Influence of Different Fiber-Reinforced Biobases on the Marginal Adaptation of Lithium Disilicate Overlay Restorations (A Comparative In Vitro Study)

Background/purpose: Fiber-reinforced materials are commonly used as biobases beneath indirect restorations, potentially affecting the seating and marginal accuracy of the restorations. This study intended to assess the impact of various biobase techniques on the marginal adaptation of lithium disilicate overlay restorations. Methods: Fifty sound maxillary first premolar teeth of comparable dimensions were prepared using a full-bevel overlay design (3 mm occlusal reduction) and allocated randomly to five groups as follows (n = 10): Group A, delayed dentin sealing; Group B, immediate dentin sealing using Optibond FL; Group C, immediate dentin sealing with a 1 mm flowable composite layer (Clearfil AP-X Flow); Group D, immediate dentin sealing followed by a 1 mm short-fiber-reinforced composite layer (everX Flow); and Group E, immediate dentin sealing coated with a 1 mm flowable composite layer reinforced with polyethylene Ribbond fibers. Digital impressions were obtained using a Medit i700 intraoral scanner, and the overlays were digitally designed via the Sirona inLab CAD software and milled via a four-axis milling machine. The overlays were luted with a preheated composite (Clearfil AP-X). Marginal gap assessments were conducted pre- and post-cementation via a digital microscope at 230× magnification. The data were statistically analyzed using a one-way analysis of variance and paired t-tests. Results: The one-way ANOVA disclosed no significant differences among the groups before or after cementation (p > 0.05). Conclusions: The presence or absence of fiber-reinforced biobases did not impact the marginal adaptation of the restorations; these biobases can be incorporated to optimize the mechanical behavior of indirect restorations without adversely affecting their seating accuracy. These findings suggest that fiber-reinforced and non-reinforced biobase techniques can be safely integrated into clinical adhesive protocols to enhance the mechanical performance of restorations without comprising their marginal adaptation.