Effect of Modalities of Curing on Flexural Strength of Three Composites pp. 7-24
Authors: Giuseppina Casella, Ernesto Rapisarda
Abstract: Introduction: In these years, industries have worked in order to reduce the limits and to improve the physicochemical and mechanical properties of composite resins, with particular consideration to wear and tear resistance, dimensional stability and aesthetics (1-4). We evaluated the flexural strength of three different composite resins, cured for definite times and standard thicknesses; it has been used as index of total (happened) polymerisation already and of intrinsic characteristics of materials, using the same release light modality and two different lamps: an halogen lamp and a LED technology one. Materials and Methods: We used three different composites for direct restoration all resins are A2 colour: CeramX Mono (Dentsply), IntenS (Ivoclar-Vivadent), Miris (Coltene). With special moulds, we fabricated samples having rectangular shape characterized by 3 cm in length, 2 mm in width, and 5 mm in thickness. All the samples were subjected to flexural test using a dynamometer LLOYD 10LR10K, with the speed of loading of 1 mm/minute. Four samples, for each group, have been subjected to halogen light of a lamp of the last generation (Astralis 10 – Ivoclar Vivadent) for seconds with “high power” modality the same sample have always been cured in “quick modality” for 20 seconds with a LED lamp (MiniLED – Satelec). All the samples have been subjected to flexural test. Results: From the observation of values we can note that the hybrid composite and the nano-ceramic subjected to photopolymerization for 20 seconds with the halogen lamp have resulted more stiff than samples cured with the LED source. In fact the samples of hybrid and micro hybrid photocured composite with the halogen light for 20 seconds show values of strength (64.9±3.1 – 80.8±2.6 MPa) and flexural modulus (8.0±0.3 – 9.3±0.2 GPa) greater than those obtained in samples having the same shape subjected to the LED lamp (respectively 42.5±3.0 – 59.5±3.2 MPa and 5.6±0.2 – 7.9±0.4 GPa). So the nano-ceramic tested composite underlines a greater flexural strength if it is cured with the LED source (96.5±2.8 MPa versus 34.7±3.3). Also the flexural modulus, expressed in GPa, results greater in CeramX samples treated for 20 seconds with the LED lamp. Conclusions: By analyzing the general trend of three composite resins for fixed times of 20 seconds, we can observe that both sources guarantee materials with good mechanical properties that are stiffness and strength. As regards the composition of filler, of average sizes of particles and the quality and quantity of photoactivators we retain that new nanoceramic composites behaviour better to LED source than to the hybrid and micro-hybrid products. So, the halogen lamp determines greater flexural strength better index and more complete conversion of composite resin, in composite characterized by fillers of greater sizes that are the hybrid and micro-hybrids previously tested products. We have to specific clearly if that experimental shown data all refer to “high power” curing modality. The data are confirmed when the use of lamps in incremental modality or in pulsing modality, gives us good mechanical properties coming from an adapt and complete photo-polymerization of the resin and from the following possibility to make the most of the mechanical strength provided from the filler.