Depth of Cure of New Flowable Composite Resins

Manufacturers have introduced new flowable composites recently that reportedly may be bulk cured in increments over 4 mm.  Objectives: Evaluate the depth of cure of Surefil SDR Flow (Dentsply), Grandio Flow (VOCO) and Venus Bulk Fill (Heraeus) and a conventional flowable composite, Revolution (Kerr) using bottom/maximum Knoop Hardness Number (KHN) ratios and the scrape technique (ISO 4049). Methods: Specimens were polymerized (Bluephase G2, Ivoclar) for 20 and 40 seconds at 0-mm distance. For KHN, five specimens were polymerized per flowable composite (shades A2, A3, and Universal for Venus) in 2-, 3-, 4-, 5-, and 6-mm-thick by 8-mm-diameter plastic molds.  All specimens were stored for 24-hours at 37ºC in 95% humidity.  KHN were determined from three measurements at each shade per thickness using a hardness tester (Leco).  Maximum hardness was determined from the mean maximum KHN from the top surface of the 2-mm thick specimens polymerized for 40 seconds.  The 4-mm thick mold was used first.  If the bottom/maximum KHN ratio exceeded 80%, the next thicker mold was used, and if less than 80%, the next thinner mold was used.  For the scraping technique, specimens were polymerized in a 10-mm-thick by 4-mm diameter plastic mold for 20 and 40 seconds at 0-mm distance.  After 24-hr storage as before, uncured resin was scraped with a plastic instrument and the remaining thickness was measured with a micrometer and divided by two.  Scrape-test data and 4-mm thick specimens were analyzed with ANOVA/Tukey (alpha=0.05). Results: In general, depth of cure using either bottom/maximum KHN or scrape technique: Venus ≥ SDR ≥ Grandio ≥ Revolution. See Table.  Conclusions:   Venus Bulk Fill predictably exceeded the manufacturer’s claim of a 4-mm depth of cure using both KHN ratios and the ISO 4049 scrape test at both 20 and 40 seconds of curing time. 

 

Flowable Composite

20-Second Curing Time Bottom/Maximum Knoop Hardness Ratios (st dev)

Scrape Test mm (st dev)

2 mm

3 mm

4 mm

5 mm

6 mm

A2

A3

A2

A3

A2

A3

A2

A3

A2

A3

A2

A3

Revolution

89.3* (2.9)

86.6* (5.8)

75.2 (2.2)

70.6 (1.9)

71.1 (1.8) a

51.9 (4.6) a

2.88 (0.03) a

2.42 (0.06) a

Grandio

87.3* (1.2)

75.5 (2.9)

79.8 (0.9)

69.1 (3.7)

67.1 (0.8) a

56.5 (2.5) ab

3.01 (0.04) a

2.77 (0.05) b

SDR

89.6* (3.0)

81.4* (1.9)

79.2 (1.2) b

59.6 (3.1) b

3.77 (0.19) b

3.88 (0.05) c

Venus

c 89.3* (3.9) c Universal

79.0 (2.4 ) Universal

c 4.88 (0.04) d Universal

KHN indicated with an asterisk (*) exceeded the minimum 80% bottom/max ratio.  Groups with a different letter per column are significantly different (p>0.05).

Flowable Composite

40-Second Curing Time Bottom/Maximum Knoop Hardness Ratio (st dev)

Scrape Test mm (st dev)

2 mm

3 mm

4 mm

5 mm

6 mm

A2

A3

A2

A3

A2

A3

A2

A3

A2

A3

A2

A3

Revolution

81.3* (5.9)

84.3* (3.1)

73.3 (2.0) a

60.1 (4.7) a

3.24 (0.11) a

3.03 (0.06) a

Grandio

85.7* (1.4)

81.4* (6.6)

76.6 (1.1) a

69.6 (2.0) b

3.56 (0.04) b

3.17 (0.04) a

SDR

85.6* (1.7)

91.3* (1.5) b

76.7 (2.4) c

77.3 (2.0)

4.51 (0.11) c

4.52 (0.25) b

Venus

b 90.9* (2.4) d Universal

82.9* (6.3) Universal

78.2 (2.7) Universal

d 5.07 (0.02) c Universal

KHN indicated with an asterisk (*) exceeded the minimum 80% bottom/max ratio.  Groups with a different letter per column are significantly different (p>0.05).