Bonding to Dentin Types of dentin surfaces fractured

Bonding to Dentin

Types of dentin surfaces: • fractured • smear layer covered • sclerotic dentin (hypermineralized) • caries altered (demineralized)

Bonding to dentin: etching the dentin • Buonocore (1956) tried to bond MMA to etched dentin • Hydrophobic resins would not adapt to etched tubules • In any case, the prevailing paradigm was that etching dentin would kill the pulp. 5 μm Resin repels pulpal fluids. These fluids keep the resin from adapting to tuble walls.

Adhesion to dentin - Steps • Conditioner • Primer • “Adhesive” Resin

Adhesion to dentin - Definitions • Conditioner – an acid the etches dentin • Total Etch – the technique that uses a single acid to simultaneously etch both dentin and enamel

Smear layer Mixture of hydroxyapatite, collagen, saliva, & blood. • weakly attached to surface • thought to seal dentinal tubules

Dealing with the smear layer - Strategies • bond primer to surface of smear layer. (strategy 1) • dissolve smear layer and demineralize near -surface dentin with an acid; treat demineralized dentin with primer. (strategy 2) • dissolve smear layer & demineralize nearsurface dentin with an acidic primer. (strategy 3)

Strategy 1: bonding to the smear layer • strategy used by in Scotchbond & subsequent DBSs marketed in early 1980 s • Produced low bond strengths 3 – 8 MPa

DBSs - bond to surface of smear layer (strategy 1) • Goal is leave the smear layer intact – smear layer is viewed to be protective – little or no etching • DBS interacts superficially with the dentin (no hybrid layer) • mechanism ? ? mechanical / chemical bond

Dealing with the smear layer - Strategies • bond primer to surface of smear layer. (strategy 1) • dissolve smear layer and demineralize near -surface dentin with an acid; treat demineralized dentin with primer. (strategy 2) • dissolve smear layer & demineralize nearsurface dentin with an acidic primer. (strategy 3)

DBS – dissolve smear layer with acid (strategy 2) Three Step (3 bottle) • Conditioner • Primer • “adhesive” resin 5 μm After treatment with acid, the smear layer has been removed and dentinal tubules are open.

Dentinal tubule diameter: Superficial vs. Deep Dentin The smaller area of intertubular dentin close to the pulp could mean lower bond strengths. That’s what was observed for some DBSs. Or maybe the tubules are the weak link? More area of tubules means weaker bonds? It is not known which factor causes the lower bond strength to deep dentin.

Conditioning with phosphoric acid demineralized dentin If dehydrated will collapse 1 μm Van Meerbeak et al. J Dent 1998 26: 1 -20

DBS – dissolve smear layer with acid (strategy 2) Three Step (3 bottle) • Conditioner • Primer • “adhesive” resin

Primers for enamel & dentin: Vocabulary – adhesives vs. primers Adhesives are applied between two materials. They adhere to each. Primers penetrate the surface of a material, changing the character of the surface

Primers for enamel & dentin: Primers penetrate the surface of a material, changing the character of the surface so that 1) an adhesive will adhere to the modified surface or 2) the second material will adhere to the modified surface without the use of an adhesive.

Primers for enamel & dentin: Goal: To modify the surface of enamel or dentin so that acrylic copolymers will copolymerize with the altered surface.

Primers for enamel & dentin: Primer Mechanisms: • Penetrates a porous surface & mechanically interlocks with that surface. • Copolymerizes with acrylic polymers placed on the surface

Primers for enamel & dentin: Penetration of surfaces promoted by: Etching the surface. High-surface-energy etched surfaces react with the liquid resin, causing it to more readily wet and penetrate the porous surface. Reducing the viscosity of the resin. Viscosity is decreased by adding diacrylate diluents to BIS-GMA. Such resins flow more easily into etched tooth structure.

Primers for enamel & dentin: Penetration of surfaces promoted by: Making the primer less hydrophobic. Adding hydrophilic moieties to an acrylic monomer will reduce its hydrophobicity, and thereby improve wetting and penetration of surfaces contaminated with aqueous fluids or surfaces within which such fluids are contained (e. g. , dentin).

Primers for enamel & dentin: Additional advantages of primers modified to be less hydrophobic: • damp or moist surfaces don’t interfere with wetting • resins are dissolved in low vapor pressure solvents; evaporation of the solvent results in high concentrations of primer resin in the conditioned surface.

Primers for enamel & dentin: Additional advantages of primers modified to be less hydrophilic: • as solvents evaporate they may chase fluids out of crevices thereby facilitating better penetration of the primer

Primer resins: HEMA H CH 3 C C H C O H C H OH hydrophobic methacrylate group HEMA hydroxyethylmethacrylate hydrophilic hydroxyl group Unlike many other acrylics, HEMA and poly. HEMA are soluble in water. Solutions of these will flow into hydrated demineralized dentin surfaces.

hybridization: The act of forming a hybrid layer. A hybrid layer is a surface layer of porous dentin or enamel that is interpenetrated on a micron scale by polymer.

Optibond FL hybrid layer 2. 0 μm

Hybrid layer resin between fibriles banded collagen 0. 20 μm

DBS – forming Hybrid Layer (strategy 2) • conditioned dentin: mixture of collagen & water • primer: hydrophilic acrylic resin dissolved in solvent (water, acetone, or ethanol) • primer diffuses into water incorporated in conditioned layer • solvent evaporates from primer

DBS – forming Hybrid Layer (strategy 2) • hydrophilic acrylic resin left behind • the hydrophilic acrylic monomer is polymerized, usually when the adhesive layer is cured. • hybrid layer: collagen embedded hydrophilic acrylic polymer

DBS – dissolve smear layer with acid (strategy 2) Three Step (3 bottle) • Conditioner • Primer • “adhesive” resin may have the advantage of protecting hydrophilic layer from the oral environment.

DBS – dissolve smear layer with acid (strategy 2) Three Step Products: • All-Bond 2 (Bisco) • Optibond FL (Kerr) • Scotchbond Multipurpose (3 M Espe)

DBSs – dissolve smear layer with acid (strategy 2) Bond 1 (Jeneric-Pentron) shear bond strength - 12. 6 MPa Vargas et al. Dent Mater 1997; 13: 316 - 324 adhesive resin composite hybrid layer 2 μm

DBSs - dissolve smear layer with acid (strategy 2) Syntac Single Component (Ivoclar-Vivadent America) shear bond strength - 7. 6 MPa Vargas et al. Dent Mater 1997; 13: 316 - 324 Maybe, incomplete adhesive layer is the reason for the relatively low bond strength 2 μm

DBS – dissolve smear layer with acid (strategy 2) Three Step (3 bottle) • Conditioner • Primer • “adhesive” resin These two can be combined in one bottle. Simpler systems work initially, but there is evidence that they are not a durable

DBS – dissolve smear layer with acid (strategy 2) Two Step (2 bottle) • Conditioner • Primer + adhesive resin

DBS – dissolve smear layer with acid (strategy 2) Two Step Products: • One-Step (Bisco) • Optibond Solo plus (Kerr) • Prime & Bond NT (Dentsply/Caulk) • Single Bond (3 M Espe)

DBSs - dissolve smear layer with acid (strategy 2) Single Bond (3 M Espe) shear bond strength 22. 2 MPa There is no evidence of an adhesive layer. The hybrid layer alone attracts water and may degrade. The more hydrophobic adhesive layer may offer protection to the Vargas et al. Dent Mater hybrid layer. 1997; 13: 316 - 324 2 μm

DBS: Strategy 2 - solvents Water: • Scotchbond MP (3 M-Espe) Ethanol-Water: • Optibond FL (Kerr) Ethanol: • Optibond Solo (Kerr)

DBS: Strategy 2 - solvents Ethanol - Acetone: • All-Bond 2 (Bisco) Acetone – Water: • Tenure Quik (Den-Mat) Acetone • Prime&Bond NT (Dentsply) • Solid Bond (Kulzer)

Dealing with the smear layer - Strategies • bond primer to surface of smear layer. (strategy 1) • dissolve smear layer and demineralize near -surface dentin with an acid; treat demineralized dentin with primer. (strategy 2) • dissolve smear layer & demineralize nearsurface dentin with an acidic primer. (strategy 3)

Primers for enamel & dentin: Penetration of surfaces promoted by: Making the primer acidic. Adding acidic moieties to an acrylic monomer enables it to etch tooth structure. The high energy of the etched surface is never reduced by exposure to the atmosphere or by rinsing. In principal, resin will be strongly attracted to this high energy surface thus increasing the likelihood that the resin will wet and penetrate the surface.

Primers for enamel & dentin: Advantages acidic primers: • etching produces high-energy surfaces that are attracted to primer resins • the porous subsurface produced by etching can never extend deeper than the primer penetrates – that is, the primer penetrates the entire depth of the etched zone

Comparing Phosphoric Acid & Acidic Primers: O Phosphoric Acid HO P OH OH Self-etching Primer (3 M – Unitek) Used for decades to etch enamel. Currently used in total etch. Below we add this group to an acrylic primer. O O C P OH O C

Acidic primers: Successful primers are all at least mildly acidic methacrylate group CH 2 C acidic O CH 3 C O hydrophobic O(CH 2)10 O P OH OH hydrophilic 10 – MDP (10 methacycloxydecyl dihydrogen phosphate) – [the primer in Panavia]

Comparing Dental Primers Primer Type in solvent hydrophilic unfilled resins useful for etched enamel only no no acidic no useful on etched dentin or enamel moisture insensitive self etching yes mildly useful on unetched dentin or enamel yes yes

DBS – use acidic primer (strategy 3) Two Step (2 bottle) • Separate enamel etch Some products are too weak to etch enamel, so a separate enamel etch is needed. • Self-etching primer (SEP) + resin

DBS – use acidic primer (strategy 3) Products: Two bottle: 1) SEP 2) “adhesive” • Clearfil SE Bond (Kuraray) • Clearfil Protect Bond (Kuraray) • Prelude (Danville Materials)

DBS – use acidic primer (strategy 3) Products: One bottle: SEP + resin together • Xeno IV (Dentsply / Caulk) * • Optibond All-on-One (Kerr) * • Clearfil S 3 Bond (Kuraray) • G-Bond (Kuraray) * requires two applications for bonding to dentin

DBS – use acidic primer (strategy 3) Products: Two bottle: 1) SEP 2) “adhesive” • Clearfil SE Bond (Kuraray) 20% Phenyl-P + 30% HEMA + water Phenyl-P is 2 -methacryloyloxyethyl phenyl phosphoric acid

DBS – advantages of SEPs • Simultaneous demineralization & resin impregnation • No post conditioning rinsing • Not sensitive to dentin wetness • Resin penetrates to the full depth of etched zone • Less post operative sensitivity ? ? More

DBS – advantages of SEPs • Less technique sensitive • Time saving

DBS – disadvantages of SEPs • Little clinical research has been done • Adhesion to enamel may be low in some systems • Some systems do not form durable bond

Technique for Total Etch Bonding

Total etch dentin bonding: etching time • etching time with H 3 PO 4 is often 15 s • extend by additional 15 s if dentin is sclerotic • more concentrated acids produce thicker hybrid layers ú bond strength is independent of hybrid layer thickness ú not known whether thickness affects the integrity of the H. L. (e. g. , the seal)

Total etch dentin bonding: etching time • etching time with H 3 PO 4 is often 15 s • careful not to over etch young dentin or deep dentin – some worry that etched dentin will not be penetrated by primers

Total etch dentin bonding: priming • primer is applied to moist dentin ú if too dry collagen fibrils may collapse ú bond strength will be low • primers that are dissolved in water will rehydrate the dentin – bond strength is regained

Total etch dentin bonding: priming • use air pressure for a few seconds to force the primer into the tubules • but some are concerned air pressure will increase the oxygen in the primer, which can inhibit its polymerization • danger of the above is balanced by the need to force the primer into tubules and side canals

Total etch dentin bonding: primers in acetone solvent • primers that are dissolved in acetone evaporate more quickly due to the low vapor pressure of the solvent • may “chase” water from between collagen fibrils

Total etch dentin bonding: primers in acetone solvent (2) • acetone solvent can evaporate – thickening the primer • some manufacturers mix the primer with excess solvent to prevent thickening – may require multiple layers • primers dissolved in acetone must be applied to moist dentin; water is necessary to rehydrate

Total etch dentin bonding: adhesives (e. g. intermediate resins) • adhesives usually contain mixture of both the hydrophilic primer monomers and a hydrophobic diacrylate monomers • do not use air pressure to thin this layer (some evidence of weakened bond – oxygen inhibition of polymerization ? ? )

Pulpal compatibility of hybrid-layer-forming adhesives: • Most studies find little pulpal response • One recent exception (Subay, 2000): ú some short term inflammation ú some evidence of bacteria ú concluded that the hybrid layer did not form a complete seal

Pulp Reaction beneath deep Cl V restorations 100 80 % with bacteria 60 40 20 none along wall 0 • • • Ca. OH 10 d Ca. OH 35 d 11 – 14 yr old premolars Calcium hydroxide – Dycal sealed with ZOE Dentin Bonding Agent – Scotchbond Multipurpose Plus DBA 10 d DBA 35 d into dentin Subay et al. , J Dent 2000; 28: 327 -332.

Pulp Reaction beneath deep Cl V restorations 100 % with inflamed cells 80 60 40 20 none along wall 0 • • • Ca. OH 10 d Ca. OH 35 d 11 – 14 yr old premolars Calcium hydroxide – Dycal sealed with ZOE Dentin Bonding Agent – Scotchbond Multipurpose Plus DBA 10 d DBA 35 d into dentin Subay et al. , J Dent 2000; 28: 327 -332.

Postoperative Sensitivity in Bonded Resin Composite Restorations

Bonding Systems for Clinical Trial of Class II Composite Restorations Code 3 step 2 step 1 step Product Description Scotchbond total etch w Multipurpose primer & adhesive Clearfil Photo etch Bond combined primer & adh Clearfil Liner self etching primer Bond Manufacturer 3 M Dental Kuraray Opdam et al. J Dent 1998; 26: 555 -562

Leakage along cervical margin of Cl II resin composite restorations 100 % in 80 category 60 40 0 3 step • • • 2 step 1 step ne el no am en tin n to de ty in i to in cav r o to flo 20 11 – 14 yr old premolars cervical margin 2 mm occlusal to CEJ one posterior resin composite used – Clearfil Ray Posterior Opdam et al. J Dent 1998; 26: 555 -562

Leakage along occlusal margin of Cl II resin composite restorations 100 80 % in category 60 40 20 • 11 – 14 yr old premolar 2 step 1 step ne no 3 step to l in me a en 0 Opdam et al. J Dent 1998; 26: 555 -562

Sensitivity to occlusal loading in Cl II resin composite restorations 100 80 % in category 60 40 20 3 step • • 2 step 1 step t e no itiv e ns itiv se ns se 0 11 – 14 yr old premolar No restoration was sensitive when exposed to a cold stimulus Opdam et al. J Dent 1998; 26: 555 -562

Retention of Bonded Class V Resin Composites Restorations

Bonded Resin Composite in Class V lesions – smear layer dissolved – dentin weakly etched Mirage 100 90 % Retained 80 70 60 50 40 30 20 1 yr. Tenure SB 2 2 yr. 3 yr. 4 yr. Time • • No retention grooves Enamel etching avoided Van Dijken Dent Mater 1994; 10: 319 -324

Bonded Resin Composite in Class V lesions – 3 -step system All-Bond Photobond Denthesive 100 90 % Retained 80 70 60 50 40 1 yr. 2 yr. 3 yr. Time • • No retention grooves Enamel etching avoided Tyas MJ. Int Dent J 1996; 46: 10 -14.

Bonded Resin Composite in Class V lesions – 3 -step system 100 %90 Retained 80 70 60 1 yr. 2 yr. 3 yr. Time • • • All Bond 2 (Bisco) No retention grooves Enamel & dentin were etched Mc. Coy et al. J Am Dent Assoc 1998; 129: 593 -599.

Bonded Resin Composite in Class V lesions – 3 -step system 103 % Retained 98 93 88 1 yr. 2 yr. 3 yr. Time • • • Clearfil Liner Bond (Kuraray) No undercuts Enamel etched ? ? Mandras et al. Oper Dent 1997: 22; 266 -270.

Bonded Resin Composite in Class V lesions – 3 -step system Retained 100 Not Discolored % Retained 90 80 70 60 1 yr. • Gluma 2000 (Bayer) • No retention grooves • Enamel & dentin were etched with an oxalic acid containing gel 2 yr. 3 yr. Time Mc. Coy et al. J Am Dent Assoc 1998; 129: 593 -599.

Bonded Resin Composite in Class V lesions – 3 -step systems SBMP Clearfil LB Bayer 1 Bayer 2 100 90 % Retained 80 70 60 50 40 1 yr. 2 yr. 3 yr. Time • • No retention grooves Enamel etching avoided Van Meerbeek et al. Quint Int 1996; 27: 775 -84.

Bonded Resin Composite in Class V lesions – 3 -step systems SBMP 50 % Discolored Margins. Clearfil LB Bayer 1 40 Bayer 2 30 20 10 0 1 yr. 2 yr. 3 yr. Time • • No retention grooves Enamel etching avoided Van Meerbeek et al. Quint Int 1996; 27: 775 -84.

Tensile Strength (MPa) Bonded Resin Composite in Class III lesions – 2 -step system (in vivo) – in dogs 30 25 20 15 10 5 0 1 d 180 d 360 d Time (days) • • • Clearfil Liner Bond II (Kuraray) Self-etching primer Microtensile w. area 0. 7 x 1. 4 mm Sano et al. J Dent Res 1999; 78: 906 -911.

Tensile Strength (MPa) Bonded Resin Composite in Class V lesions – 3 -step system (in vivo) – Cl I in primary molars 40 35 30 25 20 15 10 5 0 24 h 1 -2 y 2 -3 y Time • • Scotchbond MP (3 M) Microtensile w. area ? ? Hashimoto et al. J Dent Res 2000; 79: 509 (abstr 2924).

Tensile Strength (MPa) Resin Composite bonded to occlusal dentin – 3 -step system - aging 80 70 silicone oil 60 distilled water 50 40 30 20 10 0 3 wk 6 wk 12 wk Time • Scotchbond MP (3 M) • Microtensile w. area 0. 5 mm 2 Armstrong et al. J Dent Res 2000; 79: 453 (abstr 2476).

Microtensile bond strength tests – higher strengths: • Notice in the last slide that the bond strengths are extremely high • Due to the tiny bonded areas used in microtensile bond strength tests

Fabricating microtensile bond strength specimens:

microtensile specimen resin composite conventional specimen diameter < 1. 0 mm area less than 3. 14 mm 2 resin composite diameter 3 – 5 mm area between 12. 14 & 78. 5 mm 2 dentin This type of specimen gives larger bond strengths. 1 mm diameter 3 mm diameter A larger area surface area means that one is more likely to sample a defect that will reduce the bond strength

microtensile specimen conventional specimen resin composite typical bond strengths 40 – 80 MPa dentin typical bond strengths 12 - 25 MPa

Aging affects microtensile bond strength 60 24 h 4 y protected 4 y unprotected Sco tch bon d. M P Op tibo nd Tensile Strength (MPa) 40 20 0 Op tibo nd NOTE: Protected interfaces were not in direct contact with water three step So lo Sco thb ond 1 two step De Munck et al. 2003 J Dent Res 82: 136 -140.

Bonded Resin Composite on occlusal dentin – 3 -step system (in vitro) – bovine dentine 15 Tensile Strength (MPa) 10 5 0 1 d • • • Clearfil Photo Bond (Kuraray) Phosphoric acid etch Tensile w. area 4 mm dia. 1 yr Time 3 yr Burrow et al. Dent Mater 1996; 12: 302 -307.