Dental Adhesives

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Dental Adhesives

• A.M. Young

Biomaterials and Tissue Engineering Division
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Seminar plan

• Adhesive use in dentistry
• General bonding processes
• Composite bonding
• Enamel
• Dentine
• Adhesive resins
• Chemical composition
• Clinical effectiveness
• Microleakage
• Quantification
• Prevention

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Dental adhesive procedures

• Bond / repair direct restorations
• Composites
• GICs
• Amalgam
• Modification of tooth contour
• Pit and fissure sealing
• Bonding of ceramic restorations
• Repair / bonding of resin / porcelain veneers and
  crowns
• Fixation of bridgework
• Bond orthodontic brackets and splints
• Lute endodontic posts

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Bonded composites vs. non bonded amalgam

• Advantages
• Aesthetics
• No toxic Hg
• Provide strengthening effect on remaining tooth
• More conservative of original tooth structure
• Can enable repair instead of replacement
• Disadvantages
• Lower strength / wear resistance
• Allergenic monomers
• Greater bacterial microleakage

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Microscopic processes during bonding

• Clean / stable / rough surface
• Good wetting of adhesive
• High contact in pores
• Form strong solid
• bond to 2nd surface

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Adhesive liquid characteristics

• Rapid flow
• Low viscosity (eg unfilled HEMA)
• Good wetting / spreading
• Low surface tension
• Surfactants increase liquid / solid attractions
• To fill pores / roughness by capillary action
• High surface tension

Water 79 Ethanol 22 Acetone 25
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Surfactants

• Hydrocarbon chain hydrophillic head group
• Hydrophilic (water loving) groups
• COOH ,OH, SO, PO, ions
• Hydrophobic (oil based)
• Aromatic rings
• Hydrocarbon chains
• Like attracts like

(CH2)n
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Adhesive Cure
- - - - - - -

• Chemical reaction converts adhesive to strong
  solid
• Ionic (eg acid base ? salt water)
• Covalent (eg in C-C backbone in polymers)
• Bonding interaction with surface
• Micro mechanical
• Polymer entanglements
• Chemical reaction / physical attraction

(CH2-CH2)n
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Composite bonding
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Composite vs GIC bonding

• Composites
• Complex
• Micromechanical bond (primarily)
• Initial bond strengths
• Enamel / superficial dentine 15-35 MPa
• Deep dentine generally lower
• Mechanical and thermal cycling decrease bond
  strength
• Glass ionomer cements
• Easier procedures condition with 25 PAA
  solution
• Chemical bond
• Initially 10 MPa
• More durable

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Bond durability
Thermal expansion and conductivity
Thermal conductivity K (mcal) /(s cm ºC)
Linear thermal expansion coefficient E 10-6 / C

• Tooth 11 2
• GIC 10 2
• Composite resin 40 3
• Amalgam 25 54

E linear expansion per one degree rise in
temp.
K heat (mcal) per second through body (1cm
thick) with cross sectional area 1cm2 if there is
one degree temp difference either side
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Composition of enamel and dentine
Enamel Dentine
wt Hydroxyapatite 95 70 Water 3 10 Nonco
llagenous proteins 1 2 Collagen - 18

• Enamel wet by hydrophobic or hydrophilic
  adhesives
• Dentine requires hydrophilic adhesives / primers
  or cements
• Both need roughening for good adhesive contact

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Resin enamel bonding

• Addition of phosphoric acid for 30s
• Frosty appearance
• SEM shows etching of hydroxyapatite prisms
• Penetration of methacrylate monomers into rough
  surface provides micromechanical bonding

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History of resin dentine bonding

• Pre 1970
• Acid etch enamel (not dentine)
• self cured bonding agents
• 1970s
• Hydrophobic enamel adhesives
• Hydrophilic dentine adhesives
• light cure systems
• 1980s
• Acid etch of dentine
• Acidic hydrophilic monomers for dentine priming
• Hydrophobic low viscosity resin adhesive

• 1990s
• Common dentine and enamel adhesives
• Light and dual cure systems
• Combined
• Primer and adhesive or
• Etchant and primer
• 2000
• Combined etchant, primer and adhesive

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Van Meerbeek adhesive classification
Review of adhesive chemistry - Landuyt et al
Biomaterials 28 (2007) 3757 - 3785
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3 step dentine bonding processes

• Phosphoric acid etch for 10s
• Smear layer removal
• Hydroxyapatite dissolution
• Rinse and dry
• Collagen collapse
• Priming
• Collagen rehydration
• Adhesive penetration into tubules and collagen

• Solvent removal
• Cure
• Micromechanical adhesion
• Tubule sealing
• Add composite
• Bonding
• polymer entanglements
• Reaction with O2 inhibition layer

Composite
hybrid layer
branches especially important
dentine
Dentine tubule
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Three-step etchrinse adhesives (3-ER)
35 H3PO4
3M ESPE,
Adper Scotchbond
HEMA, polyacid, water
St. Paul, MN,
Multi-Purpose
Bis-GMA, HEMA, Initiators
USA
32 H3PO4
Bisco Inc,
All-Bond 2
NTG-GMA, BPDM, acetone, ethanol, water
Schaumburg,
Bis-GMA, UDMA, HEMA,TEGDMA, Initiators
IL, USA
37 H3PO4
Pentron Corp
Bond-it
NTG-GMA, PMGDM, Bis-GMA, HEMA, acetone
Wallingford,
Bis-GMA, HEMA, UDMA,HDDMA, Initiators
CT, USA
H3PO4
DENTSPLY
Probond
PENTA, acetone, ethanol, stabilizers
Caulk,
PENTA, UDMA, methacrylates, glutaraldehyde,
Initiators
DE, USA
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Three-step etchrinse adhesives (3-ER)
37.5 H3PO4 HEMA, GPDM, MMEP, water,ethanol, CQ,
Bis-GMA, HEMA, GDMA, initiators, ?ller (48wt)
Optibond FL
Kerr CA, USA
Dental Materials (2005) 21, 864881 Good class V
retention 86,98 and 100 in 5 yr studies
Thick adhesive resin layer - act as shock
absorber - increase polymerization
Filler particles too large to penetrate hybrid
layer
Underlying dentine
Biomaterials 28 (2007) 3757 - 3785
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Boiling point Dielectric constant

• Water 100 80
• Ethanol 79 24
• Acetone 56 21

Water more effective Expansion of collagen
Rapid evaporation with acetone Less solvent
polymerisation inhibition Poor shelf life /
reduced reproducibility
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Initiators
Toxic to cells
CQ
DMPT
BP benzoyl peroxide
Inhibition by Solvent Oxygen
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HEMA / TEGDMA / UDMA / silica strength(24 hours
in water)
Hydrophilic vs hydrophobic monomers
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Acidic monomers
Tertiary amine
Carboxylic acid
Methacrylate
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Multi functional acidic monomers
Penta early self etch primer limited bonding
to HA - phosphate group too hindered
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Two-step etchrinse adhesives (2-ER)
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Adhesion / demineralizing monomers
H in 4-AETA
Anhydride Chelating diacid Can bond
with Ca in HA

Acetone soluble only suitable solvent Water
insoluble Ethanol undergoes esterification
reaction
Improves wetting to metals
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Two-step self etch adhesives (2-SEA)
Biomaterials 28 (2007) 3757 - 3785
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Functional monomers
Hydrophobic spacer
Ca chelating

antibacterial
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Long hydrophobic spacer groups

• Separate functional groups raising
• Monomer flexibility and polymerisability
• Binding to Ca, HA demineralization, collagen
  penetration
• Decrease
• Hydrophilicity / aqueous solubility
• Water sorption
• Adhesive degradation via hydrolysis
• Enhanced surfactant properties improve
• Hydrophobic / hydrophilic component mixing
• Dentine wetting

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One-step self etch adhesives (1-SEA)
iBond Heraeus Germany
UDMA, 4-META, glutaraldehyde, acetone, water,
initiators, stabilizers
G-Bond GC,Tokyo, Japan
4-MET, phosphoric ester-monomer, UDMA,TEGDMA,
acetone, water, stabilizer, silica, initiators
Biomaterials 28 (2007) 3757 - 3785
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Problem reactions at low pH
Esterification of COOH by ethanol
Hydrolysis of phosphate
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Methacrylate hydrolysis
Low pH
high allergenic potential
Methacrylamides (-CO-NH- or CO-N- instead of
CO-O-R-) Less hydrolysis more stable one bottle
formulations
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Clinical effectiveness - Retention

Annual failure rate 3 step ER 0-16 4.8 2
step ER 0-20 6.2 2 step SE 0-20 4.7 1
step SE 0-48 8.1 GIC 0-8 1.9

• M. Peumans et al, Dental Materials (2005) 21,
  864881
• Class V non carious lesions

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Microleakage

• Microleakage
• Passage of fluid and bacteria in micro gaps
  (10-6 m) between restoration and tooth
• Most significant hazard in restorative
  dentistry and greatest risk to the pulp
• Nanoleakage
• Passage of fluid / dissolved species in nano -
  sized (10-9 m) gaps

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Effects of nano and microleakage

• Bacterial leakage
• Discoloration
• Recurrent caries
• Pulpal irritation / infection
• Nanoleakage
• Sensitivity during
• thermal
• occlusal stress

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Microleakage Reduction

• Composite shrinkage reduction
• Decrease monomer level
• Increase monomer molecular weight
• Polymerise incrementally
• Matching of tooth / restorative dynamic
• Thermal and mechanical props
• Restorative water sorption induced
• Expansion
• Continuing slow reaction
• Improved adhesion
• Release of antibacterial agents

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Antibacterial agent releasing materials

• Gluteraldehyde -toxicity concern
• MDPB only effective when bacteria contact
  surface
• Fluoride
• Fluoro apatite formation increase acid
  stability
• At sufficient levels will kill bacteria MIC
  1000mg/ml
• Antibacterial agent release
• Chlorhexidine (MIC 1mg/ml)
• Not released from
• GIC
• RMGIC
• Hydrophobic composites
• Can be released from hydrophilic composites
• Also toxic to cells

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Effectiveness of F release
GIC
1week
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In vitro microbiological investigations
Constant Depth Film Fermentor
Assess bacterial levels on surfaces using
fastidious anaerobe agar
Saliva inlet Sample port Scraper
blade Turntable Media outlet
300micron
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Live bacterial counts on dental material surfaces
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Restored cylinders of bovine dentine
Biofilm
depth
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Material interfaces (10 weeks in CDFF)
GIC
RMGIC
amalgam
Composite
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Chlorhexidine release from Fuji IX
HPAA CHXAc PAA(CHX) HAc
0.5 At 1 week
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TEGDMA / UDMA/ HEMA / silica adhesive
HEMA in monomer
1 week
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Bacterial counts on composite surfaces
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Dentine interfaces (10 weeks in CDFF)
5 CHX
Z250
No CHX
10 CHX
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Conclusions

• Further work is still required to produce a
  material with good mechanical and adhesive
  properties that also prevents bacterial
  microleakage.

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Recent reviews

• Landuytet al. Biomaterials 28 (2007) 37573785
• Norbert Moszner, Ulrich Salz. Macromol. Mater.
  Eng. 2007, 292, 245271
• M. Peumans et al. Dental Materials (2005) 21,
  864881.