Comparison between different surface treatment methods on shear bond strength of zirconia (in vitro study)

Effect of Cement Type on Fracture Resistance and Mode of Failure of Monolith vs Bilayered Zirconia Single Crowns

AIM

To compare the fracture resistance and the mode of failure between monolith second-generation zirconia and bilayered first-generation zirconia single crowns cemented by resin cement and glass ionomer cement (GIC).

MATERIALS AND METHODS

A total of 36 maxillary first premolar crowns (5 mm in length × 4 mm in cervical diameter, with a base of 6 mm) were computer-aided design-computer-aided manufacturing (CAD-CAM) milled. They were divided into the following two groups (n = 18) according to the fabrication techniques: Group M - monolith zirconia crown (1-mm axial thickness and 2-mm occlusal thickness) and group B - bilayer zirconia crown (0.5-mm axial thickness and 1-mm occlusal thickness). Each group was further subdivided into the following two subgroups (n = 9) according to the cement used: Subgroup G - cemented using GIC; subgroup R - cemented using resin cement. All crowns were cemented to their corresponding resin dies and stored in distilled water for 72 hours. Each specimen was mounted to the lower member of the universal testing machine with a load cell of 5 kN and a crosshead speed of 0.5 mm/minute. Failure modes were analyzed for fractured parts using scanning electron microscopy (SEM).

RESULTS

Subgroup MR recorded the highest fracture resistance mean value (3616 ± 347.2 N) while the BG subgroup recorded the statistically significant lowest fracture resistance mean value (1728.7 ± 115.3 N). One-way analysis of variance (ANOVA) followed by pairwise Tukey's post hoc tests revealed a statistically significant difference (p = 0.0001) between groups M and B. One-way ANOVA followed by pairwise Tukey's post hoc tests also showed a statistically significant difference (p = 0.0297) between the types of cement used (subgroups G and R).

CONCLUSION

Monolith zirconia crowns had better mean fracture resistance than bilayered zirconia crowns. Resin cement improved the fracture resistance compared to GIC. Monolith zirconia crowns showed bulk fracture while bilayered zirconia crowns showed chipping fracture.

CLINICAL SIGNIFICANCE

Monolith zirconia crowns present a good prosthetic alternative overcoming the veneer chipping drawback of bilayered zirconia crowns. In addition, resin cement could increase the fracture resistance of zirconia crowns.

Effect of Different Nd:YAG Laser Power Outputs on Bond Strength of Resin Cement to Zirconia in Comparison to Sandblasting

Introduction: This study investigated the effect of various laser powers on the shear bond strength (SBS) of resin cement to the zirconia surface. Methods: Seventy-five zirconia disks were prepared and assigned to five groups including no surface treatment (control group), sandblasting with 50 µ Al₂ O₃ particles (second group), and Nd:YAG laser treatments with 2 W, 2.5 W and 3 W powers respectively (third, fourth and fifth groups). Afterwards, composite resin cylinders were cemented on zirconia disks using dual-curing resin cement. Before thermocycling (2000 cycles, 5-55°C), all samples were placed in distilled water at 37°C for 24 hours. Using a universal testing machine at the crosshead speed of 0.5 mm/min, the SBS was examined. Also, using a stereomicroscope, the failure type was determined. Data analyses were performed using Welch and Games-Howell tests (P < 0.05). Results: The mean bond strength difference between the control group and the other groups was significant. The respective bond strength from the highest to the lowest was observed in the sandblast group, the laser group with 2.5 W power, the laser group with 3 W power, the laser group with 2 W power, and finally the control group. However, no significant difference was observed between different laser groups (P < 0.05). Also, there was no significant difference between the sandblast and laser groups with 2.5 W and 3 W power (P < 0.05). Most of the failures in the sandblasting and laser groups with powers of 2.5 W and 3 W were mixed, but in the control and 2 W laser groups, most of the failures were of adhesive nature. Conclusion: The highest bond strength was achieved by sandblasting with Al₂ O₃ particles and then using an Nd: YAG laser with a power of 2.5 W.