3D assessment of the marginal and internal gap and fracture load of ceramic surveyed inlays designed for removable partial denture support: An in vitro comparative study

PURPOSE: To assess the internal and marginal gaps and the fracture load of different machinable ceramics for an inlay acting as a support for a removable partial denture. MATERIALS AND METHODS: Sixty extracted human teeth (first maxillary premolar) were collected (n = 10 for each group). Intact teeth served as the negative control group, and there were six experimental groups: direct composite resin group (positive control); IPS Empress Direct composite (EDC); Feldspathic ceramic, VITABLOCS Mark II (FLD); Leucite glass-ceramic IPS Empress CAD (LGC); zirconia-reinforced lithium silicate Celtra Duo (ZLS); and zirconium oxide IPS E.max ZirCAD (ZRC). Disto-occlusal inlay cavities were prepared in the assigned teeth. For ceramic groups, teeth were scanned using a Trios III intraoral scanner (IOS). Inlays were virtually designed to incorporate a rest seat and then milled. The three-dimensional (3D) internal and marginal gaps were assessed with a replica technique combined with a second scan of the fit checker applied before inlay cementation. 3D inspection software was used for the superimposition of scans and the calculation of the internal and marginal gaps. Inlay restorations were cemented using a dual-polymerizing resin cement, then subjected to thermocycling and cyclic loading, followed by load till failure. The internal and marginal gap and fracture load values were recorded and statistically analyzed using One-way ANOVA with post hoc Tukey test for comparisons (α = 0.05). Failure patterns were analyzed. RESULTS: The least significant marginal gap was seen with the ZRC group (68 ± 7 µm), while the ZLS group presented the highest marginal and internal gap values (135 ± 9, 199 ± 61 µm), respectively. Internal gap comparison revealed non-significant differences among the FLD, LGC, and ZRC groups. ZRC group demonstrated significantly the highest fracture load value (1830 ± 97 N). On the contrary, composite resin and FLD groups showed the lowest fracture load in comparison to the tested groups (p < 0.001). Failure pattern with the ZRC group revealed predominance of tooth failure, as well as adhesive failure associated with debonding of the restoration. LGC and ZLS groups revealed common performance with prevalence of tooth and restoration failure of mixed type, while both direct composite restoration and FLD groups showed predominately cohesive restoration failures. CONCLUSION: Indirect machinable ceramic surveyed inlays revealed acceptable gap values in addition to outstanding fracture load when compared to direct composite inlays.