A Scanning Electron Microscopy and Energy Diffraction X-Ray Spectroscopy Study to Evaluate the Effect of Firing Temperature at the Ceramic-Noble Metal Alloy Interface in Porcelain Fused to Metal Restorations

Introduction: Porcelain Fused to Metal (PFM) restorations offer aesthetics of ceramics and the strength of metal hence are the gold standards of fixed partial dentures. However, the fracture of porcelain-metal interface still remains a matter of concern. Aim: To study the porcelain-noble metal alloy interface of PFM restorations at different firing temperatures, using Scanning Electron Microscopy (SEM) and Energy Diffraction X-ray Spectroscopy (EDS). Materials and Methods: This in-vitro study was conducted between November 2018 to October 2019 at Prosthodontics Departments of Saraswati Dental College and Hospital and King George's Medical University Lucknow, Uttar Pradesh, India. A total of 75 strips of noble metal alloy were prepared and layered with 1mm of porcelain on one surface, conforming to American National Standard/American Dental Association Specifications (ANSI/ADA) specification no.38 for Metal-Ceramic Dental Restorative Systems: 2015. These were randomly divided equally into 3 groups. Specimens of each group (n=25) were fired at different temperatures that is 850 degrees C, 900 degrees C and 960 degrees C, respectively. Scanning electron microscopy and Energy diffraction X-ray spectroscopy were performed at the noble metal alloy and ceramic interface of all specimens. Data was recorded and statistically analysed using one-way Analysis of Variance (ANOVA) and post-hoc Tukey HSD test. Results: Irregularities/Coarseness (50 mu m) was seen on the noble metal alloy surface adjacent to ceramic layer in SEM images at all the three chosen temperatures. EDS study revealed intermingled zones of partial oxygen depletion at the interface region with formation of intermetallic compound, lead zirconate titanate and complete oxygen depletion zone near metal alloy end of interface. The mean value of Shear Bond Strength (SBS) was 16.31 MPa at 850 degrees C, 24.33 MPa at 900 degrees C and 19.41 MPa at 960 degrees C (p-value <0.05). Conclusion: Difference in properties and location of the intermetallic compound formed at the interface, as well as the location of the oxygen depletion zone could account for the weaker bond formed between noble alloy-porcelain interface compared to base metal-porcelain interface.

Automated summary

The study revealed irregularities and coarseness on the noble metal alloy surface adjacent to ceramic layer at different firing temperatures, while intermingled zones of partial oxygen depletion and intermetallic compound formation were observed at the interface region. This difference in properties at the interface could contribute to the weaker bond formed between noble alloy-porcelain interface compared to base metal-porcelain interface.