IADR Abstract Archives
Fracture toughness by energy development of bleached enamel
Objectives: To determine the effect of 38% hydrogen peroxide bleaching agent on enamel fracture toughness (Kc) immediately, after 24h, and after one week by nanoindentation and scanning electronic microscope (SEM).
Methods: Four recently extracted bovine incisors were selected and polished using a mechanical grinder (Labopol-5, Struers) on polishing cloths with alumina suspension slurry of 3µm and OP-A. Hardness (H) and elastic modulus (E) of labial enamel surfaces were determined by nanoindentation using a Berkovich tip (Nanoindenter XP-MTS). A Continuous Stiffness Measurement methodology (CSM) was set to determine H and E with a maximum penetration depth of 300nm. To estimate Kc, three indentations were performed on each sample (n=12) with a maximum penetration depth of 2000nm to generate cracks. These measurements were performed immediately after bleaching the specimens for 1 hour with 38% hydrogen peroxide (Opalescence® Boost, Ultradent), 24h later, and a week after the treatment application. During the timeouts, the samples were stored in artificial saliva. Moreover, photographs were taken of the residual imprints by SEM for each treatment condition to measure the size of the cracks. Kc results were calculated according to the formula included in the table and were analyzed by paired Studentxs t-test (p<0.05).
Results: Kc mean values (sd) are shown in the table. Similar letters indicate no differences on Kc mean values. Bleaching treatment significantly increased Kc mean values (p<0.001) with no statistical differences after 24h (p=0.927). Kc mean values were statistically higher than control, immediately and 24h after the bleaching procedure (p<0.01).
E (GPa) | H (GPa) | KC (MPa Ѵm) | |
CONTROL | 92.13 (6.01) | 4.68 (0.31) | 2.63 (0.59) a |
BLEACHING | 86.05 (7.34) | 4.30 (0.46) | 3.92 (0.41) b |
24 H | 83.22 (7.11) | 4.16 (0.50) | 3.94 (0.49) b |
1 WEEK | 76.56 (6.42) | 4.25 (0.52) | 4.83 (0.55) c |
σ (Poisson ratio); C (Crack length from indentation center); Du (Area below the force-displacement indentation curve);
(Where a is the crack lenght from indentation edge and ht is the maximun penetration depht)
Conclusion: Kc was affected by bleaching procedure with 38% hydrogen peroxide. Kc increased with time after the bleaching application.