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The objective of this study was to determine the influence of height and thickness of the one wall remaining coronal tooth structure on the fracture resistance of an endodontically treated root with resin abutment build-up using resin composite and fiber-reinforced resin composite post. Static and dynamic fracture tests were performed by placing the remaining tooth wall on the tensile side and applying loads at an angle of 30° from the tooth axis. Superior static fracture resistance was observed when the wall remaining on the tooth had a height and thickness greater than 1.0 mm. The dynamic fatigue test showed high loading capacity or fracture resistance in specimens with large height and thickness. The dynamic fatigue test showed the influence of the remaining tooth structure on fracture resistance clearly. In conclusion, the static and dynamic fracture resistances increased with the height and thickness of the one wall remaining tooth structure.

This study investigated the optical properties and flexural strength of translucent TZP layered with high-translucent PSZ using resin cement of various shades. Zirconia specimens (translucent TZP; Zpex and high-translucent PSZ; ZpexSmile) were 13 mm in diameter, layered at thickness ratios of 0.3/0.7, 0.5/0.5, and 0.7/0.3 mm (ZpexSmile/Zpex), and then luted using resin cement of 3 shades. Monolithic specimens of both were used as controls. CIE L*a*b* color coordinates and translucency parameter (TP) were evaluated as optical properties. Biaxial flexural strength was also determined as a mechanical evaluation. The a* and b* values of layered specimens varied depending on the shade of cement. TP values were not affected by shade of cement and thickness ratio. The biaxial flexural strength was intermediate value between both monolithic specimens. The layering method of zirconia with various translucencies using resin cement of different shades can improve color expression while maintaining clinically sufficient flexural strength.