Depth of cure of radiation-activated materials--effect of mould material and cavity size

Dental composite depth of cure with halogen and blue light emitting diode technology

OBJECTIVES

To test the hypothesis that a blue light emitting diode (LED) light curing unit (LCU) can produce an equal dental composite depth of cure to a halogen LCU adjusted to give an irradiance of 300 mWcm-2 and to characterise the LCU's light outputs.

MATERIALS AND METHODS

Depth of cure for three popular composites was determined using a penetrometer. The Student's t test was used to analyse the depth of cure results. A power meter and a spectrometer measured the light output.

RESULTS

The spectral distribution of the LCUs differed strongly. The irradiance for the LED and halogen LCUs were 290 mWcm-2 and 455 mWcm-2, when calculated from the scientific power meter measurements. The LED LCU cured all three dental composites to a significantly greater (P < 0.05) depth than the halogen LCU.

CONCLUSIONS

An LED LCU with an irradiance 64% of a halogen LCU achieved a significantly greater depth of cure. The LCU's spectral distribution of emitted light should be considered in addition to irradiance as a performance indicator. LED LCUs may have a potential for use in dental practice because their performance does not significantly reduce with time as do conventional halogen LCUs.

Light curing unit effectiveness assessed by dental radiometers

OBJECTIVES

The purpose of this investigation was to assess the effectiveness of five commercially available hand-held dental radiometers and a computer-based experimental radiometer.

METHODS

Light intensity of five visible light activation units was determined using the dental radiometers. The influence of curing light intensity on depth of cure of a hybrid composite material was determined using a digital penetrometer.

RESULTS

The radiometers evaluated varied with respect to sensor aperture diameter, scale readings (analogue or digital) and the units of measurement (arbitrary or mW cm2). The experimental computer-based radiometer allowed continuous recording of intensity against time; thus the light output could be monitored over the entire irradiation period.

CONCLUSIONS

When light intensity readings were normalized with regard to a standardized light sensing device aperture of 4 mm diameter, a linear relationship was found between depth of cure and the logarithm of the intensity of the light. The results of this investigation support the use of dental radiometers for periodically monitoring visible light activation units.

Depth of cure of radiation-activated composite restoratives--influence of shade and opacity

Inadequate depth of cure may reduce the longevity of visible light-activated composite restorations. Radiation-activated composites, originally marketed for the restoration of anterior teeth, have been developed and refined for restoring occlusal and proximal cavities in posterior teeth. Clinical factors such as the accessibility of the light source, the direction of the light, intervening tooth tissue and cavity depth may limit depth of cure. Unfortunately, a hard top surface is no indication of adequate polymerization at the base of the cavity. The current investigation used a penetrometer to evaluate the depth of cure of a range of recently introduced 'universal' composite materials and assess the influence of shade and opacity on depth of cure. Depth of cure of the enamel opacity is always greater than that of the same shade of dentine for each manufacturer's product range.

Determination of radiation energy emitted by light activation units

Since the introduction in the 1970s of single paste composite materials, there has been a rapid increase in the range of both materials and activation light units. This investigation is being undertaken as part of a larger study where the characteristics of both composite materials, light activation units and composite material/light activation unit combinations, are being evaluated. This section of the study was undertaken to determine the characteristics of four light activation units. The equipment was developed to measure radiation energy over a wide range of illumination. This range can be from the relatively low intensity of radiation transmitted through restorative materials to the intensities of direct radiation from light activation units. The four light units tested had various radiation outputs between 225,000 lx and 75,000 lx. All the units, apart from one, showed a decrease in light output with successive applications. The units emitted radiation outside the optimum range of 440-500 nm, which may produce damaging radiation and glare. Although the extreme intensities varied threefold the effect on depth of cure of one-material varied by only 16%.