Characterization of Polydimethacrylates and Their Composites by Dynamic Mechanical Analysis

Abstract

The objective was to characterize, by dynamic mechanical analysis (DMA), the polymeric materials used to restore teeth and, in particular, to assign a glass transition temperature, Tg. Generally, in DMA work, Tg is taken as the temperature at which the internal damping, i.e., tan delta, has a maximum value. However, in the present work it was shown that the classical method of assigning Tg corresponds more closely to an assignment based on changes in elastic modulus. On this basis, a bis-GMA copolymer and a proprietary dental composite, both polymerized by exposure to light, were assigned Tg values of -25 degrees C and +10 degrees C, respectively. The composite had an even lower value, Tg = -10 degrees C, after saturation with water. The value of Tg can be increased considerably by treatments which are known to increase the degree of polymerization, i.e., by heating or by gamma-irradiation. The present findings imply that composites made by photopolymerization may undergo marked changes in mechanical state (becoming glassy, leathery, and rubbery) in the oral cavity, due to changes in temperature from about 0 degree C to 50 degrees C. It is not known which of these states would give best service properties, such as wear resistance, but in any case variation of properties in service would appear to be undesirable.

Multiple transitions in a dimethacrylate network

“…In contrast, better agreement with changes in thermal expansion was obtained by noting the temperature at which E' began a more marked decrease. 16 The onset of this decrease was defined by …”

Dynamic mechanical analysis of heat, microwave and visible light cure denture base resins

“…Because of the wide range of mechanical behaviour involved, and the close relationship of this mechanical behaviour with the viscoelastic properties centred around one or more glass transition phenomena (such as the a, [3 or other transitions), dynamic mechanical analysis (DMA) is a very valuable method to characterize dental polymeric systems. The sensitivity of DMA for the detection of glass transitions is well known and many investigators have used the technique to characterize viscoelastic properties of different dental polymers [1][2][3][4][5][6][7][8][9][10][11][12][13]. The information provided in DMA tests, such as storage modulus, loss modulus and tan delta, have been used to study heat cure denture resins in the past [10 13].…”

Effect of filler content on mechanical strength in bis-GMA-based resins with urethane linkages

“…Because of incomplete polymerization of resin composites cured by visible light, maximum mechanical strength is not attained [1][2][3][4]. The monomer compositions and the concentration of catalyst in the resins need to be optimized in visible light polymerization [5,6].…”