An 8 year old male patient complains of food lodgement with a history of previous restoration of the same tooth. Intra-oral examination reveals fractured Class II amalgam restoration with mandibular molar. Which of the following is not responsible for the fracture of restoration?
Moisture contamination of an amalgam restoration can promote failure. If zinc is present in the alloy, it will react with water, and hydrogen gas will be formed. As this gas builds up within the amalgam, a significant delayed expansion  can  occur  and  may  cause  protrusion  of  the amalgam  from  the  cavity  preparation,  which  enhances the possibility of fracture at the margins. If the restoration is improperly finished by the dentist, a thin ledge of amalgam may be left that extends slightly over the enamel at the margins. These thin edges of such a brittle material cannot support the forces of mastication. In time they fracture, leaving an opening at the margins. Poor cavity design resulting in an insufficient bulk of material across the isthmus can lead to failure of even a high-strength alloy.
Unlike a resin matrix composite, amalgam gains strength slowly over the first 24 hours. Premature loading can result in minute fractures that are not apparent for weeks or even months. The use of a rapid-setting amalgam with a high 1-hour compressive  strength  should  be  considered  during  the treatment  of  a  pediatric  patient,  in  whom  compliance with instructions to refrain from biting down hard on the freshly placed amalgam is in question.
Poor cavity design resulting in an insufficient bulk of material across the isthmus can lead to failure of even a high-strength alloy
Avoiding moisture contamination of amalgam
Non-compliance of the child with instructions to refrain from biting down hard on the freshly placed amalgam
Thin edges of restoration