A Study on Dimensional and Marginal Gap Changes Through Application of Different Sintering Methods and Veneer Firings on Zirconia Crowns

Background: The marginal fit of dental restorations is a vital\rfactor for long-term success. The veneering process of zirconia,\rwhich involves multiple firings at high temperatures, has shown\rto affect the marginal fit of zirconia cores. The aim of this study is\rto observe dimensional and marginal gap changes during\rveneer firing of zirconia frameworks sintered with different\rprocedures.\rMethods: 30 Y-TZP ((inCoris ZI, Sirona, Bensheim, Germany)\rcrown frameworks sintered with three different durations of 8\rhours, 2 hours and 10 minutes. Occlusal and buccal dimensional\rmeasurements based on reference points measured with\rtoolmaker’s microscope. Frameworks subjected to veneer firings\rwithout application of veneering material to observe the effect of\rfiring process only. All dimensional and marginal gap\rmeasurements were repeated and after veneer firings. Data were\ranalysed with one-way ANOVA and paired t test.\rResults: No significant differences observed between the\rsintering shrinkage of three groups. Marginal gaps decreased\rafter veneer firings for all groups and the decrease was\rsignificant for 2 hour and 10-minute sintering groups (p <.05).\rThe occlusal surface dimensional changes were negative which\rindicates shrinkage; again, buccal surface was positive which\rindicates enlargement. No significant differences between the\rthree groups regarding surface dimensions were detected.\rConclusion: For all three sintering groups, veneer firing caused\rdistortion on zirconia structures in the form of shrinkage in\rocclusal surfaces and enlargement in buccal surfaces, whereas\rmarginal gap values decreased after firing in all groups.