Statement of problem. Accurate marginal and internal fit of dental restorations are essential for their long-term success. The fit of zirconia restorations prepared using digital scan systems has not been fully evaluated.Purpose. The purpose of this in vitro study was to compare the marginal and internal fit of 3-unit zirconia frameworks fabricated using direct and indirect digital scans.Material and methods. In a maxillary model, the left first premolar and first molar were prepared to receive 3-unit zirconia fixed dental prostheses. Conventional impressions were made using stock trays and 2-step putty/wash polyvinyl siloxane material and were scanned using laboratory scanner (Conventional Impression-Laboratory scanner [CIL] group). The impressions were then poured, and the stone casts were scanned (Dental Cast-Laboratory scanner [DCL] group). Digital scans were made using TRIOS (TRIOS Intraoral scanner [TRI] group) and CS3600 (CS3600 Intraoral scanner [CSI] group) scanners (n=10). Zirconia copings were designed and milled from presintered blocks and subsequently sintered. Marginal, mid-axial, axio-occlusal, and mid-occlusal discrepancies were measured using the silicone replica technique with stereomicroscopy at ×50 magnification. The data were analyzed using 1-way ANOVA (a=.01).Results. The ANOVA revealed significant differences among the studied groups in terms of all studied characteristics (P.01). Marginal gap was significantly higher in the DCL group (106 ±45 mm) compared with all other groups (P.01). However, no significant differences were observed in marginal gap between the TRI (60 ±15 mm) and CSI (55 ±13 mm) groups (P>.01). Internal gap in the mid-occlusal and axio-occlusal regions were significantly higher in the CIL (238 ±92 mm and 227 ±95 mm) and DCL (248 ±71 mm and 216 ±68 mm) groups than those recorded in the TRI (104 ±27 mm and 126 ±31 mm) and CSI (128 ±16 mm and 147 ±28 mm) groups (P.01). Internal discrepancies in the mid-axial position were similar between the TRI (70 ±15 mm) and CSI (72 ±23 mm) groups (P>.01), but these values were significantly lower than those recorded in the CIL (88 ±31 mm) and DCL (85 ±30 mm) groups (P.01). Conclusions.Within the limitations of this study, zirconia frameworks in the TRI and CSI groups had lower marginal and internal gaps compared with those in the DCL and CIL groups. Marginal gap in all groups was within a clinically acceptable range. (J Prosthet Dent 2020;123:105-12)

Aim:The purpose of this in vitro study was to investigate the effect of interimplant distance and cyclic loading on the retention of two locator attachment systems. Materials and methods:A total of 72 acrylic resin blocks were fabricated and divided into six groups of six pairs each. Locators of DIO and 3i implant systems were positioned on analogs in three different interimplant distances (19, 23, and 29 mm). The blocks were attached to a universal testing machine, and 1,440 dislodging cycles by the force of 136 N were applied. After 0, 120, 360, 720, and 1,440 cycles, the retention was recorded. Three-way analysis of variance (ANOVA) was used to test for differences in retention between the various combinations of the locator, interimplant distance, and cyclic loadings. Results:Interimplant distance was significantly associated with retention, independent of the locator system used, and dislodgement force cycles. Mean retention was significantly higher under the 3i system relative to the DIO system (p < 0.0001). This association varied with both interimplant distance (p > 0.0001) and dislodgement force (p < 0.0001) as well as across the various combinations of distance and cycle (p < 0.0001). Conclusion:Interimplant distances could affect the initial retention of locator attachments. There was little difference in retention between distances of 23 and 29 mm across all cycles when both locator systems were combined. Distance of 23 mm was associated with superior retention in the DIO system. With regard to the speed of retention decrease, the 23 mm distance was associated with better performance.Clinical significance: Interimplant distance could play a significant role in overdenture retention with locator attachments.