Effect of Aging and Repressing on Fracture Resistance of Lithium Disilicate Glass Ceramic / By Mahmoud Mohamed Metwally Ahmed ; supervisors Ashraf Hussein Sherif, Gihan Abde Elhady El-Naggar, Amr Saleh El-Etreby.

Thesis (M. Sc.)-Future University, Faculty of Oral and Dental Medicine, 2019.

Includes bibliographical references.

The recycling of e.max press left over buttons by dental laboratories is controversial with unknown clinical outcomes especially when it is functioning inside the oral cavity with subsequent exposure to temperature changes and cycles of mastication, Therefore, in our present study, the effect of ageing and repressing on fracture resistance of lithium disilicate glass ceramic was investigated and compared to newly pressed restorations and compared to non-aged newly pressed and re-pressed restorations under laboratory conditions. Twenty-eight epoxy resin duplicated die with 1.5 mm occlusal reduction and a shoulder finish line of I mm thickness were performed. A CAD/CAM was used to make wax patterns for the duplicated epoxy die to be pressed later and to ensure standardization protocols. The pressed and re-pressed crowns were then cemented to their corresponding teeth using resin cement after proper and strict surface treatment. 7 samples of both the pressed and re-pressed crown were subjected to fracture resistance without aging while the remaining samples underwent aging before fracture resistance by applying 5,000 thermal cycles and 120,000 chewing cycles. Afterwards teeth were statically compressed until fracture. Al data was collected, tabulated and statistically analyzed to detect any significant values among the different groups, The following results were obtained: Non aged samples had significantly higher fracture resistance (1634,494123.36) N than aged samples (1514.38+127.27) N, while re-pressed samples had significantly higher fracture resistance (1709.95+73.06) N than pressed samples (1559.03+117.5) N.