Degree of conversion of two lingual retainer adhesives cured with different light sources

Abstract

The aim of this study was to evaluate the degree of conversion (DC) of two lingual retainer adhesives, Transbond Lingual Retainer (TLR) and Light Cure Retainer (LCR), cured with a fast halogen light, a plasma arc light and a light-emitting diode (LED) at various curing times. A conventional halogen light served as the control. One hundred adhesive samples (five per group) were cured for 5, 10 or 15 seconds with an Optilux 501 (fast halogen light), for 3, 6 or 9 seconds with a Power Pac (plasma arc light), or for 10, 20 or 40 seconds with an Elipar Freelight (LED). Samples cured for 40 seconds with the conventional halogen lamp were used as the controls. Absorbance peaks were recorded using Fourier transform infrared (FT-IR) spectroscopy. DC values were calculated. Data were analysed using Kruskal-Wallis and Mann-Whitney U-tests. For the TLR, the highest DC values were achieved in 6 and 9 seconds with the plasma arc light. Curing with the fast halogen light for 15 seconds and with the LED for 40 seconds produced statistically similar DC values, but these were lower than those with the plasma arc light. All of these light exposures yielded a statistically significantly higher DC than 40 seconds of conventional halogen light curing. The highest DC value for the LCR was achieved in 15 seconds with the fast halogen light, then the plasma arc light curing for 6 seconds. These two combinations produced a statistically significantly higher DC when compared with the 40 seconds of conventional halogen light curing. The lowest DC for the LCR was achieved with 10 seconds of LED curing. The overall DC of the LCR was significantly higher than that of the TLR. The results suggest that a similar or higher DC than the control values could be achieved in 6-9 seconds by plasma arc curing, in 10-15 seconds by fast halogen curing or in 20 seconds by LED curing.

Effects of thermocycling on the degree of cure of two lingual retainer composites

“…On the effect exerted by the type of composite used on DC, it is noteworthy that the two composite materials tested in this study differed in numerous aspects: viscosity, chemical structure of the dimethacrylate monomer, translucency, photoinitiator concentration, and color tone (shade). Consequently, the results obtained in this study reflected these differences 2,16,24) . It has also been reported that monomers such as 2,2-bis[4-(2-hydroxy-3 methacryloxypropoxy)phenyl]propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) reached 85-90% of their final DC in 40 seconds with a QTH light unit 13) .…”

“…The DC values determined by Üşümez 2) et al for TLR and LCR were 55.5±10.3% and 67.6±5.7% respectively. In the present study, statistical evaluation of the pooled overall DC data of the same two composites yielded 68.38±9.31% for TLR and 84.37±3.54% for LCR.…”

“…In other words, any possible DC differences between the top and bottom surfaces of the cured resin were not taken into consideration. Another limitation of this research was the relatively small number of specimens per test group (n=5), although many published studies had used smaller sample sizes 2,6,17,[20][21][22] . According to many researchers that have used different indirect methods to evaluate the DC from monomer to polymer 23) , the DC for restorative resins reportedly ranged from 50% to 80%.…”

“…While these excellent handling properties are both desirable and important, the degree of cure (DC) is also another very important factor for lingual retainer adhesives. This is because lingual retainers -unlike orthodontic brackets -are supposed to serve in the mouth for a long period of time 2) . To achieve an optimum degree of cure for PARBCs, adequate light output and irradiation time are two indispensable requisites 3) .…”

“…It has been suggested that there is a correlation between DC and the resin formulation Received Jun 3, 2009: Accepted Sep 17, 2009 of dental restorative resins 8) . According to one study 2) that investigated and compared the DC of two lingual retainer composites which were cured with fast halogen, plasma arc, and LED lights at different curing times, statistically significant differences were found between the DC values of the two lingual retainer composites cured with different light source-and exposure time combinations. Then, for most investigations on orthodontic materials, the focus was on shear bond strength assessment and comparison between chemically-cured and light-cured materials.…”