IADR Abstract Archives

Polymerization Behavior of Composites at Top/Bottom of Cavity Using Various-Lights

Objectives: We reported homogeneous polymerization of resin composite improved resin-cavity adaptation in Dent Mater 2001. The aim of this study was to evaluate microhardness and hardness ratio of hybrid resin composites using various lights irradiation related to cavity wall adaptation.
Methods: Light-curing units were LED light-curing unit (Demi Ultra; Kerr) and experimental quartz-tungsten-halogen light-curing unit (QTH; GC). The light-cured resin composites were Clearfil AP-X (AP, shade A3, Kraray Noritake Dental), Estelite Σ Quick (EQ, shade A3, Tokuyama Dental) and Clearfil Photo Bright (PB, shade US, Kraray Noritake Dental). Composite specimens of 2 mm thickness were polymerized in Teflon molds using energy density of 24,000 mJ/cm². Light irradiance were LED: 1,200 mW/cm² 20s, LED: 600 mW/cm² 40s (light tip–resin distance: 6mm) and QTH: 600 mW/cm² 40s. Just after light curing, Knoop hardness (KHN) was measured at the top and bottom surfaces of each specimen using hardness tester. The hardness ratio=KHN of bottom surface/KHN of top surface was calculated. All experiments were performed at room temperature of 23±2 ^oC with humidity of 50±10%. Data (n=8) were analyzed using Bonferroni/Dunn test.
Results: At 40s after start of light curing, KHN at the bottom surfaces of resin composites were significantly lower than that of at the top surfaces except for PB with QTH: 600 mW/cm² 40s (p < 0.05). LED: 1,200 mW/cm² 20s showed significantly smaller hardness ratio compared with that of LED: 600 mW/cm² 40s and QTH: 600 mW/cm² 40s for every resin composite (p < 0.05).
Conclusions: When energy density was the same, polymerization of resin composite at the bottom surface was inhibited compared with that of at the top surface using high irradiance light. Supported by Grant #25462950 and #16K11543 from JSPS.

Division: IADR/AADR/CADR General Session
Meeting: 2020 IADR/AADR/CADR General Session (Washington, D.C., USA)
Location: Washington, D.C., USA
Year: 2020
Final Presentation ID: 0399
Abstract Category|Abstract Category(s): Dental Materials 2:Polymer-based Materials

Authors

Yoshikawa, Takako ( Tokyo Medical & Dental University , Tokyo , Japan )

Sadr, Alireza ( University of Washington School of Dentistry , Seattle , Washington , United States )

Tagami, Junji ( Tokyo Medical & Dental University , Tokyo , Japan )

Financial Interest Disclosure: NONE

SESSION INFORMATION

Oral Session
Polymer-based Materials: General Properties

TABLES

Knoop hardness at top and bottom surfaces of resin composites and Hardness ratio

Light-curing method/ Material	KHN				Hardness ratio
		QTH: 600 mW/cm² 40s	LED: 1,200 mW/cm² 20s	LED: 600 mW/cm² 40s	QTH: 600 mW/cm² 40s	LED: 1,200 mW/cm² 20s	LED: 600 mW/cm² 40s
AP	Top	57.2 (1.4)^a	65.2 (1.2)^a	59.5 (1.2)^a	0.93 (0.01)^A	0.86 (0.02)^{A, B}	0.93 (0.01)^B
	Bottom	53.4 (1.1)^a	56.7 (1.2)^a	56.1 (1.4)^a
EQ	Top	35.2 (0.9)^b	37.1 (0.9)^b	35.1 (0.5)^b	0.93 (0.03)^A	0.88 (0.02)^{A, B}	0.93 (0.02)^B
	Bottom	32.6 (1.5)^b	32.6 (1.3)^b	32.6 (1.1)^b
PB	Top	37.3 (1.2)	38.0 (0.8)^c	39.7 (1.7)^c	0.94 (0.02)^A	0.89 (0.02)^{A, B}	0.92 (0.02)^B
	Bottom	35.1 (0.7)	33.8 (1.5)^c	36.7 (1.1)^c

Intragroup data designated with same superscript lowercase letters for each top or bottom knoop hardness are significantly different (p < 0.05). Intergroup data designated with same superscript uppercase letters for each irradiation are significantly different (p < 0.05).