Influence of irradiance on Knoop hardness, degree of conversion, and polymerization shrinkage of nanofilled and microhybrid composite resins

Self-Instruction Exercise No. 382
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Exercise No. 382
Subject Code: 017
Dental Materials

The 15 questions for this exercise are based on the article, Influence of irradiance on Knoop hardness, degree of conversion, and polymerization shrinkage of nanofilled and microhybrid composite resins, on pages 26-31. This exercise was developed by Jean Carlson, DDS, FAGD, in association with the General Dentistry Self-Instruction committee.

Reading the article and successfully completing the exercise will enable you to:

  • understand the impact of irradiance on nanofilled and microhybrid composite resins;
  • recognize the effects of irradiance on Knoop hardness number (KHN), degree of conversion (DC), and shrinkage; and
  • understand the clinical effects of irradiance levels on both types of resin.

Answers for this exercise must be received by February 28, 2017.
  1. Light-emitting diode (LED) curing lights produce light energy at a wavelength of _______ nm.

    A. 270
    B. 370
    C. 470
    D. 570

  2. Composite traits affecting polymerization include all of the following except one. Which is the exception?

    A. particle size
    B. translucency
    C. molecular weight
    D. viscosity

  3. Higher irradiances generate _________________.

    A. increased numbers of free radicals
    B. increased numbers of photons
    C. decreased numbers of activated photoinitiators
    D. decreased rate of polymerization

  4. The photoactivation protocol for group B was _______ mW/cm2.

    A. 1250
    B. 950
    C. 650
    D. 300

  5. The nanofilled composite showed a statistically significant difference between top and bottom surfaces at an irradiance of ________ mW/cm2.

    A. 300
    B. 650
    C. 900
    D. 1200

  6. High irradiances generate multiple growth centers in the monomer. Multiple growth centers are associated with the formation of lower density polymer crosslinks.

    A. Both statements are true.
    B. The first statement is true; the second is false.
    C. The first statement is false; the second is true.
    D. Both statements are false.

  7. A determinate energy density above _____ J/cm2 will not improve the mechanical properties of a composite.

    A. 3
    B. 4
    C. 5
    D. 6

  8. The gap between matrix and composite in group C was measured to be ________ µm.

    A. 19.13
    B. 17.43
    C. 15.24
    D. 12.34

  9. Nanofilled composite resins contain ____________ as their filler material.

    A. barium glass
    B. zirconia
    C. quartz
    D. silica

  10. Inadequate polymerization of composite can result in all of the following except one. Which is the exception?

    A. decreased bonding strength
    B. marginal deterioration
    C. decreased leaching of monomers
    D. development of recurrent caries

  11. A microhybrid composite contains _______________.

    A. Bis-GMA
    B. DEGDMA
    C. Bis-EMA
    D. UDMA

  12. High–molecular weight monomers exhibit _________ than lower molecular weight monomers.

    A. greater mobility
    B. less free radical interaction
    C. less ionic bonds
    D. greater shrinkage

  13. The mean KHN for the bottom of specimens in group C was ____________.

    A. 50.94
    B. 75.28
    C. 90.94
    D. 101.28

  14. The DC for the top of the specimens of group D was _____%.

    A. 49.89
    B. 54.73
    C. 54.97
    D. 56.89

  15. An increase in DC for both composites on the bottom was exhibited at an irradiance of _________ mW/cm2.

    A. 1200
    B. 900
    C. 650
    D. 300

Evaluation
Please respond to the statements below, using the following scale:
1 Poor; 2 Below average; 3 Average; 4 Above average; 5 Excellent
Practicality of the content 1 2 3 4 5
Benefit to your clinical practice 1 2 3 4 5
Quality of illustrations 1 2 3 4 5
Clarity of objectives 1 2 3 4 5
Clarity of exercise questions 1 2 3 4 5
Relevance of exercise questions 1 2 3 4 5
 
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