Search Results (4)

This in vitro study evaluated the internal surface trueness and the marginal and internal fit of interim crowns fabricated from intraoral scanner (IOS; i500, MEDIT, Seoul, Republic of Korea) data, considering variations in subgingival finish line depth and the use of gingival retraction. A right maxillary first molar was prepared using a milled ceramic abutment, with subgingival finish line depths set at 0, 0.25, 0.50, 0.75, and 1.00 mm from the gingival crest. All specimens were scanned with an IOS, both with and without gingival retraction. Interim crowns were designed from the scan data and produced via three-dimensional (3D) printing. Internal surface trueness was measured using 3D inspection software (Geomagic Control X version 2022.0.0; 3D Systems, Rock Hill, SC, USA), while marginal and internal fit were assessed with the silicone replica technique. Data were analyzed using the Mann–Whitney U test and Kruskal–Wallis H test (α = 0.05). In the absence of gingival retraction, internal surface trueness and crown fit decreased significantly with increasing finish line depth (p < 0.05). At a 1.00 mm depth without retraction, internal trueness reached 100.1 ± 44.5 µm and marginal fit was 189.1 ± 42.2 µm, both exceeding clinical thresholds. With gingival retraction, trueness and fit remained stable across all depths (p > 0.05). At 1.0 mm depth, trueness was 82.0 ± 61.8 µm and marginal fit was 95.2 ± 22.9 µm, both within clinically acceptable limits. A significant correlation was observed between marginal trueness and overall fit when retraction was not performed (p < 0.05). These results demonstrate that increasing subgingival finish line depth can significantly reduce intraoral scanning accuracy, resulting in suboptimal interim crown adaptation when gingival retraction is omitted. To achieve clinically acceptable internal trueness and marginal fit, gingival displacement with a retraction cord is recommended during intraoral scanning for subgingival prosthesis fabrication. Full article

One of the most critical aspects in intraoral impression is the detection of the finish line, particularly in the case of subgingival preparations. The aim of this in vitro study was to evaluate the accuracy among four different Intra Oral Scanners (IOSs) in scanning a subgingival vertical margins preparation (VP). A reference maxillary typodont (MT) was fabricated with a VP for full crown on #16 and #21. The MT was scanned with a laboratory scanner (Aadva lab scanner, GC, Tokyo, Japan) to obtain a digital MT (dMT) in .stl format file. A group of 40 digital casts (dIOC) were obtained by scanning the MT 10 times with four different IOSs: Trios 3, 3Shape A/S; I700, Medit; Vivascan, Ivoclar; and Experimental IOS, GC. All the obtained dIOCs were imported into an inspection software program (Geomagic Control X; 3D SYSTEMS) to be superimposed to the dMT in order to calculate trueness. Therefore, in order to calculate precision, all the scans of the same scanner group were superimposed onto the cast that obtained the best result of trueness. The results were collected as the root mean square value (RMS) on the #16 and #21 abutment surfaces and on a marginal area positioned 1 mm above and below the gingival margin. A nonparametric analysis Kruskal–Wallis test was performed to compare the RMS values obtained in the different iOS groups for trueness and precision. Statistical significance was set at 0.05. For the trueness on the #16 abutment, the Vivascan reported statistically lower values, while on the #21 abutment, Vivascan (56.0 ± 12.1) and Experimental IOS, GC (59.2 ± 2.7) performed statistically better than the others. Regarding precision, Experimental IOS, GC were significantly better than the others on #16 (10.7 ± 2.1) and in the #21 area Experimental, GC, and Trios 3 performed statistically better(16.9 ± 13.8; 18.0 ± 2.7). At the subgingival marginal level for both #16 and #21, all the IOS reported reduced accuracy compared to clinical acceptance. Full article

Tooth preparation for a metal-ceramic crown with a subgingival finish line can lead to inflammatory changes in the gingival tissue, often accompanied by cell damage. This study aimed to evaluate the clinical signs of inflammation and the cytomorphological status of the gingival tissue before and after tooth preparation. The research included a homogeneous group of 19 patients with an indication for upper canine preparation. Before and after treatment, the gingival and the gingival bleeding indexes were determined, gingival swabs were taken, and direct smears prepared on slides for cytomorphometric analysis. The values of the measured gingival indexes were statistically significantly higher (p < 0.001) after tooth preparation. They decreased over time, which indicated the reversibility of the resulting changes. Cytological examination showed no statistically significant difference between the values of nuclear area, perimeter, Feret diameter, Feret angle, integrated optical density, MinFeret, and roundness, before and after the treatment. Significantly higher values of circularity, integrated optical density, MinFeret (p < 0.05), as well as roundness (p < 0.001) were found after 72 h, compared to those taken 15 min after tooth crown preparation. This study is a pioneering attempt to show gingival changes during fixed prosthodontic treatment and may shed new light on pathogenetic events in prosthodontic patients. Full article

An important issue with digital impression techniques is the difficulty in replicating the subgingival zone, particularly when abutments are prepared with a vertical finish line. We propose a novel procedure, the reverse subgingival scan (RSS), to depict the subgingival area via digital impression without a retraction cord or the distortion of the sulcus. The software workflow, beginning with a digital dental impression, was performed using Exocad^® (Align Technology) and Meshmixer^® (Autodesk). The approach is based on the direct alignment of the surface of abutments, which is used as a reference point. The efficacy of the RSS approach was confirmed via fit tests, radiographic control assessments, and evaluations of the rate of tissue compression of the final prosthetic restoration, so long as the provisional had a perfect fit. RSS yields information on the transversal dimension and depth of the gingival sulcus. The procedure depends on the quality and characteristics of the provisional restoration, and is suitable only for cases in which the finish line of the final crown is at the same level or more coronal than that of the provisional. Full article