Reliability and failure modes of anterior zirconium-oxide crowns dependent on coping design
Bibliographic record
Abstract
Objectives: The objective of this thesis was to determine the effect of two different zirconia coping designs on the fatigue strength and fracture propagation of the corresponding anterior all-ceramic crown. Materials and methods: One group consisted of 18 crowns with a constant zirconia coping thickness of 0.5 mm (group S). The other group included 18 crowns with an anatomically designed zirconia coping (increased incisal and interprox-imal coping thickness) (group A). The crowns were hand-veneered (IPS e.max Ceram, Ivoclar) and adhesively cemented (Multilink Implant, Ivoclar) on zirconia dies. The zirconia copings and dies were CAD/CAM produced (copings: NobelProcera, Nobel Biocare; dies: IPS e.max ZirCAD, Ivoclar Vivadent). A single load to failure test was performed to estimate the initial ultimate strength (n=4). 32 specimens were subjected to one out of three stress-time varying profiles using mouth motion (2Hz) step-stress accelerated life testing (ELF-3300, Bose). After mechanical testing, a fractographic analysis was performed by means of the stereomicroscope and the SEM. The reliability of the crowns was computed using a cumulative-damage step-stress analysis (Alta-7-Pro, Reliasoft). Results: Chipping of the veneering porcelain was the main failure mode in both groups. Nine specimens showed areas of delamination. The mean loads at failure were 313 ± 82 N (n=6) for group S and 367 ± 123 N (n=6) for group A (profile 1). The use level probability Weibull plot at 200 N and 50k loading cycles showed a statistically significant difference between the two groups, associated with early failures, in group S. For longer loading cycles, the significance remained uncertain, but showed a clear trend towards higher reliability of the crowns with the anatomical coping design. The reliability calculations at 200 N and 50k cycles (2-sided at 90.0 % confidence bounds) resulted in 0.48 (0.64/0.29) reliability for group S, and 0.8 (0.91/0.6) reliability for group A. In general, group A generated higher mean reliability values than group S. Cracks leading to failure evolved from the area directly below the indenter slide path. No cracks were observed in the zirconia coping or die. Conclusion: The tested crowns are suitable for clinical application in the anterior region. There was a clear trend towards higher reliability of the crowns with the anatomical coping design. The anatomical coping design should have the potential to reduce the probability of early clinical failures by veneer chipping. The failure modes in both crown systems were similar.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".