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Current adhesives and their development. Enamel and dentine adhesion principles. Use possibility, working procedure. Common mistakes and their consequences in the clinical praxis.

Stomatolog Julia Morozova, Ph.D.

Operative Dentistry 1 ST1/ZAA35

Basic mechanism of adhesion

• The primary aim of dental adhesives is to provide retention to composite fillings or composite cements

• Twofold adhesion • Co-polymerization of residual double bonds (-C=C-) in

the oxygen inhibition layer • Exchange process– replacement of inorganic components • from hard tissue

– by resin monomers• micromechanically interlocked

Enamel structure • The hardest tissue of the human body (96 % of mineral

components)• Prisms

http://tre.docdat.com/docs/835/index-57516.html

Enamel bonding • Developed by Buonocore (1955)• Etching by 32–37% H3PO4:

– interprismatic and intraprismatic strucure will be disrupted– creates micropores (5 – 50 microns deep)– increases surface energy– increases wettability

• 3 types of etching:• Central intraprismatic• Peripheral interprismatic • Combined

Adhesion onto enamel

• Enamel adhesive (bond), strength >20 MPa• It forms the interlayer allowing the resin adhesion

onto tne enamel• Contain: unfilled or partially filled composite resin

with smaller molecules of monomers

http://www.blogdental.es/Keogh/?p=131

Dentine structure

• Live tissue with methabolism• Dentine composition• Hydrophilic tissue (10–30 % H2O)• Dentinal tubules with odontoblasts’ process and

tubular liquid• Changes in dentine structure• Smear layer• Dentinal wetness

Adhesion onto dentine• Presence of smear layer• Hydrophilic tissue • Etching → dissolving of smear layer and mineral components →

opening of dentinal tubules’ entrances, denaturation of surface proteins → baring of collagenous fibers’ net

• Primer (has influence on hydrophilic properties of the dentine and accents its hydrophobic properties)- hybridization of the dentine

Requirements for adhesives

• High strength and permanence of adhesion onto dentine and enamel

• Biocompatibility for tooth tissues, organismus in generally and personnel

• Perfect marginal integrity without risk of microleakage, secondary caries or marginal percolation

• Perfect and permanent contact with dentine and closure of dentinal tubules

• Suitable for moist and dry environments• Fluoride-releasing• Easy procedure and application• Sufficient long expiration time

Classification of adhesives

• According to chemical composition (type of solvent)• According to influence on smear layer• According to generation criterion

Chemical composition of adhesives

• Monomers of composite resin• Solvents • Initiators (photo- or self-curing) • Inhibitors or stabilizers • Anorganic filler (not allways)• Specific components (polyalkenoic copolymer,

glutaraldehyd, antibacterial components, fluorides, dyes, acids)

Monomers of resin composite

• Methacrylic acid (MA)• Methylmetacrylate (MMA)• Hydroxyethyl metacrylate (HEMA)• 4-MET• 4-AETA• 10-MDP• MAC-10• Phenyl-P• Di-HEMA-phosphate and HEMA-phosphate• Di-methacrylates (BisGMA (Bowen‘s monomer), UDMA,

TEGDMA)• (Meth)acrylamides

Solvents

• Water

• Ethanol

• Acetone

• Camphorquinone/co-initiator system

• 1-phenyl-1,2 propanedione (PPD)

• Acylphosphine oxides

• Benzoylperoxide (BPO) in conjunction with tertiary amine

• Tri-n-butyl borane (TBB)

Initiator systems

Photo-initiators Chemical initiators

Inhibitors

• Antioxidants- scavenge free radicals originating from prematurely reacted initiators

• Prevent spontaneous initiation and propagation of the free-radical polymerization reaction

• Promote shelf life • Butylated hydroxytoluene (butylhydroxytoluene BHT),

monomethyl ether hydroquinone (MEHQ)

1st generation

• 1950–1970s• NPG-GMA (N-phenylglycin-glycidyl methacrylate)• Strength of adhesion: 1–3 MPa• S.S. White’s Cervident

2nd generation • Late 1970s • Combination of Bis GMA (bisphenol A and glycidyl methacrylate)

and HEMA (hydroxyethyl methacrylate)• Strength of adhesion: 4.5–6 MPa• 3 tendencies:

• Etching agent (25% citric acid - Dentin Bonding System, Den-Mat)• Adhesive with phosphate aether (Bondite, Sybron/Kerr; Scotchbond

TM, 3M ESPE; Prisma Universal, Dentsply Caulk)• Adhesive with polyurethan polymer (Dentin-Adhesit, Ivoclar Vivadent)

3rd generation

• Late 1980s• 3 parts:

• Conditioner: weak organic acid (maleic acid) or anorganic acids in low concentration (phosphoric or nitric acid)

• Primer: bifunctional monomer dissolved in solvent (acetone or ethanol) Bifunctional monomer has one hydrophilic end (it is adapted onto the dentine) and another one is hydrophobic (it is adapted onto composite resin); HEMA, 4-META, NPG, NSMA

• Adhesive: non-filled or low-filled resin, that connects with primer and forms hybrid layer (1–5 µm), that penetrates into dentinal tubules and forms composite tags

• Strength of adhesion: 12–15 MPa• Scotchbond TM Multi-Purpose (conditioner maleic acid); Scotchbond

TM Multi-Purpose Plus (conditioner phosphoric acid, 1994) (3 M ESPE)

• XR Bonding System (Sybron/Kerr), Gluma (Heraeus Kulzer), Tenure (Den-Mat), Syntac Classic (Ivoclar Vivadent)

4th generation• Start of revolution in aesthetic dentistry (early 1990s) • Complet removing of smear layer• Total etching of enamel and dentine („total-etch“)• The dentine surface after gentle drying must be wet to

prevent the collapse of collagen fibres after the etching („wet bonding“)

• Technique sensitive• Gold standard• OptiBond FL (Sybron/Kerr); All-Bond (Bisco, Inc.)

5th generation • Mid 1990s• „One bottle systems“ (primer and adhesive are in one bottle)• Two steps technique: etching and adhesive application (Etch &

Rinse) • OptiBond Solo (Sybron/Kerr), Gluma One Bond (Heraeus

Kulzer), Single Bond (3M ESPE)

6th generation

• Early 2000s• „Self-etching“: acidic primer• Etching is not required→ decreasing of postoperative sensitivity• Strength of adhesion: 18–23 MPa• All-Bond SE (Bisco Inc.); ClearfilTM SE Bond (Kuraray); AdheSe

(Ivoclar Vivadent), Nano-Bond (Pentron)

7th generation

• 2002–2003• One-bottle self-etching systems• One step system • OptiBond All-In-One (Sybron/Kerr); Xeno IV (Dentsply

Caulk), ClearfilTM S3Bond (Kuraray), iBond (Heraeus Kulzer)

Currently available generations

• Fourth Generation– Three-step Etch & Rinse

• Fifth Generation– Two-step Etch & Rinse

• Sixth Generation– Two-step Self-Etch– One-step Self-Etch

• mix

• Seventh Generation– One-step Self-Etch

• no mix

Pros/Cons of Etch & Rinse (Col Kraig S. Vandewalle Enamel and Dentin Adhesives)

• Separate acid etch– good enamel etch pattern

• Potential to over-etch dentine– except sclerotic dentin

• Post-conditioning rinse is necessary– sensitive to level of dentine wetness

• Multiple long-term clinical studies

• Acetone and ethanol based primers– displace remaining water– carry monomers into

collagen– gently air-dried– leaving monomers behind

• Examples– One-Step– Prime & Bond NT

• Overwet phenomen– too moist (too much water)– not completely displaced

• Phase separation– blister and globule formation

• Disadvantages: • Cannot check for enamel

“frosted” etch• Technique sensitivity

– not too wet or too dry

• Solvents evaporate from bottle– may reduce monomer

penetration

Wet bonding (Col Kraig S. Vandewalle Enamel and Dentin Adhesives)

Dry bonding (Col Kraig S. Vandewalle Enamel and Dentin Adhesives)

• Water-based primers– effective on wet or dry dentine– self-rewetting effect– re-expand collapsed collagen

• Permits check of “frosted” enamel• Examples– Scotchbond Multi-Purpose– Optibond

Pros/Cons of Self-Etch (Col Kraig S. Vandewalle Enamel and Dentin Adhesives)

• Good dentine conditioning– simultaneous infiltration– depth of demineralization

• Possible reduction in post-operative sensitivity• No post-etching rinse– not sensitive to level of dentine wetness

• Reduced application time• Relatively lower bond strengths

Unit Dose (Col Kraig S. Vandewalle Enamel and Dentin Adhesives)

• Improved infection control• Simple working procedure• Minimizes loss of volatile components over time• Higher cost• Examples– Optibond Solo Plus– Excite– Prime and Bond NT– Prompt L-Pop

Polymerization shrinkage and polymerization stress

• 3.5–4 % • They are affected by fast photopolymerization• Factors:• C-factor (size and geometry of cavity)• Application technique • Light intensity and direction during the photopolymerization• Viscosity and elastic modulus of composite resin, value of

polymerization shrinkage• Hydroscopic and thermal expansion of resin composite • Consequences: bad marginal integrity, microleakage between

filling and cavity, filling percolation, secondary caries, postoperative sensitivity, cusp break

C-factor

Ratio of bonded to unbonded surfaces of cavity

Scientific Compendium SDR, 2011

C-factor of different classes

Karthic K., Sivakumar K., Geetha Priya P.R., Shankar S.: Polymerization Shrinkage of Composites-A Review. JIADS, vol. 2, issue 2, April-June, 2001, pp. 32–36

Incremental technique minimizing C-factor

Common mistakes

• Non-adequate etching• Insufficient drying or overdrying of dentine• Too thick or too thin layer of adhesive• Insufficient polymerization • Non-adequate material adaption onto the cavity walls

The influence of resins on the general health

• Contact allergy of personnel on adhesives and resins• Cytotoxic and endocrine-disruptive effects of non-

polymerated monomers (esp. dimethacrylates)

Thank you for attention