Measuring the residual stress in dental composites using a ring slitting method.
OBJECTIVE
The objective of this experiment was to employ the ring slitting method for the measurement of the residual stress (RS) produced in dental composite materials after polymerization. This study was designed to determine the effect of slitting and measuring time on the residual stress.


METHODS
Rings were made in a split brass mold from three composites (Z100/3MESPE; Herculite/Kerr; Heliomolar/Ivoclar) and cured in a Triad II (Dentsply). Two points were scribed, and the rings were slit at either 1 h (Early-group) or 24 h (Delayed-group) after curing the composite. The change in the distance between the scribed points was measured using an image analyzer system at both 1 and 24 h after slitting. From the measured change, circumferential RS was calculated and statistically analyzed with ANOVA/Tukey's (P<0.05). The degree of conversion of each composite at 1 and 24 h was measured with FTIR and analyzed using Student's t-test (P<0.05).


RESULTS
In general, the residual stress (range=0.42-2.84 MPa) was highest for Z100 and lowest for Heliomolar, but this depended upon the test conditions. The early cut (1 h slitting), 24 h measurement groups showed the highest residual stress values.


CONCLUSIONS
This study, describes a ring slitting method to measure residual stress generated in dental composites during and after curing. The stress of composite can be affected by the cutting and measurement time.
Park
Jeong Won
JW
Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, 101, Dongin-dong 2-ga, Joong-gu, 700-422 Daegu, South Korea. pjw@knu.ac.kr
Ferracane
Jack L
JL
D000180:Acrylic Resins / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation / Q000379:methods; D004548:Elasticity; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008422:Materials Testing; D008956:Models, Chemical; D011108:Polymers / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013314:Stress, Mechanical; D013997:Time Factors; D015040:Zirconium / Q000737:chemistry
D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D003764:Dental Materials; C513708:Heliomolar; D011108:Polymers; D011140:Polyurethanes; D019279:Resin Cements; C083568:Z100 composite resin; C060386:Triad resin; C065770:Herculite XR; D012822:Silicon Dioxide; D015040:Zirconium