Einfluss des Vor-Erwärmens auf die Materialeigenschaften dentaler Komposite

Composites take an elementary part in dentistry and dental work is not imaginable without them anymore. Requests by patients for high class, aesthetic and hygienic unobjectionable fill material and a permanent effort of the developers have lead, among other things, to the ability of using composite in load-bearing posterior teeth. There is a continuous pursuit for further options of improvement of material properties and handling. Pre-warming composites before using them is seen as one potential approach. The aim of this study is to examine the impact of the composite heaters Calset (AdDent Inc.) and Ease-It (Rønvig Dental Mfg. A/S) on material properties of com-posites with different chemical compositions. The composites Charisma® and Venus Diamond® (Heraeus Kulzer GmbH), Kalore® (GC Corporation) and Tetric EvoCeram® (Ivoclar Vivadent GmbH) were used as testing material. The temperatures of 40 °C, 50 °C and 68 °C were determined as testing temperatures with room temperatures as a reference value. First of all, thermal history within the composite heater and the composite car-pules of Charisma, Venus Diamond and Tetric Evoceram were checked in each case. Furthermore, temperature change within the pulp was examined by using an extracted and prepared tooth. Therefore, the material properties dispensing force out of a carpule, consistency, stickiness, flexural strength, Young’s modulus, shrinkage, shrinkage stress, curing depth and double bond conversion were investigated. Before each checking the composite was preheated for 10 minutes. In total, there were four groups for each of the four materials, corresponding to the temperatures of approx. 21 °C, 40 °C, 50 °C and 68 °C. The amount of samples varied from experiment to experiment. Testing the dispensing force using the universal testing machine Z010 (Zwick) the amount of samples was n = 10. The testing speed was determined at 50 mm/min, the forward force at 5 N and the testing distance at 7 mm. Respectively, by testing the materials at 68 °C the testing speed was changed to a forward force of 5 N, the testing speed to 6 mm. Consistency and stickiness (n = 6) were measured with the texture analyzer TA.XT.plus (Winopal). For measuring flexural strength and Youngs modulus (n = 10) according to DIN EN ISO 4049:2009, the test pieces were positioned on the corresponding appliance of the universal testing machine Z010 (Zwick). The preload was determined at 0,4 N, the testing speed at 0,75 mm/min. Shrinkage was analyzed by using the AccuPyc 1340 helium pycnometer (Micromeretics GmbH) through altering the pressure of helium gas. For testing shrinkage stress (n = 3) photoelastic method was used. Test pieces for testing curing depth (n =3) were produced in a cylindrical form and thickness of the polymerized composite was measured according DIN EN ISO 4049:2009. The Fourier transform infrared spectroscopy was utilized for measuring double bond conversion. The pulp simulation showed an increase of temperature within the pulp up to 12,5 °C. Significant lower dispensing force of all tested composites could be achieved be-cause of pre-warming. At 50 °C forces could be reduced by more than 50 %, com-pared to those of room temperature. Consistency was also decreased while in-creasing pre-warming temperature. The examination of stickiness did not show any temperature-dependent change. Furthermore, shrinkage, Youngs modulus, flexural strength and curing depth were not affected by temperature change. The three last mentioned properties fulfilled the requirement defined in DIN EN ISO 4049:2009. Shrinkage stress on the other hand showed a slight dependence on temperature. It could be proved that double bond conversion was influenced spe-cifically depending on the material tested. Charisma and Kalore showed an in-creased double bond conversion with increasing pre-warming temperature, while Venus Diamond and Tetric EvoCeram displayed a depression until 50 °C and an increase at 68 °C.