Objectives: The aim of this study was to investigate the influence of laboratory fabrication and type of veneering on chipping of veneered zirconia fixed partial dentures (FPDs).
Material and Methods: Human molars were inserted in PMMA resin to create three-unit (10mm) oral situation. The roots of the teeth were covered with an about 1mm thick layer of polyether to simulate the periodontium. After circular preparation and impression taking, the plaster models were send to three different laboratories in order to fabricate copy-milled YTZP-zirconia 3-unit FPD cores (#1-#3; ICE; Zirkonzahn, I; n=8 per group). The individual cores were veneered with the same ceramic. One laboratory fabricated a second core group, which was veneered with an alternative ceramic (#4), with that the laboratory was accustomed to. As a reference (#5), one series was milled as full zirconia FPDs without veneering (Prettau Zirkon, Zirkonzahn, I). All FPDs were cemented with Variolink2/Syntac classic (Ivoclar-Vivadent, FL). Thermal cycling and mechanical loading (TCML) was performed for aging (1,200,000 mechanical loadings [ML] x 50N and 6000 thermal cycles [TC] -2min between 5°C and 55°C). During TCML appearing failures (cracks, chipping, etc.) were reported. The type of failure was analyzed in detail by scanning electron microscopy (SEM; Quanta; FEI-Philips, NL). Fracture force (UTM 1446; Zwick; v=1mm/min) was determined. Statistics: One-way ANOVA (α=0.05).
Results:
Group | Laboratory | Veneering | Number of failures | Median fracture force [N] after TCML (25%/75%) |
1 | Lab 1 | Type #A | 2 cracks | 1276 (1073/1446) |
2 | Lab 2 | 4 chippings | 2126 (1748/2387) |
3 | Lab 3 | 5 chippings | 1011 (983/1752) |
4 | Lab 3 | Type #B | No failures | 1141 (803/1485) |
5 | Lab 3 | Full zirconia | No failures | 1569 (1376/1795) |
Conclusions: The number of cracks and chipping of the veneering was highly dependent on the individual design of the core of the different laboratories. As expected, full zirconia showed no chipping.
