Abstract
The third part of the study is oriented toward emphasizing the effect of aggressive media on mechanical behaviour of orthodontic systems. As the incisive teeth are suffering the largest loads during feeding this study is focused on accidental failure of incisive-bracket systems after their use in a manner not recommended by doctors. As in the previous two articles the bovine rib is used to simulate the teeth but in this case the orthodontic systems are tested in aggressive conditions meaning the systems are employing to bite from apples considering that the apples are containing enough acids to chemically affect the bond between incisive and bracket – one hand and, on the other hand, they are enough hard peeled in order to mechanically load the orthodontic system. Another aspect concerns with the fact that apples are most eaten fruits in Romania, especially in schools, and being about kids a failure of orthodontic system caused by inattention is more probable. Forty teeth were prepared for this study and twenty of them were new while the other twenty were used before for other studies and the brackets were newly mounted. The number of bites was set after an analysis regarding the human feeding behaviour namely by considering that a normal person or a normal kid might eat three apples a day. The shear strength of orthodontic system was determined in accidental conditions if the system did not fail during the biting part of tests. Keywords: orthodontics, adhesive, bracket, shear strength