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Effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resin

Effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resin

Article information

Restor Dent Endod. 2008;33(4):341-351
Publication date (electronic) : 2008 July 31
doi : https://doi.org/10.5395/JKACD.2008.33.4.341
Department of Conservative Dentistry, College of Dentistry, Yonsei University, Korea.
Corresponding Author: Chan Young Lee. Department of Conservative Dentistry, College of Dentistry, Yonsei University, 134 Shinchon-Dong, Seodaemun-Ku, Seoul, 120-752, Korea. Tel: 82-2-2228-8700, Fax: 82-2-313-7575, chanyoungl@yuhs.ac
Received 2008 April 22; Revised 2008 May 15; Accepted 2008 May 20.

Abstract

This study investigated the effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resins.

The linear polymerization shrinkage of each composite was measured using the custom-made linometer along with the light shutter specially devised to block the light at the previously determined interval. Samples were divided into 4 groups by light curing method; Group 1) continuous light (60s with light on); Group 2) intermittent light (cycles of 3s with 2s light on & 1s with light off for 90s); Group 3) intermittent light (cycles of 2s with 1s light on & 1s with light off for 120s); Group 4) intermittent light (cycles of 3s with 1s light on & 2s with light off for 180s). The amount of linear polymerization shrinkage was measured and its maximum rate (Rmax) and peak time (PT) in the first 15 seconds were calculated. For the measurement of cuspal deflection of teeth, MOD cavities were prepared in 10 extracted maxillary premolars. Reduction in the intercuspal distance was measured by the custom-made cuspal deflection measuring machine. ANOVA analysis was used for the comparison of the light curing groups and t-test was used to determine significant difference between the composite resins.

Pyramid showed the greater amount of polymerization shrinkage than Heliomolar (p < 0.05). There was no significant difference in the linear polymerization shrinkage among the groups. The Rmax was group 4 < 3, 2 < 1 in Heliomolar and group 3 < 4 < 2, 1 in Pyramid (p < 0.05). Pyramid demonstrated greater cuspal deflection than Heliomolar. The cuspal deflection in Heliomolar was group 4 < 3 < 2, 1 and group 4, 3 < 2, 1 in Pyramid (p < 0.05).

It was concluded that the reduced rate of polymerization shrinkage by intermittent polymerization can help to decrease the cuspal deflection.

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Article information Continued

Figure 1

Upper view of the light shutter.

Figure 2

Close up of the cuspal deflection measuring machine, the light shutter and the curing light tip. Samples were placed between rod ends.

Figure 3

Change in the amount of linear polymerization shrinkage of Heliomolar versus time.

Figure 4

Change in the amount of linear polymerization shrinkage of Pyramid versus time.

Figure 5

Change in the rate of polymerization shrinkage versus time on Heliomolar.

Figure 6

Change in the rate of polymerization shrinkage versus time on Pyramid.

Figure 7

Change of cuspal deflection of Heliomolar versus time.

Figure 8

Change of cuspal deflection of Pyramid versus time.

Table 1

Restorative materials used in this study

Table 1

Table 2

List of investigated curing methods with their curing cycles

Table 2

Table 3

Amount of linear polymerization shrinkage (µm)

Table 3

There is no statistical difference in all groups of the same resin. *indicates significant difference in the amount of linear polymerization shrinkage between Heliomolar and Pyramid at 95% level of confidence. Figures in the parenthesis indicate standard deviations.

Table 4

Peak time (PT) which showed the highest rate of polymerization and maximum rate of polymerization shrinkage (Rmax)

Table 4

Means with the same letter are not significantly different at p < 0.05 level. *indicates different maximum rate of polymerization shrinkage (Rmax) between Heliomolar and Pyramid at 95% levels of confidence.

Table 5

Mean value of cuspal deflection at 10 min (µm)

Table 5

Means with the same letter are not significantly different at p < 0.05 level. *indicates different the mean value of cuspal deflection between Heliomolar and Pyramid at 95% levels of confidence.