effect of abutment taper on the fracture resistance of all-ceramic three-unit bridges

statement of problem: the connector area is the weakest zone of an all-ceramic fixed partial denture (fpd), where most catastrophic failures of the prostheses tend to occur. purpose: the aim of the present study was to assess the effect of the convergence angle of abutments on the fracture resistance of three-unit fixed partial dentures made of ips-empress2. materials and methods: forty extracted human premolars and molars were used to reproduce twenty, 3-unit fixed partial dentures, for the replacement of second premolars. all teeth were prepared according to the guidelines outlined for all-ceramic crowns and bridges, except for the convergence angles of the abutments. the specimens were randomly divided into two groups of 10, with total occlusal convergence angles of 12° and 22°. fixed partial dentures with a uniform thickness of 0.8 mm were fabricated using ips-empress2 and were bonded to the corresponding models. connector dimensions were set to 4 mm height and 4mm width. the radius of curvature at the gingival embrasure was carved to 0.9 mm. all specimens were exposed to 10,000 pre-loading cycles and a load of 40 n at a frequency of 1.3 hz in a standardized testing machine at a cross head speed of 1mm/min. student t-test was performed to detect any difference in the mean fracture resistance between the two groups (α = 0.05). results: mean failure loads (and standard deviations) of the 12° and 22° groups were 1009.12 n (208.05) and 1182.72 n (144.67), respectively. statistical analysis revealed a significant difference (p <0.04) between the mean failure loads of the two groups. most fractures occurred through the connectors. conclusion: the mean failure loads of the investigated fixed partial dentures were higher in the abutments with 22° taper as compared to those with a taper of 12°.