Effect of screw access hole on fracture strength of implant supported cement-retained monolithic zirconia and metal supported porcelain crowns

In cement-retained implant crowns, when screw loosening is observed or in case of any problem, it is very difficult to remove the restoration without damage. In addition, the presence of residual cement that cannot be removed is a predisposing factor for periimplantitis. Combination implant crown; it offers the advantages of providing both cement and screw retention in order to facilitate access to the screw hole of restorations and to allow removal of the subgingival cement. The aim of this study is to evaluate how opening a screw access hole affects fracture strength in metal-supported porcelain and monolithic zirconia crowns. Forty-four abutments (Dentis Implant, Daegu, South Korea) and 44 analogues (Dentis Implant, Daegu, South Korea) were used for the study. 11 metal supported porcelain crowns, 11 metal supported porcelain crowns with screw access holes, 11 monolithic zirconia crowns, 11 monolithic zirconia crowns with screw access holes were produced. After the produced crowns were cemented to the abutments, their fracture resistance was measured with a Universal testing machine (Lloyd LRX instruments, Hampshire, England). There was no statistically significant difference between the metal supported porcelain groups with and without screw access holes in terms of maximum load averages (p>0.05). There was no statistically significant difference between the monolithic zirconia groups with and without screw access holes in terms of maximum load averages (p>0.05). When there is a screw access hole and there is no hole; maximum load average of monolithic zirconia groups was found to be statistically significantly higher than metal supported porcelain groups (p<0.05). The fracture strengths of all samples are higher than the maximum chewing forces of natural toothed individuals. The combination implant crown offers the advantage of retrievability. In this way, it can be easily displaced due to possible screw loosening or in any situation that requires removal of the crown, without damaging the restoration, and it can be an alternative solution against negativities such as periimplantitis, which may be caused by residual cement that may remain after cementation in cement-retained crowns. Keywords: Combination implant crown, monolithic zirconia, metal-supported porcelain, fracture resistance