Double veneering, low-temperature porcelain, and total glaze application methods to overcome failures of...

The purpose of this in vitro study was to evaluate the efficacy of double veneering, low-temperature porcelain, and total glaze application methods to overcome failures of zirconia-based restorations.

Ninety yttrium-stabilized tetragonal zirconia materials with 1.2 × 5 × 24 mm dimensions were cut from pre-sintered blocks. According to the fabrication process of the samples, 3 main groups were formed in the beginning. Low-temperature porcelain and press-on ceramic were used for veneering. First, the samples were divided into 9 sub-groups. Then they were arranged to form triple groups. Triple groups were arranged according to the sample preparation and applied test methods, respectively. After three-point bending tests, marked samples were oriented for stereomicroscope and scanning electron microscope to evaluate and identify the fracture types. Data were statistically analyzed (p < 0.05).

Delamination counts were higher than the chipping counts at all the samples with press layer. Chipping count was higher than the delamination count at low-temperature porcelain-veneered triple group. Delamination count was the highest at double-layered triple group. Scatter sample count was the least at ceramic-veneered triple group. Standard triple group was found to be more fracture-resistant. Accelerated aging increased delamination and/or scatter counts at all sub-groups and significantly (p = 0.01 < 0.05) degreased the mean fracture strength values. Total glaze application significantly (p = 0.01 < 0.05) improved the fracture strength values.

All-round thinking is very important considering fracture strength, fracture type, delamination, chipping, normal fracture, and scattering. Applying low-temperature porcelain on zirconia substructure is more efficient than a transition material. Press-on material alone as a superstructure is not sufficient for successful restoration. Double veneering method is highly questionable.

Zirconia-based all-ceramic restorations meet many criteria, especially durability and esthetics, which are necessary for a successful restoration. However, the harmony/integrity of substructure and superstructure is still an issue. Therefore, choosing of the veneering and/or protective method used during the fabrication of the restoration is very determinative for long-term success.