Evaluation of Dentin-Polymer Material Interfaces in Restorative Dentisry: In Vitro & In Vivo Studies

Objectives: Over the past decades bonding in resin-based composite restorations (RBCR) has been revolutionized due to advances in dentin bonding technology. However, dentin-polymer interfaces remain a clinical dentistry challenge.The aim of the study is to develop new experimental and clinical strategies that make it possible to objectively determine the longevity of adhesive interfaces (AI) of RBCR.
Methods: The project was arranged around 2 programs.
The 1st one involved in vitro studies on how mechanical and thermal shock loadings affect the stability of dentin-polymer bonds. The specimens of restorations including AI were subjected to mechanical loadings and up to 2000 cycles with various temperature drops. Visualization of bonded interfaces was performed using AFM & SEM.
The 2nd one involved in vivo, in situ studies of degradation of AI using standard clinical methods, digital processing (DP) of color images of RBCR and optical computer tomography (OCT). A group of volunteers was selected and observed over a period of 4 years and the state of their RBCR was analyzed. In the 1-st series of experiments color digital photographs of RBCR were processed using PTC MathCAD software to estimate a width of AI zone. In the 2-nd series of experiments an OCT Imaging System OCP 930 SR 022 was selected to detect hidden lesions and defects in the volume of AI.
Results: Destructive changes in AI subjected to mechanical and thermal shock loadings were researched quantitatively and qualitatively. The cracks were visualized along dentin–polymer junctions and their depths were calculated.
In the series of in vivo experiments the results of OCT studies revealed the drawbacks of standard clinical methods and DP of RBCR, which appeared to be insufficient for AI evaluation. The OCT images diagnosed hidden lesions in the areas of AI which had been considered as defectless.
Conclusions: A comparative in vitro evaluation of degradation of AI of restorations subjected to machanical & thermal shock loadings with various temperature drops revealed the localization of destructive changes and their character sizes.
The joint application of standard methods of clinical diagnostics, DP and OCT allows to objectivise and prognosticate the clinical longevity of RBCR including AI.