Effects of Surface Abrasion on the Flexural Strength of Glazed and Re-glazed Metal Ceramics: An In Vitro Study

Abstract

The functional surfaces of the porcelain fused to metal fixed partial dentures are often abraded to adjust occlusion, such restorations are often found to fail in service. This study was therefore conducted to study the effect of surface abrasion on flexural strength of glazed porcelain fused to metal samples. It was also the aim of this study to find the effect of re-glazing on flexural strength of abraded samples. A total of ninety glazed porcelain fused to metal bar samples of the dimension 15 mm × 2 mm × 1.5 mm were fabricated. These samples were then divided into three groups (30 samples each) according to the surface treatments: group A-glazed (control); group B-abraded and group C-abraded and then re-glazed (self-glazed). Flexural strength was measured by using three point bend test on universal testing machine (texture analyser) with a cross-head speed of 0.6 mm/min. Peak force at the time of failure for all the samples was recorded. Statistical analysis found that mean flexural strength was highest for group A-80.65 ± 12.81 MPa; as compared to group B-74.18 ± 10.74 MPa and group C-77.85 ± 9.39 MPa. Student's t test indicated that the difference in the flexural strength between groups A and B was significant while it was non-significant between groups B and C and also between groups A and C. The 'f' test indicated that the difference between the groups was non-significant. This study therefore showed that there is a marked decrease in the flexural strength of the porcelain fused to metal restorations after occlusal abrasion. The study also found that reglazing of these restorations may not restore their flexural strength significantly.

The Effect of Glazing, Reglazing, and Polishing on Zirconia Biaxial Flexural Strength

“…The results of research by Bassir et al [1], Preis et al [6], Yener [18], and Her [24] stated that glazing did not increase the flexural strength, indicating that glazing did not cause changes in the flexural strength of the zirconia samples [3]. The Firing of ceramics after occlusal adjustment also showed the same result did not increase flexural strength [1,26]. The study by Chang [3] and Manawi [19] reported that glazing on the ceramic surface and glazing after grinding increases flexural strength because it can reduce the crack depth and close porosity on the ceramic surface [3][4][5]19].…”

“…The goals of clinical procedures carried out in the manufacturing stage of zirconia restorations are to improve aesthetic, natural appearance, and reduce wear on opposing teeth. Finishing and polishing procedures can significantly reduce the surface roughness of ceramics [8,9,15,[26][27][28]. Aravind et al [15] stated that the surface results after finishing and polishing on ceramics were the same as those of auto glazed ceramics.…”

“…Previous studies and literature suggest that glazing after grinding can increase the flexural strength of zirconia by reducing crack depth. This remains controversial because other studies have stated that glazing cannot increase the biaxial flexural strength of zirconia [1,16,18,26]. The glazing process after grinding reduces the crack depth significantly and does not increase the flexural strength, it is probably due to humidity factors, a combination material manufacture, grinding, and heating process [1,18].…”