Fatigue resistance of monolithic and layered zirconia and LiSi2 crowns.
Baldissara P, Valandro L.F,* Fonseca R.G,** Gobbetti E, Monaco C.
DIBINEM, School of Dentistry, Alma Mater Studiorum, University of Bologna, Italy; *Santa Maria University, Brazil; **Araraquara University, Brazil.
Zirconia and lithium disilicate ceramic materials can be milled to obtain both layered and monolithic crowns. Monolithic all-ceramic crowns are reported to be more resistant than layered counterparts and cost-effective. However, many studies just evaluate the ultimate fracture resistance of the restorations by static loading, a condition which seldom occurs in the oral environment. Fatigue stresses are more closely related to the damage accumulation that leads to the restoration failures observed in the clinical practice. The aim of this study was to evaluate the fatigue resistance of zirconia and lithium disilicate monolithic crowns comparing the surviaval rate with their layered counterparts.
MATERIALS AND METHODS:
An upper incisor and a canine were prepared to receive all-ceramic restoration. For each tooth, 6 monolithic and 6 layered crowns were replicated using CAD/CAM technology. The ceramics used to make the monolithic crowns were IPS e.max CAD lithium disilicate (Ivoclar-Vivadent) and Lava Plus zirconia (3M-ESPE); layered crowns were made by veneering the ceramic copings of the same above-mentioned ceramics with pressed-on IPS e.max Ceram (lithium disilicate) and IPS e.max ZirPress (zirconia). The crowns were cemented on epoxy resin composite abutment replicas using a luting cement (BisCem, Bisco). The fatigue machine used in this study is a sealed rotating stainless steel drum which contains alumina and zirconia spheres along with the specimen population to be tested. During rotation at 172.5 rpm in 37°C saline solution, the balls generate wear and random impact stresses of a known maximum theoric energy (0.316 J) able to induce cracks growth and fracture propagation in brittle materials. The ball-mill was opened after 10 minutes then every 30 minutes for specimens weighing (total testing time 340 minutes). Failures pattern were evaluated under a stereomicroscope using transillumination. Kaplan-Meier survival curves and multiple comparison tests have been performed (α=0.05).