Resin-based Composite Light-cured Properties Assessed by Laboratory Standards and Simulated Clinical Conditions

Abstract

The irradiation technique, used to measure mechanical properties of resin-based composites according to international standards, consistently differs from clinically simulated conditions, calling into question whether laboratory findings can be unrestrictedly applied clinically, especially at short polymerization times. The study analyzes whether degree of conversion measurements at short post-polymerization time (five minutes) are able to predict the long-term material behavior. SUMMARYThe following parameters were varied: 1) irradiation technique: top and bottom polymerization according to the ISO standard, and polymerization from only the top, simulating clinical situations; 2) polymerization time: 5, 10, 20, and 40 seconds; 3) storage conditions: 24 hours in distilled water, thermocycling followed by storage for four weeks in artificial saliva or alcohol. Flexural strength (FS), flexural modulus (E flexural ), indentation modulus (E), Vickers hardness (HV), and degree of conversion (DC) were measured.The laboratory results were similar to those measured by mimicking clinical conditions only at high polymerization times and mild storage conditions (20 seconds and 40 seconds and storage for 24 hours in water, and 40 seconds with aging and storing in saliva). Significantly higher DC values were measured on the top than on the bottom of a 2-mm layer for all polymerization times. Overall, 5-second

Influence of successive light-activation on degree of conversion and knoop hardness of the first layered composite increment

“…The probable explanation is that, despite the PE protocol delivering an extremely high energy (3200 mW/cm 2 ), it promoted a rapid initiation of polymerization, inducing to shorter chain lengths and, hence, leading to a lower molecular weight, compromising the hardness of the bottom surface. This behavior is similar to observe for plasma arc curing units [18] and for short polymerization times of 5 or 10 s, even for high-powered LED LCUs [8].…”

“…They last significantly longer and their power of density does not decrease with time. Some high-powered LED LCU manufacturers suggested short polymerization times of up to 5 s [8,9].…”

“…Since the introduction of light-activated resin composites, light-curing units (LCUs) have become an important device, and the knowledge of the characteristics of resin composite and LCU are fundamental to success of tooth restoration and clinical longevity. The options of LCU include quartz-tungsten-halogen (QTH) lamps, plasma arc, argon laser and lightemitting diodes (LEDs) [8]. QTH is used since the beginning of visible light-activated resin composite, but some of the components deteriorate, decreasing significantly the power density over time, requiring constant monitoring and maintenance.…”

Effects of aging and irradiation time on the properties of a highly translucent resin-based composite

“…Our previous study showed that the mechanical properties of IPS Empress Direct Trans Opal were lower than those of Dentin shade 28) . It was also shown that IPS Empress Direct Trans Opal had below-average macro-mechanical properties when compared to other nanohybrid RBCs; its mechanical properties were more comparable to those of microfilled RBCs, flowable RBCs and compomers 29,30) .…”

Effect of a third‐generation LED LCU on microhardness of tooth‐colored restorative materials

“…Nevertheless, LED technology has two main drawbacks: First, because first‐ and second‐generation LEDs emit light matching the absorption spectrum of camphorquinone (430–500 nm), they may not provide adequate curing of composite resins containing alternative initiators. Second, the manufacturers of LED units recommend irradiation times of 20 s and 40 s, whereas shorter curing times are always preferable in clinical conditions. In an attempt to overcome these problems, so‐called ‘third‐generation’ LED curing units with multiple diodes and dual emission peaks have been introduced.…”