Analyzing the Accuracy of Estimates of Dental Curing Light Degradation from Cell Phone Images

Abstract

Modern dentistry uses light-curing resin-based composites as restorative/flling materials. The LCU (dental light curing unit) is a device emitting blue light or a combination of blue and ultraviolet light to be placed directly over the tooth to harden the resin-based material in it. The curing effect depends on the irradiance and the time the material is exposed to the light. The LCU output light intensity degrades over time and with usage. Thus, curing times need to be updated accordingly to avoid an under-curing or over-curing process. Measuring the irradiance is a challenging task that is currently performed by trained professionals and laboratory grade spectrometers that are not cheap or portable. Dental clinics have to rely on measurements done by external consultants. But it is not usually possible for them to do the measurements frequently. Between two measurements, the light output of LCUs can deteriorate signifcantly and curing with inadequate time would result in restoration failures. This gives rise to the need for a low-cost, portable device that allows dentists to measure the degradation in the output of any LCU routinely. To study the effect of using cell phones for monitoring the LCU’s degradation, this thesis uses different modes of an LCU to simulate the degradation and use the readings of an existing LCU calibration equipment as the baseline to evaluate the result from the analysis of the cell phone images. We capture the light source images for fve different LCUs and calculate the total pixel intensity of the light foreground in the image to estimate the irradiance. We compare the raw images of DNG format and the images of JPG format in terms of relative error and overall variation on different aspects and conclude that for the data considered, the raw images provide superior accuracy in the case of poorly chosen exposure times.