Fracture resistance and marginal fit of the zirconia crowns with varied occlusal thickness

Abstract

PURPOSE The present study aimed to evaluate the clinical applicability of monolithic zirconia (MZ) crowns of different thickness via determination of fracture resistance and marginal fit. MATERIALS AND METHODS MZ crowns with 0.5, 0.8, 1.0, and 1.5 mm thickness and porcelain fused to metal (PFM) crowns were prepared, ten crowns in each group. Marginal gaps of the crowns were measured. All crowns were aged with thermal cycling (5 – 55℃/10000 cycle) and chewing simulator (50 N/1 Hz/lateral movement: 2 mm, mouth opening: 2 mm/240000 cycles). After aging, fracture resistance of crowns was determined. Statistical analysis was performed with one-way ANOVA and Tukey's HDS post hoc test. RESULTS Fracture loads were higher in the PFM and 1 mm MZ crowns compared to 0.5 mm and 0.8 mm crowns. 1.5 mm MZ crowns were not broken even with the highest force applied (10 kN). All marginal gap values were below 86 µm even in the PFM crowns, and PFM crowns had a higher marginal gap than the MZ crowns. CONCLUSION The monolithic zirconia exhibited high fracture resistance and good marginal fit even with the 0.5 mm thickness, which might be used with reduced occlusal thickness and be beneficial in challengingly narrow interocclusal space.

Evaluation of Marginal/Internal Fit and Fracture Load of Monolithic Zirconia and Zirconia Lithium Silicate (ZLS) CAD/CAM Crown Systems

“…The marginal gap found in this study for monolithic Zi crowns (37.7 ± 11.7 µm) was comparable with the mean ± SD values reported in other recent studies assessing similar restorations, as follows: 44.5 ± 7.9 µm [ 55 ], 53 ± 2 µm [ 60 ], mean range 15–47 µm [ 61 ], 26.8 ± 10.5 µm [ 38 ], 38 ± 12 µm [ 62 ], and 53 ± 7 µm [ 63 ]. The current mean internal gaps (142 ± 21 µm) seemed to be congruent with some recent studies, at 160 ± 23 µm [ 64 ] and 110–162 µm [ 65 ].…”

“…A cast metal die was used as a master model in this study for evaluation of marginal and internal fit, based on several other papers that had used similar types of dies for fit evaluation of ceramic crowns [ 27 , 34 , 36 , 38 , 55 , 68 , 70 ]. An anatomical tooth preparation design complete with finish line curvatures and tooth reduction following the occlusal anatomy was used in this study, instead of the routine single-plane margins with flat occlusal surfaces used in many other recent investigations [ 25 , 34 , 55 , 70 ], to simulate the clinical situation better.…”

“…A cast metal die was used as a master model in this study for evaluation of marginal and internal fit, based on several other papers that had used similar types of dies for fit evaluation of ceramic crowns [ 27 , 34 , 36 , 38 , 55 , 68 , 70 ]. An anatomical tooth preparation design complete with finish line curvatures and tooth reduction following the occlusal anatomy was used in this study, instead of the routine single-plane margins with flat occlusal surfaces used in many other recent investigations [ 25 , 34 , 55 , 70 ], to simulate the clinical situation better. Recent studies have shown that marginal fit of zirconia crowns is on par or even better than that of ceramo-metal crowns [ 55 , 70 ], which were long considered as a gold standard in fixed prosthodontics; hence, monolithic Zi crowns were used as a ‘control’ in this study to compare against the new ZLS crowns.…”

“…In the current report, an upgraded version of micro-CT, the nano-CT, was used in the evaluation of crown fit accuracy. Fit measurements were carried out at a total of 64 sites for each crown specimen, for both marginal (16 sites) and internal gaps (48 sites), based on earlier studies [ 28 , 55 , 63 ]. The pre-set sagittal and coronal slice positions on each abutment–crown sample allowed for easy identification, orientation, and performance of measurements on similar sections on each crown, thus ensuring uniformity of the process between individual samples.…”

“…Cemented crown specimens along with their bases were held in position in the loading device and subjected to 500,000 load cycles of 200 ± 50 N at 10 Hz [ 37 , 46 , 48 , 50 , 51 , 52 , 53 ]. The number of cycles used simulated a 2 year functional loading period in the mouth at an estimated rate of 240,000 cycles/year [ 54 , 55 ]. The Instron machine was programmed to stop if force dropped by 40%.…”