No abstract

In this study diametral tensile strength and microhardness of composites were investigated in relation to various temperatures during curing. It has been demonstrated that temperatures elevated up to 60 degrees C can improve the mechanical properties considerably. Also the stability of the resin system in aggressive environments was improved due to more efficient cross-linking. Thermal analysis of the material showed an endothermic reaction between 60 and 70 degrees C that is believed to be responsible for the initiation of the extra cross-linking. Heating of composite fillings during clinical use is suggested.

In this study the curing of photo-initiated composites was investigated. After irradiation, the material in an experimental cavity could be divided into three zones: zone A which showed physical properties comparable to those of chemical initiated composites, zone B which was markedly softer than the first one, and zone C which showed no signs of curing at all. The location of the zones was dependent on the energy of the u.v. radiation, the exposure time, the storage time, and the storage conditions. The uncured material of zone C showed no tendency to set. The clinical implications of the observations are discussed.

The purpose of this study was to investigate the properties of composite materials that had been heated to temperatures which may occur during dry polishing. Bulk composite material was submitted to thermal analysis from R.T. to 200 degrees C. Two distinct stages of thermal reaction in this range could be identified. One at approximately 70 degrees C, which could be related to a further initiating of unreacted groups, and one above 100 degrees C, which could be related to the glass transition. The glass transition was also observed microscopically. Hardness measurements were carried out on the warm material at different temperatures as well as on the material being cooled down to R.T. With temperature rise, a continuous increase in hardness and abrasion resistance could be demonstrated. The observed phenomena for bulk material are related to the properties measured on dry polished surfaces.