The use of zirconia for the fabrication of tooth- or implant-supported restorations is very popular amongst dentists worldwide [1,2]. The development of various zirconia formulations has made it even easier to use zirconia in a monolithic approach in an esthetical context. However, the colouring of restorations is often not sufficient to achieve esthetic results. In addition, the wear of polished monolithic zirconia is minimal under clinical conditions and does not reflect the natural change and adaptation in occlusion [3], [4], [5], [6]. Thus, the use of a veneering ceramic might be favorable to better simulate the natural appearance and wear of a restoration.

Even if the survival rates of both tooth-supported (5-year survival ≥ 89.4%) and implant-supported (5-year survival ≥ 93.0%) zirconia restorations are high [7], the veneering of zirconia has shortcomings, since an increased reduction of hard tooth substance is necessary in comparison to monolithic restorations. Moreover, chipping is a very common complication [8,9]. To overcome these disadvantages, modifications in the composition of zirconia were made to achieve higher translucency. These compositions determine a higher thickness of zirconia restorations and a decreased span lengths of fixed partial dentures. This is a relevant aspect, since, e.g., most zirconia materials with 5 mol% yttria (5Y-TZP) are only available for use in 3-unit fixed dental prosthesis.

As of late, a new way of zirconia veneering was introduced that combines anatomical design of the zirconia restorations and a thin layering with veneering ceramic [10,11]. This veneering technique is called heterogeneously, i. a., micro-layering, liquid ceramic system, internal stain technique. All terms include that the zirconia framework is fabricated anatomically – sometimes minimally reduced in dimension - and that a small veneering of 0.1–0.6 mm thickness is applied. In this way, texture, shape and color of restorations can be modified. To date, no investigations about wear or stability of restorations fabricated of zirconia with micro-layering are available.

The aim of this study was to investigate the in-vitro performance of tooth-supported zirconia single crowns with micro-layering in terms of wear and stability. The working hypotheses were that zirconia crowns with micro-layering reveal similar performance than monolithic zirconia crowns.