The MARC Patient Simulator (MARC PS) enables researchers to observe the influence of handling errors on the radiant exposure that is delivered by light curing units (LCUs). Changes in the tilt angle and distance of the light guide exit face in relation to the surface of the composite increment have a distinct effect on the total amount of light delivered during polymerization and may cause insufficient conversion of the material. Therefore, the aim of the present study was to determine the influence of the tilt angle and distance of irradiance on the efficiency of light application by recording the total amount of energy using the anterior tooth sensor of the MARC PS.
The influence of the tilt angle and distance of the light guide to the sensor surface on the delivered radiant exposure was examined for three different LCUs (Celalux 2 [C2], Bluephase [BP] and Translux Powerblue [TPB]). The measurements were performed for 20 s each with five different tilt angles ( α = 0°, 5°, 10°, 15°, 20°) and nine different distances ( L = 1, 2, 3, 4, 5, 6, 7, 8, 9 mm).
For all LCUs, a distinct influence of the tilt angle on the delivered amount of fluence was found. At 0° tilt the C2 delivered a total light energy of 38.55 J/cm 2 . By increasing the tilt of the light guide the amount of energy applied significantly decreased. At 20° tilt a reduction by 31.2% of the original light fluence was recorded. However, the C2 was the most powerful LCU measured. Even under optimum measurement conditions, the BP delivered a fluence of only 14.8 J/cm 2 . At a tilt angle of 20°, though, the light sensor still registered 92.7% of the original output power. Under the same conditions, the TPB delivered 81.4%.
With increasing distance of the light guide exit face to the surface of the sensor all LCUs showed a significant loss in delivered light energy. At a distance of 2 mm the C2 showed a reduction by 46.7%, whereas total fluence of BP and TPB were reduced by 3.8% and 4.8%, respectively.
The choice of LCU and the application of an appropriate curing time are important for successful polymerization. Nevertheless, a perpendicular positioning of the light guide as close as possible to the surface of the composite increment is of essential importance in order to ensure sufficient delivery of light.
Light-curing composites have become well established in dental practice. Because of their natural appearance, they satisfy patients’ growing esthetic demands; meanwhile, they are among the most frequently used dental biomaterials.
In recent years various studies have shown that the polymerization conditions are very important for the durability and quality of the fillings . Researchers have examined how the thickness of a composite layer and the type of light-curing unit (LCU) used – and, thus, the irradiance delivered – influence the mechanical properties of the composite . Current investigations by our team have studied the effect of different LCUs on the degree of polymerization and, as a consequence, on the potential cytotoxic effects of the material .
It is well known that an insufficient delivery of light energy leads to an incomplete conversion of the composite, leaving residual monomers that are toxic to the dental pulp cells .
Therefore, professional polymerization should aim to maintain such decisive factors as the depth of cure of the composites according to ISO 4049 .
However, a current study shows considerable variations in the way LCUs are handled in clinical practice, and that these variables may have an influence on the actually delivered light energy as well as on the curing result .
The light energy delivered to the cavity is modified by the technical parameters of the LCU, but more so by the cavity depth, the layer thickness and type of the material and, last but not least, by the individual way the LCU is handled .
Subjective factors, such as the polymerization time, the tilt angle of the light curing unit and the distance of the light guide to the surface of the composite increment have a direct influence on the polymerization result . Energy transfer can further be influenced by the use of an infection control sleeve and/or safety goggles, and the tactile guiding of the light applicator . In particular, infection control sleeves seem to have a marked influence .
The delivered irradiance of halogen-lamp and LED LCUs as a function of their distance to the composite has been discussed in several studies . LED LCUs delivered a higher energy over shorter distances, whereas halogen lamps (QTH), have been used in earlier studies and, therefore, not universally applicable, had their highest irradiance at a greater distance. Correlations between polymerization time and distance to the composite and the resulting depth of cure have also been ascertained .
So far, no studies have become known that would investigate energy transfer of LCUs especially as a function of the tilt angle.
The present study was aimed to investigate, by means of the MARC Patient Simulator, the influence of (a) the tilt angle of the light guide relative to the anterior tooth sensor, and of (b) the distance of the light guide (with and without infection control sleeve) on the energy delivered in polymerization.
Materials and methods
MARC Patient Simulator (MARC PS)
The MARC PS (BlueLight Analytics Inc., Halifax, Nova Scotia, Canada) is a laboratory energy measurement system integrated into a phantom head and permitting to check and train the use of light curing units under near-clinical conditions. For this purpose, two light sensors, one of 4 mm diameter in the molar region of the second quadrant, and another light sensor of 4 mm diameter between the two central incisors of the maxillary are installed. These light sensors correspond to a composite-filled cavity in practice. The energy delivered by the LCU is recorded digitally, analyzed by means of a special software package, and presented as a diagram ( Fig. 1 ). The parameters hereby generated, i.e. (mean and maximum) irradiance [mW/cm 2 ] and radiant exposure [J/cm 2 ], provide clues for the correct manipulation of the LCU ( Table 1 ) . By recognition and avoidance of possible error sources one can optimize the light energy delivered to the light sensor.