The aim of the present study was to investigate the fracture resistance of zirconia crowns and to compare the results with crowns made of a material with known clinical performance (alumina) in away that reflects clinical aspects. Sixty crowns were made, 30 identical crowns of alumina and 30 of zirconia. Each group of 30 was randomly divided into three groups of 10 crowns that were to undergo different treatments: (i) water storage only, (ii) pre-loading (10 000 cycles, 30-300 N, 1 Hz), (iii) thermocycling (5-55 degrees , 5000 cycles) + pre-loading (10 000 cycles, 30-300 N, 1 Hz). Subsequently, all 60 crowns were subjected to load until fracture occurred. There were two types of fracture: total fracture and partial fracture. Fracture strengths (N) were: group 1, alumina 905/zirconia 975 (P = 0.38); group 2, alumina 904/zirconia 1108 (P < 0.007) and group 3, alumina 917/zirconia 910 (P > 0.05). Total fractures were more frequent in the alumina group (P < 0.01). Within the limitations of this in vitro study, it can be concluded that there is no difference in fracture strength between crowns made with zirconia cores compared with those made of alumina if they are subjected to load without any cyclic pre-load or thermocycling. There is, however, a significant difference (P = 0.01) in the fracture mode, suggesting that the zirconia core is stronger than the alumina core. Crowns made with zirconia cores have significantly higher fracture strengths after pre-loading.

The objective of this study was to test inter-observer variability in shade selection for porcelain restorations, using three different shade guides: Vita Lumin Vacuum, Vita 3D-Master and Procera. Nineteen young dental professionals acted as observers. The results were also compared with those of a digital colorimeter (Shade Eye Ex; Shofu, Japan). Regarding repeatability, no significant differences were found between the three shade guides, although repeatability was relatively low (33-43%). Agreement with the colorimetric results was also low (8-34%). In conclusion, shade selection shows moderate to great inter-observer variation. In teaching and standardizing the shade selection procedure, a digital colorimeter may be a useful educational tool.

Objectives. The aims of this literature review are to provide answers to questions on how to improve bonding between titanium and dental porcelain and how to further implement, in clinical practice, ceramic-veneered titanium as an alternative to conventional metal-ceramic systems. Material and methods. A literature search of PubMed and also among referenced published scientific papers was performed and 24 fulfilled the search criteria, namely mentions of titanium, ceramics and bond strength. These papers were compiled for comparison and evaluated regarding the bond strength achieved with different methods. Results. The results strongly indicate that there are possibilities to improve both the present materials and methods for titanium-ceramic veneering. Conclusions. The results indicate that present knowledge is sufficient to conclude that veneering titanium with low-fused porcelain for crowns and fixed partial dentures can be recommended for routine clinical use.

Although the roughness of all surfaces investigated was <0.4 mum, the study disclosed significant differences in cellular attachment and proliferation associated with the various surface modifications.

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