Dreidimensionale Untersuchungen zur Morphologie der oberen Frontzähne

Bisher waren Längenmessungen und deskriptive Charakterisierungen die einzigen Anhaltspunkte zur Beschreibung der Oberflächenmorphologie von Frontzähnen. Für die Erstellung eines Datensatzes bei computergestützten Verfahren in der Zahnmedizin ist dies nicht mehr ausreichend. In der Literatur existieren bisher keine Ansätze zur Morphometrie der Oberflächen oberer Frontzähne, die für automatische Rekonstruktionsverfahren verwertbar wären. Für diese Arbeit wurde in einem ersten Schritt eine Zahnbibliothek aus natürlichen, unversehrten Frontzahnoberflächen aufgebaut. Mit Hilfe dieser Zahndatenbank konnten verschiedene dreidimensionale morphometrische Untersuchungen durchgeführt werden, bei denen Analysen zur Spiegelsymmetrie eine wichtige Rolle einnahmen. Zudem wurden die gewonnenen metrischen Ergebnisse mit dem visuellen Eindruck von Experten verglichen. Diese Beobachterdaten wurden außerdem zur explorativen Detektion jener morphologischen Merkmale genutzt, die maßgeblich die subjektive menschliche Wahrnehmung beeinflussen. Durch einen mathematischen Oberflächenvergleich wurde es möglich die morphologische Variabilität von oberen Frontzähnen zu quantifizieren. Die Durchschnittswerte für die mittlere Abweichung nach Überlagerung der Vestibularflächen (Quant_80_20_halbe) betragen bei symmetrischen Zähnen zwischen 44 µm und 53 µm, bei Zähnen unterschiedlicher Probanden sind die Werte um den Faktor zwei höher. Die benutzten statistischen Verfahren (u.a. Multidimensionale Skalierung, Multidimensionale Entfaltung) weisen auf eine mäßige Übereinstimmung der metrisch ermittelten Ähnlichkeiten mit der visuellen Wahrnehmung von Zahnärzten hin. Den Ergebnissen multivariater Analysen zufolge hatten die beurteilenden Zahnärzte eine vergleichbare Vorstellung der Zahnmorphologie, wobei sie einzelne Merkmale der Zahnstruktur scheinbar verschieden gewichten. Ein übergeordneter Parameter der visuellen Bewertung ist das Längen-Breiten-Verhältnis, über die anderen Merkmale kann bisher nur spekuliert werden. In einer dreidimensionalen Versuchsanordnung wurde simuliert, inwieweit es möglich ist, dass ein achsensymmetrisch gespiegelter Zahn seinen kontralateralen Zahn ersetzen kann. Dieser Ansatz wurde unter approximalen, okklusalen und ästhetischen Gesichtspunkten evaluiert. Es zeigte sich eine zufriedenstellende metrische Passung hinsichtlich der approximalen und okklusalen Verhältnisse. Bemerkenswert war die bessere visuelle Akzeptanz der modifizierten Frontzahnansichten im Vergleich zu den jeweiligen Originalansichten. Insgesamt erscheint der spiegelsymmetrische Ersatz als ein brauchbares Basiskonzept für vollautomatische Rekonstruktionsmaßnahmen im oberen Frontzahnbereich

Learning Multiple Defaults for Machine Learning Algorithms

The performance of modern machine learning methods highly depends on their hyperparameter configurations. One simple way of selecting a configuration is to use default settings, often proposed along with the publication and implementation of a new algorithm. Those default values are usually chosen in an ad-hoc manner to work good enough on a wide variety of datasets. To address this problem, different automatic hyperparameter configuration algorithms have been proposed, which select an optimal configuration per dataset. This principled approach usually improves performance, but adds additional algorithmic complexity and computational costs to the training procedure. As an alternative to this, we propose learning a set of complementary default values from a large database of prior empirical results. Selecting an appropriate configuration on a new dataset then requires only a simple, efficient and embarrassingly parallel search over this set. We demonstrate the effectiveness and efficiency of the approach we propose in comparison to random search and Bayesian Optimization

Hemorrhagic shock after endoscopic biopsy of sigmoid cancer: pseudoaneurysm of the rectal superior artery

An 86-year-old man without significant comorbidity presented with weight loss, diarrhea, and iron deficiency anemia. No signs of gastrointestinal bleeding were noticed. Colonoscopy was performed, and sigmoid cancer was suspected (a). Biopsies were obtained, which confirmed colonic adenocarcinoma. Eight hours after the endoscopy, the patient developed massive hematochezia, followed by hemodynamic instability (blood pressure 60/30 mm Hg; heart rate 120 bpm; and hemoglobin drop from 9.8 g/dL to 6.1 g/dL within 2 hours). After stabilization with intravenous fluids, norepinephrine, and transfusion of 1 unit of red blood cells, endoscopy was repeated and ruled out ongoing bleeding. A computed tomography scan confirmed a mass of the sigmoid colon, which extended along the inferior mesenteric artery and to the os sacrum. Within the sigmoid wall, extravasation of the contrast medium was seen into a structure of 2.3 × 1.7 cm. Computed tomography reconstructions suspected pseudoaneurysm of the inferior mesenteric artery (Figures B, C). In the absence of distant metastases, surgical resection was attempted urgently. However, owing to infiltration of the aortic wall, curative resection was impossible and colostomy was performed. Angiography confirmed a large pseudoaneurysm of the rectal superior artery, and embolization was performed successfully. The further course was unremarkable

Magnetic resonance imaging basedcomputer-guideddental implant surgery-A clinical pilot study

Background: Computer-guided implant surgery is currently based on radiographic techniques exposing patients to ionizing radiation. Purpose: To assess, whether computer-assisted 3D implant planning with template-guided placement of dental implants based on magnetic resonance imaging (MRI) is feasible. Materials and methods: 3-Tesla MRI was performed in 12 subjects as a basis for prosthetically driven virtual planning and subsequent guided implant surgery. To evaluate the transferability of the virtually planned implant position, deviations between virtually planned and resulting implant position were studied. Matching of occlusal surfaces was assessed by comparing surface scans with MRI-derived images. In addition, the overall image quality and the ability of depicting anatomically important structures were rated. Results: MRI-based guided implant surgery with subsequent prosthetic treatment was successfully performed in nine patients. Mean deviations between virtually planned and resulting implant position (error at entry point 0.8 +/- 0.3 mm, error at apex 1.2 +/- 0.6 mm, angular deviation 4.9 +/- 3.6 degrees), mean deviation of occlusal surfaces between surface scans and MRI-based tooth reconstructions (mean 0.254 +/- 0.026 mm) as well as visualization of important anatomical structures were acceptable for clinical application. Conclusion Magnetic resonance imaging (MRI) based computer-assisted implant surgery is a feasible and accurate procedure that avoids exposure to ionizing radiation

Digital planning and individual implants for secondary reconstruction of midfacial deformities: A pilot study

Objective To evaluate the feasibility and accuracy of implementing three-dimensional virtual surgical planning (VSP) and subsequent transfer by additive manufactured tools in the secondary reconstruction of residual post-traumatic deformities in the midface. Methods Patients after secondary reconstruction of post-traumatic midfacial deformities were included in this case series. The metrical deviation between the virtually planned and postoperative position of patient-specific implants (PSI) and bone segments was measured at corresponding reference points. Further information collected included demographic data, post-traumatic symptoms, and type of transfer tools. Results Eight consecutive patients were enrolled in the study. In five patients, VSP with subsequent manufacturing of combined predrilling/osteotomy guides and PSI was performed. In three patients, osteotomy guides, repositioning guides, and individually prebent plates were used following VSP. The median distances between the virtually planned and the postoperative position of the PSI were 2.01 mm (n = 18) compared to a median distance concerning the bone segments of 3.05 mm (n = 12). In patients where PSI were used, the median displacement of the bone segments was lower (n = 7, median 2.77 mm) than in the group with prebent plates (n = 5, 3.28 mm). Conclusion This study demonstrated the feasibility of VSP and transfer by additive manufactured tools for the secondary reconstruction of complex residual post-traumatic deformities in the midface. However, the median deviations observed in this case series were unexpectedly high. The use of navigational systems may further improve the level of accuracy

Nodal Disease and Survival in Oral Cancer: Is Occult Metastasis a Burden Factor Compared to Preoperatively Nodal Positive Neck?

Simple Summary Occult metastasis in oral squamous cell carcinoma patients is a feared complication. However, there are barely any existing data on survival of patients suffering from occult metastasis. This study aims to compare patients with oral squamous cell carcinoma, considering survival in occult metastases and different treatment approaches. The impact of neck involvement and occult metastasis (OM) in patients with oral squamous cell carcinoma (OSCC) favors an elective neck dissection. However, there are barely any existing data on survival for patients with OM compared with patients with positive lymph nodes detected preoperatively. This study aims to compare survival curves of patients suffering from lymph nodal metastases in a preoperatively N+ neck with those suffering from OM. In addition, clinical characteristics of the primary tumor were analyzed to predict occult nodal disease. This retrospective cohort study includes patients with an OSCC treated surgically with R0 resection with or without adjuvant chemoradiotherapy between 2010 and 2016. Minimum follow-up was 60 months. Kaplan-Meier analysis was used to compare the survival between patients with and without occult metastases and patients with N+ neck to those with occult metastases. Logistic regression was used to detect potential risk factors for occult metastases. The patient cohort consisted of 226 patients. Occult metastases occurred in 16 of 226 patients. In 53 of 226 patients, neck lymph nodes were described as suspect on CT imaging but had a pN0 neck. Higher tumor grading increased the chance of occurrence of occult metastasis 2.7-fold (OR = 2.68, 95% CI: 1.07-6.7). After 12, 24, 48 and 60 months, 82.3%, 73.8%, 69% and 67% of the N0 patients, respectively, were progression free. In the group with OM occurrence, for the same periods 66.6%, 50%, 33.3% and 33.3% of the patients, respectively, were free of disease. For the same periods, respectively, 81%, 63%, 47% and 43% of the patients in the N+ group but without OM remained disease free. The predictors for progression-free survival were a positive N status (HR = 1.44, 95% CI: 1.08-1.93) and the occurrence of OM (HR = 2.33, 95% CI: 1.17-4.64). The presence of occult metastasis could lead to decreased survival and could be a burdening factor requiring treatment escalation and a more aggressive follow-up than nodal disease detected in the preoperative diagnostic imaging

High resolution MRI for quantitative assessment of inferior alveolar nerve impairment in course of mandible fractures: an imaging feasibility study

The purpose of this study was to evaluate a magnetic resonance imaging (MRI) protocol for direct visualization of the inferior alveolar nerve in the setting of mandibular fractures. Fifteen patients suffering from unilateral mandible fractures involving the inferior alveolar nerve (15 affected IAN and 15 unaffected IAN from contralateral side) were examined on a 3 T scanner (Elition, Philips Healthcare, Best, the Netherlands) and compared with 15 healthy volunteers (30 IAN in total). The sequence protocol consisted of a 3D STIR, 3D DESS and 3D T1 FFE sequence. Apparent nerve-muscle contrast-to-noise ratio (aNMCNR), apparent signal-to-noise ratio (aSNR), nerve diameter and fracture dislocation were evaluated by two radiologists and correlated with nerve impairment. Furthermore, dislocation as depicted by MRI was compared to computed tomography (CT) images. Patients with clinically evident nerve impairment showed a significant increase of aNMCNR, aSNR and nerve diameter compared to healthy controls and to the contralateral side (p < 0.05). Furthermore, the T1 FFE sequence allowed dislocation depiction comparable to CT. This prospective study provides a rapid imaging protocol using the 3D STIR and 3D T1 FFE sequence that can directly assess both mandible fractures and IAN damage. In patients with hypoesthesia following mandibular fractures, increased aNMCN R, aSNR and nerve diameter on MRI imaging may help identify patients with a risk of prolonged or permanent hypoesthesia at an early time

Bone regeneration of minipig mandibular defect by adipose derived mesenchymal stem cells seeded tri-calcium phosphate- poly(D,L-lactide-co-glycolide) scaffolds

Reconstruction of bone defects represents a serious issue for orthopaedic and maxillofacial surgeons, especially in extensive bone loss. Adipose-derived mesenchymal stem cells (ADSCs) with tri-calcium phosphates (TCP) are widely used for bone regeneration facilitating the formation of bone extracellular matrix to promote reparative osteogenesis. The present study assessed the potential of cell-scaffold constructs for the regeneration of extensive mandibular bone defects in a minipig model. Sixteen skeletally mature miniature pigs were divided into two groups: Control group and scaffolds seeded with osteogenic differentiated pADSCs (n=8/group). TCP-PLGA scaffolds with or without cells were integrated in the mandibular critical size defects and fixed by titanium osteosynthesis plates. After 12 weeks, ADSCs seeded scaffolds (n=7) demonstrated significantly higher bone volume (34.8%+/- 4.80%) than scaffolds implanted without cells (n=6, 22.4%+/- 9.85%) in the micro-CT (p < 0.05). Moreover, an increased amount of osteocalcin deposition was found in the test group in comparison to the control group (27.98 +/- 2.81% vs 17.10 +/- 3.57%, p < 0.001). In conclusion, ADSCs seeding on ceramic/polymer scaffolds improves bone regeneration in large mandibular defects. However, further improvement with regard to the osteogenic capacity is necessary to transfer this concept into clinical use