Photothermal and Modulated Luminescence Detection of Demineralized Tooth Restoration Interfaces

Objectives: The aim of this study was to assess the potential of infrared photothermal radiometry and modulated luminescence (PTR-LUM) to detect in vitro demineralization around amalgam and composite-resin restorations on human teeth.

Methods: This study involved human teeth (n=3) prepared with smooth-surface amalgam and composite-resin (Heliomolar) restorations on enamel and root surfaces. Standardized burs (SS White701) were used to prepare uniform slot preparations (1-1.5mm deep) extending from enamel onto root. One restoration was placed per tooth face, amounting to 2-3 restorations per sample. The experimental set-up consisted of a semiconductor laser (659nm, 120mW), a mercury cadmium telluride IR detector for PTR, a photodiode for LUM, two lock-in amplifiers, and a computer for data processing. Samples coated in acid-resistant nail-varnish, excluding the filling and a 1x4mm window outside the filling, were immersed in an acidified-gel solution (pH 4.5) to create artificial demineralized lesions. Restoration-tooth interfaces were examined with PTR-LUM before and after treatments of 1-to-20 days of demineralization, followed by evaluation with transverse microradiography (TMR), at treatment conclusion, to validate lesion presence.

Results: PTR and LUM signals (amplitude and phase) showed gradual and consistent changes with treatment time within the demineralized zone of the restoration margin. PTR signal behaviour of both restorative materials, at 10Hz and 200Hz, remained relatively stable with increasing treatment time, providing baseline reference points for monitoring the degree of demineralization. LUM signals demonstrated high sensitivity to demineralization, however, exhibited less contrast than PTR due to baseline shifts. The consistent trends of PTR-LUM signals were verified with TMR lesion validation. PTR-LUM signals correlated to lesion presence as confirmed by TMR analysis related to mineral loss and lesion depth.

Conclusion: PTR-LUM demonstrated to be a sensitive tool for the detection of artificially demineralized lesions at the adapted tooth-restoration interface and longitudinally monitor lesion progression over time.