Axial wall height effect on failure of adhesively luted computer assisted design/computer assisted manufactured ceramic crowns on preparations containing advanced total occlusal convergence

Computerized dentistry advocates promote that CAD/CAM adhesive technology compensates for traditional crown preparation recommendations. This study was to investigate the effect of preparation axial wall height on retention of adhesively-luted, all ceramic crowns manufactured by computerized methods. Maxillary molars were prepared with a 20 ° total occlusal convergence with preparation axial wall heights of 4, 3, 2, and 1 mm as well as an additional group containing a flat surface. The preparations were scanned with a computer acquisition device with crowns milled and prepared from a lithium disilicate ceramic material. The crowns were adhesively luted to the prepared tooth surfaces and then tested under static loading at a 45 ° angle to the tooth long axis on a universal testing machine until failure. Analysis with Kruskal-Wallis/Dunn’s found that crowns with 2, 3, and 4 mm preparation axial wall height had similar failure loads and demonstrated significantly greater failure load resistance than the zero and 1 mm axial wall height groups. However, failure mode analysis revealed that the 2 mm axial wall height group demonstrated universal adhesive failures as the zero and 1 mm axial wall height groups. Under the conditions of this study, some evidence is provided that adhesive technology may provided some compensation for less than optimal preparation features as the 3 mm axial wall height preparations demonstrated equivalent failure mode as the recommended 4 mm axial wall height preparations. However, further fatigue studies are warranted.