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Multimodal Optical characterisation of the interface between dental cements and sound or carious dentinal substrates

Student thesis: Doctoral ThesisDoctor of Philosophy

Calcium silicate based cements have been mainly used for endodontic applications. Recently, a new formula has been produced as a coronal restoration. The aim of this project was to optically characterise different human dentine substrates. Then to investigate possible mineralisation effects of this new calcium-silicate based cement (BiodentineTM) and compare them with those of glass ionomer cements (Fuji IXTM) based on the optical properties of the interface.

Methodology: The interaction of both cements with in-vitro demineralised dentine samples was investigated. A model including sound and demineralised dentine tissues was created and optically evaluated. Then Biodentine and GIC were applied and evaluated using more controlled samples. Various advanced optical imaging techniques were applied; such as multiphoton fluorescence microscopy, fluorescence lifetime imaging and second harmonic generation imaging to assess optical changes before and after aging the samples. In addition, Raman spectroscopy was used to detect changes in the intensity of the mineral peak. These non-invasive optical techniques were then used on carious teeth to characterise different zones of dentine caries based on tissue’s auto-fluorescence without labelling. Each zone was then defined by its Knoop microhardness reading. Afterwards, the mineralisation effect of both cements on each dentine zone was assessed after aging the substrate in solutions of (+/- 0.015% tetracycline, PBS and water). In another set of samples, excavated carious teeth were used to mimic the clinical situation, as each half was restored with either GIC or Biodentine. The interface of the two cements was evaluated based on changes in fluorescence intensity and lifetime.

Significant changes in the fluorescence intensity and lifetime of the interfacial dentine before and after ageing were found under both cements in the demineralised dentine model samples. These optical changes were associated with significant increase in the Raman mineral peak after storage. Using KHN to indicate tissue type, the single and multiphoton fluorescence intensity, fluorescence lifetime, and SHG signal differentiated significantly between caries-infected, caries-affected and sound dentine. The cement groups showed significant fluorescence changes within infected and affected tissues, indicating possible mineralisation as they were associated with an increase in the mineral peak intensity. Tetracycline mineral-binding induced a reduction in the lifetime with comparable increase in the fluorescence intensity in the Biodentine™ and GIC groups within the affected and sound areas. Similar optical changes were detected as a band of mineralised structure under both cements with deeper infiltration of GIC within inter and peritubular dentine in the excavated caries samples.

Two-photon microscopy can be efficiently used for non-invasive in-vitro diagnostic dentine caries characterisation. Studying the same lesion-restoration interface over time, changes in the fluorescence lifetime and intensity could indicate that mineralisation may have occurred within the dentine under GIC and calcium silicate cements (Biodentine™).
Original languageEnglish
Awarding Institution
Award date2016


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