COMPOSITE TECHNIQUE    SMILE DESIGN     COMPANIES/MATERIALS    MATERIAL SCIENCE

 COMPOSITE CHEMISTRY     FILLERS    COMPOSITE CLASSIFICATION    ENAMEL BONDING    DENTIN BONDING   HOME  

DENTIN BONDING

Dentin bonding creates a hybrid layer of resin, collagen fibers, dentin surface structure and intertubule structures.  Preparation of tooth dentin with dental burs creates a smear layer of debris.  The smear layer is burnished into the underlying dentin and dentin tubules.  Rubbing the surface and rinsing cannot remove a smear layer so application of acid is used.  Alternatively, a smear layer is left in place and modified so materials penetrate through the smear layer to the dentin structures below.

Dentin structure is variable by area within a tooth, disease such as caries, abrasion or attrition and other forms of sclerotic dentin.  Dentin bond strength is variable because of dentin quality including the number, openness and size of dentinal tubules, quality of dentin structure and amount of collagen.  Collagen is an important factor in dentin bonding.  Etching dentin removes a smear layer and components of dentin structure such as inorganic minerals resulting in exposed collagen fibers. 

Shallow dentin has fewer tubules of smaller diameter.  Deep dentin has more tubules of greater diameter and more fluid flow.  There are several different types of dentin.  Peritubular dentin is the collar around the lumen of a dentinal tubule.  The ratio of peritubular to intertubular dentin increases as approach the pulp

Intertubular Dentin has less mineralization and more collagen than peritubular dentin.  There is less intertubular dentin closer to the pulp.  Reparative dentin forms as result of pulpal irritation at the pulp to dentin interface.  The structure varies from well organizes tubular to irregular atubular dentin.   Sclerotic dentin forms from long term, low level stimulation of odontoblasts. The tubules become filled with peritubular dentin. As dentin ages, there is more mineralization, the ratio of peritubular/intertubular dentin increases and the number of dentin tubules decreases.

Exposed collagen fibers collapse when dry.  Collapse also occurs if the organic matrix is denatured.  Collapsed collagen fibers block resin from reaching the dentin surface and forming a hybrid layer.  Wetness of the dentin surface is critical to successful dentin bonding.  If the surface is too dry, the collagen and demineralized dentin collapse.  If the surface is too wet, phase changes occur in the ethanol or acetone based resins and globules of water form resulting in reduced bond strength. 

General components of dentin bonding systems consist of conditioner, primer and resin.  Conditioner removes or alters the smear layer and demineralizes dentin to expose collagen fibers.  Acids remove smear layers, EDTA removes calcium to expose collagen and glutaraldehyde stabilizes collagen fibers.  Primer contains hydrophilic and hydrophobic components that create a chemical and micromechanical bond to dentin.  The primer also copolymerizes with resin bonding agent.  

Adhesive primer formulations contain acidic monomers.  Increasing the amounts of acidic monomer from 10% to over 30%, creates a pH of about 1 that can alter a smear layer.  Addition of hydroxyethyl methacrylate (HEMA), allows self priming and self etching.  Scrubbing or agitating self etching primers eliminates the smear layer while non agitating techniques incorporate the smear layer.  These materials are self etching primers to be used with a resin adhesive.  Acid etching is eliminated.

Self-etching, self-priming, self-adhesive systems are very acidic.  The systems are new and evolving.  Presently, they appear to create very thin layers of adhesive that can be affected easily by oxygen from blowing air.  The thin adhesive layer also provides minimal shock absorbing quality.