Operative Dentistry MCQ Answer 21

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Correct answer is e. all of the above.

Answers for # 1-4 contain self-explanatory responses.

Answer for #5 can be best explained as follows:

Resin composite cements are used to fill the space between the laboratory composite and the tooth surface. Bonding to the indirect composite surface is difficult. The goal is to swell the outer surfaces of the resin matrix and allow new monomers from the bonding agent to penetrate spaces among existing polymer chains. At the time of curing, the new polymer chains become micromechanically intertwined with the existing polymer chains, producing relatively strong bonding. Bonding can be enhanced by micro etching with aluminum oxide (50um) etching with hydrofluoric acid, or treating with primers. Sandblasting roughens the surface. Etching removes smear layers and partially dissolves glass filler particles. Primers provide good wetting and potential chemical bonding to exposed glass filler particle surfaces. Commercial primers foe laboratory composites contain silane, unfilled resin monomers, or silane-monomer combinations. Bonding composite cements to laboratory composites can produce bond strengths in the range of 20-35 MPa.

The formation of an optimally bonded interface has the following:

1. the surface of the substrate be clean;

2. the adhesive wets the substrate well and has a low contact angle;

3. adapts to the substrate to produce intimate approximation of the materials without entrapped air or other intervening materials;

4. the interface include the sufficient physical, chemical and or mechanical strength to resist intraoral forces of debonding; and

5. the adhesive be well cured in the “environment” or conditions for which they are to be used.

References:

Craig RG and Powers JM: Restorative Dental Materials, 11^th Ed. Mosby, 2002.