Abstract
Objective: The purpose of this in vitro study is to evaluate the effect of four finish line configurations and two cement types on the fracture resistance of zirconia copings. Material and Methods: Forty yttrium tetragonal zirconia polycrystals copings were manufactured on epoxy resin dies with four preparation designs: knife edge, chamfer, deep chamfer 0.5, 1 mm and shoulder 1 mm. The copings were cemented with two cement types (glass ionomer and resin cement); (n = 5). Two strain gauges were attached on each coping before they were vertically loaded till fracture with a universal testing machine. Data were analyzed by 2-way analysis of variance ANOVA (p < .05). Fractured specimens were examined for mode of failure with digital microscope. Results: Knife edge showed the highest mean fracture resistance (987.04 ± 94.18) followed by Chamfer (883.28 ± 205.42) followed by Shoulder (828.64 ± 227.79) and finally Deep chamfer finish line (767.66 ± 207.09) with no statistically significant difference. Resin cemented copings had higher mean Fracture resistance (911.76 ± 167.95) than glass ionomer cemented copings (821.55 ± 224.24) with no statistically significant difference. Knife edge had the highest strain mean values on the buccal (374.04 ± 195.43) and lingual (235.80 ± 103.46) surface. Shoulder finish line showed the lowest mean strain values on the buccal (127.47 ± 40.32) and lingual (68.35 ± 80.68) with no statistically significant difference. Resin cemented copings had higher buccal (295.05 ± 167.92) and lingual (197.38 ± 99.85) mean strain values than glass ionomer copings (149.14 ± 60.94) and (90.27 ± 55.62) with no statistically significant difference. Conclusion: Vertical knife edge finish line is a promising alternative and either adhesive or conventional cementation can be used with zirconia copings. KEYWORDS Cementation; Flexural strength; Prosthodontics; Tooth preparation; Zirconium.
Highlights
A s all-ceramic restorations when placed in the posterior region, had a history of being prone to fracture, strong ceramic core materials have been developed to support the weaker veneering ceramic materials [1,2]
The data showed that knife edge (KNE) had the highest mean FR (987.04 ± 94.18) followed by CH finish line (883.28 ± 205.42) S finish line (828.64 ± 227.79) and the DCH finish line (767.66 ± 207.09) (Figure 3)
The data showed that resin cemented copings (R) had higher mean FR (911.76 ± 167.95) than the glass ionomer (GI) cemented copings (821.55 ± 224.24) (Figure 3)
Summary
A s all-ceramic restorations when placed in the posterior region, had a history of being prone to fracture, strong ceramic core materials have been developed to support the weaker veneering ceramic materials [1,2]. Zirconia (ZrO2) has been introduced as a promising metalfree core structure for fixed prostheses due to its superior physical and mechanical properties, chemical stability, and excellent biocompatibility [3]. The rapid diversification in equipments and materials available for fabrication of computer-aided design/computeraided manufacturing (CAD-CAM) prostheses along with an increase in the availability of dental laboratory processed CAD-CAM restorations is driving the use of ZrO2 copings and framework materials. The concept of minimally invasive dentistry and the superior mechanical properties of ZrO2 allow clinicians to reconsider preparation guidelines such as reducing the coping thickness from 0.5 mm to 0.3 mm and changing finish line preparations from shoulder to chamfer or even KNE margins [24,25].
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