ABSTRACT
The present study aimed to investigate the effect of different storage media with different pH levels on the cement/alloy shear bond strength and interfacial pore count. A total of 186 disc shaped samples were cast from Au-Pt-Pd, Pd-Ag and Ni-Cr alloy [62 samples for each alloy] using a copper mold former with a hole of 2 mm thickness and 5 mm diameter. Two representative samples from each alloy were selected for surface topographic assessment using a scanning electron microscope [SEM]. The 60 samples for each tested alloy were divided into 2 groups according to the type of luting cement used. Group 1:15 twin alloy samples were cemented with resin modified glass ionomer cement [RMGIC]. Group 2: 15 twin alloy samples for each tested alloy were cemented with adhesive resin cement. Each group, for each tested alloy, was divided into 3 subgroups according to the type of storage media used. Subgroup A: 5 twin cemented samples [for each alloy] were stored in normal saline for 1 week. Subgroup B: 5 twin cemented samples [for each alloy] were stored in lactic acid [pH:4] for 8 hours followed by storage in buffer solution for 16 hours then this procedure was repeated for a period of 1 week. Subgroup C: 5 twin cemented samples were stored in citric acid for 8 hours followed by 16 hours in buffer solution and the procedure was repeated for a period of 1 week. A stereomicroscope was employed to measure the pore count at the cement/alloy interface. Shear bond strength values were measured using a universal testing machine. All data were collected and statistically analyzed using ONE WAY ANO-VA. The mean interfacial pore count of the three tested alloys cemented with either RMGIC or resin cement was significantly less in lactic and citric acid storage media compared to those stored in normal saline. The mean shear bond strength values of Ni-Cr and Pd-Ag alloys cemented with RMGIC were significantly higher in citric acid compared to those stored in saline or lactic acid storage media. However, for Au-Pt-Pd alloy, cemented with RMGIC, shear bond strength values were significantly higher in lactic and citric acid storage media compared to those stored in normal saline. The mean shear bond strength values of the tested alloys cemented with adhesive resin cement were significantly reduced when stored in lactic and citric acid compared to those stored in normal saline. Meanwhile, irrespective of the type of storage media, Ni-Cr samples cemented with either resin modified glass ionomer or adhesive resin cement recorded significant higher shear bond strength values than Pd-Ag and Au-Pt-Pd alloys. 1- Resin modified glass ionomer cement can be successfully used in cementation of indirect restorations in patients with low oral pH levels either from plaque, dietary fermentable products or citrus fruits. However resin cement is not recommended in these situations. 2- Base metal alloys, luted with either resin-modi tied glass ion-omer or resin cement, are more preferable than Au-Pt-Pd and Pd-Ag alloys in all the investigated storage media