Effect of Air-abrasion and Thermocycling on Flexural Strength of Zirconia

Objective: To evaluate the influence of air-abrasion and thermocycling on the flexural strength of a commercially available zirconia (Y-TZP).   

Method: Bar-shaped specimens were made from Cercon (Dentsply) and received one of the following air-abrasion conditions (n=20): (1) as-sintered (control); (2) 50 µm Al₂O₃ particles; (3) 125 µm Al₂O₃ particles; (4) 250 µm Al₂O₃ particles and (5) 110 µm silica-modified Al₂O₃ particles (Rocatec Plus - 3M ESPE). Half of the specimens were submitted to the mechanical testing after thermocycling (10,000 cycles, 5-55 ºC). Three-point flexural strength test was conducted using a mechanical testing machine (1.0 mm/min). Data were analyzed by 2-way ANOVA and Tukey HSD post hoc tests (α=.05).

Result: The Y-TZP flexural strength was affected (P<.01) by air-abrasion condition and thermocycling (Table 1).

Table 1. Flexural strength mean values (MPa), standard deviations (±) and statistical results

	No thermocycling	Thermocycling
as-sintered	1084.7 ± 159.0 Aa	863.1 ± 173.9 Ab
50 µm Al2O3	1126.3 ± 284.5 Aa	892.6 ± 145.5 Ab
125 µm Al2O3	1167.6 ± 199.8 Aa	911.2 ± 246.1 Ab
250 µm Al2O3	634.4 ± 113.6 Ba	774.8 ± 189.6 Aa
Rocatec Plus	1210.9 ± 238.7 Aa	967.6 ± 183.5 Ab

Different uppercase superscripted letters indicate significant differences in columns (P<.05)

Different lowercase superscripted letters indicate significant differences in rows (P<.05)

Conclusion: Flexural strength of zirconia (Y-TZP) was affected only by air-abrasion with larger Al₂O₃ particles (250 µm) in the non-thermocycled group. Except for the group abraded with 250 µm Al₂O₃ particles, thermocycling significantly decreased the flexural strength of all groups.