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Bonding of resin-based materials
Libyan International Medical UniversityLibyan 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 dentistry1. 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 adhesionThe prismatic structure of enamel
Micro-mechanical interlocking only
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
0
1
2
3
Sal
es (
rela
tive
pro
po
rtio
n)
Amalgam
Composite
Scientific Documentation Tetric EvoCeram®
Use of dental amalgam and composite as
posterior restoration
0
20
40
60
80
100
120
Sw e 1985 Sw e 2001 Ger 1985 Ger 1995 USA 1988 USA 1997
%
Amalgam
Composite
IADR 2006 Dublin, Hickel R (Munich University)
659 dentists
0
20
40
60
80
Composite Amalgam GIC
6.322 restorations (97-01)
%
Acta Odontol Scand 2004; 62: 82-6.
From Amalgam to Composite in Finland
The median ages of failed restorations
0
2
4
6
8
10
12
14
Composite Amalgam GIC
Ye
ars
Acta Odontol Scand 2004; 62: 82-6.
The longevity of composite resin restorations
Failures: secondary caries Bulk fracture of the
restoration wear
dentist
materialpatient
Thank you