Comparative study on the tensile bond strength and marginal fit of complete veneer cast metal crowns using various luting agents: An in vitro study.

INTRODUCTION: Several commercially available luting agents are used to cement the dental restorations such as intra-coronal, extra-coronal, and fixed partial dentures. Tensile bond strength (TBS) and accurate marginal fit are the essential factors to determine the good clinical results in fixed prosthesis. The retentivity of the luting cements is assessed by their adhesive capacity over the tooth surface and metal surface. Generally, the adhesive ability has been evaluated with in vitro testing, with tensile bond tests. The failure of fixed prosthesis may be happened as a result of incomplete seating during cementation. Most research on cementation of crowns relates seating failure to the thickness of the cement film. MATERIALS AND METHODS: The study is divided into four groups with 10 samples for each of the luting cement taken up for testing TBS and four groups with 5 samples for each luting agent chosen for assessing marginal fit. The results were tabulated and statistically analyzed. RESULTS: In this in vitro study, the TBS of luting cements, and marginal fit in relation to luting cements were tested by using appropriate testing devices. The TBS of cement is measured using universal testing machine, and the results are tabulated. The marginal gap that exists between the margin of the cast metal crown, and the finish line is measured using travelling microscope before and after cementation. The difference between these two values gives the discrepancy that is due to the film thickness of cement used for luting the restoration. SUMMARY AND CONCLUSION: The TBS value of zinc phosphate cement and glass ionomer cement were found to be almost same. The chemical adhesiveness of the glass ionomer with calcium ions of enamel and dentin may be the attributed reason (ionic bonding). In this study, the polycarboxylate is the one that showed low TBS, and it may be attributed to the weakness of the cement due to reduced film thickness, though this cement has a chemical bonding nature. The observation of results of marginal fit in this study is the increased gap found in zinc phosphate cement followed by resin cement, zinc polycarboxylate, and glass ionomer cement. It is agreeable to estimate the marginal fit of the restoration, which could be affected by the film thickness of the luting cement along with other factors.

Finite element stress analysis on the influence of cuspal angle and superstructure materials in an implant-supported prosthesis.

PURPOSE: To investigate the effect of superstructure materials and cuspal angle in an implant-supported fixed partial denture. MATERIALS AND METHODS: This finite element analysis study was carried out with varying cuspal angulations of 0°, 20° and 33° and superstructure materials. The simulated models were loaded with 300N forces under different axial and non-axial angulations. The graphical and numerical stresses were investigated. RESULTS: The results demonstrated that the maximum stress occurred in the metal framework in all the materials except acrylic, for which it occurred in the coronal part of the implant. In the acrylic, the maximum stress recorded was 78 MPa with the 20° angulation. Ni Cr recorded a maximum stress of 111 MPa with the 33° angulation. CONCLUSION: The cuspal morphology and type of superstructure material plays a pivotal role in controlling the stress transferred to the implant and the supporting bone.