Purpose: This study aimed to evaluate the fracture strength and fracture mode of ceria-stabilized tetragonal zirconia polycrystals/alumina (Al₂O₃) nanocomposites (Ce-TZP/A) and yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) ceramic restorations in different thicknesses of frameworks on resin tooth abutments and to assess the usability of Ce-TZP/A ceramic restoration with thin zirconia frameworks.

Materials and Methods: Artificial maxillary second premolars were prepared for all-ceramic and metal-ceramic restoration. Then resin tooth abutments were duplicated. Four groups of zirconia-ceramic restoration framework were fabricated (n = 10): standard 0.5 mm thickness frameworks (Y-TZPs, Ce-TZP/As) for all-ceramic restoration preparation, and modified 0.3 mm thickness with palatal support frameworks (Y-TZPm, Ce-TZP/Am) for metal-ceramic restoration preparation. Porcelains were pressed. The restorations were fixed to resin abutment teeth and loaded vertically until fracture. The maximum fracture loads were recorded as fracture strengths. One-way ANOVA and post hoc test (Tukey’s HSD) were performed. The fracture modes were observed and statistically analyzed with Fisher’s exact test. All tests were used at a significant level of 0.05.

Results: The fracture strength of Ce-TZP/Am (2,824.1 ± 320.8 N) was significantly higher than Y-TZPm (2,399.7 ± 188.8 N) but was not significantly different from Ce-TZP/As (3,056.4 ± 337.1 N). There was no significant difference in fracture mode between groups.

Conclusion: Within the limitations of this study, Ce-TZP/A can be use with the thin modified design framework. Ce-TZP/Am provided good fracture strength and sufficiency for clinical use.

Purpose: High flexibility makes polyetheretherketone (PEEK) attractive for use as a restoration material. The aim of this study was to evaluate the stress distribution within a root for five types of restoration materials.

Materials and Methods: A three-dimensional root canal-treated premolar finite element model was fabricated, and the model was reconstructed with five restoration materials. A 100-N occlusal force was loaded 45˚ to the long axis, and the stress was calculated.

Results: The magnitudes of the stress surrounding the cervical area for the palladium-silver-gold alloy, hybrid resin composite, zirconia, all ceramic, and PEEK materials were 22.7, 21.0, 22.2, 22.2, and 18.4 MPa, respectively. The magnitudes of the stress surrounding the base of the posts were 6.5, 8.8, 5.9, 6.4, and 14.6 MPa, respectively.

Conclusion: The restoration fabricated using PEEK prevented stress from occurring at the marginal area of the dentin; however, PEEK increased the stress at the base of the post to a greater degree than the other restoration materials.

Purpose: To evaluate the effect of γ-ray irradiation on resin composite/dentin bond strength and the composite adaptation to the dentin cavity wall.

Materials and Methods: Half of bovine incisors were irradiated with 60 Gy γ-rays. Flat dentin surfaces were prepared on the labial side. Half of flat dentin surfaces were treated with Clearfil SE Bond. Clearfil AP-X composite was built up. After light curing and 24 h storage, the teeth were sectioned and trimmed (ca. 1 mm²) at the adhesive-dentin interface for microtensile bond strength test. The trimmed specimens were stressed to failure. Other flat dentin surfaces were prepared cylindrical cavities. The cavities were restored with Clearfil SE Bond adhesive followed by Clearfil AP-X composite. After light curing and 24 h storage, dye penetration tests around the cavities were performed. 60 Gy γ-ray irradiation significantly decreased resin composite adaptation to the cavity wall. Bond strength data were compared using the Bonferroni test. Dye penetration test scores were analyzed using the Kruskal-Wallis and Mann-Whitney U-tests.

Results: There was no significant difference between irradiated dentin and non-irradiated dentin of resin composite bond strength (p > 0.05). However, 60 Gy γ-ray irradiation significantly decreased resin composite adaptation to the cavity wall (p < 0.05).

Conclusion: Irradiation with 60 Gy γ-ray had no effect on resin-dentin bond strength. However, 60 Gy γ-ray irradiation significantly decreased resin composite adaptation to the cavity wall.