Biocompatibility Of Dental Materials

Biocompatibility Of Dental Materials

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Biocompatibility is defined as the ability of restorative material to induce an appropriate and advantageous host response during the intended clinical usage. Murray et al. 2007

Anatomical and Pathological Aspect of Oral Tissues:

• Enamel—because of the high mineral content, enamel is much more brittle than dentin and is solubilized to a great extent by acid solutions.
• This property is used to advantage with bonding agents, where acids are used to etch the enamel to provide micromechanical retention of resin composite materials.

Biocompatibility of Dental Materials:

Microleakage: There is evidence that restorative materials may need to bond to enamel or dentin with sufficient strength to resist the forces of contraction on polymerization, wear, or thermal cycling.

• If a bond does not form or debonding occurs, bacteria, food debris, or saliva may be drawn into the gap between the restoration and the tooth by capillary action.
• This effect has been termed microleakage.
• Microleakage plays a significant role in pulpal irritation, but that the materials can also alter normal pulpal and dentinal repair.
• Restoration materials may directly affect pulpal tissues or may play an auxiliary role by causing sublethal changes in pulpal cells that make them more susceptible to bacteria or neutrophils.

Dentin Bonding:

Because the dentinal tubules and their resident odontoblasts are extensions of the pulp, bonding to dentin also involves biocompatibility tissues.

• When the dentin surface is cut, such as in cavity preparation, the surface that remains is covered by a layer of organic and inorganic debris called a smear layer.
• This smear layer is also deposited into the dentinal tubules to form dentinal plugs.
• The presence of the smear layer is important to the strength of bonds of restorative materials and the biocompatibility of those bonded materials.
• From the standpoint of biocompatibility, the removal of the smear layer may pose a threat to the pulpal tissues for three reasons:
• Increase the risk that materials can diffuse and cause pulpal irritation.
• Make any microleakage more significant because a significant barrier to the diffusion of bacteria or bacterial product towards the pulp is removed.
• Acids are used to remove the smear layer and are a potential source of irritation themselves.

Dentin Bonding agents:

A variety of dentin bonding agents have been developed and are applied to cut dentin during the restoration of the tooth.

• Many of these reagents are catatonic to cells.
• When placed on dentin and rinsed with tap water between applications of subsequent reagents as prescribed.
• Hydroxyethylmethacrylate (HEMA), a hydrophilic resin contained in several bonding systems is at least 100 times less catatonic in tissue culture than Bis-GMA.
• Resin-based materials: Freshly set chemically cured and light-cured resins afterward cause moderate cytotoxic reactions.
  The cytotoxicity is significantly reduced 24 to 48 hours after setting. With a protective liner or a bonding agent, the reaction of the pulp to resin composite materials is minimal.

Amalgam and Casting Alloys:

The biocompatibility of amalgam is throughout determined largely by corrosion products released from the restoration. Free or unreacted mercury from amalgam is toxic. Low-copper amalgams are well tolerated, but high-copper amalgams cause severe reactions when in direct contact with tissues.

• Cast alloys: These alloys contain several other noble and non-noble metals that may hurt cells if they are released from the alloys.
  However, released metals are most likely to contact gingival and mucosal tissues.
• Glass ionomers: Freshly prepared ionomers are mildly cytotoxic but this effect is reduced with increased times after settling. In usage tests the pulp reaction to glass ionomer cements is mild.