Mechanical properties of nanofilled and microhybrid composites cured by different light polymerization modes

Self-Instruction Exercise No. 328
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Exercise No. 328
Subject Code: 017
Dental Materials

The 15 questions for this exercise are based on the article, “Mechanical properties of nanofilled and microhybrid composites cured by different light polymerization modes”, on pages 30-33. This exercise was developed by Thomas C. Johnson, DMD, MAGD, in association with the General Dentistry Self-Instruction committee.

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

  • understand how the mechanical properties of composites change with the method of polymerization;
  • understand the relationship of the measured parameters with clinical performance of composites;
  • learn the general characteristics of the types of fillers used in the tested composites; and
  • decide which composite, based upon filler content and matrix composition, to select for different clinical applications.

Answers for this exercise must be received by April 30, 2014.
  1. Filler particle morphology is either spheroidal or ___________.

    A. oval
    B. tetrahedron
    C. irregular
    D. dodecahedron

  2. Which filler system enables the highest filler content by weight percent (Wt%)?

    A. nanosized particles and clusters
    B. condensed microfills
    C. agglomerated microfills
    D. microhybrids

  3. Which filler type may improve resistance to wear and fracture by reducing interstitial voids and gaps?

    A. microhybrids
    B. agglomerated microfills
    C. condensed microfills
    D. nanoclusters

  4. The manufacturer of Filtek Z350 states the inorganic filler is 78.5 Wt%. What was the value determined during this study?

    A. 76.0
    B. 78.0
    C. 78.5
    D. 80.0

  5. The light polymerization modes used were conventional continuous exposure and _____________.

    A. ramp exposure followed by conventional LED
    B. pulse-delay or interrupted step
    C. quartz-halogen step cure
    D. high-energy pulse cure with laser light

  6. What was Wt% of the inorganic filler for the Charisma composite?

    A. 57.0
    B. 62.0
    C. 66.0
    D. 70.0

  7. Statistical analysis of the overall average of each composite showed no statistically significant differences between the averages of diametral tensile strength (DTS), flexural strength (FS), and flexural modulus (FM) when photoactivated by different methods of curing. However, there was a negative correlation between Wt% of filler and flexural strength.

    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.

  8. What minimal percentage of hardness must the bottom surface of the sample have to the top, to indicate proper polymerization?

    A. 100
    B. 90
    C. 80
    D. 70

  9. The FM for the nanofilled resin was __________ than the microhybrid resin.

    A. the same
    B. lower
    C. higher
    D. higher, but not significantly

  10. The presence of TEGDMA in the resin matrix has been associated with a(n) ________ in the FS of the material, and, a(n) _________ in FM.

    A. increase; increase
    B. decrease; decrease
    C. increase; decrease
    D. decrease; increase

  11. Measurements regarding DTS and FS are poor predictors of a material’s ability to support occlusal forces on posterior teeth. The results in this study for FS are in agreement with the other studies done by da Silva et al, Rodrigues et al, and Melander et al.

    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.

  12. This study suggests that a RBC with a relatively low FM is better suited for which class of restorations?

    A. Class I
    B. Class II
    C. Class IV
    D. Class V

  13. Which of the following is a filler component of the Charisma microhybrid?

    A. barium glass
    B. aluminum chloride
    C. zirconia
    D. non-agglomerated silica

  14. The energy intensity (power/area) of the quartz-halogen (QTH) and the LED curing lights was the same, 400mW/cm2. The energy densities (energy/volume) were also identical at 16 J/cm3.

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

  15. How long was the soft start for the progressive activation mode used in this study?

    A. 5 seconds
    B. 10 seconds
    C. 15 seconds
    D. 20 seconds

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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