Einfluss des internen Bleachings auf den Haftverbund von zwei verschiedenen Befestigungskompositen

Focusing on the esthetic important region of the upper front teeth, especially at nonvital teeth, discoloration of the dental hard tissue may occur, which can be treated by bleach techniques [151]. If the bleached teeth need a further restoration during the therapy, a filling- or post-restoration depending on the destruction level will be necessary. At this time it comes to an interaction between the bleached dental hard tissue and the core build-up or post luting system. The aim of this study was to check out if the “internal bleaching” with sodium perborate influences the bond between tooth and the luting composite. Furthermore it was necessary to determine if the neutralization with calcium hydroxide has an influential factor. To complete the analysis the fracture mode between post, luting composite and tooth was analyzed. During the study 60 extracted, single root teeth with a straight root canal were decapitated at the cementoenamle junction and trimmed straight. The root canal was prepared with the mechanical BioRaCe System to a length of 8mm and a size of ISO 60 under irrigation with destilled water. The teeth were randomized and divided into two groups (1: Bifix SE and 2: Futurabond U/ Rebilda DC) as well as into three subgroups each (A-C). The subgroups differentiated as follow: Group A: Control group, no bleaching and no neutralization; Group B: Bleaching with sodium perborate + Aqua dest. for one week, following another week of neutralization with calcium hydroxide; Group C: Bleaching with sodium perborate + Aqua dest.. After a period of one more week an experimental steel spreader, adjusted to ISO 55, was cemented with the luting composite according to the main group. The luting materials hardened only chemicaly. After a storage of three weeks at 23°C and 100% humidity the samples were stressed by means of a pull-out method, derived from the method of Ebert et al. [42], by using a universal test machine until the failure of the bond. To analyze the failure mode macro shootings of the steel spreader were taken. The bond strengths of the control groups between the two different luting composits showed significantly differences (1A: 10,19 MPa; 2A: 7,52 MPa; p= 0,021). This also applies to the Aqua dest.-groups (1C: 8,08 MPa; 2C: 4,12 MPa; p=0,006). If you examine the groups 1 and 2, the bleaching with following neutralization in group 1 leads to significantly lower bond strengths compered to the control group (1A: 10,19 MPa; 1B: 7,2 MPa; p=0,034). In group 2 the bleaching without neutralization results in the lowest results of the entire test series, with significant differences to the control group and the AH Temp-group (2A: 7,52 MPa; 2B: 7,26 MPa; 2C: 4,12 MPa; p(2A/2C)=0,028; p(2B/2C)=0,016). The internal bleaching with sodium perborate has an negative influence to the bond strength between dentin and the luting composites Bifix SE and Futurabond U/ Rebilda DC. However, the amount of influence is different. The neutralization with calcium hydroxide does not lead to significantly lower results, using Futurabond U/ Rebilda DC has even a better bond strength.