A micro‐computed tomography analysis of internal and marginal fits of fixed partial dentures: Effect of preparation finish line designs on monolithic zirconia and heat‐pressed zirconia‐reinforced lithium disilicate

Abstract

Purpose: To evaluate the effect of finish line design (chamfer and feather-edge) and ceramic type on the internal and marginal fits of fixed partial dentures on abutment teeth. Materials and methods: Two typodont mandibular casts, missing right first premolar tooth, received tooth preparation on canine and second premolar abutments (one cast with chamfer finish line and the other cast with feather-edge finish line). The preparation segment of each typodont model was scanned, 3D printed in resin, and then invested and casted in metal to obtain two metal models. Polyvinyl siloxane impressions were made for the metal models and poured in type IV stone. The stone models (n = 40) were randomly assigned into four groups (n = 10): chamfer finish line with heat-pressed zirconia reinforced lithium disilicate fixed partial denture (CL), chamfer finish line with monolithic zirconia fixed partial denture (CZ), feather-edge finish line with heat-pressed zirconia-reinforced lithium disilicate fixed partial denture (FL), and feather-edge finish line with monolithic zirconia fixed partial denture (FZ). After the fabrication of ceramic restoration, micro-computed tomography was used to evaluate the internal and marginal fits of each fixed partial denture. Data were statistically analyzed with three-way ANOVA (alpha = 0.05). Results: There were no significant interactions between preparation type, material type, and tooth type at any of the areas assessed. There was significant difference (p = 0.01) between CZ (59.15 +/- 4.6 mu m) and FZ (73.6 +/- 17.1 mu m) groups at the finish line area. Regarding the horizontal marginal discrepancy area, there were significant differences between CZ (62.65 +/- 10.5 mu m) and FZ (90.05 +/- 5.6 mu m) groups (p < 0.001), CL (77.45 +/- 8.1 mu m) and CZ (62.65 +/- 10.5 mu m) groups (p < 0.001), and FZ (90.05 +/- 5.6 mu m) and CL (77.45 +/- 8.1 mu m) groups (p < 0.001). At finish line area, there was a significant difference (p = 0.018) between feather-edge with canine (72.75 +/- 13.3 mu m) and chamfer with canine (59.05 +/- 5.8 mu m); however, there was no significant difference (p = 0.774) between feather-edge with premolar (69.45 +/- 12 mu m) and chamfer with premolar (65.1 +/- 7.4 mu m). Moreover, there was no significant difference (p = 0.886) between feather-edge with canine and feather-edge with premolar. Conclusions: The internal and marginal fits of the ceramic fixed partial dentures can be affected by the finish line design and ceramic type. The feather-edge finish line had a negative impact on the marginal and internal fits of ceramic fixed partial dentures at certain measurement points. Regarding the effect of finish line design on abutment teeth, the difference in fit was only detected at the finish line area of the anterior abutment (canine) with the feather-edge finish line.