The aim of this study: was to investigate the influence of different connector surface areas on the fracture resistance of three and four units full contoured monolithic zirconia FPDs manufactured by CERCON machine and cemented by either zinc phosphate or resin cements.
Materials and methods: Sixty full contoured monolithic zirconia FPDs cementd on resin casts were divided into two main groups (30 FPDs each) according to the number of units (three and four units FPDs), each group was subdivided into three subgroups according to connector surface area dimensions (10FPDs each). Subgroup A1: Surface area of each connector didn't exceed
24 mm2. , Subgroup A2: Surface area of each connector was greater than 24 mm2 and less than
35 mm2 and Subgroup A3: Surface area of each connector was more than 35 mm2. Each subgroup was further randomly divided into two (5FPDs each). division C1 : FPDs were cemented using zinc phosphate cement and division C2 : FPDs were cemented using dual cured resin cement (Variolink N). the specimens were stored in deionized water in an incubator (QWJ500; Queue Systems Inc. USA) maintained at oral temperature (37°C) for and removed 24 hours before mechanical testing. Specimens were loaded in universal testing machine until failures were observed. The obtained data of fracture resistances were statistically analyzed.
Results: showed that for all subgroups, by increasing the connector surface area a statistically significant increase in the fracture resistance was observed, whether using resin cement or zinc phosphate cements. For three units FPDs, using adhesive resin cement produced higher fracture resistance values than using zinc phosphate cements, that were statistically non-significant for subgroupsA1,A2 while it was statistically significant for subgroup A3. (at p-value < 0.05). For four units FPDs, using adhesive resin cement produced higher fracture resistance values than using zinc phosphate cements that were statistically non-significant for subgroup A1, while they were statistically significant for subgroups A2and A3. (at p-value < 0.05). using Zinc phosphate cements with three units FPDs produced statistically significant higher values than with four units FPDs
Using resin cements with three units FPDs produced statistically significant higher values than with four units FPDsfor only subgroup A3. While the difference was not statistically significant for subgroup A1 and A2. conclusions: it was found that the fracture resistance of the full contoured three and four units FPDs made using monolithic zirconia is affected by the connector dimension , span length and the used cement. By increasing the connector surface area, the fracture resistance values increased significantly with both cements. Generally, For all tested subgroups, three units monolithic zirconia FPDs have higher fracture resistance values than four units FPDs. Using resin cement produced higher values of fracture resistance than using zinc phosphate cement.