Influence of curing light power and energy on shrinkage force and acoustic emission characteristics of a dental composite restoration.
OBJECTIVE
To evaluate the density effects of light power and energy on the volumetric polymerization shrinkage and acoustic emission (AE) characteristics of a dental resin composite in the cavities of human teeth.


METHODS
Two experiments were performed at different power levels (1,000 and 4,000 mW/cm2) using a light curing unit: (1) cylindrical cavities with diameters of 4 mm and depths of 2 mm were constructed using two symmetric steel molds. The cavities were filled with resin, and the shrinkage force during polymerization was measured using a load cell attached to the mold. Polymerization shrinkage forces were measured under four conditions (1,000 mW/cm2 x 10 seconds, 1,000 mW/cm2 x 20 seconds, 4,000 mW/cm2 x 3 seconds, and 4,000 mW/cm2 x 5 seconds); (2) tooth specimens with cavity diameters of 6 mm and depths of 2 mm were made from human molars. AE signals during polymerization shrinkage were monitored in real time for 10 minutes after irradiation and two AE factors (amplitude for defect size and hit number for defect number) were assessed in the examination of defects. Two levels of light energy (20 J/cm2 = 1,000 mW/cm2 x 20 seconds and 12 J/cm2 = 4,000 mW/cm2 x 3 seconds) were used.


RESULTS
Shrinkage occurred more quickly at 4,000 mW/cm2 than at 1,000 mW/cm2 during the initial phase. The shrinkage force became almost the same for equivalent light energy as time increased. Higher light energy (20 J/cm2) under low-power conditions (1,000 mW/cm2) caused larger cumulative numbers of AE hits than did lower light energy (12 J/cm2) under high-power conditions (4,000 mW/cm2). At 4,000 mW/cm2 and 12 J/cm2 (i.e., high power, low energy), the average amplitude of the AE signals was larger than at 1,000 mW/cm2 and 20 J/cm2 (low power, high energy).
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga-koen 6-1, kasuga, Fukuoka 816-8580, Japan. ar-s-yoon@mms.kyushu-u.ac.jp
Sang-Jae
SJ
Yoon
Department of Mechanical Engineering, Graduate School, Hanyang University, Seoul, Korea.
Ja-Uk
JU
Gu
Department of Mechanical Engineering, Graduate School, Hanyang University, Seoul, Korea.
Nak-Sam
NS
Choi
Research Institute for Applied Mechanics, Kyushu University, Kasuga-koen 6-1, kasuga, Fukuoka 816-8580, Japan.
Kazuo
K
Arakawa
D000162:Acoustics / Q000295:instrumentation; D000669:Amplifiers, Electronic; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental; D003737:Dental Cavity Preparation / Q000145:classification; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D003793:Dental Restoration, Permanent; D006801:Humans; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D058105:Polymerization; D011829:Radiation Dosage; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors
C112828:Clearfil AP-X; C515604:Clearfil Tri-S Bond; D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; D019279:Resin Cements