Effect of cement gap and drill offset on the marginal and internal fit discrepancies of crowns designed with different tooth preparations.

AIM: The aim of the present study was to evaluate the effect of cement gap and drill offset on the marginal and internal fit discrepancies of crowns designed with different tooth preparations. MATERIALS AND METHODS: Five tooth preparations were constructed, and crowns with different cement gaps and drill offsets were obtained. Then, best-fit alignment was performed on the crowns with the corresponding tooth preparations, and the fit discrepancies were expressed by color-coded difference images and root mean square (RMS) values. The RMS values of each group were analyzed by the rank-based Scheirer-Ray-Hare test (α = 0.05). RESULTS: The color segments in the sharp line angles area of the Sharp line angles group changed significantly before and after the drill offset. The cement gap had a significant effect on the marginal, internal, or overall fit discrepancies of the five design groups (P < 0.001), while the drill offset had a significant effect on the marginal fit discrepancies of the Shoulder-lip group and the internal or overall fit discrepancies of the Sharp line angles group (P < 0.001). Additionally, the interaction effect between cement gap and drill offset was significant for the marginal fit discrepancies of the Shoulder-lip group and the internal or overall fit discrepancies of the Sharp line angles group (P < 0.01). CONCLUSIONS: The cement gap and drill offset had a significant adverse effect on the marginal or internal fit discrepancies of the crowns designed with the shoulder-lip and sharp line angles designs. Tooth preparation designs with intense curvature changes such as shoulder-lip and sharp line angles should be avoided clinically.

Fit of anterior restorations made of 3D-printed and milled zirconia: An in-vitro study.

OBJECTIVES: To evaluate the fit of zirconia veneers made by either 3D printing or milling. METHODS: A typodont maxillary central incisor was prepared for a 0.5-mm-thick veneer and was reproduced 36 times from resin. Restorations were designed with a 20-µm-wide marginal and a 60-µm-wide internal cement gap, and were made from 3D-printed zirconia (LithaCon 3Y 210, Lithoz, n = 24) and milled zirconia (Cercon ht, DentsplySirona, n = 12). For milled zirconia, a drill compensation was needed to give the milling bur access to the intaglio surface. The restorations were cemented, cross-sectioned, and the cement gap size was analyzed by two raters. Inter-rater reliability was studied at 12 3D-printed veneers (intraclass correlation coefficient, ICC, mixed model, absolute agreement). Twelve remaining 3D-printed restorations were compared with 12 milled restorations regarding fit at three locations: marginally, labially, and at the incisal edge (Mann-Whitney U-tests, α<0.05). RESULTS: Inter-rater reliability was excellent, with an ICC single-measure coefficient of 0.944 (95%-confidence interval: [0.907; 0.966]). Gap sizes (mean ± SD / maximum) were 55 ± 9 / 143 µm at the margins, 68 ± 14 / 130 µm labially, and 78 ± 19 / 176 µm at the incisor edge for 3D-printed veneers. For milled veneers, gap sizes were 44 ± 11 / 141 µm at the margins, 85 ± 19 / 171 µm labially, and 391 ± 26 / 477 µm at the incisor edge. At the margins, the milled veneers outperformed the 3D-printed restorations (p = 0.011). The cement gap at the incisor edge was significantly smaller after 3D printing (p < 0.001). CONCLUSIONS: 3D-printed zirconia restorations showed clinically acceptable mean marginal gaps below 100 µm. Because drill compensation could be omitted with 3D printing, the fit at the sharp incisal edge was significantly tighter than with milling. CLINICAL SIGNIFICANCE: The fit of 3D-printed ceramic anterior restorations meets clinical standards. In addition, 3D printing is associated with a greater geometrical freedom than milling. With regard to fit this feature allows tighter adaptation even after minimally invasive preparation.

Bacterial translocation and microgap formation at a novel conical indexed implant abutment system for single crowns.

OBJECTIVES: A conometric concept was recently introduced in which conical implant abutments hold the matching crown copings by friction alone, eliminating the need for cement or screws. The aim of this in vitro study was to assess the presence of microgap formation and bacterial leakage at the Acuris conometric restorative interface of three different implant abutment systems. MATERIAL AND METHODS: A total of 75 Acuris samples of three implant-abutment systems (Ankylos, Astra Tech EV, Xive) were subjected to microbiological (n = 60) and scanning electron microscopic (SEM) investigation (n = 15). Bacterial migration into and out of the conical coupling system were analyzed in an anaerobic workstation for 48, 96, 144, and 192 h. Bacterial DNA quantification using qrt-PCR was performed at each time point. The precision of the conometric coupling and internal fit of cemented CAD/CAM crowns on corresponding Acuris TiN copings were determined by means of SEM. RESULTS: qrt-PCR results failed to demonstrate microbial leakage from or into the Acuris system. SEM analysis revealed minute punctate microgaps at the apical aspect of the conometric junction (2.04 to 2.64 µm), while mean cement gaps of 12 to 145 µm were observed at the crown-coping interface. CONCLUSIONS: The prosthetic morse taper connection of all systems examined does not allow bacterial passage. Marginal integrity and internal luting gap between the ceramic crown and the coping remained within the clinically acceptable limits. CLINICAL RELEVANCE: Conometrically seated single crowns provide sufficient sealing efficiency, relocating potential misfits from the crown-abutment interface to the crown-coping interface.

Comparison of conventional and digital workflows for implant-supported screw-retained zirconia FPD bars: Fit and cement gap evaluation using SEM analysis.

PURPOSE: To assess the fit and cement gap of fixed partial dentures supported by two implants made using conventional and digital workflows. MATERIALS AND METHODS: Patients requiring fixed partial dentures supported by two implants were included in the study. Forty-eight zirconia fixed partial denture bars supported by two implants (AnyOne, MegaGen, Daegu, South Korea) were produced using a conventional (n = 24, group C) and digital (n = 24, group D) workflow. All implants had the same internal connection prosthetic platform. Silicone open tray impressions with splinted copings (group C) and digital impressions using a Trios 3 intraoral scanner (3Shape, Copenhagen, Denmark) (group D) were taken for each patient. The fit and cement gap were assessed by scanning electron microscopy on the verified master cast. The distance between reference points on the titanium base and implant analogue was measured with and without tightening the prosthetic screw. The difference in distance was calculated and represented the misfit (Dmisfit). The cement gap (Dcement) was measured as the shortest vertical distance from the inferior edge of the bar to the top edge of the titanium base. RESULTS: The median Dmisfit values (interquartile range) differed significantly (P < 0.05) between the groups, with 59 (60) µm for group C and 78 (88) µm for group D. Fixed partial dentures fabricated using a digital workflow presented lower Dcement values (35 [26] µm) than the conventional group (38.9 [23] µm) (P < 0.05). CONCLUSIONS: Both workflows produced different levels of fit and differently sized cement gaps when measured on the master casts using scanning electron microscopy. A cast-free digital workflow was associated with a smaller cement gap, but larger misfit was detected when measuring on the verified master cast.