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The aim of this in vitro study was to analyse the performance of CAD/CAM resin-based composites for the fabrication of long-term temporary fixed dental prostheses (FDP) and to compare it to other commercially available alternative materials regarding its long-term stability. Four CAD/CAM materials [Structur CAD (SC), VITA CAD-Temp (CT), Grandio disc (GD), and Lava Esthetic (LE)] and two direct RBCs [(Structur 3 (S3) and LuxaCrown (LC)] were used to fabricate three-unit FDPs. 10/20 FDPs were subjected to thermal cycling and mechanical loading by chewing simulation and 10/20 FDPs were stored in distilled water. Two FDPs of each material were forwarded to additional image diagnostics prior and after chewing simulation. Fracture loads were measured and data were statistically analysed. SC is suitable for use as a long-term temporary (two years) three-unit FDP. In comparison to CT, SC featured significantly higher breaking forces (SC > 800 N; CT < 600 N) and the surface wear of the antagonists was (significantly) lower and the abrasion of the FDP was similar. The high breaking forces (1100-1327 N) of GD and the small difference compared to LE regarding flexural strength showed that the material might be used for the fabrication of three-unit FDPs. With the exception of S3, all analysed direct or indirect materials are suitable for the fabrication of temporary FDPs.

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The aim of the study was to investigate the effect of X-rays used in micro X-ray computer tomography (µXCT) on the mechanical performance and microstructure of a variety of dental materials. Standardised bending beams (2 × 2 × 25 mm3) were forwarded to irradiation with an industrial tomograph. Using three-dimensional datasets, the porosity of the materials was quantified and flexural strength was investigated prior to and after irradiation. The thermal properties of irradiated and unirradiated materials were analysed and compared by means of differential scanning calorimetry (DSC). Single µXCT measurements led to a significant decrease in flexural strength of polycarbonate with acrylnitril-butadien-styrol (PC-ABS). No significant influence in flexural strength was identified for resin-based composites (RBCs), poly(methyl methacrylate) (PMMA), and zinc phosphate cement (HAR) after a single irradiation by measurement. However, DSC results suggest that changes in the microstructure of PMMA are possible with increasing radiation doses (multiple measurements, longer measurements, higher output power from the X-ray tube). In summary, it must be assumed that X-ray radiation during µXCT measurement at high doses can lead to changes in the structure and properties of certain polymers.

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PURPOSE: The aim of this investigation was to generate a statistical shape model (SSM) of the midface and evaluate symmetry, gender aspects, and bone thickness. METHODS: About 102 computed tomography scans were analyzed to create the SSM. This included segmentation, landmark attribution, and Procrustes and principal component analysis. Afterward, symmetry and gender differences were visualized by registration and color coding. Bone thickness was calculated by measuring the distance between outer and inner surfaces. RESULTS: Symmetry was high in all models. The male model showed a more prominent forehead, nasal bones, and larger bizygomatic width. Bone thickness resembled the concept of vertical and horizontal maxillary pillars and buttresses. CONCLUSIONS: SSM can be used to analyze midface morphology and help in virtual surgery planning. Calculation of bone thickness could also be a useful tool in surgical planning and biomechanics.

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PURPOSE: Preformed orbital meshes (POMs) are routinely used in orbital traumatology. As the shapes of commercially available POMs differ, we wanted to evaluate whether investigators would use the same POM in a given situation and perform similar virtual positioning. Furthermore, we investigated whether these tasks could be performed more quickly and more reproducibly using a new software workflow. MATERIALS AND METHODS: Four investigators performed virtual planning of orbital fracture treatment in the Brainlab system (Brainlab, Munich, Germany) using 3 different POMs. Time effort, POM selection, minimum-maximum deviations, and fitting within a distance corridor were measured and compared with the new software workflow. RESULTS: Regarding time effort, a distinct learning curve was seen. An average of 15 minutes was needed, which compared inferiorly with 1 minute using the software algorithm. In POM selection, the individual choice of the investigators differed to a large extent. An identical POM was chosen in only 3 of 10 cases, and in 2 of 10 cases, all investigators and software choices were identical. Manual POM planning showed constant collision between bone and mesh with large interindividual maximum deviations. By defining collision prevention and achieving the highest concordance between bone and mesh geometry within a given distance slot, the new software was able to select and place the best-fitting POM and display regions of potential necessary presurgical modifications. CONCLUSIONS: Planning of orbital fracture treatment in a navigation system using POMs seems highly individual. Integrating new software workflows should reduce time effort and lead to reproducible planning results, which could be used in intraoperative navigation. Furthermore, our new workflow could be used for training and expanded to other anatomic regions.

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INTRODUCTION: Polydioxanone (PDS) sheets are commonly used in the treatment of orbital wall fractures. A potential drawback of PDS is that it may be difficult to adapt to the anatomy of the orbital walls. Therefore a study was conceived to test the feasibility of preforming PDS sheets. MATERIAL AND METHODS: PDS sheet material was water-heated and preformed using a template based on a statistical anatomical model. Then the deformed sheet was cooled, stored and compared to the original model to investigate post-deformation changes. RESULTS: PDS sheet material could easily be deformed using a mould. No significant post-cooling shape changes were noticed. CONCLUSIONS: PDS sheet material can be preformed into complex geometric shapes. This could be a benefit in the treatment of orbital wall fractures.

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PURPOSE: Aim of this study was to investigate whether a mold generated from a statistical shape model of the orbit could be generated to provide a cost-efficient means for the treatment of orbital fractures. MATERIALS AND METHODS: A statistical shape model was created from 131 computed tomographic (CT) scans of unaffected adult middle European human orbits. To generate the model, CT scans were segmented in Brainlab software, preregistered using anatomic landmarks, trimmed to an identical size, and definitely registered. Then, the model was created using the global master algorithm. Based on this model, a mold consisting of a male part and a female part was constructed and printed using a rapid prototyping technique. RESULTS: A statistical shape model of the human orbit was generated from 125 CT scans. Six scans (4.5%) presented major anatomic deviations and were discarded. A solid mold based on this model was printed. Using this mold, flat titanium mesh could be successfully deformed to serve as an orbital implant. CONCLUSION: A mold based on the statistical orbital shape could serve as a cost-effective means for the treatment of orbital fractures. It allows the anatomic preformation of titanium or resorbable implant material for orbital reconstruction. Because these materials could be cut from larger sheets, the use of a mold would be a cost-effective treatment alternative.

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PURPOSE: Preformed orbital titanium meshes have been introduced to improve outcomes in the treatment of orbital wall fractures. This study evaluated the geometry of different commercially available orbital meshes and compared them with an average human orbit. MATERIALS AND METHODS: Seven commercially available preformed orbital meshes were scanned using an optical scanner. For comparison, an average orbit was generated from 113 computed tomographic scans of unaffected orbits. Meshes and the average orbit were compared by registration and the calculation of congruence. RESULTS: All meshes showed a high similarity within a ±1.5-mm deviation corridor. Major differences were seen in the slope between the orbital floor and the medial wall and in the upturning toward the lateral orbital rim. CONCLUSION: Preformed orbital meshes conform highly to an average orbit, but differ in size and geometry. Using special software, the best fitting mesh could be chosen preoperatively to improve surgical outcome if its geometry were published.

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