Optimization of X-ray Investigations in Dentistry Using Optical Coherence Tomography.

The most common imaging technique for dental diagnoses and treatment monitoring is X-ray imaging, which evolved from the first intraoral radiographs to high-quality three-dimensional (3D) Cone Beam Computed Tomography (CBCT). Other imaging techniques have shown potential, such as Optical Coherence Tomography (OCT). We have recently reported on the boundaries of these two types of techniques, regarding. the dental fields where each one is more appropriate or where they should be both used. The aim of the present study is to explore the unique capabilities of the OCT technique to optimize X-ray units imaging (i.e., in terms of image resolution, radiation dose, or contrast). Two types of commercially available and widely used X-ray units are considered. To adjust their parameters, a protocol is developed to employ OCT images of dental conditions that are documented on high (i.e., less than 10 µm) resolution OCT images (both B-scans/cross sections and 3D reconstructions) but are hardly identified on the 200 to 75 µm resolution panoramic or CBCT radiographs. The optimized calibration of the X-ray unit includes choosing appropriate values for the anode voltage and current intensity of the X-ray tube, as well as the patient's positioning, in order to reach the highest possible X-rays resolution at a radiation dose that is safe for the patient. The optimization protocol is developed in vitro on OCT images of extracted teeth and is further applied in vivo for each type of dental investigation. Optimized radiographic results are compared with un-optimized previously performed radiographs. Also, we show that OCT can permit a rigorous comparison between two (types of) X-ray units. In conclusion, high-quality dental images are possible using low radiation doses if an optimized protocol, developed using OCT, is applied for each type of dental investigation. Also, there are situations when the X-ray technology has drawbacks for dental diagnosis or treatment assessment. In such situations, OCT proves capable to provide qualitative images.

Effect of an Anaerobic Fermentation Process on 3D-Printed PLA Materials of a Biogas-Generating Reactor.

3D-printed materials are present in numerous applications, from medicine to engineering. The aim of this study is to assess their suitability for an application of interest today, that of testing of 3D-printed polylactic acid (PLA)-based reactors for biogas production using anaerobic digestion. The impact of temperature, pH, and aqueous phase on the tested bioreactor is investigated, together with the effect of the gaseous phase (i.e., produced biogas). Two batches of materials used separately, one after another inside the bioreactor were considered, in a realistic situation. Two essential parameters inside the reactor (i.e., pH and temperature) were continuously monitored during a time interval of 25 to 30 days for each of the two biogas-generating processes. To understand the impact of these processes on the walls of the bioreactor, samples of 3D-printed material were placed at three levels: at the top (i.e., outside the substrate), in the middle, and at the bottom of the bioreactor. The samples were analyzed using a non-destructive imaging method, Optical Coherence Tomography (OCT). An in-house developed swept-source (SS) OCT system, master-slave (MS) enhanced, operating at a central wavelength of 1310 nm was utilized. The 3D OCT images related to the degradation level of the material of the PLA samples were validated using Scanning Electron Microscopy (SEM). The differences between the impact of the substrate on samples situated at the three considered levels inside the reactor were determined and analyzed using their OCT B-scans (optical cross-section images). Thus, the impact of the biogas-generating process on the interior of the bioreactor was demonstrated and quantified, as well as the capability of OCT to perform such assessments. Therefore, future work may target OCT for in situ investigations of such bioreactors.

Dental Diagnosis and Treatment Assessments: Between X-rays Radiography and Optical Coherence Tomography.

A correct diagnosis in dental medicine is typically provided only after clinical and radiological evaluations. They are also required for treatment assessments. The aim of this study is to establish the boundaries from which a modern, although established, imaging technique, Optical Coherence Tomography (OCT), is more suitable than the common X-ray radiography to assess dental issues and treatments. The most common methods for daily-basis clinical imaging are utilized in this study for extracted teeth (but also for other dental samples and materials), i.e., panoramic, intraoral radiography, and three-dimensional (3D) cone beam computed tomography (CBCT). The advantages of using OCT as an imaging method in dentistry are discussed, with a focus on its superior image resolution. Drawbacks related to its limited penetration depth and Field-of-View (FOV) are pointed out. High-quality radiological investigations are performed, measurements are done, and data collected. The same teeth and samples are also imaged (mostly) with an in-house developed Swept Source (SS)-OCT system, Master-Slave enhanced. Some of the OCT investigations employed two other in-house developed OCT systems, Spectral Domain (SD) and Time Domain (TD). Dedicated toolbars from Romexis software (Planmeca, Helsinki, Finland) are used to perform measurements using both radiography and OCT. Clinical conclusions are drawn from the investigations. Upsides and downsides of the two medical imaging techniques are concluded for each type of considered diagnosis. For treatment assessments, it is concluded that OCT is more appropriate than radiography in all applications, except bone-related investigations and periodontitis that demand data from higher-penetration depths than possible with the current level of OCT technology.