Adhesive technique I. Dentin adhesion Generations of adhesives

ADHESION Def.: state, where two surfaces are held together by interfacial forces Dentistry: anorganic tooth material replaced by bonding agent (resin) Demineralization: removal of calcium-phosphates Hibridization: infiltration of bonding agent Basically 2 types: 1. micromechanical irregularities in the surface – anorganic tooth material changes place with bond (resin) 2. chemical Range of indication: esthetic front tooth restorations, direct and indirect fillings: ceramic veneers, all- porcelain adhesive bridges and crowns, preprothetical restorations, orthodontic adhesives

ADHESIVE DENTISTRY In operative dentistry this technique is commonly used in resin- based material restorations. Filling materials used in adhesive dentistry: composites, glass- ionomers, compomers,

PHYSICAL BACKGROUND OF ADHESIVE TECHNIQUES The surface phenomena influence the employement and the adhesion of the adhesive filling materials. Surface phenomena include: Surface energy Wetting Capillary action Adhesion

SURFACE ENERGY- SURFACE TENSION I. Atoms and molecules at the surfaces of liquids and solids posses more energy than those in the interior. Reason: assymmetrical forces. Molecules on the border surface of e.g. air-liquid are in contact with each other and the air molecules. However, in liquid, molecules in the inner parts are only in contact with each other which means a different energetic state. In case of liquids this causes the formation of drops, because liquids tend to form in smallest surfaces ->surface tension.

SURFACE ENERGY- SURFACE TENSION II. In general: 1. the higher the surface energy, the higher the bonding strength and 2. smaller the extension and penetration. Importance: adhesive penetration to the etched tooth surface.

WETTING Wetting is defined in terms of the degree of a spreading liquid drop on a solid surface. 0° degree contact angle indicates complete wetting. above 90 degrees indicate poor wetting. Good wetting promotes capillary penetration and adhesion. This is important in the employment of adhesives.

CAPILLARY PENETRATION The surface energy of a liquid creates pressure that drives the liquid into tubules. A liquid with low viscosity, low surface energy and low contact angle ( good wetting ) will penetrate faster than one with opposite combination of properties.

ADHESION Adhesion is the attachement of materials in contact that resist the forces of separation. Types of adhesion: MECHANICAL: depends on mechanical interlocking of the two phases and may include microscopic attachements as in case of resin bonding to etched enamel (bonding agent- enamel) CHEMICAL: relies on chemical bonding between two phases.

ADHESIVES Bonding systems involve an unfilled or lightly filled, liquid acrylic monomer mixture placed onto an acid etched tooth surface. Types: enamel, dentin ( or both ) bonding systems. Employment depends on the type of the system.

Ideal adhesive Biocompatible, non-toxic, non-allergic Proper sealing between interfaces, prevents microleakage Good dimension stability Consist of: Etching material Primer Bonding agent

Conditioning on dentin surface Aim: removal of smear layer and demineralization of dentin surface Conditioning dentin surface with acids or chelating agents (EDTA) Acids: phosphoric, polyacrylic, EDTA, maleinic etc. In different concentrations Demineralization of intra- and intertubular dentin > collagen fibers exposition Acid contrentration, etching time! > postoperative sensitivity

Adhesive technique on dentin - Primer HEMA (hidroxietil methacrylate)+acetone/etanol/water Primer: opens gaps that appear after acidic etching, rinsing and drying of dentin surface – collagen fiber collapse Bifuncional monomer: bonding of the hidrophil group of HEMA to hidrophil dentin, and hidrophob methacrylate group of HEMA to hidrophob bonding agent Hybrid layer: bonding agent+primer+collagen fibers

Adhesive technique on dentin – Bonding agent Bonding agent, adhesive resin: consists of hydrophob monomers, such as: Bis-GMA (bisphenol-A-glycidyl methacrylate) UDMA (urethane-dimethacrylate): high viscosity, to decrease > difunctional monomer> TEG-DMA (trietilén-glikol-dimetakrilát) HEMA

Optimal bonding Adhesive should cover the dentin surface evenly, in a thin layer >intertubular area Intratubular area: resin tags Near the pulp the density of dentinal tubules increases Superficial dentin - the main bonding force is due to the penetration into intertubular dentin Deeper cavities: intratubular penetration and bonding

Evolution of dentin adhesives no-etch-total-etch-self-etch 1st generation: -1956 BUONOCORE: glicerophosphoric acid dimethacrylate bonds to dentin -Bowen: surface active co-monomer: NPG-GMA (N-fenilglicin-glicidil-metakrilát) -theoratically able to form chemical bonds with Ca ions of dentin 2-3 Mpa bond strength  poor clinical results

2nd generation dentin adhesives Phosphate esters of BIS GMA, HEMA mechanism based on polar interaction between phosphate groups in resin(Bis-GMA or HEMA) (negative) and Ca++ in smear layer 5-6 Mpa  smear layer loosely attached

3rd generation dentin adhesives Late 80’s: Modification or removal of smear layer – open dentintubules 3-8MPa Adhesive: un/partially filled resin Conditioning+primer(HEMA)

4th generation dentin adhesives Total-etch technique/etch and rinse,early 90’s Acid application on dentin surface According to instructions Applying bonding agent on dentin and enamel Etching, rinse, dry with light air Wet-bonding – aceton based primer 20-30MPa

5th generation dentin adhesives Make the procedure more simple Etching, bonding Primer+bond in one step – applying the adhesive agent in one or two layers

6th generation dentin adhesives Self-etch adhesives Self-etch primer (etch+primer in one bottle) + bonding agent Contains carboxylate / phosphoric group monomers Dentin adhesion is good, enamel inferior No need for seperate etching and bonding Self-etch adhesive: etch, primer, adhesive (bonding agent) in one Need mixing

Resin modified glass ionomer adhesives Glass ionomer is the only material that can bond to tooth structure without any pretreatment of the surface Condiotioning with polyalken acid improves bonding forces significantly

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