Effect of cement type on the retrievability of cement-retained implant supported Zirconia and Metal crowns with a Lingual retrieval slot
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Introduction: The retrievability of implant-supported crowns is essential for solving mechanical, biological and aesthetic problems. The aim of this study was to evaluate the removal torque (RT) of cement-retained implant supported Zirconia and Metal crowns with a lingual retrieval slot cemented with three different cements. Materials and methods: Studied crowns were from 2 crown materials including 24 Zirconia crowns and 24 Metal crowns. Each of the 2 crown materials was cemented to customized abutments in 3 groups, using Calibra ceram resin cement, Harvard zinc phosphate cement and FujiCem 2 SL resin- modified glass ionomer (RMGI) cement. All customized abutments had a rectangular ledge (2mm*1mm) on mid-marginal part of lingual side. All crowns had lingual retrieval slot coronally to abutment ledge. All titanium abutments, zirconia crowns and resin copings (for casting Nickel- Chromium metal crowns) were fabricated using a CAD/CAM system.Crowns were cemented according to the instructions of each cement manufacturer. A custom-made device was used to record the torque (N.cm) required to remove the crowns. The one way ANOVA test was applied for the statistical analysis using the post hoc Tukey test when required by SPSS 17 software. Level of significance was set at P<0.05. Results: Mean RT of zirconia crowns cemented with resin, zink phosphate and RMGI cements was 37.60, 27.15 and 31.06, respectively. The RT difference of RMGI cement with resin cement and zink phosphate cement was not statistically significant (p-value=0.19, 0.50), but the RT of resin cement was significantly more than zink phosphate cement (p-value= 0.02). Mean RT of metal crowns cemented with resin, zink phosphate and RMGI cements was 32.5, 33.75 and 35.83, respectively. The RT difference whithin groups was not statistically significant )p-value=0.75). Conclusions: Retrievability of zirconia crowns with a lingual retrieval slot cemented with RMGI cement was statistically similar to zink phosphate and resin cement but retrievability of resin cement was significantly less than zink phosphate cement. Also, retrievability of metal crowns with a lingual retrieval slot cemented with resin cement, zink phosphate cement and RMGI cement was statistically similar.