Daratsianos, Nikolaos: The influence of cyclic shear fatigue on the bracket-adhesive complex. - Bonn, 2008. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5M-13901
@phdthesis{handle:20.500.11811/3752,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5M-13901,
author = {{Nikolaos Daratsianos}},
title = {The influence of cyclic shear fatigue on the bracket-adhesive complex},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2008,
note = {A commonly encountered problem in orthodontics is the bond failure of brackets during treatment. The forces applied in the oral environment are more likely to be of a cyclical nature, well below the ultimate shear strengths reported in in vitro studies. Isolated or initial powerful impacts are seldom. The failure over time is much likely to be the result of fatigue. Powerful impacts may occur and lead to failure, particularly if the system has undergone fatigue loading.
The purpose of this study was to evaluate the influence of cyclic shear fatigue on the bracket-adhesive complex.
Brackets with laser structured bases (Discovery®, Dentaurum) and with foil mesh bases (Ultra–Minitrim®, Dentaurum) were bonded on silanised stainless steel flat plates with a two-component (No-Mix Bonding System, Dentaurum) and a four-component (Con-cise™, 3M Unitek) chemically-curing adhesive. The specimens were aged in distilled water at 37°C for 3 days. One group of the specimens was used as control to determine the ultimate shear bond strength without any fatigue procedure. The brackets of the second group underwent fatigue testing with a testing machine Zwick 1445 (Zwick GmbH & Co) according to the staircase method for 1,000 cycles. The survived fatigued specimens of the second group were subjected to shear strength testing. Comparisons between the values taken for fatigued and nonfatigued specimens were made to extrapolate the effect of fatigue on the shear bond strength. The shear fatigue limit and the fatigue ratio were calculated. The bracket bases were examined and photographed under 25x magnification with a scanning electron microscope. The distribution of the remaining adhesive on the bracket bases was analysed numerically and visually.
Shear fatigue of the bracket-adhesive complex for 1,000 cycles showed a variable influence on the shear strength of the bracket-adhesive complex, which was strongly dependent on the material combinations tested. Fatigued specimens showed an increase in shear strength of 8% in material group A (bracket Discovery® / adhesive No-Mix) and a decrease of 10 % in material group D (bracket Ultra-Minitrim® / adhesive Concise™). In material groups B (bracket Ultra-Minitrim® / adhesive No-Mix) and C (bracket Discovery® / adhesive Concise™) no statistically significant differences between the fatigued and nonfatigued specimens were found. The fatigue ratio was about 60 % for material groups A, B & C and 67 % for material group D, indicating a better fatigue behaviour of the combination Ultra-Minitrim® / Concise™. Among the nonfatigued specimens, the laser-structured bracket Discovery® showed about 59 % higher shear strength than the foilmesh bracket Ultra-Minitrim®. The four-component adhesive Concise™ showed about 66 % higher shear strength than the two-component adhesive No-Mix.
Concerning the distribution of residual resin on the bracket bases, fatigue was found to have different influence depending on the fracture mode tested. Fatigue played the same role on the area of favourable fracture mode (sum of fracture between bracket / resin and cohesive fracture) independently of the material combinations tested, but statistical significant differences were not always present. The area of favourable fracture mode was not significantly different between the nonfatigued and fatigued specimens. Yet when examining the fatigued specimens that failed without completing 1,000 cycles in comparison to the ones that survived and were sheared after that, a significant larger area of favourable fracture was found in groups B, C and D. In group D the area was also significantly larger compared to the nonfatigued specimens. The most favourable fracture mode, the cohesive fracture, was also fatigue-dependant, but fatigue had a different influence depending on the material groups. In groups A and B no significant influence of fatigue was found. Fatigue showed a significant increase in cohesive fracture in group D and the failed-during-fatigue specimens showed a smaller area than the survived ones. In material group C the failed-during-fatigue specimens showed a significantly higher cohesive fracture that the survived ones – in contrast to group D. Concerning the nonfatigued specimens, the influence of the bracket type on the distribution of residual resin was the same for both fracture modes and depended on the material combinations. Bracket 2 (Ultra-Minitrim®) showed a higher favourable and most favourable fracture mode than bracket 1 (Discovery®) when tested with adhesive 2 (Concise™) and no differences with adhesive 1 (No-Mix). The influence of the adhesive type was not the same for the two fracture modes and depended on the material combinations. Adhesive 1 and 2 showed no difference in the distribution of the favourable fracture area with either bracket. The most favourable fracture area was lower for adhesive 2 when tested with bracket 2 and no differences were found with bracket 1.
In general, fatigue had a variable influence on shear strength and on the distribution of the residual resin on the bracket base. Its influence depended on the material combinations tested. The distribution of the residual resin on the nonfatigued specimens was also material-dependant. Only the shear strength of the nonfatigued specimens showed similar behaviour for all combinations tested. The staircase method can provide an easily utilised, reproducible experimental protocol for the standardisation of fatigue studies, if the influence of a load near the fatigue limit is to be evaluated.},

url = {http://hdl.handle.net/20.500.11811/3752}
}

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