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BONDING AGENTS :fundamentals in bonding and adhesion

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DrSnehangshuDutta

fundamentals in bonding and adhesion for good restoration outcomes

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1 FUNDAMENTALS OF BONDING AND ADHESION IN DENTISTRY PRESENTED BY DR SNEHANGSHU DUTTA PG SECOND YEAR DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS
2 DEFINITIONS ADHESION: ”the state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking forces or both”. (ASTM) Adhesion Latin adhaerere (‘to stick to’) “Adhesive” The substance added to produce adhesion “ Adherend” The material to which it is applied A solid is the adherend and liquid is the adhesive
3 Key steps to the development of good adhesion. A. Clean adherent (devoid of smear layer or contaminants). B. Effective wetting of the substrate by the adhesive. C, Intimate adaptation of the adhesive to the intricacies of the substrate (avoiding voids or entrapped air). D Effective mechanical bonding. E, complete curing of the adhesive CRITERIA FOR OPTIMALADHESION
4 Possible mechanisms of bonding which are as follows: 1. Mechanical—Penetration of resin and formation of resin tags within the tooth surface. 2. Adsorption—Chemical bonding to the inorganic component (hydroxyapatite) or organic components (mainly type I collagen) of tooth structure. 3. Diffusion—Precipitation of substances on the tooth surfaces to which resin monomers can bond mechanically or chemically. 4. A combination of the previous three mechanisms
5 • For good adhesion, close contact must exist between the adhesive and the substrate (enamel or dentin). The surface tension of the adhesive must be lower than the surface energy of the substrate. • Failures of adhesive joints occur in three locations, which are generally combined when an actual failure occurs: 1. cohesive failure in the substrate; 2. cohesive failure within the adhesive; and 3. adhesive failure, or failure at the interface of substrate and adhesive.
6 FACTORS AFFECTING ADHESION Surface Energy: • The energy of a solid on the outer surface is comparatively higher than its interior. • The harder the surface, the higher the surface energy and adhesive properties.
7 2. Wetting: • The wetting ability of a liquid adhesive depends upon the surface energy and cleanliness of the adherend. • Higher the surface energy, greater the wetting capability. • Contamination of the substrate surface also reduces wetting by the adhesive. 3. Contact Angle- • It is a measure of wettability and is the angle formed by the adhesive with the adherend at the interface. • Smaller the contact angle greater is the wettability of the adhesive. Degree of contact angle influences the wetting of surface; (A) When contact angle is small, wettability of the adhesive is better; (B) and (C) When contact angle is large, liquid does not wet the surface completely Air incorporated in the irregularities at the interface despite low contact angle of the adhesive. Such areas are points of stress concentration and promote adhesive failure
8 TRENDS IN RESTORATIVE DENTISTRY Adhesive restorative techniques are currently used to accomplish the following • Restore Class I, II, III, IV, V and VI carious lesions or traumatic defects. • Change anterior teeth’ shape and color (e.g., with full or partial resin veneers). • Improve retention for porcelain-fused-to-metal (ceramo- metal) or metallic crowns. • Bond orthodontic brackets. • Bond fractured fragments of anterior teeth. • Bond splints for tooth luxation and periodontally involved anterior teeth and conservative tooth replacement prostheses. • Repair existing restorations (composite, amalgam, ceramic or ceramo-metal). • Provide foundations for crowns. • Desensitize non-carious cervical lesions (NCCLs) and exposed root surfaces. • Impregnate enamel and dentin, making them less susceptible to caries. • Bond prefabricated fiber, metal, and cast posts. • Reinforce fragile endodontically treated roots internally. • Seal root canals during endodontic therapy. • Seal surgically resected root apices. • Bond all-ceramic restorations. • Seal pits and fissures.
9 Fig 1: (A) Intraoral frontal view of a 20-year-old female presenting with complicated crown fracture on tooth 9 after endodontic treatment. The fracture extends subgingivally on the mesial aspect of the lingual surface. (B) A two-step etch-and- rinse ethanol-based adhesive applied to the crown fragment and tooth. (C) Extraoral view 6 months after rebonding. (D) Extraoral view 3 years after rebonding. Fig 2: (A) Preoperative view of anterior teeth in a 24-year-old patient with defective composite restorations. The treatment plan included bonded porcelain veneers on teeth 7, 8 and 10 to match the natural aspect of tooth 9; (B) porcelain veneers were bonded with a two-step etch-and-rinse adhesive and a light- activated resin cement and (C) final aspect 1 week after the bonding procedure.
10 TOOTH AS A SUBSTRATE FOR BONDING Tooth Surface & Bonding Insights • Enamel: Better bonding on prism ends than sides. • Fluoridated enamel: Harder to bond—low surface energy. • Dentin: Moisture is the main bonding challenge. • Tubule density: • Near pulp: ~45,000/mm² → high permeability. • Near DEJ: ~20,000/mm² → less permeability. • Superficial dentin: More solid, less moisture = better bonding potential
11 REQUISITE OF AN IDEAL BONDING AGENT • Biocompatible. • Bond effectively to both enamel and dentin. • Strength to resist failure as a result of masticatory forces. • Mechanical properties close to tooth structure. • Resistant to degradation in oral environment. • Easy to use.
12 ENAMELADHESION • Buonocore envisioned the use of acids to etch enamel for sealing pits and fissure. • Etchant: Most current phosphoric acid gels have concentrations of 30%–40 %, with 37% phosphoric acid gel being the most common. • Etch time: Currently, an etching time of 15s is recommended. Studies using scanning electron microscopy (SEM) showed that a 15-s etch resulted in a surface roughness similar to that provided by a 60-s etch. • Bond strength (>20 MPa). As measured in the laboratory, shear bond strengths of composite to phosphoric acid-etched enamel usually exceed 20 Mpa.
13 Phosphoric acid as an etchant: Buonocore :acid etching with 85% phosphoric acid for 30 sec 50 % phosphoric acid for 60 seconds • monocalcium phosphate monohydrate precipitate Concentrations below 25% • Dicalcium phosphate monohydrate precipitate Concentrations above 40% • Dissolve less calcium and etch patterns with poorer definitions 37% for 15 sec is considered appropriate
14 Acid Etching Essentials • Gel > Liquid for controlled placement. • Both forms give similar etching patterns. • Gel = Acid + colloidal silica/polymer beads. • Primary teeth need longer etching → more aprismatic enamel.
15 CONDITIONING AND ETCHING OF ENAMEL Conditioning vs. Etching • Conditioning = Removes organic layer → better enamel bonding. • Etching = Demineralizes surface calcium. • Gel use? → Double rinse to remove cellulose vehicle. • Etched enamel when dry = matte white/frosted look.
16 • How Acid Etching Transforms Enamel 1. Strips pellicle → exposes enamel crystallites 2. Removes ~10 μm of enamel 3. Creates pores (5–50 μm deep) 4. Boosts wettability & surface area 5. Raises surface energy → activates polar sites 6. Resin flows into pores → forms strong resin tag
17 • LASERS IN ENAMEL ETCHING 1. The use of lasers as an alternative to conventional acid etching. 2. Types of Lasers Used: Er:YAG (Erbium: Yttrium-Aluminum-Garnet) Er,Cr:YSGG (Erbium, Chromium: Yttrium-Scandium-Gallium-Garnet) CO Laser, Nd: YAG ₂ Advantages Over Acid Etching: • No need for chemical agents (ideal for children or sensitive patients) • Reduces risk of microleakage and demineralization • Can sterilize the surface and reduce bacterial load • No smear layer formation Comparative Evaluation of Acid Etching and Laser Etching Following the Application of Chlorhexidine on the Aesthetic Bracket Nidhal H Ghaib*, Bayan Ghadban College of Dentistry, University of Baghdad, Iraq
18 Enamel Etching Patterns • Type I: dissolution of prism cones without the dissolution of prism peripheries. • Type II: opposite of type I. Peripheral enamel is dissolved, but the cores are left intact. • Type III: less distinct than the other two patterns. Includes areas that resemble other patterns and areas not related to enamel prism morphology.
19 -Type IV: presents as a random scattering of shallow depressions. No clear preference for either prism cores or peripheries. -Type V: etching, like Type IV, lacks visible prism outlines. WHAT IS MICRO AND MACROTAGS? • Resin tags which form in the enamel rod peripheries, i.e. between enamel prisms are known as MACROTAGS. • A much finer network of thousands of small tags form across the end of each rod where individual hydroxyapatite crystals have been dissolved leaving crypts outlined by residual organic matter. • These fine tags called MICROTAGS.
20 RESIN MICRO TAG MECHANISM OF ENAMEL ADHESION Acid etching transforms the smooth enamel into an irregular surface and increases its surface free energy. [Fig1] Application of a fluid resin-based material to the irregular etched surface, facilitates penetration of the resin into the surface, aided by capillary action Monomers in the material are then polymerized, and the material becomes interlocked with the enamel surface. [Fig 2] The formation of resin microtags within the enamel surface is the fundamental mechanism of resin–enamel adhesion.
21 Fig 1 Scanning electron micrograph of enamel etched with 35% phosphoric acid (3M Oral Care) for 15 s. Fig 2 A and B, Transmission electron micrographs of the enamel-adhesive interface after application of Adper Single Bond (3M Oral Care) as per manufacturer’s instructions. Acid etching with 35% phosphoric acid opened spaces between enamel prisms (arrows), allowing the permeation of resin monomers between the crystallites (arrowheads). A, Adhesive; E, enamel.
22 BONDING TO DENTIN • Adhesive materials can interact with dentin in different ways— mechanically, chemically or both. • Dentin adhesion relies primarily on the penetration of adhesive monomers into the network of collagen fibrils left exposed by acid etching. (A) Dentin etched with 35% phosphoric acid and (B) higher magnification view of etched dentin. Col, Collagen exposed by the acid; D, normal dentin; T, dentinal tubule; S, residual silica particles used as acid gel thickener.
23 MECHANISM OF DENTIN BONDING • Ionic interaction between Ca² ions in the ⁺ inorganic phase and negatively charged groups in the adhesive. • For the organic phase, bonding occurs via interactions with –NH, –CONH, –OH, and – COOH groups in collagen. • Effective adhesion relies on hydrophilic monomers that infiltrate the conditioned collagen network. Bonding to inorganic portion of dentin Bonding to the organic portion of dentin Mechanism of bonding: (A) Bonding mechanism with intervening adhesive and (B) Bonding to inorganic or organic portion of dentin.
24 Mechanical Conditioning: Micro-abrasion is used to condition the dentin mechanically Within the limitations of this study, the following conclusions can be drawn: • APA with aluminum oxide particles had no negative effects on the bond strength of resin-based materials to dentin. • In a few subgroup analyses, air abrasion was able to improve the immediate bond strength to dentin when the particle size was >30 lm and air pressure was >5 bar. • APA duration had no significant effect on immediate dentin bond strengths
25 ROLE OF PRIMING IN ENAMELAND DENTIN ADHESION •Priming is the second step in the adhesive bonding process. •Primers contain hydrophilic monomers like HEMA and 4-META. •Solvents like ethanol or acetone help displace water from dentin. •Primer enables resin penetration into moist, demineralized dentin. •Even and uniform application ensures optimal bond strength.
26 Acetone has a relatively high vapor pressure value (184 mmHg at 20°C) compared to ethanol (43.9 mmHg at 20°C) and water (17.5 mmHg at 20°C). A higher vapor pressure will allow the solvent to evaporate more easily. As the solvent evaporates, the viscosity of the dentin bonding agent increases, which decreases the ability of the bonding system to penetrate around the exposed collagen fibers and the opened dentinal tubules, consequently inhibiting the proper bond formation ROLE OF SOLVENTS
27 CHALLENGES IN DENTIN BONDING FIG 1 FIG 2 Scanning electron micrograph of dentin that was fractured longitudinally to show dentinal tubules •Enamel is over 90% hydroxyapatite, making it highly mineralized. •Dentin has more water and organic material, mainly type I collagen. •Dentin contains tubules that connect the pulp to the enamel surface. •Inter-tubular dentin allows fluid and fibril movement through tiny channels. •Bond strength is lower in deep dentin compared to superficial dentin.
28 ROLE OF SMEAR LAYER IN DENTIN BONDING The smear layer is a byproduct of dental instrumentation that coats dentin surfaces (1–2μm thick) and penetrates dentinal tubules (1–5μm) as smear plugs. It consists of: • Solid phase: Debris of denatured collagen and mineral • Liquid phase: Fluid-filled channels around the debris • While it protects dentin, it can impede resin bonding by acting as a barrier to adhesive penetration. • However, some researchers suggest that it may also play a protective role by reducing the movement of bacteria and harmful substances toward the pulp. Scanning electron micrograph of a smear plug blocking the entrance of a dentinal tubule. SP, Smear plug. Reasons for retaining smear layer on the bonding substrate are: • Retention of smear layer lowers dentin permeability • Prevents decrease in bond strength seen with some bonding systems as deeper dentin is prepared • Greatly lowers the effect of pulpal pressure on
29 CONFIGURATION FACTOR • Stress relief within a three-dimensional bonded restoration is limited however by its configuration factor (C-factor). • Stress relief is limited because flow can occur only from the single free surface. • Bond disruption and marginal gaps around restorations may increase microleakage and potential postoperative sensitivity. POLYMERIZATION SHRINKAGE STRESS • Several clinical strategies have been suggested to reduce the effects of polymerization shrinkage stress, including I. control of curing light irradiance II. incremental insertion techniques III. application of intermediate low-modulus liners
30 COEFFICIENT OF THERMAL EXPANSION • Whenever a restoration is exposed to wide temperature variations the restoration undergoes volumetric changes of different magnitude compared with those of the tooth structure. • Microleakage around dentin margins is potentiated by this discrepancy in linear CTE between the restoration and the substrate. OCCLUSAL LOADING • Loading and unloading of restored teeth can result in transitional or permanent interfacial gaps. • Additionally, the tooth substrate itself might be weakened by cyclic loading. • Studies have found that cyclic loading and preparation configuration significantly reduced the bond strengths of self-etch and etch-and-rinse adhesives.
31 EVOLUTION OF DENTIN BONDING AGENTS 1. Historical Strategies i First generation (1965) ii. Second generation (1978) iii. Third generation (1984) 2. Current strategies: i. Etch and rinse adhesives a. Three-step etch and rinse adhesive (fourth generation) b. Two-step etch and rinse adhesive (fifth generation) ii. Self-etch adhesives a. Two-component self-etch adhesive (sixth generation) — Two-step two- component self-etch adhesive — One-step—two-component self-etch adhesive b. Single component—one step—self-etch adhesive (seventh generation)
32 FIRST GENERATION: • Introduced in 1965 • Chemical: Surface-active co-monomer NPG-GMA • Mechanism of action: Theoretically, this co-monomer could chelate with calcium on the tooth surface to generate water-resistant chemical bonds of resin to dentinal calcium. • Ex- Cervident (SS White) • Cosmic Bond. • Palakav (Kulzer, USA). • Bond strength: 2-3 Mpa DRAWBACKS- • Low bond strength. • No improvements in marginal leakage when compared to conventional unfilled bonding agent.
33 SECOND GENERATION • Introduced in 1978. • Chemical: Phosphate-ester material (phenyl-P and hydroxyethyl methacrylate [HEMA] in ethanol). • Bonding mechanism- Based on the polar interaction between negatively charged phosphate groups in the resin and positively charged calcium ions in the smear layer. • Mean shear bond strength- 1-5 MPa EXAMPLES: • Clearfil bond system F (Kuraray) • Scotchbond (3M ESPE) • Bondlite (Kerr) • Prisma Universal Bond (Dentsply). CLINICAL RESULT: • Smear layer was the weakest link due to its relatively loose attachment to dentin surface.
34 DRAWBACKS OF FIRST AND SECOND GENERATIONS • Lack of adequate bond strength. • Being hydrophobic in nature, close adaptation to the hydrophilic dentin could not be achieved. • Adhesive bonded to the smear layer rather than the dentin. • Lack of sufficient knowledge about the presence and nature of the smear layer. • Biocompatibility was not appropriate.
35 THIRD GENERATION • Chemical: It was a phosphate-based material containing HEMA and a 10-carbon molecule known as 10 MDP(10-methacryloxydecyl dihydrogen phosphate), which includes long hydrophobic and short hydrophilic component. • Mechanism of action: 1. The concept of phosphoric acid-etching of dentin before application of a phosphate ester type bonding agent was introduced by Fusayama et al in 1979. 2. Designed not to remove the entire smear layer but, rather, to modify it and allow the penetration of acidic monomers, such as phenyl-P or PENTA. • Brand names: 1. Clearfil New Bond (Kuraray Co, Ltd, Osaka, Japan) 2. Scotchbond 2 (3M ESPE Dental Products) • Clinical result: Clinical results were mixed, with some reports of good performance and some reports of poor performance.
36 CURRENT OPTIONS FOR RESIN–DENTIN BONDING Mechanism of Action – Three-Step Etch-and-Rinse Adhesive Acid Application to Dentin ↓ Smear Layer Removal & Dentin Demineralization Opens dentinal tubules Exposes collagen fibers Increases microporosity ↓ Depth of Demineralization Up to ~7.5 µm depending on acid type, time, and concentration ↓ Primer Application Increases critical surface tension of dentin ↓ Bonding Resin Application Penetrates intertubular dentin → Forms Hybrid Layer Penetrates & polymerize open dentinal tubules → Forms Resin Tags
37 FOURTH GENERATION Components: Etchant gel + primer (bottle I) + adhesive bottle (bottle II) They include three essential components that are applied separately and sequentially: 1. Phosphoric acid-etching gel that is rinsed off. 2. Primer containing reactive hydrophilic monomers in ethanol, acetone, or water 3. Unfilled or filled resin bonding agent. It contains hydrophobic monomers such as Bis-GMA, frequently combined with hydrophilic molecules such as HEMA Example: 1. All-Bond 2 and All-Bond 3 (Bisco, Inc, Schaumburg, IL) 2. OptiBond FL (Kerr Corporation) 3. Adper Scotchbond Multi-Purpose (3M ESPE) Bond strength: Varies from 17—30 MPa Clinical result: Adhesive systems based on the total-etch philosophy have been proven to be clinically successful.
38 FIFTH GENERATION: TWO STEP ETCH AND RINSE ADHESIVE • One bottle system. • Etchant, Primer + Adhesive (single bottle). Mechanism of Action: The primer and adhesive are combined into a single solution containing both hydrophilic(PRIMER) and hydrophobic components(ADHESIVE). Due to the higher hydrophilicity, these adhesives are more prone to hydrolytic degradation. Examples: Prime and Bond (Dentsply, Caulk), and Prime and Bond 2.1, Opti Bond Solo (Kerr), Single Bond (3M) etc. • Mean BS- 17-24 MPa. ADVANTAGES: • Bond strength is sufficient. • Time saving and simple to use. • Elimination of washing out of the acidic gel, therefore elimination of risk of collagen collapse. • Combination of etching and priming steps decreases the working time. DISADVANTAGES • Solution must be refreshed continuously.
39 Contemporary dentin bonding agents-A review. Journal of Scientific Dentistry, 8(2), 2018 HYBRID LAYER • Definition: The hybrid layer is a resin–dentin interdiffusion zone formed by the infiltration of adhesive monomers into the demineralized dentin collagen matrix. • It was first introduced by Nakabayashi et al. (1982). • The distinct zone between the bulk adhesive and non- demineralized dentin consisting of 50% collagen matrix and 50% resin is termed as hybrid layer. • There are three different zones in hybrid layer: 1. Top zone: It consists of loosely arranged collagen fibrils with inter-fibrillary spaces filled with the adhesive resin. 2. Mid-zone: This consists of collagen fibrils infiltrated with resin with residual hydroxyapatite crystals between collagen. 3. Bottom zone: It shows an abrupt transition to the underlying unaltered dentin with partially de-mineralized dentin containing hydroxyapatite crystals enveloped by adhesive resin.
40 ROLE OF HYBRID LAYER IN DENTIN BONDING • Micromechanical retention: Enhances adhesion through interlocking of resin tags with collagen matrix. • Seal integrity: Acts as a barrier to bacterial infiltration and fluid movement. • Bond strength: Critical for achieving durable resin-dentin bonds. • Stress distribution: Helps distribute occlusal and thermal stresses across the bonded interface. The promotion of adhesion by the infiltration of monomers into tooth substrates Nobuo Nakabayashi, Katsunori Kojima, and Eiichi Masuhara Institute for Medical and Dcntal Engineering, Tokyo Medical and Dental University, Kanda Surugadai, Chiyoda-ku, Tokyo 101, japan
41 Self-Etch Adhesives Concept: Omission of a separate etching step. • Two types of self-etch adhesives are available: 1. Two-component self-etch adhesive (sixth generation) i Two-step: Two-component—self-etch adhesive ii. One step: Two-component self-etch adhesive 2. Single component—one step: self-etch adhesive (seventh generation) • Advantages: 1. Less post-operative sensitivity. 2. Clinician-friendly 3. Less technique sensitive. 4. Reduces the possibility of over-wetting or over-drying of dentin. 5. Less discrepancy between depth of demineralization and the depth of resin infiltration.
42 Disadvantages: 1. Do not etch enamel as well as phosphoric acid. 2. When enamel bonds are stressed, they undergo deterioration. 3. Strong one-step SEA continues demineralization and result in collagen fibre exposure. 4. The presence of the hybrid layer that is not completely infiltrated may increase the stresses in resin dentin interfaces.
43 TWO-STEP SELF-ETCH ADHESIVES • Japan • Two-step SEAs contains an acidic monomer that functions as a self-etching primer and a hydrophobic, non-solvent-bonding resin. • The acidic primers include a phosphonated and/or carboxylated resin molecule that performs two functions simultaneously— etching and priming of dentin and enamel. • Mechanism of action: The bonding mechanism of self-etch adhesives (SEAs) involves: 1.Simultaneous etching and priming of enamel and dentin, creating a continuous bond. 2.Incorporating smear plugs into resin tags for better adhesion. Bonding to dentin using a self-etch primer.
44 SEAs are classified into three categories based on pH: • Mild SEA (e.g., Clearfil SE Bond) – better dentin bonds, weaker enamel bonds.(overcome by selective enamel etching) • Moderate SEA • Aggressive SEA – better enamel bonds, weaker dentin bonds. Selective enamel etching improves marginal adaptation and reduces marginal discoloration compared to the self-etch strategy. Monomer 10 MDP has been shown to bond chemically to hydroxyapatite through a mechanism known as nano- layering Adhesives pH Strong ( 1 or less) NRC( Dentsply) Adper prompt 1 0.4 Intermediary( 1.5) Xeno III( Dentsply) AdheSE primer( Vivadent) Optibond Solo Plus SE primer( Kerr) I Bond 1.4 1.4 1.5 1.6 Mild( around 2) Clearfil SE Panavia ED primer mixed( Kuraray) 1.9 2.6 Van Meer beck et al 2003
45 SIXTH GENERATION • Sixth generation BA are further divided into two types- Type 1 (Self-etching primer and adhesive) • Available in light-cure or dual-cure. • Two bottles, Liquid 1 (Acidic Primer), Liquid 2 (Adhesive). • Example: Opti Bond Solo plus(self etch), Clearfil SE bond • Described as non rinsing conditioners or self priming etchants. Type 2 ( Self-etching adhesive) • Available in light-cure type • Two bottles, containing acidic primer and adhesive; a drop of each liquid is mixed and applied to the tooth EXAMPLES- • Adper Prompt L Pop (3M ESPE) • Xeno III (Dentsply)
46 ONE-STEP SELF-ETCH ADHESIVES • Etchant+primer+adhesive= single bottle system Mechanism of action: In these one-step SEAs contain uncured ionic monomers ,contact the composite restorative material directly. Application of multiple coats significantly increases dentin bond strengths and decreases leakage. Limitation: • Their acidic unreacted monomers are responsible in part for the incompatibility between these simplified adhesives and self-cured composites. • Facilitates hydrolytic degradation of the resin dentin interface. ( they behave as semi-permeable membrane. • One-step SEAs tend to behave as semipermeable membranes, facilitating hydrolytic degradation of the resin–dentin interface.
SEVENTH-GENERATION/ALL-IN-ONE • Available both as light cure and dual cure type • All three components are combined in a single bottle, and they require no mixing. • More acidic pH < 1. . Eg- G-Bond, i-Bond (self etch), AdheSE One F (Ivoclar Vivadent), Adper Easy One (3M ESPE) DISADVANTAGES • Relatively short shelf-life. • Their composition is very hydrophilic leading to leaching of unpolymerized monomers or hydrolytic degradation products through water-filled channels called water trees. 47
48 EIGHT GENERATION • Modified version of 7th generation of bonding agent. • Futurabond DC introduced by Voco America. • One-step dual-cured, non-filled, self-etch adhesive. • Chemically cured mode makes the product suitable for root canals. ADVANTAGES • Can be used with light-cure, dual-cure and self-cure composites. • Moisture tolerant. • Contains fluorides. • Nano-fillers help in better cross-linking of bonding resin components.
49 UNIVERSAL ADHESIVES Universal adhesives offer flexible use across bonding strategies: self-etch, etch-and-rinse, or selective enamel etch. • Function as one-step SEAs Mechanism: • Contain 10-MDP → forms strong, durable chemical bonds with hydroxyapatite via nano-layering • More effective chemical bonding in dentin due to smaller and fewer hydroxyapatite crystals. • Active application (rubbing) boosts bonding by enhancing 10-MDP contact. • Limitations: 1. Extent of chemical bonding is weak 2. Presence of HEMA hampers bonding ability as it reduces the formation of MDP-Ca salts. 3. Interfacial bonding degradation. (in self-etch or etch-and-rinse manner)
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51 ROLE OF SILANE IN ENAMELAND DENTIN ADHESION Silane coupling agents are bifunctional molecules used in dental adhesives, especially for bonding resin composites to ceramic surfaces, and in resin-based cements. Their use in enamel and dentin adhesion is less direct but still important, especially in universal adhesives that aim to enhance bonding to various dental substrates. Structure & Mechanism of Silane: • One end: Organofunctional group (e.g., methacrylate) → bonds with resin matrix • Other end: Silane group (Si–O–R) → bonds with inorganic materials (like glass, hydroxyapatite) • In the presence of moisture, silane hydrolyzes into silanol groups (Si–OH) which form covalent bonds with hydroxyl groups on tooth or ceramic surfaces. Role in Enamel and Dentin Bonding: 1. Coupling agent 2. Improves wetting 3. Increases Bond Strength 4. Used in universal Adhesives 5. Promotes Long-Term stability Reference: Silane adhesion mechanism in dental applications and surface treatments: A review Jukka Pekka Matinlinna , Christie Ying Kei Lung , James Kit ∗ ∗ Hon Tsoi
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53 CLINICAL CONSIDERATIONS DURING ADHESION MOIST VERSUS DRY DENTIN SURFACES Moist Bonding Technique with Etch-and Rinse Adhesives: • Drying the dentin surface with air would cause the dentinal collagen to collapse, which would prevent the monomers from penetrating the nanochannels. • The ‘moist bonding’ technique used with etch-and-rinse adhesives prevents the spatial alterations (i.e., collagen collapse) that occur on drying demineralized dentin Air Drying of Etched Dentin: • When etched dentin is dried using an air syringe, in vitro bond strengths decrease substantially, especially for acetone-based and (to a lesser extent) ethanol-based dentin adhesive systems.
54 ROLE OF WATER IN SELF-ETCH ADHESIVES • In self-etch adhesives (SEAs), water plays a crucial role by ionizing acidic monomers and solubilizing calcium and phosphate ions for effective bonding. • Unlike etch-and-rinse adhesives, SEAs combine etching and priming in one step using acidic monomers. • Water content (10–30%) is essential but must be balanced: • More water improves ionization and demineralization depth. • Too much water dilutes monomers, reducing bonding strength. • One-step SEAs are more vulnerable to water-related issues like higher water absorption and lower mechanical properties, compared to two-step SEAs, which are more stable.
ROLE OF PROTEINS IN DENTIN BONDING • Collagen type I is the main organic component of dentin. In dentin bonding, ideally collagen should be demineralized as minimally as possible, keeping the demineralized collagen hydrated and infiltrated with a hydrophilic adhesive to ensure proper penetration within the exposed collagen fibrils. • Ninety per cent of the protein content of dentin is type I collagen and the remaining are non collagenous proteins. The non collagenous proteins fall into several categories: 1. proteoglycans, 2. SIBLINGs (small integrin-binding ligand, N-linked glycoprotein), 3. growth factors, 4. matrix metalloproteinases (MMPs) and 5. serum proteins 55
56 Role of Matrix Metalloproteinases Matrix metalloproteinases (MMPs) are important non-collagenous proteins in dentin bonding. They are zinc- and calcium-dependent enzymes capable of degrading the extracellular matrix. Key MMPs in dentin: • MMP-2 & MMP-9 (gelatinases) • MMP-8 (collagenase) • MMP-20 (enamelysin) • After acid etching, exposed collagen fibrils not protected by resin can be degraded by MMPs. Protease inhibitors can block MMP activity, helping preserve the hybrid layer and improve resin–dentin bond durability, especially in the early months after restoration.
57 Role of Dentin Phosphoprotein • Some non-collagenous proteins in dentin act as nucleators for mineralization, with dentin phosphoprotein (DPP) being the most prominent. • DPP is highly acidic due to its aspartic acid content, allowing it to bind calcium and aid in dentin formation by delivering calcium to collagen. • Biomimetic analogues like polyacrylic, polycarboxylic, and polyvinylphosphonic acids mimic DPP’s function. • These can form amorphous calcium phosphate precursors and bind to collagen, promoting intrafibrillar mineralization in hybrid layers when used with calcium hydroxide–releasing materials. ‘Microleakage’ is defined as the passage of bacteria and their toxins between restoration margins and tooth preparation walls. Clinically, microleakage becomes important when one considers that pulpal irritation is more likely caused by bacteria than by chemical toxicity of restorative materials.
58 Nanoleakage Nanoleakage refers to tiny porosities in the hybrid layer or its interface with mineralized dentin, allowing penetration of silver nitrate particles. Using ammoniacal silver nitrate, two nanoleakage patterns are observed: • Spotted pattern: Seen in SEAs, likely due to incomplete resin infiltration. • Reticular pattern: Seen in the adhesive layer, likely from residual water, forming structures known as “water trees.” • Both patterns indicate compromised bonding and may affect long-term durability. Nanoleakage under the electron microscope. (A) Spotted pattern in the hybrid layer formed by a one-step self-etch adhesive under the transmission electron microscope. (B) Reticular pattern and ‘water trees’ in the adhesive layer formed by a one step self-etch adhesive under the scanning electron microscope in backscattered mode.
59 BONDING IN OTHER CLINICAL SITUATIONS BONDING SPECTRUM IN DENTISTRY • BONDING OF GLASS IONOMERS TO HARD TISSUES: Calcium ions from the tooth structure (particularly hydroxyapatite) interact with the carboxylate groups of polyalkenoic acid in GIC, creating ionic bonds. 🧷 This direct ionic interaction leads to chemical adhesion to both dentin and enamel.
60 • BONDING OF COMPOSITE TO GLASS IONOMERS: Glass-ionomer is invariably used as a substitute for dentin under composite resins. This technique is commonly known as the bilayered technique (Sandwich technique) in which the enamel and cement are etched prior to placement of the restorative resin. Low viscosity resins are advisable as they have a lower contact angle and better wetting ability with the substrate. • BONDING OF COMPOSITE TO PORCELAIN: Bonding of porcelain to composite is partly because of mechanical interlocking and partly because of chemical union. Mechanical retention is obtained by etching the fitting surface of porcelain with dilute hydrofluoric acid or grit blasting with alumina to increase surface roughness. The optimal time for etching depends upon the etchant concentration as well as the type of porcelain used. To improve upon the mechanical attachment, gap between the bonding medium and the porcelain should be minimized by using an intermediate low viscosity resin which penetrates the pores by capillary action. • BONDING OF AMALGAM TO RESIN: Bonding of amalgam to resin is a relatively new treatment modality and has made bonding between amalgam and tooth structure quite a successful possibility. Agents that can be used for bonding amalgam to the substrate are All Bond, Liner Bond-2, Amalgam bond and Panavia. A specific feature desired in these materials is that they should have dual characteristics to achieve optimal wetting.
61 FAILURE OF ADHESIVES 1. MATERIAL FACTOR: Thorough knowledge of the chemistry of the material to be used is mandatory for successful bonding. 2. SUBSTRATE: Variability of the substrate has been shown to have a major effect on the clinical performance of adhesive systems 3. SIZE AND SHAPE OF LESION: The Size of the lesion or the area of dentinal substrate available for bonding is critical for adhesion. 4. MAXILLARY VERSUS MANDIBULAR ARCH: Better adhesion results are expected in the maxillary arch because of the lesser chances of moisture contamination and lower tooth flexure effects in the upper jaws. 5. PATIENT’S AGE: With age, the dentin becomes sclerosed, and the sclerosis is associated with a decrease in clinical adhesiveness and hence a higher failure rate. 6. TOOTH FLEXURE: More recently, tooth flexure is a probable factor in influencing the retention of adhesive restorations, especially the cervical restorations. 7. DENTIN WETNESS: The bonding agents with effective wetting capability ensure successful bonding. 8. ELASTIC BONDING CONCEPT: Composite resins shrink during polymerization. In order to protect the tooth composite interface from debonding during polymerization, the intervening adhesive resin should Diagram illustrating different positions of failure at the resin-adhesive-tooth interface (i) Between the mineralized and demineralized dentin (ii) Between demineralized dentin and bonding resin (iii) Within the bonding resin; and (iv) Between the bonding resin and composite resin
62 SUMMARY • Reliable bonding of resins to enamel and dentin has revolutionized the practice of operative dentistry. • Improvements in dentin bonding materials and techniques are likely to continue. • Even as the materials themselves become better and easier to use. • However, proper attention to technique and a good understanding of the bonding process remain essential for clinical success. • With advancements from the early generations to today’s universal adhesives, we've seen significant improvements in technique sensitivity, bond strength, and clinical outcomes. • Understanding the chemistry, application protocols, and indications of different bonding systems is essential for achieving long-term success in restorative procedures. • In conclusion, bonding agents have revolutionized restorative dentistry by enabling strong, durable adhesion between dental materials and tooth structures. • As research continues, future innovations promise even more efficient and biocompatible bonding solutions, enhancing both clinician performance and patient care.
63 REFERENCES • Sturdevant’s art and science of operative dentistry 4th edition • Bonillaguet ,s. and wataha; Future direction in bonding resin to dentin pulp complex 31,385,2004 • Textbook of operative dentistry 4th edition Vimal K Sikri • Pashley at el; State of the art etch and rinse adhesive; 27,1,2011 • Munck J at el; bonding effectiveness of self-adhesive composite to dentin and enamel. Dent mater 29,2,2013.
64 THANK YOU “The bond that links your true family is not one of blood, but of respect and joy in each other’s life”. - Richard Bach

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BONDING AGENTS :fundamentals in bonding and adhesion

  • 1. 1 FUNDAMENTALS OF BONDING AND ADHESION IN DENTISTRY PRESENTED BY DR SNEHANGSHU DUTTA PG SECOND YEAR DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS
  • 2. 2 DEFINITIONS ADHESION: ”the state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking forces or both”. (ASTM) Adhesion Latin adhaerere (‘to stick to’) “Adhesive” The substance added to produce adhesion “ Adherend” The material to which it is applied A solid is the adherend and liquid is the adhesive
  • 3. 3 Key steps to the development of good adhesion. A. Clean adherent (devoid of smear layer or contaminants). B. Effective wetting of the substrate by the adhesive. C, Intimate adaptation of the adhesive to the intricacies of the substrate (avoiding voids or entrapped air). D Effective mechanical bonding. E, complete curing of the adhesive CRITERIA FOR OPTIMALADHESION
  • 4. 4 Possible mechanisms of bonding which are as follows: 1. Mechanical—Penetration of resin and formation of resin tags within the tooth surface. 2. Adsorption—Chemical bonding to the inorganic component (hydroxyapatite) or organic components (mainly type I collagen) of tooth structure. 3. Diffusion—Precipitation of substances on the tooth surfaces to which resin monomers can bond mechanically or chemically. 4. A combination of the previous three mechanisms
  • 5. 5 • For good adhesion, close contact must exist between the adhesive and the substrate (enamel or dentin). The surface tension of the adhesive must be lower than the surface energy of the substrate. • Failures of adhesive joints occur in three locations, which are generally combined when an actual failure occurs: 1. cohesive failure in the substrate; 2. cohesive failure within the adhesive; and 3. adhesive failure, or failure at the interface of substrate and adhesive.
  • 6. 6 FACTORS AFFECTING ADHESION Surface Energy: • The energy of a solid on the outer surface is comparatively higher than its interior. • The harder the surface, the higher the surface energy and adhesive properties.
  • 7. 7 2. Wetting: • The wetting ability of a liquid adhesive depends upon the surface energy and cleanliness of the adherend. • Higher the surface energy, greater the wetting capability. • Contamination of the substrate surface also reduces wetting by the adhesive. 3. Contact Angle- • It is a measure of wettability and is the angle formed by the adhesive with the adherend at the interface. • Smaller the contact angle greater is the wettability of the adhesive. Degree of contact angle influences the wetting of surface; (A) When contact angle is small, wettability of the adhesive is better; (B) and (C) When contact angle is large, liquid does not wet the surface completely Air incorporated in the irregularities at the interface despite low contact angle of the adhesive. Such areas are points of stress concentration and promote adhesive failure
  • 8. 8 TRENDS IN RESTORATIVE DENTISTRY Adhesive restorative techniques are currently used to accomplish the following • Restore Class I, II, III, IV, V and VI carious lesions or traumatic defects. • Change anterior teeth’ shape and color (e.g., with full or partial resin veneers). • Improve retention for porcelain-fused-to-metal (ceramo- metal) or metallic crowns. • Bond orthodontic brackets. • Bond fractured fragments of anterior teeth. • Bond splints for tooth luxation and periodontally involved anterior teeth and conservative tooth replacement prostheses. • Repair existing restorations (composite, amalgam, ceramic or ceramo-metal). • Provide foundations for crowns. • Desensitize non-carious cervical lesions (NCCLs) and exposed root surfaces. • Impregnate enamel and dentin, making them less susceptible to caries. • Bond prefabricated fiber, metal, and cast posts. • Reinforce fragile endodontically treated roots internally. • Seal root canals during endodontic therapy. • Seal surgically resected root apices. • Bond all-ceramic restorations. • Seal pits and fissures.
  • 9. 9 Fig 1: (A) Intraoral frontal view of a 20-year-old female presenting with complicated crown fracture on tooth 9 after endodontic treatment. The fracture extends subgingivally on the mesial aspect of the lingual surface. (B) A two-step etch-and- rinse ethanol-based adhesive applied to the crown fragment and tooth. (C) Extraoral view 6 months after rebonding. (D) Extraoral view 3 years after rebonding. Fig 2: (A) Preoperative view of anterior teeth in a 24-year-old patient with defective composite restorations. The treatment plan included bonded porcelain veneers on teeth 7, 8 and 10 to match the natural aspect of tooth 9; (B) porcelain veneers were bonded with a two-step etch-and-rinse adhesive and a light- activated resin cement and (C) final aspect 1 week after the bonding procedure.
  • 10. 10 TOOTH AS A SUBSTRATE FOR BONDING Tooth Surface & Bonding Insights • Enamel: Better bonding on prism ends than sides. • Fluoridated enamel: Harder to bond—low surface energy. • Dentin: Moisture is the main bonding challenge. • Tubule density: • Near pulp: ~45,000/mm² → high permeability. • Near DEJ: ~20,000/mm² → less permeability. • Superficial dentin: More solid, less moisture = better bonding potential
  • 11. 11 REQUISITE OF AN IDEAL BONDING AGENT • Biocompatible. • Bond effectively to both enamel and dentin. • Strength to resist failure as a result of masticatory forces. • Mechanical properties close to tooth structure. • Resistant to degradation in oral environment. • Easy to use.
  • 12. 12 ENAMELADHESION • Buonocore envisioned the use of acids to etch enamel for sealing pits and fissure. • Etchant: Most current phosphoric acid gels have concentrations of 30%–40 %, with 37% phosphoric acid gel being the most common. • Etch time: Currently, an etching time of 15s is recommended. Studies using scanning electron microscopy (SEM) showed that a 15-s etch resulted in a surface roughness similar to that provided by a 60-s etch. • Bond strength (>20 MPa). As measured in the laboratory, shear bond strengths of composite to phosphoric acid-etched enamel usually exceed 20 Mpa.
  • 13. 13 Phosphoric acid as an etchant: Buonocore :acid etching with 85% phosphoric acid for 30 sec 50 % phosphoric acid for 60 seconds • monocalcium phosphate monohydrate precipitate Concentrations below 25% • Dicalcium phosphate monohydrate precipitate Concentrations above 40% • Dissolve less calcium and etch patterns with poorer definitions 37% for 15 sec is considered appropriate
  • 14. 14 Acid Etching Essentials • Gel > Liquid for controlled placement. • Both forms give similar etching patterns. • Gel = Acid + colloidal silica/polymer beads. • Primary teeth need longer etching → more aprismatic enamel.
  • 15. 15 CONDITIONING AND ETCHING OF ENAMEL Conditioning vs. Etching • Conditioning = Removes organic layer → better enamel bonding. • Etching = Demineralizes surface calcium. • Gel use? → Double rinse to remove cellulose vehicle. • Etched enamel when dry = matte white/frosted look.
  • 16. 16 • How Acid Etching Transforms Enamel 1. Strips pellicle → exposes enamel crystallites 2. Removes ~10 μm of enamel 3. Creates pores (5–50 μm deep) 4. Boosts wettability & surface area 5. Raises surface energy → activates polar sites 6. Resin flows into pores → forms strong resin tag
  • 17. 17 • LASERS IN ENAMEL ETCHING 1. The use of lasers as an alternative to conventional acid etching. 2. Types of Lasers Used: Er:YAG (Erbium: Yttrium-Aluminum-Garnet) Er,Cr:YSGG (Erbium, Chromium: Yttrium-Scandium-Gallium-Garnet) CO Laser, Nd: YAG ₂ Advantages Over Acid Etching: • No need for chemical agents (ideal for children or sensitive patients) • Reduces risk of microleakage and demineralization • Can sterilize the surface and reduce bacterial load • No smear layer formation Comparative Evaluation of Acid Etching and Laser Etching Following the Application of Chlorhexidine on the Aesthetic Bracket Nidhal H Ghaib*, Bayan Ghadban College of Dentistry, University of Baghdad, Iraq
  • 18. 18 Enamel Etching Patterns • Type I: dissolution of prism cones without the dissolution of prism peripheries. • Type II: opposite of type I. Peripheral enamel is dissolved, but the cores are left intact. • Type III: less distinct than the other two patterns. Includes areas that resemble other patterns and areas not related to enamel prism morphology.
  • 19. 19 -Type IV: presents as a random scattering of shallow depressions. No clear preference for either prism cores or peripheries. -Type V: etching, like Type IV, lacks visible prism outlines. WHAT IS MICRO AND MACROTAGS? • Resin tags which form in the enamel rod peripheries, i.e. between enamel prisms are known as MACROTAGS. • A much finer network of thousands of small tags form across the end of each rod where individual hydroxyapatite crystals have been dissolved leaving crypts outlined by residual organic matter. • These fine tags called MICROTAGS.
  • 20. 20 RESIN MICRO TAG MECHANISM OF ENAMEL ADHESION Acid etching transforms the smooth enamel into an irregular surface and increases its surface free energy. [Fig1] Application of a fluid resin-based material to the irregular etched surface, facilitates penetration of the resin into the surface, aided by capillary action Monomers in the material are then polymerized, and the material becomes interlocked with the enamel surface. [Fig 2] The formation of resin microtags within the enamel surface is the fundamental mechanism of resin–enamel adhesion.
  • 21. 21 Fig 1 Scanning electron micrograph of enamel etched with 35% phosphoric acid (3M Oral Care) for 15 s. Fig 2 A and B, Transmission electron micrographs of the enamel-adhesive interface after application of Adper Single Bond (3M Oral Care) as per manufacturer’s instructions. Acid etching with 35% phosphoric acid opened spaces between enamel prisms (arrows), allowing the permeation of resin monomers between the crystallites (arrowheads). A, Adhesive; E, enamel.
  • 22. 22 BONDING TO DENTIN • Adhesive materials can interact with dentin in different ways— mechanically, chemically or both. • Dentin adhesion relies primarily on the penetration of adhesive monomers into the network of collagen fibrils left exposed by acid etching. (A) Dentin etched with 35% phosphoric acid and (B) higher magnification view of etched dentin. Col, Collagen exposed by the acid; D, normal dentin; T, dentinal tubule; S, residual silica particles used as acid gel thickener.
  • 23. 23 MECHANISM OF DENTIN BONDING • Ionic interaction between Ca² ions in the ⁺ inorganic phase and negatively charged groups in the adhesive. • For the organic phase, bonding occurs via interactions with –NH, –CONH, –OH, and – COOH groups in collagen. • Effective adhesion relies on hydrophilic monomers that infiltrate the conditioned collagen network. Bonding to inorganic portion of dentin Bonding to the organic portion of dentin Mechanism of bonding: (A) Bonding mechanism with intervening adhesive and (B) Bonding to inorganic or organic portion of dentin.
  • 24. 24 Mechanical Conditioning: Micro-abrasion is used to condition the dentin mechanically Within the limitations of this study, the following conclusions can be drawn: • APA with aluminum oxide particles had no negative effects on the bond strength of resin-based materials to dentin. • In a few subgroup analyses, air abrasion was able to improve the immediate bond strength to dentin when the particle size was >30 lm and air pressure was >5 bar. • APA duration had no significant effect on immediate dentin bond strengths
  • 25. 25 ROLE OF PRIMING IN ENAMELAND DENTIN ADHESION •Priming is the second step in the adhesive bonding process. •Primers contain hydrophilic monomers like HEMA and 4-META. •Solvents like ethanol or acetone help displace water from dentin. •Primer enables resin penetration into moist, demineralized dentin. •Even and uniform application ensures optimal bond strength.
  • 26. 26 Acetone has a relatively high vapor pressure value (184 mmHg at 20°C) compared to ethanol (43.9 mmHg at 20°C) and water (17.5 mmHg at 20°C). A higher vapor pressure will allow the solvent to evaporate more easily. As the solvent evaporates, the viscosity of the dentin bonding agent increases, which decreases the ability of the bonding system to penetrate around the exposed collagen fibers and the opened dentinal tubules, consequently inhibiting the proper bond formation ROLE OF SOLVENTS
  • 27. 27 CHALLENGES IN DENTIN BONDING FIG 1 FIG 2 Scanning electron micrograph of dentin that was fractured longitudinally to show dentinal tubules •Enamel is over 90% hydroxyapatite, making it highly mineralized. •Dentin has more water and organic material, mainly type I collagen. •Dentin contains tubules that connect the pulp to the enamel surface. •Inter-tubular dentin allows fluid and fibril movement through tiny channels. •Bond strength is lower in deep dentin compared to superficial dentin.
  • 28. 28 ROLE OF SMEAR LAYER IN DENTIN BONDING The smear layer is a byproduct of dental instrumentation that coats dentin surfaces (1–2μm thick) and penetrates dentinal tubules (1–5μm) as smear plugs. It consists of: • Solid phase: Debris of denatured collagen and mineral • Liquid phase: Fluid-filled channels around the debris • While it protects dentin, it can impede resin bonding by acting as a barrier to adhesive penetration. • However, some researchers suggest that it may also play a protective role by reducing the movement of bacteria and harmful substances toward the pulp. Scanning electron micrograph of a smear plug blocking the entrance of a dentinal tubule. SP, Smear plug. Reasons for retaining smear layer on the bonding substrate are: • Retention of smear layer lowers dentin permeability • Prevents decrease in bond strength seen with some bonding systems as deeper dentin is prepared • Greatly lowers the effect of pulpal pressure on
  • 29. 29 CONFIGURATION FACTOR • Stress relief within a three-dimensional bonded restoration is limited however by its configuration factor (C-factor). • Stress relief is limited because flow can occur only from the single free surface. • Bond disruption and marginal gaps around restorations may increase microleakage and potential postoperative sensitivity. POLYMERIZATION SHRINKAGE STRESS • Several clinical strategies have been suggested to reduce the effects of polymerization shrinkage stress, including I. control of curing light irradiance II. incremental insertion techniques III. application of intermediate low-modulus liners
  • 30. 30 COEFFICIENT OF THERMAL EXPANSION • Whenever a restoration is exposed to wide temperature variations the restoration undergoes volumetric changes of different magnitude compared with those of the tooth structure. • Microleakage around dentin margins is potentiated by this discrepancy in linear CTE between the restoration and the substrate. OCCLUSAL LOADING • Loading and unloading of restored teeth can result in transitional or permanent interfacial gaps. • Additionally, the tooth substrate itself might be weakened by cyclic loading. • Studies have found that cyclic loading and preparation configuration significantly reduced the bond strengths of self-etch and etch-and-rinse adhesives.
  • 31. 31 EVOLUTION OF DENTIN BONDING AGENTS 1. Historical Strategies i First generation (1965) ii. Second generation (1978) iii. Third generation (1984) 2. Current strategies: i. Etch and rinse adhesives a. Three-step etch and rinse adhesive (fourth generation) b. Two-step etch and rinse adhesive (fifth generation) ii. Self-etch adhesives a. Two-component self-etch adhesive (sixth generation) — Two-step two- component self-etch adhesive — One-step—two-component self-etch adhesive b. Single component—one step—self-etch adhesive (seventh generation)
  • 32. 32 FIRST GENERATION: • Introduced in 1965 • Chemical: Surface-active co-monomer NPG-GMA • Mechanism of action: Theoretically, this co-monomer could chelate with calcium on the tooth surface to generate water-resistant chemical bonds of resin to dentinal calcium. • Ex- Cervident (SS White) • Cosmic Bond. • Palakav (Kulzer, USA). • Bond strength: 2-3 Mpa DRAWBACKS- • Low bond strength. • No improvements in marginal leakage when compared to conventional unfilled bonding agent.
  • 33. 33 SECOND GENERATION • Introduced in 1978. • Chemical: Phosphate-ester material (phenyl-P and hydroxyethyl methacrylate [HEMA] in ethanol). • Bonding mechanism- Based on the polar interaction between negatively charged phosphate groups in the resin and positively charged calcium ions in the smear layer. • Mean shear bond strength- 1-5 MPa EXAMPLES: • Clearfil bond system F (Kuraray) • Scotchbond (3M ESPE) • Bondlite (Kerr) • Prisma Universal Bond (Dentsply). CLINICAL RESULT: • Smear layer was the weakest link due to its relatively loose attachment to dentin surface.
  • 34. 34 DRAWBACKS OF FIRST AND SECOND GENERATIONS • Lack of adequate bond strength. • Being hydrophobic in nature, close adaptation to the hydrophilic dentin could not be achieved. • Adhesive bonded to the smear layer rather than the dentin. • Lack of sufficient knowledge about the presence and nature of the smear layer. • Biocompatibility was not appropriate.
  • 35. 35 THIRD GENERATION • Chemical: It was a phosphate-based material containing HEMA and a 10-carbon molecule known as 10 MDP(10-methacryloxydecyl dihydrogen phosphate), which includes long hydrophobic and short hydrophilic component. • Mechanism of action: 1. The concept of phosphoric acid-etching of dentin before application of a phosphate ester type bonding agent was introduced by Fusayama et al in 1979. 2. Designed not to remove the entire smear layer but, rather, to modify it and allow the penetration of acidic monomers, such as phenyl-P or PENTA. • Brand names: 1. Clearfil New Bond (Kuraray Co, Ltd, Osaka, Japan) 2. Scotchbond 2 (3M ESPE Dental Products) • Clinical result: Clinical results were mixed, with some reports of good performance and some reports of poor performance.
  • 36. 36 CURRENT OPTIONS FOR RESIN–DENTIN BONDING Mechanism of Action – Three-Step Etch-and-Rinse Adhesive Acid Application to Dentin ↓ Smear Layer Removal & Dentin Demineralization Opens dentinal tubules Exposes collagen fibers Increases microporosity ↓ Depth of Demineralization Up to ~7.5 µm depending on acid type, time, and concentration ↓ Primer Application Increases critical surface tension of dentin ↓ Bonding Resin Application Penetrates intertubular dentin → Forms Hybrid Layer Penetrates & polymerize open dentinal tubules → Forms Resin Tags
  • 37. 37 FOURTH GENERATION Components: Etchant gel + primer (bottle I) + adhesive bottle (bottle II) They include three essential components that are applied separately and sequentially: 1. Phosphoric acid-etching gel that is rinsed off. 2. Primer containing reactive hydrophilic monomers in ethanol, acetone, or water 3. Unfilled or filled resin bonding agent. It contains hydrophobic monomers such as Bis-GMA, frequently combined with hydrophilic molecules such as HEMA Example: 1. All-Bond 2 and All-Bond 3 (Bisco, Inc, Schaumburg, IL) 2. OptiBond FL (Kerr Corporation) 3. Adper Scotchbond Multi-Purpose (3M ESPE) Bond strength: Varies from 17—30 MPa Clinical result: Adhesive systems based on the total-etch philosophy have been proven to be clinically successful.
  • 38. 38 FIFTH GENERATION: TWO STEP ETCH AND RINSE ADHESIVE • One bottle system. • Etchant, Primer + Adhesive (single bottle). Mechanism of Action: The primer and adhesive are combined into a single solution containing both hydrophilic(PRIMER) and hydrophobic components(ADHESIVE). Due to the higher hydrophilicity, these adhesives are more prone to hydrolytic degradation. Examples: Prime and Bond (Dentsply, Caulk), and Prime and Bond 2.1, Opti Bond Solo (Kerr), Single Bond (3M) etc. • Mean BS- 17-24 MPa. ADVANTAGES: • Bond strength is sufficient. • Time saving and simple to use. • Elimination of washing out of the acidic gel, therefore elimination of risk of collagen collapse. • Combination of etching and priming steps decreases the working time. DISADVANTAGES • Solution must be refreshed continuously.
  • 39. 39 Contemporary dentin bonding agents-A review. Journal of Scientific Dentistry, 8(2), 2018 HYBRID LAYER • Definition: The hybrid layer is a resin–dentin interdiffusion zone formed by the infiltration of adhesive monomers into the demineralized dentin collagen matrix. • It was first introduced by Nakabayashi et al. (1982). • The distinct zone between the bulk adhesive and non- demineralized dentin consisting of 50% collagen matrix and 50% resin is termed as hybrid layer. • There are three different zones in hybrid layer: 1. Top zone: It consists of loosely arranged collagen fibrils with inter-fibrillary spaces filled with the adhesive resin. 2. Mid-zone: This consists of collagen fibrils infiltrated with resin with residual hydroxyapatite crystals between collagen. 3. Bottom zone: It shows an abrupt transition to the underlying unaltered dentin with partially de-mineralized dentin containing hydroxyapatite crystals enveloped by adhesive resin.
  • 40. 40 ROLE OF HYBRID LAYER IN DENTIN BONDING • Micromechanical retention: Enhances adhesion through interlocking of resin tags with collagen matrix. • Seal integrity: Acts as a barrier to bacterial infiltration and fluid movement. • Bond strength: Critical for achieving durable resin-dentin bonds. • Stress distribution: Helps distribute occlusal and thermal stresses across the bonded interface. The promotion of adhesion by the infiltration of monomers into tooth substrates Nobuo Nakabayashi, Katsunori Kojima, and Eiichi Masuhara Institute for Medical and Dcntal Engineering, Tokyo Medical and Dental University, Kanda Surugadai, Chiyoda-ku, Tokyo 101, japan
  • 41. 41 Self-Etch Adhesives Concept: Omission of a separate etching step. • Two types of self-etch adhesives are available: 1. Two-component self-etch adhesive (sixth generation) i Two-step: Two-component—self-etch adhesive ii. One step: Two-component self-etch adhesive 2. Single component—one step: self-etch adhesive (seventh generation) • Advantages: 1. Less post-operative sensitivity. 2. Clinician-friendly 3. Less technique sensitive. 4. Reduces the possibility of over-wetting or over-drying of dentin. 5. Less discrepancy between depth of demineralization and the depth of resin infiltration.
  • 42. 42 Disadvantages: 1. Do not etch enamel as well as phosphoric acid. 2. When enamel bonds are stressed, they undergo deterioration. 3. Strong one-step SEA continues demineralization and result in collagen fibre exposure. 4. The presence of the hybrid layer that is not completely infiltrated may increase the stresses in resin dentin interfaces.
  • 43. 43 TWO-STEP SELF-ETCH ADHESIVES • Japan • Two-step SEAs contains an acidic monomer that functions as a self-etching primer and a hydrophobic, non-solvent-bonding resin. • The acidic primers include a phosphonated and/or carboxylated resin molecule that performs two functions simultaneously— etching and priming of dentin and enamel. • Mechanism of action: The bonding mechanism of self-etch adhesives (SEAs) involves: 1.Simultaneous etching and priming of enamel and dentin, creating a continuous bond. 2.Incorporating smear plugs into resin tags for better adhesion. Bonding to dentin using a self-etch primer.
  • 44. 44 SEAs are classified into three categories based on pH: • Mild SEA (e.g., Clearfil SE Bond) – better dentin bonds, weaker enamel bonds.(overcome by selective enamel etching) • Moderate SEA • Aggressive SEA – better enamel bonds, weaker dentin bonds. Selective enamel etching improves marginal adaptation and reduces marginal discoloration compared to the self-etch strategy. Monomer 10 MDP has been shown to bond chemically to hydroxyapatite through a mechanism known as nano- layering Adhesives pH Strong ( 1 or less) NRC( Dentsply) Adper prompt 1 0.4 Intermediary( 1.5) Xeno III( Dentsply) AdheSE primer( Vivadent) Optibond Solo Plus SE primer( Kerr) I Bond 1.4 1.4 1.5 1.6 Mild( around 2) Clearfil SE Panavia ED primer mixed( Kuraray) 1.9 2.6 Van Meer beck et al 2003
  • 45. 45 SIXTH GENERATION • Sixth generation BA are further divided into two types- Type 1 (Self-etching primer and adhesive) • Available in light-cure or dual-cure. • Two bottles, Liquid 1 (Acidic Primer), Liquid 2 (Adhesive). • Example: Opti Bond Solo plus(self etch), Clearfil SE bond • Described as non rinsing conditioners or self priming etchants. Type 2 ( Self-etching adhesive) • Available in light-cure type • Two bottles, containing acidic primer and adhesive; a drop of each liquid is mixed and applied to the tooth EXAMPLES- • Adper Prompt L Pop (3M ESPE) • Xeno III (Dentsply)
  • 46. 46 ONE-STEP SELF-ETCH ADHESIVES • Etchant+primer+adhesive= single bottle system Mechanism of action: In these one-step SEAs contain uncured ionic monomers ,contact the composite restorative material directly. Application of multiple coats significantly increases dentin bond strengths and decreases leakage. Limitation: • Their acidic unreacted monomers are responsible in part for the incompatibility between these simplified adhesives and self-cured composites. • Facilitates hydrolytic degradation of the resin dentin interface. ( they behave as semi-permeable membrane. • One-step SEAs tend to behave as semipermeable membranes, facilitating hydrolytic degradation of the resin–dentin interface.
  • 47. SEVENTH-GENERATION/ALL-IN-ONE • Available both as light cure and dual cure type • All three components are combined in a single bottle, and they require no mixing. • More acidic pH < 1. . Eg- G-Bond, i-Bond (self etch), AdheSE One F (Ivoclar Vivadent), Adper Easy One (3M ESPE) DISADVANTAGES • Relatively short shelf-life. • Their composition is very hydrophilic leading to leaching of unpolymerized monomers or hydrolytic degradation products through water-filled channels called water trees. 47
  • 48. 48 EIGHT GENERATION • Modified version of 7th generation of bonding agent. • Futurabond DC introduced by Voco America. • One-step dual-cured, non-filled, self-etch adhesive. • Chemically cured mode makes the product suitable for root canals. ADVANTAGES • Can be used with light-cure, dual-cure and self-cure composites. • Moisture tolerant. • Contains fluorides. • Nano-fillers help in better cross-linking of bonding resin components.
  • 49. 49 UNIVERSAL ADHESIVES Universal adhesives offer flexible use across bonding strategies: self-etch, etch-and-rinse, or selective enamel etch. • Function as one-step SEAs Mechanism: • Contain 10-MDP → forms strong, durable chemical bonds with hydroxyapatite via nano-layering • More effective chemical bonding in dentin due to smaller and fewer hydroxyapatite crystals. • Active application (rubbing) boosts bonding by enhancing 10-MDP contact. • Limitations: 1. Extent of chemical bonding is weak 2. Presence of HEMA hampers bonding ability as it reduces the formation of MDP-Ca salts. 3. Interfacial bonding degradation. (in self-etch or etch-and-rinse manner)
  • 50. 50
  • 51. 51 ROLE OF SILANE IN ENAMELAND DENTIN ADHESION Silane coupling agents are bifunctional molecules used in dental adhesives, especially for bonding resin composites to ceramic surfaces, and in resin-based cements. Their use in enamel and dentin adhesion is less direct but still important, especially in universal adhesives that aim to enhance bonding to various dental substrates. Structure & Mechanism of Silane: • One end: Organofunctional group (e.g., methacrylate) → bonds with resin matrix • Other end: Silane group (Si–O–R) → bonds with inorganic materials (like glass, hydroxyapatite) • In the presence of moisture, silane hydrolyzes into silanol groups (Si–OH) which form covalent bonds with hydroxyl groups on tooth or ceramic surfaces. Role in Enamel and Dentin Bonding: 1. Coupling agent 2. Improves wetting 3. Increases Bond Strength 4. Used in universal Adhesives 5. Promotes Long-Term stability Reference: Silane adhesion mechanism in dental applications and surface treatments: A review Jukka Pekka Matinlinna , Christie Ying Kei Lung , James Kit ∗ ∗ Hon Tsoi
  • 52. 52
  • 53. 53 CLINICAL CONSIDERATIONS DURING ADHESION MOIST VERSUS DRY DENTIN SURFACES Moist Bonding Technique with Etch-and Rinse Adhesives: • Drying the dentin surface with air would cause the dentinal collagen to collapse, which would prevent the monomers from penetrating the nanochannels. • The ‘moist bonding’ technique used with etch-and-rinse adhesives prevents the spatial alterations (i.e., collagen collapse) that occur on drying demineralized dentin Air Drying of Etched Dentin: • When etched dentin is dried using an air syringe, in vitro bond strengths decrease substantially, especially for acetone-based and (to a lesser extent) ethanol-based dentin adhesive systems.
  • 54. 54 ROLE OF WATER IN SELF-ETCH ADHESIVES • In self-etch adhesives (SEAs), water plays a crucial role by ionizing acidic monomers and solubilizing calcium and phosphate ions for effective bonding. • Unlike etch-and-rinse adhesives, SEAs combine etching and priming in one step using acidic monomers. • Water content (10–30%) is essential but must be balanced: • More water improves ionization and demineralization depth. • Too much water dilutes monomers, reducing bonding strength. • One-step SEAs are more vulnerable to water-related issues like higher water absorption and lower mechanical properties, compared to two-step SEAs, which are more stable.
  • 55. ROLE OF PROTEINS IN DENTIN BONDING • Collagen type I is the main organic component of dentin. In dentin bonding, ideally collagen should be demineralized as minimally as possible, keeping the demineralized collagen hydrated and infiltrated with a hydrophilic adhesive to ensure proper penetration within the exposed collagen fibrils. • Ninety per cent of the protein content of dentin is type I collagen and the remaining are non collagenous proteins. The non collagenous proteins fall into several categories: 1. proteoglycans, 2. SIBLINGs (small integrin-binding ligand, N-linked glycoprotein), 3. growth factors, 4. matrix metalloproteinases (MMPs) and 5. serum proteins 55
  • 56. 56 Role of Matrix Metalloproteinases Matrix metalloproteinases (MMPs) are important non-collagenous proteins in dentin bonding. They are zinc- and calcium-dependent enzymes capable of degrading the extracellular matrix. Key MMPs in dentin: • MMP-2 & MMP-9 (gelatinases) • MMP-8 (collagenase) • MMP-20 (enamelysin) • After acid etching, exposed collagen fibrils not protected by resin can be degraded by MMPs. Protease inhibitors can block MMP activity, helping preserve the hybrid layer and improve resin–dentin bond durability, especially in the early months after restoration.
  • 57. 57 Role of Dentin Phosphoprotein • Some non-collagenous proteins in dentin act as nucleators for mineralization, with dentin phosphoprotein (DPP) being the most prominent. • DPP is highly acidic due to its aspartic acid content, allowing it to bind calcium and aid in dentin formation by delivering calcium to collagen. • Biomimetic analogues like polyacrylic, polycarboxylic, and polyvinylphosphonic acids mimic DPP’s function. • These can form amorphous calcium phosphate precursors and bind to collagen, promoting intrafibrillar mineralization in hybrid layers when used with calcium hydroxide–releasing materials. ‘Microleakage’ is defined as the passage of bacteria and their toxins between restoration margins and tooth preparation walls. Clinically, microleakage becomes important when one considers that pulpal irritation is more likely caused by bacteria than by chemical toxicity of restorative materials.
  • 58. 58 Nanoleakage Nanoleakage refers to tiny porosities in the hybrid layer or its interface with mineralized dentin, allowing penetration of silver nitrate particles. Using ammoniacal silver nitrate, two nanoleakage patterns are observed: • Spotted pattern: Seen in SEAs, likely due to incomplete resin infiltration. • Reticular pattern: Seen in the adhesive layer, likely from residual water, forming structures known as “water trees.” • Both patterns indicate compromised bonding and may affect long-term durability. Nanoleakage under the electron microscope. (A) Spotted pattern in the hybrid layer formed by a one-step self-etch adhesive under the transmission electron microscope. (B) Reticular pattern and ‘water trees’ in the adhesive layer formed by a one step self-etch adhesive under the scanning electron microscope in backscattered mode.
  • 59. 59 BONDING IN OTHER CLINICAL SITUATIONS BONDING SPECTRUM IN DENTISTRY • BONDING OF GLASS IONOMERS TO HARD TISSUES: Calcium ions from the tooth structure (particularly hydroxyapatite) interact with the carboxylate groups of polyalkenoic acid in GIC, creating ionic bonds. 🧷 This direct ionic interaction leads to chemical adhesion to both dentin and enamel.
  • 60. 60 • BONDING OF COMPOSITE TO GLASS IONOMERS: Glass-ionomer is invariably used as a substitute for dentin under composite resins. This technique is commonly known as the bilayered technique (Sandwich technique) in which the enamel and cement are etched prior to placement of the restorative resin. Low viscosity resins are advisable as they have a lower contact angle and better wetting ability with the substrate. • BONDING OF COMPOSITE TO PORCELAIN: Bonding of porcelain to composite is partly because of mechanical interlocking and partly because of chemical union. Mechanical retention is obtained by etching the fitting surface of porcelain with dilute hydrofluoric acid or grit blasting with alumina to increase surface roughness. The optimal time for etching depends upon the etchant concentration as well as the type of porcelain used. To improve upon the mechanical attachment, gap between the bonding medium and the porcelain should be minimized by using an intermediate low viscosity resin which penetrates the pores by capillary action. • BONDING OF AMALGAM TO RESIN: Bonding of amalgam to resin is a relatively new treatment modality and has made bonding between amalgam and tooth structure quite a successful possibility. Agents that can be used for bonding amalgam to the substrate are All Bond, Liner Bond-2, Amalgam bond and Panavia. A specific feature desired in these materials is that they should have dual characteristics to achieve optimal wetting.
  • 61. 61 FAILURE OF ADHESIVES 1. MATERIAL FACTOR: Thorough knowledge of the chemistry of the material to be used is mandatory for successful bonding. 2. SUBSTRATE: Variability of the substrate has been shown to have a major effect on the clinical performance of adhesive systems 3. SIZE AND SHAPE OF LESION: The Size of the lesion or the area of dentinal substrate available for bonding is critical for adhesion. 4. MAXILLARY VERSUS MANDIBULAR ARCH: Better adhesion results are expected in the maxillary arch because of the lesser chances of moisture contamination and lower tooth flexure effects in the upper jaws. 5. PATIENT’S AGE: With age, the dentin becomes sclerosed, and the sclerosis is associated with a decrease in clinical adhesiveness and hence a higher failure rate. 6. TOOTH FLEXURE: More recently, tooth flexure is a probable factor in influencing the retention of adhesive restorations, especially the cervical restorations. 7. DENTIN WETNESS: The bonding agents with effective wetting capability ensure successful bonding. 8. ELASTIC BONDING CONCEPT: Composite resins shrink during polymerization. In order to protect the tooth composite interface from debonding during polymerization, the intervening adhesive resin should Diagram illustrating different positions of failure at the resin-adhesive-tooth interface (i) Between the mineralized and demineralized dentin (ii) Between demineralized dentin and bonding resin (iii) Within the bonding resin; and (iv) Between the bonding resin and composite resin
  • 62. 62 SUMMARY • Reliable bonding of resins to enamel and dentin has revolutionized the practice of operative dentistry. • Improvements in dentin bonding materials and techniques are likely to continue. • Even as the materials themselves become better and easier to use. • However, proper attention to technique and a good understanding of the bonding process remain essential for clinical success. • With advancements from the early generations to today’s universal adhesives, we've seen significant improvements in technique sensitivity, bond strength, and clinical outcomes. • Understanding the chemistry, application protocols, and indications of different bonding systems is essential for achieving long-term success in restorative procedures. • In conclusion, bonding agents have revolutionized restorative dentistry by enabling strong, durable adhesion between dental materials and tooth structures. • As research continues, future innovations promise even more efficient and biocompatible bonding solutions, enhancing both clinician performance and patient care.
  • 63. 63 REFERENCES • Sturdevant’s art and science of operative dentistry 4th edition • Bonillaguet ,s. and wataha; Future direction in bonding resin to dentin pulp complex 31,385,2004 • Textbook of operative dentistry 4th edition Vimal K Sikri • Pashley at el; State of the art etch and rinse adhesive; 27,1,2011 • Munck J at el; bonding effectiveness of self-adhesive composite to dentin and enamel. Dent mater 29,2,2013.
  • 64. 64 THANK YOU “The bond that links your true family is not one of blood, but of respect and joy in each other’s life”. - Richard Bach

Editor's Notes

  • #2: Adhesion refers to the forces or energies between atoms or molecules at an interface that holds two phases together. Astm: American society of testing and materials
  • #12: The procedure that leads to this removal of organic layer, making the enamel surface more reactive is known as ‘conditioning’. The procedure that leads to demineralization of superficial calcium ion is known as ‘etching’.
  • #15: The procedure that leads to this removal of organic layer, making the enamel surface more reactive is known as ‘conditioning’. The procedure that leads to demineralization of superficial calcium ion is known as ‘etching’.
  • #18: TYPE 1 PRISM CORE REMOVAL PATTERN TYPE 2 PRISM PERIPHERY REMOVAL PATTERN TYPE 3 MIXED OR IRREGULAR PATTERN
  • #29: C-Factor = (Number of bonded surfaces) / (Number of unbonded or free surfaces
  • #32: N phenylglycine glycidyl methacrylate
  • #49: Limitations Universal adhesives show signs of interfacial bonding degradation after 12-month water storage when applied either as self-etch or etch-and-rinse adhesives, although the self-etch strategy caused less nanoleakage.