A comparative study between the degree of conversion and the flexural strength of composite resins

Abstract

Objectives: The aims of this study were to measure the degree of conversion (DC) and flexural strength (FS) of composite resins with different rheological behavior and to correlate between two properties. Materials and Methods: Four restorative (Vit-l-escence, Z-250, Tetric ceram, Esthet-X) and four flowable (Aeliteflo, Admiraflow, Permaflo, Revolution) light-cured composite resins were investigated for this study. The DC was analyzed with Fourier transfer infra-red spectroscopy (FTIR) by a potassium bromide (KBr) pellet transmission method. The composite resin was diluted with KBr powder and mixed thoroughly. The mixture was pressed with sufficient pressure (10 ton) to produce a transparent pellet. The pellet was placed in the transmission holder for analysis. The spectrum of unpolymerized specimen was measured before the specimen was irradiated for 60s with a visible light curing unit. The polymerized specimen was scanned for its FTIR spectrum. The FS was measured according to ISO 4049. A stainless steel mold (25×2×2mm) was used. Each specimen was polymerized for 40s. Flexural strength was measured with 3-point bending test after storage in water at 37 ℃ for 24 hours. The data were statistically analyzed by use of Independent Samples t-test, one way ANOVA at a significance level of 0.05. The dependence of flexural strength on the degree of conversion was also analyzed by regression analysis. Results: Mean DC and FS values ranged from 43 % to 61% and from 84.7 MPa to 156.7 MPa respectively. DC values of the flowable composite resins were significantly higher than those of restorative composite resins. Inter-material comparisons of DC were found that the value of Z-250 was lower than that of Vit-l-escence, Aeliteflo, Permaflo and the value of Esthet-X was lower than that of Aeliteflo, Permaflo (P < 0.05). The restorative composite presented that the value of Z-250 was lower than that of Vit-l-escence, Tetric ceram and the value of Vit-l-escence was higher than that of Esthet-X, Z-250. The flowable composite resin presented that the value of Aeliteflo was significantly higher than that of Admiraflow. The flexural strengths of restorative composite resins were greater than those of flowable composite resins. The highest flexural strength was obtained with Z-250. Inter-material comparisons of FS were decreased in the order of follows; Z-250 > Vit-l-escence > Tetric ceram = Esthet-X and Permaflo > Aeliteflo = Admiraflow > Revolution. (Restorative and flowable composite resins respectively) In this study, no statistically significant correlation was observed between the degree of conversion and the flexural strength tested in any of the composites. In restorative and flowable composite resins respectively, the dependence of FS on DC was not significantly correlated, too. Clinical significance: We concluded that radical polymerization of organic matrix is not a major factor in determining the flexural strength of commercially available composite resins.;목적: 본 실험의 목적은 상용되는 컴파짓 레진의 중합 전환율과 굴절강도를 계측하고, 위 두 특성간의 연관관계를 알아 보고자 함이다. 재료 및 방법: 네 종류의 수복용 (Vit-l-escence, Z-250, Tetric ceram, Esthet-X)과 네 종류의 Flowable 광중합형 컴파짓 레진 (Aeliteflo, Admiraflow, Permaflo, Revolution)이 본 실험에 이용되었다. 중합 전환율은 potassium bromide (KBr) pellet transmission 방법에 의한 FTIR로 분석되었다. 먼저 컴파짓 레진을 브롬화칼륨 분말에 섞어서 균일하게 혼합한 후 충분한 압력을 가하여서 얇은 펠렛을 만든 다음, 분석을 위해서 transmission holder에 펠렛을 위치 시킨다. 광중합기로 60초간 광중합 하기 전에 분광화학 분석을 시행하고, 중합 후에 다시 FTIR 광분석을 시행하였다. 굴절 강도는 ISO 4049 규정에 따라 시행하였다. 시편제작을 위해 스테인레스 스틸 몰드(25 2 2mm)가 이용되었다. 시편을 40초 간 광중합하여, 37 ℃ 수중에 24시간 침수 시킨 후 3-점 굽힘 test를 실시하였다. 평균값과 표준 편차를 구했으며, 95% 신뢰수준에서 one way 다중분석을 하였으며, 또한 중합 전환율과 굴절강도간의 상관관계를 분석하였다. 결과: 평균 중합 전환율과 굴절강도는 각각 43 %에서 61 %, 84.7 MPa에서 156.7 MPa로 나타났다. 본 실험에서는 Flowable 컴파짓 레진이 수복용 컴파짓 레진에서 보다 약간 높은 중합 전환율을 보였다. Z-250 의 중합 전환율은 Vit-l-escence, Aeliteflo, Permaflo 의 중합전환율보다 낮았으며, Esthet-X 의 중합전환율은 Aeliteflo, Permaflo 의 중합전환율보다 낮았다. Flowable 컴파짓레진에서는 Aeliteflo 의 중합전환율이 Admiraflow 의 중합전환율보다 통계학적으로 유의하게 높았다. 수복용 컴파짓 레진의 굴절강도가 Flowable 컴파짓 레진에서 보다 컸다. 굴절강도는 Z-250에서 가장 높았다. 굴절강도의 재료간 비교는 수복용 컴파짓 레진과 Flowable 컴파짓 레진에서 각각 다음과 같은 순으로 작아졌다. Z-250 > Vit-l-escence > Tetric ceram = Esthet-X (수복용 컴파짓 레진), Permaflo > Aeliteflo = Admiraflow > Revolution (Flowable 컴파짓 레진). 실험에서 검사된 컴파짓 레진의, 중합전환율과 굴절강도 간에는 통계학적으로 유의한 상관관계를 보이지 않는다. 임상적 유의점: 상용되는 컴파짓 레진에서, 유기 매트릭스 성분의 중합은 컴파짓 레진의 굴절강도를 결정하는데 있어서 주요한 인자가 아니라고 추론된다.