Caries removal by laser has the problem that the treatment time of caries removal is longer than that of conventional methods. This study investigated whether the treatment time of caries removal would be reduced by using an Er:YAG laser in combination with a prototype caries removal reagent, and also whether it would be affected the composite resin filling.
Thirty human extracted teeth with caries on adjacent surfaces were used; on ten of them, different caries removal methods were attempted on the left and right sides at the center of the cavity surface.
The left side was subjected to irradiation without caries removal reagent, and the right side was irradiated by Er:YAG laser after reagent application. Laser irradiation was performed at output powers of 80mJ or 100mJ for five teeth each. After caries removal was completed, the time required for treatment was measured, and the cavity surface was observed with a stereomicroscope and scanning electron microscope （SEM）. The remaining 20specimens were classified into four groups of five teeth each according to whether reagent was used or not and the difference of laser power （80mJ or 100mJ）. These experiment groups were subjected to composite resin filling after caries removal and then underwent the marginal leakage test.
There were no problems or significant differences for those cavity surfaces, regardless of whether reagent was used or differences in irradiation power. The treatment time was shortened by using the reagent at the laser irradiation power of both 80mJ and 100mJ. It is considered that the reagent enhanced the softening of the carious dentin, then facilitated the caries removal by laser.
In the results of the marginal leakage test, no significant leakage was observed in any group. Based on the above, it can be inferred that the use of a caries removal reagent in combination with the Er:YAG laser is effective for removing dental caries.

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Optical coherence tomography （OCT） is a non-destructive, non-invasive diagnostic method that uses near-infrared light, which is considered to be harmless to the human body. An OCT system includes an interferometer that illuminates light and a photodetector that detects the backscattered light obtained from inside a subject to obtain precise tomographic images of tissue.
OCT has recently been used in dental-plaque studies to measure plaque thickness and morphology.
Reports on OCT observation of biofilms: Xi C. et al. used OCT for high-resolution real-time imaging of the three-dimensional structure and development of Pseudomonas aeruginosa biofilms in a standard flow cell model and obtained useful biofilm imaging data. Thanks to its imaging capabilities and biofilm imaging data obtained, OCT has the potential for non-invasive, real-time, in situ or in vivo imaging for biofilm characterization.
Haisch C. et al. demonstrated the capability of OCT to monitor biofilm structure and its detachment behavior. Spatial resolution, 3D image quality and time-resolved profiling of biofilms were also demonstrated. The results suggest that OCT could be developed into a standard tool for monitoring biofilm density.
Using oral bacterial microcosms collected directly from plaque on the tooth-restoration interface of pediatric subjects, Chen R. et al. used cross-polarization optical coherence tomography （CP-OCT） as a means of quantifying biofilm, using aggregate scattering intensity or integrated scattering intensity, and reported that CP-OCT can quantify biofilm mass by measuring depth-resolved scattering across the entire biofilm.
Hou J. et al. developed a rescaling method that effectively eliminates the effects of autoscaling between different images and can quantitatively correlate the volumetric bacterial density and biofilm signal intensity in OCT images. Thereby, they developed a method to analyze and quantitatively compare the intensity distribution in OCT images of different biofilms, and thus derive the biofilm structure and volumetric bacterial density.
In the present study, the authors focused on the non-destructive and non-invasive nature of OCT to obtain precise tomographic images, observed biofilms formed by S. mutans in vitro by OCT, and estimated the amount of insoluble glucan and bacterial density.
Biofilms were inspected on OCT images taken at two stages; the average optical thickness of the biofilm was less than 0.15mm at the early stage of formation, but exceeded 0.4mm in less than one day. Images taken by SS-OCT demonstrated that it was possible to observe considerably well from the inside to the base of the thick S. mutans biofilm that formed in less than one day.

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