In-vitro Untersuchungen zum Einfluss der subgingivalen Lage präparierter Zahnflächen auf deren korrekte Erfassung mit Hilfe intraoraler Scanner
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Abstract
Digital impression-taking of dental arches has become an integral part of modern dentistry. In contrast to laboratory scanners, intraoral scanners allow direct optical capture of the patient's situation and, with the help of specialized software, generate virtual three-dimensional models of the oral situation. The fabrication of precisely fitting dental restorations requires the accurate digitalization of all relevant dental and jaw areas.
Objective:
The aim of this in-vitro study was to evaluate, for three commercially available intraoral scanners, to what extent the subgingival position of the preparation margin and the adjacent prepared tooth surfaces influence the sharpness and accuracy of the digitized dental areas. Additionally, a preliminary study was conducted to determine whether the orientation points required for correct digital matching in the PolyWorks® overlay software, which do not lie in a single plane, can be placed arbitrarily.
Materials and Methods:
The study is divided into two substudies.
Substudy A focused on evaluating the PolyWorks® overlay software. For this, a dimensionally stable type IV gypsum model of a fully dentate maxilla was scanned multiple times using a standard laboratory scanner (T710®, Medit™) and three commercially available intraoral scanners (TRIOS 3® – 3shape™, i700® – Medit™, CEREC Primescan® – Dentsply Sirona™), each time selecting different orientation points. The resulting scans were then compared using defined reference points.
For Substudy B, a specially constructed, dimensionally stable maxillary model was fabricated, which allows precise movement of a prepared tooth 16 along three spatial axes relative to the remaining teeth using micrometer screws. To avoid deformation of the model, the core of the plastic model consists of a stable non-precious metal framework, which is firmly bonded to the ceramic teeth. The tooth stump 16 displays different preparation forms mesially, distally, palatally, and vestibularly and is surrounded by a silicone gingival mask. Starting from an equigingival position of the preparation margin, the stump—and thus the preparation margin—was shifted apically in 0.5 mm increments, and scanned three times with each of the three intraoral scanners at each position. The scans were then digitally compared using the PolyWorks® software.
Results:
The results of sub-study A demonstrate that the "Best-Fit" function of the PolyWorks® comparison software does not introduce artificial deviations in the scans. Therefore, the null hypothesis - that the orientation points required for correctly superimposing digital scans can be arbitrarily set in the PolyWorks® software without quality loss - should be accepted. Additionally, the laboratory scanner demonstrated good reliability through repeated scans with a maximum deviation of 0.007 mm.
Furthermore, the scans were examined at 28 selected reference points using the intraoral scanners for possible deviations from the master scan.
The Primescan® showed the largest divergences of 0.22 mm in the area of anterior tooth 11, followed by the TRIOS 3® with a mean deviation of 0.19 mm at tooth 21. The i700® displayed the smallest deviations, with a maximum mean divergence of 0.0548 mm at tooth 24. In the opposing region of teeth 26 and 27, intraoral scanner scans showed mean deviations between 0.657 mm and -0.134 mm along the z-axis compared to the reference scan, indicating expansion in the anterior region and z-axis deformation in the molar area.
Sub-study B findings reveal that wide sulcus opening and clear visibility of target areas are prerequisites for accurate representation. The mesial, distinctly tapering preparation margin was reliably captured by all intraoral scanners up to a subgingival depth of 2.5 mm. However, the vestibular, distal, and oral preparation margins could no longer be accurately represented by intraoral scanners beyond 1.5 mm subgingivally.
No significant differences were observed among the three tested intraoral scanner devices regarding precision in capturing preparation margins. Beyond an apical displacement of 3.5 mm, the distal and vestibular stump surfaces in the lower third could not be captured, while the mesial and oral surfaces were digitized without clinically relevant deviations up to 5.0 mm displacement.
The hypothesis that subgingival margin location, stump form, and morphology do not affect accurate intraoral scanner capture must be rejected. Even when deeper but visible subgingival surfaces are correctly digitized, preparation margins may appear rounded at shallower subgingival depths.
Discussion and Conclusion:
The subgingival position, the circumferential shaping of the preparation margin, and the visibility of the sulcus all influence digital acquisition with intraoral scanners. The results of this study confirm that dental areas can only be accurately captured by the system if they are also clearly visible. However, being able to see a subgingival preparation margin does not guarantee its precise registration. Whether the preparation margin is captured true to form and not displayed as rounded can only be determined by carefully inspecting the enlarged scan on the screen. Ideally, this inspection should be performed promptly by the clinician who carried out the preparation. If the preparation margin is not clearly and fully visible around the entire circumference or is located significantly subgingivally, sulcus management is necessary.
The results also show that, aside from the risk of inaccurate representation of the subgingival preparation margin, tooth surfaces that are steeply sloped and located well below the gingival margin can still be depicted with clinically sufficient precision by intraoral scanners, provided they are visible.
Despite advances in scanning technology, there are clinical situations in which conventional impressions are clearly superior to digital methods. This is especially true for very deep subgingival preparation margins, long-span fixed restorations crossing the dental arch, and edentulous jaw sections.
Finally, it should be emphasized that the results of this study regarding precision and reliability strictly apply only to the three intraoral scanner types compared. Additionally, clinical factors such as saliva and blood were not simulated in this in vitro study. Further in vivo studies should be conducted to supplement the findings obtained in vitro.
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Dates
Issued: 2025-10-27
Faculty
FB20:Medizin
Language
de
Keywords
Intraoral ScannerDigitale Abformung
DFG-subjects
205-28 Zahnheilkunde; Mund-, Kiefer- und Gesichtschirurgie
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Moritz Gädicke: In-vitro Untersuchungen zum Einfluss der subgingivalen Lage präparierter Zahnflächen auf deren korrekte Erfassung mit Hilfe intraoraler Scanner. : 2025-10-27.
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This item has been published with the following license: In Copyright