MicroCT Quantification of Autofluorescence Controlled Er-YAG Laser Carious Dentine Ablation

Introduction: Micro-Computed Tomography (MicroCT) allows non-invasive investigation of 3-dimensional structures and analysis of mineral density profiles. The Er:YAG laser(KaVo Key III laser), operating at 294nm, is effective at removal of dental hard tissues. Autofluorescence, characteristic of carious dental hard tissues but not of sound tissues, has been used as an in-vitro histological marker (the basis of Diagnodent technology) providing feedback control of Er:YAG laser ablation. Objectives: To quantitatively evaluate removal of demineralised carious dentine by Er:YAG irradiation with a laser feedback mechanism, using microCT. Methods: Initially, 11 teeth laser treated to varying feedback settings were qualitatively examined using a Skyscan 1172 microCT, to observe the efficiency of demineralised dentine removal. A novel dual phase system of radiographic phantoms was developed containing submicron pure hydroxyapatite combined with TEGDMA/DIS-GMA resin, allowing calibration of grey levels to mineral density and total effective density of dental hard tissues by microCT. A further 17 carious teeth (2 controls) were quantitatively examined using microCT, before and after exposure to Er: YAG laser radiation at various feedback settings. Results: Complete ablation of demineralised tissue proceeded under feedback control to a threshold level of 7, but at greater feedback levels removal of demineralised dentine was inefficient. Average mineral densities and total effective densities for dental hard tissues obtained by microCT compared favorably with accepted norms. Conclusion: Measuring mineral density and total effective density of dental tissues by microCT allowed determination of Er: YAG laser ablative efficiency under feedback control. The utility and accuracy of microCT for quantitative caries research has been demonstrated. Funding of this project was partially supported by KaVo (KaVo Dental GmbH, Biberach, Germany).