Mathematical model for assessing true irradiance received by luting materials while curing through modern CAD/CAM resin composites

Statement of problem: Measurement of irradiance passing through a dental restoration for properly curing a dual- or light-polymerized luting composite is imprecise due to surface reflection.

Objective: To provide a mathematical correction of measured transmitted irradiance for predicting true transmitted light intensity through CAD/CAM restorations.

Methods: A total of 432 specimens were fabricated. Seven modern CAD/CAM resin-based composites (RBCs) and one CAD/CAM glass-ceramic (control group) were sectioned and polished into specimens of 0.5-5mm thickness (in 0.5mm steps, n=6). Irradiance of a violet-blue LED light curing unit (LCU) (power modes: Standard, High and Plasma) was measured after passing through each specimen with a spectrometer. Data was compared based on 95% confidence intervals and using univariate ANOVA followed by Tukey HSD (α=0.05).

Results: The measured transmitted irradiance passing through the specimens decreased exponentially. Significantly highest values of transmitted irradiance were measured for 0.5mm thick specimens for all materials (p<0.05). The decadic absorption coefficient for CAD/CAM-RBCs ranged from 0.292mm^-1 to 0.387mm^-1 while the control group (glass-ceramic) reached a significantly lower value of 0.283mm^-1. The reflection ratio for all materials ranged from 12.6% to 18.5%.

Significance: A correction can be implemented to predict the true transmitted irradiance after passing through a dental restoration as function of initial irradiance, specimen thickness and material specific parameters. For a practitioner, this model may be applied depending on the specific treatment conditions, the individual LCU's radiant emittance and restoration thickness for the tested materials.