International Journal of Computerized Dentistry, 02/2024

Aim: Quantitative dental plaque evaluation is necessary for clinical and scientific work. The present study aimed to examine the reliability of a 3D image analysis method by digitally analyzing the color 3D images obtained from an intraoral scanner (IOS) and then detecting and quantifying the plaque information and comparing it with the clinical examination results. Materials and methods: A total of 140 teeth from five subjects with a standard dentition were enrolled. Plaque examination was performed at two different time points: after 24 h without oral hygiene (T1), and after habitual brushing (T2). At each time point, the Quigley-Hein Plaque Index (PI) of each tooth surface was recorded separately, followed by color 3D images obtained using an IOS, and image analysis and calculation using Geomagic Wrap 2021 software. Results: The percentage of plaque staining area calculated from the 3D image analysis correlated well with the PI recorded during the clinical examination: the Spearman correlation coefficients were 0.9136 and 0.9061 (P < 0.001) for all tooth surfaces at T1 and T2, respectively. The measurements of the three investigators were in good agreement, with intraclass correlation coefficients of 0.989 and 0.992 (P < 0.001) for the vestibular and lingual surfaces at T1, respectively, and 0.964 and 0.983 (P < 0.001) for the vestibular and lingual surfaces at T2, respectively. Conclusion: In the present study, a digital 3D evaluation system of dental plaque suitable for research and clinical practice was initially developed and its reliability demonstrated. Keywords: dental plaque, quantitative evaluation, intraoral scanner (IOS), 3D image processing, Plaque Index

Aim: The objective of the present study was the software-supported evaluation of the measurement accuracy between CBCT and panoramic radiographs in the assessment of the periodontal bone level in patients with periodontitis, and the comparison of this with clinical periodontal parameters. Materials and methods: Twenty patients with severe periodontitis (stage III to IV) were evaluated clinically and radiographically (panoramic radiographs and CBCT). Diagnostic interpretation comprised three blinded investigators with different levels of experience. Specific software-basing measurement procedure evaluated radiologic distances for the mesial, central, and distal bone levels on the oral and vestibular sides of the teeth investigated and furcation upper and lower boundary. Jaw localization, anatomical region of interest, the number of roots, and the experience of the observers were evaluated. All measurements were carried out twice by the same observers within a 6-week interval. Results: Slightly higher measurement deviations (SD) in the range of 0.47 (0.40) mm were found for CBCT evaluation compared with panoramic imaging. Pearson correlation analysis showed statistically strong positive correlation for the mesial and distal aspects, and moderate positive correlation was found for the investigated furcations between both radiographic modalities. Compared with the clinical reference, the mean total error of measurement (SD) was larger for panoramic imaging (0.66 [0.48] mm) than for CBCT (0.27 [0.08] mm) for all three observers. Conclusions: Software-supported CBCT analysis delivers better diagnostic information about the bony periodontal conditions of the patient compared with 2D radiographs. However, it remains unclear if this additional information leads to better periodontal outcomes. Keywords: periodontitis, diagnostic imaging, CBCT, radiography, dimensional measurement accuracy, alveolar bone loss

Aim: Endodontically treated teeth are more susceptible to fractures than vital teeth because of significant coronal and radicular dentin loss during endodontic therapeutic procedures. The objective of the present in vitro study was to estimate and compare the influence of the post length and type on the fracture strength of endodontically treated maxillary central incisors. Materials and methods: Sixty extracted human maxillary central incisors were decoronated 2 mm above the cementoenamel junction. The teeth were selected and subjected to standard endodontic treatment, resulting in three groups with different preparation lengths: 5, 7.5, and 10 mm. Each group was randomly divided into two subgroups according to the post type: zirconia or fiber. After appropriate surface treatment, they were cemented with adhesive resin cement and restored with zirconia crowns. Thermocycling (5°C to 55°C, 60 s, 1500 cycles) was performed after cementing the zirconia crowns onto each tooth. Prepared samples were subjected to a compressive static load of 0.5 mm/min, at an angle of 130 degrees to the long axis of the roots, using a universal testing machine (Matest) at a crosshead speed of 0.5 mm/min, until fracture. The significance of the results was assessed using two-way analysis of variance (ANOVA) and the Tukey-Kramer test (α = 0.05). Results: The ANOVA analysis indicated significant differences (P < 0.05) between the groups. The Tukey-Kramer test revealed no significant differences among the zirconia posts with lengths of 5 mm (26.5 N ± 13.4), 7.5 mm (25.2 N ± 13.9), and 10 mm (17.1 N ± 5.2). Also, in the fiber post group, there was no significant difference when the posts with lengths of 7.5 mm (13.4 N ± 11.0) were compared with those of 5 mm (6.9 N ± 4.6) and 10 mm (31.7 N ± 13.1). The 10-mm–long post displayed superior fracture strength, and the 5-mm–long post showed significantly lower mean values (P < 0.001). Conclusions: The fracture strength of zirconia posts (with lengths of 5 and 7.5 mm) was found to be significantly higher than that of fiber posts (with lengths of 5 and 7.5 mm). The 10-mm–long fiber post group demonstrated significantly higher fracture strength values, and the 5-mm–long fiber post group showed the lowest values for the force resulting in root fracture; these groups were significantly different from each other (P < 0.001). The fracture strength analysis with a universal testing machine is the only method that enables the estimation of the differences between zirconia and fiber posts with different lengths in endodontically treated teeth. Keywords: endodontically treated teeth, fiber post, fracture strength, universal testing machine, zirconia post

Aim: A total occlusal convergence (TOC) angle (ϕ) of 6 degrees is a typical crown preparation requirement. It has been shown that this is difficult to achieve clinically. The present study therefore aims to compare the ability of students to judge different steepnesses, including a −1-degree undercut of prepared canines and molars, under clinical conditions with different analog tools. Materials and methods: The complete dentures of a patient were duplicated without denture teeth 16, 23, 33, and 46. For each of these gaps, six crown stumps were milled with ϕ/2 = −1, 3, 6, 9, 12, and 15 degrees, each of which was insertable using mini-magnets. A total of 144 dental students, 48 students each from the 1st, 6th, or 9th semester, estimated these angles intraorally with various aiding tools: In addition to basic dental instruments, they used a parallelometer mirror, an analog clock dial with a 6-degree visualization, and a scale of tooth stumps with ϕ/2 between −1 and 15 degrees. Results: The widely demanded 3 degrees were hardly recognized, but assumed to be steeper or even undercut. In contrast, the −1-degree divergent stump walls were predominantly estimated as parallel-walled or slightly conical. With increasing taper, the stumps tended to be classified as steeper, ie, “better.” The additional tools did not result in a general improvement of the estimation performance. Students from higher semesters did not achieve better results. Conclusion: The present authors question the objectivity of an exclusively visual assessment of crown stump taper. It appears that dental training should at least focus on avoiding undercuts as the minimal prerequisite for an accurate intraoral scanning procedure. Digital control of the preparation angle by an intraoral scan and immediate clinical implementation of these results could help to produce appropriate preparations. Keywords: dental students, crown stumps, convergence angle, preparation angle, intraoral estimation, parallelometer mirror, visualization tools

Aim: There is an ongoing debate about the benefits of the facebow and individual articulator settings in prosthodontics when compared with simpler methods. The present study aims to determine whether the implementation of novel algorithmic articulator concepts may be an alternative to avoid dynamic interference contacts during the design process of fixed posterior restorations, and to what extent the occlusal morphology of the restoration is affected. Materials and methods: From a chairside CAD database, a total of 50 clinical patient cases documenting 61 planned fixed restorations in the posterior tooth region were selected. A common CAD software program was used for the automated knowledge-based design process. When designing the restorations, functional concepts were applied, including the pure static occlusion, the average articulation, three different articulator settings as a control, and a combination of a broad range of articulation parameters (the full range dynamic articulation). The resulting dynamic contact points were compared both visually and metrically with a monitoring software program. Results: There is a highly significant difference in avoiding dynamic interference contacts when applying the full range dynamic articulation compared with the pure static occlusion (P < 0.001) and the average articulation (P < 0.001). Furthermore, the superimposition revealed that the surface of the restorations showed nearly no visual morphologic changes after virtually grinding-in the interpenetrating contact points. Conclusion: The full range dynamic articulation can be used for the design of small fixed posterior restorations to avoid most dynamic interference contacts without the need for determining individual parameters for each patient. Keywords: CAD/CAM, virtual articulation, virtual functionally generated path (FGP), average articulation, full range dynamic articulation, facebow

Aim: The present study aimed to evaluate the intaglio surface trueness and fit of zirconia crowns depending on the different machining strategies used with the Cerec system. Materials and methods: Thirty duplicate tooth models for a single zirconia crown were randomly assigned to three groups (n = 10) according to the machining mode used for fabrication: grinding, wet milling, and dry milling. The scan data of the final crowns were compared with their design data to evaluate the intaglio surface trueness. The marginal and internal fit were evaluated using a cross-sectional method. The time required for the machining and sintering processes was measured for each group. Results: The wet-milling group showed better trueness (root mean square: 13.8 ± 1.0 μm) than the grinding and dry-milling groups (P < 0.001). The marginal gap was greater in the grinding group (58.6 ± 28.9 μm) than that in the wet- and dry-milling groups (P < 0.001). The dry-milling group required the shortest time for the manufacturing process. Conclusion: All machining modes fabricated crowns with a clinically acceptable trueness and fit. However, the dry-milling mode was advantageous for the chairside CAD/CAM system with respect to time efficiency. Keywords: 3D printing, Cerec, comparative 3D analysis, dry milling, grinding, marginal gap

Occlusal splints are a commonly prescribed dental appliance for the management of bruxism or temporomandibular disorders. The use of digital dental technology facilitates the fabrication of this therapeutic device. The improvements in digital technology have helped in designing and producing occlusal splints that show better precision and accuracy as well as ease of manufacturing in terms of time and materials, in addition to the option of a simple and straightforward duplication process. The present technical report describes the digital workflow steps that need to be followed to design an occlusal device in a fully digital protocol. Scans of maxillary and mandibular models were acquired in centric relation, and a virtual 3D occlusal device was designed using a free, open-source 3D modeling software program. Keywords: 3D dentistry, Autodesk Meshmixer, digital dentistry, occlusal splint, open-source software