Three simple and low-cost configurations of handheld scanning probes for optical coherence tomography have been developed. Their design and testing for dentistry applications are presented. The first two configurations were built exclusively from available off-the-shelf optomechanical components, which, to the best of our knowledge, are the first designs of this type. The third configuration includes these components in an optimized and ergonomic probe. All the designs are presented in detail to allow for their duplication in any laboratory with a minimum effort, for applications that range from educational to high-end clinical investigations. Requirements that have to be fulfilled to achieve configurations which are reliable, ergonomic—for clinical environments, and easy to build are presented. While a range of applications is possible for the prototypes developed, in this study the handheld probes are tested ex vivo with a spectral domain optical coherence tomography system built in-house, for dental constructs. A previous testing with a swept source optical coherence tomography system has also been performed both in vivo and ex vivo for ear, nose, and throat—in a medical environment. The applications use the capability of optical coherence tomography to achieve real-time, high-resolution, non-contact, and non-destructive interferometric investigations with micrometer resolutions and millimeter penetration depth inside the sample. In this study, testing the quality of the material of one of the most used types of dental prosthesis, metalo-ceramic is thus demonstrated.

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Calibration loss of ovens used in sintering metal ceramic prostheses leads to stress and cracks in the material of the prostheses fabricated, and ultimately to failure of the dental treatment. Periodic calibration may not be sufficient to prevent such consequences. Evaluation methods based on firing supplemental control samples are subjective, time-consuming, and rely entirely on the technician's skills. The aim of this study was to propose an alternative procedure for such evaluations. Fifty prostheses were sintered in a ceramic oven at a temperature lower, equal to or larger than the temperature prescribed by the manufacturer. A non-destructive imaging method, swept source (SS) optical coherence tomography (OCT) was used to evaluate comparatively the internal structure of prostheses so fabricated. A quantitative assessment procedure is proposed, based on en-face OCT images acquired at similar depths inside the samples. Differences in granulation and reflectivity depending on the oven temperature are used to establish rules-of-thumb on judging the correct calibration of the oven. OCT evaluations made on a regular basis allow an easy and objective monitoring of correct settings in the sintering process. This method can serve rapid identification of the need to recalibrate the oven and avoid producing prostheses with defects.

This review emphasizes the current knowledge related to optical coherence tomography (OCT) as a non-invasive diagnostic tool to perform ex vivo and showing great potential for in vivo structural imaging of features in the oral cavity. OCT technology can generate high-resolution cross-sectional and en-face images of the internal architecture of the investigated sample (2-3 mm in depth). To this goal, en-face time domain OCT (TD-OCT) and spectral domain OCT (SD-OCT) were employed. Topics included in this review refer to OCT non-destructive evaluations of: dental abfraction and attrition, material defects and micro-leakages at the tooth-filling interface, temporal-mandibular joint disc, quality of bracket bonding on dental hard tissue, prosthetic restorations and micro-leakages at prosthetic interfaces, root canals, presence or absence of apical micro-leakages, and osteo-integration of dental implants and of bone grafting materials. OCT revealed internal features of the material investigated with greater sensitivity than current diagnostic methods. We put our research in context with others' results but the review reflects primarily our joint group experience and it presents images collected with our OCT systems only. The studies demonstrate the viability of OCT as a useful tool in dental medicine practice, as well as in research. Being completely non-invasive, OCT can be extended to soft tissue. Both TD and SD implementations prove the unique capabilities of OCT. For handheld scanning devices it is expected that the swept source principle (as one of the SD possibilities) will prevail, due to its high speed that allows for the reduction of distorting effects caused by the involuntary movements of the hand and of the patient. For high transversal resolution investigations, especially in more research oriented studies, it is expected that en-face TD-OCT will continue to coexist with SD-OCT methods, offering additionally a low cost quick provision of en-face view and compatibility with dynamic focus. Dynamic focus, that is the simultaneous adjustment of focus and coherence gate in depth is incompatible with SD-OCT methods and require repetitions of acquisitions under different focus in order to improve the transversal resolution, or more complex heads with division of the optical path in the object arm along different focus adjustments. In this respect, en-face TD-OCT provides a lower cost alternative to high transversal resolution of static samples.We have shown that complementary studies are possible embracing OCT with more traditional methods, such as confocal microscopy and microCT. Combination of principles is expected to evolve due to their limitations when considered separately.

Abstract. A fast swept-source optical coherence tomography (SS-OCT) system is employed to acquire volumes of dental tissue, in order to monitor the temporal evolution of dental wear. An imaging method is developed to evaluate the volume of tissue lost in ex vivo artificially induced abfractions and attritions. The minimal volume (measured in air) that our system could measure is 2352 μm 3 . A volume of 25,000 A-scans is collected in 2.5 s. All these recommend the SS-OCT method as a valuable tool for dynamic evaluation of the abfraction and attrition with remarkable potential for clinical use.