Charles W. Wakefield, DDS, MAGD,ABGD, FICD, FACD
Professor and
Director, AEGD Residency
Baylor College of Dentistry – TAMUHSC
Dallas, Texas cwakefield@bcd.tamhsc.edu
Objectives:
1. To develop an in-depth understanding of the concept and purpose of bonding to different materials.
2. To understand the evolution of adhesive materials, their individual components and how they function.
3. To develop a working knowledge of the mechanisms of successful bonding and how to achieve it depending on the varying microstructures of enamel and dentin.
4. To learn how to evaluate information on adhesive agents in order to choose the proper agent for each clinical situation.
5. To build hands-on knowledge of the clinical procedures and manipulation of various adhesive agents in conjunction with different restorative materials.
Adhesive agents

Materials used with the goal of predictably adhering restorative materials to enamel and dentin.

Based on multiple chemicals that prepare tooth, bond to tooth and act as the substrate to which restorative materials bond.

Different systems use varying methods to achieve successful bonding.

Adhesive systems vary widely on application as to the materials and situations in which they can be used.

Are in a constant state of evolution.

Extremely technique sensitive - - do not mix different systems. Follow directions precisely.
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Key Terms
Adhesive system, Smear layer, Bifunctional molecule, Hybridization, Wetbonding, Conditioner,
Primer, Self etching primer, Self etching adhesive
Microstructure of Teeth - Considerations:

Enamel
-Uniformity and orientation of rods, prisms

Dentin
-Variation of tubule size, density, length
Intertubular and peritubular dentin
-Sclerotic dentin
Smear layer
-Pulp pressure, wetness

Microflexure
-Abfractions - New terminology:
-Erosion-corrosion = mechanical / chemical
-Abrasion-corrosion = toothbrushing / chemical
-Abrasion-abfraction = toothbrushing / abfraction
-Biocorrosion-abfraction = caries / abfraction
Bonding - Purpose:

Retention

Contraction gap - Need to minimize or eliminate
- Polymerization contraction of composite resin
- Thermal expansion/contraction
- 18-20 MPa / 2800-3000 psi (Pashley)

Microleakage
- Staining, sensitivity, caries, pulp irritation, bond breakdown, short lifespan of
restoration
Evolution of Adhesive Systems:

ENAMEL Adhesion:
- Buonocore (1955) 80% phosphoric acid on enamel for 60 seconds
- BIS-GMA (Bowen)
- Simple micromechanical retention with hydrophobic diluted resins

DENTIN Adhesion:
1. “
First Generation”:

BIS-GMA, NTG-GMA = unfilled resins
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
Hydrophobic, contraction gap, smear layer left intact

Hydrolyzed quickly

Clinically unsatisfactory

Products:
- Adaptic Bonding Agent
- Enamel Bond Resin
- Durafill Bond
2. “
Second Generation”:

Phosphonated esters

Ionic bonds to calcium in retained smear layer

Hydrophobic

Hydrolysis - rapid bond degeneration

Limited by smear layer bond strength to underlying dentin (2-4 Mpa)

Products:
Bondlite, Creation 3 in 1, Clearfil, Dentin Enamel Bonding Agent, Prisma Universal
Bond, Dentin Bond LC, Scotchbond
3. Smear Layer:

Formation - rotary or hand instruments, endo files in root canals

Limited bond strength
 Acts as a “biologic Band-Aid”

Thickness - 1-5 microns

Components
- Ground enamel, ground dentin, dentinal fluid, collagen, saliva, microorganisms
4. “
Third Generation”:

Removed/modified smear layer

Hydrophilic

Bifunctional molecule (Primer) - HEMA, 4-META, PMDM, PMGDM, BPDM,
PENTA, GPDM

Then placed BIS-GMA adhesive, then composite

Products:
- GLUMA, XR Bond, Prisma Universal Bond 3, Tenure, Scotchbond 2, Mirage Bond
Plus, Clearfil New Bond

VLC cured for initial resistance to contraction gap formation

Bond strengths varied widely due to differences in dentin. Great improvement.
5. “ Fourth Generation”:

Extremely hydrophilic primers.

Aqueous solutions, acetone, ethanol as water chasers to enhance permeation of hydrophilic portion of primer into demineralized dentin after etching

Smear layer removed/modified

Intentional etching of dentin (Fusayama)

Hybridization (Nakabayashi)
- Demineralized zone
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- Collagen fibrils - Collagen Smear Layer if unsupported collagen dried
- Resin Impregnated layer (Hybrid layer)
- Wetbonding (Kanca)
- Microleakage vs. Nanoleakage

Strength of bond:
- Not dependent on thickness of hybrid layer
- Dependent on a) Ability of bond agent to wet demineralized zone b) Permeability of dentin

Concept of universal adhesive systems initiated.
- Enamel, dentin (wet, dry, sclerotic), porcelain, composite, metals, fresh and
set amalgam

Products:
- All-Bond 2, Amalgambond Plus, ABC Enhanced, Imperva Dual/Bond,
Tenure S, Restobond 4, Optibond MU, Scotchbond M.P. Plus, ProBOND A.P.,
Clearfil Liner Bond, GLUMA 2000, Panavia 21, DenTASTIC, Aelitebond,
WetBond, Bond It!, OptiBond FL, LuxaBond Total Etch, PermaQuik,
All-Bond 3
 “OptiBond FL not only proved insensitive to variations in moisture control and different degrees of wetness, but it was insensitive to effects of increased polymerization shrinkage stress (C-factor up to 5).
6. “ Fifth Generation”:

Consolidated systems. Etch separate. Primer and adhesive combined.

Advertised as time savers

No mixing

VLC only - not universal or dual cure

Products: One Step, Prime & Bond 2.1, Tenure Quik with Fluoride,
PermaQuik, Bond-1, Syntac Single-Component, OptiBond Solo, Espe Bonding
System, 3M Single Bond, Prime & Bond 2.1 Dual Cure, STAE, Easy Bond, Clearfil
Liner Bond 2, PermaQuik -1, SnapBond, GLUMA One Bond, One Coat Bond, Prime &
Bond NT, Prime & Bond NT Dual Cure, Excite DSC, Clearfil Liner Bond SE, New
Perma Quik, OptiBond Solo Plus, Cabrio, Gluma Comfort Bond and Desensitizer,
Bond-1 C & B, One-Up Bond F, Touch & Bond, One-Step Plus, Adper
Single Bond Plus, XP Bond, MPa DIRECT, I Bond Total Etch, Excite F, Excite F DSC
7.
“Sixth Generation”:

Self –Etch products- Etchant and primer combined. Adhesive separate step. In some cases, etchant, primer and adhesive combined in one all-encompassing step.

Advantages – Etch and prime certain to be same depth. Time saver. Minimal postoperative sensitivity. Don’t open tubules. Good under amalgam as well.

Disadvantages – extremely technique sensitive. May not work well on uninstrumented enamel. Some researchers say this is the wave of the future, but these are too inconsistent at present. Light cured only . CRA states they are universally compatible with different cure modes of composite, but unconfirmed in other studies.
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
Products: Panavia-F, Prompt L-Pop, Clearfil SE Bond, One-Up Bond F Plus,
Touch & Bond, Tyrian SPE, OptiBond Solo Plus Self-Etch, Adper Prompt L-Pop,
Nano-Bond, iBond (claim 7 th
generation), Simplicity, Brush & Bond, Xeno III, AdheSE,
UniFil Bond, Clearfil Protect Bond, G-Bond, Clearfil S 3 Bond, Xeno IV, Prelude SE,
Futurabond NR, Frog, Clearfil DC Bond, Peak, Adper Scotchbond SE, Clearfil SE
Protect , Prelude SE (curing options)
Fifth and Sixth generations are the most technique sensitive
8.
“Seventh Generation”:

Advertised to be “ seventh generation” simply because they have etchant, primer and adhesive in one bottle and require no mixing at all, in contrast to Adper Prompt. Adper
Prompt also comes in two bottles as an alternative to the original dispenser. Also ‘all-inone’ adhesives – i Bond, G-Bond, Clearfil S 3
, Xeno IV, OptiBond All-In-One, AdheSE
One F, Adper Easy Bond, Go!, Excel Bond LC, I Bond SE, Bond Force, TECO, ExciTE
F (total etch), ImageBond SE, Bond 1 SF, BeautiBond, Ace One and Done All Bond SE,
Xeno IV DC, Futurabond DC, Clearfil DC Bond, BeautiBond, Surpass (advertised to be
Eighth Generation), G-aenialBond, OptiBond XTR, Bond 1 SF, Oxford Bond SE (dual cure), Bond Force Pen
9.
 “New Classification”

Type I: 4 th generation – three separate steps:
Total etch: Etch + primer + adhesive

Type II: 5 th
generation – two separate steps:
Total etch: etch + primer/adhesive

Type III: 6 th
generation – two separate steps:
Self etch primer + adhesive

Type IV: 6 th
generation – One step, “All in One”
Self etch primer/adhesive. Some say this could be 7 th
generation:
Examples: G-Bond, iBond, Clearfil S
3
, Xeno IV, OptiBond All-In-One,
Go!, Adper Easy Bond, Bond Force, AdheSE One, ImageBond SE
Components in an Adhesive System

Etchant
- Usually describes enamel treatment
- Commonly uses 32-40% H
3
PO
4
- Weaker acids may not etch adequately (self-etch products)
- Enamel - must see frosted surface
- Gels, Liquids - remove inorganic components of tooth structure

Conditioner
-
Not needed in “total etch” technique
- Actually a low pH weak acid etchant
- Dissolves smear layer so primer can contact intact demineralized dentin, yet
leave tubules occluded
- Created demineralized zone containing collagen fibrils
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- Weak acids: Phosphoric, maleic, citric, acetic, nitric, PENTA, EDTA
- Simultaneous dentin-enamel etch may be inadequate
- Don’t over-etch and denature collagen

Primer
- Bifunctional molecule with one end hydrophobic, one end hydrophilic
- Permeation of conditioned dentin by hydrophilic end assisted by water and
water chasers such as ethanol or acetone.
- Hydrophobic end available for bonding to adhesive
- Best examples: HEMA, 4-META derivatives, BPDM, GPDM, PAAMA,
PMDM, PMGDM, PENTA

Adhesive (Bonding agent)
- Unfilled resin - BIS-GMA or UDMA, thinned with TEG-DMA diluent
- Cure - VLC, Auto, Dual
- Follow directions!
- Filled adhesives
- Increase bond strength
- Better stress absorbers
- Resist microflexure
- Intermediate modulus of elasticity between tooth and restorative
- “Contraction stress was absorbed and relieved by the application of an increasing thickness of low-stiffness adhesive”, J Dent Res ,
March 2000
- “..this finding at three years may indicate that the filled adhesive is more resistant to fatigue forces and could provide more durable retention than the unfilled adhesive.” Swift,
JADA , August 2001
Adhesion to Restorative Materials

For Composite
- To enamel only - etch, unfilled VLC adhesive only
- To dentin - etch, prime, VLC adhesive before composite placement
- Consider filled adhesives to absorb polymerization stress of composite
and assure adequate thickness so it is cured by light

For Amalgam: (Consider dentin only)
- Etch, VLC Primer
- Do not cure adhesive – optional if is dual cure system. If VLC product, cure.
- Don’t rely on agent for retention. Amalgam requires mechanical retention.
(Controversial with some 4-META containing adhesives)
- Is a sealant to protect dentin from microleakage
- New systems may be VLC only - oxygen inhibited layer bonds to amalgam (?)
- “Adhesives should be used to prevent reinfection of endodontically treated teeth
built up or restored with the coronal-radicular amalgam technique.” Howdle, et al,
Quint Int , Jan 2002
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
For Porcelain:
- Microetch with sandblaster
- Acid etch with HF (porc) and phosphoric (tooth)
- Silanate
- Primer, bond agent, opaquers
- VLC (veneers) or Dual Cure (crowns, onlays, inlays) - depends on type/thickness of
porcelain restoration

For Zirconia: Zirconia is too hard to etch with HF acid. Many opinions are in
circulation, but evidence is showing that air abrasion followed by one of the new primers (Ex: Z-Prime plus) provide highest bond strength.

Place adhesive before matrix when possible to minimize pooling
Adhesives As Liners (Controversial) and additional comments:

Pulp Capping - “Several new adhesive systems are biologically compatible and form new dentin bridges just like Ca(OH)
2 does. Acid etching and priming are neither irritants or toxic to pulp tissue” (Cox,
Amer J Dent , Jan 1998)

Pulp Capping - “Until another technique or material is scientifically proven as successful as calcium hydroxide, the use of the ‘Total Etch’ technique and dentin bonding agents in vital pulp capping is contraindicated” (Pameijer and Stanley, Amer J Dent , Jan 1998)

Pulp Capping - Calcium hydroxide has an improved formulation that doesn’t wash out, stimulates dentin bridging, and is antibacterial. Bonding agents yield little to no bridging. A good seal only eliminates bacterial induced inflammation. (Stanley, J Dent Res , Sept 1996)

Calcium Hydroxide - CH does not seal, is not sedative, is not therapeutic, does not lead to secondary dentin or maintain antibacterial properties. (Cox, 1995)

Suggested direct pulp capping technique:
- Always isolate with rubber dam
- Disinfect with 2% CHG for 60 seconds
- Gently dry
- CH over exposure. Best is MTA – it causes less inflammation and more bridging
than CH. Dr. Joe Camp says MTA reacts with the phosphate and calcium in tissue
fluid to make hydroxyapatite. Says this works much better than CH.
- RRGI over CH
- Etch, wash
- Adhesive, restorative (Pameijer and Stanley, Am J Dent , Jan 1998)
 “Neither pulp repair nor dentin bridging was observed with Vitrebond, which seems to contraindicate its application as a pulp capping agent”. “Pulp repair by Ca(OH)
2 on human
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pulp exposures was confirmed by the present study”. (Nascimento, et al, Am J Dent , Feb
2000
 “RRGI’s show strong toxicity to pulp cells, and it is not recommended that they be applied directly onto dental pulp cells.” Lan,
Oper Dent , May/June 2003
 Resin in direct pulp capping: “Adhesive resin induces cell-cycle arrest of cells that are involved in pulp healing and dentin bridging. Degree is related to D/C and unpolymerized resin due to low light intensity and humidity of the exposure.” Mantellini,
J Dent Res ,
August 2003

Adhesives in direct contact with healthy pulps do not lead to pulp repair. Ca(OH)
2
is biocompatible and induces reparative molecules ,and is the material of choice for accidental pulp exposures” Fernandez, OOOO, March 2008
 “MTA is more predictable than Ca(OH)
2
. It is not effected by moisture, maintains a pH of
12.5, is antibacterial, generates reactive layer of HA, has a zero micron seal, and is nonabsorbable once set”. Bogan,
JADA , March 2008

Self-priming (6 th
generation) adhesives: Self-priming systems show an inverse relation between the SBS of chemically cured composites and the acidity of the adhesive. These allin-one systems are very acidic, and are not compatible with chemical- or dual-cured resin systems. (Swift, J Esth and Rest Dent , 2001)
 “Additional phosphoric acid etching of enamel significantly increased the SBS of all selfetch adhesives. This should be considered when using all self-etch adhesives, especially on restorations with a high C-factor”. Luhrs, Oper Dent , Mar/Apr 2008

Most reliable dentin bonding: “If all margins are in enamel, two and three-step total etch agents are good. If any portion of the margins is in dentin, three-step total etch adhesives are preferred. The best performer of all was OptiBond Dual Cure.” DeMunck, Van Meerbeek, et al, J Dent Res , Feb 2003. “Simplified all-in-one adhesives need pre-etching of the enamel margins with phosphoric acid for effective seal.”, Khosravi, K, J Oper Dent , Sep/Oct 2009

Be careful of durability of self etching systems. They act as a semipermeable membrane with dentin. “Simplified self etch systems provide acceptable clinical retention, but hydrophilicity of the acidic monomers increases hydrolytic degeneration and restricts efficacy at two years.”
Van Dijken, Amer Jnl Dent , Feb 2004
 Curing lights important: “Inadequate polymerization of composite, both intensity and duration, directly affects the cytotoxic/genotoxic effect on vital cell culture as well as durability and quality of the final restoration”. Knezevic, Oper Dent , Jan/Feb 2008

Suggested USAF Website for up-to-date research: The USAF Dental Evaluation and
Consultation Service (DECS): https://decs.nhgl.med.navy.mil
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“The inability of some SE adhesives to bond adequately to roughened enamel questions whether dentists are currently considering the ease of application to be more important than longevity of bonded restorations”. Dent Invest Svc Report , 3 rd Qtr, 2005
 “Water sorption of adhesive interfaces remains the principal mechanism of bond degradation.
Two-step etch and rinse adhesives are more prone to hydrolytic degradation than multi-step adhesives that include a separate hydrophobic bonding resin”, DeMunck, J, J Dent Res , Dec
2009
 “SE adhesives act like permeable membranes after polymerization. Lack of a non-solvent hydrophobic layer allows for rapid dentinal fluid transudation across polymerized adhesives.” Reis, A, et al,
JADA , July 2009

The Bottom Line:
- Of the four options for bonding to tooth structure, the all-in-one self-etch adhesives have the shortest and least proven clinical track record.
- All-in-one adhesives do not seal dentin as well as more complex systems do.
- All-in-one adhesives bond less effectively to enamel than etch-and-rinse adhesives do, particularly if the enamel has not been instrumented in any way.
- All-in-one adhesives bond less effectively to dentin than two-step, self-etch primer systems.
- As measured in the laboratory, and to a lesser extent in clinical trials, the performance of all-in-one adhesives appears to be improving as newer materials are developed. Swift, E,
J Esth and Rest Dent , July 2010
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