Study Of Mechanical Behavior Of A Cast Crown Cemented By Rosette Gauge Technique

ObjectiveThe full crown is mostly used for the tooths repair and retainer of fixed partial denture (FPD) in the clinical practice of prosthodontics. It is discovered that secondary caries and losing of retention are the main reasons for the failure of fixed prostheses. The luting cement may seal the prosthesis and abutment well and make them an integral structure but the crown will deform and the cement layer may crack while be loaded. The crack will gradually propagate as the prosthesis is loaded day after day, and the cement will dissolve and destroy, thus cause the secondary caries and the losing of retention, and then the failure of fixed prostheses take place. There are many types of luting cements and it is important to select an ideal one for the dentist in dental clinical practice. In this experiment the deformations of crown and the failure of cements are measured and the relationship between them is discussed. Type IV gold alloy and casting Co - Cr alloy, zinc phosphate cement ( ZPC) , glass ionomer cement (GIG) and resin cement (Super Bond C&B, SB) are evaluated in this study.Materials and methodsThe crowns with cantilever are made by Type IV gold alloy and casting Co - Cr alloy: thickness of occlusal surface 1. 5mm, cantilever length 11 nun, width 5mm, thickness 3mm, thickness of axial surfaces1.0 ram. The fifteen crowns made by casting Co - Cr alloy are divided into three groups randomly, each group have five crowns, cemented by ZPC, GIG and SB, respectively. The five Type IV gold alloy crowns are cemented by GIG. Rosette gauge technique is used to measure the load - strain of crowns and the fracture strength of cements at two states and two loading ways, respectively. SpsslO. 0 is used to make statistical process.ResultsThe main strains of all the crowns non - cemented become 0 while the load decreases to 0 when loaded at the center of the occlusal surface, it is the same as when loaded at the end of the cantilever . But the former have no significant difference among the four gauges, while it is come to the latter, the strain is biggest just under the cantilever. There is no significant difference between the two types of alloy.The main strains of cemented crowns have no obvious variation as the load at the center of the occlusal surface increases, and become 0 when the load decreases to 0, too. But when the load is given at the end of the cantilever, the load - stain curves of the cemented crowns have sudden changes, and the strain couldnt decrease to 0 as the load become to 0. Statistical analysis confirm that different types of alloy and luting cements have no significant effect on the strains of cemented crowns and the failure load of cements.ConclusionThe results of this study confirm that fixed prostheses have better rigidity after cemented. The three types of cements used have no significant difference in luting results just by mechanical characteristics.The crowns deformed and the cements fracture more easily when the load is given at the end of the cantilever. The rigidity of the prostheses doesnt increase as the rigidity of materials increases if the thickness of the axial surface is enough.