The effect of thermocycling on the bonding of different restorative materials to access opening through porcelain fused to metal restorations.

12 An interpretation of the results indicated that all restorative materials showed leakage but the dye did not reach the metal part of the PFM, and this is due to low difference in linear coefficient of thermal expansion (LCTE) between Ni-Cr alloy and amalgam or composite, this is in agreement with the previous studies 1 , 7 , 13 , 14 Group A (with highly significant difference) had the highest dye penetration compared to other groups and this may be due to the high difference between LCTE of porcelain and amalgam15 or due to the contact angel that formed between the PFM walls and the amalgam, which is considerably sufficient for the dye particles to penetrate. 15 Our finding agreed with those 1 who concluded that amalgam is not the material of choice for restoration of access opening through the PFM crowns, but did not agree with those 13 who founded that the use of lathe-cut and admixed amalgam would reduce the marginal microleakage.

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