Study of lumineers' interfaces by means of optical coherence tomography

OCT has been used to evaluate dental materials, and is employed here to evaluate lumineers for the first time. Lumineers are used as esthetical indirect restoration, and after wearing and aging, several undesirable features such as gaps, bubbles and mismatch can appear in which would only be seen by invasive analysis. The OCT (spectral domain SD-OCT, 930nm central wavelength) was used to evaluate noninvasively the lumineer-cement-tooth interface. We analyzed 20 specimens of lumineers-teeth that were prepared in bovine teeth and randomly allocated in 4 experimental groups (n=5) with two different cementation techniques and two different types of cementing agent (RelyX U200 and RelyX Veneer, 3M ESPE, with the adhesive recommended by the manufacture). The lumineers were made of lithium disilicate and obtained using a vacuum injection technique. The analysis was performed by using 2D and 3D OCT images, obtained before and after cementing and the thermal cycling process to simulate thermal stress in a oral cavity. Initial measurements showed that the SD-OCT was able to see through the 500 mu m thick lumineer, as delivered by the fabricant, and internal stress was observed. Failures were found in the cementing process and also after ageing simulation by thermal cycling. The adhesive failures as bubbles, gaps and degradation of the cementation line are the natural precursors of other defects reported by several studies of clinical follow-up (detachments, fractures and cracks). Bubble dimensions ranging from 146 mu m to 1427 mu m were measured and the OCT was validated as an investigative and precise tool for evaluation of the lumineer-cement-tooth.