Fracture resistance of monolithic and veneered all-ceramic four-unit posterior fixed dental prostheses after artificial aging

Effect of cement spacer on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks

BACKGROUND

Cement spacer is essential for compensating deformation of zirconia restoration after sintering shrinkage, allowing proper seating and better fracture resistance of the restoration. Studies assessing the effect of cement spacer on fit accuracy and fracture strength of zirconia frameworks are missing in the literature. Therefore, the aim of this study was to evaluate the effect of different cement spacer settings on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks.

METHODS

Sixty standardized stainless-steel master dies were manufactured with 2 prepared abutments for fabricating 3-unit and 4-unit zirconia frameworks. The frameworks were assigned into 6 groups (n = 10) according to cement spacer setting (30 μm, 50 μm, and 80 μm) as follows: 3-unit frameworks; 3u-30, 3u-50, 3u-80, and 4-unit frameworks; 4u-30, 4u-50, and 4u-80. The frameworks were assessed for fit accuracy with the replica method. The specimens were cemented to their corresponding dies, and the fracture strength was measured in a universal testing machine. The Weibull parameters were calculated for the study groups and fractured specimens were inspected for failure mode. Two-Way ANOVA followed by Tukey test for pairwise comparison between study groups (α = 0.05).

RESULTS

The cement spacer had a significant effect on both fit accuracy and fracture strength for 3-unit and 4-unit frameworks. The 50 μm spacer had significantly better fit accuracy followed by 80 μm, and 30 μm spacers. Both 50 μm and 80 μm spacers had similar fracture strength, and both had significantly better strength than 30 μm spacer.

CONCLUSIONS

For both 3-unit and 4-unit zirconia frameworks, 50 μm cement spacer can be recommended over 30 μm and 80 μm spacers for significantly better fit accuracy and adequate fracture strength.

Impact of the Veneering Technique and Framework Material on the Failure Loads of All-Ceramic Computer-Aided Design/Computer-Aided Manufacturing Fixed Partial Dentures

Objectives: Zirconia (Y-TZP) ceramics are considered as posterior fixed partial denture (FPD) materials; however, their applications are limited due to chipping. The use of monolithic lithium disilicate (LiDi) glass ceramics in posterior FPDs can be advantageous. This in vitro study aims to compare the loads until failure of posterior Y-TZP-FPDs and LiDi-FPDs before and after aging.

Bond strength between a veneering composite resin and zirconia frameworks with attached mechanical retentive devices

The effects of mechanical retentive devices and various surface treatments on the shear bond strength between a veneering composite resin and zirconia was investigated. Zirconia disks were classified into three surface-treatment groups: airborne-particle abrasion, overglazing, and overglazing with white alumina particles of three different grain sizes (50, 70, and 105 μm) attached onto zirconia disks (ZR-50, ZR-70, and ZR-105, respectively). They were further divided into four groups (n=44): unprimed, Clearfil Porcelain Bond Activator (CA), Clearfil Photo Bond (CB), and CA+CB. An indirect composite resin was bonded to zirconia specimens. Shear bond strengths were measured. For the ZR-70 and ZR-105 groups, the CB and CA+CB specimens exhibited higher bond strengths than the other two specimens after thermocycling. The ZR-70 and ZR-105 groups achieved micromechanical interlocking, and priming with a phosphate monomer (MDP) yielded stable bond strengths between the composite resin and zirconia with alumina particles attached as retentive devices.