Effect of Connector Design on Fracture Resistance in All-ceramic Fixed Partial Dentures for Mandibular Incisor Region

Abstract

Yttrium tetragonal zirconia polycrystal frameworks were prepared for all-ceramic fixed partial dentures (FPDs) for the mandibular incisor region. The effects of the cross-sectional area and morphology of the connector on its strength were evaluated by fracture tests. Nine types of zirconia framework for a 3-unit FPD for a defect of 1 mandibular central incisor were prepared, each differing in cross-sectional area and morphology. Fracture tests were performed by loading until fracture using a universal testing machine. Fracture load was determined and fracture site examined. Significant differences were observed in fracture load according to the morphology and crosssectional area of the connector (p<0.05, p<0.01, p<0.001). Fracture load differed significantly among all groups according to cross-sectional area, and was also greater when the shape of the connector formed an isosceles triangle widest at the base and the connector had the same height and width. These values still far exceeded 311 N, however, which is the average occlusal force in the incisor region. The results of this study suggest that connector design affects fracture load.

Effect of Connector Design on Fracture Resistance in Zirconia-based Fixed Partial Dentures for Upper Anterior Region

“…Therefore, connectors with different cross-sectional areas (9.0, 7.0, 5.0, and 3.0 mm 2 ) were subjected to the fracture test in the present study. In earlier studies on the cross-sectional form of the connector, this group found that a crosssectional area of 5.0 mm 2 was sufficient to withstand fracture 2,16,21) . Indeed, until recently, it has been impossible to prevent cracking with a cross-sectional area of only 3.0 mm 2 when using the CAD/CAM system.…”

“…The physical properties of zirconia frames have been investigated using various types of destruction test 1,15,16,21,32) and finite-element analysis 17,36) . Some studies using the former employed a thermal cycle to simulate aging 1,15) .…”

“…Filser et al reported that the cross-sectional area of a connector in a molar zirconia three-unit FPD should be >6.9 mm 2 , as such connectors should be able to withstand a maximal occlusal force of >880 N, and hence, would be able to withstand forces generated by certain types of parafunctional behavior 4) . The manufacturer of the GN-1 system recommends that the cross-sectional area of the connector used However, from an esthetic point of view 13) , and taking into account periodontal considerations 16,26) , the cross-sectional area should be as small as possible. Therefore, connectors with different cross-sectional areas (9.0, 7.0, 5.0, and 3.0 mm 2 ) were subjected to the fracture test in the present study.…”

“…This can cause some difficulty in designing an FPD for this region, as if the connector is too large, it might result in esthetic and periodontal problems. The larger, the connector, however, the greater its strength 13,16) . Many manufacturers 16,21,32) recommend a cross-sectional area of 7.0 to 9.0 mm 2 for connectors in zirconia FPD frameworks for the upper anterior region designed using the CAD/CAM system.…”

“…The larger, the connector, however, the greater its strength 13,16) . Many manufacturers 16,21,32) recommend a cross-sectional area of 7.0 to 9.0 mm 2 for connectors in zirconia FPD frameworks for the upper anterior region designed using the CAD/CAM system. With a narrow FPD connector, mechanical stress is distributed vertically in the lower anterior region.…”