Objectives: To evaluate clasp-retained removable partial dentures (C-RPDs) with a metal framework for survival, maintenance requirements, and biologic implications. Method and materials: C-RPDs were retrospectively analyzed based on patient records. Treatment failure was defined as fracture of a framework component (metal base or connector) or loss of an abutment tooth. Other outcome variables included factors that might conceivably impact C-RPD survival (maxilla vs mandible, Kennedy classes, opposing dentitions, treatment by students vs certified dental practitioners), mobility and caries of abutment teeth (in relation to clasp designs), and maintenance requirements (relining, clasp or resin fractures). Differences were evaluated by appropriate statistical tests at the P ≤ .05 level. Results: A total of 612 patients (339 men, 273 women) 60.0 ± 11.5 years old at delivery were included, covering 842 C-RPDs and a mean observation period of 42.1 ± 33.2 months. Kaplan–Meier C-RPD survival was 76.2% after 5 years and 49.5% after 10 years. Biologic complications (ie, loss of abutment teeth) accounted for the vast majority (95.6%) of C-RPD failures, and Kaplan–Meier C-RPD survival was significantly better in the mandible (P = .015). Some clasp designs contributed significantly to caries and removal of abutment teeth (both P .05). No other significant differences were noted. Conclusion: Tooth loss both emerges as the main cause of C-RPD failure and might be amenable to careful selection of clasp designs. Overall, better C-RPD survival should be expected in the mandible. A noncontributory role of Kennedy classes and opposing dentitions is tentatively suggested based on numerically heterogenous subgroups. Keywords: clasp-retained removable partial dentures, dentures, maintenance requirements, prosthodontic treatment, secondary caries

Methode: Die digitale Bilddaten von 343 Patienten, bei denen sowohl eine DVT- als auch eine PSA-Aufnahme vorlag, wurden auf apikale Läsionen um Unterkiefer untersucht. Für entdeckte Läsionen wurden die Abmessungen der Läsion und die Dicke des kortikalen Knochens in der betroffenen Region gemessen. Die Ergebnisse wurden einer statistisches Analyse unter Verwendung einer Statistiksoftware (IBM SPSS 25, Fa. IBM, Armonk, USA) unterzogen. Ergebnisse: Mittels DVT wurden an 115 Zähnen apikale Läsionen entdeckt. Von diesen Läsionen waren 77 auch in der PSA sichtbar. Die Unterschiede zwischen den beiden bildgebenden Verfahren waren in der Prämolaren- und Molarenregion signifikant (McNemar-Test, p < 0,001), nicht jedoch im Frontzahnbereich (p = 0,063). Bezüglich der Läsionsgröße wurden keine signifikanten Unterschiede gefunden (Wilcoxon-Test, Frontzähne: p = 0,60, Prämolaren: p = 0,90, Molaren: p = 0,61). Der Mann-Whitney-U-Test ergab weder für die vestibuläre noch für die linguale Kortikalisdicke einen signifikanten Einfluss auf die Sichtbarkeit der Läsionen in DVT und PSA (vestibulär: p = 0,93, palatinal: p = 0,15). Schlussfolgerung: Apikale Läsionen scheinen in digitalen Volumentomografien wesentlich besser sichtbar zu sein. Die Dicke des kortikalen Knochens und die Größe der Läsionen haben keinen signifikanten Einfluss auf die Darstellung apikaler Läsionen. Keywords: apikale Läsion, DVT, digitale Volumentomografie, kortikale Knochendicke, Panoramaschichtaufnahme, PSA

Introduction: This study compares the accuracy of panoramic radiography and CBCT in detecting and diagnosing mandibular apical lesions, analysing the effect of the thickness of the cortical bone on the radiological visibility of apical lesions. Methods: Digital images of 343 patients who had CBCT scans and panoramic radiographs were inspected for mandibular apical lesions. The dimensions of the lesion and the thickness of the cortical bone in the affected region were measured. Statistical analyses were made using statistical software (IBM SPSS 25, IBM, Armonk, NY, USA). Results: CBCT detected apical lesions around 115 teeth; 77 of these were also visible on a panoramic radiography. The differences between the two methods were statistically significant in the premolar and molar regions (McNemar test; p 0.001) but not in the anterior region (p = 0.063). For the size of the lesions no significant differences were found (Wilcoxon test; anterior, p = 0.60; premolar, p = 0.90; molar, p = 0.61). In the Mann-Whitney U test, buccal and palatal cortical thickness did not significantly influence the visibility of lesions in CBCT and panoramic measurements (buccal, p = 0.93; palatal, p = 0.15). Conclusion: Apical lesions seem to be much more readily visible on CBCT scans. The thickness of the cortical bone and the size of the lesions do not significantly influence the representation of apical lesions. Keywords: apical lesions, CBCT, cone-beam computed tomography, cortical bone thickness, panoramic radiography

Purpose: The aim of this in vitro study was to evaluate the accuracy of template-guided implantation planned with implant-planning software (Implant Studio), comparing computer-aided design/computer-assisted manufacture (CAD/CAM)-based measurements with measurements via cone beam computed tomography (CBCT). Materials and Methods: Thirty template-guided implantations were planned and performed on acrylic-resin models. The implant positions were detected with an intraoral scanner, evaluated with CAD quality-control software, and compared with the planned positions in the test group. Preliminary deviations were measured via CBCT in the control group of the first 10 samples and compared with the first 10 samples of the test group. Results: When directly compared, measurements obtained using CBCT (control group) showed a trend toward greater deviations. In the CAD/CAM-based evaluation of the 30 samples, the mean ± SD deviation of the insertion axis from the planned implant axis was 2.011 ± 0.855 degrees. The mean deviations of the implant shoulders in the horizontal direction and at the implant apices were 0.725 ± 0.142 mm and 0.990 ± 0.244 mm, respectively. In the vertical direction, the mean deviation was 0.541 ± 0.129 mm. Conclusion: CAD/CAM-based measurements are more accurate than CBCT measurements. Therefore, this radiation-free measurement method is a viable diagnostic alternative. Implant planning with planning software and subsequent placement using surgical templates appears to be a reliable and precise therapeutic option in vitro. However, these findings will still have to be supported by in vivo studies. Keywords: dental implant, guided surgery, implant planning accuracy, intraoral scanner, navigated surgery, surgical template

Purpose: The aim of this study was to investigate the effects of tightening torque, screw head angle, and thread number on the preload force of abutment screws. Materials and Methods: The test specimens consisted of three self-manufactured components (ie, a thread sleeve serving as an implant analog, an abutment analog, and an abutment screw). The abutment screws were fabricated with metric M1.6 external threads. The thread number varied between one and seven threads. The screw head angles were produced in eight varying angles (30 to 180 degrees). A sensor unit simultaneously measured the preload force of the screw and the torsion moment inside the screw shank. The tightening of the screw with the torque wrench was performed in five steps (15 to 35 Ncm). The torque wrench was calibrated before each step. Results: Only the tightening torque and screw head angle affected the resulting preload force of the implant-abutment connection. The thread number had no effect. There was an approximately linear correlation between tightening torque and preload force. Conclusion: The tightening torque and screw head angle were the only study parameters that affected the resulting preload force of the abutment screw. The results obtained from this experiment are valid only for a single torque condition. Further investigations are needed that analyze other parameters that affect preload force. Once these parameters are known, it will add value for a strong, but detachable connection between the implant and abutment. Short implants and flat-to-flat connections especially will benefit significantly from this knowledge. Keywords: abutment, abutment screw, abutment screw configuration, dental implant, preload force, thread pitch

Objectives: Stock Abutments are a common therapeutic method in implant dentistry. The geometric form is round like the implant. Teeth have a natural geometry which is individual for every patient. Apart from the purely functional side of the implant restorations, aesthetic aspects are very important for the patient. The design of the emergence plays an important role. Prefabricated abutments have a rotationally symmetrical basic shape and do not correspond to the passage area of the shape of natural teeth. Atlantis® Abutments (Astra Tech GmbH, Elz) are individual abutments, CAD-designed and CAM- fabricated. The VAD® (Virtual-Abutment-Design) reduces the nature tooth geometry to an individual abutment. This leads to an emergence profile that supports the gingiva like the lost tooth. It is possible to produce the abutments in zirconia, titanium and in titanium-gold hue. Methods: In this retrospective study, from July 2008 to November 2012 a total of 225 Atlantis abutments (titanium, zirconia, gold hue) were incorporated in 109 patients and followed up using a standardised findings arc. Clinical and radiographic parameters were evaluated one year after inclusion and compared to the baseline conditions. After the first year, clinical examinations were made once a year and radiographic every two years. Results: 70 patients with a total of 124 abutments were followed in the observation period. The mean observation time was 21 months (SD ± 9.7). During the observation period, there were only 2 ceramic fractures with exposure of the framework (Fig. 2). All abutments were in situ; only one abutment loosening (during the second year) occurred, which could be fastened again (Fig. 3). The radiograph showed stable peri-implant bone conditions in comparison to the initial situation. The design of the abutments allowed for optimal adaptation of the peri-implant soft tissue. Conclusion: The production of individual abutments using prefabricated pieces is often difficult and costly. With the Atlantis method, abutments are designed starting from the ideal shape of the individual crown. This saves time and therefore costs. The data presented reveal that Atlantis is a viable method to treat patients. Furthermore, functionally and natural aesthetic results can be achieved. The application of this method can be recommended. Keywords: CAD/CAM Abutments, Emergence profile, Individual Abutments

Die digitale Revolution, auch dritte industrielle Revolution genannt, begann im 20. Jahrhundert und hat auch vor der Zahnmedizin nicht Halt gemacht. Durch die Digitalisierung von Arbeitsprozessen wird eine Beschleunigung und Vereinfachung dieser Prozesse angestrebt. In der Zahnmedizin ist die CAD/CAM-Technologie mittlerweile ein fester Bestandteil geworden. Eingeführt wurde sie für die Herstellung von Zahnersatz in den 80er Jahren. Seither wird sie fortwährend weiterentwickelt und das Spektrum der Einsatzgebiete erweitert. Zunächst wurden die Systeme hauptsächlich für festsitzenden Zahnersatz aus Hochleistungskeramiken wie Zirkondioxid verwendet. Mittlerweile kann eine große Bandbreite an Materialien für verschiedene Indikationsbereiche verarbeitet werden. Den derzeitigen Standard in der CAD/CAM-gestützten Herstellung von Zahnersatz stellt die konventionelle Abformung von Präparationen, gefolgt von einem Gipsmodell dar. Dieses wird anschließend im Labor digitalisiert, um den Zahnersatz am Computer zu designen und nachfolgend zu fräsen. Der Trend entwickelt sich heutzutage stetig hin zu volldigitalisierten Arbeitsabläufen mithilfe von Intraoralscannern.

Purpose: This study aimed to test bacterial microleakage at the implant-abutment interface (IAI) before and after dynamic loading using a new chewing simulation. Materials and Methods: Fourteen implant systems (n = 5 samples of each) were divided into two groups: (1) systems with conical implant-abutment connections (IACs), and (2) systems with flat IACs. For collecting samples without abutment disconnection, channels (Ø = 0.3 mm) were drilled into implants perpendicularly to their axes, and stainless-steel cannulas were adhesively glued inside these channels to allow a sterilized rinsing solution to enter the implant interior and to exit with potential contaminants for testing. Implants were embedded in epoxy resin matrices, which were supported by titanium cylinders with lateral openings for inward and outward cannulas. Abutments were tightened and then provided with vertically adjustable, threaded titanium balls, which were cemented using composite cement. Specimens were immersed in a bacterial liquid and after a contact time of 15 minutes, the implant interior was rinsed prior to chewing simulation (0 N ⩠ static seal testing). Specimens were exposed to a Frankfurt chewing simulator. Two hundred twenty force cycles per power level (110 in ± X-axis) were applied to simulate a daily masticatory load of 660 chewing cycles (equivalent to 1,200,000 cycles/5 years). The applied load was gradually increased from 0 N to a maximum load of 200 N in 25-N increments. The implant interior was rinsed to obtain samples before each new power level. All samples were tested using fluorescence microscopy; invading microorganisms could be counted and evaluated. Results: No bacterial contamination was detected under static loading conditions in both groups. After loading, bacterial contamination was detected in one sample from one specimen in group 1 and in two samples from two specimens in group 2. Conclusion: Controlled dynamic loading applied in this study simulated a clinical situation and enabled time-dependent analysis regarding the bacterial seal of different implant systems. Conical IACs offer a better bacterial seal compared with flat IACs, which showed increased microleakage after dynamic loading. IAC design plays a crucial role in terms of bacterial colonization. Taking samples of the implant interior without abutment disconnection eliminates an error source. Keywords: abutment disconnection, bacterial microleakage, chewing simulator, implant-abutment connection

Schon lange gilt Bruxismus als potenzieller Risikofaktor in der dentalen Implantologie. Knirschen und Pressen induzieren hohe Kräfte in den implantatprothetischen Restaurationen, dem Implantatkörper und den umliegenden Strukturen. Durch diese ist das Risiko technischer Komplikationen deutlich erhöht. Typische Folgeschäden sind Frakturen der Verblendung oder des Gerüsts einer Restauration, Schäden der unterschiedlichen Implantatkomponenten oder Lockerungen der Abutmentschraube. Daher empfiehlt sich die Anwendung von Strategien zur Risikominimierung. Diese implizieren die Berücksichtigung chirurgischer und biologischer Aspekte, die korrekte Formgebung des Gerüsts und der Verblendung, eine präzise Einstellung der Okklusion, die Anwendung adäquater Materialien, Implantatsysteme und Implantatdurchmesser sowie eine funktionelle Gestaltung der prothetischen Suprastruktur. Auf diese Weise lassen sich auch unter ungünstigen Voraussetzungen sichere und erfolgreiche implantatprothetische Therapien durchführen. Keywords: Implantat, Implantatprothetik, Abutment, Bruxismus, Parafunktionen, Knirschen, Pressen