in vitro evaluation of fracture resistance of zirconia restorations veneered by two different systems: rapid layer technique and zir/cad/cam

& lt;strong& gt;background:& lt;/strong& gt; this study aimed to assess the fracture resistance of zirconia restorations fabricated with rapid layer (rl group) technique and zirconia computeraided design/computeraided manufacturing (zir/cad/cam) system (zc group).& lt;br /& gt; & lt;strong& gt;methods:& lt;/strong& gt;this study evaluated 30 allceramic crowns in two groups of 15. after fabricating the metal dies and scanning them by the cad/cam scanner, the crowns in rl group were anatomically designed and divided into two parts of the core and the veneering. each part was milled separately by the machine. the core and the veneering were fabricated and cemented. an index was obtained from the restorations and used for the fabrication of samples in the zc group. in the latter group, the metal dies were scanned and zirconia cores were milled by the machine. the veneering porcelain powder was then applied. samples in both groups were cemented over metal dies using a glass ionomer cement. the fracture resistance of the complex was measured by a universal testing machine. data were analyzed using spss software version 16.& lt;br /& gt; & lt;strong& gt;results:& lt;/strong& gt;the mean fracture resistance of rl and zc groups was not significantly different (p& gt;0.05). the mode of failure was adhesive in all samples in rl group and cohesive in 85% of samples in zc group. the remaining samples in zc group showed a total fracture in the core and the veneering.& lt;br /& gt; & lt;strong& gt;conclusion:& lt;/strong& gt; the fracture resistance of restorations fabricated by the zir/cad/cam and rl systems is not significantly different.