Effects of Temperature Variations during Sintering of Metal Ceramic Tooth Prostheses Investigated Non-Destructively with Optical Coherence Tomography

Abstract

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.

Temperature variations in sintering ovens for metal ceramic dental prostheses: Non-destructive assessment using OCT

“…The latter clearly show a good, uniform granulation for Group N samples, while for samples from Group L100 and Group L30 they show darker zones that correspond to unsufficiently baked ceramics. In contrast, Group H30, and especially Group H50 samples display much brighter areas and spots, which demonstrate more numerous, larger ceramic grains, and even defects for the highest considered sintering temperature, defects that are sources of cracks, and thus of the destruction of these dental prosthesis -and of failure of th dental treatment [31].…”

“…1), using Duceram Kiss ceramics (DeguDent GmbH (a Dentsply Sirona Company), Hanau-Wolfgang, Deutschland). (a) OCT B-scan/cross-section inside a metal ceramic dental prostheses sintered at a temperature 100°C lower than the normal one prescribed by the manufacturer (Group L100 in the present study [31]). The dimensions of the image are: 3.25 mm in the x-direction (parallel to the surface of the sample) and 3.75 mm in the zdirection (in-depth with regard to the surface of the sample).…”

“…2(a), to select the depth from which C-scans/en-face images were obtained -see the example in Fig. 2(b) -for each sample, as described in detail in [31].…”

“…The choice of this material was made based on its good mechanical and esthetic properties [31]; these specific prostheses (corresponding to the first maxillary incisor) were manufactured due to how often they are utilized by patients in dental medicine.…”

Special Feature Development and Application of Optical Coherence Tomography (OCT)

“…State of the art quality metrics of this process are either time-consuming or subjective. C. Sinescu et al [8] propose the use of OCT for a non-destructive investigation of temperature effects during this process.…”