الفهرس 
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Abstract
Because of its ability to halt the loss of dental hard tissue, inlay-retained fixed partial dentures (FPDs) have been more popular in the last few years. After all, metal inlays for FPDs have been shown to be effective in clinical trials. When conventional FPD retainers are used, a substantial amount of tooth structure is lost during the creation of the full-coverage crown; this may be as much as 70% of the clinical crown depending on the restoration material. Despite the fact that they have permission. Regardless of the kind of ceramic employed, the pulp’s vitality is always at risk during crown preparation, and this hazard may lead to pulpal responses. Teeth for all-ceramic crowns should have 63-73% of their coronal tooth structure removed, according to current recommendations.
Repairing posterior teeth with ineffective indirect fillings, such as inadequate wear resistance, poor proximal or occlusal morphology, or mechanical qualities of filling materials utilised in direct installation were among the reasons given for using the Inlay/Onlay approach.
Since metal-oxide zirconia is so strong in flexure, it may be used for posterior restorations in patients with limited occlusal space who need to satisfy their mechanical requirements for load-bearing posterior restorations. This laboratory study tries to solve the issue of how FPD retention impacts fracture resistance and microleakage.
FPD inlays and onlays were used to create forty samples of two distinct zirconium repair types (monolithic zirconia and zirconia core with layerd ceramics). made consisting of a pair of subgroups. Afterwards, the samples were submitted to mechanical ageing equipment utilising ROBOTA’s chewing simulator. Then, dye immersion in 2 percent methylene blue solution at 37°C for 24 hrs. The spaceman was next subjected to a dye penetration test, the results of which were examined under a stereomicroscope to determine the marginal penetration value.
The highest fracture resistance recorded with Monolithic onlay group (925.6±11.85N) followed by Monolithic inlay group (896.02±65.87N) then layer onlay group (535.1±61.87 N), and finally layer inlay group (520.4±79.93N). the highest leakage recorded with layer inlay group (2.25±0.36) followed by layer onlay group (1.75±0.37score) then Monolithic inlay group (1.5±0.5), and finally layer onlay group (1.25±0.37).
Conclusion
1. The monolithic group was shown to be more resistant to fracture and leakage than the layer.
2. It is possible to use monolithic zirconia to complete inlays and onlays.
3. It is possible that zirconia might be the best alternative to all metal or all ceramic onlays and inlays in terms of characteristics.