Marginal discrepancy and retention post-cementation of unretentive crowns in conometric systems: An in vitro comparative study

Background: This in vitro study was carried out to determine the marginal discrepancy (MD) and retention force (RF) values in the conometric systems (CSs) having poor retention after cementation using two distinct cements and procedures. Materials and methods: This study used 24 monolithic zirconia crowns that were cemented into 24 conometric caps and 24 conometric abutments attached to implant analogues. The researchers repeated the pull-out test until they achieved the RF values <40N. All samples were classified into two categories (n=12): grooved and ungrooved crowns. Every group was separated into 2 subgroups (n=6) depending on the cement type that was used i.e., either zinc phosphate cement (ZPC) or resin-modified glass ionomer cement (RMGIC). After cementation, the researchers calculated the MDs with a stereoscopic microscope, and the RFs were calculated with the help of pull-out tests. The researchers statistically analysed the data using a two-way analysis of variance (ANOVA) test with a significance level <0.05. Results: They noted that the ungrooved crowns that were cemented using RMGIC (163±17.13µm) and ZPC (173.16±23.13µm) exhibited the highest average MDs. On the other hand, the grooved crowns that were cemented with RMGIC displayed the lowest average MD (38.16±22.85µm). Also, RMGIC showed a higher RF value (355.54±102.23N, 373.48±46.33N) compared to that shown by ZPC (199.79±114.01N, 189.86±21.33N). Conclusions: Both the cement groups in this study showed a higher and acceptable retention. Furthermore, it was seen that the incorporation of grooves in the crowns during the cementation procedure decreased the MD. Additionally, RMGIC-cemented grooved crowns displayed the best post-cementation MD and RF values.