Bonding of resin-based materials Libyan International Medical University

All modern composite restorations are based on effective adhesive procedures using dental adhesives. Dental adhesive systems are complex mixtures containing hydrophilic and hydrophobic monomers, solvents (including water), sometimes fillers and polymerization initiators and co-initiators. Their challenge is firstly to completely penetrate a hydrophilic etched tooth surface (enamel or dentine) to obtain an acceptable mechanical retention.

Secondly to achieve a strong bond through the reaction of co-polymerization (hybrid layer) with the hydrophobic matrix of composites or luting resins. This process can be performed clinically in different ways according to the presentation of the adhesive system. Enamel adhesion through the acid-etching has been shown to be effective whereas the development of dentine adhesion techniques is in constant progress.

The generation of adhesive systems developed in the early 1990s according to the total-etch concept are applied using a multi-step procedure. More recently further types of adhesive systems have been developed in order to simplify and reduce the stages of application (etch and rinse adhesive in two steps or self-etching systems in either two or one steps, according to the classification of Van Meerbeek et al. 2003). However, the three-step system (etching+primer+adhesive resin) still seems to provide the most reliable bonding.

Enamel and dentine adhesion The acid-etching of a tooth surface allows for the micro-mechanical adhesion of resin to the tooth. Etching with acid remove a portion of the superficial mineral component of enamel and dentine. Micro porosities or open dentinal tubules produced in which resin will penetrate and mechanically grip the tooth providing retention for an overlying restoration.

Advantages of adhesive dentistry 1.Less tooth structure removed 2.Reduce microleakage at margins 3.Better distribution of stresses 4.Possible reinforcement of tooth structure 5.Easy to repair filling with minimal tooth preparation 6.Tooth colored restorative materials like veneers may be added without preparation.

Enamel and dentine adhesion Tooth strength after restoration…amalgam vs composite? Strength of uncut tooth = 100% MOD amalgam prep = 50% MOD prep + varnish + amalgam = 50% MOD prep + composite resin = 88%

Indications of adhesive dentistry 1.Restoration of carious teeth 2.Abraded and eroded surfaces 3.Veneers 4.Re-contouring….e.g diastemas 5.Preventative sealants 6.Bonding orthodontic brackets 7.To treat dentinal hypersensitivity

Requirement for good adhesion/bonding  Materials must be in contact.  Wetting of the tooth surface must occur.  Enamel is high surface-free energy.  Dentine is low surface-free energy.  Tooth surface must be clean to provide high surface-free energy.

Factors affecting adhesion to tooth structure 1.Physical and chemical properties of adhesive resin. 2.Surface contamination (saliva, blood). 3.External stresses. 4.The way loads are applied to the bond joint. 5.Degree of resin cure.

BECAUSE the composition of enamel and dentine are different (organic, inorganic, water), adhesion to the two tooth tissues is also different. Problems with bonding to dentine! 1.High organic content 2.Smear layer 3.Variability of dentine 4.Vitality of the pulp

Acids used to prepare tooth surfaces Citric acid Nitric Oxalic Polyacrylic acid (10%) Phosphoric acid (10-37%) most common

Micromechanical Bonding Technique

Enamel adhesion The prismatic structure of enamel Micro-mechanical interlocking only

Etched enamel

SEM micrograph of the enamel surface after etching for 40 seconds with 35% phosphoric acid Micro-mechanical interlocking only

White frosted appearance

Dentine smear layer

Smear layer Is present on the surface of freshly cut dentine. Its loosely bonded layer of cutting debris including dentine chips, micro-organisms, salivary proteins and collagen from dentine. The smear layer is formed by process of cavity preparation and extended over the whole prepared surface of dentine and into dentinal tubules (smear plug).

Primer (hydrophilic monomer HEMA) and adhesive resin BisGMA

Resin tag Hybrid layer

SEM of dentine surface after primer (conditioner) application

The interface of a resin-enamel bond….resin tags 25 micron

Failure or debonding surface

Testing of bond strength mpa Shear bond strength Micro-tensile bond strength

Background  Resin composites are the most common dental restorative materials used in developed countries.

Sales of amalgam and composites in Germany Scientific Documentation Tetric EvoCeram®

Use of dental amalgam and composite as posterior restoration IADR 2006 Dublin, Hickel R (Munich University)

Acta Odontol Scand 2004; 62: From Amalgam to Composite in Finland

The median ages of failed restorations Acta Odontol Scand 2004; 62: 82-6.

The longevity of composite resin restorations Failures:  secondary caries  Bulk fracture of the restoration  wear dentist materialpatient

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