFECTS OF ACID ETCHING

• INCREASES SURFACE ENERGY• INCREASES SURFACE AREA• REMOVES ACQUIRED DEBRIS• INCREASES WETTABILITY• CREATES MICROPORES(of about 5-10µ)

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PATTERN OF ETCHING:TYPE -dissolution of enamel prism cores; honeycomb appearance

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TYPE - dissolution of enamel prism peripheries; cobblestone appearance

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TYPE - Mixed

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Dentine Adhesion

Adhesive materials can interact with dentine in different ways( Chemically, mechanically or both).

Unlike bonding to enamel, dentine bonding poses peculiar challenges:

Dentine contains a substantial amount of water(25%) and 25%organic material ( type I collagen ).

Network of dentine tubules connecting the pulp to the dentine-enamel junction.

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Composition of Enamel & Dentin by volume %(A & B)

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Network of dentine tubules connecting the pulp to the dentine-enamel junction.

Dentinal tubules enclose cellular extensions from the odontoblast and is also fluid filled.

Smear layer which is a residual organic and inorganic debris of cut tooth tissue forms a layer over dentine and also plugs the tubules.

Presently ,Dentine adhesion relies on micro-mechanical bonding achieved by the penetration of adhesive monomers into the fibrils of collagen fibres left exposed by acid etching.

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Dentine Bonding

•Bonding to dentine is achieved through several processes which may be carried out in one or several steps hence the preference for the term “systems” rather than “agents”.•Adhesion to dentine has been more elusive because dentine is more biologically active and is complex in composition and morphological structure.

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Dentine Bonding

•Dentine has a much higher organic content than enamel. Composition of dentine expressed in volume percent is 45% inorganic content, 33% organic compounds and 22% chiefly water.

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Challenges of bonding to dentine

• Etching may open up dentinal tubules, sometimes, resulting in pulpal irritation.

• Fluid from the dentinal tubules seeps continuously to wet the cut dentine surface.

• The smear layer impedes adhesion of the restorative material to the prepared tooth surface.

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Smear Layer

Cutting processes can produce smear layers on any material. Dentine smear layer contains hydroxyapatite crystals and partially denatured collagen and is generally 1-5 microns thick.

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Management of Smear Layer

The management of the smear layer depends on the material to be bonded to the dentine surface.

This includes the following:•Removal•Retention•Fixing•Replacement

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Removal of Smear layer

The application of 37% phosphoric acid for 15 seconds will remove the smear layer. It will also open up the dentinal tubules, allowing seepage of dentinal fluid to the prepared dentine surface.

Immediate application and curing of a dentine bonding agent will prevent this wetting. The bonding agent penetrates the dentinal tubule, etched intertubular and peritubular dentine to form a resin impregnated dentine known as the interdiffusion zone or hybrid layer.

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Retention of Smear layer

The smear layer is retained when dentine bonding systems based on phosphate esters of BIS-GMA or its modifications are used.

Adhesion depends on chelation between the bonding agent and calcium ions in the smear layer and dentine surface as well as mechanical entanglement with the dentine surface.

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Fixing of Smear Layer

The application of materials like tannic acid or ferric chloride will remove the superficial smear layer while fixing the smear plugs of the dentinal tubules to the dentine surface.

The collagen in the smear layer becomes cross-linked with the matrix of the underlying dentine.

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Replacement of Smear Layer

Treatment of cut dentine surface with substances such as ferric or aluminium oxalate will result in the replacement of the smear layer with a new complex capable of developing high bond strength with the dentine bonding agent.

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IDEAL DENTIN BONDING AGENT

• PROVIDE HIGH BOND STRENGTH TO DENTIN, WHICH SHOULD BE PRESENT AFTER PLACEMENT & BE PERMANENT.

• PROVIDE BOND STRENGTH TO DENTIN SIMILAR TO ENAMEL

• SHOW GOOD BIOCOMPATIBILITY TO DENTAL TISSUE, INCLUDING THE PULP

• MINIMIZE MICROLEAKAGE @ THE MARGINS OF RESTORATION

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IDEAL DENTIN BONDIN AGENT

• PREVENT RECURRENT CARIES & MARGINAL STAINING

• BE EASY TO USE & MINIMALLY- TECHNIQUE SENSITIVE

• BE COMPATIBLE WITH WIDE RANGE OF RESIN• HAVE THIN FILM THICKNESS• FLUORIDE-RELEASING• POSSESS A GOOD SHELF LIFE

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Classification of Dentine Bonding Agents/ Systems

Dentine - bonding agents may be classified based on:

Their mode of action, Their evolution.

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Classification according to mode of action

• Those that bond with calcium ions.• Those that bond with amine or hydroxyl

group.• Those that bond with reprecipitated smear

layer.

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Those that bond with calcium ions

These are agents based on phosphate esters of BIS-GMA and its modifications. They bond with the calcium ions in dentine and intact smear layer.E.g. Bondlite, Scotchbond 1. 2nd generation DBAs are example.

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These are based on isocyanate or aldehyde. They bond with amine or hydroxyl group of the organic component of dentine. The smear layer has to be removed and the dentine decalcified. E.g. Gluma.

Some 4th generation DBAs belong here

Those that bond with amine or hydroxyl group

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Those that bond with reprecipitated smear layer

These agents require the partial removal and modification of the smear layer. Bonding is by mechanical entanglement of with the collagen fibrils on the dentine surface. E.g. Scotchbond 2, Tenure.

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First Generation• Buonocore in 1956 demonstrated the use of

glycerophosphoric acid dimethacrylate- containing resin to bond to acid etched dentine through the calcium ions of hydroxyapatite.

• Bowen in 1965 showed that NPG-GMA, a bifunctional molecule would bond to dentine after it had been treated with glycerophosphoric acid.

• The bond strengths exhibited by this systems were very low, about 1-3 MPa.

• Example is CERVIDENT.

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Second Generation• Introduced in the late 1970s, the majority of

these incorporated halophosphorous esters of unfilled resins such as BIS-GMA or HEMA.

• Bonding mechanism was through ionic bond to calcium by chlorophosphate groups.

• Dentine was not etched hence much of the adhesion was to the smear layer, which is weakly attached to the dentine.

• Bond strength ranges from 1 – 6.8 MPa.• E.g. Scotchbond 1, Prisma Universal Bond,

Bondlite, Dentin Adhesit. 11/30/2011


Third Generation-Late ’80s

• Utilizes acid-etching of dentin to partially remove and modify the smear layer.

• The acid is rinsed off before applying the primer, which contains 4-META(or any of BPDM, PENTA, HEMA) & Ethanol.

• The hdrophilic group of the primer infiltrates the smear layer, modifies it and promotes adhesion to dentine and the other end of the primer bonds to the resin.

• Can bond to ceramics & dental metals-1st of DBA to do this.

• Bond strength is in the order of 12 MPa(8-15MPa).• E.g. Tenure, Scotchbond 2, Prisma Universal Bond,

Gluma .11/30/2011


From 1st-3rd generation

• NO DIRECT BOND TO DENTIN; IT IS EITHER TO SMEAR LAYER OR IT’S MODIFICATION.

• HENCE POOR BOND STRENGHT COMPARED TO THAT OF ENAMEL.

• HOWEVER, 4th GENERATION DBAs EXPLORED DIRECT BONDING TO DENTIN DUE TO INTRODUCTION OF TOTAL ETCH TECHNIQUE( by FUSAYAMA et al 1979), HYBRID LAYER FORMATION ( by NAKABAYASHI et al 1982) &WET BONDING( by KANCA 1992).

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Dentine bonding follows three main processes1. Acid etching (conditioning):Application of acid to

dentine results in partial or total removal of the smear layer and demineralization of the underlying dentine to open dentine tubules and expose collagen fibres

A wide range of organic (maleic, tartaric, citric, EDTA, acidic monomers), polymeric( polyacrylic acid), and mineral ( hydrochloric, hydrofluoric) acids have been investigated as etchants but phosphoric acid (30-40%) solutions and gels produce the most reliable etching.

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SMEAL LAYER

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2. Priming: Primers are hydrophilic molecules usually carried in a solvent. Acidic primers containing carboxylic acid groups are used in self etching bonding agents. Solvents used in primers are acetone, ethanol-water, or water. Some are solvent free.

Primers permeate the collagen fibrils and the tubules to increase their surface energy and render them receptive to the hydrophobic adhesive.

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ADVANTAGES AND DISADVANTAGES OF PRIMERS WITH VARIOUS SOLVENTS

Solvent Advantages Disadvantages

Acetone Dries quickly Evaporates quickly after being dispensed; can evaporate from container; sensitive to wetness of dentine; multiple coats may be required; offensive odour

Ethanol/water Evaporates less quickly; less sensitive to wetness of dentine

Extra drying time

Water Slow evaporation, not sensitive to wetness of dentine

Long drying time; water can interfare with adhesive if not removed

Solvent-free No drying, single coat Higher film thickness

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3. Bonding: this requires the placement of adhesives which are generally hydrophobic dimethacrylate oligomers that are compatible with monomers used in the primer and composite. It is applied to the etched and primed tooth surface and cured.

When primer and bonding resins are applied to etched dentine they penetrate the intertubular dentin forming a resin-dentine interdiffusion zone called the HYBRID layer.

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• This three step adhesion process marked the commencement of the Fourth generation bonding systems ( Type 1 adhesives) and the basic principle for dentine bonding presently.

• Subsequent generations are designed to simplify the process by reducing the number of clinical stages required. This shortens chair-side time and reduces procedural errors.

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Fourth Generation-Early 1990s

• Complete removal of smear layer – “total etch” - is achieved with these agents.• This permits the simultaneous etching of enamel

and dentine using phosphoric acid for 15-20 secs.• Dentine must be moist or “wet” for good bonding.

Hybrid layer is formed after the primer is applied. • Adhesive resin is then applied.• E.g. All-bond II, Clearfil Photo-Bond, Scotchbond MP,

e.t.c• Bond strenght-17-25Mpa

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The 5th generation-Mid 1990s• This combines the primer and adhesive in one

bottle and 30-40% phosphoric acid as etchant thus reducing the stages from 3 to 2 (PRESENTLY AVAILABLE @ O.A.U.T.H.C.).

• Bond strenght-20-25MPa.• Unit-Dose packaging was introduced.• Examples are Single bond, Excite, Gluma

Comfort Bond e.t.c

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These includes self etching primers where the etchant and primer are in one bottle and adhesive resin in another bottle.

Manipulation is easy , show good bond strength to dentin but not to enamel

Etching and rinsing not required Primer applied first then adhesive. ACIDIC PRIMER ADHESIVE:- Methacrylated phosphates SOLVENT:- Water Eg:- SE bond, XENO, Linear Bond II Bond strenght-18-23Mpa Some are Fluoride releasing e.g FL-BOND II

SIXTH GENERATION:-late ‘90s

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Total etch vs Self etch systems Total etch adhesive systems: require the simultaneous

application of an acid (usually 30-40% phosphoric acid) to enamel and dentine for 15-20secs after which it is rinsed off. There is complete removal of the smear layer. This is the hallmark of 4th generation

Self etch systems: these are acidic primers that utilize a phosphonated resin molecule that performs two functions simultaneously(etching and priming dentine) they are not rinsed off but incorporate the smear plugs into the resin tags. They reduce the possibility of overwetting or overdrying dentine during adhesion process. This is applied in 6th generation.

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7th Generation-late 2002

• This is “all-in-one” DBA that contains etchant, primer & adhesive in a single bottle.

• No mixing is therefore needed.• It’s operator friendly-no multiple steps• Any available curing light can be used-plasma arc,

LED, Quartz Tungsten Halogen.• Unit dose packaging & single bottle available• Bond strength- 18-25MPa• Examples are iBond, OptiBond, XENO IV, G-Bond e.t.c

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4th-7th generation

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Bonding of all direct composite resin restoration,both anterior& posterior including pit & fissure sealants

Bonding of indirect composite resin restorations( inlays, onlays and veneers).

For bonding ceramic veneers & crowns Bonding of amalgam restorations Management of dentin hypersensitivity Luting post and core restorations Bonding of orthodontic brackets Repair ed porcelain, amalgam & resin restoration Treatment of erosion, abrasion & abfraction

INDICATIONS

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CONCLUSION

• DENTIN(ENAMEL & DENTIN) BONDING AGENTS HAVE MADE REMARKABLE PROGRESS FROM THE NO ETCH ERA OF BUONOCORE TILL DATE.

• COST OF THIS MATERIALS & TECHNIQUE SENSITIVITY STILL REMAIN A CHALLENGE TO THEIR EFFECTIVE USE .

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REFERENCES

• RESTORATIVE DENTAL MATERIALS(11th Edition) EDITED BY CRAIG R.C. & POWERS J.M.

• STURDEVANT’S ART & SCIENCE OF OPERATIVE DENTISTRY(4th Edition) EDITED BY ROBERTSON T.M. et al.

• G.KUGEL, M. FERRARI. The science of bonding: from first to sixth generation. JADA 2000

• FACULTY OF DENTAL SURGERY(NPMCN) UPDATE LECTURE BY D.C. UMESI-KOLEOSO & I.C.ADEGBULUGBE

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Thank you !!

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Adhesive Dentistry